Strong Base/Urea Catalyzed Ring-opening Polymerization Of ?-butyrolactone And Its Derivatives

Aliphatic polyesters have been widely used in biomedical materials,food packaging,etc.,considering their advantages of biocompatibility,biodegradability and good mechanical properties.Compared with other aliphatic polyesters,poly??-butyrolactone??P?BL?has better biocompatibility and suitable degradation rate,which can be prepared from cheap and commercially available?-BL.However,?-BL is genarally considered as a“non-polymerizable”monomer because of the low strain energy of the five-membered ring.This thesis focuses on the ring-opening polymerization of?-butyrolactone and its derivative using organic catalytic systems.The following two aspects have been studied:1.In the first section of this thesis,several ureas with different substituents were synthesized.A strong base/urea binary catalytic system was used to catalyze the ring-opening polymerization of?-BL.In this study,alkaline alkoxide?potassium methoxide,potassium tert-butoxide?or organophosphazene superbase?CTPB?were used as strong bases.It was found that the strong base/urea binary catalyst showed higher catalytic activity and higher selectivity than the single base.Compared with the alkaline alkoxide/urea system,the organophosphazene superbase/urea showed better catalytic activity.The effects of strong base,urea and polymerization conditions on the conversion of?-BL and the molecular weight of P?BL were systematically studied.Using cyclic trimeric phosphazene superbase?CTPB?and suitable urea as catalysts,P?BL with molecular weights up to 35.0 kDa can be synthesized.2.?-Methylene-?-butyrolactone?MBL?is a typical derivative of?-BL.The ring-opening polymerization of MBL can produce polymer with pendent double bond,which can be post-modified.In the second section of this thesis,the CTPB/urea binary catalytic system was used to catalyze the ring-opening polymerization of MBL,and successfully realized the chemoselective ring-opening polymerization of MBL.The CTPB/urea binary catalytic system was also used to catalyze the depolymerization of obtained P?MBL?_ROP,and MBL was quantitatively recovered.We proved that the recyclable unsaturated polyester can be produced by the organophosphazene superbase/urea binary catalytic system.