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Synthesis and quantitative analyses of acrylamide-grafted poly (lactide-co-glycidyl methacrylate) amphiphilic copolymers for environmental and biomedical applications

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... Crosslinking led to the enhancement of mechanical and thermal properties and was dependent on the content of GMA units. In another study, P(LA-co-GMA) copolymer and its partly UV crosslinked counterpart were grafted with a pH-responsive polyacrylamide (PAAm), by UV-assisted reactions using acrylamide (AAm) and N,N -methylene bisacrylamide monomers, and various photoinitiator systems [77]. These materials have the potential for use in biomedical and environmental applications due to their amphiphilic and pH-responsible properties. ...
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Polylactide (PLA) is presently the most studied bioderived polymer because, in addition to its established position as a material for biomedical applications, it can replace mass production plastics from petroleum. However, some drawbacks of polylactide such as insufficient mechanical properties at a higher temperature and poor shape stability have to be overcome. One of the methods of mechanical and thermal properties modification is crosslinking which can be achieved by different approaches, both at the stage of PLA-based materials synthesis and by physical modification of neat polylactide. This review covers PLA crosslinking by applying different types of irradiation, i.e., high energy electron beam or gamma irradiation and UV light which enables curing at mild conditions. In the last section, selected examples of biomedical applications as well as applications for packaging and daily-use items are presented in order to visualize how a variety of materials can be obtained using specific methods.
... The chemical shifts at δ = 1.19 (H c ), and δ = 3.65 (H d ) ppm correspond to -COCH 2 -, and -NHCH 2groups on the molecular chains of PAM/BIS/GO and PAM/ BIS, respectively. The sharp formant at δ = 4.80 ppm is associated with a proton of solvent D 2 O [56]. Furthermore, the characteristic resonance peaks of PAM/BIS/GO observed at δ = 6.23 (H f ) are attributed to protons in the -CONHvia the reaction of PAM(-CONH 2 ) and GO ( -COOH) rather than PAM/BIS and PAM. ...
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Herein, a flexible and robust hydrogel, polyacrylamide hydrogel containing graphene oxide and N, N-isopropyl di-acrylamide, was developed through a novel in-situ synthesis procedure. A high-sensitive capacitive pressure sensor was then fabricated through an assembly of the hydrogel wrapped by an insulated ultra-thin polyethylene film as the primary dielectric, and two soft-plated woven fabrics as conductive layers. The nanocomposite (NC) hydrogel displayed superior strength and resilience that the breaking strength and elongation at break are close to 45 kPa and 2110 %, and a 50% cyclic compressive strain for 50 times along with a compressive strength of 84.17 kPa was exhibited, implying NC-hydrogel was ideal. The sensitivity of the as-made capacitive pressure sensor reached incredibly up to 2.6; the sensing range was available from 0∼80%. Consequently, this conductive pressure sensor is profoundly high-potential for capturing some slight limbs' movements and strain in response to even the slightest amounts of pressure.
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In the present investigation, we have evaluated the in vitro drug release of 5-aminosalicylic acid (5-ASA) using polyacrylamide grafted oatmeal (OAT-g-PAM). The graft co-polymer was synthesized by following free radical co-polymerization pathway using acrylamide as a monomer and ceric ammonium nitrate as a free radical initiator in the presence of microwave. The matrix tablet was prepared using the different grades of developed graft co-polymers following standard protocol. In vitro release phenomena of 5-ASA from the prepared matrix tablet up to 12 h in different buffer solution, i.e., pH 2.0, 7.0 and 7.4, an ideal condition for colon specific drug delivery was studied. The release rate of 5-ASA can be controlled efficiently by tuning the pH value. The drug release kinetic of 5-ASA from different matrix tablet was evaluated on the basis of in vitro controlled drug release results. The result indicates that the novel pH-sensitive matrices under study showing Fickian diffusion mechanism and potentially constructive for colonic drug delivery system.
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Abstract A polymeric adsorbent based on sodium alginate (SAG) grafted with polyacrylamide (PAM) (SAG- g-PAM) was synthesized using an ultrasound-assisted method. The addition polymerization was carried out with ammonium persulfate as the initiator, at different acrylamide (AM) concentrations. The SAG-g-PAM copolymers were evaluated by FTIR and 13C NMR spectroscopies, thermogravimetric analysis, grafting efficiency (%GE) and intrinsic viscosity in NaCl solution at 25 °C. Graft copolymers could be obtained in reaction lasting until 10 min by using ultrasound energy with grafting efficiency above 75%. The decolorization efficiency and adsorption capacity of the SAG- g-PAM copolymers were investigated in the adsorption of methylene blue (MB). The dye adsorption was pH dependent, and adsorption capacity (69.13 mg/g) maxima was at pH 10. All the graft copolymers have shown the same decolorization efficiency (99%), and the best one for MB removing is the SAG-g-PAM6 (%GE = 75%), since lower acrylamide content is required in the synthesis.
