The Copolymerization Of Epoxides With Cyclic Anhydrides,COS And The Mechanism

By the copolymerization of epoxides with other monomers,various functionalized polymers can be synthesized in an atom-economic manner.Although a varity of catalysts have been reported in synthesizing polyesters and poly(monothiocarbonate)s from the copolymerization of epoxides with cyclic anhydrides and carbonyl sulfide(COS).It still remains a big challenge in seeking or designing new epoxides(esp.biomass derived epoxides)and highly efficient catalysts for such copolymerization process.We have made an effort to catalyze the alternating copolymerization of epoxides with cyclic anhydrides or COS.In terms of developing epoxides from biomass,we synthesized several eugenol and guaiacol-based epoxides via the reaction of bio-derived compounds with epichlorohydrin that can also derived from biomass.These new epoxides were used to copolymerize with COS,afforded well-defined poly(monothiocarbonate)with excellent optical properties.In terms of catalysts,a metal-free ogranic Lewis pairs catalytic system has been developed to catalyze the copolymerization of epoxides and anhydrides.The infulence of Lewis acids and Lewis bases on epoxides/anhydrides copolymerization were investigated.The investigation on the copolymerzation mechanism using these Lewis pairs has also been carried out in detail.Block polyesters and poly(ester-b-monothiocarbonate)s were prepared by copolymerization of epoxides with different anhydrides,COS in the presence of Lewis pairs.First,we report the catalytic formation of alternating and regioregular copolymers from carbonyl sulfide(COS)and epoxides along with eugenol-based glycidyl ether(EGE)and guaiacol-based glycidyl ether(GGE),derived from eugenol and guaiacol,respectively.The(salen)CrCl complex,accompanied with various organic bases,was highly active towards the EGE/COS,GGE/COS copolymerization and EGE/GGE/COS terpolymerization.The turnover of frequency(TOF)of the(salen)CrCl complex for the EGE/COS copolymerization was up to 12 000 h-1.The number-average molecular weight(Mn)of the resultant EGE/COS copolymer was up to 62.2 kg/mol-1.In the presence of 0.5-1.5 mol%chlorohydrin,which was a by-product of the synthetic process of EGE,a-Cl,u-OH EGE/COS copolymers were obtained.This result suggests that chlorohydrin could act as a very efficient chain transfer agent for the copolymerization.The EGE/COS,GGE/COS,and EGE/GGE/COS copolymers were soluble in most of the common solvents and exhibited a high refractive index of more than 1.58 with high Abbe numbers of up to 40.4.Moreover,EGE/COS copolymers were crosslinked via the free radical addition reaction of sulfur(S8)with the pending double bond,afforded thermosets with improved Tg of 46.7-114.9 ? and Td,5wt?s of 261-267 ?,improved nd of 1.640-1.734 and Vd of 33.5-39.8.Second,polyester synthesis from the alternating copolymerization of epoxides with cyclic anhydrides via a metal-free route remains a key challenge.This work reports the development of a highly active organocatalytic route for the copolymerization of a spectrum of epoxides and cyclic anhydrides.Fully alternating polyesters were synthesized by a variety of organic Lewis acid-base pairs including organoboranes and quaternary onium salts.The effect of the acidity,type,and size of Lewis pairs on the catalytic activity and selectivity of the copolymerization is presented.The undesirable transesterification and etherification were effectively suppressed even in the case of complete conversion of the cyclic anhydride.This could be ascribed to the formation of a unique tetracoordinate bond-carboxylate(or alkoxide)anion.The Lewis pairs are highly active,with a turnover frequency of 102 and 303 h-1 for the copolymerization of propylene oxide with maleic anhydride and phthalic anhydride,respectively,at 80 ?.Block polyester with narrow polydispersity of 1.05 was achieved via a sequential addition strategy.This work provides robust organocatalysts for the selective copolymerization of epoxides with cyclic anhydrides.Finally,the alternating copolymerization of PO and various anhydrides was achieved in the presence of TEB/organic bases,providing copolymers with Mn up to 35.8 kg/mol and D of 1.06.TEA/TEB pair exhibited highest acitivity towards the copolymerization of PO and MA.And the MTBD/TEB pair exhibited highest activity and regioselectivity for the PO/PA copolymerization.The contents of head-to-tail(H-T)linkages of the resultant polyester was up to 98%.Furthermore,the block copolymer of polyester and poly(monothiocarbonate)was achieved via the terpolymerization of PO,PA and COS catalyzed by TEB/DBU pair.