Preparation of water‐soluble,syndiotacticity‐rich,low molecular weight poly(vinyl alcohol) microfibrils in high yields with the low‐temperature polymerization of vinyl pivalate in tetrahydrofuran and saponification

To prepare water‐soluble, syndiotacticity‐rich poly(vinyl alcohol) (PVA) microfibrils for various industrial applications, we synthesized syndiotacticity‐rich, low molecular weight PVA by the solution polymerization of vinyl pivalate (VPi) in tetrahydrofuran (THF) at low temperatures with 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN) as an initiator and successive saponification of poly(vinyl pivalate) (PVPi). Effects of the initiator and monomer concentrations and the polymerization temperature were investigated in terms of the polymerization behaviors and molecular structures of PVPi and the corresponding syndiotacticity‐rich PVA. The polymerization rate of VPi in THF was proportional to the 0.91 power of the ADMVN concentration, indicating the heterogeneous nature of THF polymerization. The low‐temperature solution polymerization of VPi in THF with ADMVN proved to be successful in obtaining water‐soluble PVA with a number‐average degree of polymerization (P_n) of 300–900, a syndiotactic dyad content of 60–63%, and an ultimate conversion of VPi into PVPi of over 75%. Despite the low molecular weight of PVA with P_n = 800, water‐soluble PVA microfibrillar fibers were prepared because of the high level of syndiotacticity. In contrast, for PVA with P_n = 330, shapeless and globular morphologies were observed, indicating that molecular weight has an important role in the in situ fibrillation of syndiotacticity‐rich PVA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1103–1111, 2002     

Low-temperature suspension polymerization of vinyl pivalate for the preparation of syndiotacticity-rich ultrahigh molecular weight poly(vinyl alcohol) microfibrils with high yield

To prepare ultrahigh molecular weight (UHMW) poly(vinyl pivalate) (PVPi) with high conversion and high linearity for a precursor of syndiotacticity-rich UHMW poly(vinyl alcohol) (PVA), vinyl pivalate (VPi) was suspension polymerized using a low-temperature initiator, 2,2'-azobis(2,4-dimethylvaleronitrile) (ADMVN), and the effects of polymerization conditions on the polymerization behavior and molecular structures of PVPi and PVA prepared by saponifying PVPi were investigated. Suspension polymerization was slightly inferior to bulk polymerization in increasing the molecular weight of PVA. In contrast, the former was superior in increasing the conversion of the polymer. Suspension polymerization of VPi at 25 °C by controlling various polymerization factors proved to be successful in obtaining PVA of UHMW (number-average degree of polymerization (P_n): 14,700-16,700), high syndiotactic diad content (62%), and of high yield (ultimate conversion of VPi into PVPi: 85-90%). In the case of bulk polymerization of VPi under the same conditions, maximum P_n, conversion of 15,800-17,000, and 25-35% were obtained, respectively. The degree of branching was lower and the P_n and syndiotacticity were higher with PVA prepared from PVPi polymerized at lower temperatures. All PVAs from PVPi suspension-polymerized at 25 °C were fibrous, with a high degree of crystallinity and orientation of the crystallites.     

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

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

Preparation of Syndiotacticity-Rich High Molecular Weight Polyvinyl Alcohol by Low Temperature Emulsifier-Free Emulsion Copolymerization of Vinyl Acetate and Vinyl Pivalate

