Heterotactic poly(vinyl alcohol)

Bulky substituents in vinyl trialkylsilyl ethers and vinyl trialkylcarbinyl ethers led to heterotactic polymers (H = 66%). The polymers were converted into poly(vinyl alcohol) (PVA) and further to poly(vinyl acetate), and tacticity was determined as poly(vinyl acetate). Vinyl triisopropylsilyl ether in nonpolar solvents yielded a heterotactic polymer with a higher percentage of isotactic triads than syndiotactic triads (Hetero-I). Vinyl trialkylcarbinyl ethers in polar solvents gave a heterotactic polymer with more syndiotactic triads than isotactic (Hetero-II). Heterotactic PVA was soluble in water and showed characteristics infrared absorptions. Interestingly, Hetero-I PVA showed no iodine color reaction, but Hetero-II showed a much more intense color reaction than a commercial PVA. The mechanism of heterotactic propagation was discussed in terms of the Markóv chain model.     

Synthesis of high-molecular-weight poly(vinyl alcohol) with high yield by novel one-batch suspension polymerization of vinyl acetate and saponification

Generally, owing to tautomerism of vinyl alcohol monomer, poly(vinyl alcohol) (PVA) cannot be obtained by direct polymerization but it can be obtained by the saponification of poly(vinyl ester) precursors such as poly(vinyl acetate) (PVAc). In this study, to obtain high-molecular-weight (HMW) PVA with high yield through a one-batch method, we tried continuous saponification of PVAc prepared by suspension polymerization of vinyl acetate (VAc). We controlled various polymerization conditions, such as polymerization temperature, initiator concentration, suspending agent concentration, agitation speed, and VAc/water ratio, and obtained PVAc with a maximum conversion of VAc into PVAc of over 95-98%. PVA beads having various molecular parameters were prepared by continuous saponification of PVAc microspheres. Despite our employing a one-batch process, a maximum degree of saponification of 99.9% could be obtained. Continuous heterogeneous saponification of prepared PVAc yielded HMW PVA having a number-average degree of polymerization of 2,500-5,500, a syndiotactic diad content of 51-52%, and degree of saponification of 85.0-99.9%.     

Structure–property relationships of poly(vinyl alcohol). I. Influence of polymerization solvents and temperature on the structure and properties of poly(vinyl alcohol) derived from poly(vinyl acetate)

The solubility properties of poly(vinyl alcohol) (PVA) vary with the method of preparation of the poly(vinyl acetate) (PVAc) from which it is derived. PVAc was prepared with free-radical catalysts over a range of temperatures from ?78 to 90°C. with solvents of varying chain-transfer ability. The corresponding PVA samples varied in their resistance to dissolution in water. Their high-resolution proton nuclear magnetic resonance spectra showed on differences in tacticity. Data on 1,2-diol content showed only minor differences. Hence, the increase in resistance of PVA to dissolution in water arising from changes in chain-transfer activity of the solvent used in vinyl acetate polymerization is largely attributable to a decrease in molecular weight, and the increase in resistance of PVA to dissolution in water arising from a decrease in the temperature of the vinyl acetate polymerization is largely attributable to a decrease in both long and short branches. Evidently, with polar polymers having small side groups, tacticity is not the only factor influencing property variation; that is, variations in stereoregularity influence more the crystallinity of the sample as measured by density or x-ray methods than the ultimate crystallizability under conditions of mechanical and thermal treatment. In this regard polar polymers having small side groups differ from nonpolar polymers.     

Synthesis and characterization of some trithiols

The preparation of 1,3,5-pentanetrithiol is described to provide model systems for poly(vinyl mercaptan). In addition, the preparation and identification of the three stereoisomers of 2,4,6-heptanetriol are reported as models for isotactic, syndiotactic, and heterotactic poly(vinyl mercaptan).     

