摘要:

AbstractPolypropylene produced by the TiCl3–diethylaluminum chloride catalyst system was separated into two kinds of polymers, a minor atactic fraction with little or no steric order and a major fraction with a high degree of steric order. Each fraction had a wide molecular weight distribution. The relative amounts, the molecular weights and the molecular weight distributions of the fractions responded differently to changing reaction conditions. This indicates that the fractions are produced by separate catalysts and by different reaction mechanisms. Polymer/catalyst mole ratios from polymerizations at various conditions showed that a least one‐half of the TiCl3content of a catalyst may become directly involved in the polymerization process. A theory is developed which states that (1) the (unactivated) stereospecific fraction of the catalyst consists of molecules containing eight TiCl3units which are separated from each other by AlCl3in solid solution; (2) two chlorine atoms in this molecule are replaced with alkyl groups in the first step of activation; (3) the molecule contains two active sites, oned‐and the otherl‐orienting; (4) the molecules are crystallized in an open structure which has equally reactive sites uniformly spaced; and (5) the AlCl3component is not an inherent part of the stereospecific catalytic structure but it contributes to high activity by opening the crystal st

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080501

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractSamples of “as produced” polypropylene particles at progressively higher yield levels (grams polymer/gram catalyst) were sliced and examined by electron microscopy. In the polymerization of propylene with the TiCl3–(C2H5)2AlCl catalyst system the catalyst breaks up immediately into basic 100–1000 Å particles. As the yield increases, the catalyst particles gradually disappear and finally become completely dispersed in the polymer particle. These results are compatible with a theory which views the catalyst as a porous crystal containing a single species of active sites uniformly distributed. As polymerization progresses, all sites should eventually initiate a polymer chain whose length should be inversely proportional to the depth of the site below the surface of the particle. Two apparently equivalent statistical models were developed on the basis of this concept. Both models predict a slow increase in the X̄w/X̄nration(Q)with increasing molecular weight, after an initial rapid increase. The most useful of these models states thatQis equal to the sum of X̄wterms of the simple harmonic series, and that a complete spectrum ofx‐mers should be present in the product. This agrees satisfactorily with analytically dete

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080502

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractLiving polyanions were generated by the passage of electrolytic current through solutions in tetrahydrofuran (THF). The concentration of living polyanions was controlled by the current and could be increased by further electrolysis or decreased by electrolysis with reversal of polarity. Inasmuch as the living end (LE) concentration determines the molecular weight at a given monomer concentration it was possible to program a molecular weight distribution. Model distributions were attempted by (1) indirect methods in which an electrolytic formation of initiating dianions was followed by monomer addition, polymerization, current reversal and further polymerization and (2) direct methods in which monomer was present throughout the electrolysis. The molecular weight distributions were obtained by gel‐permeation chromatography and corresponded closely to the values calculated from the simple kinetic model of anionic polymerization. For styrene a sharp low molecular weight fraction and a clear binodal high molecular weight fraction were obtained. The binodal character was attributed to the growth of active single‐ended and double‐ended polyanions. The yields of high and low molecular weight material, the ratios of molecular weights obtained, and the values of the molecular weights were in agreement with expectation. The direct electrochemical polymerization methods were employed for α‐methylstyrene, but the highkpfor styrene thwarted efforts to apply the direct technique with this

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080503

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractThe decomposition of hydrogen peroxide and the graft copolymerization of methyl methacrylate has been investigated by use of cellulose samples adsorbing various metallicions. Metallic ions generally accelerate the decomposition of hydrogen peroxide, increase the number of grafts, and lower the average molecular weight. However their effects are much influenced by the range of pH values. It is clear that the amount of grafts formed is not necessarily proportional to the amount of decomposed hydrogen peroxide and is dependent upon a function peculiar to each metallic ion. The effective metallic ions in the neutral system were Cu2+, Ag+, Fe2+, Co2+, Cr3+, and Zn2+. The effects of Ce3+, Mg2+, Hg3+, Cd2+, Ni2+and Mn2+were either negligible or negative. Comparative studies on various conditions confirmed that Fe2+in the neutral system gives graft copolymer having a minimum average molecular weight and the greatest number of grafts.

