No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Factorial design of nanosized polyisoprene synthesis via differential microemulsion polymerization
Abstract
The synthesis of nanosized polyisoprene latex was carried out by differential microemulsion polymerization using 2, 2′-Azoisobutyronitrile (AIBN) initiator system under various reaction conditions. A fractional factorial experimental design was applied to study the effects of reaction variables: amount of initiator and surfactant, monomer-to-water ratio, reaction temperature, and stirring speed on rubber particle size and monomer conversion. The analysis of the results from the design showed the main effects on the observed response and the amount of initiator, reaction temperature and stirring speed in the range of the test had significant effects on polyisoprene particle size. The significant effects on monomer conversion were reaction temperature, stirring speed, and interaction between reaction temperature and stirring speed in the range of the test. The optimum conditions gave highest monomer conversion of 90% and average particle size of polyisoprene of 27 nm. The nanosized polyisoprene was also characterized by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Copyright © 2009 John Wiley & Sons, Ltd.
... One way analysis of variance (ANOVA) was used for statistical analysis of data collected from evaluated formulations [20]. ...
Background
The present study aimed to design, optimize , and evaluate primaquine loaded nanoemulgel for malaria treatment. Nanoemulgel was prepared with the help of different components such as castor oil, Tween 80:Transcutol P ( S mix ratio), and polymers. Pseudoternary phase diagram was constructed to optimize S mix ratio. Response surface methodology was used for the optimization of nanoemulsion preparation based on characterization parameters such as droplet size (nm), zeta potential (mv), polydispersity index (PDI), viscosity (mPa·S), conductivity (mS/cm), and percent drug release. Based on these parameter results, F5 formulation was selected as an optimized formulation. F5 formulation was loaded in hydrogel preparation which was developed by using hydroxypropyl methylcellulose (HPMC K15M) 1-2% concentrations. The prepared nanoemulgel was evaluated with the following parameters: percent drug content, in vitro drug release, ex vivo skin permeation, pH determination, spreadability determination, and viscosity measurement.
Results
The droplets of primaquine loaded nanoemulsion were nanosized (10–200 nm) in the transmission electron microscope (TEM) images. Zeta potential for all formulations (F1-F9) was observed as − 0.7 ± 0.02 to 2.12 ± 0.04 mv. Response surface curves were plotted for optimization of perfect nanoemulsion preparation. Nanoemulgels (F5, F5 a , F5 b, and F5 c ) were evaluated for their different parameters such as pH (F5, 5.2 ± 0.2; F5 a , 5.3 ± 0.1; F5 b , 5.3 ± 0.1; and F5 c , 5.4 ± 0.1), viscosity (mPa·S) (F5, 9876 ± 0.61; F5 a , 14,564.6 ± 0.42; F5 b , 14,841.9 ± 0.82; and F5 c , 16,872.1 ± 0.921), spreadability (g.cm/s) (F5, 7.89 ± 0.10; F5 a , 5.09 ± 0.03; F5 b , 4.30 ± 0.02; and F5 c , 3.13 ± 0.01), and percent drug content (F5, 100 ± 0.46; F5 a , 98.10 ± 0.38; F5 b , 99.70 ± 0.41; and F5 c , 97.34 ± 0.51), and ex vivo skin flux of F5 b was evaluated for 24 h. Ex vivo skin permeability was found ~ 70% within 12 h and ~ 86% within 24 h.
Conclusion
The nanoemulsion loaded hydrogel of primaquine with optimum viscosity was prepared for transdermal application. Nanoemulgel was prepared by using HPMC K15M into nanoemulsion because HPMC K15M was responsible for significant viscosity. The permeation rate of nanoemulgel was greater than other drug solutions. The great permeation rate was achieved by the incorporation of Transcutol P (cosurfactant). The optimized formulation was justified by using statistics. Stability studies confirmed that nanoemulgel is a promising carrier for the delivery of primaquine.
... The data obtained for different formulations was analyzed by one way analysis of variance (ANOVA). [34] ...
Background:
The purpose of this study was to develop microemulsion-based hydrogel formulation for topical delivery of bifonazole with an objective to increase the solubility and skin permeability of the drug.
Materials and Methods:
Oleic acid was screened as the oil phase of microemulsions, due to a good solubilizing capacity of the microemulison systems. The pseudo-ternary phase diagrams for microemulsion regions were constructed using oleic acid as the oil, Tween 80 as the surfactant and isopropyl alcohol (IPA) as the cosurfactant. Various microemulsion formulations were prepared and optimized by 32 factorial design on the basis of percentage (%) transmittance, globule size, zeta potential, drug release, and skin permeability. The abilities of various microemulsions to deliver bifonazole through the skin were evaluated ex vivo using Franz diffusion cells fitted with rat skins. The Hydroxy Propyl Methyl Cellulose (HPMC) K100 M as a gel matrix was used to construct the microemulsion-based hydrogel for improving the viscosity of microemulsion for topical administration. The optimized microemulsion-based hydrogel was evaluated for viscosity, spreadability, skin irritancy, skin permeability, stability, and antifungal activity by comparing it with marketed bifonazole cream.
Results:
The mechanism of drug release from microemulsion-based hydrogel was observed to follow zero order kinetics. The studied optimized microemulsion-based hydrogel showed a good stability over the period of 3 months. Average globule size of optimized microemulsion (F5) was found to be 18.98 nm, zeta potential was found to be -5.56 mv, and permeability of drug from microemulsion within 8 h was observed 84%. The antifungal activity of microemulsion-based hydrogel was found to be comparable with marketed cream.
Conclusion:
The results indicate that the studied microemulsion-based hydrogel (F5) has a potential for sustained action of drug release and it may act as promising vehicle for topical delivery of ibuprofen.
