Graft copolymer: Graft PLLA with hydroxyl end-group was synthesized by ring-opening polymerization of L-LA [25]. The Mn and the polydispersity index were 1.52×104 and 1.14, respectively. Branched PCO polymers were synthesized by connecting castor oils with HDI. Graft PLLA with hydroxyl end-groups was reacted with hexamethylene diisocyanate, and then grafted into PCO to produce branched PCO-g-PLLA copolymers. The weight fraction of PLLA in PCO-g-PLLA copolymer is ca. 20%.