Studies of the polymerization of diallyl compounds. XII. Cyclocopolymerization of dimethallyl phthalate with vinyl acetate

Dimethallyl phthalate was copolymerized with vinyl acetate at 60°C with the use of benzoyl peroxide as an initiator. The rate and degree of copolymerization increased with an increase in the mole fraction of vinyl acetate. The residual unsaturation of the copolymer was nearly constant, regardless of the feed molar ratio. The monomer reactivity ratios (MRR) were obtained on the basis of the copolymer composition equation in which the intramolecular cyclization reaction was considered: γ₁ = 1.08 (MRR of the uncyclized radical), γ₂ = 0.99 (MRR of vinyl acetate radical), γ_c = 0.73 (MRR of the cyclized radical). The difference between γ₁ and γ_c is discussed.     

Structure and property relationships in ethylene–vinyl acetate copolymers

The effects of vinyl acetate content on crystallinity of ethylene–vinyl acetate (E/VA) copolymers were investigated by x-ray diffraction and differential thermal analysis (DTA). The values of these parameters obtained from DTA were found to agree quantitatively with data calculated from x-ray, probability equations, and copolymer theory. The melting points of the crystalline copolymers, and the molar amounts of vinyl acetate to produce a completely amorphous rubber corresponds exactly to that predicted by the Flory theory. The random character expected in E/VA copolymers is thereby confirmed. The physical properties of E/VA copolymers of all ranges of compositions and crystallinity were determined. Depending directly upon vinyl acetate content, the copolymers changed progressively from highly crystalline polyethylene to semicrystalline polyethylene, a completely amorphous rubber, a soft plastic with a glass transition near room temperature. Properties which were correlated with copolymer composition include: crystallinity, melting point, density, modulus, tensile strength, glass transition, and solubility. Finally, the effect on crystallinity and physical properties of replacing the acetoxy group in E/VA with the smaller, highly polar hydroxyl group (ethylene—vinyl alcohol copolymer) was also investigated.     

乙烯-醋酸乙烯酯-α-烯烃三元共聚物

以乙烯、醋酸乙烯酯和α-烯烃为原料,以偶氮二异丁腈为引发剂,通过高压本体聚合制备三元聚合物.考察了聚合条件对共聚物数均分子量和醋酸乙酯(VA)质量分数的影响.结果表明:在引发剂用量为1.1g,反应压力为6 MPa,反应温度95℃,醋酸乙烯酯和α-烯烃的质量比为2:1的条件下能得到数均分子量为8 600和VA质量分数为0.35的产物.实验证明该产物性能优良,可作为蜡的添加剂.     

Copolymerization of vinyl acetate with 1-octene and ethylene by cobalt-mediated radical polymerization

The cobalt-mediated radical polymerization of vinyl acetate was extended to copolymerization with 1-alkenes (ethylene or 1-octene). In agreement with the low amount of 1-alkene that could be incorporated into the copolymer, a gradient structure was predictable, but a rather low polydispersity was observed. A poly(vinyl acetate)-b-poly(octene) copolymer was also successfully synthesized, leading to a poly (vinyl alcohol)-b-poly(octene) amphiphilic copolymer upon the methanolysis of the poly (vinyl acetate) block. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2532–2542, 2007     

Preparation of Syndiotacticity-Rich High Molecular Weight Polyvinyl Alcohol by Low Temperature Emulsifier-Free Emulsion Copolymerization of Vinyl Acetate and Vinyl Pivalate

