The free radical initiated polymerization of diethylfumarate

The kinetics of polymerization of diethylfumarate initiated by 1,1′ azo-bis-isobutyronitrile have been studied at temperatures between 60 and 80°. Difficulty in isolating the polymer was overcome by using a petroleum ether-methanol two-phase system to separate the monomer and polymer, and by precipitating the polymer from the methanol phase with an aqueous salt solution. The density of the polymer varied from 1·183 g/cm³ at 80° to 1·211 g/cm³ at 20°, giving volume contractions of approximately 16 per cent for complete conversion of monomer into polymer. The initiator exponent was about 0·45, i.e. slightly lower than normally obtained from free radical initiated vinyl polymerization. The overall energy of activation for the polymerization was 89 ± 2 kJ/mole. Constants for chain transfer with monomer, determined from rate and molecular weight measurements at 60, 70 and 80, were in the region of 0·005 0·017.     

Anionic polymerization of 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane

In the first of a two-part series, a study has been made of the anionic polymerization of a five-membered cyclocarbosiloxane, 2,2,5,5-tetramethyl-1-oxa-2,5-disilacyclopentane. The polymerization was initiated by lithium n-butyldiphenylsilanolate in the presence of tetrahydrofuran. The chemical shifts of the protons of the cyclic monomer and the polymer were found to be different, and therefore the rate of polymerization was obtained in an NMR spectrometer. The effects of varying the concentrations of THF, initiator, and water upon the rate of polymerization and upon the molecular weight and the molecular weight distribution were investigated. At a constant concentration of monomer and initiator, the rate of polymerization increased when the THF concentration was increased. At a constant concentration of monomer and THF the rate of polymerization reached a constant value when the initiator concentration was varied. The molecular weight and the molecular weight distribution were dependent upon the initiator to water ratio, whereas water concentration had little effect on the rate of polymerization. Essentially monodispersed polymers were obtained when the concentration of initiator was in large excess to that of water or vice versa. A bimodal distribution in molecular weight was obtained when the concentration of initiator was approximately equal to that of water. The apparent activation energy of polymerization was 12.7 kcal/mole.     

PHOTOINITIATED INVERSE EMULSION POLYMERIZATION OF SODIUM ACRYLATE

Photoinitiated inverse emulsion polymerization of sodium acrylate (AANa) in kerosene was carded out at room or lower temperature, using 2,2-dimethoxy-2-phenylacetophenone (DMPA) as the initiator. Kinetic investigations indicated that the polymerization could be completed in about 30 min and produce polymer with high molecular weight (10^6-10^7). It was found that monomer droplets are the main sites for the polymerization (nucleation). With the increase of DMPA concentration, polymerization rate (Rp) reaches a maximum value while molecular weight of the produced polymer has an adverse result, but the dependence of Rp on incident light intensity is similar. Influences of other parameters such as monomer concentration, emulsifier content and reaction temperature, etc. were also studied. At lower pH values of water phase, Rp depends strongly on the pH due to the electrostatic interaction between the ionized radicals and the monomer. At higher pH, Rp shows a slight dependence on pH.     

Effect of amount of monomer on radiation-induced polymerization of styrene adsorbed on silica gel

The effect of amount of monomer on radiation-induced polymerization of styrene adsorbed on silica gel was investigated with the monomer amounting from less than monolayer adsorption to more than the equilibrium adsorption. The rate of graft polymerization and the molecular weight of the polymer changed with the amount of monomer adsorbed on silica gel. Maximum grafting efficiency was obtained at monolayer adsorption. The molecular weight of graft polymer was higher than that of homopolymer in both radical and cationic polymerizations, and the ratio in molecular weight of graft polymer to that of homopolymer tends to be unity with increasing amount of adsorbed monomer. These results can mainly be explained in terms of the number of initiating species (radical and cation) that change in relation to the amount of adsorbed monomer. Propagation and termination change with amount of adsorbed monomer in relation to the molecular mobility of adsorbed monomer. A very high-molecular-weight graft polymer is formed only with a small amount of adsorbed monomer in the initial stage. The grafting percent with a large amount of adsorbed monomer increased after most of the monomer has been polymerized. Secondary effect of radiation on the graft and homopolymers due to energy transfer from silica gel is suggested from the complicated phenomena in the later stage of the reaction.     

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.     

