Degradation of Condensation Polymers

Volatile products are formed in the latter two reactions. The mechanism of degradation of condensation polymers is often complicated by the presence of traces of water which are difficult to eliminate from the samples. Hydrolysis then occurs at high temperature and competes with the pure thermal degradation. New chain ends are formed which may in some cases markedly affect the polymer stability. 

Montaudo, G. and Puglisi, C., Thermal Degradation of Condensation Polymers, in Comprehensive Polymer Science, First Sup>plement. Pergamon Press, Oxford, 1992. p. 227. 

A WBL can also be formed within the silicone phase but near the surface and caused by insufficiently crosslinked adhesive. This may result from an interference of the cure chemistry by species on the surface of substrate. An example where incompatibility between the substrate and the cure system can exist is the moisture cure condensation system. Acetic acid is released during the cure, and for substrates like concrete, the acid may form water-soluble salts at the interface. These salts create a weak boundary layer that will induce failure on exposure to rain. The CDT of polyolefins illustrates the direct effect of surface pretreatment and subsequent formation of a WBL by degradation of the polymer surface [72,73]. 

In 1929 Carothers proposed a generally useful differentiation between two broad classes of polymers condensation polymers in which the molecular formula of the structural unit (or units) lacks certain atoms present in the monomer from which it is formed, or to which it may be degraded by chemical means, and addition polymers, in which the molecular formula of the structural unit (or units) is identical with that of the monomer from which the polymer is derived. Condensation polymers may be formed from monomers bearing two or more reactive groups of such a character that they may condense intermolecu-larly with the elimination of a by-product, often water. The polyamides and polyesters referred to above afford prime examples of condensation polymers. The formation of a polyester from a suitable hydroxy acid takes place as follows ... 

Representative condensation polymers are listed in Table I. The list is by no means exhaustive, but it serves to indicate the variety of condensation reactions which may be employed in the synthesis of polymers. Cellulose and proteins, although their syntheses have not been accomplished by condensation polymerization in the laboratory, nevertheless are included within the definition of condensation polymers on the ground that they can be degraded, hydrolytically, to monomers differing from the structural units by the addition of the elements of a molecule of water. This is denoted by the direction of the arrows in the table, indicating depolymerization. 

The combined results of kinetic studies on condensation polymerization reactions and on the degradation of various polymers by reactions which bring about chain scission demonstrate quite clearly that the chemical reactivity of a functional group does not ordinarily depend on the size of the molecule to which it is attached. Exceptions occur only when the chain is so short as to allow the specific effect of one end group on the reactivity of the other to be appreciable. Evidence from a third type of polymer reaction, namely, that in which the lateral substituents of the polymer chain undergo reaction without alteration in the degree of polymerization, also support this conclusion. The velocity of saponification of polyvinyl acetate, for example, is very nearly the same as that for ethyl acetate under the same conditions. ... 

H. Othani and S. Tsuge, Degradation mechanisms of condensation polymers, in Applied Pyrolysis Handbook, T.H. Wampler (Ed.), Marcel Dekker, New York, 97 124 (1999). 

Mechanisms of degradation in condensation polymers, and the stabilisation of these polymers and non-polyolefin polymers such as poly(vinyl chloride) using organophosphites is discussed in terms of the stability of colour, thermal properties and molecular weight. Stabilisation of poly(ethylene terephthalate) and polycarbonate by organophosphites was studied experimentally. 5 refs. 

A. Potthast, T. Rosenau, J. Sartori, H. Sixta, and P. Kosma, Hydrolytic processes and condensation reactions in the cellulose solvent system A,iV-diemthylacetamide/lithium chloride. Part 2 Degradation of cellulose, Polymer, 44 (2003) 7—17. 

C Degradation Mechanisms of Condensation Polymers Polyesters and Polyamides... 

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