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The aim of present study was to develop a pH responsive rate controlling polymer by acrylamide grafting onto pullulan. Grafting was performed using free radical induced microwave assisted irradiation technique using ceric ammonium nitrate as free radical inducer. Acrylamide grafted pullulan (Aam-g-pull) was characterized by Fourier transform infrared spectroscopy, solid state 13C nuclear magnetic resonance and field emission scanning electron microscopy. In vitro enzymatic degradation of Aam-g-pull showed degradation of 22.45% after 8 h with degradation rate constant (k) of 0.019 min-1. In vitro cytotoxicity test did not show cell viability below 80% on HepG2 cell line. Pirfenidone tablets were prepared by utilizing wet granulation method using Aam-g-pull as the only rate controlling polymer. The tablets were characterized in terms of in-process quality control parameters like weight variation, hardness, assay, and in vitro dissolution study. The dissolution study showed that the cumulative drug release in phosphate buffer pH 6.8 (rel3 h = 44.12 ± 0.56%) got a significant jump as compared to the release in 0.1 N hydrochloric acid (rel2 h = 26.78 ± 0.23%), confirming the material to be pH responsive. Aam-g-pull can be used as pH responsive rate controlling polymer.
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A controlled release fertilizer system based on phosphate bound-carboxymethyl starch-graft-polyacrylamide (P-CMS-g-PAM) has been prepared in order to deliver the phosphate fertilizer to the plant at a constant rate thereby. This system aims to increase fertilizer phosphorus use efficiency (FPUE) and maintaining a hydration level for the plant at the same time. Two types of starch phosphate monoesters were prepared using mono-ammonium (MAP) and di-ammonium phosphate (DAP). First, starch was converted to carboxymethyl starch and then was phosphorylated with mono-ammonium dihydrogen phosphate and di-ammonium dihydrogen phosphate. After phosphorylation, the samples were grafted with acrylamide in presence of methylene bisacrylamide as a crosslinking agent. The prepared systems of P-CMS-g-PAM were differently characterized by Fourier transformer infrared (FT-IR), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and phosphorous analysis. The swelling behavior was investigated. The kinetics of grafting reaction were also studied. The release behavior of phosphate bound was studied at pH 7 and 25 °C. The mechanism of the phosphate release from P-CMS-g-PAM was examined using the Korsmeyer-Peppas model.
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Spent Nickel cadmium (Ni-Cd) batteries are classified as hazardous waste due to the presence of toxic cadmium (Cd). Sustainable solution to this problem can be adoption of resource recovery methods for the reuse of Cd. This has been attempted in the present work using the biopolymer chitosan having inherent affinity for metals. Stability of chitosan in acidic medium was improved by grafting it with a suitable grafting agent and crosslinking. Further, it was used for the synthesis of acrylamide grafted chitosan based Cd ion imprinted polymer (CdIIP) using Cd as template and epichlorohydrin (EPI) as crosslinker for the selective recovery of Cd. Density Functional Theory (DFT) confirmed acrylamide as the best grafting agent with ΔG of −17.98 Kcal/mol for the acrylamide grafted chitosan. FTIR confirmed the grafting of acrylamide on chitosan as well as successful synthesis of CdIIP. EPI proved to be a better crosslinking agent as compared to glutaraldehyde (GLA) for CdIIP as confirmed by EDS. Adsorption of Cd on the CdIIP was influenced by pH, time, initial Cd concentration and CdIIP dose. The kinetic data fitted well to pseudo-second-order equation than first order with R² equals to 0.997. The monolayer adsorption capacity for Cd (167 mg/g) calculated using Langmuir isotherm model was in close approximation to the experimental adsorption capacity of 152 ± 3 mg/g. The thermodynamic data confirmed exothermic and spontaneous nature of adsorption. 84.3% of Cd could be recovered by CdIIP from the acidic leachate of the Ni-Cd battery waste. CdIIP could be effectively reused for five cycles.
