Preparation of high molecular weight poly(vinyl alcohol) with high yield by emulsion polymerization of vinyl acetate using 2,2′‐azobis(2‐amidinopropane) dihydrochloride

To prepare high molecular weight (HMW) poly(vinyl acetate) (PVAc) with high yield and high linearity as a precursor of HMW poly(vinyl alcohol) (PVA), vinyl acetate (VAc) was emulsion polymerized using, azo initiator, 2,2′‐azobis(2‐amidinopropane) dihydrochloride (AAPH). This was compared with the polymerization using potassium peroxodisulfate (KPS) as an initiator at various polymerization conditions. PVA, having a maximum number average degree of polymerization (P_n) of 3500 was obtained by the saponification of PVAc with P_n of 13,000–14,000, degree of branching (DB) for the acetyl group of about 3.4–3.5, and a maximum conversion of VAc into PVAc of 95%, which was polymerized by AAPH. These numerical values were superior compared with 14,500–15,000 of P_n of PVAc, obtained by KPS, and 3100 of maximum P_n of resulting PVA, DB of about 3.7–3.8, and maximum conversion of 90%. From the foregoing experimental results, we found that AAPH was a more efficient initiator than KPS in increasing both conversion of PVAc and molecular weight of PVA. In addition, PVAc microspheres, obtained by these emulsion polymerizations, can be converted to PVA / PVAc shell / core microspheres through a series of surface‐saponifications, maintaining their spherical morphology. Various surface morphologies, such as flat or wrinkled and swellable or nonswellable ones formed by the various molecular parameters and saponification conditions, were examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2356–2362, 2004     

Preparation of ultrahigh molecular weight syndiotactic poly(vinyl alcohol) microfibrillar fibers by low‐temperature solution polymerization of vinyl pivalate in tertiary butyl alcohol and saponification

Vinyl pivalate (VPi) was solution polymerized in tertiary butyl alcohol (TBA) and in dimethyl sulfoxide (DMSO) with a low chain transfer constant using a low temperature initiator, 2,2′‐azobis(2,4‐ dimethylvaleronitrile) (ADMVN). The effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl pivalate) (PVPi) and its saponification product poly(vinyl alcohol) (PVA). TBA was absolutely superior to DMSO in increasing the syndiotacticity and molecular weight of PVA. In contrast, TBA was inferior to DMSO in causing conversion to polymer, indicating that the initiation rate of VPi production in TBA was lower than that in DMSO. These effects could be explained by a kinetic order of ADMVN concentration, calculated by the initial rate method. Low‐temperature solution polymerization of VPi in TBA or DMSO by adopting ADMVN proved to be successful in obtaining PVA of ultrahigh molecular weight [maximum number‐average degree of polymerization (P_n): 13,500–17,000] and of high yield (ultimate conversion of VPi into PVPi: 55–83%). In the case of bulk polymerization of VPi at the same conditions, maximum P_n and conversion were 14,500–17,500 and 22–36%, respectively. The P_n and syndiotactic diad content were much higher and the degree of branching was lower with PVA prepared from PVPi polymerized at lower temperatures in TBA. Moreover, PVA from the TBA system was fibrous, with a high degree of orientation of the crystallites, indicating the syndiotactic nature of TBA polymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1992–2003, 2002     

Synthesis of syndiotacticity‐rich high molecular weight poly(vinyl alcohol) by suspension polymerization of vinyl pivalate and saponification

Vinyl pivalate (VPi) was suspension‐polymerized to synthesize high molecular weight (HMW) poly(vinyl pivalate) (PVPi) with a high conversion above 95% for a precursor of syndiotacticity‐rich HMW poly(vinyl alcohol) (PVA). Also, the effects of the polymerization conditions on the conversion, molecular weight, and degree of branching (DB) of PVPi and PVA prepared by the saponification of PVPi were investigated. Bulk polymerization was slightly superior to suspension polymerization in increasing the molecular weight of PVA. On the other hand, the latter was absolutely superior to the former in increasing the conversion of the polymer, indicating that the suspension polymerization rate of VPi was faster than that of the bulk one. These effects could be explained by a kinetic order of a 2,2′‐azobis(2,4‐dimethylvaleronitrile) concentration calculated by the initial rate method. Suspension polymerization of VPi at 55°C by controlling various polymerization factors proved to be successful in preparing PVA of HMW [number‐average degree of polymerization (P_n): 8200–10,500], high syndiotactic diad content (58%), and very high yield (ultimate conversion of VPi into PVPi: 94–98%). In the case of the bulk polymerization of VPi at the same conditions, the maximum P_n and conversion of 10,700–11,800 and 32–43% were obtained, respectively. The DB was lower and the P_n was higher with PVA prepared from PVPi polymerized at lower initiator concentrations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 832–839, 2003     