Condensative chain polymerization. II. Preferential esterification of propagating end group in Pd-catalyzed CO-insertion polycondensation of 4-bromophenol derivatives

For a development of condensative chain polymerization where polycondensation proceeds from an initiator in a chain polymerization manner to yield polymer with a defined molecular weight and a narrow molecular weight distribution, the Pd-catalyzed polycondensation of 4-bromophenol derivatives with CO is studied. Model reactions showed that monomer reacted the polymer terminal Br preferentially compared to the monomer Br, but that the ester exchange reaction of polymer backbone with monomer phenoxide occurred in some extent. In the polymerization of 4-bromo-2-n-octylphenol with CO using 4-bromo-2,6-dimethylphenyl benzoate as an initiator, the molecular weight of polymer increased in proportion to time up to 30 min. The GPC elution curves showed that oligomers were produced from the initiator. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2607–2618, 1999     

极性单体阴离子型聚合反应产物的分子量分布

关于任意官能度多官能团引发剂瞬时引发并有单体链终止的阴离子型聚合反应体系,本工作通过非稳态动力学分析,求得了分子量分布函数和平均聚合度的一般表示式,讨论了单体的最大消耗量和聚合物的官能度分布问题,建立了从反应的初始条件和单体转化率计算产物的各种分子参数的方法。上述理论结果适用于甲基丙烯酸甲酯等极性单体在极性溶剂中的阴离子型聚合反应。数值计算的结果表明:当引发剂的官能度为2时,除了少数例外,所得聚合物的分子量分布一般具有双峰。     

旋光性聚{(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯}的合成与表征

设计、合成了一个带有横挂三联苯侧基的手性乙烯基单体——(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯,进行了普通自由基和原子转移自由基聚合反应.所得聚合物具有比单体低30°左右的比旋光度,且在侧基的紫外吸收处呈现明显不同于单体的Cotton效应,说明其主链可能形成了具有相反旋光方向的螺旋构象.在所研究范围内,聚合条件对聚合物的旋光度没有明显的影响.在分子量较小时,聚合物的比旋光度随着分子量的增加而降低,说明主链螺旋构象的贡献在增大,而当分子量达到一定值后,聚合物的比旋光度不再随分子量的增加而显著变化.     

Characterization of hydrophilic networks synthesized by group transfer polymerization

Group transfer polymerization was used to synthesize several series of hydrophilic random and model networks. Cationic random networks were prepared both in bulk and in tetrahydrofuran (THF) using a monofunctional initiator and simultaneous polymerization of monomer and branch units, while a bifanctional initiator was employed in THF for the synthesis of model networks comprising basic or acidic chains. Upon polymerization of the monomer, the latter initiator gives linear polymer chains with two “living” ends, which are subsequently interconnected to a polymer network by the addition of a branch unit. Homopolymer network star polymers were also synthesized in THF by a one‐pot procedure. The synthesis involved the use of a monofunctional initiator and the four‐step addition of the following reagents: (i) monomer, to give linear homopolymers; (ii) branch unit, to form “arm‐first” star polymers; (iii) monomer, to form secondary arms and give “in‐out” star polymers; and, finally (iv) branch unit again, to interconnect the “in‐out” stars to networks. Different networks were prepared for which the degree of polymerization (DP) of the linear chains between junction points was varied systematically. For all networks synthesized, the linear segments, the “arm‐first” and the “in‐out” stars were characterized in terms of their molecular weight (MW) and molecular weight distribution (MWD) using gel permeation chromatography (GPC). The degrees of swelling of both the random and model networks in water were measured and the effects of DP, pH, and monomer type were investigated.     

Heterogeneity Features of Bulk Atom Transfer Radical Polymerization of Methyl Methacrylate in an Ampoule Reactor

Summary: This work demonstrated the severity of heterogeneity issues with ampoule reactors in bulk atom transfer radical polymerization of methyl methacrylate. The kinetic data of Cu^II concentration, monomer conversion, and polymer molecular weight varied from location to location along the ampoule. However, the polymer molecular weight versus conversion data from different locations fell into a single theoretical line. All locations except for the bottom part of the ampoule produced polymers having narrow molecular weight distribution.

Conversion versus time at different locations for the ATRP of MMA at 70 °C.     

Radiation-induced polymerization at high dose rate. VI. Butadiene in n-hexane solution

Polymerization of butadiene by electron-beam irradiation was studied in n-hexane solution. Kinetic features of the polymerization and microstructure of the product were similar to those in bulk polymerization, which indicated a cationic mechanism. Both the rate of polymerization and average molecular weight of the product decreased by about 20% in the solution system. Soluble polymer was obtained up to ca. 40% conversion at the monomer concentration of 50 mol%, whereas in the bulk system the gel formed in polymer conversion exceeded 10%. A kinetic equation was proposed to explain the change in rate of polymerization with the monomer concentration.     

