Study Of Aliphatic Polyesters Initiated By The Multi-hydroxyl Groups Biomass

At present,there is a great interest in biodegradable polymers,which can be used as a substitute for plastics,thereby reducing pollution caused by plastic waste.Aliphatic polyesters have shown great advantages in the processing of commodity polymers from cheap daily necessities to expensive special composite materials(including advanced medical materials)(for example,with a good supply balance,low cost and excellent Processability),which has received widespread attention.However,these polymers are usually obtained by ring-opening polymerization of lactone monomers initiated by petroleum-based initiators.Their recovery rate is low and they are not completely degradable.Residual petroleum-based initiators can also affect the performance of products.Therefore,the development of highly effective non-toxic bio-based initiators is the focus of solving this problem In this paper,a five membered ring initiator with three hydroxyl groups was prepared by using glucolactone as the bio-initiator raw material;three-arm polycaprolactone(PCL)and three-arm polylactic acid(PLA)were prepared by ring opening polymerization under the action of nonmetal catalyst1,5,7-triaazabicyclo[4.4.0]decane-5-ene(TBD),and their properties and applications were systemically studied.The main contents and results are as follows:(1)Using glucolactone as raw material can protect the primary hydroxyl group selectively and then a six membered lactone monomer with three secondary hydroxyl groups—P-GDL was obtained.By using the intramolecular rearrangement of open-loop,the"six membered ring"was converted into"five membered ring"to obtain a five membered ring three-terminal initiator with thermodynamic stability.(2)A series of three-arm PLA with different molecular weight were obtained by ring opening polymerization with five-member-ring initiators,and TBD as catalyst.Results indicated that three-arm PLA were successfully synthesized via the controlled polymerization method initiated by the bio-based,five-member-ring initiators.The influence of single arm length and branching on the thermal properties of three-arm PLA was studied:with the increase of single arm length,the temperature of glass transition(T_g)of PLA increased gradually.Compared with single arm PLA,T_g of three arm PLA was lower due to the influence of branching structure.(3)A series of three arm PCL with different molecular weight were obtained by ring opening polymerization with the small five-membered-ring molecules as initiator and TBD as catalyst.Results indicated that three-arm PCL were successfully synthesized via the controlled polymerization method initiated by the bio-based,five-member-ring initiators.The effects of single arm length and branching on the thermal properties of three-arm PCL were studied:with the increase of single arm molecular weight,the temperature of crystallization(T_c)and temperature of melting(T_m)increased.The crystallization temperature(T_c)and melting temperature(T_m)of three arm polycaprolactone were lower than that of one arm polycaprolactone initiated by benzyl alcohol.(4)Through the hydrolysis of three-arm PLA and three-arm PCL,the protective group was removed successfully,then three-arm PLA and three-arm PCL with primary hydroxyl group was obtained.The amphiphilic PLA and PCL were prepared by hydroxy coupling polyethylene glycol,and the hydrophobic drug DOX was successfully encapsulated with the particle sizes ranging from 100 nm to 150 nm,which exhibited great potentials as the drug carriers.