Facile And Controlled Synthesis Of Functional Polyester Using Metal-Free Catalyst

Functional polyesters are a class of oxygen-containing polymers whose improved properties usually originate from the alterations in their chain structure,topological structure or functional groups.Hence,rising attentions have been paid to the achievement of new properties of polyesters through elaborate design of their microstructures.Suffering from the inability of traditional polycondensation routes to precisely control the microstructure of the resulting polyester,studies on the synthesis and the structure-property relationships of functional polyester are retarded.With the developments of organic/metal-free catalyst,many polyester structures that are difficult to construct previously are now available through the ring-opening alternating copolymerization?ROAP?of epoxides and cyclic anhydrides,which emerges as a promising strategy that is capable of tuning the chain and topological structure of the resultant polyester with precision.The present dissertation mainly focuses on revealing the unique advantages of the ROAP strategy in producing post-modifiable functional polyesters and constructing bottlebrush structure.Details are given as followed.Epichlorohydrin?ECH?,a chloromethyl-carrying epoxide monomer,is subject to ring-opening copolymerization with cyclic anhydrides using a mild phosphazene base?t-Bu P₁?or a Lewis pair comprising t-Bu P₁and triethylborane as an organic/metal-free catalyst.The products exhibit controlled molar mass and strictly alternating sequence distribution without any ether linkages though ECH is added in large excess.The use of single-component organobase catalyst triggers the nucleophilic substitution?NS?of the ECH chloromethyl groups by the chain-end carboxylate species and leads to a relatively high molar mass distribution.On one hand,this side reaction suspends the propagation of some chains and generates chloride anions that can reinitiate the copolymerization,thus leads to low-molar-mass byproducts.On the other hand,the epoxy-terminated copolymers may undergo chain-end ring opening to form high-molar-mass byproducts.The two-component catalyst has a higher preference toward epoxide groups and allows for a highly adjustable catalytic activity.Ring-opening reaction of epoxy chain ends can be greatly suppressed at room temperature,resulting in narrowly distributed molar mass,ranging from 2 to 30 kg mol^-1,at high anhydride conversion.With optimized catalyst loading and composition,NS still occurs,however,at late stages of the copolymerization so that pendent-and end-group bifunctionalized polyester can be achieved in one synthetic step.Bottlebrush polyesters are synthesized using a tandem ROAP-ROMP“graft through”strategy.Phophazene?t-Bu P₁?catalyzed ROAP of phthalic anhydride and epoxides initiated by norbornenyl alcohol are first performed to produce macromonomers with norbornenyl end groups.Benefitting from its non-nucleophilic nature,t-Bu P₁ does not poison the Grubbs catalyst which catalyze the ring opening metathesis polymerization?ROMP?and can coexist with it harmoniously.Consequently,Grubbs catalyst can be directly fed into the diluted solution of unprecipitated macromonomers to produce high-molar-mass bottlebrush polyester in one pot.Mismatch of the k_i and k_p value of the ROMP process are believed to be responsible for the moderate dispersity of bottlebrush polyester.Upon optimization of the reaction conditions,k_i and k_p are nicely balanced and successful preparation of narrowly distributed bottlebrush polyester is achieved.In summary,results listed in this thesis demonstrate the advantages of organic/metal-free catalysts in opening new ROAP-based pathways to well-defined functional polyesters with novel structures.