Structure–Property relationships of poly(vinyl alcohol). III. Relationships between stereo-regularity,crystallinity, and water resistance in poly(vinyl alcohol)

Structure–property relationships of poly(vinyl alcohol) have been studied by measuring the crystallinity and water resistance of films derived from samples of varying, known tacticity. Crystallinities of unannealed and annealed films were examined by means of density, infrared, and x-ray measurements. Higher tacticity did not lead to higher crystallinity. The apparent order of crystallizability was atactic ≧ syndiotactic-rich ? isotactic-rich. Water resistance of these films was determined by measuring the swelling index at 30°C. and solubility at 70 and 130–140°C. Water resistance increases as tacticity increases, with syndiotactic-rich PVA exhibiting the highest water resistance. Since water resistance also increases with crystallinity, both stereoregularity and crystallinity must be considered when evaluating structure–solubility relationships. Differential thermal and thermogravimetric analyses of these samples are also presented, together with a correlation of tacticity index as measured by an infrared technique with that of an NMR technique.     

Perturbed enantiomorphic-site model

The perturbed enantiomorphic-site (E) model was developed for the analysis of tacticity of Ziegler-Natta polymers. Theoretical probability expressions for tacticity diads, triads, tetrads and pentads were derived, and a computer program incorporating perturbed enantiomorphic-site and Bernoullian models was written to facilitate NMR analysis. Examples are shown of the use of the perturbed models to study the ¹³C NMR tacticity of poly(propylene) made with homogeneous metallocene catalysts. The perturbed E model is shown to be a suitable theoretical framework for the analysis of many polymers made with these catalysts.     

丙烯丁烯共聚物的组成和等规度分布

丙烯丁烯共聚物的组成和等规度分布徐君庭封麟先杨士林（浙江大学高分子科学与工程学系杭州３１００２７）关键词丙烯丁烯共聚物，Ｚｉｅｇｌｅｒ Ｎａｔａ催化剂，分级用负载型Ｚｉｅｇｌｅｒ Ｎａｔａ催化剂制备的聚丙烯其等规度往往分布较宽，具有一定的分散性...     

Polymerization of coordinated monomers. III. Copolymerization of acrylonitrile–zinc chloride,methacrylonitrile–zinc chloride or methyl methacrylate–zinc chloride complex with styrene

The 1:1 or 2:1 complex of acrylonitrile, methacrylonitrile, or methyl methacrylate with ZnCl₂ was copolymerized with styrene at the temperature of 0–30°C without any initiator. The structure of the copolymer from methyl methacrylate complex and styrene was examined by NMR spectroscopy. The complexes of acrylonitrile or methacrylonitrile with ZnCl₂ gave a copolymer containing about 50 mole-% styrene units. The complexes of methyl methacrylate yielded an alternating copolymer when the feed molar ratio of methyl methacrylate to styrene was small, but with increasing feed molar ratio the resulting copolymer consisted of about 2 moles of methyl methacrylate per mole of styrene. The formation of a charge-transfer complex of styrene with a monomer coordinated to zinc atom was inferred from the ultraviolet spectra. The regulation of the copolymerization was considered to be effected by the charge-transfer complex. The copolymer resulting from the 2:1 methyl methacrylate–zinc chloride complex had no specific tacticity, whereas the copolymer from the 1:1 complex was richer in coisotacticity than in cosyndiotacticity. The change of the composition of the copolymer and its specific tacticity in the polymerization of the methyl methacrylate complex is related to the structure of the complex.     

Statistical models in the study of stereospecific polymerization

Triad tacticity data obtained by NMR analysis have previously been interpreted in terms of two basic statistical models in order to elucidate the stereospecific polymerization mechanism. In this paper the characteristics of these two basic models for stereospecific polymerization, the enantiomorphic-sites (EMS) model, and the polymer-end control (PEC) model, are examined and compared. The tacticity values accessible to the two-parameter EMS model, which includes the influence of the chain end unit, are shown to be highly restricted. Only about 20% of the isotacticity versus syndiotacticity plot is accessible to this model. To this extent the consistency of a set of triad tacticity data with the model can be tested. No such tacticity limits are exhibited by the two-parameter PEC model, which includes the influence of the penultimate unit. Any set of tacticity values which can be interpreted in terms of the two-parameter EMS model can also be interpreted in terms of the two-parameter PEC model.     

