Preparation and structure of poly(vinyl alcohol)–poly(vinyl acetate) composite porous membrane

The preparation of poly(vinyl alcohol) (PVA)–poly(vinyl acetate) (PVAc) composite porous membrane was investigated by extracting PVAc with solvent from films of PVAc lattices which were obtained by the emulsion polymerization of vinyl acetate (VAc) in the presence of PVA. The formation of the porous membrane depended upon whether or not PVAc in the latex film was easily extracted with solvent. In the case of using hydrogen peroxide (HPO)–tartaric acid (TA) as an initiator, in the film of the latex which was produced from the batch method in which all ingredients of the batch were put into the reaction vessel before starting polymerization, PVAc could be extracted over 90% of total PVAc with common organic solvents. In the film of the latex which was produced from the dropwise addition method of VAc and initiator, the PVAc extraction was about 20-30%. On the other hand, in the case of using ammonium persulfate as an initiator, the desired porous membrane was not obtained. The structure of the porous membrane obtained from the latex of the batch method by using HPO—TA consisted of spherical cells which were made up of PVA and grafted PVAc or insoluble PVAc like microgels, which were not extracted with organic solvent and were connected by small pores. The PVA—PVAc composite porous membrane is permeated by n-hexane with 5.58 × 10² mL/cm²·s at 0.5 kg/cm², by benzene with only 1.33 × 10^?3mL/cm²·s even at 60 kg/cm².     

High‐resolution solid‐state NMR and SEM study of the interaction behavior of poly(ethylene‐co‐vinyl acetate)/poly(vinyl acetate) blends

Binary blends formed by two types of ethylene‐co‐vinyl acetate (EVA), which have different vinyl acetate contents, and poly(vinyl acetate) (PVAc) were prepared in a Haake Rheocord 9000 plastograph. A series of samples were obtained varying the PVAc amount up to 50%. The studies were carried out employing solid‐state nuclear magnetic resonance spectroscopy (NMR) and scanning electronic microscopy (SEM). The xenon‐129 (¹²⁹Xe) and carbon‐13 (¹³C) NMR response together with the microscopy results showed that the systems are heterogeneous. Therefore, EVA with a higher vinyl acetate content presented some interaction between the polymer blend components. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 116–124, 2002     

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     

Permeation characteristics of poly(vinyl alcohol)–poly(vinyl acetate) composite porous membranes

Poly(vinyl alcohol) (PVAc) composite porous membrane has been prepared from PVAc latex film by extraction with acetone. The PVAc latex was prepared by emulsion polymerization of vinyl acetate in the presence of PVA, employing the hydrogen peroxide–tartaric acid systemm as an initiator. The extraction degree of PVAc could be controlled in a wide range by changing the addition method of the initiator, and, acoordingly, PVA–PVAc omposite porous membranes which had variosu void volumes were obtained. The maximum void volume attained was ca. 90%. Permation characteristics of organic solvents wre investigated on the membranes whose extraction degrees were 95.6% and 80.7%. Thge feeds were benzene, n-hexane, cyclohexane, and their mixtures. neither swelling nor shrinkage in tje appearance size of the while benzene hardly permeated even at 20 kg/cm². The grafted PVAc in the mebrane was removed or converted into grafted PVA by treatment with sodium methylate, and then the depression of benzene permeation was lost. The grafted PVAc was suggested to be localizd on the cell wall and was found to function as a valve which closes with nenzene or a good solvent for PVAc and opens with n-haxane or a poor solvent for PVAc.     

Preparation of high‐molecular‐weight poly(vinyl alcohol) with high yield by solution polymerization of vinyl acetate in methanol using 4,4′‐azobis(4‐cyanovaleric acid)

Vinyl acetate (VAc) was solution‐polymerized at 40°C and 50°C using 4,4′‐azobis(4‐cyanovaleric acid) (ACVA) as an initiator and methanol as a solvent, and effects of polymerization temperature and initiator concentration were investigated in terms of conversion of VAc into poly (vinyl acetate) (PVAc), degree of branching (DB) for acetyl group of PVAc, and molecular weights of PVAc and resulting poly(vinyl alcohol) (PVA) obtained by saponifying with sodium hydroxide. Slower polymerization rate by adopting ACVA and lower viscosity by methanol proved to be efficient in obtaining linear high‐molecular‐weight (HMW) PVAc with high conversion and HMW PVA. PVA having maximum number–average degree of polymerization (P_n) of 4300 could be prepared by the saponification of PVAc having maximum P_n of 7900 polymerized using ACVA concentration of 2 × 10^?5 mol/mol of VAc at 40°C. Moreover, low DB of below 1 could be obtained in ACVA system, nevertheless of general polymerization temperatures of 40°C and 50°C. This suggests an easy way for producing HMW PVA with high yield by conventional solution polymerization without using special methods such as low‐temperature cooling or irradiation. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 4831–4834, 2006     

