CRYSTALLIZATION KINETICS OF ETHYLENE-PROPYLENE COPOLYMERS PREPARED BY LIVING COORDINATION POLYMERIZATION

In this paper,crystallization kinetics of a series of ethylene-propylene copolymers prepared by living polymerization coordination catalyzed by a fluorinated bis(phenoxyimine)Ti catalyst(FI-EP copolymers)was studied,and was compared with that of ethylene-propylene copolymers prepared by a conventional Ziegler-Natta catalyst(ZN-EP copolymers).It is found that,the Avrami exponent and the crystallization rate constant of the FI-EP and ZN-EP copolymer show similar dependence on crystallization temperature,bu...     

Strain birefringence in ethylene-propylene copolymers

A series of polymeric networks were prepared by the γ-radiation crosslinking of two ethylene-propylene copolymers containing 62 and 69 mol % ethylene units. The elastomeric materials thus obtained were studied in elongation, both swollen and unswollen, over the temperature range ?30 to 95°C. The experiments involved measurements of both the elastic force and birefringence, using primarily changes in temperature at constant length (rather than changes in length at constant temperature). There is evidence for crystallization in these networks, as manifested by marked decreases in force and increases in birefringence at relatively low elongations and at temperatures as high as 70°C. As expected, the birefringence and related quantities were found to be more sensitive to crystallization than the force, with the stress-optical coefficient showing the greatest sensitivity. The results obtained in the elongation-temperature regions presumably free from effects of network crystallization were used to calculate values of the temperature coefficient of the unperturbed dimensions of the chains, and values of the optical-configuration parameter. Both are widely used to characterize (spatial) configurations of chain molecules. Values of the former quantity are in very good agreement with those predicted some years ago using a rotational isomeric state model for ethylene-propylene chains of various chemical and stereochemical compositions. The extension of these theoretical calculations to include the stress-optical coefficient should provide further information on crystallization in ethylene-propylene elastomers and the configurational characteristics of these copolymeric chains.     

不同催化体系对乙丙共聚物序列分布的影响

<正> 乙丙橡胶的性能不仅取决于共聚物的组成、分子量及其分布,而且依赖于共聚物的微结构。Natta等认为共聚物中乙烯和丙烯单体链节呈无规分布时可获得性能最好的弹性体。但因催化剂及聚合条件不同,共聚物的单体链节总是存在不同程度的无规、交替及长序列分布。本文采用红外吸收光谱研究了乙丙共聚物的组成及不同催化体系和加入添加剂后对乙丙共聚物序列分布的影响。     

聚丙烯-聚乙烯嵌段共聚物的分子结构及性能的研究

本工作用核磁共振(~(13)C-NMR)、示差扫描量热(DSC)、动态力学分析(DMA)和扫描电子显微镜(SEM)等技术研究了将丙烯、乙烯单体两步分段共聚、预期为聚丙烯-聚乙烯嵌段共聚物的合成物(简称为聚丙烯-聚乙烯嵌段共聚物或嵌段共聚物)。结果表明,在嵌段共聚物中含有一定量的、能为正庚烷抽提出来的乙丙无规共聚物(EPR);分段共聚的产物并非预想的PP-b-PE两嵌段共聚物,而是含有多种组分的共混物;形态表征的结果表明了嵌段共聚物为多相体系,EPR和PE形成分散相以球形无规分布于PP基体中。     

Features of rubber swelling in transformer oil,according to NMR data

NMR spectroscopy, NMR relaxation, and NMR with a pulsed magnetic field gradient methods are used to study the swelling of the elastomers based on ethylene-propylene rubber, butadiene-nitrile rubber, and fluororubber SKF-26 in transformer oil. Components corresponding to the fractions of oil and polymer network are identified. It is shown that the affinity of the polymers toward transformer oil displays an increase in the orderly sequence of ethylene-propylene rubber, fluororubber, and butadiene-nitrile rubber; the stability of the polymers towards carbon tetrachloride falls in the same sequence. Based on an analysis of the spin–spin relaxation time depending on the degree of swelling, it is found that fluororubber elastomers are characterized by the formation of a polymer network that prevents further sorption, In contrast, elastomer based on ethylene-propylene rubber gives no indication of the formation of a rigid polymer network.     

Chemical inequivalence behavior of the protons attached to the same carbon in ethylene-propylene copolymer（EPC）

Six ethylene-propylene copolymer samples with different structural parameters were analyzed by ^1H NMR,^13C NMR and ^1H-^13C COSY in this paper.With the aid of the ^1H-^13C COSY spectra of ethylene-propylene copolymer,the chemical inequivalence behavior of the protons attached to the same carbon in the ethylene-propylene copolymer could be observed. Four basic types of chemical bonds were divided,and two kinds of main conformations were proposed to explain this phenomenon. Based on the calculation of conformation distribution,it can be proved that the explanation of this phenomenon was reasonable.     

