This paper investigates in detail the ring-chain competition in A,,-B,, type polycondensations by use of a molecular model of tree branching and the basic principles of probability. The intramolecular cyclization equations and the critical gelation condition containing both intermolecular and intramolecular reaction parameters have been obtained.

By means of the gelation equation containing both inter-and intramolecular reaction parameters obtained by the authors, this paper deduces the gelation range of Aai-Bbj type polycondensation. The experimental data are essentially in agreement with our theoretical results. K e y words: curing theory, Aai-Bbj type polycondensation, gelation range, gelation region, intramolecular reaction.

An alternative way is proposed to approach the sol-gel distribution of A,,-B,, type polycondensation by taking into consideration intramolecular reaction. The equations deduced basically from the definition of the sol fraction and the chemical equilibrium of reactants in this paper can be reduced to those of Tang Au-chin's and Miller's expressions. Comparing experimental with theoretical values, we found that the results of this paper are closer to the real cases than those of other authors.

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