Effect of tetralin on polymer degradation in solution. [Quarterly report, January--March 1995]

Abstract

DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document. AbstractThe effect of a hydrogen-donor solvent (tetralin) on the thermal degradation of poly(styrene-allyl alcohol) in solution was investigated in a steady-state tubular flow reactor at 1000 psig (6.8 MPa), at various tetralin concentrations (0-50 %), polymer concentrations ( 1-4 g/L), and temperatures (1 30-200 C). The molecular weight distributions of the emuent at each condition were examined as a fbnction of residence time by gel permeation chromatography. In the presence of tetralin, the polymer degrades by depolymerization to specific low molecular weight compounds and by random chain scission. No reaction was observed in the solvent 1-butanol in the absence of tetralin. The experimental data were interpreted with a rate expression first-order in polymer concentration based on continuous mixture kinetics, and rate coefficients were determined for the specific and random degradation processes. Activation energies were in the range of 5-10 kcaVmol for specific degradation and 33 kcdmol for the random degradation process. A plot of rate coefficients versus tetralin concentration indicates a fist-order rate at low tetralin concentrations and a zero-order dependence at high tetralin concentrations. In fro ductionThe thermal degradation of polymers is of considerable importance fiom both practical and theoretical points of views (Allen and Edge, 1992) : the degradation of polymers in high-temperature environments can limit their applications (Hawkins, 1984); induced degradation can potentially be used in recycling waste plastics (Powell, 1990; Miller, 1994); thermal degradation by pyrolysis coupled with gas chromatography is an important analytical procedure for identitj?ng polymeric structure (Flynn and Florin, 1985).Thermolytic degradation of polymers is similar in some respects to other important thermal decomposition processes, e.g., petroleum cracking and coal thermolysis. All these processes involve complex mixtures, both as reactants and as products. Simha and Wall (1958) and Jellinek (1955) did some early work on the degradation of polymers by measuring the yield of monomer, rate of decrease of molecular weight, and rate of volatilization. They developed rate expressions using tiee-radical mechanisms. This research was later followed by Madorsky (1964) McGrady, 1985, 1986). The treatment of the general set of equations for initiation, propagation, transfer, and termination reactions can be classified by two approaches: a. b.A statistical theory of random breaking of links (Simha and Wall, 1958; Wall, 1962;Jellinek, 1978) was proposed, and all reactions that form the intermediates and the species were assumed to start From a monodisperse sample (single MW).The desired fbnctions were either obtained by probability considerations of breakage of links, or by the solution of differential rate equations. However, since these theories were derived for a...