CHANGE IN MOLECULAR-WEIGHT DISTRIBUTION DURING FORMATION AND DEGRADATION OF STAR POLYMERS

A general model has been derived to describe the formation of star pol ymers via various polymerization mechanisms. The model gives the bivar iate distributions of molecular weight and number of branches of the s tar polymers. Key parameters determining the distributions include the distribution of primary polymers and the branching density. Analytica l distribution functions are obtained for the systems having branches of uniform, random, or Schulz-Zimm distributions. The distribution pol ydispersity of the star polymers approaches unity for sufficiently hig h branching densities regardless of the distribution of primary chains . The model has also been extended to give the change in the average m olecular weights when star polymers undergo degradation. The scheme of disconnecting branches from star cores is considered. Polydispersity of polymer mixture shows a maximum value at an intermediate degree of degradation.