[show abstract][hide abstract] ABSTRACT: Free-radical homo- and copolymerization of acryl-
amide (AAm) and diallyldimethylammonium chloride
(DADMAC) initiated with potassium persulfate (KPS) were
performed in the presence of 0.1 M NaCl solution in D 2 O at
50 °C. Online 1 H-NMR kinetic experiments were used to study
polymerization kinetics via determination of the individual and
overall conversion of the comonomers and compositions of the
comonomer mixture and produced copolymer as a function of
the reaction time. Reactivity ratios of the AAm and DADMAC
were calculated by Mao-Huglin (MH) and extended Kelen-
Tudos (KT) methods to be 7.0855±1.3963, 0.1216±0.0301
and 6.9458±2.0113, 0.1201±0.0437 respectively. “Lumped”
kinetic parameter (k p k t
−0.5 ) was estimated from experimental
data. Results showed that k p k t
−0.5 value increases by increasing
mole fraction of the AAm in the initial reaction mixture. Drift in
the comonomer mixture and copolymer compositions with
reaction progress was evaluated experimentally and theoretical-
ly. Theoretical values were calculated from Meyer-Lowry equa-
tion by using reactivity ratios obtained from MH method. A
good fitting between the experimental and theoretical values
was observed, indicating accuracy of the reactivity ratios esti-
mated in the present work. It was found from following changes
in the copolymer composition with the comonomer conversion
that produced copolymer has a statistical structure.
Journal of Polymer Research 07/2013; 20:239. · 2.02 Impact Factor
[show abstract][hide abstract] ABSTRACT: Poly(p-methylstyrene) (Pp-MS) was synthesized at three different temperatures of 50, 150 and 250 °C via bulk thermal polymerization method. The assignment of all stereosequences at triad and pentad levels for two quaternary aromatic carbons and hexad level for methylene carbon was carried out by 13C liquid nuclear magnetic resonance spectroscopy (NMR) in deuterated chloroform at similar conditions. The probability of meso addition (P m) was calculated from second quaternary aromatic carbon and used to predict the relative intensities of methylene and first quaternary aromatic carbon by Bernoullian and first-order Markov statistical models. The results were compared with experimental data. It is shown that the Bernoullian statistics fit better than first-order Markov model for all three samples. The results indicate that P m increases by increasing polymerization temperature. The corresponding P m values determined for synthesized Pp-MSs at 50, 150 and 250 °C were 0.383, 0.392 and 0.404, respectively. It was observed that higher resolutions and better splitting patterns were achievable by increasing the NMR acquisition temperature from 20 to 50 °C. When temperature increased during NMR acquisition, the resolution improved for the first and second quaternary aromatic carbons and methylene carbon, though there was no splitting pattern observed for methyl carbon atom at the para-position of the aromatic ring.
[show abstract][hide abstract] ABSTRACT: Aqueous free-radical polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) in the presence of potassium persulfate
(KPS) as thermal initiator was studied by differential scanning calorimetry (DSC). Effect of temperature, monomer, and initiator
concentration on polymerization rate was studied. Obtained recorded data represented order of reaction with respect to monomer
greater than unity (1.56). Among the theories presented order of reaction more than one, the gage effect theory in the range
of monomer concentration (0.966–2.410 mol/L) had a good agreement with mechanism of AMPS polymerization. The order with respect
to KPS was 0.52 which was consistent with classical kinetic theory. Calculated amount of activation energy in overall rate
of reaction was 83 kJ/mol K.
[show abstract][hide abstract] ABSTRACT: Polymers play a very important role in electrical systems as insulation materials. The microscopic failures occurring in the polymer under working conditions will be important in its required characteristics. In this work we focused on the effects of accelerated aging on the electrical properties of low density polyethylene (LDPE) and crosslinked polyethylene (XLDPE). The samples of LDPE were prepared in sheet form with the thickness of 0.6 ± 0.1 mm and were irradiated under the 10 MeV electron beam of a Rhodotron accelerator at the dose range of 70 to 370 kGy. Then, the samples were stored in an oven at temperature 75°C for 3, 6, 10 and 13 days. Electrical properties such as the breakdown voltage and resistance of the aged samples were measured and compared. Increasing the aging time for unirradiated samples has a serious and moderate influence on their surface resistivity and breakdown voltage, respectively. The results indicated a maximum value for the surface resistance at the optimum radiation absorbed dose, which is approximately 220 kGy for all the samples.