Low temperature emulsifier-free emulsion copolymerization of vinyl acetate (VAc) and vinyl pivalate (VPi) was carried out using a redox initiation system to prepare syndiotacticity-rich high-molecular weight (HMW) polyvinyl alcohol (PVA) with high yield. The effects of the polymerization conditions on the conversion, the molecular weight, the structure of poly (vinyl acetate-co-vinyl pivalate) (P (VAc-VPi)) and syndiotacticity of PVA were investigated. With the increases of the initiator concentration, the VPi molar ratio in monomer and polymerization temperature, the degree of polymerization (DP) of PVA decreases distinctly, but VPi contents in copolymer and syndiotactic diad (S-diad) contents of PVA increase obviously. PVA with the maximum DP of 11030 can be prepared by complete saponification of P(VAc-VPi) obtained under condition that the molar ratio of KPS to monomer is 1/2000, the molar ratio of VAc to VPi is 7:3 and reaction temperature is 12°C. The highest S-diad content in PVA can be up to 59.31% while the DP of PVA decreases to 5180 under the condition that the feed ratio of VPi is 70 mol%, which means the syndiotacticity-rich HMW PVA can be prepared successfully. And the conversions of all reactions are above 80%. Syndiotacticity-rich HMW PVA is effectively prepared in this study, which is useful for the preparation of high-strength and high-modulus PVA fiber.     

小分子药物在半结晶乙烯-醋酸乙烯酯共聚物(EVA)中的扩散机理:自由体积理论

半结晶乙烯 醋酸乙烯酯共聚物 (ＥＶＡ)是扩散控制药物释放体系中使用最多的聚合物 ,它具有生物相容性好 ,加工成型方便 ,机械性能好及理化性质稳定等特点 ,是经ＦＤＡ批准的可用于人体的高分子材料之一 ,已广泛应用于宫内给药体系 ,眼用给药体系 ,透皮给药体系及植入给药体系等 ,并且已有商品化的以ＥＶＡ为基质的药物控制释放系统[1～ 3 ] ,然而对于小分子药物在半结晶ＥＶＡ共聚物中的扩散机理却少见报道 .本文将自由体积理论应用于ＥＶＡ基质型药物扩散控制释药体系 ,阐明了小分子药物在半结晶ＥＶＡ聚合物中的扩散系数随共聚物组成的…     

Miniemulsion copolymerization of vinyl acetate and butyl acrylate. I. Differences between the miniemulsion copolymerization and the emulsion copolymerization processes

Differences between the emulsion copolymerization and miniemulsion copolymerization processes, in terms of emulsifier adsorption, emulsion stability, polymerization kinetics, copolymer composition and dynamic mechanical properties were studied for the comonomer mixture of 50:50 molar ratio vinyl acetate (VA+)—butyl acrylate (BuA), using sodium hexadecyl sulfate (SHS) as a surfactant and hexadecane (HD) as a co-surfactant. The use of hexadecane with the appropriate SHS initial concentration led to a higher adsorption of surfactant, smaller droplet size, higher stability of the emulsions, lower polymerization rates, and larger latex particle size. The copolymer composition during the initial 70% conversion was found to be less rich in Vac monomer units for the miniemulsion process. The dynamic mechanical properties of the copolymer films showed less mixing between the BuA-rich core and the VAc-rich shell in the miniemulsion latexes compared to the conventional latex films.     

STUDIES ON ULTRASONIC GRAFTING OF POLY(VINYL ACETATE) WITH POLY(ETHYLENE OXIDE)

The ultrasonic degradation of poly(ethylene oxide) and poly(vinyl acetate) in benzene solution, and grafting reaction of poly(vinyl acetate) with poly(ethylene oxide) were studied. It is found that the chain-scission reactions follow the course suggested by D. W. Ovenall. The structure of the copolymer was identified by IR, NMR and DTA, showing that the copolymer prepared is a graft copolymer mainly. The copolymer formed by irradiating 1% PEO/PVAc solution (PEO/PVAc:1/1 by weight) for a period of 10 rain at 18.2 kHZ, with 2.0 A input current on reversed main circuit, amounts to 10.5%.     