Cis-1,4-polyisoprene latex (IRL) is the best alternative to natural rubber latex (NRL) because it is free from proteins and can avoid allergic reactions in the human body. Poor mechanical properties of IRL film are a major obstacle to replacing NRL. To address this issue, a novel strategy was developed by a simple one-pot method to prepare a composite latex introducing hexadecyltrimethylammonium bromide (CTAB) modified sodium montmorillonite (org-Mnt) into the IRL preparation process. The microstructures and morphology of the resulting org-Mnt were characterized by Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), and Energy Dispersive Spectrometer (EDS). In addition, the dispersion state of the org-Mnt in the composite latex and the morphology of the composite films were determined by transmission electron microscopy (TEM) and SEM. The properties of the composite latex were investigated. Crosslink density, thermogravimetric analysis (TGA), mechanical properties, and thermal oxygen aging properties of the composite latex films were also studied. Finally, the mechanism of org-Mnt reinforcement of IRL was described comprehensively. The results showed that the org-Mnt/IRL (1phr and 2phr) composite latexes had a stable state, excellent film-formation performance, and excellent mechanical properties. Compared with pure IRL films, the tensile strength of org-Mnt/IRL (2phr) composite films increased by 74%, and after thermal oxygen aging, property change rates of the tensile strength and elongation at break increased by 37.2% and 32.1%, respectively, which exceeded those of NRL. The current research provides an effective method for preparing high-performance composite films suitable for high-end medical applications.
In this study, the oil-in-water nanoemulsion (NE) was prepared and loaded with vitamin D3 in food-grade (edible) canola oil and stabilized by Tween 80 and Span 80 by using a water titration technique with droplet sizes of 20 to 200 nm. A phase diagram was established for the influence of water, oil, and S-Mix concentration. The outcomes revealed that the particle size of blank canola oil nanoemulsion (NE) ranged from 60.12 to 62.27 (d.nm) and vitamin D3 NE ranged from 93.92 to 185.5 (d.nm). Droplet size and polydispersity index (PDI) of both blank and vitamin D3-loaded NE results were less than 1, and zeta potential results for blank and vitamin D3 loaded NE ranged from −9.71 to −15.32 mV and −7.29 to −13.56 mV, respectively. Furthermore, the pH and electrical conductivity of blank NE were 6.0 to 6.2 and 20 to 100 (μs/cm), respectively, whereas vitamin D3-loaded NE results were 6.0 to 6.2 and 30 to 100 (μs/cm), respectively. The viscosity results of blank NE ranged from 0.544 to 0.789 (mPa.s), while that of vitamin D3-loaded NE ranged from 0.613 to 0.793 (mPa.s). In this study, the long-term stability (3 months) of canola oil NE containing vitamin D3 at room temperature (25 C) and high temperature (40 C) was observed.
Rubber is one of the most commonly used industrial materials worldwide. However, there is a gap in the literature on the production of rubber thin films in nanoscale. When the rubber thin films are produced in nanoscale, they can be used in high‐tech applications where bulk rubbers have never been used before. This study is one of the first investigations to focus on the vapor‐based production of the polyisoprene (PI), which is an important member of the synthetic rubber class. For this purpose, a single‐step, rapid and environmentally friendly method based on plasma enhanced chemical vapor deposition (PECVD) was employed to produce PI thin films using 2‐methyl‐1,3‐butadiene (isoprene). The high‐vapor pressure of isoprene makes it a promising monomer for the production of chemical vapor deposition polymers. The effect of plasma processing parameters on the PI deposition rate was investigated. The deposition rate of PI thin film as high as 40 nm/min was achieved and the contact angle of PI coated bamboo surface was found to be 146.8°. The mechanical durability and laundering tests of PI thin films were performed. Based on this study results, PI thin films produced by PECVD can be used in a number of potential applications.
The nitroxide-mediated polymerization (NMP) of isoprene (I) initiated by the poly(ethylene-stat-butylene)-(SG1)2 dialkoxyamine (PEB-(SG1)2) at 115 oC in 50 vol% pyridine led to cis-1,4-rich poly(isoprene)s (PIs), exhibiting Mn,GPC = 52-59K (PI equivalents) and Ð = 1.46-1.59. S-I-S triblock copolymers (S = styrene, Mn,GPC = 95-109K, Ð = 2.11-2.29, FS = 0.30-0.49) were synthesized via subsequent S chain-extensions in bulk at 115 oC from these PI-(SG1)2 macro-initiators. A micro-phase separation, exhibiting possibly a cylindrical or lamellar morphology, was observed by atomic force microscopy for a S-I-S having FS = 0.30. Tensile strength at break σB = 2.8-4.1 MPa and elongation at break εB ∼ 375-450 % were measured for S-I-S samples with FS = 0.30-0.38. The substitution of the PS outer segments by more rigid segments rich in isobornyl methacrylate (IBOMA) units allowed to improve the stress-strain properties, with σB = 11.4 ± 0.6 MPa and εB = 1356 ± 214 %. This IBOMA-I-IBOMA type copolymer also displayed an upper service temperature greater than 150 oC.
This study reports CdTe quantum dots synthesis in an aqueous medium using cadmium chloride and sodium tellurite as precursors and sodium borohydride and mercaptosuccinic acid as reducing and capping agents, respectively. The synthesis process was optimized through experimental design, and particle characterization was carried out by UV-Vis spectroscopy and molecular fluorescence. In the first stage, a factorial design was used to establish the significance of each of the synthesis variables; i.e., the temperature, pH, reaction time and precursor molar ratios. In the second stage, a multivariate design was constructed to relate the synthesis variables with the maximum absorbance wavelengths, which allowed for predictions of the diameters of the CdTe quantum dots, which were compared with direct measurements of the particles analyzed by high-resolution transmission electron microscopy, HR-TEM and X-ray diffraction, XRD. Finally, there is a brief discussion regarding the existing models predicting particle sizes.