Conference Paper
Amphiphilic surface-grafted poly(L-lactide-co-glycidyl methacrylate-graft-acrylamide-co-N,N’-methylenebisacrylamide) copolymer, P(LLA-co-GMA-g-AAm-co-MBAm) has been synthesized by a UV photopolymerization process. The grafted copolymer particles possess a combination of unique properties of biodegradable PLLA, PGMA, and PAAm polymers. The success of the grafting process was verified by FTIR and 1H NMR spectroscopy. FTIR results confirm the presence of P(AAm-co-MBAm) chains as grafted chains. Two characteristics 1H NMR signals of polyacrylamide appear at 2.0-2.1 and 1.5-1.6 ppm (overlap with PLLA methine proton) in the grafted copolymer, further ensuring the existence of polyacrylamide. Along with qualitative data, 1H NMR results also show that 0.8 mole % of acrylamide had been grafted, for which 58% of GMA double bonds had reacted. The grafted copolymers have high potential for use in various applications, especially in biomedical and environmental fields.
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An effort was made to formulate and evaluate pH-sensitive spray dried microspheres using hydrolyzed polyacrylamide-graft-gum karaya (PAAm-g-GK) for colon specific delivery of an anti-cancer agent, capecitabine. The synthesis of pH-sensitive PAAm-g-GK copolymer was done by free radical polymerization followed by alkaline hydrolysis and characterized satisfactorily. The microspheres were spherical in shape; drug entrapment efficiency was found to be in the range of 77.30% to 88.74%. Pulsatile swelling study indicates that the PAAm-g-GK consists of considerable pH-sensitivity. The in-vitro drug release suggested that the microspheres prepared using native GK were incapable to retard the drug release within 5h in the environment of stomach and small intestine. While, those microspheres prepared using pH-sensitive PAAm-g-GK copolymer having crosslinked with glutaraldehyde (GA), released little amount of drug within 5h, but maximum amount of drug was targeted to colonic region in a controlled manner up to 24h. For example, GK10 microspheres showed only 19.16% drug release at the end of 5th h, while about 80.14% of drug was targeted to colonic region. Cross-linking with GA reduced the early drug release in the upper part of gastrointestinal tract and guaranteed maximum drug release in the colonic region. A rapid enhancement in drug release was witnessed in rat caecal content medium due to the action of colonic bacteria on PAAm-g-GK copolymer.
Article
In the present work, a new flocculant, polyacrylamide-grafted chitosan nanoparticles (NCS-g-PAM), was synthesized by the copolymerization of acrylamide (AM) and chitosan nanoparticle (NCS) under ultraviolet irradiation using 2-hydroxy-4'- (2-hydroxyethoxy)- 2-methylpropiophenone as photo-initiator. The NCS was prepared by the ionic gelation between chitosan and sodium tripolyphosphate. The structure and morphology of NCS-g-PAM were characterized by Fourier Transform Infraredspectroscopy (FT-IR), X-ray diffraction, 1H-nuclear magnetic resonance spectrometry, scanning electron microscopy, and thermogravimetric analysis. The factors affecting the intrinsic viscosity and the yield of copolymer were studied, which showed that the optimum conditions for the synthesis of NCS-g-PAM were m AM: m NCS = 8:1, 0.15 g of initiator dosage, mCS: mTPP = 4.5:1, 1 min of ultrasonication time, 4 h of illumination time, and 30 min of stirring time. The NCS-g-PAM was found to be more effective than NC-g-PAM in the flocculation of both kaolin suspension and Cu2+ simulated wastewater. With 5 mg/L of polyaluminium chloride (PAC) coordinated and 1 mg/L of NCS-g-PAM it was confirmed to be appropriate for flocculating kaolin suspension.
Chapter
Polylactic acid (PLA) belongs to the family of aliphatic polyesters commonly made from α-hydroxy acids which include polyglycolic acid, [1, 2] or polymandelic acid [3] and are considered biodegradable and compostable. PLA is a thermoplastic, high strength, high modulus polymer which can be made from annually renewable resources to yield articles for use in either the industrial packaging field [4] or the biocompatible/bioabsorbable medical device market [5]. It is easily processed on standard plastics equipment to yield molded parts, film, or fibers. It is one of the few polymers in which the stereochemical structure can easily be modified by polymerizing a controlled mixture of the L or D isomers to yield high molecular weight amorphous or crystalline polymers which can be used for food contact and are generally recognized as safe (GRAS)[6]. PLA is degraded by simple hydrolysis of the ester bond and does not require the presence of enzymes to catalyze this hydrolysis. The rate of degradation is dependent on the size and shape of the article, the isomer ratio, and temperature of hydrolysis. A more detailed summary of degradation and lactic acid manufacturing is given in recent monographs [7, 8].
