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.     

Effect of degree of saponification on the rheological properties of syndiotactic poly(vinyl alcohol)/ water solution

To identify the effect of degree of saponification (DS) of syndiotactic poly(vinyl alcohol)s (s‐PVA)s having similar tacticity and molecular weight on the rheological properties of s‐PVA/water solution, four kinds of (s‐PVA)s with assigned (DS)s, from 93.1 to 97.5%, were prepared by copolymerization of vinyl pivalate (VPi) and vinyl acetate (VAc), followed by saponifying the corresponding copoly(VPi/VAc). The DS played a significant role in rheological behavior. Over the frequency range of 10^?1 to 10² rad/s s‐PVA with higher DS shows more shear thinning at similar molecular weight and tacticity of polymer, suggesting that PVA molecules are more readily oriented as DS increases. This may provide indirect evidence of the spontaneous in situ orientation of s‐PVA molecules at the late stage of saponification. Yield stress is higher for s‐PVA with higher DS at similar molecular weight and tacticity of s‐PVA. This indicates that more domains with internal order are produced at higher saponification. These facts result from increase in stiffness of s‐PVA molecules with proceeding the saponification reaction. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 463–467, 2002     

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     

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     

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     

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     

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     

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.     

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 high molecular weight poly(vinyl pivalate) with high yield and high molecular weight poly(vinyl alcohol) by emulsion polymerization of vinyl pivalate and saponification

To prepare high molecular weight (HMW) poly(vinyl pivalate) (PVPi) with high yield and high linearity which is a promising precursor for syndiotactic poly (vinyl alcohol) (PVA), vinyl pivalate (VPi) was emulsion polymerized, using 2,2′‐azobis(2‐amidinopropane) dihydrochloride (AAPH) as an initiator and sodium dodecyl sulfate (SDS) as an emulsifier. The effect of the polymerization conditions on the conversion, molecular weight, and degree of branching was investigated. PVA with maximum number‐average degree of polymerization (P_n) of 6200 could be prepared by complete saponification of PVPi, with P_n of 13,300–16,700 obtained at polymerization temperature of 50°C, using SDS and AAPH concentration of 2.0 × 10^?3 mol/L of water and 1.0 × 10^?3 mol/L of water, respectively, and the maximum conversion was about 90%. From the emulsion polymerization of VPi, spherical PVPi with high yield was effectively prepared, which might be useful for the precursor of syndiotactic PVA micro‐ and nano‐spheres with various surface properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 410–414, 2007     

Role of the stereosequences of poly(vinyl alcohol) in the rheological properties of syndiotacticity‐rich poly(vinyl alcohol)/water solutions

Syndiotacticity‐rich poly(vinyl alcohols) (s‐PVAs) with various syndiotactic dyad (S‐dyad) contents were prepared by the copolymerization of vinyl pivalate and vinyl acetate with various monomer feed ratios, which was followed by the saponification of copoly(vinyl pivalate/vinyl acetate) to investigate the effect of the stereosequences of s‐PVA on the rheological properties of s‐PVA/water solutions. Through a series of experiments, we identified that the syndiotacticity had a profound influence on the rheological properties of s‐PVA/water solutions. Over a frequency range of 10^?1 to 10² rad/s, s‐PVAs with higher S‐dyad contents showed larger values of complex viscosity and storage modulus and more shear thinning at similar molecular weights and degrees of saponification of the polymer, suggesting that poly(vinyl alcohol) molecules were stiffer and more readily oriented as syndiotacticity increased. All the yield stresses of s‐PVA represented positive values, and s‐PVAs with higher syndiotacticity showed higher yield stresses. This suggests that as syndiotacticity increased, more pseudostructures were present in s‐PVA/water solutions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1858–1863, 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 gold‐coated syndiotactic poly(vinyl alcohol) microfibrils by sputtering

To prepare a syndiotactic poly(vinyl alcohol) (PVA)/gold complex for various biomedical applications, ultrahigh‐molecular‐weight syndiotactic PVA microfibrils were directly prepared by the saponification of poly(vinyl pivalate) that was obtained through bulk polymerization of vinyl pivalate at 30°C. PVA microfibrils with a number‐average degree of polymerization, syndiotactic diad content, and degree of saponification of 14,300, 61.7%, and 99.9%, respectively, were gold‐coated by sputtering at 140 and 150 W (Watt) for 1, 2, and 3 min, respectively. A weight gain of up to 7% by the gold atoms for the PVA microfibrils treated at 150 W for 3 min was found. Morphological changes at the surface were observed by a microscopic method. A mechanism of gold coating on PVA microfibrils is suggested. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2369–2372, 2003     

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     

Structure and properties of syndiotacticity‐rich poly(vinyl alcohol) prepared through saponification of drawn poly(vinyl trifluoroacetate) with gaseous ammonia