The aim of this research was to investigate the important effects and their interaction on production of Green High Impact Polystyrene (HIPS) synthesized by using natural rubber (NR) as elastomeric phase via suspension polymerization initiated and stabilized by using benzoyl peroxide (BPO) and poly(vinyl alcohol) (PVA), respectively. The effects of reaction parameters: wt ratio of NR/styrene and PVA/NR including agitation rate on HIPS bead size were studied by using 2k factorial design experiment. The HIPS bead size increased with increasing the NR content (0.01–0.08 w/w of NR/ST) in the mixture of NR/styrene syrup. Whereas, the increase in the PVA content (1.5–2.5 w/w of PVA/NR) and agitation rate (350–450 rpm) decreased HIPS bead size. Thermal gravimetric analysis (TGA) results were showed that HIPS containing the various amounts of NR had more thermal stability than the neat PS. Moreover, the glass transition temperature (Tg) of PS phase in the obtained HIPS bead was shifted from 97.9 to 84.2 °C when the wt ratio of NR/ST was increased to 0.08.
Rhodium catalysts are effective catalysts for catalytic hydrogenation of unsaturated polymers in aqueous media under optimum conditions. Hydrogenation of a nanosized polyisoprene (PIP) emulsion was carried out in a Parr reactor. Rhodium trichloride (RhCl3 center dot 3H(2)O) and different ligand types, triphenylphosphine (PPh3), trisulfonated triphenylphosphine (TPPTS) and monosulfonated triphenylphosphine (TPPMS) were used as a catalyst precursor. The hydrogenated PIP (HPIP) was characterized by proton nuclear magnetic resonance spectroscopy (H-1 NMR). Low conversions of C=C were observed when RhCl3/PPh3 or RhCl3/TPPTS was used as catalyst precursors, however, 96.0% hydrogenation (HD) was achieved when using RhCl3/TPPMS. The Hartley ionic spherical micelle model was proposed to explain the catalytic behavior. The process variables did not affect PIP particle size after hydrogenation. Mechanistic aspects of the hydrogenation of PIP in the presence of RhCl3/TPPMS were proposed on the basis of the observed kinetic results. Kinetic experiments for PIP hydrogenation in aqueous media indicate that the hydrogenation rate is first order with respect to catalyst and carbon-carbon double bond concentration. The hydrogenation rate was dependent on catalyst concentration, temperature and hydrogen pressure, and PIP particle size. The apparent activation energy over the temperature range of 120-140 degrees C was found to be 117.0 kJ/mol. HPIP (96%HD) has high thermal stability with a maximum decomposition temperature of 462 degrees C and a glass transition temperature of -49 degrees C. Dynamic mechanical analysis indicated that HPIP had a maximum storage modulus due to the saturated carbon domains of the ethylene segments in the polymer chains.
The aim of this study is to modify demolition concrete waste (CW) with oleic acid (OA), to be used as filler in polymeric composites for the building industry. The OA was chosen in order to ease the mixing of the CW into the polymeric matrix. In this article, we report the preparation and characterization of this CW–OA filler. After crushing and sifting, the CW particles were chemically modified with OA via sonication. The results of the modification were assessed using X-ray fluorescence, Fourier transform infrared spectroscopy, thermogravimetry, differential scanning calorimetry, wide angle X-ray diffraction, and scanning electron microscopy coupled with energy-dispersive X-ray detector. The FT-IR spectrum revealed that the OA was bonded to the surface of the CW particles by the carboxylate group. The TG/DTG curves showed an increase in the thermal stability of the OA, due to this bonding on the CW surface. The SEM and EDX analysis showed the insertion of OA on the CW surface. The results suggest that the proposed CW–OA modification was successful. This material can be used as an interesting ecofriendly filler in polymeric composites.
The graft copolymerization of styrene onto nanosized polyisoprene (PIP) was carried out by using cumene hydroperoxide and tetraethylene pentamine as redox initiators. The high conversion and high degree of grafting could be achieved when a small particle was used as the core polymer. The grafting efficiency and monomer conversion increased with increasing reaction temperature and monomer concentration. Transmission electron microscopy indicated that the small PIP nanoparticles were completely coated with polystyrene (PS) by grafting resulting in a core shell morphology of nanosized graft PIP. Nanosized PIP and nanosized PS-g-PIP could be used as compatibilizers for vulcanized rubber latex. The addition of nanosized PIP and PS-g-PIP strongly influenced the mechanical properties of the natural rubber (NR)-based compound. Incorporation of nanosized PIP and PS-g-PIP resulted in an improvement of the resistance of the compounds to heat aging. Copyright © 2011 John Wiley & Sons, Ltd.
