Oxidative polymerization of acrylamide in the presence of thioglycolic acid

Chemical polymerization of acrylamide at room temperature was examined by using thioglycolic acid-cerium (IV) sulfate and thioglycolic acid-KMnO₄ redox systems in acid aqueous medium. Water soluble polyacrylamides containing thioglycolic acid end groups were synthesized. The effects of the molar ratio of acrylamide to Ce(IV) n _AAm /n _Ce(IV) , the polymerization time, the temperature, the monomer concentration, the molar ratio of cerium (IV) sulfate to thioglycolic acid and the concentration of sulfuric acid on the yield and molecular weight of polymer were investigated. Lower molar ratios of acrylamide/Ce(IV) at constant monomer concentration resulted in an increase in the yield but a decrease in molecular weight of polymer. The increase of reaction temperature from 20 to 70°C resulted in a decrease in the yield but generally resulted in a constant value for the molecular weight of polymer. With increasing polymerization time, the yield and molecular weight of polymer did not change substantially. Ce(IV) and Mn(VII) ions are reduced to Ce(III) and Mn(II) ions respectively in the polymerization reaction. The existence of Ce(III) ion bound to polymer was investigated by UV-visible spectrophotometry and fluoresce measurements. The amount of Mn(II) incorporated into the polymer was determined using graphite furnace atomic absorption spectrometry. The mechanism of this phenomenon is discussed.     

Cationic polymerization of formaldehyde in liquid carbon dioxide. Part I

A cationic polymerization of formaldehyde which gave a high molecular weight polymer was studied in liquid carbon dioxide at 20–50°C. In the polymerization without any catalyst both the rate of polymerization and the molecular weight of the resulting polymer increased rapidly with a decrease in the loading density of the monomer solution to the reaction vessel, and also increased with an increase in the initial monomer concentration. From these results it was concluded that the initiating species could be ascribed to an impurity contained in the monomer solution. Both the rate of polymerization and the degree of polymerization of the polymer also increased with rising temperature. The carboxylic acid added acted as a catalyst in the polymerization because of increase in the polymer yield, the molecular weight of polymer formed, and the number of moles of polymer chain with increasing dissociation constant of acid used. It was concluded that the polymerization in liquid carbon dioxide proceeded by a cationic mechanism. Methyl formate had no influence on the polymerization, but methanol and water acted as a chain-transfer agent.     

Use of block copolymer surfactants in the inverse-suspension polymerization of acrylamide

A comprehensive experimental investigation of the inverse microsuspension polymerization of acrylamide using an oil-soluble initiator and a block copolymeric surfactant whose hydrophobic miety is poly(12-hydroxystearic acid) and whose hydrophilic moeity is polyethylene oxide was carried out. It was found that the initial polymerization rate was first order with respect to molar monomer concentration, first order with respect to molar initiator concentration and zeroth order with respect to molar emulsifier concentration. Based on these experimental findings, a mechanism was proposed which includes initiation, propagation transfer to monomer and termination. It also includes transfer to impurities which are believed to be found in the surfactant. The kinetic model developed from the proposed mechanism is found to be in good agreement with the experimental conversion and weight-average molecular weight data. Comparing with sorbitan esters of fatty acids, the copolymeric surfactant provides higher polymerization rate and very high and linear molecular weight comparable to those obtained by solution polymerization.     

Biodegradable Polymers for Orthopedic Applications: Synthesis and Processability of Poly (l-Lactide) and Poly (Lactide-co-€-Caprolactone)

Abstract

The synthesis of poly(l-lactide) (PLLA), poly(l-lactide-co-e-caprolactone), and poly(DL-lactide-co-e-caprolactone) by ring-opening bulk polymerization was investigated. Polymerization temperature had a significant effect on the PLLA molecular weight. At 184°C a polymer with a molecular weight of only 10 × 10⁴ resulted. This was lower by a factor of 2 than that obtained at 103 and 145°C. The stannous octoate (SnOct) concentration, with a monomer/SnOct molar ratio in the range of 1,000 to 10,000, was not found to have a significant effect on the PLLA molecular weight. A heterogeneous structure in polymerized PLLA was observed. The intrinsic viscosity of poly(lactide-co-€-caprolactone), obtained at 130°C, monomer/SnOct molar ratio 5,000, and polymerization time of 30 hours, decreased with increasing €-caprolactone content within the first 9 wt% and then leveled off. Die-drawing of PLLA cylinders, for the purpose of increasing the polymer's mechanical strength, was unsuccessful due to the brittleness of the polymer. The drawability of poly(l-lactide), however, was greatly improved by copolymerization with €-caprolactone. With only 3 wt% of €-caprolactone, for example, the tensile strength of die-drawn poly(l-lactide-co-e-caprolactone) was increased by a factor of more than 3. Polymer processing temperature was also investigated. The requirement for low processing temperatures in melt manufacture of controlled release matrix devices containing thermal sensitive drugs was accomplished by three methods: through the use of low molecular weight poly(DL-lactide), adding (DL-lactic) acid oligomer to high molecular weight PDLLA, and copolymerizing DLLA with €-caprolactone. The glass transition temperatures of the modified high molecular weight PDLLA decreased significantly. Melt extrusion below 100°C could be performed.     