Polymerization of vinylpyridinium salts. III. Further studies on the interfacial and isotropic polymerization of 4-vinyl-N-methylpyridinium methylsulfate

In the present study the polymerization of 4-vinyl-N-methylpyridinium methylsulfate at liquid–liquid interfaces is investigated. Various experimental procedures that may favor the interfacial mode of polymerization over the isotropic one are discussed. The effectiveness of the methods was evaluated by physical characterization studies and particularly polymer tacticity. This last property is directly associated with the achieved organization of the monomers at interfaces. ¹³C-NMR technique was used for tacticity determination. According to tacticity, random polymers are primarily obtained that result from an isotropic polymerization in the aqueous phase, where the monomer is extremely soluble. The small predominance of the syndiotactic triad over the isotactic one is explained by the occurrence of an interfacial polymerization induced by the orientation of the monomers. A polymerization model is proposed that justifies the stereospecificity modification of polymerization.     

The sequence length in polymethyl methacrylate

The sequence length and tacticity of methyl methacrylate polymers prepared at 303–363°K in the presence of trichlorobromomethane as a transfer agent were measured from NMR spectra. The lengths did not change appreciably but there was an increase in syndiotacticity with increasing concentration of transfer agent. There is no marked change in tacticity with molecular weight.     

负载型催化剂制备的聚丙烯等规度分布

负载型Ziesler－Natta催化剂中存在许多活性中心［'3，为了解其本质，需对其各自产生的聚合物进行分离，以往采用的溶剂抽提法［'－'j只能将聚合物大致分级．最近，升温淋洗分级法（TREF）已被运用于聚丙烯的分级卜，'，其原理是根据聚合物的结晶度分级D'，影响聚丙烯结晶性的主要因素是等规度，而分子量到达一定程度后其影响较小，故通过TREF分级可得到聚丙烯的等规度分布．TREF法的淋洗温度可控，故分级效果较好．该法在分级前需对样品进行等温结晶处理，以消除抽提法由于样品未必充分结晶而带来的误差．本文用TREF法对不同催化…     

甲基丙烯酸甲酯原子转移自由基聚合等规度研究

在0～100℃温度范围内,由原子转移自由基聚合方法,采用助催化和非助催化体系,引发甲基丙烯酸甲酯聚合,利用¹³CNMR测定聚甲基丙烯酸甲酯的等规度.发现原子转移自由基聚合仍以间同立构为主,随着聚合温度的升高间同立构等规度降低,与通常自由基聚合对有规立构控制特征相似.助催化剂异丙醇铝和活性端羰基配位,对聚合物的立构规整性有一定的影响.     

聚合温度对聚甲基丙烯酸三丁基锡酯等规度的影响(Ⅰ)

本文测定了0—130℃温度范围内,由~(60)Co-γ射线和两种活性不同的引发剂引发聚合的聚甲基丙烯酸三丁基锡酯的等规度。利用~(13)C-NMR测定聚合物分子链的等规度,如预料的那样,以间同立构为主,并随着聚合温度的升高间同立构等规度降低。作者认为影响聚合物等规度的因素主要是取代基的极性效应。计算出的控制等规度的活化能参数与聚甲基丙烯酸甲酯和聚甲基丙烯酸三甲基锡酯的属同一数量级,可相互比较。     

Evaluation of molecular mass and tacticity of polyvinyl alcohol by non-equilibrium capillary electrophoresis of equilibrium mixtures of a polymer and a dye

Non-equilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) has been used to characterize polyvinyl alcohol (PVA). Commercial PVA samples with different molecular masses, from M(w)=15 up to 205 kDa, were used. According to the (13)C NMR spectra, the samples also differed in tacticity (stereoregularity). Mixtures of PVA and the anionic azo-dye Congo Red (CR) were injected in the presence of a borate buffer. The electropherograms gave a band and a peak due to the residual PVA-CR complex and the excess dye, respectively, plus a superimposed exponential decay due to the partial dissociation of the complex during migration. The stoichiometry of the PVA-CR complex, q=[monomer]/[dye], reached a maximum, q(sat), which depended on both M(w) and tacticity of PVA. Thus, q(sat) decreased from a molar ratio of ca. 4.9 to 3.6 at increasing M(w) values, this variation also being largely dependent on tacticity. A similar dependence of the electrophoretic mobility of the complex on both M(w) and tacticity was also observed. A possible explanation, based on the formation of a stack of CR ions inside the PVA-CR complex, was proposed and discussed. Finally, at increasing M(w) values, the stability constant of the complex increased slightly, and the pseudo-first order dissociation rate of the complex decreased, this later parameter also showing a dependence on both M(w) and tacticity.     