Nanosized ethylene–propylene rubber (EPM) latex with a particle size of 47 nm was synthesized via an alternative route consisting of isoprene (IP) polymerization followed by hydrogenation. First, the IP monomer was polymerized by differential microemulsion polymerization to obtain polyisoprene (PIP) rubber latex with a particle size of 42 nm. The structure of synthetic PIP was hydrogenated at the carbon–carbon double bonds to produce an ethylene–propylene copolymer by diimide reduction in the presence of hydrazine and hydrogen peroxide using boric acid as promotor. The degree of hydrogenation was determined by proton nuclear magnetic resonance (1H‐NMR) spectroscopy and the structure of the ethylene–propylene copolymer was identified by 13C‐NMR spectroscopy. In nanosized PIP hydrogenation, the hydrogenation level was found to be increased by boric acid addition. An EPM yield of 94% was achieved using a hydrogen peroxide : hydrazine ratio of 1.5 : 1. The EPM produced from PIP has high thermal stability with the maximum decomposition temperature of 510°C and a glass transition temperature of ‐42.4°C close to commercial ethylene–propylene diene rubber. Dynamic mechanical analysis indicated that EPM had a maximum storage modulus due to the saturated carbons domains of the ethylene segments in the polymer chains. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Hydrogenated polyisoprene (HPIP) nanoparticles, synthesized via organic solvent-free hydrogenation using RhCl3/TPPMS as catalyst, are novel nanofillers for natural rubber (NR) blends. Hydrogenation of a polyisoprene (PIP) emulsion was carried out in a Parr reactor. Rhodium trichloride (RhCl3.3H2O) and monosulfonated triphenylphosphine (TPPMS) were used as the catalyst precursor. The HPIP was characterized by proton nuclear magnetic resonance spectroscopy. The PIP hydrogenation in the absence of organic solvent is a first-order reaction with respect to carbon– carbon double bond concentration, and the rate constant was dependent on catalyst concentration. The highest hydrogenation degree of 93 % was achieved at a catalyst concentration of 250 μM with a reaction time of 12 h. The NR/HPIP blends (blend ratio = 80:20) after thermal ageing show high % retention of their tensile strength and modulus, maintaining 94.5% and 93.7%, respectively. Moreover, a combination of HPIP in NR improved the ozone resistance at the surface of the rubber blends. Therefore, the NR/HPIP composite exhibited a good retention of tensile properties after thermal aging and good resistance toward ozone.
Polyisoprene–montmorillonite (PIP–Mt) nanocomposites with an average particle size of 30 ± 7.2 nm and narrow size distribution (20–50 nm) were successfully synthesized via differential microemulsion polymerization. X-ray diffractometry analysis revealed that PIP was intercalated in the Mt layers expanding the d spacing of the Mt layer from 3.1 nm to 3.8 nm. The SDS (surfactant) concentration, isoprene monomer (IP) to water ratio and Mt loading were all found to affect the IP conversion level, and the solid content and particle size of the obtained PIP–Mt nanocomposites. An IP conversion level of 81% and a solid content of 20% were achieved at 0.25 wt.% 2,2-azoisobutyronitrile (AIBN), 10 wt.% Mt, 10 wt.% SDS and an IP:H2O ratio of 0.24:1. These PIP–Mt nanocomposites could be used as an effective nano-filler in natural rubber (NR) latex for the preparation of NR/PIP–Mt composites, improving the mechanical properties compared to the unfilled NR. NR filled with PIP–Mt at 2 wt.% showed a 1.6 and 1.1 fold higher tensile strength and a modulus of elasticity at 300% elongation, respectively. Furthermore, NR/PIP–Mt composites at 2 wt.% Mt loading improved the thermal aging compared to unfilled NR, with an 87.6%, 96.2% and 84.0% retention of the tensile strength, elongation at break and modulus of elasticity, respectively compared to 52.5%, 88.9% and 58.8% for the unfilled NR.
Hydrogenated polyisoprene (HPIP)-SiO2 nanocomposites were synthesized via differential microemulsiion polymerization followed by diimide hydrogenation. First, the isoprene monomer was polymerized on the silane treated nanosilica by differential microemulsion polymerization to obtain polyisoprene (PIP)-SiO2 nanoparticles with a particle size of 43 nm. PIP-SiO2 latex was subsequently hydrogenated at the carbon–carbon double bonds by diimide reduction in the presence of hydrazine and hydrogen peroxide with boric acid as promotor to provide HPIP-SiO2 nanocomposites. Core–shell morphology consisting of silica as the nano-core encapsulated by HPIP as the nano-shell was formed. The highest hydrogenation degree of 98 % was achieved at a ratio of hydrogen peroxide to hydrazine of 1.5:1. The nanosized HPIP-SiO2 at 98 % hydrogenation showed a maximum degradation temperature of 521 °C resulting in excellent thermal stability, compared with unfilled PIP (387 °C). A new nanocomposite of HPIP-SiO2 could be used as a novel nanofiller in natural rubber. Consequently, HPIP-SiO2/NR composites had improved mechanical properties and exhibited a good retention of tensile strength after thermal aging and good resistance toward ozone exposure.
Monodispersed polyisoprene–SiO2 nanoparticles were successfully synthesized by a differential microemulsion polymerization of isoprene on silane treated nanosilica. Core–shell morphology was formed consisting of silica as the nano-core encapsulated by polyisoprene (PIP) as the nano-shell, as confirmed by TEM. PIP–SiO2 nanoparticles were produced at 20–60 nm with a narrow size distribution resulting in a reduced nano-SiO2 aggregation in the PIP matrix. The influence of surfactant concentration, monomer/water ratio and SiO2 loading on particle size, monomer conversion as well as grafting efficiency was investigated. The monomer conversion was 87% and the polymer grafting efficiency was as high as 78% at an extremely low surfactant concentration (3 wt.% based on monomer). For rubber applications, the PIP–SiO2 nanocomposite has been used as an effective nano-filler in natural rubber (NR) latex and the NR filled with PIP–SiO2 prevulcanizate clearly showed an improvement in the storage modulus, tensile strength, tensile modulus, and anti-ageing properties.
A water-soluble rhodium catalyst has been found to be an efficient catalyst for hydrogenation of unsaturated polymers in the absence of any organic solvent. Natural rubber (NR) latex and synthetic polyisoprene (PIP) emulsion were hydrogenated using rhodium trichloride (RhCl3·3H2O) and different ligand types, triphenylphosphine (PPh3), trisulfonated triphenylphosphine (TPPTS) and monosulfonated triphenylphosphine (TPPMS) as a catalyst precursor. The hydrogenated NR and PIP were characterized by proton nuclear magnetic resonance (1H NMR). A low degree of hydrogenation (HD) was observed when using RhCl3/PPh3 or RhCl3/TPPTS. In contrast, a high HD of 85.8% was achieved by using RhCl3/TPPMS. The catalytic behavior could be well explained by the Hartley ionic spherical micelle model. The HD increased with increasing catalyst amount, reaction temperature and H2 pressure. The catalyst activity of RhCl3/TPPMS for NR hydrogenation was found to be lower than that for PIP hydrogenation for all conditions due to impurities in the latex, including protein. The hydrogenated NR (86%HD) has high thermal stability with a maximum decomposition temperature of 466 °C and a glass transition temperature of −60 °C. From dynamic mechanical analysis, hydrogenated NR had a maximum storage modulus due to the saturated carbon domains of the ethylene–propylene segments in the polymer chains.