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The poly(L-lactic acid) (PLLA) has potential medical usage such as drug delivery since it can degrade into bioabsorbable products in physiological environments, while the degradation is affected by its crystallites. In this paper, the effects of film formation method and annealing on the crystallites formed in PLLA films are investigated. The films are made through solvent casting and spin coating, and subsequent annealing is conducted. The resulting morphology, molecular order, conformation, and intermolecular interaction are examined using optical microscopy, wide-angle X-ray diffraction, and Fourier transform infrared spectroscopy. It is observed that solvent casting produces category 1 spherulites while annealing the spin coated films leads to spherulites of category 2. The crystal structure of the two kinds of films also shows distinct features. The results enable better understanding of the crystallites in PLLA, which is essential for its medical application.
Article
I n this study polyacrylamide was prepared in various molar ratio contents of ethyl acetate and ethanol at 60ºC by free-radical precipitated polymerization method. The assignment of all stereosequences at pentad level of methine, hexad level of methylene, and triad level of carbonyl carbons of the polyacrylamide were observed using 13 C nuclear magnetic resonance spectroscopy (13 C NMR) in deuterium oxide at room temperature. Bernoullian and 1st-order Markov statistics were used for all carbons and the results were compared with experimental data by statistical method. It was shown that Bernoullian statistics model fit slightly better than 1st-order Markov statistics model for the assigned sequences. The results indicated that corresponding values of the probability (P m) and length average (N m) of meso addition were 0.443 and 1.698, respectively and no significant differences were observed by changing the molar ratios of the two solvents. By heteronuclear multiple quantum coherence (HMQC) as two-dimensional NMR spectroscopy, the methylene and methine groups were assigned by triad sequences in which isotactic contour was thoroughly isolated from syndiotactic and atactic contours. Therefore, isotactic triad sequence could only be calculated by 1 H NMR. In other words, isotactic placement value was calculated by using the integration of areas of methylene and methine protons (mm = 0.21) peaks.
Article
Polyacrylamide grafted graphene (PAM-g-graphene) from graphite oxide (GO) was successfully prepared by γ-ray irradiation with acrylamide monomers in aqueous at room temperature in this paper. Our strategy involves the PAM chains graft on the surface and between the layers of GO by in situ radical polymerization which led to the exfoliation of GO into individual sheets. Results show that the degree of grafting of PAM-g-graphene samples is 24.2%, and the thickness is measured to be 2.59 nm. Moreover, the as-prepared PAM-g-graphene with some amino from PAM and little oxygen functional groups exhibit superior adsorption of Pb(II) ions. The adsorption processes reach equilibrium in just 30 min and the adsorption isotherms are described well by Langmuir and Freundlich classical isotherms models. The determined adsorption capacity of PAM-g-graphene is 819.67 mg g−1 (pH 6) for Pb(II), which is 20 times and 8 times capacities of that for graphene nanosheets and carbon nanotubes according to reports, respectively. This chemically modified graphene synthesized by this fast one-step approach, featuring a good versatility and adaptability, excellent adsorption capacity and rapid extraction, may provide a new idea for the global problem of heavy metal pollutants’ removal in water.
Article
Films of 1:1 blend and films non-blended were prepared from poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) with a solution casting method, and the mechanical properties and morphology of the films were investigated using tensile tests, dynamic mechanical relaxation measurements, polarizing optical microscopy, differential scanning calorimetry (DSC) and X-ray diffractometry. The tensile strength, Young’s modulus, and the elongation-at-break of 1:1 blend films were found to be higher than those of non-blended films when their weight-average molecular weight (Mw) was in the range 1×105–1×106. The enthalpy of melting for stereocomplex crystallites in 1:1 blend films was higher than that of homo-crystallites when Mw of polymers was below 2×105, while this relationship was reversed when MW increased to 1×106. Spherulites formation was suppressed in 1:1 blend films, whereas large-sized spherulites with radii of 100–1000 μm were formed for non-blended PLLA and PDLA films, irrespective of Mw. The mechanical properties of 1:1 blend films superior to those of non-blended films were ascribed to the micro-phase structure difference generated as a result of formation of many stereocomplex crystallites which acted as intermolecular cross-links during solvent evaporation of blend solution. On the contrary, non-blended films had larger-sized spherulites of less contacting area with the surrounding spherulites.
