Preparatioin And Properties Of Intinsic Self-healable UV-curable Transparent Silicone Elastomers

silicone elastomers reveal pervasive applications in aerospace,electronics,light industry,chemical industries,construction,textile,cosmetics,encapsulation,military products and biomedical fields,due to their excellent chemical stability,thermostability,compressibility,insulativity,air permeability,flexibility,hydrophobicity,non-toxic,tasteless and physiological inertia,etc.Especially,it is the ideal material for the fabrication of transparent wearable and flexible electronic devices that are attracting tremendous attention.However,the traditional vulcanization process,such as room temperature vulcanization and high temperature vulcanization molding,still has serious time-consuming and energy-consuming problems.UV-curing technology is a fast,efficient,energy-efficient and environmental-friendly new green technology,with only 1/5?1/10 energy consumption of thermocuring,and corresponding materials can be cured quickly within seconds under UV radiation.At present,commercially available silicone materials can not UV-cure quickly,the polysiloxane chain need to be photoactivated in advance.But it is easy to gel and difficult to be transparent during the preparation process,because of the UV-curing groups have cerain polarity which increases the difficulty of preparation of UV-cured silicone materials.In addition,unpredictable damage and microcracks will be produced under the processing,use and aging processes of silicone materials,expecially microcracks are usually difficult to detect.Decline or even failure of material performance and serious safety risks will be brought if continuous using.Therefore,it is of great significance for silicone materials to improve their competitiveness and broaden their application prospects by incorporating high efficiency-fast UV-curing and automatic self-healing when damage.Thereinto,self-healing capabilities can actively eliminate internal microcracks,recover their original performance index,improve service life,safety and reliability,reduce the cost of replacement cycle.In this dissertation,the main purpose was to assemble the UV-curing technology and self-healing properties on the same silicone materials,so that the UV-curable and self-healable transparent silicone elastomers could be successfully prepared.And the photo-curing kinetics,self-healing mechanism and related properties were studied in detail.The specific research contents are as follows:1.Preparation and properties of self-healing transparent silicone elastomers based on photo-induced thiol-ene click reaction and ionic bonds(1)Thiol modified silicone oil(PDMS-SH)of different structures were prepared by hydrolysis-copolymerization with 3-mercaptopropylmethyldimethoxysilane(KH970),decamethylcyclopentasiloxane(D5)and hexamethyldisiloxane(MM).Their structures and components were characterized in detail by Fourier transform infrared spectroscopy(FTIR),elemental analysis(EA),Nuclear Magnetic Resonance Hydrogen(1H NMR)Spectrum,Nuclear Magnetic Resonance Silicone Spectrum(29Si NMR)and gel permeation chromatography(GPC)measurement,and their viscosity,density,refractive index,refractive index and transmittance were measured in detail.(2)Reversible/irreversible hybrid dual-crosslinked silicone elastomers(S-DCSE)were constructed by the photo-induced thiol-ene click reaction of PDMS-SH and vinyl-terminated silicone oil(PDMS-Vi),as well as the thermal reversible dynamic ionic-crosslinked network of carboxyl-and amino-modified silicone oil.Dynamic reversibility of the S-DCSE was systematically studied by variable-temperature infrared(VT-FTIR),in situ rheological test,dynamic mechanical analysis(DMA)and stress relaxation test,etc.Analysis showed that the elastomer S-DCSE had excellent dynamic reversibility,and ionic crosslinked network was liable to be dissociated at high temperature,but it tended to be reformed at low temperature(3)The self-healing and reprocessing properties of S-DCSE were studied by stress-strain tensile test,DMA,crosslinking density,thermogravimetric analysis(TGA)and X-ray diffraction(XRD).The results shown that the elastomer S-DCSE had excellent self-healing and reprocessing properties because of the dynamic reversibility of the ionic cross-linked networks.And when the concentration of ionic-crosslinked networks was 10 wt.