Poly[(butyl acrylate)-co-(methyl methacrylate)-co-(methacrylic acid)] latex particles were synthesized via differential microemulsion polymerization. The effect of initiator type and methacrylic acid incorporation were investigated. The initiator type could significantly affect the particle size and the molecular weight of the resulting polymer and 2,2′-azobisisobutyronitrile produced the smallest particle size. The incorporation of methyl methacrylate (MAA) in the copolymer and terpolymer structures was confirmed by FTIR and NMR spectroscopy, and DSC in that the carbonyl peak of carboxylic acid at 1,700 cm−1 in the FTIR spectrum was observed when the MAA amount was high enough, the peak areas at 0.9 ppm in the NMR spectrum confirmed the participation of MAA from the increasing proton signals and the glass transition temperature and polarity of the polymer increased when the MAA amount was increased. This supported that the MAA was incorporated into the polymer chains. MAA was found to produce a vitrification effect during the polymerization.
The gel content of rubber from high-ammonia latex (HA-latex) decreased significantly after deproteinization with proteolytic enzyme. The addition of 1-2% ethanol in toluene solution reduced the gel content of rubbers from HA-latex, deproteinized HA-latex (HA-DP) and pale crepe. Transesterification of the rubber in toluene solution with sodium methoxide dissolved the gel fraction. The gel fractions solubilized after transesterification showed molecular weight distribution rich in low molecular-weight fraction. The Huggins k′ constant of the fractionated rubbers from solubilized-gels was in the range of 0.42-0.45, lower than that of the fractionated HA-DP of 0.5-0.8. This indicates that all the branch-points were decomposed by transesterification to form linear molecules. The M̄n values of rubber chains assembling the gel was 5.5-8.3 × 105 by 13C-NMR measurements of the ratio between cis- and trans-isoprene units, which were comparable to the molecular weight between crosslinks, Mc, of 7-11 × 105 by swelling measurements. These findings suggest that the branching and crosslinks are composed of two types of branch-points, i.e. one by association or aggregation of proteins or oligopeptides at the initiating end and the other by ester linkages including phosphoric ester at the terminal end.
This article summarizes the recent advances made in the synthesis of nanoparticles of polymer latexes with high ratios of polymer to surfactant by microemulsion polymerization, particularly in the last 10 years. One emerging theme is the increasing use of semi-continuous microemulsion polymerization to prepare a wide range of nanoparticles of polymer latexes with polymer/surfactant ratios larger than 10 and particle sizes ranging from 20 to 80 nm in diameters, among which, the pioneering work was polymerization in Winsor I-like systems (monomer in equilibrium with o/w microemulsion). Based on a similar principle, microemulsion polymerization by either drop-wise addition (at specified points or continuously) or hollow-fiber feeding of monomer was developed.
The polymerization of vinyl acetate in oil-in-water microemulsions stabilized with cetyltrimethylammonium bromide (CTAB) is reported here as a function of surfactant concentration. Reaction rate decreases as the CTAB/water ratio is increased in the parent microemulsions. Polymer particles in the latexes grow with conversion; they also become bigger as the initial surfactant content is increased. Number-average molar masses are smaller than those expected by termination by chain transfer to monomer, but weight-average molar masses increased as the surfactant concentration in the parent microemulsion is raised. However, the latter are much smaller than those obtained by polymerization in an emulsion stabilized with the same surfactant. Possible explanations to this unusual behavior are provided here.
A comprehensive experimental study concerning the influence of various types of initiator–emulsifier systems on emulsion polymerization of methacrylate monomers (2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA) and butyl methacrylate (BMA)) reveals interesting relations between initiator and surfactant hydrophilicity on the one hand and the hydrophilicity of the monomers on the other hand. For the water-soluble HEMA stable latexes are only obtained if hydrophobic initiators such as 2,2′-azobisisobutyronitrile or dibenzoyl peroxide in combination with alkyl sulfate surfactants with carbon chain lengths greater than 10 or surface active initiators of the 2,2′-azobis(N-2′-methylpropanoyl-2-amino-alkyl-1)-sulfonate type with alkyl chain lengths greater than 8 are employed. Stable nano size range poly(2-hydroxyethyl methacrylate) (PHEMA) particles have been prepared also by batch emulsion polymerization using ionic surface active initiators (inisurfs). The results clearly show that the formation of stable latex particles requires a proper choice of the initiator–emulsifier system regarding its hydrophilic–hydrophobic balance. The PHEMA particles prepared with surface-active initiators keep their identity and spherical shape even in the dried state whereas in the case of the other initiator–emulsifier systems complete coagulation and coalescence occurs during drying.
A series of emulsion systems based on styrene and a mixture of styrene/butyl acrylate (BA) in the presence of the polystyrene-co-maleic anhydride cumene terminated (SMA) copolymer as surfactant were developed. The extent to which varying the monomer and surfactant concentration, as well as the copolymer molecular weight (Mw) could affect the polymer particle size during the polymerization was examined. The particle size was determinated by dynamic light scattering (DLS) and atomic force microscopy (AFM). The system showed that the particle diameter is increased with increased content of monomer. It was also observed that as surfactant concentration is decreased the particle size is increased. On the other hand, by increasing the copolymer molecular weight the particle diameter is also increased. The experimental results demonstrated that it is possible to obtain nano-sized particles with the SMA block copolymer as surfactant.Surface tension measurements were made in order to understand the SMA copolymers behavior in aqueous solution. SMA copolymers of 1600, 1700 and 1900 Mw were studied under two different alkaline conditions in order to understand its behavior at different ionic strength.