Low temperature emulsifier-free emulsion copolymerization of vinyl acetate (VAc) and vinyl pivalate (VPi) was carried out using a redox initiation system to prepare syndiotacticity-rich high-molecular weight (HMW) polyvinyl alcohol (PVA) with high yield. The effects of the polymerization conditions on the conversion, the molecular weight, the structure of poly (vinyl acetate-co-vinyl pivalate) (P (VAc-VPi)) and syndiotacticity of PVA were investigated. With the increases of the initiator concentration, the VPi molar ratio in monomer and polymerization temperature, the degree of polymerization (DP) of PVA decreases distinctly, but VPi contents in copolymer and syndiotactic diad (S-diad) contents of PVA increase obviously. PVA with the maximum DP of 11030 can be prepared by complete saponification of P(VAc-VPi) obtained under condition that the molar ratio of KPS to monomer is 1/2000, the molar ratio of VAc to VPi is 7:3 and reaction temperature is 12°C. The highest S-diad content in PVA can be up to 59.31% while the DP of PVA decreases to 5180 under the condition that the feed ratio of VPi is 70 mol%, which means the syndiotacticity-rich HMW PVA can be prepared successfully. And the conversions of all reactions are above 80%. Syndiotacticity-rich HMW PVA is effectively prepared in this study, which is useful for the preparation of high-strength and high-modulus PVA fiber.     

Preparation of ultrahigh‐molecular‐weight syndiotactic poly(vinyl pivalate) monodisperse microspheres by low‐temperature suspension polymerization of vinyl pivalate

The particle size distributions of poly(vinyl pivalate) (PVPi) produced from low‐temperature suspension polymerization of vinyl pivalate (VPi) with 2,2′‐azobis(4‐methoxy‐2,4‐dimethylvaleronitrile) (AMDMVN) as an initiator have been studied. By controlling various synthesis parameters, near‐monodisperse PVPi microspheres from 100 to 400 μm were obtained that are expected to be precursors of near‐monodisperse syndiotactic poly(vinyl alcohol) (PVA) microspheres for biomedical embolic applications. The mean particle diameter follows the relationship: the volume average diameter, D_vad ∝ Y^0.26[VPi]^0.52[AMDMVN]^?0.25[PVA]^0.40T^?8.35Rpm^?0.67, where Y, [VPi], [AMDMVN], [PVA], T, and Rpm are the fractional conversion, concentrations of VPi, AMDMVN, and suspending agent, polymerization temperature, and agitation speed during the polymerization of VPi, respectively. The polydispersity of the particle size distribution of PVPi decreased with decreasing conversion, [AMDMVN], T, and Rpm and with increasing [VPi]. In the case of [PVA], optimization of the suspension stability led to a narrow particle size distribution. Ultrahigh‐molecular‐weights PVPi and PVA (number‐average degrees of polymerization of PVPi (25,000–32,000) and PVA (14,000–17,500), of high syndiotactic diad content (63%), and of high ultimate conversion of VPi into PVPi (85–95%) were obtained by suspension polymerization at 10 °C, followed by saponification. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 789–800, 2005     

Preparation of poly(vinyl pivalate) microspheres by dispersion polymerization in an ionic liquid and saponification for the preparation of poly(vinyl alcohol) with high syndiotacticity

We report here a successful free-radical dispersion polymerization of vinyl pivalate (VPi) in an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][TFSI]) using poly(vinyl pyrrolidone) (PVP) as a stabilizer. Morphological analysis by FE-SEM revealed that poly(vinyl pivalate) (PVPi) obtained from dispersion polymerizations were in the form of spherical particles. Micron-sized, PVPi particles with a number-average molecular weight (M_n) of 166,400 g/mol could be obtained using 5% stabilizer (w/w to monomer) at 65 °C for 20 h. The effects of varying concentration of stabilizer, initiator and monomer upon polymer yield, molecular weight, and morphology of PVPi were also investigated. Analogous polymerizations in dimethyl sulfoxide (DMSO) and bulk served as references. In addition, the preparation of poly(vinyl alcohol) (PVA) by saponification of the resultant PVPi was described.     