Synthesis of high-molecular weight poly(vinyl alcohol) by low-temperature emulsifier-free emulsion polymerization of vinyl acetate and saponification

High-molecular weight (HMW) poly(vinyl alcohol) (PVA) was prepared via an emulsifier-free emulsion polymerization of vinyl acetate (VAc) using a redox initiation system in low temperatures, and the subsequent saponification with potassium hydroxide in methanol. The effect of the polymerization conditions on the conversion, molecular weight, and branching degree was investigated. PVA with maximum viscosity-average degree of polymerization (DP) of 8270 could be prepared by saponification of poly(vinyl acetate) (PVAc), with DP of 10,660 obtained at temperature of 10°C, monomer concentration of 30%, potassium persulfate molar ratio to monomer of 1/2000, agitation speed of 160 rpm. The conversion was above 90%. From the emulsifier-free emulsion polymerization of VAc in low temperature, PVAc with HMW and high linearity was effectively prepared, which might be useful for the preparation of high-strength and high-modulus PVA fiber. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation of novel syndiotactic poly(vinyl alcohol) microspheres through the low‐temperature suspension copolymerization of vinyl pivalate and vinyl acetate and heterogeneous saponification

Syndiotactic poly(vinyl alcohol) (PVA)/poly(vinyl pivalate/vinyl acetate) [P(VPi/VAc)] microspheres, with a skin–core structure, were prepared through the heterogeneous saponification of copolymers of vinyl pivalate (VPi) and vinyl acetate (VAc). For the preparation of P(VPi/VAc) microspheres with various particle sizes and a uniform particle size distribution (which are promising precursors of syndiotactic PVA embolic materials to be introduced through catheters for the management of gastrointestinal bleeders, arteriovenous malformations, hemangiomas, and traumatic rupture of blood vessels), VPi and VAc were suspension‐copolymerized at 30°C with a room‐temperature initiator, 2,2′‐azobis(2,4‐dimethylvaleronitrile). The effects of the polymerization conditions were investigated in terms of the size and size distribution of the suspension particles. P(VPi/VAc) microspheres, with various syndiotactic dyad (s‐dyad) contents, were produced through the control of the monomer feed ratio. In addition, monodisperse P(VPi/VAc) particles of various particle diameters were obtained by the separation and sieving of the polymerization product. Monodisperse P(VPi/VAc) microspheres of various particle sizes were partially saponified in the heterogeneous system, and the effects of the particle size and particle size distribution on the saponification rate were investigated in terms of the tacticity and the saponification time and temperature. Novel skin–core PVA/P(VPi/VAc) microspheres of various s‐dyad contents and degrees of saponification were successfully produced through the control of the various polymerization and saponification parameters. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1539–1548, 2005     

Preparation of high molecular weight poly(vinyl alcohol) with high yield using low‐temperature solution polymerization of vinyl acetate

Vinyl acetate (VAc) was solution‐polymerized in tertiary butyl alcohol (TBA) and in dimethyl sulfoxide (DMSO) having low chain transfer constant at 30, 40, and 50°C, using a low temperature initiator, 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN). The effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl acetate) (PVAc) and corresponding poly(vinyl alcohol) (PVA) obtained by saponification with sodium hydroxide. The polymerization rates of VAc in TBA and in DMSO were proportional to the 0.49 and 0.72 powers of ADMVN concentration, respectively. For the same polymerization conditions, TBA was absolutely superior to DMSO in increasing the molecular weight of PVA. In contrast, TBA was inferior to DMSO in causing conversion to polymer, indicating that the initiation rate of VAc in TBA was lower than that in DMSO. These effects could be explained by a kinetic order of ADMVN concentration calculated using initial rate method and by an activation energy difference of polymerization obtained from the Arrhenius plot. Low‐temperature solution polymerization of VAc in TBA or DMSO by adopting ADMVN proved successful in obtaining PVA of high molecular weight (number–average degree of polymerization (P_n): 4100–6100) and of high yield (ultimate conversion of VAc into PVAc: 55–80%) 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 and lightness were higher, and the degree of branching was lower with PVA prepared from PVAc polymerized at lower temperatures in TBA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1003–1012, 2001     