Polymerization of methyl methacrylate initiated with benzoyl peroxide was studied in O/W microemulsion stabilized with SBOA (sodium 12-butinoyloxy-9-octadecenate). The growth of monomer-swollen polymer particles was studied with photon correlation spectroscopy (PCS). It was found that nucleation process continues to very high conversion and the polymerization in large polymer particles formed at the early stage could not be ignored. The polymerization kinetics was also studied with a dilatometer. The growth of particles and the polymerization kinetics both suggest that the polymerization takes place in the core of the particles.
Oil-in-water-type (o/w) microemulsion and emulsion polymerizations of butyl acrylate (BA) initiated by ammonium peroxodisulfate (AP, a water-soluble radical initiator) and dibenzoyl peroxide (DBP, an oil-soluble radical initiator) with sodium dodecylsulfate (SDS) as an anionic emulsifier were kinetically investigated. Emulsion polymerizations were faster than those in microemulsion. The rates of emulsion or microemulsion polymerization were larger with AP. The size of particles and the polymer molecular weight decreased with increasing temperature. The number of particles and the average particle radical number increased with increasing temperature. The overall activation energy (Eo) for the BA radical polymerization was found to decrease in the following order: bulk or solution (ca 120 kJ mol−1) > microemulsion (ca 60 kj mol−1) > emulsion polymerization (ca 15 kj mol−1). The Eo for the microemulsion polymerization was independent of conversion ca up to 60%. The strong decrease in the Eo observed after 60% conversion and the low value for Eo in disperse systems were ascribed to diffusion controlled termination.
The mechanisms of microemulsion polymerizations stabilized by sodium dodecyl sulfate in combination with pentanol were investigated with a water-insoluble dye as the probe. The major parameters chosen for study were the types of initiators [water-soluble sodium persulfate (SPS) vs oil-soluble 2,2′-azobisisobutyronitrile (AIBN)] and the polarity of the monomers [relatively hydrophobic styrene (ST) vs relatively hydrophilic methyl methacrylate (MMA)]. Both continuous particle nucleation and limited particle flocculation had a significant influence on the polymerization kinetics. For the polymerizations investigated in this work, the relatively low initiation efficiency of AIBN resulted in a reaction system showing a quite different particle nucleation mechanism than that of the ST polymerization with SPS. The formation of particle nuclei in water was suppressed to some extent, and microemulsion droplet nucleation predominated in the ST polymerization initiated by AIBN. Homogeneous nucleation played an important role, and a mixed mode of particle nucleation (microemulsion droplet nucleation and homogeneous nucleation) was operative in the MMA polymerization. The MMA polymerization experienced stronger particle flocculation than its ST counterpart. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2005–2013, 2005
A water-in-oil microemulsion, water-in-cyclohexane stabilized by poly(ethylene glycol) tert-octylphenyl, was developed to prepare poly(methacrylic acid) (PMAA) particles. Up to 100% conversion of the amphiphilic monomer, methacrylic acid (MAA), which could not be converted to the polymer efficiently in a dioctylsulfosuccinate sodium salt/toluene microemulsion, was achieved. The viscosity-average molecular weight of the PMAA prepared was 1.45 × 105 g/mol. The effects of some polymerization parameters, including the reaction temperature and the concentrations of the initiator and the monomer, on the polymerization of MAA were investigated. The results showed that the polymerization rate of MAA was slower than that of acrylamide in the microemulsions reported in the literature. The degree of conversion increased with the initiator concentration, reaction temperature, and monomer concentration. However, the stable microemulsions became turbid during the polymerization when the reaction temperature was at 70°C or at a high monomer concentration (40 wt %) The synthesized PMAA particles were spherical and had diameters in the range of ∼50 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2497–2503, 2006
The synthesis of nanosized poly(methyl methacrylate) initiated by 2,2′‐azoisobutyronitrile via differential microemulsion polymerization has been investigated. Poly(methyl methacrylate) with a molecular weight of around 1 × 10 ⁶ and a particle size of about 20 nm was achieved under mild reaction conditions. A typical condition was that the surfactant amount required could be as low as 1/130 of the monomer amount in weight, and the surfactant/water ratio could be as low as 1/600, which is much less than the corresponding amounts reported in the literature. “Molecular bricks”, i.e., nanoparticles in which there are only one or two polymer chains, can be achieved using mild conditions by differential microemulsion polymerization, which may have potential applications for making molecular devices.
magnified image
The emulsion and microemulsion copolymerizations of partially water-soluble monomers ethylacrylate (EA) and methylmethacrylate (MMA) were studied with the water-soluble initiator KPS and the oil soluble initiator AIBN. On changing from an emulsion to microemulsion system the shift in relative contribution of the different phases involved in particle formation is expected to control the kinetic and colloidal parameters and hence the solid content and latex stability. This has been tested using the water-soluble initiator KPS and the oil-soluble initiator AIBN. The microemulsion system initiated with KPS resulted in a much higher particle size and lower particle stability, whereas the emulsion system initiated with KPS at identical reaction conditions resulted in a stable colloidal polymer particles of very low particle size at a higher solid content. On the contrary, AIBN-initiated microemulsion generated a stable nanolatex as compared to the emulsion system. The copolymers, isolated during the nucleation stage, were analyzed for their composition using H NMR and for their thermal properties using DSC.
