Aluminum-catalyzed Copolymerization Of Lactones With Epoxides

The ring-opening copolymerization of epoxides and lactones afford polyether-polyester copolymers which pocesse not only good biocompatibility and biodegradability of polyesters but also good hydrophilicity and physical and mechanical properties of polyethers.The polyether-polyester copolymers have broad application prospects in self-assembly,elastomer and biomedical applications.In this thesis,the copolymerization of epoxides（including ethylene oxide（EO）,epichlorohydrin（ECH）,propylene oxide（PO））with lactones（including caprolactone（CL）and valerolactone（VL））by i-Bu₃Al/H₃PO₄/DBU has been carried out.The effect of the structure of epoxides and lactones on copolymerization activity and copolymers structure was revealed by copolymerization kinetics and copolymers structure analysis.A series of polyether-polyester copolymers with controllable molecular weight and composition have been prepared efficiently.1.The copolymerization of epoxides and lactones by i-Bu₃Al/H₃PO₄/DBU has been successfully achieved at room temperature to afford EO-CL,ECH-CL,PO-CL,PO-VL copolymers with controllable compositions in 99%yield by changing the feed ratio of epoxides and Lactones.The GPC analysis of these copolymers showed that these copolymers possessed high molecular weight（M_n=2.5×10⁴～18.1×10⁴）and narrow distribution（M_w/M_n=1.42～1.62）.The molecular weight of these copolymers can be adjusted by changing the molar ratio of monomers to catalyst.The EO-CL copolymers with different compositions possessed a melting point（T_m）of 60℃;The ECH-CL,PO-CL,PO-VL copolymers possessed a T_m of 55℃ when the lactone content in these copolymers was higher than 20 mol%.2.For a further understanding of copolymerization process,in situ ¹H-NMR kinetic studies of epoxides/lactones copolymerization were carried out.Reactivity ratios of r _EO=12.87±0.57,r _CL=0.11±0.02,r _ECH=8.53±0.15,r _CL=0.13±0.01,r _PO=2.08±0.20,r _CL=0.59±0.08and r _PO=1.81±0.14,r_VL=0.55±0.04 calculated via the Nonterminal Model of Chain Copolymerization indicated that the obtained EO-CL,ECH-CL,PO-CL,PO-VL copolymers were statistical copolymers with tapered,gradient and random structure.The sequence structure of epoxide-lactone copolymers can be adjusted by changing the structures of lactone and epoxide.3.The terpolymerization of EO,ECH with CL by i-Bu₃Al/H₃PO₄/DBU has also been successfully achieved to afford EO-ECH-CL terpolymers with controllable compositions by changing the feed ratio of epoxides and Lactone.The EO-ECH-CL terpolymers with different compositions possessed a glass transition temperature（T_g）from-38 ^oC to-55 ^oC originating from the random copolymerization sequence of EO-ECH and a T_m of about 53 ^oC originating from poly（CL）block.EO and ECH were randomly copolymerized,and then copolymerized with CL to form poly（CL）block in the terpolymerization of EO,ECH and CL.