Uniform nonspherical latex particles as model interpenetrating polymer networks

Polystyrene/polystyrene latex interpenetrating polymer networks (IPNs) were prepared by seeded emulsion polymerization of styrene–divinylbenzene mixtures in crosslinked monodisperse polystyrene particles. The resulting latexes comprised uniform nonspherical particles, e.g., ellipsodal and egg-like singlets, symmetry and asymmetric doublets, and ice cream cone-like and popcorn-like multiplets. The nonspherical particles, which were formed by separation of the second-stage monomer from the crosslinked seed network during swelling and polymerization, are excellent models for studying phase separation in IPN's. The degree of phase separation increased with increasing degree of crosslinking of the seed particles, monomer/polymer swelling ratio, polymerization temperature, and seed particle size, and with decreasing divinylbenzene concentration in the swelling monomer. The results were consistent with a thermodynamic analysis based on the elastic-retractile force of the polymer network, the monomer/polymer mixing force, and interfacial tension force.     

Synthesis and Antibacterial Activity of Selenium-functionalized Poly(ε-caprolactone)

A selenium-functionalizedε-caprolactone was synthesized by introducing a phenyl selenide group at the 7-position.A polymer was obtained through the ring-opening polymerization of this monomer in a base/thiourea binary organocatalytic system.A living polymerization process was achieved under mild conditions.The resulting polymers had a controlled molecular weight with a narrow molecular weight distributions and high end-group fidelity.Random copolymers could be obtained by copolymerizing this monomer withε-caprolactone.The thermal degradation temperature of the obtained copolymers decreased with the increasing molar ratio of selenide functionalized monomer in copolymers,while the glass transition temperature increased.In addition,the phenyl selenide side group could be further modified to a polyselenonium salt,which resulted in a polymer with good antibacterial properties.The survival rate of E.coli and S.aureus was only 9%with a polymer concentration of 62.5μg/mL.     

Preparation and properties of two-component hydrogels based on 2-acrylamido-2-methylpropane sulphonic acid

Xerogels comprising 2-acrylamido-2-methylpropane sulphonic acid (AMPS) and acrylic acid as well as AMPS and acrylamide crosslinked with hexafunctional crosslinking agent have been prepared by catalytic initiation polymerization to complete conversion. Different percentages of hexafunctional crosslinker, 1,1,1-trimethylolpropane trimethacrylate, were used to prepare crosslinked copolymers having different degree of crosslink densities. The crosslinked copolymers were swollen in water to equilibrium. The volume fraction of polymer, the swelling capacity and the equilibrium water content were obtained. Low conversion polymerization was used to determine the reactivity ratios of both monomer pairs. Fourier transform spectroscopy was utilized to measure the molar ratio of copolymers constituents. © 1998 John Wiley & Sons, Ltd.     

Hydrophilic,cationic large‐core star polymers and polymer networks: Synthesis and physicochemical characterization

Group transfer polymerization was used to prepare hydrophilic, cationic large‐core star polymers (LCSPs) and networks of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) and ethylene glycol dimethacrylate (EGDMA) in a two‐step procedure involving the synthesis of linear DMAEMA arms, followed by their crosslinking using a mixture of DMAEMA monomer and EGDMA crosslinker. The degree of polymerization of the linear chains prepared in the first step was kept constant, while the composition of the crosslinking mixture was varied systematically at a constant amount of crosslinker. The monomer/crosslinker molar ratio determined whether LCSPs or polymer networks would be produced. In particular, a high monomer/crosslinker molar ratio led to the formation of networks, whereas LCSPs were formed when a low monomer/crosslinker molar ratio was used. The absolute weight‐average molecular weight of the LCSPs was determined using static light scattering, whereas their hydrodynamic radii and radii of gyration were determined using dynamic light scattering and small‐angle neutron scattering, respectively. The sol fraction extracted from the networks decreased as the monomer/crosslinker molar ratio increased. The degrees of swelling of all of the networks were measured as a function of pH and were found to increase below pH 7. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3958–3969, 2008     

