Polymerization with isomerization

The polymerization of lactams does not necessarily lead to polyzimides composed of the corresponding open chain units. Reimschuessel [245] introduced a new category of lactam derivatives the polymerization of which does not yield polyamides. Certain carboxyl substituted lactams prefer to polymerize in an isomerization—polycondensation process resulting in the formation of linear polyimides [245—251], viz. 

The repeating units (i.e. cyclic imides) could result either from dehydration of the polyamide formed in a ring opening polymerization 

The polymerization reaction followed second-order kinetics which was rationalized by assuming that the bimolecular rearrangement involving two monomer molecules was the rate determining step. It has been assumed that the isomerization results in the formation of the amino anhydride (XXXIV) or its dimer (XXXV), viz. 

The polymerization of the carboxy-lactam (XXXIII) proceeded with a distinct induction period [247] (tj) which was taken into account in the evaluation of the conversion data. The monomer is consumed in the isomerization reaction (152) with the formation of the amino anhydride (S) the rate being 

The polycondensation reactions (151) and (153) resulting in a decrease of the concentration of the linear species (S) follow the rate equation 

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Kennedy, J. P. and Otsu, T. Polymerization with Isomerization of Monomer Preceding Propagation. Vol. 7, pp- 369-385. 

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