Free-radical polymerization of vinyl esters using fluoroalcohols as solvents: Effect of monomer structure on stereochemistry

Free-radical polymerization of vinyl esters including vinyl propionate (VPr), vinyl isobutylate (ViBu), vinyl 2,2-dimethylbutylate (VDMB), vinyl 2,2-dimethylvalerate (VDMV), vinyl 2,2-bis(trifluoromethyl)propionate (VF6Pi), and vinyl benzoate (VBz) was carried out using fluoroalcohols as solvents, and the tacticity of the obtained polymers was determined by NMR analysis of the produced poly(vinyl alcohol) (PVA). The polymerization of VPr, ViBu, VDMB, and VDMV, which are bulkier than VAc, in fluoroalcohols afforded polymers rich in heterotacticity (up to mr = 61%) similar to that of vinyl pivalate (VPi) whereas VAc is known to give a syndiotactic polymer under the reaction conditions used here. The polymerization of VF6Pi, which is the bulkiest among the monomers used in this study, gave a polymer rich in syndiotacticity in bulk and in fluoroalcohols regardless of the structure of the solvents. On the other hand, the polymerization of VBz in fluoroalcohols gave polymers with a higher isotacticity (up to mm = 33%) than bulk polymerization. Thus the monomer structure strongly affected the stereochemistry of the free-radical polymerization of vinyl esters in fluoroalcohols. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2677–2683, 1999     

Viscoelastic behaviors and molecular motions of highly syndiotactic poly(vinyl alcohol) fibers

The viscoelastic behavior and molecular motion of highly syndiotactic poly(vinyl alcohol) (S‐PVA) fibers with a dyad syndiotacticity (r) of 69% were studied by dynamic mechanical thermal analysis and wide‐angle X‐ray diffraction and compared with those of atactic poly(vinyl alcohol) (A‐PVA) fibers with r = 54%. The β_c dispersion, based on the molecular motion of the chain molecules in the crystalline regions, was observed for A‐PVA around 120–140 °C, and the only primary (α_c) dispersion was observed for S‐PVA around 180 °C. The thermal expansion coefficients for the a and c axes of the A‐PVA crystal changed discontinuously around 120 °C, which corresponded to the β_c dispersion. For S‐PVA, the coefficient for the (002) plane changed discontinuously around 100 °C, similarly to A‐PVA, but that for the (100) plane remained unchanged between 20 and 220 °C. These results showed that the intermolecular hydrogen bonding of S‐PVA was stronger in the direction of the a axis than in the other directions, suppressing the β_c dispersion. The storage modulus and thermal expansion coefficient of the (020) plane (molecular axis) of S‐PVA decreased markedly around 180 °C, and this indicated that the α_c dispersion was due to the torsional motion of the molecular chains in the crystalline regions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 800–808, 2004     

Free‐radical copolymerization of vinyl esters using fluoroalcohols as solvents: The solvent effect on the monomer reactivity ratio

Free‐radical copolymerizations of vinyl acetate (VAc = M₁) and other vinyl esters (= M₂) including vinyl pivalate (VPi), vinyl 2,2‐bis(trifluoromethyl)propionate (VF6Pi), and vinyl benzoate (VBz) with fluoroalcohols and tetrahydrofuran (THF) as the solvents were investigated. The fluoroalcohols affected not only the stereochemistry but also the polymerization rate. The polymerization rate was higher in the fluoroalcohols than in THF. The accelerating effect of the fluoroalcohols on the polymerization was probably due to the interaction of the solvents with the ester side groups of the monomers and growing radical species. The difference in the monomer reactivity ratios (r₁, r₂) in THF and 2,2,2‐trifluoroethanol was relatively small for all reaction conditions and for the monomers tested in this work, whereas r₁ increased in the VAc‐VF6Pi copolymerization and r₂ decreased in the VAc‐VPi copolymerization when perfluoro‐tert‐butyl alcohol was used as the solvent. These results were ascribed to steric and monomer‐activating effects due to the hydrogen bonding between the monomers and solvents. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 220–228, 2000     

High molecular weight syndiotacticity-rich poly(vinyl alcohol) gel in aging process