Article
Crosslinkable poly(lactic acid-co-glycidyl methacrylate), P(LLA-co-GMA), copolymer was systematically synthesized by ring-opening polymerization. Synthesis parameters, i.e., catalyst type, comonomer ratio and polymerization time and temperature were studied. The incorporated GMA content strongly affected the physical and thermal properties of the obtained copolymers, which varied from semi-crystalline to completely amorphous polymers. Melting and glass transition temperatures, and molecular weights of the copolymers decreased as the GMA content in the copolymer increased. Curing behavior of the copolymers was assessed by employing thermo- and photo-crosslinking processes, and the crosslink density was evaluated via their gel content and solvent swelling ratio. A photo-crosslinking process was proven as a practical method in the curing of the copolymers, as the reaction was almost complete within 2 min, as indicated by a gel content of 96%. In the thermo-crosslinking process, at least a 15-min curing time was required at 120 °C. The cured products of copolymers with 19.2 mol% GMA showed the highest compressive stress at 25.5 MPa.
Article
Agar has been modified by microwave assisted grafting with acrylamide monomer, resulting in poly acrylamide grafted agar (Ag-g-PAM). The synthesized grades of Ag-g-PAM were characterized by standard physico-chemical characterization techniques (FTIR spectroscopy, elemental analysis, scanning electron microscopy (SEM)) to ascertain the intended grafting. The synthesized graft copolymer (Ag-g-PAM) has been investigated (in-vitro) for controlled and colon targeted release of 5-Amino salicylic acid (5-ASA).
Article
The blends of polylactide (PLA) and poly(polyethylene glycol-co-citric acid) (PEGCA) were prepared by melt mixing in an internal mixer. The effects of PEGCA content on the processibility, morphological, thermal, mechanical properties as well as hydrophilicity of PLA/PEGCA blends are investigated by rheometer, scanning electron microscopy, differential scanning calorimetry, mechanical testing, and water contact measurements. During thermal processing, the presence of PEGCA delayed the melting of PLA and lowered the viscosities of the blends. PLA/PEGCA blends exhibited a phase-separated morphology. The sizes of the dispersed phase increased with increased PEGCA content. The glass transition temperature of PLA decreased with the addition of PEGCA. The crystallization behaviors of PLA and PEGCA in their blends were influenced by each other. Ductility and toughness of PLA were significantly improved by the presence of PEGCA. PEGCA also greatly improved the hydrophilicity of PLA significantly.
Article
Polyacrylamide chains (PAM) were grafted onto the backbone of gum ghatti by microwave assisted method. The grafting of the PAM chains on the polysaccharide backbone was confirmed through intrinsic viscosity study, FTIR spectroscopy, elemental analysis (C, H & N) and SEM morphology study. The intrinsic viscosity of gum ghatti appreciably improved on grafting of PAM chains, thus resulting grafted product with potential application as superior viscosifier. Further, flocculation efficacy of the graft copolymer was studied initially in kaolin suspension and then in municipal wastewater through ‘Jar test’ procedure, toward possible application as flocculant for wastewater treatment.
Article
To improve the thermal stability and mechanical properties of PLA, crosslinking was introduced via chemical treatment of the melt by adding small amounts of crosslinking agent triallyl isocyanurate (TAIC) and dicumyl peroxide (DCP). A series of crosslinked PLA materials with different gel fraction and crosslink density were prepared. The crosslinked PLA samples were characterized by fourier transform infra-red spectrometry (FTIR). The thermal and mechanical properties of samples were also investigated by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile testing and dynamic mechanical analysis (DMA). The results showed that the crosslinking of PLA started at a low content of either TAIC or DCP, resulting in a decrease of crystallinity and a significant improvement of the thermal degradation initiation and completion temperatures, which indicated better thermal stability than neat PLA. Crosslinking was also responsible for the improved tensile modulus and tensile strength.
