Preparation And Study Of(Fluorine-Containing)Polysiloxane Thermoplastic Elastomer

Because polysiloxane elastomer has excellent biocompatibility,chemical stability,aging resistance,etc.,these excellent properties are advantageous for various fields,such as military,aerospace,artificial skin,medical devices,wearable devises,etc.At present,most polysiloxane elastomers are cross-linked by covalent bonds,resulting in the loss of the recyclability and reprocessibility.The development of thermoplastic materials not only can increase the utilization rate of resources and expand the source of renewable resources,but also diversify suitable processing methods and improve production efficiency.In view of innovations involving polysiloxane thermoplastic elastomer have been scarce,in this thesis,thermoplastic polysiloxane elastomers with high mechanical properties and multifunctionality were prepared by dynamically vulcanization and chemical synthesis,thereby exploring and broadening its application fields.Through the core-shell dynamic vulcanization method,in situ interfacial reactive compatibilization and selective distribution of nanofillers,a series of fluorine-containing polysiloxane thermoplastic elastomers with shape memory performance and high mechanical properties were prepared,and its enhancement behavior and shape memory mechanism were investigated as well.Also a series of polysiloxane thermoplastic elastomers with shape memory performance,self-healing performance and high mechanical properties were prepared by designing and regulating the phase-separated structure,and the effect of the phase-separated structure on its mechanical properties and functionality were investigated as well.The specific research contents and main results are as follows:(1)Due to the mandatory encapsulation of fluororubber(FKM)-shell on silicone rubber(SR)-core and the similar natural properties of FKM and poly(vinylidene fluoride)(PVDF),the interfacial compatibility between PVDF and SR was significantly improved,thereby achieving high mechanical strength.Then,the study on the shape memory behavior of TPV shows that the formation of the core-shell structure contributes to TPV's shape memory performance.At160°C,P6F2S2 show approximately full recovery(R_r>95%)with a fast shape recovery rate compared with P6F0S4.The shape memory mechanism was proposed:(i)the formation of core-shell structure can effectively improve the interface compatibility of PVDF and SR,thereby facilicating the stress transfer between the PVDF phase and SR/FKM particles,and assisting the cross-linked SR/FKM particles served as crosslinks to prevent the molecular chain slippage of the PVDF phase.(ii)the compatibilized PVDF/SR interface contributed to the reduction of D_n of SR/FKM particles and and the increment of small PVDF crystals,which could effectively fix the deformed SR/FKM particles.(2)PVDF was dehydrofluorinated via?-H elimination reaction to introduce reactive double bonds,and the firmly anchoring structure of SR-g-PVDF formed between PVDF and SR via interfacial grafting reaction.With the increase of m PVDF content,the tensile strength,elongation at break,tear strength and tensile toughness of TPV increased from 7.2 MPa,13%,24 k N/m and 1.2 k J/m³ to 14.5 MPa,174%,43 k N/m and 12.3 k J/m³,respectively.For shape memory performance,the strong anchoring effect of SR-g-PVDF between PVDF and SR still existed even after multiple fixed-recovery cycles,so m60 and m80 maintain good shape recovery ratio(?85%)after multiple fixing-recovery cycles.(3)Taking PVDF/FKM/SR(20/40/40)TPV with core-shell structure as the research object,reinforancing SR phase and improving the FKM/SR compatibility are achieved simultaneously by adjusting the selective distribution of nano-SiO₂.The results show that P2F4S4-5%exhibited a higher tensile strength of 5.2 MPa and elongation at break of 172%than P2F4S4-0%(3.5 MPa,113%),on account of the the reinforcement and thermal migration of nano-SiO₂.On this basis,the surface modification of nano-SiO₂ by KH570 and different processing procedures were implemented to further improve the mechanical properties of P2F4S4-x%.For OS-P2F4S4-5%@Ky%prepared by one-step method,the thermodynamic migration and surface modification of nano-SiO₂ by KH570 occurred simultaneously.One-step method not only preserved the selective distribution of nano-SiO₂ in FKM phase and FKM/SR interface to improve the interfacial compatibility between FKM and SR,but also achieved rubber reinforcement by regulating the amount of KH570.OS-P2F4S4-5%@K10%tensile strength and elongation at break are 7.6 MPa and 156%respectively,which are significantly higher than the best mechanical properties of TS-P2F4S4-5%@Ky%system(5.9 MPa,150%).(4)By taking advantage of the chain rigidity and linearity of polyimide,and the high flexibility of polysiloxane,as well as strong intermolecular interactions(dipole-dipole interaction and?-?stacking),the polysiloxane segments prefer to curl up as a separate phase from the hard glassy matrix by the thermodynamic incompatibility between polysiloxane and polyimide.The separated structure featured long-range gradient transition,ranging from?40°C to?100°C.The continuous glassy polyimide assembled from hard segments could effectively resist external force,thus endowing the polymers with highly ameliorated mechanical strength.The elongation at break and tensile strength of PISi-1500-4 are 75%and 2.07 MPa,respectively.When the temperature T increases,the interaction between the hard segments in the gradient-transition layers with low T_g(T _g(27)T)would be break,while the gradient-transition layers with high T_g(T_g(29)T)would remain stable.According to the principle,setting proper temperature T as the transition temperature,the shape fixity ratio and shape recovery ratio of PISi-1500-4 are96.4%and 84.3%,respectively.The reversibility of the interaction between the hard segments in the gradient-transition layers with low T_g(T _g(27)T)and the high flexibility of the polysiloxane endowed the elastomer with self-healing performance.After healing for 16 h,the healing efficiency of tensile strength and tensile toughness of PISi-1500-4 were 96%and 76%,respectively.With the further increase in the temperature T,the polymer fractions with high T_g(T_g(29)T)gradually decreased and even disappeared completely,thereby endowing the elastomers with the recyclability.(5)Simultaneously robusting and toughening the polysiloxane thermoplastic elastomer network was achieved by embedding the dynamic Fe(III)-pyridine coordination bond/ion cluster with a higher activation energy.When Fe(III)/pyridine molar ratio is 1:3,PDMS-DAP@Fe-1/3 acieved high tensile strength(2.8 MPa),extremely strong tensile toughness(32.5MJ/m³)and excellent ductility(1473%).Meanwhile,based on the thermal reversibility of intermolecular interactions(coordination and intermolecular hydrogen bonding[-NH···O=C-]),the prepared elastomer has self-healing ability.After healing for 48 h at 70°C,PDMS-DAP@Fe-1/3 almost recovered completely.As such,the potential of the as-prepared robust,tough and repairable polysiloxane thermoplastic elastomer for a substrate material of flexible electronic devices is discovered.