Effect of syndiotacticity on the morphology of water-soluble low molecular weight poly(vinyl alcohol) by solution copolymerization of vinyl pivalate/vinyl acetate in tetrahydrofuran and saponification

Syndiotacticity-rich low molecular weight (LMW) poly(vinyl alcohol) (PVA) was synthesized by solution copolymerization of vinyl pivalate (VPi) and vinyl acetate (VAc) with various monomer ratios in tetrahydrofuran at low temperature using 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN) as an initiator and successive saponification of copoly(VPi/VAc). Solution copolymerization of VPi and VAc by ADMVN and saponification produced water soluble syndiotacticity-rich LMW PVA with number-average degrees of polymerization (P_n)s of 220-520, syndiotactic diad (s-diad) contents of 55.5-61.3%, and with maximum conversions of VPi and VAc into copoly(VPi/VAc) of 70-80%. The effect of stereosequences of PVA was investigated in terms of morphology of water-soluble LMW PVA. Especially, to precisely identify the effect of syndiotacticity of LMW PVA on the change of morphology, we prepared various PVAs with similar P_n of 1200 and with different s-diad contents of 55.5-61.3%, respectively. The PVA with s-diad content of 61.1% revealed a well-defined fibrous morphology. Each fiber was composed of a number of microfibrils. As the s-diad content of PVA decreased, some morphological change was observed. The specimen with s-diad content of 59.9% formed a divided precipitate with microfibrillar structure. In contrast, in the case of PVA with s-diad content of 55.7%, irregular shaped particles were observed.     

乳液聚合法合成高相对分子质量聚醋酸乙烯酯的研究

采用过硫酸铵/亚硫酸氢钠氧化还原体系低温引发醋酸乙烯酯乳液聚合,合成出分子量为1.07×106、分子量分布为2.75的聚醋酸乙烯酯。讨论了聚合温度、单体用量、十二烷基硫酸钠(SDS)用量、过硫酸铵用量、亚硫酸氢钠用量等因素对聚醋酸乙烯酯黏均分子量的影响,并用GPC法对其进行表征。     

Preparation of water‐soluble syndiotacticity‐rich high molecular weight poly(vinyl alcohol) microfibrillar fibers using copolymerization of vinyl pivalate and vinyl acetate and saponification

Water‐soluble high molecular weight (HMW) syndiotactic poly(vinyl alcohol) (s‐PVA) microfibrillar fibers were prepared by the saponification with various conditions such as amount of alkali solution, saponification temperature, and saponification concentration from copoly(vinyl pivalate (VPi)/vinyl acetate (VAc)) copolymerized using various VPi/VAc feed ratios. To produce s‐PVA microbrillar fibers having various water‐soluble temperatures for many industrial applications, the intrinsic viscosities, syndiotactic diad (S‐diad) contents, and degrees of saponification (DS)s of PVAs were finely controlled to 1.2–3.6 dL/g, 56.3–58.3%, and 91.4–98.3%, respectively. Through a series of experiments, it was found that the amount of alkali may alter the structure of the saponified polymers, primarily the DS, and the structural variation changes viscosity. That is, intrinsic viscosity was sharply decreased as the amount of alkali solution was increased. DS was increased with an increase in the amount of alkali solution. S‐diad content was increased with an increase in the VPi content. HMW s‐PVA microfibrillar fibers having S‐diad content of 56.3–58.3% prepared by the saponification of copoly(VPi/VAc) were completely soluble in water at 100°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1482–1487, 2003     

Characterization of grafting in the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as stabilizer

Emulsion polymerizations of vinyl acetate (VAc) with polyvinyl alcohol (PVA) as emulsifier were carried out by both batch and semicontinuous processes. The extent of grafting of vinyl acetate onto the PVA chains was investigated by a new method for separating the various polymer fractions in high solids content latexes. The quantification was carried out by a three‐step separation and selective solubilization of the PVAc latexes. After the separation, the water‐soluble PVA and the solvent‐soluble PVAc components were characterized by gel permeation chromatography and ¹³C–NMR, from which the accuracy of this method was verified. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1739–1747, 2001     

