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.     

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.     

The sorption of poly(vinyl acetate) on cellulose. I. The nature and extent of the sorbed layer

The sorption of poly(vinyl acetate) from benzene solution onto cellulose fibers has been investigated with particular attention to the nature and extent of the sorbed layer of polymer. The cellulose substrate has been varied by swelling pretreatments with water, ethylenediamine, and 18% sodium hydroxide. The density of the sorbed polymer after drying was found to be similar to that of the bulk polymer (1.19–1.20 g/cm³). Water vapor sorption isotherms were used to evaluate the internal surface of cellulose and the decrease in the surface area accessible to water after sorption of the polymer. This decrease was considered equivalent to the area covered by sorbed polymer. The amount of polymer sorbed per unit area (5.0–5.5 mg PVAc sorbed from benzene per 1 m² of cellulose surface) was found to be substantially independent of the amount of sorbed polymer and of the swelling pretreatment, indicating that the thickness of the sorbed layer was quite uniform (40–50 Å). A comparison of the thickness of the sorbed layer in the dry state with the thickness of a monolayer with polymer molecules lying flat on the solid surface indicated that the fraction of the polymer segments attached directly to the surface was about 0.10. The amount of polymer sorbed per unit area of cellulose and consequently the thickness of the sorbed layer and the fraction of attachment can be affected by the nature of the solvent from which the polymer is sorbed.     

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.     

Modeling poly(vinyl alcohol)-stabilized vinyl acetate emulsion polymerization. II. Comparison with experiment

The mathematical model presented in Part I, accommodating the emulsion polymerization of vinyl acetate stabilized with poly(vinyl alcohol), predicts experimental conversion and particle size data with reasonable accuracy. Model predictions of measurable variables exhibit sensitivity to variables affecting either primary ungrafted particle nucleation of flocculation kinetics, but are relatively insensitive to variables affecting poly(vinyl alcohol) grafting reactions and the resulting primary grafted particle concentration. Semibatch simulations indicate that independent increases in the vinyl acetate, poly(vinyl alcohol), and initiator levels of all increase the primary grafted particle population. It is unlikely, however, that this population exceeds the ungrafted counterpart under most commercial polymerization conditions. This relative insignificance of grafting during particle nucleation is also noted in literature data simulations where, with appropriate parameter adjustments, the model predictions agree well with the batch, thermal initiation data. © 1993 John Wiley & Sons, Inc.     

Radiation grafting of poly(ethylene terephthalate) (PET) fibre,II. Hydrolysis of grafted poly(vinyl acetate) to poly(vinyl alcohol)

Poly(ethylene terephthalate) fibres grafted with poly(vinyl acetate) by γ-radiation were hydrolysed under alkaline and acidic conditions in order to obtain poly(ethylene terephthalate)-graft-poly(vinyl alcohol) fibres. In alkaline media poly(ethylene terephthalate) degraded without appreciable conversion of acetate to hydroxyl groups. During acid hydrolysis no change in tensile properties of the fibres was observed up to an extent of 50% conversion of acetate to hydroxyl groups. Further change in the tensile strength and the elongation at break was attributed partly to the grafted poly(vinyl acetate)/poly(vinyl alcohol) balance and partly to the loss due to degradation of the fibres.     

Synthesis of latices with hydrophobic cores and poly(vinyl acetate) shells. 2. Use of poly(vinyl acetate) seeds

A strategy is explored for synthesizing latex particles with polystyrene cores and poly(vinyl acetate) shells. The seed particles are poly(vinyl acetate), which theory indicates should be immune to secondary particle formation when a second-stage seeded emulsion polymerization with styrene is carried out. The objective is to form a single hydrophobic core by inversion of the second and first stages. While this morphology is favoured thermodynamically, conditions need to be optimized so that it is kinetically achievable: many attempts to implement this using straightforward synthetic procedures result in either no core (acorn morphology) or multiple polystyrene cores. A series of experiments enables this goal to be implemented by ensuring sufficiently fast diffusion of the first-stage hydrophilic polymer (using chain-transfer agent to reduce the molecular weight and, more importantly, the degree of branching of the parent poly(vinyl acetate) seed polymer), an initiator which minimized grafting between the first- and second-stage polymers, and modifying the seed poly(vinyl acetate) to increase its hydrophilicity.     