Article
Stable CaSO4 β-anhydrite II (AII), a specific type of dehydrated gypsum and a by-product of the lactic acid (LA) production process, was melt–blended with bio-sourced polylactide (PLA) to produce highly filled composites. Samples containing different amounts of filler (10–40 wt.%) with various granulometries were used for preparation of films by compression moulding. The influence of adding filler (calcium sulphate) on the photochemical behaviour of PLA–AII composites was studied by irradiation under photo-oxidative conditions (λ > 300 nm, temperature of 60 °C and in the presence of oxygen). Several analytical methods were used to characterise the polymer degradation. Oxidation of the polymer matrix was evaluated by infrared and UV–visible spectroscopies, differential scanning calorimetry (DSC) and size exclusion chromatography (SEC). The main photoproducts formed upon UV-light irradiation of the PLA were identified along with the influence of filler content and its particle size on the rate of oxidation. It was shown that oxidation of PLA and PLA–AII composites occurred without any induction time and that the presence of the CaSO4 filler (AII) increased the oxidation rate of the polymer. Moreover, a faster degradation rate of PLA was observed in composites containing natural anhydrite of lower particle size (4 μm).
Article
Starch was modified through chemical grafted of acrylamide on the starch polymer. Various of grafting percentages have been obtained by changing the concentration of initiator. The prepared polymer has been characterized by IR spectroscopy. The gelation of raw material (starch) and modified polymer (acrylamide grafted starch) according to the equilibrium swelling degree has been investigated in different media (distilled water, n-saline and buffer solution pH 2). Acrylamide grafted starch shows higher uptake of water compared with starch, suggests more hydrophilicity. In vitro controlled release of (CS: Ceftriaxone Sodium) drug from starch and acrylamide grafted starch hydrogel were studied in three different media (distilled water, n-saline and buffer solution pH 2) using ultra violate absorption follow quantities released at different times. The concentrations of drug released increased gradually and then attain affixed value at certain drug load.
Article
Thermal properties and crystallization behaviors of polylactide and its enantiomeric blends are investigated. DSC results demonstrate that only homopolymer crystallite is observed in PDLA and PLLA single polymers. A relatively stronger crystal structure, stereocomplex, can be achieved by mixing the two PLAs in a 1:1 ratio. For non-equimolar blends, both types of crystallites are formed at lower temperature than that of the single polymer counterparts. The degree of reduction in crystallization temperature is dependent on the degree of deviation of blend content from the equimolar value and the mobility of the polymer chain. The composition of the two crystallite domains is also dependent on the blend content, where the stereocomplex content is maximized in a 1:1 blend, and decreases upon varying the mixing ratio from equimolar value. Infrared spectroscopy is employed to follow the crystallization mechanisms of the non-equimolar blend. Results indicate a domination of stereocomplex formation band characteristics, despite evidences suggesting an existent of homopolymer crystallite formation, probably due to the involvement of CH··OC hydrogen bonding, which leads to larger change in dipole moment responsible for infrared transitions.
Article
Poly(lactic acid) is a new biopolymer material which is marketed by Cargill Dow Polymers under the tradename Nature Works*. One major application for this material is biaxially oriented films for food packaging because it possesses excellent barrier for flavor constituents, deadfold and heat sealability. Shrinkage must be minimized when the film is heat sealed for these applications and, therefore, characterization of the orientation of the amorphous phase of PLA films is necessary.Raman spectroscopy methodology has been developed to quantify orientation in PLA films. Bands were assigned to crystalline and amorphous phases of PLA such that orientation in both phases could be monitored. Raman depolarization ratios were used to characterize uniaxial systems but were insufficient for most biaxial draws. A new phenomenon for oriented films involving Raman band shifts was observed in these systems, and was shown to be capable of determining orientation, even for symmetrical biaxially drawn films. The origin of these shifts, as well as their use for the quantification of orientation will be discussed. Further, since the line widths of the bands could be used to quantify crystallinity, both crystallinity and orientation could be determined with one measurement.
Article
This study was undertaken in order to rationalize the peculiar 1H NMR chemical shifts of cyclopropane (delta 0.22) and cyclobutane (delta 1.98) which are shifted upfield and downfield with respect to larger cycloalkanes (delta 1.44-1.54). This is conventionally accounted for by shielding contributions arising from an aromatic-like ring current in cyclopropane, involving six electrons in the three C-C bonds, and deshielding coming from the sigma antiaromatic CC framework of cyclobutane. The shielding pattern arising from the cyclopropane and cyclobutane CC framework response to a perpendicular magnetic field was visualized as two-dimensional grid distribution of NICS values. Further insight into the origin of chemical shift values was obtained by the NCS-NBO analysis of proton shielding tensor. In the case of cyclopropane, the CC framework shielding pattern implies the existence of both delocalized and localized currents which have a dominant shielding effect on protons. The magnitude of C-H bonds shielding effect is significant, too. Unlike the conventional interpretation, the CC framework shields cyclobutane hydrogens, and its response to a perpendicular magnetic field is quite similar to responses of other planar sigma CC frameworks.