PVA作用下含氟丙烯酸酯共聚乳液的制备与表征

以聚乙烯醇(PVA)为乳化剂,采用Fe2+-H2O2引发体系,以全氟烷基乙基甲基丙烯酸酯(FM)、丙烯酸丁酯(BA)、苯乙烯(St)、甲基丙烯酰氧乙基三甲基氯化铵(DMC)、丙烯酸羟乙酯(HEA)为主要单体进行乳液聚合,制得了阳离子含氟丙烯酸酯多元共聚物乳液。通过FTIR、1HNMR、透射电镜(TEM)、示差扫描量热(DSC)及接触角测试对共聚物结构、乳胶粒径及形态、乳胶膜表面性能进行了研究。结果表明,该乳液的粒子形态呈球形,单分散性良好,平均粒径为90～100nm;随着共聚物中含氟单体质量分数的增加,乳胶膜的表面自由能显著降低;退火处理有助于含氟基团迁移到乳胶膜表面,乳胶膜表面自由能进一步降低。     

Grafting and adsorption of poly(vinyl) alcohol in vinyl acetate emulsion polymerization

Poly(vinyl alcohol) is often used in vinyl acetate emulsion polymerization as a protective colloid, but its role is complex and controversial since it partakes in grafting reactions with the monomer, influencing process mechanisms, and affecting the colloidal properties of the latex. Furthermore, in industrial operations, the wide scatter of macromolecular properties of the commercial types of poly(vinyl alcohol) causes process irreproducibilities. In this work different types of polyvinyl alcohol were used to perform a series of polymerizations, and their kinetics were compared. A selective solubilization procedure was applied to separate the three fractions of poly(vinyl alcohol) in the final latex: free in the water phase, physically adsorbed onto the polymer particles and chemically grafted. These results were compared with those obtained from pure adsorption measurements of polyvinyl alcohol onto ‘emulsifier-free’ polyvinyl acetate dispersions. The rheological behavior of the different latexes was also compared, and the results were used to formulate an hypothesis on the interaction mechanisms acting in these systems.     

Bulk polymerization of vinyl pivalate using low-temperature azoinitiator and saponification for the preparation of poly(vinyl alcohol) microfibrils

Vinyl pivalate (VPi) was bulk-polymerized at 30, 40, and 50°C using a low temperature initiator, i. e. 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN). The effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl pivalate) (PVPi) and corresponding poly(vinyl alcohol) (PVA) microfibrillar fiber obtained by saponification in KOH/methanol/water. Low polymerization temperature using ADMVN proved to be successful in obtaining PVA of syndiotacticity-rich high molecular weight. PVPi had a number-average degree of polymerization (P_n) of 27 100–35 900, and a degree of branching for pivaloyl group of 0.8–1.0 at 30°C, 1.0–1.3 at 40°C, and 1.4–1.7 at 50°C at conversions below 40%. Saponification of PVPi yielded PVA having a P_n of 10  400–16  500, and syndiotactic diad (S-diad) content of 58.8–61.5%. It was found that all PVA specimens represented microfibrillar morphologies, with high crystallinity and orientation. The S-diad content and crystal melting temperature were higher with PVA prepared from PVPi polymerized at lower temperatures.     

乳液聚合法合成高相对分子质量聚醋酸乙烯酯的研究

本文采用过硫酸铵/亚硫酸氢钠氧化还原体系低温引发醋酸乙烯酯乳液聚合,分别讨论了聚合温度、单体用量、十二烷基硫酸钠(SDS)用量、过硫酸铵用量、亚硫酸氢钠用量等因素对聚醋酸乙烯酯粘均相对分子质量的影响。通过调节单体浓度、SDS浓度、过硫酸铵浓度、亚硫酸氢钠浓度和聚合温度,合成出高相对分子质量的聚醋酸乙烯酯,用GPC法对其进行表征,粘均相对分子质量为1.07×106,相对分子质量分布为2.75。     

Preparation of monodisperse poly(vinyl alcohol) microspheres by heterogeneous surface saponification and iodine complex formation