The effect of residual acetate groups on the structure and properties of vinyl alcohol–ethylene copolymers

Vinyl alcohol–ethylene (VAE) copolymers, commercially manufactured by hydrolysis of the corresponding vinyl acetate–ethylene copolymers, can contain small amounts of unhydrolyzed vinyl acetate. This article shows the influence of these residual groups on the structure of the resulting copolymers, studied by nuclear magnetic resonance and wide‐angle X‐ray scattering. Thermal and mechanical properties of these materials were investigated by differential scanning calorimetry, thermogravimetry, drawing behavior, birefringence measurements, and dynamic mechanical analysis. The structure of the copolymers is considerably affected by the volume of the residual acetate groups, bigger than that of the hydroxyl ones, which hinders the crystallization process. In relation to the thermal and mechanical properties, the temperature and enthalpy of melting as well as the Young's modulus and yield stress, decrease as vinyl acetate molar fraction increases. Moreover, the α and β relaxations are shifted to lower temperatures as residual content in the copolymer is raised. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 573–583, 2000     

Fluorocyclopropanes. IV. Copolymers of perfluorocyclopropene

Perfluorocyclopropene undergoes free-radical copolymerization with ethylene, isobutylene, cis- and trans-2-butene, vinyl acetate, methyl vinyl ether, vinyl chloride, styrene, acrylonitrile, tetrafluoroethylene, vinyl fluoride, and vinylidene fluoride. The copolymerization proceeds most readily with electron-rich olefins such as methyl vinyl ether (to yield a 1:1 copolymer), but conditions were found to give copolymers with electron-deficient olefins such as tetrafluoroethylene and vinylidene fluoride. Copolymers with methyl vinyl ether, tetrafluoroethylene, vinyl fluoride, and vinylidene fluoride were examined in detail. Evidence is presented that the perfluorocycloproply ring is incorporated intact into the copolymer and can be subsequently isomerized to a perfluoropropenyl unit by heating at 200–300°C.     

Synthesis and Characterization of Poly(N-isopropylacrylamide) and Poly(vinyl acetate) Diblock Copolymers via MADIX Process

The synthesis of diblock copolymers of poly(N-isopropylacrylamide) (PNIPAM) and poly(vinyl acetate) (PVAc) was performed by macromolecular design via interchange of xanthates (MADIX) process. Following the preparation of methyl (isopropoxycarbonothioyl) sulfanyl acetate (MIPCTSA) as chain transfer agent, it was reacted with vinyl acetate to obtain PVAc macro-chain transfer agent. Then, block copolymerization was completed by successive addition of N-isopropylacrylamide (NIPAM). ¹H NMR spectroscopy confirmed the presence of both blocks in the copolymer structure, with the expected composition based on the feed ratio. Size Exclusion Chromatography (SEC) was used to investigate the relative values of molecular characteristics. Only 20% of PVAc was converted to block copolymer. The resultant block copolymer structures were further examined in terms of their morphologies as well as critical micelle concentration (CMC) by using ESEM and Fluorescence Excitation Spectroscopic techniques, respectively. Morphological characterization confirmed amphiphilic block copolymer formation with the existence of mainly ca. 100 nm well distributed micelles. The thermo responsive amphiphilic behavior of the block copolymer solutions were followed by Dynamic Light Scattering (DLS) technique.     

聚苯乙烯大单体与乙酸乙烯酯的共聚及其接枝共聚物的表征

研究了聚苯乙烯大单体与乙酸乙烯酯的溶液聚合,结果表明,接枝效率随引发剂用量、聚合温度及小单体与大单体的投料比的增加而增加,随大单体的分子量增加而减少,而随单体浓度的变化呈现一最大值。共聚过程中大单体的转化率开始较小单体的增加快,后期变慢。用萃取法纯化的接枝共聚物经GPC、IR、~1H-NMR及PGC等表征,并算得平均接枝数为4—7。透射电镜表明接枝共聚物中存在微观相分离。     

Alkyl chain branching in ethylene–vinyl acetate copolymer

Ethylene–vinyl acetate copolymers contain two kinds of side chains: acetoxy branches originating from incorporated vinyl acetate and alkyl branches. The alkyl branching was determined by infrared analysis after converting the ethylene–vinyl acetate copolymer to a hydrocarbon polymer by three steps: hydrolysis, iodation with hydriodic acid containing red phosphorus, and reductive hydrogenation with lithium aluminum hydride. It was found that physical properties such as stiffness were dependent both on the degree of alkyl chain branching and on vinyl acetate content.     