Article
Infrared spectroscopy is a fine tool with which to experimentally explore the effect of chain connectivity and functional group accessibility in hydrogen-bonded polymer blends. Such factors directly affect the fraction of intermolecular hydrogen-bonded groups that are formed and effectively reduce the hydrogen-bonding contribution to the free energy of mixing vis-à-vis analogous low-molar-mass analogues. In this study we report the results obtained from blends of copolymers containing vinyl cinnamate (VCIN) with copolymers containing 4-vinylphenol. The VCIN segment undergoes facile photocross-linking upon exposure to UV radiation, permitting the effect of cross-linking on functional group accessibility and phase behavior to be studied.
Article
The photoinitiated grafting of N-vinylpyrrolidone (NVP) onto poly(lactic acid) (PLA) film with the use of benzophenone (BP) as the initiator, modified the natural hydrophobic PLA behavior to an hydrophilic film with desirable wettability. The surface photografting parameters-percent conversion of monomer to overall photopolymerization (Cp), percent conversion of monomer to the photograft polymerization (Cg), and grafting efficiency (Eg) were calculated. The resulting film surface was analyzed using ATR-FTIR and UV spectroscopy, derivative spectroscopy and water contact angle. Besides, we demonstrated that the grafted polyvinylpyrrolidone chains could easily react with iodine to form a complex as the homopolymer does with antibacterial activity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Article
Co-electrospinning of core-shell polymer nanofibers (see Figure) is introduced. This process can be used for manufacturing of coaxial nanofibers made of pairs of different materials. Non-spinnable materials can be forced into 1D arrangements by co-electrospinning using a spinnable shell polymer. The method results in a novel two-stage approach for fabrication of nanotubes instead of the previously used three-stage process.
Article
The synthesis of poly(lactic acids) from the cyclic lactides and properties of the polymers prepared have been described. Degradation rates in vitro under homogeous and heterogeneous conditions have been measured. The kinetics of deesterification under homogeneous conditions is second order and an activation energy of 11 Kcal/mol has been calculated. This is comparable to the value found for the hydrolysis of alkyl acetates. A biological in vitro method for determining the degradation of poly(lactic acids) has been described. The method indicates, in accordance with expectations, that poly(dl-lactic acid) degrades at a faster rate than L(+) lactic acid. Initial results of medical evaluation of the polymers in suture, rod, and film form are presented.
Article
Chitosan grafted poly(lactic acid) (CS-g-PLA) copolymer was synthesized and characterized by FT-IR and elemental analysis. The degree of poly(lactic acid) substitution on chitosan was 1.90 ± 0.04%. The critical aggregation concentration of CS-g-PLA in distilled water was 0.17 mg/ml. Three methods of preparing CS-g-PLA nanoparticles (diafiltration method, ultrasonication method and diafiltration combined with ultrasonication method) were investigated and their effect was compared. Of the three methods, diafiltration combined with ultrasonication method produced nanoparticles with optimal property in terms of size and morphology, with size ranging from 133 to 352 nm and zeta potential from 36 to 43 mV. Also, the hemolytic activity and cytotoxicity of the CS-g-PLA based nanoparticles was tested, and results showed low hemolysis rate (<5%) and no significant cytotoxicity effect of these nanoparticles.
Article
A nondestructive "grafting-from" method has been developed using poly(lactide) (PLA) particles of different shapes as substrates and three hydrophilic monomers as grafts. Irregularly shaped particles and spheres of PLA were covalently surface functionalized using a versatile method of photoinduced free radical polymerization. The preservation of the molecular weight of the PLA particle bulk and the retention of the original particle shape confirmed the negligible effect of the grafting method. The changes in surface composition were determined by FTIR for both spherical and irregular particles and by XPS for the irregular particles showing the versatility of the method. Changes in the surface morphology of the PLA spherical particles were observed using microscopy techniques showing a full surface coverage of one of the grafted monomers. The method is applicable to a wide set of grafting monomers and provides a permanent alteration of the surface chemistry of the PLA particles creating hydrophilic PLA surfaces in addition to creating sites for further modification and drug delivery in the biomedical fields.