The interaction between sodium dodecyl sulfate (SDS) and ethyl(hydroxyethyl)cellulose (EHEC) has been investigated at different temperatures by means of surfactant and counterion self-diffusion, conductivity, and time-resolved fluorescence quenching. A strengthened polymer-surfactant interaction with increasing temperature is demonstrated in several ways: in particular, a reduced critical micelle concentration, a reduced cooperativity in surfactant binding to the polymer, a decreased degree of counterion binding, and a lowered micelle aggregation number as temperature is increased. In the absence of polymer, these quantities are apparently higher and approximately invariant on temperature changes. The information on the polymer-surfactant interaction provides insight into the thermal gelation in aqueous mixtures of a nonionic polymer and an ionic surfactant.
Low relative molecular weight trans-1,4-polyisoprene oligomers were synthesized successfully by bulk precipitation and solution polymerization with supported titanium catalyst using hydrogen as relative molecular weight modifier. The effects of polymerization conditions on intrinsic viscosity ([η]), catalyst efficiency (CE) and structure of polymer were studied. Increasing the hydrogen pressure resulted in the decrease of [η] of the polymer. With the increasing of hydrogen pressure and reaction temperature, CE decreased but still maintained above 2500 g polymer/g Ti. The percentage composition of (trans-1, 4-unit) in the polymer was over 90% in all results. The crystallinity of polymer was about 50–60% with Tm being about 60°C. The relative molecular weight distribution index (MWD) was quite difference according to the polymerization method. While number average molecular weight (Mn) exceeded 860, polymer turned from viscous materials to fragile wax materials, and then to toughness materials at 1800. Dynamic property testing showed that the additional of this oligomer could increase the wet-skid resistance of the rubber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
The kinetics of microemulsion polymerization depend on the structure of the initial microemulsion and the transport of species between the aqueous domain, the micelles, and the polymer particles. The water solubility of the monomer and the proximity of the initial microemulsion composition to a phase boundary are key considerations for studying microemulsion polymerization kinetics and producing the desired products. Complications frequently arise in the synthesis of copolymers or the incorporation of controlled polymerization mechanisms because of the compartmentalized nature of microemulsion polymerizations.
magnified image
Poly(methyl methacrylate) nanosize particles were synthesized by a differential microemulsion polymerization process. Sodium dodecylsulfate and ammonium persulfate were used as the surfactant and initiator, respectively. The effects of reaction conditions on the particle size have been investigated. A particle size of less than 20 nm in diameter has been achieved with surfactant/monomer and surfactant/water weight ratios of 1:18 and 1:120, i.e. much milder conditions than those previously reported in the literature.
TEM image of nanoparticles prepared via differential microemulsion polymerization.
magnified image TEM image of nanoparticles prepared via differential microemulsion polymerization.
The batch emulsion polymerization kinetics of styrene initiated by a water-soluble peroxodisulfate at different temperatures in the presence of sodium dodecyl sulfate was investigated. The curves of the polymerization rate versus conversion show two distinct nonstationary-rate intervals and a shoulder occurring at a high conversion, whereas the stationary-rate interval is very short. The nonstationary-state polymerization is discussed in terms of the long-term particle-nucleation period, the additional formation of radicals by thermal initiation, the depressed monomer-droplet degradation, the elimination of charged radicals through aqueous-phase termination, the relatively narrow particle-size distribution and constant polydispersity index throughout the reaction, and a mixed mode of continuous particle nucleation. The maximum rate of polymerization (or the number of polymer particles nucleated) is proportional to the rate of initiation to the 0.27 power, which indicates lower nucleation efficiency as compared to classical emulsion polymerization. The low activation energy of polymerization is attributed to the small barrier for the entering radicals. The overall activation energy was controlled by the initiation and propagation steps. The high ratio of the absorption rate of radicals by latex particles to the formation rate of radicals in water can be attributed to the efficient entry of uncharged radicals and the additional formation of radicals by thermally induced initiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1477–1486, 2000
Polymer nanoparticles were prepared from monomers such as styrene (St), butyl methacrylate (BMA), butyl acrylate (BA), methyl methacrylate (MMA), and methyl acrylate (MA) using a modified microemulsion polymerization process. With this process high polymer: surfactant weight ratios (7 : 1 or greater), relatively concentrated (10–30 wt.-%) latexes and small (10–20 nm) particle diameters were attained. Nucleation mechanisms were investigated through observations of the particle size change during the polymerization.
Phase diagrams for monomer (methyl acrylate containing microemulsions) are shown and described. Polymerizations of a series of microemulsified monomer reveals the expected linear dependence of 1/DS vs. [S]/[M] for pentanol acting as a chain transfer agent and giving a value of 5.1 × 10−4 for Cs. No break in molecular weight behavior was shown as a result of micellization at higher water contents. A comparison of molecular weights obtained by various classical methods (solution, emulsion, bulk) are also given.
Microparticles and nanoparticles of poly(lactic acid-co-glycolic acid) (PLAGA) are excellent candidates for the controlled release of many pharmaceutical compounds because of their biodegradable nature. The preparation of submicron PLAGA particles poses serious challenges that are not necessarily present when preparing microparticles. We have evaluated several combinations of organic solvents and surfactants used in the formulation of PLAGA nanoparticles. Critical factors such as the ability to separate the nanoparticles from the surfactant, the ability to re-suspend the nanoparticles after freeze-drying, formulation yield and nanoparticle size were studied. The smallest particles were obtained using the surfactant/solvent combination of sodium dodecyl sulfate and ethyl acetate (65 nm) and the largest particles were obtained using poly(vinyl alcohol) and dichloromethane (466 nm). However, the optimal nanoparticles were produced using either acetone or ethyl acetate as the organic solvent and poly(vinyl alcohol) or human serum albumin as the surfactant. This is because the most critical measure of performance of these nanoparticles proved to be their ability to re-suspend after freeze-drying.