Radiation-induced heterogeneous polymerization of methyl methacrylate in precipitants

The radiation-induced heterogeneous polymerization of methyl methacrylate in various precipitants, mainly methyl alcohol, was carried out, and the effects of reaction conditions on the polymerization behavior and the molecular weight distribution of polymer were studied. Bimodal molecular weight distributions were found for the polymer produced by the heterogeneous polymerizations in methyl alcohol and in tert-butyl alcohol. The apparent activation energy is 1.0 and 4.5 kcal/mole, respectively, for the polymerization at a monomer concentration of 10 vol-% in methyl alcohol above and below 35°C. The polymerization at a monomer concentration lower than 40 vol-% in methyl alcohol proceeded with the precipitation of polymer. The dose rate exponent of the mean rate of heterogeneous polymerization decreased from 0.5 to a smaller value as the polymerization progressed. The ratio of the two peaks in the bimodal molecular weight distributions of polymer produced in methyl alcohol was affected by the reaction conditions. These results show the coexistence in the polymerizations of two different physical states of propagating chain, a loose state and a rigid one. The reaction scheme is discussed in connection with the physical factors which affect the solubility or the mobility of propagating chains, and the rate of elementary reactions, which influences the degree of propagating chains.     

Biocatalytic hydrogels by template polymerization

Novel ionizable hydrogels were prepared from poly(acrylic acid) and dimethylaminoethyl methacrylate monomer employing template polymerization technique as an alternative to traditional physical and chemical crosslinking. The mode of interaction, as proved by Fourier Transform Infrared Spectroscopy (FTIR), was multiple H‐bonding between the tertiary amino group of the monomer and the carboxylic groups of the polymer. The hydrogels represented suitable matrices for enzyme immobilization. The effect of varying the polymer–monomer molar ratio on the swelling kinetics and parameters was investigated. The dynamic swelling isotherm exhibited a Fickian mode of penetrant sorption and a plateau that increases with the amino group content. A polymer complex of molar ratio (polymer:monomer) 0.5:0.8 had a weight swelling ratio of 10 and 7 at pHs 3 and 8, respectively. The proven pH sensitivity together with the amphoteric character of these hydrogels make them good candidates for another bioapplication such as oral delivery systems of therapeutic peptides and proteins. The structural integrity of the hydrogels was proved by their swelling reversibility. β‐Galactosidase, as an acidic model enzyme, was immobilized covalently on the synthesized hydrogels. The maximum enzyme velocity (V_max) was enhanced to 19 µmol/min/mg, for polycomplex of molar ratio 0.5:0.8, compared with 3.2 µmol/min/mg for the free enzyme. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of shell-cross-linked polymer networks and large-core star polymers: Effect of the volume of the cross-linking mixture

Group transfer polymerization and sequential addition of monomer and cross-linker were employed for the preparation of two new polymer structures, one of a polymer network and the other of a star polymer. The synthesis was completed in two steps, involving the synthesis of linear methyl methacrylate (MMA) arms of degree of polymerization of 20, followed by their cross-linking using a mixture of MMA monomer and ethylene glycol dimethacrylate (EGDMA) cross-linker. In this study, the volume of the cross-linking mixture was varied systematically. Furthermore, two mixture compositions were employed, involving MMA:EGDMA molar ratios of 1:1 and 3:1, leading to two series of polymeric materials. It was found that at a given cross-linking mixture composition, a larger volume of the cross-linking mixture favored the formation of polymer networks, whereas a smaller volume favored the formation of star polymers. The linear precursors, the star polymers and the extractables from the polymer networks were characterized by gel permeation chromatography in tetrahydrofuran (THF). The absolute weight-average molecular weight, the number of arms and the hydrodynamic radii of the star polymers, as determined using static and dynamic light scattering in THF, respectively, and their average radii as determined by atomic force microscopy, increased as the volume of the cross-linking mixture increased. The gravimetrically measured degrees of swelling in THF, the network sol fraction and the percentage of branched polymer in the sol fraction decreased as the volume of the cross-linking mixture increased.     