NMR study of poly(vinyl formate)

The high resolution nuclear magnetic resonance spectrum of poly(vinyl formate), yielded, upon examination at 100 Mc./sec., and under the conditions of decoupling, information on the three tactic forms present. The normal and decoupled spectra indicate that only the CHO resonance is sensitive to the stereochemical configuration. The three components of the CHO resonance are tentatively assigned to isotactic (i), heterotactic (h), and syndiotactic (s) triads with increasing field strength, respectively. This assignment was made on the basis of poly(vinyl alcohol) and poly(vinyl acetate) derived from poly(vinyl formate). The results show that the tacticity is slightly dependent upon the temperature of free-radical polymerization.     

Vibrational assignments for the CCL stretching region of the Raman spectrum of poly(vinyl chloride)

It is shown that, by assuming that each of the peaks resolved in the CCl stretching region of the Raman spectra of a series of poly(vinyl chloride) gels can be associated with a definite triad structure, most of the peaks can he assigned to syndiotactic, isotactic, or heterotactic triad configurations without reference to the spectra of model compounds or to vibrational calculations. The results are in general agreement with most previous assignments except for the assignment of the peak at 646 cm^–1. Previously this was assigned to syndiotactic material, but it is here assigned to a structure consisting of consecutive syndiotactic, isotactic, and syndiotactic placements in a conformation not very distorted from the planar zigzag conformation.     

Effect of solvent for vinyl acetate polymerization on microstructure of poly(vinyl alcohol)

The solution polymerization of vinyl acetate was carried out in several solvents at 0 to 100°C, using 2,2′-azobisisobutyronitrile as initiator. For the resulting poly(vinyl alcohol) (PVA), iodinecoloration, 1,2-glycol structure and tacticity were observed. The pentad tacticity of PVA was estimated from its methine carbon spectra by means of ¹³C-FTNMR spectrometer. Iodine-coloration ability of PVA varied markedly with the type of polymerization solvent and decreased in the following order: phenol > aq. phenol > methyl alcohol > ethyl acetate > DMSO, ethylene carbonate. The syndiotactic fraction in PVA also decreased with polymerization solvent in the same order as that of iodine coloration, while 1,2-glycol content of PVA was not almost affected by polymerization solvent except for phenol and aq. phenol. In solution polymerization performed, effect of polymerization temperature on tacticity was less than that of solvent.     

Fluorine NMR spectra of poly(vinyl trifluoroacetate)

Samples of poly(vinyl trifluoroacetate) with differing stereosequences have been prepared. The NMR signals at 56.4 Mc./sec. corresponding to the three types of triadstereosequences of the trifluoroacetate groups (isotactic, heterotactic, and syndiotactic) can be resolved. The results for specific polymers are discussed.     

Block copolymers of poly(ethylene oxide) and poly(vinyl alcohol) synthesized by the RAFT methodology

A methodology for the synthesis of well‐defined poly(ethylene oxide)‐block‐poly(vinyl alcohol) (PEO‐b‐PVA) and PVA‐b‐PEO‐b‐PVA polymers was reported. Novel xanthate end‐functionalized PEOs were synthesized by a series of end‐group transformations. They were then used to mediate the reversible addition–fragmentation chain transfer polymerization of vinyl acetate to obtain well‐defined poly(ethylene oxide)‐b‐poly(vinyl acetate) (PEO‐b‐PVAc) and PVAc‐b‐PEO‐b‐PVAc. When these block copolymers were directly hydrolyzed in methanol solution of sodium hydroxide, polymers with brown color were obtained, which was due to the formation of conjugated unsaturated aldehyde structures. To circumvent these side reactions, the xanthate groups were removed by adding a primary amine before hydrolysis and the products thus obtained were white powders. The polymers were characterized by gel permeation chromatography, ¹H NMR spectroscopy and FT‐IR. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1901–1910, 2009     

NMR study of model compounds of vinyl polymers

Complicated NMR spectra of vinyl polymers provide conformational and configurational knowledge of the polymers in solution. Explicit expressions for the spectral frequencies and intensities are obtained by the analysis of vinyl polymers and their model compounds as weakly coupled systems. The classified spectra expected for common vinyl polymers are presented by using the results of the analysis. The analysis is applied to model compounds of poly(vinyl alcohol) and poly(vinyl acetate) in solution. The results show that conformations of poly(vinyl alcohol) are determined by the intramolecular hydrogen bonding so that the syndiotactic isomer forms a helical structure, the isotactic one a planar zigzag structure. The poly(vinyl acetate) produces a helical structure for isotactic isomer by the repulsion of side chains and a planar zigzag for the syndiotactic isomer.     

