摘要:

On the basis of the high-pressure polymerization of ethylene, in which organic peroxides are increasingly used as initiators, the problems which play an important part in selecting the most suitable initiators are discussed. Starting from the rate of decomposition of the initiator at the actual conditions of the high-pressure polymerization, the consumption of the initiators and its costs as well as its influence on the process control are considered. A second important point is the influence of the initiator on the properties of the polymer which can be exerted by the reaction of the initiator or its decomposition products with the polymer and the polymer chain radicals or the initiator decomposition products and residual initiator which remains dissolved in the polymer. The last part is devoted to the handling of peroxides during storage and metering in the reactor which are questions of process technology and safety techniques. The criteria discussed in respect to the choice of peroxidic initiators are illustrated by two concrete examples, the synthesis of low-density polyethylene in a triple chamber autoclave and in a tubular reactor with multiple feed.

ISSN:0022-233X    

DOI:10.1080/00222338108066428

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The problem of describing quantitatively the selectivity of cationic copolymerizations leads to a new method of calculating kinetic parameters of the copolymerization. The “individual rate constants” for the binary first-order copolymerization calculated this way are well suited to describe the “dynamics of the copolymerization” and to predict copolymer characteristics, e. g., composition and microstructural parameters. By means of cationic copolymerizations of vinyl monomers, theoretical calculated copolymer characteristics and experimentally independently determined ones are compared.

ISSN:0022-233X    

DOI:10.1080/00222338108066429

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Free radical copolymerization of 6-methyl-2-phenyl-3-pyridazinone (I) with styrene (M1) has been carried out in the presence of BF3OEt2. Lewis acid was found to decrease the copolymerizability of I, perhaps due to the increased resonance stabilization of the pyridazinone ring by chelation of acid on the carbonyl-oxygen atom of the ring.

ISSN:0022-233X    

DOI:10.1080/00222338108066430

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The Monte Carlo models of binary irreversible copolymeriza-tion with ultimate and penultimate effect are applied to the copolymerization of acrylic acid and methyl acrylate, and styrene and benzylidene malononitrile, respectively. The agreement with available experimental data is quite good. A comparative study between the formal kinetics model and the Monte Carlo model reveals that statements concerning the copolymer composition are robust, but statements concerning the sequence distribution are not always robust.

ISSN:0022-233X    

DOI:10.1080/00222338108066431

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

This paper discusses an improved and efficient version of the MEMØRY-7 computer program described in a previous paper. The program, called MEMØRY-7/1, implements a Monte Carlo algorithm to compute reactivity ratios in binary irreversible copolymerizations. For the copolymerization of acrylic acid and methyl acrylate, the computed r1, r2values (r1= 1.374, r2= 1.038) compare quite well with experimentally determined ones (r1= 1.4, r2= 1.0; Eldridge and Treloar).

ISSN:0022-233X    

DOI:10.1080/00222338108066432

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Vinyl acetate and maleic anhydride are known to give 1:1 radical alternating copolymerization regardless of the monomer feed composition. The mechanism of this copolymerization involves free monomers and a complex between them (charge transfer complex). We undertook a study of the microstructure of different alternating copolymers (bylH,13C NMR, and thermogravimetric analysis). Starting from the results obtained, we determined the influence of the participation of the complex on the microstructure of the alternating copolymers.

ISSN:0022-233X    

DOI:10.1080/00222338108066433

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

l, l, 4, 4-Tetraphenyl-2-tetrazene (TPT) inhibits the polymerization of vinyl acetate (VAc) initiated by 2, 2′-azoisobutylonitrile. The induction period is proportional to the concentration of TPT. The ratio of the rate constants of propagation and termination reactions, kp2/2kt, were estimated from the consumption rate of TPT. The chain transfer constant of TPT in the radical polymerization of VAc was also calculated.

ISSN:0022-233X    

DOI:10.1080/00222338108066434

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The thermal decomposition and the glass transition temperature of poly-p-tert-butylstyrene (PptBuS) were studied with a (DSC-2) differential scanning calorimeter. The undecomposed and decomposed polymers were analyzed by gel permeation chromatography for molecular weight distributions and by DSC-2 for changes in the polymer glass transition temperatures. Decomposition of PptBuS under isothermal conditions during 50 min periods in the 25 to 360°C region led increasing quantities of high molecular weight polymer withMw= (12 to 19) × 104to yield lower molecular weight products withMw= (6 to 14) × 103, suggesting the involvement of partial depolymerization reactions. Decompositions at fixed temperature (320°C) for different periods-10 to 180 min-showed that in the early stages of the reaction (< 10 min) random scissions occur in some of the chains which later undergo partial or total depolymerization. Activation energies for the decomposition of PS and its homologs follow the order EPS> EPpMeS> EPpiPrS> EPpTBuSVariation of Tge(at q = l°K/min) withMnobeys the following relation: Tge(°K) = 446 - 7.33 × 105/Mn. The Tg∞value of 446°K for PptBuS is far removed from that of PpMeS (384°K) and PS (379° K) due primarily to increased steric hindrance and decreased chain flexibility which arise because the effective bulk size (packing ability) of the tert-butyl group in PptBuS is lower than its apparent bulk size.

ISSN:0022-233X    

DOI:10.1080/00222338108066435

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

A comparison of the synthetic and thermal characteristic of Group IVB polythioethers is made. In general, yield follows the trend interfacial systems > aqueous solution systems and Hf > Ti > Zr. [Graphic]

ISSN:0022-233X    

DOI:10.1080/00222338108066436

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The aim of the present paper is to find out a suitable stabilizer for natural rubber latex foam. For this, condensatioii reactions of formaldehyde with various aliphatic amines and with ethyl chloride were carried out to obtain polyamine-type polynieric products. The resultant products were characterized and evaluated for their stability effects in the natural rubber latex foam. In addition to this, efforts were successfully made to find out an effective formulation to get a foam of maximum strength and durability. The majority of the products synthesized were unable to make the foam stand satisfactorily for a critical duration of time; however, one exhibited an excellent stabilization effect in such foams. It is a triamine-type polymeric base prepared by a new route.

ISSN:0022-233X    

DOI:10.1080/00222338108066437

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor