Study On Structure Regulation And Thermal Conductivity Of Poly(Butylene Succinate) Ionomers

The polymer matrix usually exhibits poor thermal conductivity due to the defects of slow phonon propagation velocity and high thermal resistance of the interface between the crystal and amorphous region,which greatly limits its application in the field of thermal management materials.For the ionomers,due to the strong coulomb force between the ionic groups,the molecular chain undergoes microphase separation and forms nanoscale ionic clusters,giving the ionomer a unique molecular chain structure and macroscopic properties.The molecular chain structure and condensed structure are the key factors affecting the thermal conductivity of the polymer.Therefore,to investigate the regulation mechanism of ionic group types and content on crystallization and thermal conductivity of ionomers,the ionization modification of poly?butylene succinate??PBS?was carried out.Furthermore,to obtain the regulation mechanism of the thermal conductivity of ionomers,the effects of molecular chain flexibility,condensed structure and crystallization environment on the thermal conductivity of ionomers were investigated.To investigate the impact of rigid phosphorus-containing ionic groups?PCIG?content on the molecular chain structure,crystal morphology and thermal conductivity of the ionomer,a phosphorus-containing PBS ionomer?PBSIs-K?with 8-?2-hydroxy-ethoxy?carbon-yl-phosphonium hypophosphorous acid potassium phosphate?DHPPO-K?as ionic monomer was prepared by copolycondensation reaction in the third chapter.The rheological,crystallization and thermal conductivity of PBSIs-K were determined by dynamic rheology,DSC,POM,XRD and comprehensive physical property measurement system?PPMS?,respectively.The results revealed that the melt viscosity of the ionomer significantly increased due to the physical cross-linking effect caused by the aggregation of PCIG ionic clusters.Moreover,the thermal conductivity of PBSIs-K was highly correlated with the crystal morphology.The thermal conductivity of PBSI1-K was strikingly promoted from 110 to 320 mW/m?k as the spherulitic diameter increased from 181 to 353?m.The thermal conductivity of PBSIs-K was then decreased to 130 mW/m·k due to the decreased crystallization ability of higher PCIG content.The crystallinity and crystallization temperature of PBSI7.5-K were only 45.2%and 43.2°C,respectively.The effects of PCIG content on the physical properties of PBSIs-K were investigated by stretching,hydrolytic degradation and oxygen permeability.The results indicated that PBSIs-K with good degradation,oxygen barrier and tensile properties has been successfully obtained.The results of this chapter showed that the unique molecular chain structure and crystal morphology of PBS due to the introduction of PCIG realized the regulation of the thermal conductivity of ionomers and ensured the good comprehensive performance.To evaluate the effect of flexible urethane ionic group?UIG?content on molecular chain structure,crystal morphology and thermal conductivity of the ionomer,the PBS urethane ionomer?PBSUI?with diethanolamine hydrochloride?DEAH?as ionic monomer was prepared by polycondensation-chain extension reaction in the fourth chapter.The rheological,crystallization and thermal conductivity of PBSUI were characterized by dynamic rheological,XRD,POM and PPMS,respectively.The results revealed that the complex viscosity of PBSUI-1 exhibited a slight increase,and the crystallinity and spherulite diameter decreased slightly.The tight packing of the UIG hard segment molecular chain under low melt viscosity increased the thermal conductivity of PBSUI-1 from 94 to 207 mW/m·k.As the content of UIG increased,the complex viscosity of PBSUI increased remarkably and the diameter of spherulites gradually decreased from 185 to 105?m,and thus the thermal conductivity decreased to 94 mW/m·k.To further investigate the influence of phase morphology and molecular chain flexibility on the crystallization behavior and thermal conductivity of the ionomer,the PBSUI-1 modified by boron nitride?BN?and ethylene glycol?EG?was prepared by melt blending.The crystallization and thermal conductivity of PBSUI-1 were characterized by DSC and PPMS,respectively.The results showed that with the corporation of BN and EG,the crystallinity of PBSUI-1significantly decreased from 58.4%to 45.3%and 47.6%,respectively.And the thermal conductivity of PBSUI-1 reduced from 207 mW/m·k to 186 mW/m·k and 164 mW/m·k,respectively.While with the corporation of the BN/EG blends,the crystallinity of PBSUI-1reduced to 44.3%and its thermal conductivity increased to 219 mW/m·k.The results of this chapter showed that the introduction of UIG,BN and EG can change the molecular chain structure or condensed structure of PBS to different degrees,thus achieving the regulation of the thermal conductivity of ionomer.To investigate the effect of crystallization and foam morphology on the condensed structure and thermal conductivity of the ionomers,the PBSUI was processed by isothermal crystallization and supercritical CO₂?sc-CO₂?foaming,respectively.The crystallization and thermal conductivity of PBSUI-1 after isothermal crystallization treatment were characterized by DSC,XRD and PPMS,respectively.The results showed that the crystallinity?X_c?and crystallite diameter?D_c?of PBSUI-1 treated isothermally at 0°C were only 32.6%and 15.9 nm,respectively.Meanwhile,the thermal conductivity of PBSUI-1 was 171 mW/m·k.As the treatment temperature decreased,the X_c and D_c of PBSUI-1 gradually decreased while its thermal conductivity gradually increased.The morphology of the PBSUI sample after sc-CO₂foaming was observed by SEM and the cell size was measured by Image-Pro-Plus software.The results demonstrated that foams morphologies were sensitive to melt viscosity and dominated their mechanical and thermal conductivity properties.PBSU and PBSUI-1 exhibited an open ratio of 88%and the thermal conduction channel formed by the cell walls was interrupted.The thermal conduction was mainly dominated by the air inside the microcell,thus their thermal conductivity decreased from 94,207 mW/m·k before foamed to 52?54 mW/m·k,respectively.While PBSUI-3 and PBSUI-5 microcellular foams exhibited elliptical shape and stretched in the foam-mold height direction,their cells size and opening ratio were smaller than7.0?m and 13%.The thermal conductivity was mainly dominated by the ionomers matrix and increased to 83 mW/m·k.The results of this chapter indicated that using the processing approach of isothermal crystallization or sc-CO₂ foaming to change the condensed structure or three-dimensional structure of PBS,can realize the regulation of the thermal conductivity of the ionomers.