Solvent-free generation of poly(vinyl acetals) directly from poly(vinyl acetate)

The simultaneous methanolysis and butryalization of poly(vinyl acetate) was conducted via the reaction of methanol and butyraldehyde with polyvinyl acetate under batch conditions at temperatures from 70°C to 90°C at the vapor pressure of the reactants. It was found that use of an acid catalyst allowed for the methanolysis to be the rate limiting step of a simultaneous methanolysis-butyralization reaction, minimizing the buildup of alcohol repeat units in the polymer during the reaction. As such, use of an excess of aldehyde was counterproductive in that it served to dilute both the methanol and the acetate groups in the polymer phase, lowering the overall rate of the reaction. With 20% stoichiometric excesses of methanol and butyraldehyde, it was possible to produce poly(vinyl butyral) directly from poly(vinyl acetate) with very low residual acetate and overall conversions equivalent to commerical samples. Further, carbon dioxide was evaluated as a reversible plasticizer for polyvinyl acetate during methanolysis. Results at various pressures were consistent with the expectation that the presence of CO₂ would lower the reaction rate, primarily because of dilution of reactants in the CO₂-swollen polymer phase. Finally, it was shown that the simultaneous reaction procedure can be used to generate polyvinyl acetals from a variety of aldehydes.     

Studies on the miscibility and phase structure in blends of poly(epichlorohydrin) and poly(vinyl acetate)

The miscibility of atactic poly(epichlorohydrin) (aPECH) with poly(vinyl acetate) (PVAc) was examined under two different conditions: (i) in dilute solution, using vicometeric measurements and (ii) as cast films, using differential scanning calorimetric (DSC) and FT-infrared spectroscopy. Phase separation on heating, i.e. lower critical solution temperature (LCST) behavior of the aPECH/PVAc blends was examined by the measurement of transmitted light intensity against temperature. From viscosity measurements, the Krigbaum-Wall polymer-polymer interaction (ΔB) was evaluated. The DSC results show that the aPECH/PVAc blends are miscible as evidenced by the observation of a single composition-dependent glass-transition temperature (T_g) which is well described by the Couchman and Gordon Taylor models. The Flory-Huggins interaction parameter (χ₁₂) calculated from the T_g-method was negative and equal to −0.01, indicating a relatively low interaction strength. The FT-IR results match very well with those of DSC. The cloud point phenomenon is thermodynamically driven but phase separation, once taken place, is diffusion controlled in normal accessible time.     

Influence of temperature on the ultrasonic degradation of poly(vinyl acetate) and poly(vinyl chloride)

This study investigates the effect of temperature on the ultrasonic degradation of polyvinyl acetate and polyvinyl chloride in chlorobenzene. The time evolution of molecular weight distribution was determined using gel permeation chromatography. Continuous distribution kinetics was used to obtain the degradation rate coefficients. The rate coefficients decrease with increasing temperature, and this is attributed to the increase of vapor pressure and the decrease of kinematic viscosity. The degradation rate coefficient also changes sharply near the glass transition temperature, indicating that this factor may play a role in the degradation process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2818–2822, 2003     

Effect of alkalies on suspension polymerization of vinyl acetate monomer,properties of poly(vinyl acetate) beads and poly(vinyl alcohols)

The use of weak alkalies such as sodium carbonate (Na₂CO₃), sodium bicarbonate (NaHCO₃) and their 1 : 1 molar mixture, and strong alkalies such as sodium hydroxide (NaOH) and sodium methoxide (NaOMe) as pH controllers in suspension polymerization of vinyl acetate monomer (VAM) has shown to have diverse effects on the yield of resulting poly(vinyl acetate) (PVAC) beads. Carbon dioxide as such or the carbonate seems to influence the yield. Further, these alkalies have a deep-seated effect not only on properties like viscosity, stereoregularity, glass transition temperature (T_g), and swelling coefficient (Q) of the PVAC beads but also on those of poly(vinyl alcohol) (PVA) obtained by alcoholysis of PVAC beads. The PVAC beads obtained using Na₂CO₃ showed higher viscosity, higher swelling coefficient (Q), and the PVA derived from these beads had higher Q, higher syndiotacticity/isotacticity ratio, and lower T_g.     