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080504

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractThe nonvolatile products in thermal‐oxidized polypropylene sheet have been quantitatively identified by infrared analysis and chemical reaction. The molecular weight changes with oxidation have been studied by gel‐permeation chromatography. It was determined that there is a functional group at each end of a chain. A general oxidation mechanism scheme for polypropylene is presented. The discovery of γ‐lactone is an indication of the importance of an intramolecular backbiting process. The overall functional group distribution is found to differ from that found in a polyethylene

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080505

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractPerfluorinated elastomeric copolymers of tetrafluoroethylene and perfluoro(methyl vinyl ether), containing 20–50 mole‐% of the vinyl ether moiety, were prepared in aqueous emulsion free radical initiated polymerization systems. The two monomers show sufficiently similar relative reactivity ratios to permit the preparation of homogeneous copolymers at high monomer conversions. Detailed properies of a 65/35 (molar) copolymer, including outstanding fluid and chemical resistance, to aqueous media and to nearly all organic and inorganic fluids, excellent thermal and oxidative stability, and very low permeability, are given. Efforts to vulcanize the copolymer to achieve good mechanical properties over a wide temperature range were not particularly successful. Through the incorporation of an unspecified cure site monomer, vulcanizates showing to a large degree the desirable properties of the raw copolymer along with good stress‐strain properties and compression set resistance have been obt

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080506

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractNMR analysis of the low molecular weight poly(vinyl chloride) obtained from polymerizations initiated byt‐BuMgCl in THF solution suggests that all the polymer chains have the structure:Enhanced signal/noise ratio by NMR spectrum accumulation confirms this structure in products of higher molecular weights. Examination of the NMR spectrum of vinyl chloride monomer in THF solution reveals the formation of a monomer–THF complex; it seems that the initiation step of the polymerization is governed by this complexation phenome

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080507

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractA systematic investigation of the thermal stability of nine structurally related polyquinoxalines has been conducted. The relative oxidation resistance of these polymers is controlled by two opposing structural effects. Phenyl sidegroup substitution in the heterocycle greatly improves oxidative stability, while the introduction of oxygen into the main polymer chain, in the form of ether groups, produces a negative effect of equal magnitude. These results are discussed from a mechanistic point of view. Simultaneous, dynamic thermal analysis in vacuum up to 1400°C and analysis of volatile and nonvolatile products indicates three major decomposition regions. Between 500 and 640°C, main polymer degradation takes place involving the heterocycle. This event is followed by dehydrogenation of a stable degradation product between 640 and 690°C. Above 1360°C an exothermic reaction takes place to yield highly condensed aromatic resid

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080508

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractPolyacrylylglycinamide (PAG) and its thermally reversible aqueous gels have been investigated and comparisons made with gelatin. For unfractionated PAG homopolymers in 2MNaCNS at 25°C, the Mark‐Houwink‐Sakurada equation is [η] = 1.16 × 10−3M̄n0.52. The Hugginsk′ value is found to be about 0.9 and the Flory‐Huggins polymer‐solvent interaction parameter, 0.49. A theoretically calculated value ofKθis very close to the experimental one and it is for this reason and the observed μ and M̄nexponent values that 2MNaCNS at 25°C approaches being a θ solvent for PAG. A thermodynamic approach based on equilibrium swelling and modulus measurements indicates that a single thermally reversible crosslink in a gelatin gel involves numerous peptide backbone units, whereas in PAG gels a crosslink perhaps involves only one residue from each of two chains. These results complement the very high exothermic heat of gelation crosslinking, δHc, for gelatin compared to PAG. ΔHchas been measured on PAG samples of differentDPand found to be independent of chain length. Similar measurements on acrylylglycinamide copolymers and terpolymers containing basic and acidic groups produce no change in δHcso that coulombic forces do not appear to be significant. Data are also included relating to the density of PAG, its glass transition and thermal decomposition temperature, the tensile modulus of equilibrium‐swelled PAG films in water and the chain‐transfer constant of methanol with the acry

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080509

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY

摘要:

AbstractButadiene‐1,3 and acrylonitrile were copolymerized by alkylaluminum halides alone or, more effectively, by the alkylaluminum halide/vanadium compound systems, into an alternating copolymer in which the butadiene units are linked predominantly in thetrans‐1,4 configuration. The efficiency of the aluminum components in the latter catalyst systems appear to decrease in the following order: AlEtCl2>Al2Et3Cl3≫ AlEt2Cl(≫AlCl3). The alkylaluminum halides could also be used effectually in the form of the complex with acrylonitrile. The catalytic activity was markedly affected by the order of mixing of the catalyst components and the monomers. Effective catalysts could be prepared only when the catalyst components were mixed in the presence of acrylonitrile. The catalyst activity was also found to depend upon the Al/V ratio, reaching its maximum when the ratio was about 20 in the AlEtCl2·AN/VO(Ot‐Bu)3system. Other combinations of conjugated diene with conjugated polar vinyl monomer were similarly copolymerized by these catalysts. It was found that different feed ratios between the diene and the vinyl monomer which were varied over a wide range always resulted in the formation of a 1:1 copolymer. The butadiene‐acrylonitrile copolymer thus formed gave an NMR spectrum in which there was only one peak assignable to the methylene protons (7.72 τ) of the butadiene unit. On the basis of these findings, it may be suggested that alternating copolymerization prevails in the polymerization systems here

ISSN:0449-296X    

DOI:10.1002/pol.1970.150080510

出版商:John Wiley&Sons, Inc.    

年代:1970

数据来源: WILEY