%,the elastomers S-DCSE had excellent mechanical strength,self-healable and recovery properties.The healing efficiency could still reach over 90%after multiple self-healing times.these elastomers with 10%ionic concentration could be repeatedly reprocessed with preserving virgin mechanical strengths of 90%,and the reprocessed elastomers could still repair damages with efficiency over 90%.Furthermore,the as-prepared S-DCSE exhibited visible light transmittance of over 90%,excellent hydrolysis resistance,thermal stability and hydrophobicity.Their also had low water absorption and curing shrinkage.At last,the silicone elastomers S-DCSE were used as the raw materials to be fabricated into various architectures with excellent self-healing properties via SLA 3D printing.Therefore,a new feasible approach was provided to impart reversible ionic association induced self-healing and reprocessing to 3D printable transparent silicone elastomers2.Preparation and properties of self-healing transparent silicone elastomers based on radical photopolymerization and ionic bonds(1)Acrylic ester modified silicone oil(PDMS-AE)was prepared by hydrolysis-copolymerization with[diethoxy(methyl)silyl]methyl 2-methylprop-2-enoate(KH571),D5 and MM.Acrylic ester modified MDT silicone resin(MDT-AE)was prepared by hydrolysis-copolymerization with 3-Methacryloxypropyltrimethoxy silane(KH570),dimethoxydimethylsilane(DMOS)and MM.The structures of PDMS-AE and MDT-AE were characterized by FTIR,EA,1H NMR,Nuclear Magnetic Resonance Carbon(13C NMR)Spectrum and GPC measurement,and their vinyl content,viscosity,density,refractive index,refractive index and transmittance were analysed in detail.(2)Reversible/irreversible hybrid dual-crosslinked silicone elastomers(R-DCSE)were constructed by the radical photopolymerization of PDMS-AE and MDT-AE,as well as the thermal reversible dynamic ionic-crosslinked network of carboxyl-and amino-modified silicone oil.The results showed that the addition of MDT-AE could effectively increase the crosslinking density of curing networks and thus overcome oxygen inhibition.The mechanical strength and crosslinking degree of R-DCSE were higher than that of S-DCSE.Besides,it was verified that the ionic cross-linked network still had strong dynamic reversibility in R-DCSE of higher cross-linking density.Through the study of self-healing properties,R-DCSE of 20 wt.%ionic concentration had excellent self-healing properties,but higher temperature(?150?)and longer time(?24 h)were needed for the carboxyl-and amino-modified silicone oil moved to the fracture surface recombination after dissociation to achieve effective repair.Furthermore,the R-DCSE elastomers had excellent transparency(over 90%),hydrolysis resistance and yellowing resistance.Therefore,A new feasible scheme was provided for the preparation of self-healing and transparent silicone elastomer induced by the network of reversible ion association.3.Preparation and properties of self-healing transparent silicone elastomers based on thiol-ene photopolymerization and boronic ester bonds(1)The high refractive index thiol modified MDT silicone resin(MDT-SH)of various R/Si values(molar ratio of organic group R to Si atoms)structures were prepared by hydrolysis-copolymerization with 3-mercaptopropy ltri ethoxysilane(KH580),dimethoxydiphenylsilane(DDS)and MM.Their structures were characterized by FTIR,EA,1H NMR,29Si NMR and GPC measurement in detail,and their thiol content,viscosity,density,R/Si values,mole ratio of M/D/T,refractive index and transmittance were analysed in detail.(2)Allyl ether oxy-modified p-phenylene diborate(GAPA)crosslinker was prepared by esterifiable dehydration with 1,4-phenylenebisboronic acid(PA)and glycerol alpha-monoallyl ether(GA).And their structures were characterized by FTIR?1H NMR?13C NMR and electrospray ionization-high resolution mass spectrometry(ESI-HRMS)in detail.(3)Reversible/irreversible hybrid dual-crosslinked silicone elastomers(B-DCSE)were constructed by the thiol-ene photo-click reaction of MDT-SH with GAPA crosslinker and vinyl-terminated phenyl silicone oil(VPS).This preparing method only needed one-step fast thiol-ene photo-polymerization,without secondary heat-curing.It was verified that the ratio of boronate ester cross-linking network did not affect the rapid curing process of B-DCSE by the UV-curing kinetics.Comparing with S-DCSE and R-DCSE,B-DCSE had better mechanical strength,self-healing properties,transparency and yellowing resistance.Thereinto,the tensile strength and elongation at break of the B-DCSE were 3.03 MPa and 207.74%,respectively.The fracture surface of B-DCSE could be effectively repaired under mild conditions(healing temperature was 80?,healing time was only 3 h),and the healing efficiency was over 96%.A new feasible scheme was provided for the preparation of self-healing and transparent silicone elastomer induced by the network of dynamic reversible boronic ester bonds.