Characterization of poly(vinyl alcohol) during the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as emulsifier

During the emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as stabilizer and potassium persulfate as initiator, the VAc reacts with PVA forming PVA-graft-PVAc. When the grafted polymer reaches a critical size it becomes water-insoluble and precipitates from the aqueous phase contributing to the formation of polymer particles. Since particle formation and therefore the properties of the final latex will depend on the degree of grafting, it is important to quantify and to characterize the grafted PVA. In this work, the quantitative separation and characterization of the grafted water-insoluble PVA was carried out by a two-step selective solubilization of the PVAc latex, first with acetonitrile to separate PVAc homopolymer, followed by water to separate the water-soluble PVA from the remaining acetonitrile-insoluble material. After the separation, the water-soluble and water-insoluble PVA were characterized by Fourier Transform Infrared (FTIR) spectroscopy and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses, from which the details of the PVA-graft-PVAc structure were obtained. © 1996 John Wiley & Sons, Inc.     

Synthesis of high-molecular-weight poly(vinyl alcohol) with high yield by novel one-batch suspension polymerization of vinyl acetate and saponification

Generally, owing to tautomerism of vinyl alcohol monomer, poly(vinyl alcohol) (PVA) cannot be obtained by direct polymerization but it can be obtained by the saponification of poly(vinyl ester) precursors such as poly(vinyl acetate) (PVAc). In this study, to obtain high-molecular-weight (HMW) PVA with high yield through a one-batch method, we tried continuous saponification of PVAc prepared by suspension polymerization of vinyl acetate (VAc). We controlled various polymerization conditions, such as polymerization temperature, initiator concentration, suspending agent concentration, agitation speed, and VAc/water ratio, and obtained PVAc with a maximum conversion of VAc into PVAc of over 95-98%. PVA beads having various molecular parameters were prepared by continuous saponification of PVAc microspheres. Despite our employing a one-batch process, a maximum degree of saponification of 99.9% could be obtained. Continuous heterogeneous saponification of prepared PVAc yielded HMW PVA having a number-average degree of polymerization of 2,500-5,500, a syndiotactic diad content of 51-52%, and degree of saponification of 85.0-99.9%.     

Effect of initiators on grafting in the initial stage of the emulsion polymerization of methyl methacrylate using poly(vinyl alcohol) as a protective colloid

 To make clear the reason of unsuitability of poly(vinyl alcohol) (PVA) protective colloid for the emulsion polymerization of conjugated monomers, a model experiment of emulsion polymerization of methyl methacrylate (MMA) was carried out with ammonium persulfate (APS) or azobis(isobutyronitrile) (AIBN) initiators, where a small amount of MMA (1/100th of the concentration compared with ordinary emulsion polymerization) was employed. This corresponds to the initial stage of the emulsion polymerization. Grafting of MMA onto PVA took place remarkably irrespective of the kind of the initiators. Formation of homo-poly(MMA) was observed to a small extent. The formation of new emulsion particles smaller than 100 nm continued to increase to almost the end of the polymerization. PVA molecules in the grafted polymer are supposed to act as stabilizers of newly formed particles. From kinetic treatment using the experimental data, the important issues were derived as follows. Firstly, the sulfate anion radical from APS is much more reactive than the isobutyronitrile radical from AIBN in terms of hydrogen abstraction from PVA. Secondly, high grafting ability of the latter initiator system, notwithstanding the much lower reactivity in the hydrogen abstraction compared with the APS system, is attributed to the relative reactivity of the primary radicals, i.e., hydrogen abstraction reaction from PVA to initiation reaction with MMA. The much slower rate of addition of the isobutyronitrile radical to the monomer compared with that of hydrogen abstraction from PVA facilitates the grafting, although the rate constant of hydrogen abstraction is far smaller than that with the sulfate anion radical by 10⁻⁴ times. Received: 26 April 2001 Accepted: 6 September 2001     

Grafting of Polymers Having Pendant Peroxycarbonate Groups Onto Carbon Black and Postpolymerization of Vinyl Monomers