International Journal of Polymeric Materials 04/2011; 60(4):269-275. · 1.87 Impact Factor
[show abstract][hide abstract] ABSTRACT: The purpose of this study was to investigate the effect of three aliphatic esters, ethyl heptanoate, methyl heptanoate, and
ethyl nonanoate on the in vitro degradation behavior of in situ forming systems. In situ forming implants based on 33% (w/w)
poly (lactide-co-glycolide) (PLGA)/57% (w/w) N-methyl-2-pyrrolidone (NMP)/10% (w/w) esters were prepared after injection of the final formulation in phosphate buffer solution
(pH 7.4, 0.2M) at 37°C. The influence of additives on the implants formation, morphology, and also on their in vitro degradation
behaviors over a period of 45days was investigated. The degraded matrices were evaluated to determine morphological analysis
by SEM and 1H-NMR study. The solution of degradation medium was studied to indicate NMP removal and altering acidity. The results showed
that the additives generated a high porous structure and caused the fast phase inversion. However, the 1H-NMR spectra indicated that ester additives remained in the matrices during degradation periods. The results of the acidity
study showed that the degradation rates in the matrices containing esters were higher than the control matrix. In addition,
it is shown that esters with lower molecular weight have affected the polymer degradation more efficiently than higher molecular
KeywordsIn situ forming systems–Biodegradation–Solvent removal–Morphology–Poly (lactide-co-glcolide)–Aliphatic esters
[show abstract][hide abstract] ABSTRACT: Tacticity of poly-2-acrylamido-2-methylpropane sulfonic acid samples that were prepared via free radical polymerization in four different solvents, ethanol, dimethyl sulphoxide (DMSO), N, N-dimethylformamide (DMF) and water, were studied by C nuclear magnetic resonance (C-NMR) techniques. In order to change isotacticity, two rare metal triflates, yttrium trifluoromethane sulfonate (Y(OTf)3) and ytterbium trifluoromethane sulfonate (Yb(OTf)3), were used. The stereoregularity of the obtained polymers in DMSO, water and DMF in the presence of the mentioned triflates did not show a noticeable alteration. But isotacticity of the samples prepared in ethanol was increased by about 17% in the presence 75 wt% Y(OTf)3. In the absence of metal triflates, solvents did not have any significant effect on stereocontrol. In addition, the influence of temperature on isotacticity of the prepared samples was studied. By decreasing the reaction temperature, the isotacticity increased slightly.
Journal of Macromolecular Science, Part A. 01/2011; 48(7):526-530.
[show abstract][hide abstract] ABSTRACT: Thermal degradation of polybutadiene (PBD) in anaerobic atmosphere at 250 °C had been studied by carbon-13 nuclear magnetic resonance spectroscopy (13C NMR) before complete crosslinking. In this investigation four types of low molecular weight PBD with different 1,2-vinyl isomer content had been chosen, then pure and mixed samples of PBD were heated in different time periods. 13C NMR spectra showed that two kinds of crosslinking mechanisms occur that both of them produce methyl groups. The first mechanism is a reaction between 1,2-vinyl isomers of two PBD chains, and the second one occurs between 1,2-vinyl isomer of one chain via methylene carbon of cis or trans isomer in another chain. Also 13C NMR results showed that the presence of 1,2-vinyl isomer in the PBD structure is necessary and without it none of the mentioned reactions will occur. Furthermore isomers sequence is another important parameter which affects crosslinking. Results show that cis or trans isomer which is not adjacent to 1,2-vinyl isomer does not take part in crosslinking reaction. Moreover such cis or trans isomer can take part in second mechanism of crosslinking that 1,2-vinyl isomer was attached from head to cis or trans isomer, thus in this arrangement of isomers second mechanism of crosslinking will become dominant rather than first mechanism of crosslinking.
Polymer Degradation and Stability 01/2011; 96(10):1805-1811. · 2.77 Impact Factor
[show abstract][hide abstract] ABSTRACT: Various polybutadienes (PBDs) of low molecular weight were heated below complete crosslinking at 250 °C under anaerobic nonpyrolytic conditions, and the structural changes were investigated. The predominant crosslinking reactions arise from the presence of 1,2-vinyl isomer and the most important one is intermolecular reaction accompanied with methyl group formation. The analysis showed that two crosslinking types as well as two types of methyl groups have been produced in which one was the result of 1,2-vinyl isomer of one chain crosslinked via methylene carbon of another chain of cis or trans isomer, and the second methyl group was the product of the reaction between 1,2-vinyl isomers of two PBD chains. Chain scission also occurred in two pathways due to the presence of 1,2-vinyl isomer, scission at two adjacent 1,2-vinyl isomer and scission at adjacent 1,2-vinyl with cis or trans isomer giving rise to methyl carbons.
