Synthesis And Properties Of Bio-based Thermoplastic Elastomers Based On γ-butyrolactone And Its Derivatieves

Thermoplastic elastomers are used in many industrial fields,such as footwear,automotive components,medical devices and aerospace,since they combine the processing and molding abilities of thermoplastics and the flexibility and elasticity of cross-linked rubbers.Currently,most thermoplastic elastomers are derived from fossil fuels.The non-renewability of fossil fuels and the environmental impact caused by petroleum production have led to an increasing interest to develop new thermoplastic elastomers from renewable resources.Triblock copolymers are an important branch of thermoplastic elastomers.The microphase separation of the soft and hard segments provides the material high tensile strength,elongation at break and elastic recovery.In this thesis,triblock copolymers PLLA-b-(PBL-co-PCL)-b-PLLA with well-defined structures was successfully prepared from monomers derived from renewable biomass resources with using organic cyclic trimetic phosphazene base(CTPB)/urea binary catalyst.The effects of catalyst structure and reaction conditions on the sequence structures,molecular weights and molecular weight distributions of block copolymers were studied.The thermodynamic and mechanical properties of the obtained triblock copolymers were investigated.The related tests indicated that the obtained block copolymers exhibited thermoplastic elastomer behaviors with high elongation and strength at break.Some triblock copolymers exhibited shape memory behaviors.This thesis mainly includes the following two sections:1.The PBL-co-PCL copolyesters were prepared by ring-opening copolymerization ofγ-butyrolactone(γ-BL)withε-caprolactone(ε-CL)by using cyclic trimetic phosphazene base(CTPB)/urea as catalyst and 1,4-benzenedimethanol as initiator.The effects of catalyst,reaction time,feed ratio,and monomer ratio on the copolymerization ofγ-BL withε-CL were systemmatically investigated.The main conclusions were as followed:(1)When CTPB/U3 was used as a catalyst,copolyesters with high molecular weights and narrow molecular weight distributions were prepared;(2)The molecular weight distributions of PBL-co-PCL copolyesters increased significantly as the reaction time increased,which is probably ascribed to the transesterification reaction;(3)The molecular weights of PBL-co-PCL copolyesters increased with the increase of the feeding molar ratio within a certain range;(4)The molecular weights of PBL-co-PCL copolyester decreased with the increase of monomer ratio ofγ-BL/ε-CL.2.The PLLA-b-(PBL-co-PCL)-b-PLLA triblock polymers were prepared by a one-pot,sequential ROP ofγ-BL/ε-CL and L-LA.The structures of obtained triblock copolymers PLLA-b-(PBL-co-PCL)-b-PLLA were carefully examined collaboratively with one-dimensional NMR(~1H-NMR),two-dimensional NMR(DOSY NMR)techniques and size exclusion chromatography(SEC).The thermodynamic and mechanical properties of the triblock copolymers were investigated with using differential scanning calorimeter(DSC),thermogravimetric analysis(TGA),dynamic thermomechanical analysis(DMA),small angle X-ray scattering(SAXS)and uniaxial tensile test.Microphase separation structure was demonstrated by DSC and SAXS.The obtained block copolymers behaved as thermoplastic elastomers.The strength and elongation at break of the TPE-2 sample is 12 MPa and 1200%,respectively.The cyclic tensile test showed that the elastic recovery is as high as 92%.