Abstract

Postpolymerization of vinyl monomers initiated by pendant peroxycarbonate groups of grafted polymer chains on carbon black (CB) was investigated. The grafting of polymers having pendant peroxycarbonate groups onto CB was achieved by the trapping of polymer radicals formed by the thermal decomposition of copolymers of t-butylperoxy-2-methacryloyloxyethyl-carbonate (HEPO) with vinyl monomers such as vinyl acetate (VAc), styrene (St) and methyl methacrylate (MMA). The copolymers having pendant peroxycarbonate groups were prepared by copolym-erization of HEPO with vinyl monomers using azo initiator under irradiation of UV light at room temperature. The amount of remaining pendant peroxycarbonate groups of the poly(VAc-co-HEPO)-grafted CB obtained from the reaction at 90°C was maximum and decreased above the temperature. Furthermore, the postpolymerization of vinyl monomers, such as St, MMA, and VAc was initiated in the presence of poly(VAc-co-HEPO)-grafted and poly(St-co-HEPO)-grafted CB and the corresponding polymers were postgrafted onto CB to give branched polymer-grafted CB. The percentage of poly(St)-postgrafting (proportion of post-grafted poly(St) to poly(MMA-co-HEPO)-grafted CB used) increased with increasing polymerization time, but became constant at 20% after 4 hours.     

Biodegradability of poly(3-hydroxybutyrate) film grafted with vinyl acetate: Effect of grafting and saponification

Radiation-induced graft polymerization of vinyl acetate (VAc) onto poly(3-hydroxybutyrate) (PHB) film was carried out. At a degree of grafting higher than 5%, the grafted films (PHB-g-VAc) completely lost the enzymatic degradability that is characteristic of PHB due to the grafted VAc covering the surface of the PHB film. However, the biodegradability of the PHB-g-VAc films was recovered when the films were saponified in alkali solution under optimum conditions. Graft chains of the PHB-g-VAc film reacted selectively to become biodegradable polyvinyl alcohol (PVA). The biodegradability of the saponified PHB-g-VAc film increased rapidly with time.     

Copper(0)‐mediated radical copolymerization of vinyl acetate and acrylonitrile in DMSO at ambient temperature

In this work, Cu(0)‐mediated radical copolymerization of vinyl acetate (VAc) and acrylonitrile (AN) was explored. The polymerization was carried out at 25°C with 2,2′‐bipyridine as ligand and dimethyl sulfoxide as solvent. The copolymerization proceeded smoothly producing moderately controlled molecular weights at low VAc feed ratios. The high VAc feed ratios generated low polymerization rate and poorly controlled molecular weights. FTIR, ¹H NMR, and differential scanning calorimetry confirmed the successful obtaining of the copolymers. Based on ¹H NMR spectra, the reactivity ratios of VAc and AN were calculated to be 0.003 and 1.605, respectively. This work conveyed the first example for the Cu(0)‐mediated radical polymerization of AN and VAc, wherein VAc cannot be homopolymerized by Cu(0)‐mediated radical polymerization technique. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Low temperature suspension polymerization of vinyl acetate using 2,2′-azobis(2,4-dimethylvaleronitrile) for the preparation of high molecular weight poly(vinyl alcohol) with high yield

 To obtain high molecular weight (HMW) poly(vinyl acetate) (PVAc) with high conversion and high linearity for a precursor of HMW poly(vinyl alcohol) (PVA), vinyl acetate (VAc) was suspension-poly-merized using a low-temperature initiator, 2,2′-azobis (2,4-dimethyl-valeronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior and molecular structures of PVAc and PVA prepared by saponifying PVAc were investigated. On the whole, the experimental results well corres-ponded to the theoretically predicted tendencies. Suspension polymerization was slightly inferior to bulk polymerization in increasing molecular weight of PVA. In contrast, the former was absolutely superior to the latter in increasing conversion of the polymer, which indicated that the suspension polymerization rate of VAc was faster than the bulk one. These effects could be explained by a kinetic order of ADMVN concentration calculated by initial-rate method and an activation energy difference of polymerization obtained from the Arrhenius plot. Suspension polymerization at 30 °C by adopting ADMVN proved to be successful in obtaining PVA of HMW (number-average degree of polymerization (P _n)): (4200–5800) and of high yield (ultimate conversion of VAc into PVAc: 85–95%) with diminishing heat generated during polymerization. In the case of bulk polymerization of VAc at the same conditions, maximum P _n and conversion of 5200–6200 and 20–30% was obtained, respectively. The P _n, lightness, and syndiotacticity were higher with PVA prepared from PVAc polymerized at lower temperatures. Received: 10 February 1998 Accepted: 15 April 1998     

Solvent effects in the free radical copolymerization of vinyl acetate and methyl methacrylate

A study was made of the effects of five solvents on the compositions of copolymers of vinyl acetate (VA) and methyl methacrylate (MMA) produced by free radical polymerization from feeds rich in VA. The MMA content was reduced significantly by propanol, unaffected by benzene and ethyl acetate and increased by acetonitrile and acetone. The effects observed for propanol, acetonitrile and acetone all reached a maximum at a solvent to monomer molar ratio of about 7:1. Experiments showed that neither monomer physical aggregation nor monomer carbonyl polarization phenomena could explain completely the observed effects. A complete explanation probably requires several factors including some associated with polymer radical reactivity.     

