The effect of limited monomer solubility in heterogeneous step-growth polymerization.

Limited monomer solubility imposes very intriguing features on poly(p-phenylenebenzobisoxazole) polymerization. Only one type of functional group is detected at oligomer chain ends, and a high-molecular-weight polymer is obtained even when an excess of the monomer with low solubility is used. These remarkable phenomena are interpreted as an unprecedented "spoon-feeding-of-monomer" mechanism. A novel apparatus for staged polymerization is described that was triggered by the uniqueness of the heterogeneous step-growth polymerization. Hyperbranched polyesters and a polyurethane/polyethylene blend, which represent two phases in the polymerization process, are also discussed.