The properties of the aged gels of high molecular weight syndiotacticity-rich poly(vinyl alcohol)s (HMW S-PVAs) with different syndiotactic diad (s-diad) contents were investigated. HMW S-PVA gels with s-diad content of 61.5% and 58.2% showed the rapid increases of the syneresis and the turbidity from the early stage of aging time, which is ascribable to the phase separation, while that with s-diad content of 55.7% did not. From the morphological study, it was confirmed that the phase separation in HMW S-PVA gel with s-diad content of 61.5% occurred without the liquid-liquid phase separation in sol state, whereas both the liquid-liquid phase separation in sol state and the subsequent phase separation in gel state occurred in the case of HMW S-PVA gel with s-diad content of 58.2%. On the other hand, HMW S-PVA gel with s-diad content of 55.7% showed neither the liquid-liquid phase separation in sol state nor the phase separation in gel state in the long period of time. It was also confirmed from wide angle X-ray diffractogram that the crystallization was accompanied by the phase separation in gel state in the aging process of PVA gel. However, the crystallization was hindered by the fast network formation at the initial stage of time. Later the syndiotacticity promoted the crystallization. The tensile modulus of HMW S-PVA gel with higher syndiotacticity increased more significantly with time. Received: 2 December 1999/Accepted: 12 July 2000     

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

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

Effect of stereosequences on crystallinity and properties of zone‐drawn poly(vinyl alcohol) microfibrils

To effectively orient the molecular chains of novel syndiotactic poly(vinyl alcohol) (PVA) microfibrillar fiber (PVA fibril), a high‐temperature zone‐drawing method was adopted. The PVA fibrils were directly prepared from the saponification and in situ fibrillation without a spinning procedure. The maximum draw ratio of the PVA fibril increased with a decrease in the syndiotactic diad (r‐diad) content, indicating that the deformability of PVA molecules was lowered in higher syndiotactic PVA. Degree of crystal orientations up to 0.990 were achieved by stretching the PVA fibril with the r‐diad content of 65.1% and the original degree of crystal orientation of 0.902 at 250 °C close to its crystal melting temperature (T_m). When the same draw ratio was applied to the fibrils, a higher crystal orientation was achieved for the fibrils having higher syndiotacticity. Wide‐angle X‐ray data show that the longitudinal crystal sizes of drawn PVA fibrils were larger in higher syndiotacticities. The degree of crystal orientation, crystallinity, T_m, longitudinal crystal size, and tensile strength of the maximum drawn PVA fibril with a r‐diad content of 65.1% were 0.99, 0.97, 279 °C, 187 Å, and 4.66 N/tex, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1263–1271, 2001     

细乳液聚合法合成高分子量聚乙烯醇的研究

采用十二烷基硫酸钠(SDS)为乳化剂、十六醇(CA)为难溶助剂,引发醋酸乙烯酯(VAc)进行细乳液聚合,以偶氮二异庚腈(ADMVN)为引发剂时,制得了平均聚合度达1.5×104~2.0×104聚醋酸乙烯酯(PVAc)和4.1×103~6.6×103的聚乙烯醇(PVA);以偶氮二脒基丙烷盐酸盐(AAPH)为引发剂时,制得了平均聚合度达1.5×104~2.0×104的PVAc和2.1×103~4.4×103的PVA.研究了引发剂浓度、温度、油水比对产物聚合度、转化率的影响,讨论了SDS∶CA摩尔比对PVAc微球粒径分布及其成粒机理的影响.当cCA∶cSDS=3∶1时得到的细乳液体系稳定性最好,以ADMVN和AAPH引发聚合时均为液滴成核为主,其中以ADMVN引发得到PVAc微球的粒度分布窄于AAPH.     

Synthesis and micellar behavior of poly(vinyl alcohol-<Emphasis Type="Italic">b</Emphasis>-styrene) copolymers containing PVA blocks with different syndiotacticity

Poly(vinyl alcohol-b-styrene) (poly(VA-b-St)) diblock copolymers with different syndiotacticity of poly(vinyl alcohol) (PVA) block were synthesized via consecutive telomerization, atom transfer radical polymerization, and saponification. These amphiphilic block copolymeric micelles were prepared by dialysis against water. Dynamic light scattering and transmission electron micrograph measurements confirmed the formation of a micelles, and the size of a micelle was less than 100 nm and increased with the molecular weight of polystyrene (PS) block. From the fluorescence emission spectrum measurements using pyrene as a fluorescence probe, the copolymers formed micelles with critical micelle concentration (CMC) in the range of 0.125–4.47 mg/l. The CMC values increase with decrease of the molecular weight of the PS block and increase of the syndiotacticity of PVA block. Kinetic stability study of micelles showed increased stability for block copolymers containing PVA block with higher syndiotacticity.     

