Synthesis of star-branched polymers by means of reactive melt blending of end-functionalized polymers

Chain-end-functionalized poly(ε-caprolactone)s with one or two anhydride moieties (PCL-Anh and PCL-Anh2, respectively) were successfully synthesized by the successive reactions starting from a chain-end hydroxy group of the polymer. This involves an introduction of carboxylic acid by the reaction of hydroxy group with succinic anhydride, an introduction of conjugated diene function by Mitsunobu reaction with 2,4-hexadien-1-ol, and an introduction of anhydride moiety by Diels-Alder reaction with maleic anhydride. The melt blending of PCL-Anh with amino-functionalized polystyrene (PS-NH₂) was carried out at 180°C. The SEC curves showed a new peak at the high molecular weight region corresponding to the objective AB diblock copolymer within 5 min, suggesting the smooth reaction of anhydride moiety and amino group. On the other hand, the melt blending of PCL-Anh2 with PS-NH₂ proceeds smoothly to afford AB diblock copolymer, however, the quantitative reaction to produce A₂B star-branched polymer seems to be difficult.