A segment concept in the dissolution of stereoregular isotactic polyacrylonitrile into three dinitrile solvents, CN-(CH2) n -CN (n = 1, 2, and 3), at elevated temperatures

The dependence of the dissolution temperature (T _sol) of isotactic polyacrylonitrile (PAN) on tacticity was studied for three dinitrile solvents. A linear relationship was obtained in the inverse plots of the tacticity dependence of the T _sol of PAN. A phenomenological analogy between the tacticity dependence of the T _sol of isotactic PAN and the molecular-weight dependence of the glass-transition temperature of amorphous polystyrene is discussed from a thermodynamic point of view. The linear relationships in both phenomena are explained in terms of a common mechanism: a breakdown of thermodynamic competition, enthalpy, and entropy through the segment mobility. The significance of segment concept and molecular mobility at elevated temperatures are discussed. Received: 7 July 1999/Accepted in revised form: 21 October 1999     

Poly(alkyl α-chloroacrylates). V. Preparation and properties of methyl,ethyl, and isopropyl polymers of varied tacticity

Polymers of different tacticities, from highly isotactic to highly syndiotactic, were prepared from methyl, ethyl, and isopropyl α-chloroacrylates. These polymers were characterized for tacticity by infrared spectroscopy and 100 and 300 MHz nuclear magnetic resonance (NMR) and for thermal properties by differential scanning calorimetry (DSC). After corrections were made for molecular weight effects, the observed glass temperature-tacticity results were analyzed, and it was determined that the maximum differences in glass temperatures of the purely isotactic compared to the purely syndiotactic polymers should be 92°C for the methyl ester, 86°C for the ethyl ester, and 68°C for the isopropyl ester polymers. The highly isotactic polymers of all three esters were crystalline. Possible polymerization reaction mechanisms are discussed on the basis of the triad and tetrad tacticity values observed and the calculated propagation statistics.     

Preparation of p-[(S)(—)-2-phthalimidopropionyl] polystyrene

Samples of atactic and isotactic polystyrene were acylated with N-phthaloyl-L -alanyl chloride under the conditions of Friedel-Crafts reaction. The degree of acylation was strongly dependent on molecular weight, but not on the tacticity of polystyrene. Similarly the specific rotation of acylated polymers was not influenced by the structure of the polymer chain.     

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.     

Cationic polymerization of p-substituted α-methylstyrenes. III. Effect of polymerization conditions on tacticity and molecular weight for p-chloro-α-methylstyrene

The cationic polymerization of p-chloro-α-methylstyrene was investigated for the effect of initiator and solvent on polymer tacticity, molecular weight, and molecular weight distribution. The products were generally crystalline polymers of 80–90% syndiotactic content with fairly high molecular weights and broad molecular weight distributions. Tacticities and molecular weight distributions followed similar patterns suggesting that the effect of reaction conditions on ionpair end-group structures was the dominant factor.     

Nouvelle méthode de détermination des taux de réativité des copolymères par résonance magnétique nucléaire: Application aux poly(méthacrylate de méthyle–chlorure de vinylidène)

Constant-composition copolymers of methyl methacrylate and vinylidene chloride produced by radical copolymerization are studied by ¹H-NMR at 60 and 250 MHz. The different methods of the literature for the derivation of reactivity ratios from either the copolymer composition or the sequence average lengths, or even the diad distribution, are applied but lead to rather dispersed results. A new graphical method is proposed, based on the use of peculiar values of the triad distribution functions. It allows us to detect a penultimate effect for the vinylidene chloride-rich region. In the same range, a change in tacticity of the diads and triads on the methylmethacrylate sequences, as compared with homopolymers, is observed; it suggests that the anomaly is caused by the competition of the depropagation reaction.     

Sequence analysis of ethylene sulphide-propylene sulphide copolymers by carbon-13 nuclear magnetic resonance

Ethylene sulphide-propylene sulphide copolymers, prepared with anionic type catalysts, have been investigated by ¹³C NMR. The peaks have been assigned both in terms of diad and triad monomer sequences and in terms of tacticity. It has been shown that the propylene sulphide monomer units were directionally oriented and the tacticity was approximately random. We have also determined the effect of methyl substitution in various positions on the chemical shift of the main chain carbon atoms.     

Effect of Hydrogen,Electron Donor,and Polymerization Temperature on Poly(propylene) Microstructure

Summary: Polypropylene made with an industrial heterogeneous Ziegler-Natta catalyst was characterized using high temperature GPC, ¹³C NMR, and Crystallization Elution Fractionation (CEF). The effect of hydrogen and electron donor during polymerization on poly(propylene) microstructure was investigated at two temperatures. In addition to the expected electron donor effect on polypropylene tacticity, hydrogen was also found to increase polypropylene tacticity. The effect of changing these polymerization conditions on molecular weight and polydispersity was also investigated. Finally, CEF profiles show how the crystallizability of polypropylene increases by adding hydrogen and electron donor to the reactor.     

Ionic Polymerization of α, α -Disubstituted Vinyl Monomers

Alkyl α-chloroacrylates and p-substituted α-methylstyrenes were investigated for the effect of polymerization conditions on tacticity, molecular weight, and distribution, and for the relationship between tacticity, glass temperature, and crystalline properties.