摘要:

A deeper understanding of the dynamics of macromolecules in polymer melts (reptation theory—de Genne and others refer to PVC-Cleveland on long term aging of glassy polymers) has sparked a number of investigations on the modelling of the termination and propagation reactions in free radical homopolymerization. These recent contributions will be reviewed and some statements will be made about limitations of the present models and recommendations will be made for future study.

ISSN:0098-6445    

DOI:10.1080/00986448308940070

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A dilatometric technique was used to obtain kinetic data for UV-photoinitiated polymerization of acrylamide and methacrylamide. In this study, benzoinmethylether was the initiator. Two mixed-solvent systems, 30% acetic acid in water (for both monomers) and 40% methanol in water (for acrylamide only) were examined. In all three systems the rate of polymerization varies with the monomer concentration to the 1.4 to 1.5 power and to the initiator concentration to the 0.4 to 0.8 power. Energies of activation are very low, less than 1.5 kcal/mol. Molecular weights estimated from viscosity measurements support the idea that chain transfer to monomer is important in the case of methacrylamide.

ISSN:0098-6445    

DOI:10.1080/00986448308940071

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

A bench-scale batch reactor was used to study the polymerization of butadiene with nickel(II) stearate Et2AlCl catalyst. In particular, the effects of moisture on polymerization were investigated. The initiation reaction is sensitive to temperature. At 0°C an induction period was observed, but at room temperature initiation can be assumed instantaneous. Water enhances catalytic reactivity, however at water concentrations greater than 10 mmol/L, termination reactions become significant. Maximum conversion is obtained in the 6 to 15 mmol/L range of water. The determining step for the molecular weight of polymer is the chain transfer to monomer. At low H2O concentration the molecular weight increases with water concentration, however it becomes independent of water concentration at high moisture content. With the help of statistical analysis of the experimental data, a two-active-species model was developed to describe the kinetics of the system and to explain certain polymerization characteristics.

ISSN:0098-6445    

DOI:10.1080/00986448308940072

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

An earlier computer model for tubular high pressure polyethylene reactors is extended to take into account two radical generating sources, in addition to an injected initiator: a long-lived intermediate, possibly generated from the interaction of ethylene with trace amounts of oxygen, and the ethylene itself undergoing thermal polymerization. The first of these reactions can account for the smoothing of the temperature profile near the peak temperature, attributed by Lee to initiator and radical carryover; the second, whose inclusion is justified by experiments recently performed by Buback, can account for the explosive decomposition of ethylene known to occur in LDPE reactors if the temperature is allowed to exceed about 350°C, and it also can contribute significantly to polymer production at very high temperatures. The contribution of both reactions must be evaluated quantitatively, if reliable heat transfer coefficients are to be obtained from experiment.

ISSN:0098-6445    

DOI:10.1080/00986448308940073

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Butylacrylate (BA)-Styrene (St) copolymers have been synthesized via a semicontinuous emulsion process in which the monomers feeding rate and weight ratios (BA/St) were varied. The feed consisted of only pure monomers which were added to an aqueous solution that contained the emulsifier and initiator

ISSN:0098-6445    

DOI:10.1080/00986448308940074

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The Trommsdorf or gel effect in free radical polymerization is due to the fact that the termination reaction becomes strongly diffusion controlled above a critical concentration associated with the onset of molecular entanglements. Therefore, an understanding of polymer self-diffusion in entangled systems becomes essential to understanding the Trommsdorf effect. Our group has previously proposed a molecular model for the gel effect which uses a specific theory for polymer diffusion (reptution). The present work represents an experimental attack on the same problem Experimental studies of polymer self-diffusion in entangled systems are scarce. Quasielastic light scattering from ternary systems composed of solvent(l)-polymer(2)-polymer(3), in which species (3) is isorefractive to the solvent (i.e. 0n/0c3= 0), offers an attractive way to study the tracer diffusion coefficient of species (2) in a binary mixture of compositionc3. In regimes of low momentum transfer (qRG< 1,) whereqis the scattered wave vector andRGis the polymer radius of gyration, we have shown that the correlation function of the scattered electric field should decay with a single exponential decay time, given by (D22q2)−1whereD22(c2,c3) is the main ternary diffusion coefficient of component (2). Extrapolation to zero concentration of 2) at fixed concentration of (3) yields the tracer diffusion coefficient of (2) in the binary mixture of (1) and (3). The systems toluene(l)-polystyrene(2)-polymethylmethacrylate(3) (0n/0c3≈ 0.007 at 25°C) and toluene(l)-polystyrene(2)-polyvinylmethylether (3) (0n/0c3≈ 0.012 at 60°C) very nearly satisfy the above criteria. In both systems, we have found that the tracer diffusion coefficient of the polystyrene decreases with increasing concentration of the isorefractive polymer. Further studies have focused upon the dependence of the tracer diffusion coefficient upon polystyrene molecular weight, and upon the effect of incomplete index matching.

ISSN:0098-6445    

DOI:10.1080/00986448308940075

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

This paper deals with the modelling of a Sulzer-Koch motionless mixer. A flow model involving convection and diffusion has been solved to characterize the dispersive mixing in one node of the network and this result was then complemented by a network analysis to obtain the flow distribution. Experimental data are in general agreement with the theory. The approach of this study is shown to provide valuable conclusions about the design of the mixer and to complement the more commonly used integral or statistical treatments. In particular, it has been shown that the ratio of internal resistances controls the distributive mixing in one mixer unit and that significant convective mass transport takes place within the node even when there is no net cross-flow.

ISSN:0098-6445    

DOI:10.1080/00986448308940076

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

The sensitivity of rheological behavior to the presence of long chain branched (LCB) molecules in a matrix of ostensibly linear high density polyethylene (HDPE) is examined. Branching is introduced by gamma irradiation of the HDPE just short of the gel dose. The irradiated and unirradiated polymers are blended to obtain various concentrations of LCB from 1 to 7.2 LCB/10,000 carbon atoms. Dramatic changes in viscoelasticity and temperature dependencies far in excess of those expected from molecular weight changes are detected. While the Mw¯ observed by low angle laser light scattering (LALLS) and size exclusion chromatography (SEC) increases by a factor of only about 1.2, the dynamic viscosity at low frequencies and 190°C increases by a factor of 14. Furthermore, flow activation energy values increase from 8 to 40 kcal/mole.

ISSN:0098-6445    

DOI:10.1080/00986448308940077

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor

摘要:

Recycling of thermoplastics recovered from waste products is an interesting issue for the great variety of convergent aspects involved in its consideration (i.e., ecologic, technologic, economic, etc.). In the case of specific applications of an already used resin (packaging materials, films, consumer goods, etc.), it is necessary to find the new set of processing conditions, the most adequate proportions of virgin and recycled material (if any) and the nature and the concentrations of contaminants

ISSN:0098-6445    

DOI:10.1080/00986448308940078

出版商:Taylor & Francis Group    

年代:1983

数据来源: Taylor