Morphology of micron-sized monodispersed poly(butyl methacrylate)/polystyrene composite particles produced by seeded dispersion polymerization

In order to develop the seeded dispersion polymerization technique for the production of micron-sized monodispersed core/shell composite polymer particles the effect of polymerization temperature on the core/shell morphology was examined. Micron-sized monodispersed composite particles were produced by seeded dispersion polymerizations of styrene with about 1.4-μm-sized monodispersed poly(n-butyl methacrylate) (Pn-BMA) and poly(i-butyl methacrylate) (Pi-BMA) particles in a methanol/water (4/1, w/w) medium in the temperature range from 20 to 90 °C. The composite particles, PBMA/polystyrene (PS) (2/1, w/w), consisting of a PBMA core and a PS shell were produced with 2,2′-azobis(4-methoxy-2,4-dimethyl valeronitrile) initiator at 30 °C for Pn-BMA seed and with 2,2′-azobis(isobutyronitrile) initiator at 60 °C for Pi-BMA seed. The polymerization temperatures were a little above the glass-transition temperatures (T _g) of both Pn-BMA (20 °C) and Pi-BMA (40 °C). On the other hand, when the seeded dispersion polymerizations were carried out at much higher temperatures than the T _g of the seed polymers, composite particles having a polymeric oil-in-oil structure were produced. Received: 14 October 1998 Accepted in revised form: 2 June 1999     

Solid‐state 13C and 129Xe NMR study of poly(vinyl alcohol) and poly(vinyl alcohol)/lactosilated chitosan gels

Dry and hydrated poly(vinyl alcohol) (PVA) gels with 55% (a‐PVA) and 61% (s‐PVA) syndiotacticity and related PVA/lactyl chitosan (LC) blends have been investigated with ¹²⁹Xe and cross‐polarization/magic‐angle‐spinning ¹³C NMR techniques. Although the dry gels exhibit two broad ¹²⁹Xe resonances in the slow‐to‐intermediate exchange limit, both hydrated gels show three resonances. The corresponding dry blends exhibit two signals, the chemical shifts and line widths of which change with respect to those of pure PVA, whereas one (a‐PVA/LC) or two (s‐PVA/LC) signals appear in the spectra of the hydrated blends. A comparative analysis of the data demonstrates that LC rearranges the domains of the polymeric matrix in both the dry and hydrated blends according to the syndiotacticity of the PVA chains. Information on the molecular motions of the amorphous and swollen polymeric domains in the kilohertz range has been obtained from an analysis of the spin‐lattice relaxation times. These data indicate that the dynamics and arrangement of the PVA chains in the gels are strongly affected by their tacticity and the addition of the copolymer LC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3123–3131, 2003     

The negative biodegradation of poly(vinyl alcohol) modified by aldehydes

Due to the wide application of PVA acetals, the biodegradation of PVA modified by formaldehyde, n-butyraldehyde, glyoxaldehyde and glutaraldehyde was conducted in an intensive biodegradation environment. Spectrophotometric analysis and weight loss were used to determine the biodegradation of PVA, and the changes of the mechanical properties of PVA acetals were also studied.An obvious decrease in biodegradation levels of all the modified samples was found, and a decrease in biodegradation level with increasing degree of acetals of PVA. The biodegradation of poly(vinyl formal) is better than poly(vinyl butyral) with the same degree of acetals whereas the biodegradation levels of poly(vinyl glyoxal) are lower than poly(vinyl glutaral) which has the same degree of crosslinking. The difference between the FT-IR of the samples before and after biodegradation indicated scission of residual PVA chain during the process.     