Synthesis of poly(vinyl acetate)‐graft‐polystyrene and application to preparation of porous membranes

Poly(vinyl acetate)–TEMPO (PVAc–TEMPO) macroinitiators were synthesized by bulk polymerization of vinyl acetate in the presence of benzoyl peroxide (BPO) followed by termination with 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO). Radicals were mainly transferred to the acetoxy methyl groups in PVAc during the polymerization. The PVAc–TEMPO macroinitiators had several TEMPO‐dormant sites and styrene bulk polymerization with the macroinitiators produced poly(vinyl acetate)‐graft‐polystyrene (PVAc‐g‐PS). All the TEMPO‐dormant sites of PVAc–TEMPO macroinitiators participated in the styrene polymerization with almost equal reactivity. Methanolysis of PVAc‐g‐PS broke the PS branches apart from the PVAc backbone chains. Hydrophobic or hydrophilic porous membranes with controlled pore size could be prepared by removing the PVAc domains or the PS domains from the graft copolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1658–1667, 2001     

Characterization of poly(vinyl alcohol)

Molecular weight distributions, long chain branching frequency, and solution viscosities of samples of commercial poly(vinyl alcohol) (PVA) are reported. The PVA was fully reacetylated to poly(vinyl acetate) (PVAc) for characterizations by size exclusion chromatography using a low angle light scattering detector. The Mark–Houwink constants for PVAc in toluene were determined to be K = 0.106 cm³ g^?1 and α = 0.59, at 25°C. Long chain branching frequency in the commercial PVAs studied was small and was little affected by polymer molecular weight. Some 95% or more of the branches in these species were short. Aqueous solutions at 10% (w/v) of PVA were Newtonian. The polymers examined differed in chemical composition, molecular weight distributions, and mean block lengths of vinyl acetate residues. Variations in a single characteristic, like a solution or intrinsic viscosity, cannot be used to deduce structural differences between PVAs.     

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     

Synthesis of poly(vinyl acetate) containing diblock copolymer by DPE method

Diblock copolymer poly(methyl methacrylate)‐b‐poly(vinyl acetate) (PMMA‐b‐PVAc) was prepared by 1,1‐diphenylethene (DPE) method. First, free‐radical polymerization of methyl methacrylate was carried out with AIBN as initiator in the presence of DPE, giving a DPE containing PMMA precursor with controlled molecular weight. Second, vinyl acetate was polymerized in the presence of the PMMA precursor and AIBN, and PMMA‐b‐PVAc diblock copolymer with controlled molecular weight was obtained. The formation of PMMA‐b‐PVAc was confirmed by ¹H NMR spectrum. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to detect the self‐assembly behavior of the diblock polymer in methanol. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

Thermal characteristics of poly(ethylene terephthalate) fiber grafted with poly(vinyl acetate) and poly(vinyl alcohol)

Poly(ethylene terephthalate) (PET) fibers were grafted with poly(vinyl acetate) (PVAc) and poly(vinyl alcohol) (PVA). The effects of graft copolymers PVAc and PVA on morphological properties of PET were evaluated by differential thermal analysis, differential scanning calorimetry, and thermogravimetric analysis. Melting temperature, heat of fusion, and mass fractional crystallinity of PET was not affected by graft PVAc and PVA. No individual glass transition and melting points corresponding to the graft PVAc and PVA were observed, indicating thereby that graft copolymer mainly exists in the form of free chains inside the PET matrix. Poly(vinyl alcohol) graft copolymer degraded at much lower temperatures than poly(vinyl alcohol) in powder form. Thermal stability of PET fiber was not affected by graft PVAc, where as PET–g–PVA showed an additional degradation point at 360°C.     

