Preparation And Properties Of Poly (Lactic Acid)/Polyethylene Glycol Block Copolymer Composites

PLA-PEG-PLAtriblockcopolymerhasgoodbiodegradabilityand biocompatibility PLA-PEG-PLA triblock copolymer can form hydrogels in water.In the hydrogels of PLA-PEG-PLA triblock copolymer,the hydrophilic and hydrophobic structure of the copolymer has great influence on the physical and mechanical properties of the hydrogels.The driving forces for forming PLA-PEG-PLA hydrogels are hydrophobic and stereotactic.The stereotactic complexation between PLA chain segments can form stereotactic crystals in the hydrogel,and forming a stereotactic complexation crosslinking network,and forming a hydrogel with good physical and mechanical properties.Therefore,studies on the crystallization of PLA-PEG-PLA triblock copolymer can provide theoretical guidance for the design of copolymer materials.Althoughthephysicalandmechanicalpropertiesof PLLA-PEG-PLLA/PDLA-PEG-PDLA hydrogel system are better than that of PLLA-PEG-PLLA system,it is still difficult to meet the application requirements in the field of biomedicine.In this paper,The structure,molecular weight and molecular weight distribution of PLLA-PEG-PLLA triblock copolymer with different chain length and proportion were confirmed by ft-ir,NMR and GPC.The DSC,XRD and POM tests were carried out to study the effects of chain length and proportion on the crystallization of PEG chain segment and the homogenization of PLLA chain segment in the copolymer,and the crystallization limitation mechanism between PLA chain segment and PEG chain segment in the three-block copolymer was found.By changing the length of the PLA chain segment and the isomer ratio of the triblock copolymer in the PLLA-PEG-PLLA/PDLA-PEG-PDLA stereolithical complex,it was found that the closer the proportion of the stereolithical complex was to 50:50,the more the melt cooling crystallization favored the formation of SC crystals,and the formation of SC crystals would limit the formation of HC crystals.When the composite ratio is greater than 50:50,HC and SC crystals will appear at the same time,but the formation of HC crystal is more preferred.The longer the length of PLA segment,the easier the crystallization of SC crystal and the higher the crystallinity.The formation of SC crystal is greatly affected by the length of PDLA segment,followed by the proportion.Nanostructured composite hydrogels with different LAP concentrations were prepared by lamination of LAP with triblock copolymer LA₄₄^0.8EG²₅₆LA₄₄^0.8.With the increase of temperature,all the hydrogels exhibited thermo-sensitive mechanical changes.It was found that the formation of HC crystal was hindered by the addition of low LAP,and the formation of HC crystal was promoted by high LAP.Hydrogen bond interaction exists between PEG segment and LAP nanoparticles.The modulus of composite hydrogel is mainly affected by LAP concentration,but the formation of HC crystal and SC crystal has little effect on the modulus of composite hydrogel.