Self-branching in the polymerization of vinyl acetate

Abstract

Polyvinylacetate labelled with the radioactive isotope carbon-14 has been used to study the reactions by which side-chains are introduced into polyvinylacetate. It is believed that the first stage in the growth of a branch is the process of 'transfer to polymer' in which a growing radical abstracts a hydrogen atom from a polymer molecule so forming a new reactive point along the length of the molecule. Inactive monomer was polymerized in the presence of radioactive polymer and from the product was isolated material consisting of the original active polymer with inactive side-chains grafted on it. It was possible to calculate the number of branches and their average length and also to determine the value for the velocity constant for the process of 'transfer to polymer'. It was found that the abstraction of a hydrogen atom from a dead polymer molecule by a polyvinylacetate radical occurs at a rate very similar to that with which the radical abstracts a hydrogen atom from a small molecule.