Dehydrochlorination of Poly(vinyl Chloride) in Pyridine. 1. Effect of Conditions

Poly(viny1 chloride) (PVC) was dehydrochlorinated thermally in pyridine solution under N₂ atmosphere and the effect of variation of reaction time, temperature, and concentration of PVC in pyridine was studied. The extent of dehydrochlorination (or conversion, x%) increases with an increase in reaction time and temperature, and with a decrease in the concentration of PVC. Incomplete precipitation of dehydrochlorinated PVC (DHPVC) occurs by nonsolvent (methanol). During dehydrochlorination there is no HCl evolution as it forms a pyridine hydrochloride complex which is supposed to act as a catalyst for dehydrochlorination. A possible mechanism has been proposed. Chain scission and cross-linking reactions are responsible for the molecular weight changes that take place during the reaction.     

Structure and Dehydrochlorination of Poly(vinyl Chloride)

The wide applicability of poly(vinyl chloride) (PVC), a tough thermoplastic resin, is due to a combination of moderate cost with the following characteristics [1]: (i) good general properties as a plastic material: (ii) great variation in properties, e.g., increase in heat distortion temperature, resistance to hot melt flow, improvement in mechanical, electrical properties, and processability of unplasticized PVC through external plasticization, block and graft copolymerization (internal plasticization), and chemical modification, e.g., chlorination, Friedel-Crafts, and cross-linking reactions: and (iii) processing versatility including injection molding, extrusion, blow molding, calendering, and lamination to produce many products of potential uses.     

The Kinetics and Mechanism of the Thermal Dehydrochlorination of Poly(vinyl Chloride)

Poly(vinyl chloride) degrades thermally by an acceleratory reaction in which the rate of hydrogen chloride evolution is slow at the beginning, increases with time (passing through a maximum), and then decreases. A kinetic model based on the zipper mechanism shows excellent agreement with observed data from the initial to the final stages of each dehydrochlorination. Hydrogen chloride is shown to be essential for the initiation of zip chains and may or may not be essential for the zip reaction. When hydrogen chloride is removed in a stream of inert gas, as it is in some tests purported to study the kinetics of degradation, the initiation of zip chains is significantly inhibited. The zip reaction, once it has been initiated, is not inhibited or stopped even by long exposure to atmospheric conditions.     

Synthesis of Poly(lactide)s with Modified Thermal and Mechanical Properties

The use of poly(lactide)‐based materials is, in part, limited by their physical and mechanical properties. This article reviews the methods that have been employed to enable enhancement of the materials properties through synthetic manipulation of the polymer structure including block copolymer synthesis and modification of the lactide monomer structure, focusing on the application of ring‐opening polymerization. In turn the effect of these structural modifications on the properties of the resultant materials are reported.

     

Dilute Solution Properties of Poly(Vinyl Chloride)

Light scattering and viscosity studies were made on dilute solutions of poly(vinyl chloride) (PVC) in three solvents: cyclo-hexanone, cyclopentanone, and tetrahydrofuran. Eight samples of PVC (M_w = 25,400 to 145,000) were used to determine the intrinsic viscosities, molecular weights, and the polymer-solvent interaction parameters over a range of temperatures. The solutions were found to behave normally and to exhibit no evidence of aggregate formation. The molecular weights obtained in all three solvents were independent of temperature and agreed well within the experimental errors. The interaction parameters observed were independent of concentration and molecular weight, and functions only of temperature. The intrinsic viscosities were related to molecular weight by the Mark-Houwink equation between 20 and 50°C. The temperature coefficient of the interaction parameter obtained by light scattering agrees well with that found by viscometry. Cyclohexanone, cyclopentanone, and tetrahydrofuran are all good solvents for PVC, and the order of solvent quality is cyclohexanone > cyclopentanone > tetrahydrofuran.     

Hydrogen Halide-Catalyzed Thermal Decomposition of Poly(vinyl Chloride)

The thermal decomposition of solid PVC was studied in the presence of added hydrogen chloride and hydrogen bromide over the temperature range 170–210°C. Under certain conditions the decomposition was shown to be dependent in a first-order manner on the hydrogen halide pressure. These gases acted as catalysts, increasing the rate of HCl evolution and the degree of discoloration but not producing longer polyene sequences. Activation energy for the HCl-catalyzed process was found to be similar to that of the uncatalyzed decomposition of PVC. A unified mechanism is presented for an overall process consisting of three steps: random generation of a single carbon-carbon double bond in the cis configuration; 1,4-elimination of HCl via a six-centered transition state yielding a polyene; HCl- or HBr-catalyzed isomerization of the polyene formed by HC1 elimination to regenerate the initial structure. Hydrogen chloride catalysis is seen as an integral part of the overall process.     

