Preparation Of Polycarbonate Based Multipolymers Catalyzed By Chromium Complexes

In order to cope with the crisis of natural resources and the ecological environment caused by traditional non-degradable polymer materials,the design and development of eco-friendly polymer materials have become a research hotspot.Among which,CO₂-based polycarbonate material is one of the most important degradable polymer materials with good biocompatibility and thermodynamic properties.However,attempts at regulating the performance range of commercial materials have thus far met with limited success because of some inherent defects,such as brittle nature of poly（cyclohexene carbonate）.Multi-polymerization is regarded as a valuable strategy to tailor material performances.That is,incorporating well-chosen polymer chain segments into the polymer backbones,material properties can be tailored in a wide range by adjusting monomer sequence distribution and chain length.In this paper,a novel dissymmetric chromium complex was designed,and the catalytic performances were investigated via the ring-opening copolymerization（ROCOP）of cyclohexene oxide（CHO）and CO₂,and ring-opening polymerization（ROP）ofε-caproolactone（ε-CL）.Furthermore,introducing the third monomer（ε-CL or 6-membered cyclocarbonate（6CC））into polymerization of CHO and CO₂,the reaction process and thermal properties catalyzed by the dissymmetric chromium complex were studied systemically.The main contents are summarized as follows:i.A novel dissymmetric chromium complex was designed and synthesized basis of the Salen-Cr（III）complex.The ROCOP of CHO and CO₂and the ROP ofε-CL were investigated.The binary catalytic system composed of the dissymmetric Cr complex and the co-catalyst bi（triphenylphosphine）ammonium chloride（PPNCl）exhibited better catalytic performance and maintained higher selectivity of polycarbonate units than the Salen-Cr（III）complex in ROCOP of CHO and CO₂.In addition,the catalytic system also shows excellent catalytic activity in ROP ofε-CL.ii.Gradient polycarbonate-polyester copolymers possess distinctive physicochemical properties in comparison with block or random copolymers.However,their synthesis is still a challenge due to the distinct chain-growth mechanisms among various monomers.In this work,the novel gradient terpolymers were achieved from one-pot/one-step terpolymerization of CHO,CO₂ andε-CL mixture,by using the dissymmetric Cr（III）complex.Specifically,the gradient terpolymers were validated by investigating the reaction processes and chain microstructures.In addition,the chain configurations could be modulated by adjusting reaction conditions（temperature,pressure,or component ratio）,which further affected their physicochemical properties.iii.To further expand the sequence structures of the terpolymers,and establish the relationship between the chain structure and the properties of the material,6CC monomers with a variety of substitution structures were selected to replace theε-CL monomer.Specifically,in the terpolymerization of CHO,CO₂ and TMC,kinetics and NMR spectroscopy revealed the ROCOP and ROP reactions occurred simultaneously along with cross-chain exchange reactions,producing random terpolymers with uniform composition.In addition,the microstructures（average chain lengths of both sequences）of terpolymers could be modulated by changing the CO₂ pressure or reaction temperature.Furthermore,the substituents of 6CCs had a significant effect on the terpolymerization process and polymer chain structures（from random to gradient and block-like）.