Observations on intramolecular reaction in addition polymerization systems

Abstract

The polymerization of monomers containing two or more double bonds leads to the formation of cross-linked polymers, but very little information is available on the reaction mechanisms involved. This paper presents a systematic study of fourteen members of one group of such systems, the diallyl esters, and attempts to correlate the structure of the monomers with their behaviour on polymerization. Intramolecular reaction was observed in all cases. Two types of this reaction could be distinguished and quantitatively estimated as the fraction of total monomer units in the polymer so reacted. Multiple cross-linking, involving the formation of more than one cross­ link between polymer chains, occurred in one system, and chain cyclization, involving the presence of both allyl radicals of a monomer unit in the same polymer chain, was observed in all other cases. A detailed investigation of the diallyl o -phthalate system showed that termination of chain growth occurs by degradative chain transfer to monomer, although a significant proportion of the degraded radicals are able to re-initiate chain growth. The ratio of cyclization to propagation reaction coefficients can be calculated and provides a quantitative measurement of the tendency of the monomer to undergo chain cyclization. The αω -ester monomers decrease in tendency to cyclize as the distance between allyl groups increases, except in the case of diallyl succinate which shows an exceptionally high tendency. This is in accordance with measurements of other physical properties of the homologous ester series which indicate abnormal behaviour of the succinate. The results support the theory that the tendency of a monomer to cyclize is largely con­trolled by the distance between polymerizable groups. The steric limitations imposed by the number and nature of the atoms in the cyclic structures do not appear to exert the same influence as they do in bifunctional condensation systems.