PVB存在下PVC化学法脱氯化氢的研究

ＰＶＢ存在下ＰＶＣ化学法脱氯化氢的研究刘恒＊李大成陈朝珍（四川联合大学化工学院成都６１００６５）关键词聚氯乙烯，脱氯化氢，聚乙烯醇缩丁醛１９９６－０９－０８收稿，１９９７－０５－２６修回国家教育委员会留学归国人员资助费资助课题近年来在ＰＶＣ脱氯化氢制...     

Effects of Chain Ends on Thermal and Mechanical Properties and Recyclability of Poly(γ-butyrolactone)

This work investigates effects of poly(γ-butyrolactone) (PγBL) with different initiation and termination chain ends on five types of materials properties, including thermal stability, thermal transitions, thermal recyclability, hydrolytic degradation, and dynamic mechanical behavior. Four different chain-end-capped polymers with similar molecular weights, BnO-[C(=O)(CH₂)₃O]_n-R, R = C(=O)Me, C(=O)CH=CH₂, C(=O)Ph, and SiMe₂CMe₃, along with a series of uncapped polymers R′O-[C(=O)(CH₂)₃O]_n-H (R′ = Bn, Ph₂CHCH₂) with M_n ranging from low (4.95 kg mol⁻¹) to high (83.2 kg mol⁻¹), have been synthesized. The termination chain end R showed a large effect on polymer decomposition temperature and hydrolytic degradation, relative to H. Overall, for those properties sensitive to the chain ends, chain-end capping renders R-protected linear PγBL behaving much like cyclic PγBL. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2271–2279     

酞侧基聚芳醚酮的热学性能

酞侧基聚芳醚酮的热学性能谢红卫，李滨耀（中国科学院长春应用化学研究所长春１３００２２）关键词酞侧基聚芳醚酮，ｐｖＴ行为，导热系数，定压比热容酞侧基聚芳醚酮（ＰＥＫ－Ｃ）具有较高的玻璃化转变温度，其流变加工性能和力学性能已被广泛研究［１～３］，被证明是...     

氯化镁增塑改性聚乙烯醇

以氯化镁为增塑剂, 采用流延法制备了增塑改性聚乙烯醇(PVA). 研究了氯化镁与PVA的相互作用以及氯化镁增塑改性PVA的结晶性能、 热性能和机械性能. 研究结果表明, 氯化镁能与PVA大分子发生较强的相互作用, 从而破坏PVA分子链内和链间的氢键, 降低PVA的结晶度. 氯化镁对PVA的热性能影响显著, PVA在加入氯化镁后的热分解过程由纯PVA的两段失重过程转变成三段失重过程. 氯化镁可有效增塑PVA, 其玻璃化转变温度降低, 拉伸强度下降, 断裂伸长率上升, 储能模量下降.     

脱氯化氢法合成聚(2,5-二乙氧基对苯乙炔)

聚对苯乙炔（ＰＰＶ）及其衍生物具有独特的光电性能，经强氧化剂掺杂后是一类重要的导电材料［１］，而且具有良好的非线性光学（ＮＬＯ）性质［２］，也是目前为止性能最好的电致发光材料［３］，因而ＰＰＶ及其衍生物的合成成为电致发光领域研究的热点之一。目前国内外...     

Gamma Irradiation Effects on Mechanical and Thermal Properties and Biodegradation of Poly(3-hydroxybutyrate) Based Films

Summary: Their biodegradable properties make polyhydroxyalkanoates (PHAs) ideal candidates for innovative applications. Many studies have been primarily oriented to poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-valerate) (PHBV) and afterwards to blends of PHAs with synthetic biodegradable polymers, such as poly(ε-caprolactone) (PCL). Medical and pharmaceutical devices require sterilization and γ irradiation could provide a proper alternative since it assures storage stability and microbiological safety. This contribution presents the effect of γ irradiation on the mechanical and thermal properties and on the biodegradation of PHB, PHBV and a commercial PHB/PCL blend. Samples, prepared by compression moulding, were irradiated in air at a constant dose rate of 10 kGy/h, from 10 to 179 kGy. Polymer chain scission was assessed by changes in the molecular weight, thermal properties and tensile behaviour. The correlation between absorbed dose and changes in the mechanical properties and biodegradation is discussed in detail. The optimum dose to guarantee microbiological sterilization without damage of the structure or meaningful loss of the mechanical properties is also reported.     