Influence of additives on model emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as a protective colloid

To clarify the influence of additives on the grafting phenomenon as well as the particle behavior more precisely, we carried out a model emulsion polymerization of vinyl acetate (VAc) in a 1% aqueous solution with ammonium persulfate (APS) using poly (vinyl alcohol) (PVA) as a protective colloid in the presence of additives. The addition of alcohol to the system remarkably affected the particle formation, especially grafting. This is thought to be attributed to competition between hydrogen abstraction from PVA and alcohol with a sulfate radical. Especially, the addition of acetone to the system decreased grafting to a great extent, resulting in an increase in the particle size together with an increase in the number of polymer molecules in a polymer particle. This result is thought to arise from a combination of electron abstraction from acetone with a sulfate radical and the chain-transfer reaction of the propagation radical with acetone.     

Synthesis and Biodegradation of St-g-poly（MMA-co-VAc） Initiated by Manganic Pyrophosphate

Methyl methacrylate (MMA) and vinyl acetate (VAc) were grafted onto corn starch with manganic pyrophosphate { [Mn(H2P2O7)3]^3- } as the initiator and water as the reaction medium, The influences of reaction conditions, including pH value, initiator concentration, monomer concentration and its composition, on percent grafting and grafting efficiency were investigated. The graft copolymer was characterized by means of IR spectroscopy, scanning electron micrograph(SEM) and ^1H NMR spectroscopy. The biodegradation experiment showed that the degradation of corn starch-g-poly(MMA-co-VAc) was mainly from starch. However,after poly VAc in the side chain was transformed into poly vinyl alcohol(PVA), both starch and the grafted side chain could be degraded completely.     

Chain transfer to solvent in BN 2-vinylnaphthalene radical polymerization

The synthesis of vinyl alcohol copolymers is limited due to the poor radical reactivity of vinyl acetate (VAc), the traditional precursor to polyvinyl alcohol (PVA). Main group monomers such as BN 2-vinylnaphthalene (BN2VN) have attracted attention as alternatives to VAc to form side chain hydroxyls via oxidation, but outstanding questions of molecular weight control remain. Herein we report systematic investigation of solvent, temperature, and initiator concentration as factors influencing BN2VN degree of polymerization. We find increased chain transfer to toluene, hypothesized to arise from differences in radical stabilization and reactivity by aromatic and BN aromatic rings. As a result of these combined efforts, high molecular weight (M_w ~ 10⁵ g mol⁻¹) BN2VN homopolymers and BN2VN-styrene copolymers were obtained.     

Synthesis and characters of hyperbranched poly(vinyl acetate) by RAFT polymeraztion

Reversible addition-fragmentation chain transfer (RAFT) polymerization of VAc in the presence of ECTVA, which capable of both reversible chain transferable through a xanthate moiety and propagation via a vinyl group, led to highly branched copolymers by a method analogous to self-condensing vinyl polymerization (SCVP). The ECTVA acted as a vinyl acetate AB^∗ inimer. It was copolymerized with vinyl acetate (VAc) in ratios selected to tune the distribution and length of branches of resulting hyperbranched poly(vinyl acetate). The degree of branching increased with chain ECTVA concentration, as confirmed by NMR spectroscopy. The polymer structure was characterized via MALDI–TOF. Retention of the xanthate compound during the polymerization was evidenced by successful chain extension of a branched (PVAc) macroCTA by RAFT polymerization. The branched PVAc led to better dissolution as compared to linear PVAc, an effect attributed primarily to an increased contribution of end groups.     