Efficient carbonyl hydrosilylation reaction: Toward EVA copolymer crosslinking

In this article, the hydrosilylation reaction of carbonyl groups of acetate derivatives and SiH groups of hydride‐terminated polydimethylsiloxane at high temperature (100–130 °C) are described. Triruthenium dodecacarbonyl, Ru₃(CO)₁₂, was used as effective catalyst for hydrosilylation reaction. The hydrosilylation reactions with octyl acetate and 4‐heptyl acetate were investigated by multinuclear NMR spectroscopy (¹H, ¹³C, and ²⁹Si). This work provides evidence of the addition reaction of SiH groups onto carbonyl groups. The influence of the nature of the acetate structure on the reaction kinetics was shown and the slight contribution of side reactions at high temperature highlighted. Hydrosilylation reaction was extent to the crosslinking of ethylene‐vinyl acetate (EVA) copolymer in the same range of temperature. The formation of EVA chemical network was demonstrated by HR‐MAS NMR spectroscopy and by measuring the gel fraction of EVA chains in hot toluene. From Flory theory, the crosslinking density of elastic strand was calculated to be 80 mol m^?3 in agreement with the measurements from swelling ratio (VA/SiH molar ratio: 11.8). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Thermal analysis and FT‐IR studies of adsorbed poly(ethylene‐stat‐vinyl acetate) on silica

Adsorbed poly(ethylene‐stat‐vinyl acetate) (PEVAc) on fumed silica was studied using temperature‐modulated differential scanning calorimetry (TMDSC) and FT‐IR spectroscopy. The properties of the copolymers were compared with poly(vinyl acetate) (PVAc) and low density polyethylene (LDPE) as references. TMDSC analysis of the copolymer‐silica samples in the glass transition region was complicated for the copolymers because of the ethylene crystallinity. Nevertheless, examination of the glass transition region for small adsorbed amounts of these copolymers indicated the presence of tightly‐ and loosely‐bound polymer segments, similar to other polymers which have an attraction to silica. Compared with bulk polymers with the same composition, the tightly‐bound polymers showed an increased glass transition temperature (T_g) and a loosely‐bound fraction with a lower T_g than bulk. FT‐IR spectra of the surface copolymers indicated that the fraction of bound carbonyls (p) increased as the fraction of vinyl acetate in the copolymers decreased, consistent with the notion that the carbonyls from vinyl acetate preferentially find their way to the silica surface. Spectra from samples with different adsorbed amounts of polymer were used to obtain the amount of bound polymer (M_b) and the ratio of molar absorption coefficients of bound carbonyls to free carbonyls (X). The copolymers had very large p values (up to 0.8) at small adsorbed amounts and dependent on the composition of the polymer. However, an analysis of the bound fractions, based on only the vinyl acetate groups, superimposed the data, suggesting that the ethylene units simply dilute the vinyl acetate groups in the surface polymer. The sample with the smallest fraction of vinyl acetate did not show this behavior and may be considered to be “carbonyl poor.” © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 727–736     

Stabilizer‐free dispersion copolymerization of maleic anhydride and vinyl acetate. I. Effects of principal factors on microspheres

A novel dispersion copolymerization of maleic anhydride (MAn) and vinyl acetate (VAc) without adding stabilizer is developed, which gives uniform copolymer microspheres with tunable sizes. Some principal factors affecting the microspheres, such as reaction time, monomer concentration and feed ratio, reaction media, and cosolvent, were investigated. It was found that the stabilizer‐free dispersion copolymerization of MAn and VAc is a rapid process, and the particle size grows in accordance with the evolution of polymerization. The chemical composition of the copolymer microspheres was characterized by FT‐IR and ¹³C NMR spectroscopies. Over a wide range of monomer concentrations, the microspheres can always be formed and stably dispersed, with uniform sizes ranging from 180 nm to 740 nm. The yield of copolymer microspheres reaches a maximum at 1:1 feed ratio of MAn to VAc, owing to the alternating copolymerization between the binary monomers by a known charge‐transfer‐complex mechanism. However, the diameter of microspheres drastically increases when MAn content is enhanced. Only some specific alkyl ester solvents, such as n‐butyl acetate, isobutyl acetate, n‐amyl acetate, are desirably fit for this unique stabilizer‐free dispersion polymerization. Furthermore, we found that when some acetone is added as a cosolvent, the copolymer microspheres can still be formed, with much larger diameters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3760–3770, 2005     