Synthesis,crystallization, and morphology of star‐shaped poly(ε‐caprolactone)

Six‐arm star‐shaped poly(ε‐caprolactone) (sPCL) was successfully synthesized via the ring‐opening polymerization of ε‐caprolactone with a commercial dipentaerythritol as the initiator and stannous octoate (SnOct₂) as the catalyst in bulk at 120 °C. The effects of the molar ratios of both the monomer to the initiator and the monomer to the catalyst on the molecular weight of the polymer were investigated in detail. The molecular weight of the polymer linearly increased with the molar ratio of the monomer to the initiator, and the molecular weight distribution was very low (weight‐average molecular weight/number‐average molecular weight = 1.05–1.24). However, the molar ratio of the monomer to the catalyst had no apparent influence on the molecular weight of the polymer. Differential scanning calorimetry analysis indicated that the maximal melting point, cold crystallization temperature, and degree of crystallinity of the sPCL polymers increased with increasing molecular weight, and crystallinities of different sizes and imperfect crystallization possibly did not exist in the sPCL polymers. Furthermore, polarized optical microscopy analysis indicated that the crystallization rate of the polymers was in the order of linear poly(ε‐caprolactone) (LPCL) > sPCL5 > sPCL1 (sPCL5 had a higher molecular weight than both sPCL1 and LPCL, which had similar molecular weights). Both LPCL and sPCL5 exhibited a good spherulitic morphology with apparent Maltese cross patterns, whereas sPCL1 showed a poor spherulitic morphology. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5449–5457, 2005     

茂基二价钐配合物高效催化己内酯开环聚合

研究了二茂基二价钐配合物(C5H5)2Sm(THF)作为单组分催化剂催化己内脂开环聚合反应,考察了催化剂用量、聚合反应时间、聚合反应温度对己内酯聚合反应的影响。结果表明,配合物(C5H5)2Sm(THF)对己内酯聚合有极高的催化活性且产物的数均分子量较高,当催化剂与单体摩尔比为1：5000时,聚合产率仍可达50.3%,数均分子量可高达32.4万;温度升高,聚合反应的转化率增加,聚合产物数均分子量降低;催化剂用量增加,聚合转化率增加,聚合产物分子量降低;聚合产物的分子量分布较窄;通过凝胶色谱法对聚合产物的分子量及分子量分布进行了表征。     

Ring-opening precipitation polymerization of poly(D,L-lactide-co-glycolide) in supercritical carbon dioxide

The biodegradable polymer poly(D ,L -lactide-co-glycolide) was synthesized by a ring-opening precipitation polymerization in supercritical CO₂ using stannous octoate as initiator. Following polymerization, unreacted monomer was removed by supercritical fluid extraction and the polymer was recovered as a porous solid upon depressurization of the CO₂ phase. The lactide to glycolide ratio of the polymer was determined to be 70.7 : 29.3 using ¹³C NMR spectroscopy. The weight-average molecular weight of the product was measured to be 3 500, with a polydispersity of 1.4 using gel permeation chromatography.     

自由基聚合反应挤出过程的化学流变分析

进行了甲基丙烯酸正丁酯在异向旋转双螺杆挤出机内的自由基聚合反应过程数值模拟,描述了单体转化率、重均分子量、流体粘度等物理量的变化特点,分析了其影响因素,获得了材料体系的化学流变规律.模拟结果与实验结果基本吻合.     

Kinetic study of the alternating copolymerization of butadiene and methyl methacrylate

A kinetic investigation of the alternating copolymerization of butadiene and methyl methacrylate with the use of a system of ethylaluminum dichloride and vanadyl chloride as a catalyst was undertaken. The relation between the polymer yield and the molar fraction of methyl methacrylate in the feed was examined by continuous variation of butadiene and methyl methacrylate, the concentrations of total monomer, ethylaluminum dichloride, and vanadyl chloride being kept constant. This continuous variation method revealed that the polymer yield attains its maximum value with a monomer feed containing less than the 0.5 molar fraction of methyl methacrylate. This value of the molar fraction of methyl methacrylate affording the maximum polymer yield decreased on increasing the total monomer concentration but was not changed on varying the concentration of ethylaluminum dichloride. The number of active species estimated from the relation between yield and molecular weight of the polymer was almost constant, regardless of the molar fraction of methyl methacrylate in the feed. Consequently, it can be said that the maximum polymer yield depends mainly on the propagation reaction, not on the initiation reaction or the termination reaction. Three types of the mechanism have been discussed for this alternating copolymerization: polymerization via alternating addition of butadiene and methyl methacrylate complexed with ethylaluminum dichloride by the Lewis-Mayo scheme; polymerization via the ternary intermediate of butadiene, methyl methacrylate, and ethylaluminum dichloride; polymerization via the complex formation of butadiene and methyl methacrylate complexed with ethylaluminum dichloride occurring only at the growing polymer radical. From the kinetic results obtained, it was shown that the first and third schemes are excluded, and polymerization by way of the ternary intermediate is compatible with the data.     