Phase structure in the blend of atactic poly(vinyl alcohol) with atactic poly(vinyl alcohol‐block‐vinyl acetate)

An almost fully saponified atactic poly(vinyl alcohol) and an atactic poly(vinyl alcohol‐block‐vinyl acetate) of which degree of saponification is 89 mol % were blended by a solution casting method. The phase structure of the blend film was analyzed by optical microscopy, ¹³C‐NMR, and differential scanning calorimetry. The most remarkable structure of the blend was composed of cylindrical domains penetrating the film. The swelling behavior of the blend films was also investigated in the dimethylsulfoxide and water mixed solvents to find differences in solubility and diffusion behavior between the matrix and the domain. The cylindrical domains could be selectively dissolved away in water and the film became porous. We tried to change the size of the cylindrical domain with various film preparation conditions. This aimed to turn the film into the useful filter membrane. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1807–1815, 2002     

The structure of cellulose acetate membranes II. The physical and transport characteristics of the porous layer of anisotropic membranes

By a technique involving the removal of successive layers of an anisotropic cellulose acetate membrane, and the measurement of solute and volume flow through the remaining structure, it is possible from the results to calculate some of the properties of each decrement which characterizes its structure. These are: average pore diameter, area ratio of pores to total surface, and pore volume fraction.     

Sorption of dye wastes by poly(vinyl alcohol)/poly(carboxymethyl cellulose) blend grafted through a radiation method

The instability in water of poly(vinyl alcohol) (PVA)/poly(carboxymethyl cellulose) (CMC) was improved through radiation-induced grafting with a styrene monomer. The PVA/CMC blend graft copolymer was used as a sorbent for dye wastes normally released from textile factories. The factors that may affect the sorption process such as time, temperature, weight of the blend graft copolymer, and volume of the dye waste were investigated. The sorption of dyestuffs by the blend graft copolymer was determined by a method based on spectroscopic analysis. The results showed that the blend graft copolymer has a high affinity for basic, acid, and reactive dyes. Meanwhile, it was observed that the sorption of dyes is more effective at the high temperature of 70^oC. Moreover, it was found that the sorption of dyes depends on the weight of the blend graft copolymer and does not depend on the volume of the waste solution. The sorption of the dyestuffs by a PVA/CMC graft copolymer may be considered to be a practical method to remove organic pollutants. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 136–142, 2001     

Kinetics of formalization of poly(vinyl acetate)

Kinetic information on the formation of poly(vinyl formal) by the reaction of poly(vinyl acetate) and formaldehyde in presence of aqueous acid has been derived from the spectroscopic analysis of polymer samples after different periods of reaction. The hydroxyl content of poly(vinyl formal) is found to be nearly independent of reaction time and only slightly affected by temperature while the fall of acetate content and the increase in formal content are most rapid in the initial period and are largely influenced by temperature. The rate expression formulated on the assumption that the formalization reaction is of first order with respect to both poly(vinyl acetate) and formaldehyde explains the observed variation of polymer composition with reaction time. The activation energy for the reaction is found to be 17.3 kcal/mol.     

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.     

Polymer compatibility II. The system poly(methyl methacrylate)–poly(vinyl acetate). Preparation and impact behavior

Blends of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) were prepared by mixing the polymers in the melt and in the absence of a solvent. PMMA was the major constituent of the blend. Traces of gel permeation chromatograms showed that the starting materials retain their polymeric character after Brabender processing. Data obtained from notched Izod impact strength tests at 23°C showed that blends may exhibit values ranging from about 0.3 to 0.9 ft-lb/in. notch. Differences in mix conditions afford blends which, from a phenomenologic viewpoint, consist of a mixture of two glassy polymers or of a rubbery polymer dispersed in a glassy matrix. Micrographs of a crack pattern in companion blends consisting of PMMA/PVAc 85/15 are consistent with impact strength test results.     

Grafting of vinyl acetate onto poly(vinyl chloride) in solution

Radiation-induced grafting of vinyl acetate (VAc) onto poly(vinyl chloride) (PVC) was performed in solution with dimethylformamide (DMF). Grafting was studied as a function of dose, dose rate, and VAc/PVC ratio. The amount of grafting was measured by IR spectroscopy on the graft copolymer fraction insoluble in hot methanol. The homopolymerization of VAc was also studied in the same conditions, in order to check the influence of the solvent on radiochemical reactions leading to graft copolymers. The results show that the grafting can be easily obtained and the graft copolymer will be tested for the preparation of ultrafiltration membranes.