Dual xanthan gum/poly(vinyl acetate) or alkyl‐functionalized poly(vinyl alcohol) films as models for advanced coatings

Double‐layer films, prepared by casting films of xanthan gum (XG), and subsequently poly(vinyl acetate) (PVAc) onto the former, are reported. The resulting XG/PVAc films provide high protection as coatings to a bleaching agent, 6‐(phthalimido)peroxyhexanoic acid, in liquid detergents, due to the combined roles of the outer PVAc layer as water‐barrier and the inner XG layer as water‐sink. PVAc films cast from either homogeneous solutions in acetone or aqueous dispersions were used; the stabilities exerted by the former were markedly superior. For comparison, poly(vinyl alcohol) (PVA) was also used as outer wall material, resulting in much lower protection due to its hydrophilicity. Functionalization (silylation or acetalyzation) of PVA films is also suggested as a means to decrease the surface hydrophilicity of the material. The dual hydrophilic–hydrophobic films presented herein serve as models for advanced coatings in (micro)encapsulation processes, owing to the straightforward study of their morphology and transport phenomena. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40870.     

Synthesis of spherical core‐shell poly(vinyl acetate)/poly(vinyl alcohol) particles for use in vascular embolization: Study of morphological and molecular modifications during shell formation

Transarterial vascular embolization and chemoembolization has become common medical procedures, where partially hydrolyzed poly(vinyl alcohol) (PVA) beads remains as one of the most used embolic agent materials. Although synthetic, PVA cannot be synthesized by direct polymerization and must be obtained by chemical modification of another polymer, usually poly(vinyl acetate) (PVAc). The aim of the present work is to synthesize spherical core‐shell PVAc/PVA particles and study the morphological and molecular modifications during shell formation. The polymer particles where produced in two stages, where first the PVAc core was obtained by suspension polymerization of vinyl acetate (VAc) and then the PVA shell synthesized through hydrolysis. Spherical PVAc particles were successfully produced and isolated using an optimized suspension polymerization process. During the shell formation, it was shown that none of the conditions used affected the overall morphology of the particles although changes in the final size distribution could be observed. However, it was possible to identify the process variables and reaction condition that affect the molecular weight averages and polydispersities of the final copolymer. POLYM. ENG. SCI., 55:2237–2244, 2015. © 2015 Society of Plastics Engineers     

Rheological properties of high molecular weight (HMW) syndiotactic poly(vinyl alcohol) (PVA)/HMW atactic PVA blend solutions

To identify the effect of blend ratios of syndiotacticity‐rich poly(vinyl alcohol) (s‐PVA)/atactic PVA (a‐PVA) having similar number‐average degrees of polymerization (P_n)s of 4000 and degrees of saponification (DS)s of 99.9% on the rheological properties of s‐PVA/a‐PVA/water solutions, water‐soluble s‐PVA and a‐PVA with different syndiotactic diad contents of 58.5 and 54.0%, respectively, were prepared by bulk copolymerization of vinyl pivalate and vinyl acetate (VAc) and solution polymerization of VAc, followed by saponifying the corresponding copoly(vinyl pivalate/vinyl acetate) and poly(vinyl acetate). The blend ratios played a significant role in rheological behavior. Over the frequency range of 10^?1–10² rad/s, s‐PVA/a‐PVA blend solutions with larger s‐PVA content show more shear thinning at similar (P_n)s and (DS)s of polymer, suggesting that PVA molecules are more readily oriented as s‐PVA content increases. Yield stress is higher for s‐PVA/a‐PVA blend solutions with larger s‐PVA content at similar (P_n)s and (DS)s of polymer. This indicates that more domains with internal order are produced at larger s‐PVA content in s‐PVA/a‐PVA blend solutions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3934–3939, 2006     

Measurement and modeling of poly(vinyl acetate)–solvent viscosity mixtures

The viscosities of various poly(vinyl acetate) (PVAc)–solvent mixtures (PVAc–toluene, PVAc–benzene, and PVAc–cyclohexanone) were measured at different temperatures with a Haake viscometer. The required molecular weight of a commercial‐grade PVAc sample was measured with an Ubbelohde viscometer. The measured viscosities were correlated with a previously proposed viscosity model, and the model parameters were calculated. The results indicated the applicability of the model to the viscosity calculations of PVAc–solvent mixtures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1244–1249, 2005     

Preparation and characterization of colloidal dispersions of vinyl alcohol–vinyl acetate copolymers: application as stabilizers for vinyl chloride suspension polymerization