RAFT Polymerization of Styrene in the Presence of 2‐Nonyl‐benzoimidazole‐1‐carbodithioic Acid Benzyl Ester

A novel dithiocarbamate, 2‐nonyl‐benzoimidazole‐1‐carbodithioic acid benzyl ester ( 1a ), was synthesized and successfully used in RAFT polymerization of styrene in bulk with thermal initiation. The effect of molar ratio of styrene to RAFT agent on the polymerization was investigated. The linear relationship between ln([M]₀/[M]) and polymerization time indicated that the polymerization was first‐order with respect to monomer concentration. The molecular weights increased linearly with monomer conversion and were close to corresponding theoretical values. The molecular weight distributions (M _w /M _n ) kept very narrow (M _w /M _n <1.1) at a wide range of conversions of 14.2% to 73.3%. The obtained polymer had a strong ultraviolet absorption at 329 nm, which indicated that the 1a moiety remained at the end of polymer chain.     

Radiation-induced emulsion copolymerization of tetrafluoroethylene with propylene. IV. Effects of emulsifier concentration and dose rate

Radiation-induced emulsion copolymerization of tetrafluoroethylene with propylene was carried out by batch operation with an initial molar ratio of tetrafluoroethylene to propylene of 3.0 in the emulsifier concentration range of 0.1 to 3.0% and in the dose rate range of 2 × 10⁴ to 2 × 10⁵ R/hr. The effects of emulsifier concentration and dose rate on the polymerization rate and the number-average degree of polymerization are discussed in comparison with the Smith-Ewart theory. The polymerization rate is proportional to the 0.26 power of emulsifier concentration and to the 0.7 power of dose rate. The degree of polymerization is independent of the emulsifier concentration and the dose rate above the critical micelle concentration (CMC) of the emulsifier. These results are not in agreement with the Smith-Ewart theory. It is explained that the termination reaction is a degradative chain transfer of propagating radicals to propylene. On the other hand, the copolymerization in emulsion occurs either below the CMC or in the absence of emulsifier. Under these conditions, however, it is impossible to obtain a copolymer of high molecular weight at a high rate of polymerization because of the presence of a small number of polymer particles formed and the short interval of chain growth in the polymer particle.     

Synthesis of Acid Dyeable Acrylonitrile Copolymer

In this paper, a unique and updated technique was applied to obtain an acid dyeable copolymer of acrylonitrile by solution polymerization of acrylonitrile, and a kind of alkaline monomer F (N,N‐dialkylaminoethylacrylate). Azodiisobutyronitrile (AIBN) was used as initiator to prepare the copolymer in sodium sulfocyanate aqueous solution. The effect of initiator concentration on the polymer's molecular weight and conversion during polymerization was studied. The relation between concentration of the alkaline monomer F and the polymer conversion, as well as the relation between concentration of the alkaline monomer F and the % dye‐uptake of the copolymer are discussed. The influence of pH was also researched. The structure of the copolymer was characterized by IR and NMR. The copolymer has excellent acid dyeable characteristics.     

甲醛分子印迹聚合物的制备、性能及水产品测定

以甲醛为模板分子,α-甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸酯为交联剂,用氯仿做溶剂,制备了甲醛分子印迹聚合物,并优化了此制备方法,在模板分子、功能单体和交联剂的摩尔比为1:2:20,预聚合时间为4 h,聚合时间为8 h的条件下制备的聚合物对甲醛的特异性吸附能力最好,当甲醛溶液的浓度为2 mmol/L时聚合物对甲醛的吸附量达到了12.40×10^-2 mmol/g。 对市售鱿鱼处理后用高效液相色谱法测定得样品中甲醛的浓度是5.92 mg/Kg,将该样稀释100倍以后甲醛已无法检出,经MIP柱富集后检测计算样品中甲醛浓度为5.76 mg/Kg,表明该聚合物用于样品前处理高效且结果无显著性差异。