Controllable Syntheses Of Homopolymer And Copolymer Of Mandelic Acid

The polyesters of poly(?-hydroxy acid)s derived from biorenewable have received widespread attention as an ideal substitute for traditional petroleum-based plastics.As a representative of poly(?-hydroxy acid),poly(lactic acid)is widely used in packaging materials,textiles,biomedicine and other fields.However,its low glass transition temperature(T_g?60?)limits its application range.Poly(mandelic acid),an analogue of poly(lactic acid),has attracted widespread scientists'attention due to excellent thermodynamic properties,which has a high T_g(?100?)and a thermal decomposition temperature(T_d)of up to 300?.The ring-opening polymerization(ROP)of mandelic acid-O-carboxyanhydride(man OCA)is currently the most effective method to prepare poly(mandelic acid).However,due to the strong acidity of the methine in the monomer of mandelic acid,the side reaction of racemization is prone to occur during the polymerization process.As a result,it is difficult to control the stereoregularity of poly(mandelic acid).At present,there are only a few reports on the synthesis of poly(mandelic acid)with high stereoregularity.The stereoregularity and sequence structure of the polymer are closely related to the physical and mechanical properties of the polymer.Therefore,the activity-controllable and stereoselective ring-opening polymerization of manOCA is a very meaningful and challenging subject.On the basis of controlling the structure of homopolymer of mandelic acid,the controlling of the structure of mandelic acid and other monomer copolymers is an important mean to further control the properties of poly(mandelic acid);the degradation rate of biodegradable polyester is an important indicator in practical applications.Copolymerization of other monomers and mandelic acid monomers and controlling the sequence structure of the copolymer is an effective method to control the degradation rate of mandelic acid copolymers.There are few reports on mandelic acid polymers in this area.Based on the above background,the main content of this thesis is to design various metal complex catalysts,and use these complexes for the stereo controllable polymerization of mandelic acid cyclic monomers,stereoselective polymerization,and controllable synthesis of alternating copolymers of salicylic acid and mandelic acid,and tested the effects of stereo-structure and sequence structure on the properties of mandelic acid polymers.Part 1:Review the progress of the synthesis of poly(mandelic acid)in recent years.Part 2:A series of weak Lewis pairs were designed and synthesized with bisphenol zinc complex as the Lewis acid and weakly basic 3-fluoropyridine as the Lewis base,which can successfully inhibit the racemization of the monomer of L-manOCA in the process of ring-opening polymerization,then the controllable,highly stereoregular isotactic poly(L-mandelic acid)were obtained.The experimental results showed isotactic poly(L-mandelic acid)has higher thermal stability(T_g=107?,T_m=180?;M_n=24.2 kg/mol),and has similar properties to polystyrene with a high glass transition temperature and melting temperature.The WAXS experiments proved that two highly isotactic poly(L-mandelic acid)and poly(D-mandelic acid)mixed in equal proportions can form a stereocomplex.The melting temperature of the stereocomplex after isothermal crystallization was 173?.Part 3:Based on part 2,isotactic poly(rac-mandelic acid)was synthesized for the first time using the Lewis pairs as catalysts for the ring-opening polymerization of rac-man OCA.The effects of bisphenol zinc complexes with different ligands as Lewis acids on the stereoselective ring-opening polymerization of rac-man OCA are studied,the increase of steric hindrance around the central metal zinc is not conducive to this stereoselective ring-opening polymerization of rac-man OCA.The isotactic stereoselectivity(P_m)of the ring-opening polymerization of bisphenol zinc complexes with tert-butyl as substituents is high up to 0.92,and the glass transition temperature of the high stereoselectivity of poly(rac-mandelic acid)(P_m=0.92)is 10?higher than poly(rac-mandelic acid)(P_m=0.60)with a similar molecular weight.The melting point of poly(rac-mandelic acid)(P_m=0.92)after isothermal crystallization(crystallization from methanol and DCM)is 116?.Part 4:In order to solve the problem of low molecular weights of the obtained poly(mandelic acid),high-activity OOO-tridentate bisphenol zinc complexes were designed and synthesized,and applied in the ring-opening polymerization of manOCA.These zinc complexes overcome the easy racemization of manOCA in the polymerization process.The experimental results show that such zinc complexes can catalyze the ring-opening polymerization of manOCA monomers with a controllable living manner.These complexes can be used to synthesize high stereoregularity poly(mandelic acid)with a molecular weight of 32.5 kg/mol.Using this living polymerization method,the precise synthesis of stereo di-and tri-block poly(mandelic acid)can be further achieved in a one-pot method.Thermal analysis(DSC)and X-ray diffraction(XRD)show that stereo multi-block poly(mandelic acid)can quickly form a stereocomplex with a melting temperature(T_m)as high as 178?.During the research process,it was also found that the solubility of stereoblock poly(mandelic acid)and pure chiral poly(mandelic acid)is very different.Part 5:Poly(mandelic acid)has relatively poor degradability.The ring-opening polymerizations of the new dimeric monomer of mandelic acid and salicylic acid(salicylic phenyl glycolide,SPG)catalyzed by the triphenol magnesium/zinc ion-pair complexes were studied.And the sequence-regular cyclic alternating copolymers with high-molecular-weight were obtained.These polyesters not only have a high glass transition temperature(T_g=94?)but also have the potential to be degraded under mild conditions.Finally,all the works during the doctoral period were summarized and the future development for the research topic was proposed.