Effect of syndiotacticity on the aqueous poly(vinyl alcohol) gel 4. X-ray diffraction analysis of gel

Summary The structure of syndiotacticity-rich poly(vinyl alcohol) (PVA)-water gel was investigated by the X-ray diffraction analysis. Diffuse haloes appeared in the gel prepared from lower aqueous solution of PVA (5 wt%) but diffraction pattern became sharper with increasing concentration of PVA. Thed-spacings of gels and films are agreed with each other. The half height width of value of peak position of (101) obtained by photodensitometer decreased with increasing syndiotacticity of PVA. The radius of gyration of gel obtained from theGuinier's plots by the small angle X-ray diffraction increases with increasing syndiotacticity. These results suggest that the syndiotactic sequence length increases with increasing content of syndiotacticity and the crystallites in gel networks become also larger with increasing syndiotacticity. The average size of gel junction is 73–89 Å (s-(diad)% = 49.₄-66.₂).

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Zusammenfassung Es wurden mit Röntgeninterferenzen die Strukturen von einem Polyvinylalkohol-Wasser-Gel mit syndiotaktisch angereichertem Polyvinylalkohol untersucht. Es erscheinen diffuse Halos in dem Gel, das aus niedrigeren wäßrigen Lösungen (5% PVA) präpariert wurde. Doch wurden die Beugungsinterferenzen schärfer mit steigender Konzentration an PVA. Died-Abstände in Gelen und Filmen stimmten miteinander überein. Die Halbwertsbreite der 101-Interferenzen, gemessen mit einem Photodensitometer, nahm mit steigender Syndiotaktizitat des PVA ab. Der Trägheitsradius des Gels aus Guinier-Auftragungen für die Kleinwinkelstreuung nimmt mit steigender Syndiotaktizitat zu. Diese Ergebnisse legen nahe, daß die syndiotaktische Segmentläange mit steigendem Gehalt an Syndiotaktizitat zunimmt und daß die Kristallite in den Gelnetzwerken mit zunehmender Syndiotaktizität gröBer wurden. Die mittlere Größe des Netzwerkabstandes ist 73–89 Å (s-(diad)% = 49.₄-66.₂).

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With 7 figures in 15 details and 3 tables     

Cyclopolymerization of divinyl esters of dibasic acids and structure of poly(vinyl alcohol) derived from the polymers

Divinyl esters of dibasic acids, CH₂?CHOCO(CH₂)_n?2COOCH?CH₂, n = 2–10, were synthesized and polymerized with a radical initiator, and the structure of poly(vinyl alcohol)(PVA) derived from the polymers were studied. The cyclopolymerizability of these monomers was nearly equal to or less than that of divinyl carbonate which was previously reported, and the extent of cyclization was 15–65%. All the monomers yielded gelled polymers. The monomers which are to yield even-membered rings tend to cyclopolymerize more easily than those of odd-membered rings. PVA derived from these polymers showed a similar structure with respect to 1,2-glycol content and stereoregularity to that from poly(vinyl acetate).     

Cobalt‐mediated radical polymerization routes to poly(vinyl ester) block copolymers

Cobalt‐mediated radical polymerizations (CMRPs) utilizing redox initiation are demonstrated to produce poly(vinyl ester) homopolymers derived from vinyl pivalate (VPv) and vinyl benzoate (VBz), and their block copolymers with vinyl acetate (VAc). Combining anhydrous Co(acac)₂, lauroyl peroxide, citric acid trisodium salt, and VPv at 30 °C results in controlled polymerizations that yield homopolymers with M_n = 2.5–27 kg/mol with M_w/M_n = 1.20–1.30. Homopolymerizations of scrupulously purified VBz proceed with lower levels of control as evidenced by broader polydispersities over a range of molecular weights (M_n = 4–16 kg/mol; M_w/M_n = 1.34–1.65), which may be interpreted in terms of the decreased nucleophilicity of these less electron donating propagating polymer chain ends. Based on these results, we demonstrate that sequential CMRP reactions present a viable route to microphase separated poly(vinyl ester) block copolymers as shown by small‐angle X‐ray scattering analyses. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010