Role of grafting in the emulsion polymerization of vinyl acetate with poly(vinyl alcohol) as an emulsifier. I. Effect of the degree of blockiness on the kinetics and mechanism of grafting

The role of grafting in particle nucleation during the emulsion polymerization of vinyl acetate with partially hydrolyzed poly(vinyl alcohol) (PVA) as an emulsifier and potassium persulfate as an initiator was investigated. The polymerizations were carried out in batch with a low solids (10%) recipe. An automated reaction calorimeter (Mettler RC1) was used for the direct monitoring of the kinetics of emulsion polymerizations with three medium molecular weight PVAs differing in their degrees of blockiness (Poval 217EE > 217E > 217). Smith–Ewart case 1 kinetics (average number of free radicals per particle < 0.5) were followed in all cases, and no constant rate in interval II was observed. Contrary to what was expected, a nonlinear relationship was observed between the rate of polymerization (R_p) and the number of particles (N_p). At R_{p max,} N_p (217E) > N_p (217EE) > N_p (217), and the final N_p was independent of the degree of blockiness of PVA. The particle size distributions were broad (particle diameter = 20–100 nm) and bimodal. On the basis of these data, we concluded that particle nucleation was continuous and was accompanied by extensive limited aggregation during the particle growth stages. The evolution of the amounts of grafted PVA and poly(vinyl acetate) (PVAc) were determined in polymerizations employing the two PVAs differing the most in blockiness (Poval 217EE and 217). The grafted PVAc followed similar profiles, increasing with conversion, particularly near the end of the two reactions. The amounts of grafted PVAc were about the same in the final latexes (37–39%). In contrast, the grafting of PVA was nearly complete by the time monomer droplets had disappeared in each reaction (25% conversion). However, the extent of grafting differed significantly, with the blockier PVA having about one‐third the grafting of the more random PVA (～10% vs ～30%). In these low solids recipes, grafting appeared to be primarily a solution event, occurring predominantly in the aqueous phase and not at the particle/water interface, as was previously speculated. The PVAc grafts grew until the molecules became water‐insoluble and precipitated, forming polymer particles. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3633–3654, 2001     

Correlation of thermal degradation mechanisms: Polyacetylene and vinyl and vinylidene polymers

The thermal degradation of poly(vinyl bromide) (PVB), poly(vinyl chloride) (PVC), poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), poly(vinyl fluoride) (PVF), poly(vinylidene chloride) (PVC₂), and poly(vinylidene fluoride) (PVF₂) has been studied by direct pyrolysis–mass spectrometry (DP-MS) and flash pyrolysis–gas chromatography–mass spectrometry techniques. Vinyl and vinylidene polymers exhibit two competitive thermal degradation processes: (1) HX elimination with formation of polyene sequences which undergo further moleculaar rearrangements, and (2) main-chain cleavage with formation of halogenated or oxigenated compounds. The overall thermal degradation process depends on the prevailing decomposition reaction in each polymer; therefore, different behaviors are observed. The thermal degradation of polyacetylene (PA) has also been studied and found important for the elucidation of the thermal decomposition mechanism of the title polymers.     