Kinetics of the Alkaline Dehydrochlorination of Polyvinyl Chloride)

From previous investigations of the alkaline dehydrochlorination of PVC it is well known that polyene sequences are formed. In this paper the true overall kinetics of the dehydrochlorination reaction between PVC and alcoholic KOH in tetrahydrofuran solution was studied at 9.5°C by measuring the rate of disappearance of KOH. Titrations of the hydroxide ions consumed and the chloride ions evolved showed close agreement. IR spectra of the samples did not show any evidence of substitution by hydroxide ions. Small amounts of DMSO present in the solvent were found to increase the reaction rate markedly. The kinetic scheme was discussed and the first rate constant was determined. Preliminary results of reactions of the polyene sequences with various reagents are presented. These reactions were made in order to introduce new functional groups into the PVC chains.     

Polymerization Mechanism of Vinyl Chloride with Trialkylaluminum-Lewis Base Catalyst and Thermal Stability of Poly(vinyl Chloride)

The mechanism of vinyl chloride polymerization by the tri-ethylaluminum-Lewis base-carbon tetrachloride catalyst system and the thermal stability of the resulting polymer were investigated. When the Lewis base is multidentate, the resultant complex with triethylaluminum shows significantly high catalytic activity for radical polymerization of vinyl chloride in the presence of carbon tetrachloride to give a white powder with high molecular weight. Carbon tetrachloride accelerates the rate of polymerization and participates in an initiating process rather than in a propagating step. The thermal stability of the polymer prepared with this catalyst system is much superior to that of commercial polyvinyl chloride), although the numbers of the double bonds in a chain end and of the head-to-head linkage are similar in both samples, suggesting that the thermally unstable structures of the former react with triethylaluminum to give the thermally stable structure on the polymerization process.     

Diethylenetriammonium Aquapentachloroferrate(III) Chloride: Structure and Magnetic Properties

Diethylenetriamine (dien) and iron(III) chloride in aqueous HCl yield (dienH₃) [FeCl₅(H₂O)]Cl, in which the chloroferrate(III) anion is significantly distorted from octahedral symmetry due to the extensively hydrogen‐bonded lattice. On cooling, the high spin Fe^III material shows weak antiferromagnetic coupling that results in a Néel temperature of 2.70 K.     

Fabrication of Single Wall Carbon Nanotubes-Based Poly(vinyl butyral) Nanocomposites with Enhanced Mechanical and Thermal Properties

In this research, poly(vinyl butyral) (PVB)/single wall carbon nanotubes (SWCNT) composites were prepared via solution blending method. Dispersion degree of SWCNT in the composites was characterized by Scanning Electron Microscopy (SEM) and mechanical properties were measured with tensile testing. Thermal degradation of composites was investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). SEM analysis confirmed good dispersion of the nanotubes in the PVB. The tensile tests showed significant increases in mechanical properties such as exceptional improvement in tensile strength, Young's modulus and flexibility for the composites compared to PVB at low SWCNT content.The TGA curves indicated that adding SWCNT improved the thermal stability of the PVB significantly and the degradation of the polymer matrix shifted to the higher temperatures. For the sample containing 0.6 wt%, an increase of 171% in modulus and a 258.4% enhancement of tensile strength were achieved. Also, elongation at break increased 28.7% at this loading. In fact, intrinsic properties of nanotubes caused enhancement of strength and flexibility simultaneously. Also, for this composite, T_onset and T_max enhanced remarkably and weight loss reduced greatly and residue at 600°C increased to high values. These results are promising for application of the PVB in industry.     

The Thermal Stability of Poly(vinyl Chloride) Prepared by Radiation Polymerization

The thermal stability of poly(vinyl chloride) prepared by radiation polymerization has been examined by thermogravimetric analysis, hydrogen chloride evolution, and visible spectra measurements in films and solutions. Radiation polymerized PVC, prepared with relatively high radiation doses, is much less stable than a commercial suspension polymerization PVC. On the other hand, the stabilities of radiation polymerized PVC, prepared with relatively high radiation doses, is much less stable than a commercial suspension polymerization PVC. On the other hand, the stabilities of radiation polymerized samples, which had received less than 0.45 Mrad, are comparable with commercial PVC. It is suggested that the allylic chlorine atoms produced in the radlysis of the polymer, concurrent with its formation, are chiefly responsible for the instability of the high doses samples.