Chain transfer to polymer in emulsion copolymerizations

Chain transfer to polymer in emulsion copolymerizations of (i) vinyl acetate (VAc) with n‐butyl acrylate (BA) and (ii) BA/acrylic acid with (a) methyl methacrylate (MMA) and (b) styrene (S) has been studied using ¹³C NMR spectroscopy to quantify the level of branching in the copolymers produced. The results reveal synergistic effects in which the inclusion of a small amount of comonomer leads to disproportionate changes in the level of branching. The data from the VAc/BA copolymerizations show that radicals with VAc end units abstract hydrogen atoms from BA repeat units more frequently than from VAc repeat units and that radicals with VAc end units are more effective in abstracting hydrogen atoms from BA repeat units than are radicals with BA end units. These effects lead to higher levels of branching in VAc/BA copolymers than results from the corresponding homopolymerizations and are a consequence of the efficacy of hydrogen abstraction at BA backbone tertiary C‐H bonds by the highly‐reactive VAc‐ended chain radicals. In contrast, the effect of introducing MMA or S to an acrylate polymerization is to disproportionately reduce the level of branching, with S being more effective than MMA in moderating chain transfer to polymer. These effects arise because propagating radicals with MMA or S end‐groups have longer lifetimes compared to those with acrylate end groups and have a very much lower tendency to abstract hydrogen atoms from acrylate repeat units.     

醋酸乙烯(VAc)的活性/可控自由基聚合

本文综述了醋酸乙烯(VAc)单体的活性/可控自由基聚合研究进展.醋酸乙烯是一种重要的单体,是生产聚醋酸乙烯(PVAc)和聚乙烯醇(PVA)的原料.传统的自由基聚合方法如溶液、乳液、悬浮和分散等都可以用来实现VAc的聚合,得到不同分子量的PVAc和PVA.由于醋酸乙烯增长自由基的高活性,存在向聚合物链的链转移从而导致聚合物的分子量分布比较宽,为了得到分子量分布更窄的聚合物,活性可控聚合方法也被用来实现VAc的聚合.     

Core‐shell microspheres with surface grafted poly(vinyl alcohol) as drug carriers for the treatment of hepatocellular carcinoma

Core(polyvinyl neodecanoate‐ethylene glycol dimethacrylate)‐shell(polyvinyl alcohol) (core (P(VND‐EGDMA))‐shell(PVA)) microspheres were developed by seeded polymerization with the use of conventional free radical and RAFT/MADIX mediated polymerization. Poly(vinyl pivalate) PVPi was grafted onto microspheres prepared via suspension polymerization of vinylneodecanoate and ethylene glycol dimethacrylate. The amount of grafted polymer was found to be independent from the technique used with conventional free radical polymerization and MADIX polymerization resulting into similar shell thicknesses. Both systems—grafting via free radical polymerization or the MADIX process—were found to follow slightly different kinetics. While the free radical polymerization resulted in a weight gain linear with the monomer consumption in solution the growth in the MADIX controlled system experienced a delay. The core‐shell microspheres were obtained by hydrolysis of the poly(vinyl pivalate) surface grafted brushes to form poly(vinyl alcohol). During hydrolysis the microspheres lost a significant amount of weight, consistent with the hydrolysis of 40–70% of all VPi units. Drug loading was found to be independent of the shell layer thickness, suggesting that the drug loading is governed by the amount of bulk material. The shell layer does not appear to represent an obstacle to the drug ingress. Cell testing using colorectal cancer cell lines HT 29 confirm the biocompatibility of the empty microspheres whereas the clofazimine loaded particles lead to 50% cell death, confirming the release of the drug. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3256–3272, 2007     

反应诱导相分离制备新型温度敏感光学材料

反应诱导相分离制备新型温度敏感光学材料李兴林陈文杰江明（复旦大学高分子科学系和国家教委聚合物分子工程实验室上海２００４３３）关键词高分子合金，旋节线相分离，光散射，温度敏感光学性能温度敏感光学材料是一种具有广泛用途的功能材料，可用作记录材料、显...     

A facile approach to surface graft vinyl acetate onto polyolefin articles

A facile and environment friendly approach was developed to graft vinyl acetate (VAc) onto plastic articles in an aqueous solution using tert‐butyl alcohol (TBA) as a compatiblizer and benzoyl peroxide (BPO) as an initiator. In a novel setup, excessive monomer suspended in a water phase, VAc could be conveniently grafted on the model substrate of low‐density polyethylene (LDPE) film and the graft percentage (GP) could be developed up to 7.3%. Reaction temperature could increase GP significantly, while adding monomer over a critical volume did not influence GP. By adding some paradioxybenzene, i.e. 0.06–0.08% in VAc phase, homopolymer PVAc could be avoided practically, while graft polymerization proceeded favorably in aqueous solutions. It was proved by attenuated total reflection‐infrared (ATR‐IR) spectroscopy that grafted VAc was located mainly at the surface of the LDPE film and hydrophilic nature of both grafted and alcoholyzed films were improved via contact angle measurements. Copyright © 2004 John Wiley & Sons, Ltd.     