Energetic Stress in Rubbery Copolymers

Thermoelastic measurements were performed for four rubbery copolymers: Viton A, ethylene-propylene rubber (EPR), Hycar, and styrene-butadiene rubber (SBR). The relative energy contribution, f_e/f, for these elastomers were calculated by means of a recently proposed equation which is based on the temperature coefficient of shear modulus. It was found that the relative energy contribution or the temperature coefficients of the unperturbed dimensions of EPR and SBR are not simply related to those of the parent homopolymers. In addition, the copolymers appear to bear an opposite sign compared with the homopolymers. The thermoelastic behavior of one elastomer, Viton A, was investigated over a 200°C range up to high loads. Linear relations were obeyed within experimental error. Calculations on the basis of statistical theory of rubber elasticity shows that this is to be expected for elastomers that are Gaussian in behavior.     

乙烯-丙烯共聚物磺酸盐离聚物的研究——Ⅰ.乙烯-丙烯共聚物及其氯磺化反应

本文用钛系高效催化剂合成了四种乙烯-丙烯共聚物,测定了共聚物的单体组成、序列结构分布、分子量和结晶度.在考察了引发剂和氯磺化试剂对氯磺化反应影响的基础上,制备了不同磺化度的氯磺化乙丙共聚物,并用~(13)C-NMR分析其化学结构,表明共聚物分子链上CH没有发生反应,CH_3只被-SO_2Cl取代,而CH_2可被-SO_2Cl或-Cl取代.     

Compression yielding of polypropylenes above glass transition temperature

Yielding behaviour under compressive loading of two materials based on polypropylene, an isotactic homopolymer and an ethylene-propylene block copolymer, is studied at different strain rates and temperatures. Quasi-static tests, performed in electromechanical machines, and dynamic tests, carried out in a Hopkinson bar, were compared and simultaneously analyzed to generate a master curve representative of the material yielding, assuming the strain rate-temperature superposition principle. Experimental data were fitted to equations based on the cooperative model for semi-crystalline polymers.     

Formation of C7-species pyrolysis products from ethylene-propylene heterosequences of poly(ethylene-co-propylene)

Properties of ethylene-propylene copolymer (EPM) are determined by ethylene/propylene ratio and degree of block and random sequences. EPM was pyrolyzed and the pyrolysis products were analyzed using gas chromatography/mass spectrometry (GC/MS) to examine pyrolysis products formed from the ethylene-propylene heterosequences. Pyrolysis products formed from EPM were compared with those formed from polyethylene (PE) and polypropylene (PP) to determine the pyrolysis products formed from ethylene-propylene heterosequences of EPM. Principal pyrolysis products formed from ethylene-propylene heterosequences were 3-methyl-1-hexene, 4-methyl-1-hexene, 2-methyl-1-hexene, and 2-heptene. Order of the relative intensity of the pyrolysis products was 2-methyl-1-hexene > 4-methyl-1-hexene > 3-methyl-1-hexene > 2-heptene. The relative abundances of the pyrolysis products decreased as the pyrolysis temperature increased. Relative abundances of the specific pyrolysis products formed from ethylene-propylene heterosequences may be used for determination of the relative degree of random sequences of EPM as well as ethylene-propylene-diene terpolymer (EPDM).     

聚苯乙烯及其合金的热释放电流研究

聚苯乙烯及其合金的热释放电流研究盛京，李凤奎，胡静（天津大学材料科学与工程系，天津，３０００７２）关键词聚苯乙烯，聚苯乙烯松弛，热释电谱，聚苯乙烯合金，乙丙橡胶合金用热释放电流（ＴＳＣ）法研究聚苯乙烯（ＰＳ）的松弛过程只见Ｓｈｉｎｉｃｈｉ的报道［１］...     

Flocculation studies of non-aqueous poly(methyl methacrylate) dispersions. II. Stabilization with the diblock copolymer poly (styrene-b-[ethylene-co-propylene])

Well defined non-aqueous dispersions of poly(methyl methacrylate) stabilized by the diblock copolymer poly(styrene-b-[ethylene-co-propylene]) have been studied with a dispersion medium consisting of a binary liquid mixture of n-heptane and n-propanol. Flocculation was induced by adding n-propanol at constant temperature, to find the critical flocculation volume, and by cooling, to find the critical flocculation temperature. Theta conditions for ethylene-propylene copolymer in the same binary liquid mixture were determined using samples obtained by hydrogenating polyisoprene standards. These dispersions just retained stability at theta conditions, with flocculation occurring when the dispersion medium was slightly worse than a theta system for the stabilizing ethylene-propylene chains.     