Well‐defined colloidal dispersions of vinyl alcohol–vinyl acetate copolymers (PVAs) with different degrees of hydrolysis (DH) were prepared by a coacervation technique. Colloidal particles in the size range 150–250 nm, with an acetate‐rich core and a hydrophilic PVA corona, were obtained using a combination of a hydrophobic PVA (PVA II) having an average DH ( ) value of 43 mol% with a ‘blocky’ hydrophilic PVA (PVA I) with a value of 72 mol%. The core–shell structure of these particles was demonstrated using ¹H NMR and using fluorescence‐labelled PVA I. The stabilization efficiency of PVA I and PVA II and their combination was examined for 1‐chlorobutane–water emulsions, as a ‘model solvent’ for vinyl chloride–water emulsions. Preliminary tests of vinyl chloride suspension polymerization confirmed the beneficial effect of PVA I and PVA II combinations as stabilizers on the granulometry and the porosity specifications of the poly(vinyl chloride) grains. Copyright © 2006 Society of Chemical Industry     

Controllable synthesis of a novel poly(vinyl alcohol)‐based hydrogel containing lactate and PEG moieties

Tunable hydrogel that contained well‐defined poly(vinyl alcohol) (PVA), labile lactate groups, and hydrophilic poly(ethylene glycol) (PEG) segments was prepared through a combination of reversible addition‐fragmentation chain transfer (RAFT) polymerization and esterification reaction. A diol was prepared via the esterification between lactic acid (LA) and PEG. Then the diol was allowed to react with maleic anhydride to produce a diacid. Meanwhile, well‐defined PVA was synthesized by the alcoholysis of poly(vinyl acetate) (PVAc) obtained by RAFT polymerization of vinyl acetate. The hydrogels with tailor‐made structure were generated by crosslinking PVA with LA‐based diacid. The structures and properties of LA‐based intermediates and the hydrogels were characterized with Fourier transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. Both LA‐based diol and diacid were semicrystalline and water‐soluble, their melting temperature and glass transition temperature were 52 and ?51, 54 and ?41°C, respectively. The polydispersity indexes of the precursor of PVA samples were within the range of 1.03–1.10. It was found that the thermal stability of hydrogel was higher than that of LA‐based diacid. Both the swelling and release properties of the hydrogels depend on the feeding ratio of PVA/LEM and the chain length of PVA, which reflected that the structure and properties of the hydrogels were controllable. POLYM. ENG. SCI., 54:1366–1371, 2014. © 2013 Society of Plastics Engineers     

Compatibility of nylon 6 with poly(vinyl alcohol), hydroxylated poly(vinyl acetate) and poly(vinyl acetate)

Summary The compatibility of nylon 6 with poly(vinyl acetate)(PVAc) and poly(vinyl alcohol)(PVA) was investigated in terms of the melting-temperature depression. In order to vary the compatibility systematically, a hydroxylated poly(vinyl actate)(m-PVAc) was prepared by hydrolyzing PVAc with KOH in CH₃OH. It was found that the compatibility with nylon 6 is better in the systematic order PVA> m-PVAc> PVAc.     

Atom transfer radical polymerization of methyl methacrylate initiated with a macroinitiator of poly(vinyl acetate)

Well‐defined poly(vinyl acetate‐b‐methyl methacrylate) block copolymers were successfully synthesized by the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in p‐xylene with CuBr as a catalyst, 2,2′‐bipyridine as a ligand, and trichloromethyl‐end‐grouped poly(vinyl acetate) (PVAc–CCl₃) as a macroinitiator that was prepared via the telomerization of vinyl acetate with chloroform as a telogen. The block copolymers were characterized with gel permeation chromatography, Fourier transform infrared, and ¹H‐NMR. The effects of the solvent and temperature on ATRP of MMA were studied. The control over a large range of molecular weights was investigated with a high [MMA]/[PVAc–CCl₃] ratio for potential industry applications. In addition, the mechanism of the polymerization was discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1089–1094, 2006     

Study of polymer–solvent interactions by gas chromatography. Copolymers of vinyl acetate and vinyl alcohol with hydrocarbons and alcohols

The specific retention volumes of nine hydrocarbons and 12 alcohols were measured at several temperatures within the range 120–150°C in columns whose stationary phases were poly(vinyl acetate) (PVAc) and four copolymers of vinyl acetate and vinyl alcohol with 94.8, 74.4, 60.9, and 43.4 mol % of vinyl acetate units (mol % VAc). No chromatographic retention for hydrocarbons was detected in columns loaded with poly(vinyl alcohol) (PVA) or a copolymer with 11.9 mol % VAc. The retention trends are discussed and the polymers solubility parameters (δ₂) were computed from the measured Flory–Huggins χ parameters. The copolymers δ₂ values increase almost linearly with decreasing mol % VAc; PVAc, however, has a distinct behavior. The limitations of the approach in the prediction of χ parameters are discussed.