聚苯乙烯大单体与乙酸乙烯酯的共聚及其接枝共聚物的表征

 研究了聚苯乙烯大单体与乙酸乙烯酯的溶液聚合,结果表明,接枝效率随引发剂用量、聚合温度及小单体与大单体的投料比的增加而增加,随大单体的分子量增加而减少,而随单体浓度的变化呈现一最大值。共聚过程中大单体的转化率开始较小单体的增加快,后期变慢。用萃取法纯化的接枝共聚物经GPC、IR、¹H-NMR及PGC等表征,并算得平均接枝数为4—7。透射电镜表明接枝共聚物中存在微观相分离。     

Emulsion Copolymerization of Vinyl Acetate and Vinyl Silanes: Kinetics and Development of Microstructure

The batch emulsion copolymerization of vinyl acetate with different vinyl silane functional monomers (vinyl trimethoxysilane [VTMS], vinyl triethoxysilane [VTES], and vinyl silanetriol [VSTO]) is studied. The nature of the silane strongly affects the development of the microstructure and crosslinking ability of the latexes. A combination of techniques (Soxhlet extraction, centrifugation, assymetric‐flow field flow fractionation AF4/MALS/RI) shows that the factor controlling the molar mass and crosslinking density is the degree of hydrolysis of the alkoxysilane, producing higher molar masses and degrees of crosslinking when the degree of hydrolysis is high. Thus, the copolymer containing VSTO produced a very crosslinked latex, the one with VTMS produced a latex with a low degree of crosslinking in the wet state that can yield high degrees of crosslinking upon drying, and the latex with VTES do not produce significant amounts of crosslinking neither before nor after drying.     

Preparation of a xanthate‐terminated dextran by click chemistry: Application to the synthesis of polysaccharide‐coated nanoparticles via surfactant‐free ab initio emulsion polymerization of vinyl acetate

Stable monodisperse poly(vinyl acetate) (PVAc) submicronic latex particles were synthesized by ab initio batch emulsion polymerization using a dextran derivative from renewable resource as an efficient steric stabilizer. The dextranend‐functionalized by a xanthate moiety was synthesized by Huisgen's 1,3‐dipolar cycloaddition (click chemistry). It was applied as a macromolecular RAFT (reversible addition fragmentation chain transfer) agent in surfactant‐free emulsion polymerization of vinyl acetate to form in situ an amphiphilic block copolymer able to efficiently stabilize the latex particles. The method afforded the preparation of high solids content (27%) latices coated by dextran. Both the kinetic study and the molar mass analyses confirmed the involvement of the dithiocarbonate group in the emulsion polymerization process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2845–2857, 2008     

聚氧化乙烯和聚醋酸乙烯酯在超声波辐照下接枝反应的研究

本文分别研究了聚氧化乙烯(PEO)和聚醋酸乙烯酯(PVAc) 在苯溶液中的超声波辐照降解,PEO与PVAc在苯溶液中的超声波辐照共聚反应。实验证明,降解反应可用Ovenall方程描述。用IR、NMR和DTA分析了在超声波辐照作用下PEO与PVAc在苯溶液中生成的共聚物的结构,证明所得产物主要为接枝共聚物,将浓度为1％的(PEO-PVAc)苯溶液在频率为18.2kHz、逆变器主迥路输入电流为2.0安的超声波强度下,辐照10分钟,共聚物的产率为10.54％,接枝点密度为33.3％,平均接枝链长为17。