Article
Well-defined polyacrylamide was grafted successfully from the fibrillar clay, attapulgite, by a three-step process: (i) the γ-aminopropyltriethoxyl silane was chemical-bonded onto the surfaces of the attapulgite; (ii) the surface amino groups were amidated with bromoacetylbromide; and (iii) the bromo-acetamide modified attapulgite was used as macro-initiator for the surface-initiated atom transfer radical polymerization (SI-ATRP) of acrylamide with the catalyst of the complex of 1,10-phenanthroline and Cu(I)Br. The percentage of grafting (PG%) was found to increase linearly with the increasing of the polymerizing time and that of 21.4% was achieved after the SI-ATRP in aqueous solution at 90 °C for 6 h. The graft polymerizations exhibited the characteristics of a controlled/“living” polymerization. The product, polyacrylamide grafted attapulgite (PAM-ATP), had been characterized with elemental analysis (EA), Fourier transform infrared (FT-IR) spectroscopy analysis, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). It's adsorption properties towards the heavy metal ion (Hg(II)) and dyes (methylene blue (MB) and methyl orange (MO)) were also studied preliminarily.
Article
New spherically shaped cross-linked hydrogels of polyacrylamide-grafted guar gum were prepared by the emulsification method. These were selectively derivatized by saponification of the –CONH2 group to the –COOH group. The derived microgels were characterized by FTIR and elemental analyses. The derivatized microgels were responsive to pH and ionic strength of the external medium. The swelling of microgels increased when the pH of the medium changed from acidic to alkaline. Transport parameters, viz., solvent front velocity and diffusion coefficients were calculated from a measurement of the dimensional response of the microgels under variable pH conditions. The variation in pH changed the transport mechanism from Case II (in 0.1 N HCl) to non-Fickian (in pH 7.4 buffer), and these processes are relaxation-controlled. Ionic strength exerted a profound influence on the swelling of the microgels. Swelling was reversible and pulsatile with the changing environmental conditions. The pH-sensitive microgels were loaded with diltiazem hydrochloride and nifedipine (both antihypertensive drugs) and their release studies were performed in both the simulated gastric and intestinal pH conditions. The release was relatively quicker in pH 7.4 buffer than observed in 0.1 N HCl; the release followed non-Fickian transport in almost all the cases.
Article
Biodegradable nanoparticles have been used frequently as drug delivery vehicles due to its grand bioavailability, better encapsulation, control release and less toxic properties. Various nanoparticulate systems, general synthesis and encapsulation process, control release and improvement of therapeutic value of nanoencapsulated drugs are covered in this review. We have highlighted the impact of nanoencapsulation of various disease related drugs on biodegradable nanoparticles such as PLGA, PLA, chitosan, gelatin, polycaprolactone and poly-alkyl-cyanoacrylates.
Article
A pH-sensitive graft co-polymer of polyacrylamide (PAAm) and sodium alginate (SA) was synthesized by free radical polymerization under a nitrogen atmosphere followed by alkaline hydrolysis. The co-polymer was characterized by Fourier transform infrared (FT-IR) spectroscopy, elemental analysis and thermogravimetric analysis (TGA). Ketoprofen-loaded graft co-polymer beads were prepared by ionotropic gelation/covalent cross-linking. The beads were characterized by swelling studies, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). A pulsatile swelling study indicated that the co-polymer exhibits considerable pH-sensitive behavior. Release of ketoprofen was significantly increased when the pH of the medium was changed from acidic to alkaline. Stomach histopathology of albino rats indicated that the beads were able to retard the release of the drug in the stomach, and gastric side-effects like ulceration, hemorrhage and erosion of gastric mucosa were diminished when the drug was entrapped into PAAm-g-SA-based pH-sensitive hydrogel beads.
Article
In vivo and in vitro degradation of high molecular weight poly(L-lactide) used for internal bone fixation has been investigated. Within 3 months as-polymerized, microporous PLLA (Mv = 6.8-9.5 X 10(5] exhibited a massive strength-loss (sigma b = 68-75 MPa to sigma b = 4 MPa) and decrease of Mv (90-95%). At week 39, the first signs of resorption were evident (mass-loss 5 wt%). Except for dynamically loaded bone plates no differences between in vivo and in vitro degradation of PLLA were observed. The increase of crystallinity of PLLA upon degradation (up to 83%) is likely to be attributed to recrystallization of tie-chain segments. A more ductile PLLA exhibiting a lower rate of degradation was prepared by extraction of low molecular weight compounds with ethyl acetate.