The structure and properties of syndiotacticity‐rich poly(vinyl alcohol) (s‐PVA) prepared through the saponification of drawn poly(vinyl trifluoroacetate) (PVTFAc) with gaseous ammonia were studied. The PVTFAc samples with s‐diad % of 59 and 64 were used. The s‐PVAs had low densities and showed X‐ray diagrams similar to the fiber diagram of PVA with indistinct 100, 101, 101¯, and 200 plane reflections and without the plane reflections seen at the equator of a typical fiber diagram, such as 001, 201, and 002. The s‐PVAs had melting points comparable to those of saponified and heat‐drawn samples, indicating a PVA with the typical fiber structure as seen in the X‐ray diagram of a sample. The intensity of the 916 cm⁻¹ band in the infrared spectrum related to syndiotactic diads decreased with drawing, suggesting an increase in the crystallinity. Crystals with more defects are thought to be produced in saponification. The s‐PVA films drawn 16 times and saponified had a Young's modulus and strength at break of 22 and 1.5 GPa for the sample from S‐59 and 14 and 1.2 GPa for the sample from S‐64, respectively. The crystallization‐sensitive band of 1145 cm⁻¹ in the infrared spectra of the saponified samples was weak. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 467–474, 2001     

Water stability of high‐molecular‐weight (HMW) syndiotacticity‐rich poly(vinyl alcohol) (PVA)/HMW atactic PVA/iodine complex blend films

To precisely identify the effect of blend ratios of syndiotacticity‐rich poly(vinyl alcohol) (s‐PVA)/atactic PVA (a‐PVA) on the water stability of s‐PVA/a‐PVA/iodine complex blend films, we prepared two PVAs with similar number‐averaged degrees of polymerization of 4000 and degrees of saponification of 99.9% and with different syndiotactic diad contents of 58.5 and 53.5%, respectively. The desorption behavior of iodine in s‐PVA/a‐PVA/iodine complex films in water was investigated in terms of the solubility of s‐PVA/a‐PVA blend films in water. The degree of solubility of s‐PVA/a‐PVA blend films with s‐PVA content over 50% in water at 70°C was limited to about 10–20%, whereas that of s‐PVA/a‐PVA blend films with s‐PVA content of 10% was 85% under the same conditions. The degree of iodine desorption of complex blend films decreased with increasing s‐PVA content. The degree of iodine desorption of s‐PVA/a‐PVA drawn film with s‐PVA content of 90% was limited to 7%, regardless of the soaking temperature from 30 to 70°C. The desorption of iodine in water was strongly affected by the dissolution of blends. Moreover, the stability of iodine in the drawn s‐PVA/a‐PVA/iodine blend films in hot water was far superior to that of the undrawn film. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1435–1439, 2004     

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     

Water‐absorptive blend fibers of copoly(acrylic acid–acrylamide) and poly(vinyl alcohol)

Through the addition of N‐hydroxymethyl acrylamide as a potential crosslinker, water‐absorptive blend fibers of copoly(acrylic acid–acrylamide) and poly(vinyl alcohol) with three‐dimensional network structures were prepared with heat‐crosslinking technology after fiber formation. Fourier transform infrared, scanning electron microscopy, dynamic mechanical analysis, and thermogravimetry were used to analyze the structures and properties of the fibers. The tensile behavior and absorbent capacities of the fibers were also studied. The results showed that there were lots of chemical crosslinking points in the fibers, the compatibility of copoly(acrylic acid–acrylamide) and poly(vinyl alcohol) was perfect, and the tensile properties of the fibers could be improved effectively through stretching in a vapor bath. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3353–3357, 2006     

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     

Drug‐release behavior of chitosan‐g‐poly(vinyl alcohol) copolymer matrix

Chitosan‐g‐poly(vinyl alcohol) (PVA) copolymers with different grafting percent were prepared by grafting water‐soluble PVA onto chitosan. The drug‐release behavior was studied using the chitosan‐g‐PVA copolymer matrix containing prednisolone in a drug‐delivery system under various conditions. The relationship between the amount of the released drug and the square root of time was linear. From this result, the drug‐release behavior through the chitosan‐g‐PVA copolymer matrix is shown to be consistent with Higuchi's diffusion model. The drug‐release apparent constant (K_H) was slightly decreased at pH 1.2, but increased at pH 7.4 and 10 according to the increasing PVA grafting percent. Also, K_H was decreased by heat treatment and crosslinking. The drug release behavior of the chitosan‐g‐PVA copolymer matrix was able to be controlled by the PVA grafting percent, heat treatment, or crosslinking and was also less affected by the pH values than was the chitosan matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 458–464, 1999