Ring-opening polymerization of ε-caprolactone initiated by diphenylzinc

In the present work the polymerization of ε-caprolactone (ε-CL) using Ph₂Zn as initiator is reported. The effects of reaction temperature, molar ratio of monomer/initiator and reaction time on the yield and the molecular weight are investigated. The temperature is varied between 20 and 120 °C and the molar ratio of monomer to initiator between 200 and 800 mol/mol. The results indicate that the Ph₂Zn induces the polymerization of ε-CL to high conversion and produces polymer with high molecular weight at temperatures around 40-60 °C.     

γ-Radiation-initiated post-polymerization of methacrylic acid in the solid state

The solid-state postpolymerization of slowly crystallized methacrylic acid was studied at 0°C with ⁶⁰Co γ-radiation as the initiator. The yield, molecular weight, molecular weight distribution, and stereosequencing of the polymer product were determined as a function of polymerization time. The narrow molecular weight distribution and the linear dependence of molecular weight on polymer yield were attributed to a polymerization mechanism characterized by both independent chain propagation and essentially no termination step. The overall polymerization rate was substantially faster than that reported previously for shock-crystallized monomer, a result which was attributed to termination by the occlusion of propagating radicals at defects in the shock-crystallized monomer. Although largely atactic, the polymer synthesized in the solid state contained a secondary kind of stereosequencing; the meso triad probability was highest at the end of the chain, where propagation had initiated and decreased continuously with chain growth. The gradient in stereosequencing along the chains was attributed to defects that were introduced into the monomer crystals by the growing polymer chains.     

Anionic graft polymerization of methacrylonitrile on potassium starch alkoxide

The anionic graft polymerization of methacrylonitrile on potassium starch alkoxide in dimethyl sulfoxide was studied. Factors affecting the graft polymerization such as monomer and alkoxide concentrations as well as temperature were investigated. The yield of the graft polymers was found to increase with alkoxide concentration, and it was possible to incorporate all the starch into graft polymer. On increasing the monomer concentration the graft polymer yield increased to a flat maximum. At the higher monomer concentrations, the efficiency of monomer in giving graft polymer decreased due to increased homopolymer formation. The composition of the graft polymers varied with increasing monomer concentration, graft polymers having about 40–65% of grafted starch were obtained. With increasing temperature (10 to 60°C), the yield of graft polymer decreased, there was more homopolymerization, but the amount of starch incorporated in the graft remained constant. The structure of the graft polymers was deduced from hydrolysis of the starch backbone of the graft polymers by dilute mineral acid and the determination of the molecular weights of the grafted side chains, and from oxidation by periodic acid, which showed the extent of grafting at the secondary hydroxyl groups. These results have shown that by anionic graft polymerization it is possible to obtain graft polymers having more densely packed grafted side chains of relatively low molecular weights than those obtained previously by free-radical graft polymerization.     

二茂钛/锡/环氧化合物引发苯乙烯活性自由基聚合的研究

采用单茂钛CpTiCl3和二茂钛金属化合物(n-BuCp)2TiCl2,引发剂4-甲氧苯基缩水甘油基醚(I1),1,4-丁二醇二缩水甘油基醚(I2),4,4′-亚甲基二(N,N-二缩水甘油基苯胺)(I4)和苯基缩水甘油基醚甲醛共聚物(I5)及还原剂Sn组成引发体系,引发苯乙烯活性自由基聚合,合成线型和多臂聚合物.探讨了不同茂钛金属化合物、引发剂和还原剂对苯乙烯聚合的影响;并采用13C-NMR和GPC对聚苯乙烯的结构和性能进行了表征.结果表明所得聚合物是无规聚苯乙烯,聚合物分子量高,分子量分布窄.聚合行为属于活性自由基聚合.     