Thickness, stability and contact angle of liquid films on and inside nanofibres, nanotubes and nanochannels

While the stability of liquid films on substrates is a classical topic of colloidal science, the availability of nanostructured materials, such as nanotubes, nanofibres and nanochannels, has raised the question of how the stability of liquid films and their wetting behaviour is affected by nanoscale confinement. This paper will present the conditions for the stability of liquid films on and inside cylindrical solid substrates with nanometre scale characteristic dimensions. It is shown that the stability is determined by an effective disjoining/conjoining pressure isotherm which differs from the corresponding disjoining/conjoining pressure isotherm of flat liquid films on flat solid substrates. From the former, the equilibrium contact angles of drops on an outer or inner surface of a cylindrical capillary have been calculated as a function of surface curvature, showing that the expressions for equilibrium contact angles vary for different geometries, in view of the difference in thickness of the film of uniform thickness with which the bulk liquid (drops or menisci) is at equilibrium. These calculations have been extended to the case of glass nanocapillaries and carbon nanotubes, finding good agreement with experimental results in the literature.     

Functionalization of an amorphous ethylene-propylene copolymer by free radical initiated grafting of unsaturated molecules

Functionalization of an amorphous ethylene-propylene copolymer, EPM, has been performed by means of homogeneous grafting reactions of unsaturated molecules such as dibutylmaleate, diethylfumarate, itaconic anhydride, and maleic anhydride, initiated by free radicals. Dicumylperoxide and dibenzoylperoxide have been used as a free radical source and their efficiency has been compared. A different reactivity of the unsaturated molecules has been evidenced. The influence of the nature of the solvent on the functionalization degree has been investigated, revealing a noticeable effect of the solvent either on the amounts of grafted molecules or on the secondary reactions which lead to partial degradation of the functionalized EPM chains.     

Temperature rising elution fractionation of PP/PE alloy and thermal behavior of the fractions

In this paper, a PP/PE alloy prepared by sequential polymerization of ethylene and propylene was fractionated with temperature rising elution fractionation and a variety of fractions were obtained. Thermal analysis was conducted to probe the microstructures of fractions. Four types of fraction with different melting behaviors were identified: random copolymer with no melting peak, multiple-block ethylene-propylene copolymer exhibiting plural melting peaks, ethylene-predominant copolymer with single melting peak and ethylene-propylene block copolymer with double melting peaks. The production of these components was also discussed in terms of polymerization process and the nature of active sites in the catalyst.     

乙烯-丙烯嵌段共聚物的鉴别

应用扫描电子显微镜(SEM)研究乙烯-丙烯嵌段共聚物和聚乙烯/聚丙烯共混物的冲击断裂表面形态。结果表明,这二种材料力学性能的差别,明显地反映在它们的断面形态上。前者显示出一种典型的韧性断裂特征;后者则呈现出一种剥离层状结构。~(13)C-NMR分析结果表明,在上述乙烯-丙烯嵌段共聚物中,确实存在着乙烯-丙烯共聚链段。这是该材料具有良好的抗冲击性能的主要原因。     

Photodegradation of Heterophasic Ethylene-Propylene Copolymers in the Solid State

The photodegradations of various heterophasic ethylene-propylene (E-P) copolymer films were studied at 30 and 55°C in air for varying time intervals. The photochemical behavior of E-P copolymers is quite different from amorphous polypropylene and polyethylene homopolymers but resembles that of isotactic polypropylene. The nonvolatile products in photooxidized copolymer films have been quantitatively identified by infrared analysis. The kinetics and general oxidation mechanism scheme for E-P copolymer are presented. The identification of γ-lactone is an indication of the importance of an intramolecular back-biting process. The overall functional group distribution is found to differ from that in polyethylene and E-P copolymers.     

Gamma radiation effects on an amine antioxidant added in an ethylene-propylene copolymer

The aim of this work was to compare the gamma radiation induced effects on samples of an ethylene-propylene copolymer antioxidant free with samples loaded with an antioxidant characterised by the presence of an -NH functional group. The employed techniques were Electron Spin Resonance spectroscopy (ESR) and High Performance Liquid Chromatography (HPLC). Stable radicals R---NO° due to the interaction of free radicals produced in the irradiated polymer with the antioxidant have been observed by ESR at room temperature. The time evolution of the ESR signals following the irradiation was examined at different doses. The amount of antioxidant not involved in the oxidation reactions has been determined using HPLC.     

Impact resistant resins based on olefinic terpolymers containing a system of conjugated double bonds—V. Influence of reaction solvent on the physico-chemical properties of ungrafted SAN and some technological properties of ATS resins

Radical induced grafting of styrene (S) and acrylonitrile (AN) on to an unsaturated ethylene-propylene based terpolymer (EPTM) in mixed solvents has been investigated. Molecular weight, molecular weight distribution, conversion of ungrafted poly(styrene-co-acrylonitrile) (SAN) with 25 w% of AN and its degree of graft on to EPTM have been reported as functions of composition of the toluene/η-heptane mixture used as solvent. Mechanical properties of ATS resins are strongly dependent on the degree of graft of SAN resins and the molecular parameters of the ungrafted SAN; both are influenced by toluene content in the solvent mixture.