Monodisperse poly(vinyl acetate) (PVAc) microspheres with high molecular weight obtained by suspension polymerization of vinyl acetate were saponified in alkaline aqueous solution to keep their spherical structure. The saponification was restricted on the surface of the PVAc microspheres and obtained particles had skin/core structure. Various poly(vinyl alcohol) (PVA) microspheres with different diameters and degrees of saponification (DSs) were obtained. The conversion of PVAc to PVA during the heterogeneous surface saponification time were examined by nuclear magnetic resonance spectroscopy and after 72 h hydrogel type PVA microspheres completely saponified were obtained. The crystal melting temperatures of the microspheres obtained by the saponification were measured a constant value of 238°C irrespective of varying DS, and the peaks became enlarged as reaction time. Iodine complexes were formed in saponified microspheres with DS of 41% and 99% by immersing them in I₂/KI aqueous solution and decomposed by the reduction of I₂ in the complexes to 2I^? using sodium sulfite to confirm whether the skin formed through the saponification was composed of PVA with high VA content. Obviously, characteristic blue color developments owing to I₅^?‐PVA complexes were observed in both saponified regions and a red in the PVAc core. Consequently, it was concluded that the PVA skins formed by heterogeneous surface saponification had high DSs. Such complexes endowed polymeric microspheres a good radiopacity which would be useful in clinical treatment of vascular diseases and were examined by X‐ray irradiation image. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

高分子量聚醋酸乙烯酯的醇解研究

探讨了催化剂浓度、醇解温度和反应时间等对高分子量聚醋酸乙烯酯醇解的影响,得出高分子量聚醋酸乙烯酯醇解的适合条件。     

Preparation of syndiotacticity‐rich high molecular weight poly(vinyl alcohol)/iodine polarizing film with high water resistance

To enhance durability of poly(vinyl alcohol) (PVA)/iodine polarizing film under humid and warm atmospheres and to identify the effects of syndiotacticity on the polarizing efficiency (PE) and durability of PVA/iodine complex film, we prepared three high molecular weight (PVA)s with similar number‐average degree of polymerization (P_n) of 4000 and with different syndiotactic diad (s‐diad) contents of 53, 56, and 59%, respectively. It was found that syndiotacticity of PVA had a significant influence on the durability of PVA/iodine complex film in warm and humidity conditions (relative humidity of 80% and temperature of 50°C). That is, both desorption of iodine in PVA/iodine film and transmittance of film decreased with increasing syndiotacticity of PVA. In the case of PE, the values of over 99% were obtained at each optimum conditions. The change of PE (durability) of PVA/iodine complex films having P_n of 4000 and s‐diad contents of 56 and 59%, respectively, in warm and humidity conditions was almost zero, whereas those of PVA/iodine film with s‐diad content of 53% and with (P_n)s of 1700 and 4000 were about 60% and 50%, respectively, under same conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Controlled synthesis of poly(vinyl acetate) by traditional radical emulsion polymerization

A new redox initiation system, potassium persulfate/N,N‐dimethylethanolamine, was used to initiate traditional radical emulsion polymerization of vinyl acetate at low temperature. Polymers were characterized using gel permeation chromatography, scanning electron microscopy and dynamic light scattering. The results showed that poly(vinyl acetate) with high molar mass and small dispersity (?) was successfully synthesized. © 2016 Society of Chemical Industry     

高粘度醋酸乙烯-乙烯共聚乳液的研制

介绍了一种粘度在 3 3 0 0～ 45 0 0mPa·s之间的醋酸乙烯 -乙烯 (VAE)共聚乳液的工艺制备方法。讨论了乳化剂、聚乙烯醇、醋酸乙烯、乙烯、引发剂等对乳液性能的影响。本产品具有粘度高、粘接性强、柔韧性好、耐水性强等特点。     

紫外光引发乳液聚合制备P(St-co-MMA)复合微球

以十二烷基硫酸钠为乳化剂,2,2-二甲氧基-2-苯基苯乙酮等为引发剂,在水中由紫外光引发苯乙烯(St)和甲基丙烯酸甲酯(MMA)进行乳液聚合,研究了引发剂种类及乳化剂用量对反应收率和微球粒径的影响,并与光引发分散聚合体系进行了比较。结果表明,乳液聚合速率大于分散聚合,由乳液聚合得到的P(St-co-MMA)微球的粒径均一,可控制在70～140 nm之间。