Mn2(CO)10‐induced controlled/living radical copolymerization of vinyl acetate and methyl acrylate: Spontaneous formation of block copolymers consisting of gradient and homopolymer segments

The controlled/living radical polymerization of vinyl acetate (VAc) and its copolymerization with methyl acrylate (MA) were investigated in bulk or fluoroalcohols using manganese complex [Mn₂(CO)₁₀] in conjunction with an alkyl iodide (R? I) as an initiator under weak visible light. The manganese complex induced the controlled/living radical polymerization of VAc even in the fluoroalcohols without any loss of activity. The R? I/Mn₂(CO)₁₀ system was also effective for the copolymerization of MA and VAc, in which MA was consumed faster than VAc, and then the remaining VAc was continuously and quantitatively consumed after the complete consumption of MA. The ¹H and ¹³C NMR analyses revealed that the obtained products are block copolymers consisting of gradient MA/VAc segments, in which the VAc content gradually increases, and homopoly(VAc). The use of fluoroalcohols as solvents increased the copolymerization rate, controllability of the molecular weights, and copolymerizability of VAc. The saponification of the VAc units in poly(MA‐grad‐VAc)‐block‐poly(VAc) resulted in the corresponding poly(MA‐co‐γ‐lactone)‐block‐poly(vinyl alcohol) due to the intramolecular cyclization between the hydroxyl and neighboring carboxyl groups in the gradient segments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1343–1353, 2009     

Radical copolymerization of novel trifluorovinyl ethers with ethyl vinyl ether and vinyl acetate: Estimating reactivity ratios and understanding reactivity behavior of the propagating radical

Two novel trifluorovinyl ether (TFVE) monomers were copolymerized with either ethyl vinyl ether (EVE) or vinyl acetate (VAc) in a redox‐initiated aqueous emulsion: 1‐(2‐phenoxyethoxy)‐1,2,2‐trifluoroethene (Ph‐TFVE) and 1‐[2‐(2‐ethoxyethoxy)ethoxy]‐1,2,2‐trifluoroethene (Et‐TFVE). Previous studies demonstrated a propensity for radical hydrogen abstraction from the oligoether pendant group during the homopolymerization of Et‐TFVE with continued propagation of the resulting radical, thereby providing the rationale to investigate the copolymerization of our new TFVEs with EVE or VAc. Reactivity ratios were estimated using the error‐in‐variables model from a series of bulk free radical copolymerizations of Ph‐TFVE with EVE or VAc. The reactivity ratios were r_Ph‐TFVE = 0.25 ± 0.07, r_EVE = 0.016 ± 0.04; r_Ph‐TFVE = 0.034 ± 0.04, r_VAc =0.89 ±0.08. Partial hydrolysis of polymers containing VAc to vinyl alcohol (VA) resulted in two terpolymers: poly(Ph‐TFVE‐co‐VAc‐co‐VA) and poly(Et‐TFVE‐co‐VAc‐co‐VA), respectively. We investigated the possibility of hydrogen abstraction from VAc during polymerization by comparing the molar mass before and after hydrolysis. Abstraction from VAc was not apparent during polymerization; however, abstraction from the oligoether pendant group of Et‐TFVE was again evident and was more significant for those copolymers having a greater fraction of Et‐TFVE in the monomer feed. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1344–1354, 2000     

致孔剂对HP（MA—VAc—MMA）载体孔结构的影响

以二乙烯苯和双丙烯酸多缩乙二醇酯为交联剂、聚醋酸乙烯酯（ＰＶＡｃ）或它与醋酸丁酯（ＢＡＣ）的混合物为致孔剂、ＢＰＯ为引发剂，用悬浮聚合随后水解的方法制得了部分水解聚（丙烯酸甲酯－醋酸乙烯酯－甲基丙烯酸甲酯）［ＨＰ（ＭＡ－ＶＡｃ－ＭＭＡ）］多孔载体，研究了ＰＶＡｃ及（ＰＶＡｃ＋ＢＡＣ）用量、分子量及混合比对ＨＰ（ＭＡ－ＶＡｃ－ＭＭＡ）孔结构的影响。结果表明，当ＰＶＡｃ的Ｍ＞２．５×１０５，ＰＶＡｃ／ＢＡＣ为２．３，用量为１０～２０％时，可制得孔隙率较高，孔径分布较窄，孔表面积较大的多孔载体。这种载体适用于微生物固定化。