Ring-opening Polymerization Of O-carboxyanhydride(OCA):Topology Structure And Crystallization Study

ROP of lactones is one of the most effective approaches to prepare PAHAs,which has been found wide applications in various fields such as biomedical science and gene delivery.When such a favorable synthetic strategy is applied to the OCAs,a group of PAHAs with side-chain functionality could be obtained.However,regardless of great efforts have been done in this field,it was still plagued by many problems,for example,poor catalytic activity,low stereoselectivity,and single topology.Therefore,to overcome above issues,we are dedicated to find a high active and enantioselective catalytic system to prepare crystalline isotactic PAHAs with controlled topologies.?1?The system based on Zn[N?SiMe₃?₂]₂/BnOH was demonstrated to be beneficial for the highly active ROP of 5-phenyl-1,3-dioxolane-2,4-dione?ManOCA,prepared from mandelic acid?,which produced poly?mandelic acid??PMA?with phenyl side chain.PMA is an attractive biodegradable polymer based on renewable resources as it shares many physical and mechanical properties with polystyrene.By investigating the effects of temperature,solvent,Zn[N?SiMe₃?₂]₂ and BnOH feed ratio,a highly isotactic PMA with controlled topologies?from fully linear to mixture of linear and cyclic structures?could be synthesized.DSC results of linear PMA suggest that a relatively large amount of a high melting polymorph with a T_m around 185°C along with a very small amount of a lower melting polymorph with a T_m around 135°C was observed.The highest enthalpies of fusion?H could be up to 28.4 J/g.Mixing of these opposite enantiomerically pure linear polymers in equivalent amounts affords the crystalline stereocomplexed PMA.The wide-angle X-ray diffraction?WAXRD?profile of linear PMA involves strong crystalline diffraction signals,which is different from stereocomplex one.?2?By regulating the influences including the acidity of center metal of catalyst,temperature and initiator type,a highly isotactic PMA with predominantly cyclic structure was prepared employing Ln[N?SiMe₃?₂]₃?Ln=La,Y,Sm?system.DSC analyses of cyclic samples suggest that a relatively large amount of a low melting polymorph with a T_m around140°C,along with a small amount of a higher melting polymorph with a T_m around 180°C was observed.The highest enthalpies of fusion?H could be up to 10.6 J/g.The cyclic stereocomplex could be obtained in a similar way to linear one.In contrast to linear stereocomplex,stereocomplex from cyclic PMA has double endothermic peaks at 172°C and131°C respectively.WAXRD study confirmed that the crystalline diffraction peaks of cyclic stereocomplex are different from linear one,which highlights a potential method for distinguishing cyclic and linear PMAs.?3?The Y???-[OOOO]complex was applied to achieve ROP for rac-5-benzyl-1,3-dioxolane-2,4-dione?rac-PheOCA,prepared from phenylalanine?,and PAHA with benzyl side chain could be prepared with a molecular weight up to 14.0 kg/mol.It can also achieve rapid ROP of benzyl 2-?2,5-dioxo-1,3-dioxolan-4-yl?acetate?MalOCA,derived from aspartic acid?with a turnover frequency of 3000 h^-1.After alternating the monomer with ManOCA,a highly isotactic PMA with a cyclic topology as the major ion peak could be obtained.