Recent Results on Chemical Modification of Polymers

Abstract

Abstract Some characteristic features of chemical transformations of polymers are examined on three examples: 1 The reactions of various organo-lithium bases onto the ester carbonyls of polymethylmethacrylate are typical examples of one-step substitutions involving retardation, i.e. decreased reactivity of units vicinal to substituted ones. 2 The reaction of phenyl-lithium onto the carbonyl groups of PMMA is a typical two-step substitution process, with additional possibilities of cyclization via lactonization or via acetalization. To understand the reactions involved it is necessary to make use of model-molecules and of copolymers where cyclizations are avoided. It was established that retardation characterizes the first step (ketone formation) but the probability of the second step to occur subsequently is rather high. Lactonization (by attack of an alcoolate onto a vicinal ester) is therefore somewhat privileged. 3 Chemical modification of polyvinylalcohol by metallation and subsequent reactions of alkylhalides or of propane sultone was investigated thoroughly. It was found that sequential substitution was obtained. This is due to enhanced reactivity of units vicinal to substituted ones (case or propane sultone); but it may also be due to the tendency of side chains to crystallize in double layers, in which case the placement of the substituted units is determined by physical effects rather than by purely chemical factors.