The prepolymer polyurethanes (PUs) based on isophorone diisocyanate (IPDI), poly(propylene glycol) (PPG), 1,4-butanediol (BDO)
and dimethylopropionic acid (DMPA) were synthesized at 75–80 °C for 7–8 hours, using dibutyltin dilauate (DBTDL) as catalyzer,
and polyurethane-acrylate hybrid emulsion was prepared after methyl methacrylate (MMA) was polymerized, using potassium persulfate
and azobisisobutyronitrile (AIBN) as initiator, respectively. The influences of these factors such as the kind of initiator,
the feed method of initiator and the addition of initiator on properties of polyurethane-acrylate were studied. The FTIR and
GPC of aqueous polyurethane were analyzed. The FTIR spectra show that the degree of microphase-separate between the soft segments
and rigid segments is high. The analysis of molecular weights stated that molecular weights increased most significantly after
amine was added. The experimental results reveal that the appearance of emulsion is excellent, the film is harder and the
water absorption radio of the film is less when oil-solubility AIBN is used as initiator. The semi-continuous can increase
the molecular weight of polymer and the optimum amount of the initiator was 3% for MMA.
Seeded and ab initio emulsion polymns. of isoprene using redox initiation systems were investigated and suitable reaction conditions detd. to prep. polyisoprene latexes with minimal crosslinking. Polymns. initiated with the potassium persulfate/sodium bisulfite (KPS/SBS) redox couple had a significant inhibition period and low yield. Polymns. initiated with the tert-Bu hydroperoxide/tetraethylenepentamine redox couple showed reasonable yields and no apparent inhibition. It is postulated that the lipophilic nature of the t-Bu group plays a favorable role in the entry of hydroperoxide-initiated oligomeric radicals, while persulfate-initiated radicals are more likely to undergo aq. phase termination before entry. The crosslinking reaction by benzoyl peroxide (BPO) at 70 °C was investigated using this lightly crosslinked polyisoprene latex. 1H NMR and gel permeation chromatog. results were consistent with a reaction mechanism in which the radicals formed by the decompn. of BPO react exclusively with polyisoprene to abstr. a hydrogen atom, and the resulting radicals react by termination to form crosslinks. No loss of double bonds was found, suggesting that radical formation is overwhelmingly achieved by hydrogen abstraction and crosslinking occurs by termination between two radicals. Crosslinking was accompanied by chain scission, which was obsd. only at the beginning of the reaction. At low wt.-fractions of polymer, the rate of crosslinking was dependent on the concns. of BPO and abstractable hydrogens in a manner consistent with the postulated mechanism. [on SciFinder(R)]
The two-component redox-initiation system, cumene hydroperoxide (CHP) and tetraethylene pentamine (TEPA), was used to polymerize dimethylaminoethyl methacrylate (DMAEMA) in the presence of synthetic polyisoprene latexes. The modified latex particles are postulated to possess a 'hairy layer' of surface-grafted poly(DMAEMA) chains formed via an abstraction reaction between cumyloxy radicals and the isoprene moieties present in the seed polymer. The modified latexes exhibited enhanced colloidal stability to low pH, and dynamic light scattering showed that the apparent particle size was sensitive to pH. The rate of polymerization was followed by reaction calorimetry. No steady-state polymerization was observed, with a continual increase in the number of propagating chains at all initiator feed rates investigated. The data for particle size and colloidal stability, together with the calorimetric data, are consistent with radical production at the particle surface, and with abstraction near the interface being a rare event. Further, there is evidence that radical production by the redox couple is relatively slow. While this 'topology-controlled' reaction is responsible for the formation of the hairy layer and latex stability, the dominant polymerization process appears to be the formation of ungrafted poly(DMAEMA) in the water phase. (C) 2004 Elsevier Ltd. All rights reserved.
The kinetics of o/w electrostatically and sterically-stabilized microemulsion polymerization of styrene with and without macromonomeric azoinitiator (macroinimer; MIM) have been investigated. The microemulsion polymerization stabilized by the ionic emulsifier sodium dodecyl sulfate (SDS) or the non-ionic emulsifier Tween 20 (Tw 20) was initiated by ammonium peroxodisulfate (APS)/sodium thiosulfate (STS) redox system. The rate of polymerization vs. conversion curve shows the two non-stationary rate intervals. This behavior is a result of two opposing effects, the continuous particle nucleation and the decrease of monomer concentration at the reaction loci. The addition of MIM favors the additional particle nucleation. The sterically (Tw 20)-stabilized microemulsion polymerization is much faster than that of the electrostatically (SDS)-stabilized microemulsion polymerization. This was attributed to the higher Tw 20 concentration and increased solubilization of MIM and comonomer concentration in the polymer particles. The formation of initial large polymer particles is attributed to the intensive agglomeration polymer particles with monomer droplets. The continuous decrease in the average size is mainly attributed to the additional particle nucleation.
Miniemulsions are specially formulated heterophase systems consisting of stable nanodroplets in a continuous phase. The narrowly
size distributed nanodroplets of 50 to 500 nm can be prepared by shearing a system containing oil, water, a surfactant, and
an osmotic pressure agent which is insoluble in the continuous phase. Since each of the nanodroplets can be regarded as a
batch reactor, a whole variety of reactions can be carried out starting from miniemulsions clearly extending the profile of
classical emulsion polymerization. This articles gives an overview about the mechanism of formation of and polymerizations
in miniemulsions and reviews the current standing of the field for both the synthesis of new polymers and of dispersed hybrid
systems.
Synthesis of nanosized polyisoprene via differential microemulsion polymerization, the 4th Mathematics and Physical Graduate Congress (MPSGC)
- B Suppaibulsuk
- P Prasassarakich
Suppaibulsuk, B., P. Prasassarakich and G. L. Rmpel (2008). Synthesis of nanosized polyisoprene via differential
microemulsion polymerization, the 4th Mathematics and Physical Graduate Congress (MPSGC).
- Lamp