Characterization of poly(vinyl alcohol) during the emulsion polymerization of vinyl acetate using poly(vinyl alcohol) as emulsifier

During the emulsion polymerization of vinyl acetate (VAc) using poly(vinyl alcohol) (PVA) as stabilizer and potassium persulfate as initiator, the VAc reacts with PVA forming PVA-graft-PVAc. When the grafted polymer reaches a critical size it becomes water-insoluble and precipitates from the aqueous phase contributing to the formation of polymer particles. Since particle formation and therefore the properties of the final latex will depend on the degree of grafting, it is important to quantify and to characterize the grafted PVA. In this work, the quantitative separation and characterization of the grafted water-insoluble PVA was carried out by a two-step selective solubilization of the PVAc latex, first with acetonitrile to separate PVAc homopolymer, followed by water to separate the water-soluble PVA from the remaining acetonitrile-insoluble material. After the separation, the water-soluble and water-insoluble PVA were characterized by Fourier Transform Infrared (FTIR) spectroscopy and ¹H and ¹³C nuclear magnetic resonance (NMR) analyses, from which the details of the PVA-graft-PVAc structure were obtained. © 1996 John Wiley & Sons, Inc.     

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     

Synthesis of Poly(Vinyl Alcohol) and/or Poly(Vinyl Acetate) Particles with Spherical Morphology and Core-Shell Structure and its Use in Vascular Embolization

Poly(vinyl alcohol), PVA, is the most frequently used material in embolization of tumors, aneurisms and arteriovenous malformations due to its low toxicity, good biocompatibility and desirable physical properties. It is well known that PVA particles cannot be prepared by direct polymerization of vinyl alcohol. Its synthesis is typically performed by the suspension polymerization of vinyl acetate to produce poly(vinyl acetate), PVAc, followed by the saponification of the PVAc particles. This work shows that, using the suspension polymerization technique, it is possible to obtain spherical particles with a core-shell structure of PVA/PVAc with regular morphology, instead of particles with irregular shapes and sizes, as usually found in many commercial embolization products. Therefore, this work presents the production of PVA/PVAc spherical particles that can be used to occlude blood vessels, eliminating the disadvantages of commercial PVA. In vivo clinical tests with white “New Zealand” rabbits undergoing kidney inflammation reaction have shown that these spherical particles are much more efficient for vascular embolization.     

Stereoregular poly(methacrylic acids)

A convenient method is described for the preparation of isotactic and syndiotactic poly(trimethylsilyl methacrylates) by using the monomer trimethyl silyl methacrylate and butyllithium initiation in toluene and tetrahydrofuran, respectively. The structure of these polymers enables complete hydrolysis to the corresponding poly(methacrylic acids), which were characterized with respect to tacticity and molecular weight. The asymmetric induction in toluene produced 89% isotactic polymer, while that in tetrahydrofuran gave polymer <90% syndiotactic and heterotactic in terms of triads. A method of fractionation of the polyelectrolytes by gel-permeation chromatography on a preparative scale was shown to be applicable.     

Poly(vinyl alcohol) obtained through polymerization of some vinyl esters

Bulk and/or solution polymerizations of a series of vinyl esters, e.g., vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, and vinyl benzoate were conducted. Iodine-coloration, 1,2-glycol structure, molecular weight, and tacticity (triad and pentad) were measured for the resulting poly(vinyl alcohol)s (PVAs). The iodine-coloration abilities of PVAs, derived from poly(vinyl ester)s that were obtained through bulk polymerization at 60°C, depended on the starting monomer, increasing in the following order: vinyl benzoate < vinyl acetate < vinyl propionate < vinyl butyrate < vinyl pivalate. In solution polymerizations of vinyl propionate and vinyl butyrate, it was revealed that the tacticity of the derived PVAs apparently depended on the type and amount of polymerization solvent employed, as found previously in the case for vinyl acetate. The iodine-coloration of these PVA samples varied in the same order as their syndiotactic content, while no relationship was observed toward their 1,2-glycol content. The probabilities of the syndiotactic propagation at 60°C were estimated as 0.49 (benzoate), 0.54 (acetate), 0.55 (propionate), 0.56 (butyrate), and 0.60 (pivalate), respectively.     