[show abstract][hide abstract] ABSTRACT: A series of novel self-crosslinkable and biodegradable polymers, poly(hexamethylene carbonate-fumarate) and poly(hexamethylene carbonate) diacrylate, and their amphiphilic copolymers with polyethylene glycol, poly(ethylene glycol fumarate-co-hexamethylene carbonate-fumarate) (PEGF-co-PHMCF), were developed for tissue engineering using propylene oxide as an acid scavenger. The synthesized polymers are white, which makes them more suitable for self-crosslinking via photopolymerization. These novel polymers were fully characterized using nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, and rheometry. The cytocompatibility of the photocrosslinked networks were evaluated by [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. These polymers can be used as precursors to prepare polymer networks and scaffolds with controlled hydrophilicity, biodegradability, and mechanical characteristics. Results obtained suggest that these polymers are potentially useful as injectable and photocrosslinkable materials for cell delivery, tissue engineering, and drug delivery applications.
Journal of Biomedical Materials Research Part A 08/2008; 90(3):830-43. · 2.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: Biodegradable, injectable and in situ photocrosslinkable macromers based on fumaric acid and polycaprolactone (PCLF) were prepared and characterized by FTIR, 1HNMR, and 13CNMR spectroscopy. The multifunctional macromers dissolved in N-vinyl pyrollidone (NVP) were photopolymerized by visible light irradiation in the presence of camphorquinone as photoinitiator. The photocrosslinking reaction was monitored by measuring shrinkage strain and shrinkage strain rate. The degree of photopolymerization reaction i.e. degree of conversion (DC%) was traced using FTIR spectroscopy. A three level factorial design was developed to study the effects of initiator concentration, NVP concentration, and molecular weight of PCLF upon photocrosslinking characteristics including degree of conversion and shrinkage strain. Results revealed that although neat PCLF was photopolymerized, but it was putty like after 220 seconds of irradiation and showed a very low degree of conversion (29%). Adding about 20% NVP caused a dramatic increase in its degree of conversion (63.33%). Increasing NVP up to 50% resulted in a decrease in DC% because of lower reactivity of NVP and leaving more unreacted NVP monomers. Sol fraction studies supported these results indicating that at higher NVP concentration, most of NVP and PCLF have not undergone the crosslinking reaction, leading to 55% decrease in DC%. Shrinkage strain measurement also confirmed the FTIR results.
Journal of Biomedical Materials Research Part A 03/2008; 84(2):545-56. · 2.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: K inetics of radical telomerization of vinyl acetate (VAc) with CDCl 3 as a telogen in the presence of AIBN initiator was studied by 1 H NMR. Structure of the chains was analyzed in detail by 1 H NMR spectroscopy technique. It was observed that two telomers with different α-ends including trichloromethyl-and dichloromethyl-termi-nated VAc telomers were formed during the telomerization reaction. Therefore, two dif-ferent mechanisms of the transfer reaction to CDCl 3 telogen have been proposed which were supported in details by the abstraction of either deuterium or chlorine rad-icals from CDCl 3 molecules. 1 H NMR analysis also allowed us to calculate the conver-sion of VAc (X VAc), number-average degree of polymerization (DPn), telomer percent-age (%), and the ratio of the abstractions of deuterium radicals to chlorine radicals (R D/Cl) from CDCl 3 molecules. These results showed that at the same conversion, at first, DPn decreases with increase of the initial concentration of AIBN but then increas-es. Also, DPn at the same conversion decreases by increasing of the R 0 and decreas-ing of the reaction temperature. Moreover, at the same conversion, telomer percent-age increased by decreasing [AIBN] 0 and reaction temperature while decreased by decreasing of the R 0 (or equivalently [CDCl 3 ]). The highest yield of telomer was about 60%. There was not any significant difference between the R D/Cl at various conditions used in VAc telomerization by CDCl 3 . 1 H NMR analysis showed that the rate of the abstraction of deuterium radical from CDCl 3 molecule is favoured relative to its rate of chlorine radical abstraction.
[show abstract][hide abstract] ABSTRACT: Photocrosslinkable and biodegradable polymeric networks were formulated based on N-vinyl pyrrolidone-poly(epsilon-caprolactone fumarate) (NVP/PCLF) compositions for hard tissue engineering applications using a new proton scavenger, propylene oxide (PO). The synthesized macromers; were obtained as a white clear paste with no colorization. The obtained macromers were thoroughly characterized using spectroscopic (NMR and FT-IR) and chromatographic (gel permeation chromatography (GPC)) techniques. Photocrosslinking of the PCLF/NVP compositions was achieved using camphorquinone and dimethyl toluidine (DMT) as a photoinitiator system. The cytocompatibility of the macromers and their corresponding networks were evaluated via MTT assay. Characterization of the networks indicated the importance of NVP content on the network properties. Sol fraction studies indicated that more than 90% of the PCLFs were crosslinked over the studied range of PCLF/NVP compositions; however most of the NVP above a stoichiometric ratio of one NVP to fumerate unit remained unreacted. It was also found that in the concentrations more than 10% NVP, the unreacted NVP monomer neither participated in the crosslinking reaction nor homopolymerized to poly(vinyl pyrrolidone) (PVP). The elastic modulus (G') and estimated molecular weight between crosslinks also confirmed that at the higher NVP content the PCLF photocrosslinking was hindered. Copyright (C) 2008 John Wiley & Sons, Ltd.