High‐molecular‐weight poly(1,5‐dioxepan‐2‐one) via enzyme‐catalyzed ring‐opening polymerization

To avoid organometallic catalysts in the synthesis of poly(1,5‐dioxepan‐2‐one), the enzymatic ring‐opening polymerization of 1,5‐dioxepan‐2‐one (DXO) was performed with lipase CA (derived from Candida antarctica) as a biocatalyst. A linear relationship between the number‐average molecular weight and monomer conversion was observed, and this suggested that the product molecular weight could be controlled by the stoichiometry of the reactants. The monomer consumption followed a first‐order rate law with respect to the monomer, and no chain termination occurred. Water acted as a chain initiator, but it could cause polymer hydrolysis when it exceeded an optimum level. An initial activation via the heating of the enzyme was sufficient to start the polymerization, as the monomer conversion occurred when samples were left at room temperature after an initial heating at 60 °C. A high lipase content led to a high monomer conversion as well as a high molecular weight. An increase in the monomer conversion and molecular weight was observed when the polymerization temperature was increased from 40 to 80 °C. A further increase in the polymerization temperature led to a decrease in the monomer conversion and molecular weight because of the denaturation of the enzyme at elevated temperatures. The polymerization behavior of DXO under lipase CA catalysis was compared with that of ε‐caprolactone (CL). The rate of monomer conversion of DXO was much faster than that of CL, and this may have been due to differences in their specificity toward lipase CA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4206–4216, 2005     

Gamma Radiation-Induced Template Polymerization of Acrylic Acid in the Presence of Polyactrylamide

Abstract

Poly(acrylamide-acrylic acid) resin p(AM-AA) was prepared by gamma radiation-induced polymerization of acrylic acid in the presence of polyacrylamide as a template polymer. The polymerization was studied by a free radical mechanism at different experimental conditions such as: absorbed dose, monomer concentration, polymer/monomer molar ratio and the weight-average molecular weight or the swelling degree of added polymer. The resin was obtained at dose > 10 KGy and there is no significant change in the swelling degree of the resin. The results showed that the capacity of the resin increases by increasing the monomer concentration, the weight-average molecular weight of the added polymer and decreases by increasing polymer/monomer molar ratio and the swelling degree of the added polymer. It was also found that the capacity of the resin depends on the radiation dose.     

Synthesis and characterization of monomers and polymers for adhesives from methyl oleate

The focus of this work is to synthesize a monomer from a fatty acid methyl ester capable of forming high molecular weight polymers. The mono‐unsaturation in the starting material, methyl oleate, was first epoxidized using a peroxy acid. This intermediate material was further modified using acrylic acid. The acrylated molecule is able to participate in free‐radical polymerization reactions to form high molecular weight polymers. The rate of polymerization was low because of the long aliphatic structure of the monomer. It is hypothesized that the polymerization reaction occurred in the interface between the particle and water, thereby slowing down the reaction. After 18 h of reaction, a monomer conversion of approximately 91% was achieved. A maximum weight‐average molecular weight of approximately 10⁶ g/mol was observed after 14 h of reaction. At early reaction times linear polymers were formed. However, as the reaction time increased, the amount of branching that occurred on the polymer molecule increased, as indicated by gel permeation chromatography and light scattering. This has been attributed to chain transfer to polymer via hydrogen abstraction from a tertiary backbone C–H bond. The resulting polymer may be of considerable interest for pressure‐sensitive adhesive applications. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 451–458, 2002; DOI 10.1002/pola.10130     

Living radical miniemulsion polymerization by RAFT in the presence of beta-cyclodextrin

Living radical polymerization of styrene in a miniemulsion by reversible addition–fragmentation chain transfer (RAFT) was successfully realized in the presence of beta-cyclodextrin (CD), using sodium dodecyl sulfate and hexadecane as surfactant and costabilizer, respectively. The drawback of instability (red layer formation) encountered in the living radical polymerization in emulsion or miniemulsion was overcome. The linear relationship between the monomer conversion and the molecular weight, as well as lower molecular weight distribution (MWD), shows that the polymerization process was under control. The addition of CD was found to have little influence on the polymerization rate. However, MWD of the polymer synthesized is obviously decreased. The mechanism of stability and controllability improvement in the presence of CD proposed that the complex formation between CD and RAFT agent or RAFT agent-ended oligomer increased their diffusion ability from monomer droplet to polymerization locus and improved the homogeneity of the RAFT agent level among the polymerization loci.     

丁基锂引发的活性宽分布聚双烯烃的合成

<正> 用烷基锂引发的丁二烯“活性”聚合,通常只能得到分子量分布较窄的聚合物。这类聚合物的门尼粘度较高,不易加工,且易冷流。为了解决这些问题,一般是合成分子量分布较宽且有一定支化的聚合物。但在以往的合成宽分布聚合物的方法中,大多只能得到非“活性”聚双烯烃,因而无法进行“活性”高分子的一些典型反应,如嵌段、接枝及偶