Adsorption of stereoregular poly(vinyl alcohols) at air-water interface

Summary The time dependency of the surface tension of the aqueous solutions of syndiotactic, isotactic and atactic poly(vinyl alcohols) (PVAs) for various concentrations were studied.The rate of the decrease in the surface tension was highest for syndiotactic PVA and lowest for atactic PVA at the same concentration. The results were analysed as crystallization and diffusion processes. The rate is controlled by an intermolecular hydrogen bond formation of syndiotactic sequences at the surface for syndiotactic PVA and the easy arrangement of segments at the surface for isotactic and syndiotactic PVAs to influence the rate of diffusion of PVA molecules.A filament could be made by picking up the multilayer formed at the surface of the syndiotactic PVA solution. The filament had the high orientation of PVA molecules and the similar properties as that from commercial PVA.

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Zusammenfassung Die Zeitabhängigkeit der Oberflächenspannung der wäßrigen Lösungen von syndiotaktischem, isotaktischem und ataktischem Poly(vinylalkohol) (PVA) wurde für verschiedene Konzentrationen untersucht.Die Geschwindigkeit der zeitlichen Zunahme der Oberflächenspannung für das syndiotaktische PVA war die höchste und diejenige für ataktischen PVA die niedrigste. Die Ergebnisse wurden als Folge der Kristallisation und der Diffusionsprozesse gedeutet. Die Geschwindigkeit wird auf Grund einer zwischenmolekularen Wasserstoffbriickensbildung der syndiotaktischen Sequenzen bei syndiotaktischem PVA an die Oberfläche und mit der leichteren Einordnung der Segmente der isotaktischen und ataktischen PVA-Moleküle erklärt. Dies-beeinflußt die Diffusionsgeschwindigkeit der PVA-Moleküle entsprechend.Man kann einen Faden dadurch spinnen, daß man die an die Oberfläche erzeugte Multischicht herauszupft. Das Filament hat die hohe Orientierung der PVA-Moleküle und ähnliche Eigenschaften wie die im Handel befindlichen PVAFasern.

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With 6 figures and 5 tables     

Synthesis and Characterization of a Diblock Copolymer of Methyl Methacrylate and Vinyl Acetate by Successive Photo‐Induced Charge Transfer Polymerization Using Ethanolamine as the Parent Compound

Communication: A diblock copolymer consisting of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) with hydroxyl group at one end is prepared by successive charge transfer polymerization (CTP) under UV irradiation at room temperature using ethanolamine and benzophenone as a binary initiation system. The diblock copolymer PMMA‐b‐PVAc could be selectively hydrolyzed to the block copolymer of poly(methyl methacrylate) and poly(vinyl alcohol) (PVA) using sodium ethoxide as the catalyst. Both copolymers, PMMA‐b‐PVAc and PMMA‐b‐PVA, are characterized in detail by means of FTIR and ¹H NMR spectroscopy, and GPC. The effect of the solvent on CTP and the kinetics of CTP are discussed.     

Effect of a few repeating stereosequences on electrical space charge behavior of poly(methyl methacrylate)

Three films of poly(methyl methacrylate) (PMMA) (samples X, Y, and Z) were prepared by compression molding of purified polymers as polymers having different tacticities. They were exhaustively characterized by ¹H NMR spectroscopy so as to be able to evaluate the differences in content of the repeating stereosequences:… mmrm … (termini of isotactic sequences); …. rrrmr (breaking off syndiotactic sequences; pure heterotactic … mrmr … moistures; and atactic parts. By applying the so‐called thermal step method, the behavior in space charge showed a priority charge injection from both electrodes and some polarization at the cathode. Some strong differences between the samples were evidenced and they accurately agree with the variations in the above repeating stereosequences for the samples. The results allow to define every stereosequence as specific trap of the distinct sorts of space charge, namely injection from the anode or the cathode and polarization. These attributions are common with those proposed for poly(vinyl chloride) (PVC) and poly(propylene) (PP) in earlier work. Conversely, whether the priority charge is of injection or polarization type, depends markedly on the type of polymer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 633–639, 2009