Polymers for Advanced Technologies 01/2008; 19(12):1828-1838. · 1.64 Impact Factor
[show abstract][hide abstract] ABSTRACT: H ydrogels produced by in situ polymerization have been extensively studied as biomaterials in applications such as scaffolds for tissue engineering and drug delivery systems. In situ polymerization process allows the hydrogel to be gen-erated in vitro or in vivo from a low viscosity solution of monomer or low molecular weight polymer by free radical pathway. In this study, polyethylene glycol-diacrylate (PEG-DA) macromer has been synthesized by esterification of PEG with acryloyl chlo-ride and characterized by NMR and FTIR spectroscopies and swelling study. Cross-linking was initiated by a pair of redox initiator, i.e. ammonium persulphate and N,N,N',N'-tetramethylethylenediamine. The conversion rate of the macromers to a cross-linked network was determined using 1 H NMR and dynamic oscillatory test at 37ºC and continuous disappearance of vinyl group upon addition of redox agent to a macromer solution was evaluated.
[show abstract][hide abstract] ABSTRACT: A series of novel self-crosslinkable and biodegradable polymers; poly(hexamethylene carbonate-fumarate), poly(hexamethylene carbonate) diacrylate and their amphiphilic copolymers with polyethylene glycol, poly(ethylene glycol fumarate-co-hexamethylene carbonate-fumarate) (PEGF-co-PHMCF) were developed for tissue engineering using novel synthesis approach. These novel polymers were fully characterized using nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, rheometry and shrinkage strain measurement. The cytocompatibility of macromers and their networks were evaluated by [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] MTT assay. The synthetic macromers were light colored with self-crosslinking ability via both photocrosslinking and chemical crosslinking. These polymers can be used as precursors to prepare polymer networks and scaffolds with controlled hydrophilicity, biodegradability and mechanical characteristics for application in cell delivery, tissue engineering and controlled release of biologically active agents.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2006; 1:791-4.
[show abstract][hide abstract] ABSTRACT: Many reports exist in the literature about the application of H and C‐NMR techniques to analyze the copolymer structure and composition and also determination of reactivity ratios. In this work, on‐line H‐NMR spectroscopy has been applied to identify reactivity ratios of itaconic acid and acrylonitrile in the solution phase (DMSO as the solvent) and in the presence of AIBN as the radical initiator. All the peaks corresponding to the existing protons were assigned quietly. Therefore, the kinetics of the copolymerization reaction was investigated by studying the variation of integral of two characteristic peaks regarding each monomer. The obtained data were used to find the reactivity ratios of acrylonitrile and itaconic acid by linear least‐squares methods such as Finemann‐Ross, inverted Finemann‐Ross, Mayo‐Lewis, Kelen‐Tudos, extended Kelen‐Tudos and Mao‐Huglin. In addition, a non‐linear least‐square method (Tidwell‐ Mortimer) was used at low conversions. Extended Kelen‐ Tudos and Mao‐Huglin were applied to determine reactivity ratio values at high conversions as well.
Journal of Macromolecular Science, Part A. 01/2006; 43(10):1583-1596.
[show abstract][hide abstract] ABSTRACT: Monomer reactivity ratios in free radical copolymerization of styrene and butyl acrylate monomers at 80°C in toluene solution under reduced pressure were determined for low and high conversions. Mayo-Lewis, Finemann-Ross, inverted Finemann-Ross, Kelen-Tüdós, extended Kelen-Tüdós. Tidwell-Mortimer and Mao-Huglin methods for low conversion and extended Kelen-Tüdós and Mao-Huglin methods for high conversion were used to calculate rSand rB in this paper. Using the Mao-Huglin method, for conversions below 15%, monomer reactivity ratio values of 0.887 and 0.216 were calculated for styrene and butyl acrylate, respectively. For conversions greater then 15%, these values were found to be 1.006 and 0.232, respectively. In addition, the reactivity ratios calculated from the second-order Markov reaction were compared with that of calculated using the first-order Markov reaction.