| Addition-cure liquid silicone rubber(ALSR)is widely applied in aerospace,electronics,medical equipment and other aspects,because of its excellent weather resistance,electrical insulation property,high and low temperature resistance,etc..However,the side groups of molecular chain of ALSR are mainly unreactive and non-polar groups(methyl,phenyl,ethyl,etc.),which results in its low surface energy and poor adhesion property.Especially in the humid areas,rain and moisture are easy to erode to the adhesion interface of ALSR and destroy its adhesion strength,which seriously affects the application of ALSR in the field of bonding and sealing.Therefore,on the basis of self-synthesis of hydrogen-containing MQ silicone resin in this dissertation,the acrylate group was introduced into the hydrogen-containing MQ silicone resin to prepare acrylate-containing MQ silicone resin adhesion promoter(HMQ-g-TPGDA).ALSR adhesive with high adhesion strength and excellent water resistance was prepared by adding HMQ-g-TPGDA into ALSR.The main research contents and results are listed as follows:(1)Hydrogen-containing MQ silicone resin(HMQ)was prepared by hydrolytic condensation reaction of ethyl orthosilicate(TEOS)and tetramethyldisiloxane(~HMM~H)under the catalysis of hydrochloric acid.The structure of HMQ was characterized by Fourier transform infrared spectrometry(FT-IR),~1H nuclear magnetic resonance spectrometry(~1H NMR)and gel permeation chromatography(GPC).The effect of molar ratio n(~HMM~H)/n(TEOS),reaction time,reaction temperature,hydrochloric acid and deionized water content on the hydrogen content,viscosity and yield of HMQ was investigated.The results showed the optimal synthesis condition of HMQ was as follows:n(~HMM~H)/n(TEOS)was 0.9,reaction time was 3 h,reaction temperature was 30℃,hydrochloric acid and deionized water content was 10%and 30%of the total mass of monomer,respectively.Under this condition,number-average molecular weight(M_n)of HMQ was 1581,molecular weight distribution index(PDI)was 1.09,hydrogen content was0.917wt%,viscosity was 35.0 m Pa·s and yield reached 90.11%.(2)Acrylate-containing MQ silicone resin adhesion promoter(HMQ-g-TPGDA)was prepared by hydrosilylation reaction of tripropylene glycol diacrylate(TPGDA)and HMQ under the catalysis of chloroplatinate-isopropanol.The structure of HMQ-g-TPGDA was characterized by GPC,FT-IR and ~1H NMR.The effect of ratio of n(Si-H)in HMQ and n(C=C)in TPGDA,platinum catalyst content,reaction time and reaction temperature on structure,yield and adhesion promoting of ALSR of HMQ-g-TPGDA was studied.And storage stability of HMQ-g-TPGDA was also investigated.The results showed when n(Si-H)/n(C=C)was 0.500,platinum catalyst content was 2 ppm,reaction time was 2 h and reaction temperature was 80℃,the yield of HMQ-g-TPGDA reached 70.34%,the adhesion promoting property of ALSR was the best,and HMQ-g-TPGDA showed excellent storage stability.(3)ALSR adhesive was prepared by adding HMQ-g-TPGDA into ALSR.The effect of HMQ-g-TPGDA on the vulcanization characteristics,mechanical properties and adhesion property of ALSR adhesive to polycarbonate(PC),nylon 66(PA66)and aluminum(Al)was systematically investigated.And the adhesion promoting mechanism of HMQ-g-TPGDA on ALSR adhesive was discussed.The results showed that HMQ-g-TPGDA can significantly improve the mechanical properties and adhesion property of ALSR adhesive.With the increase of HMQ-g-TPGDA content,the adhesion strength of ALSR adhesive first increased and then decreased.When HMQ-g-TPGDA content was 2 phr,the adhesion strength of ALSR adhesive was the highest.The tensile shear strength of ALSR adhesive to PC、PA66 and Al increased from 0.44 MPa、0.43 MPa and 0.84 MPa without adhesion promoter to 3.44 MPa、1.61 MPa and 2.34 MPa,respectively.(4)ALSR adhesive containing HMQ-g-TPGDA was immersed in deionized water to study its water resistance.The effect of immersion temperature and immersion time on the adhesion strength of ALSR adhesive to PC、PA66 and Al was investigated.The chemical structures of ALSR samples immersed in boiling water at 100℃for different times were characterized by attenuated total reflection Fourier transform infrared(ATR-FTIR)spectroscopy.The results demonstrated that bonded joints of ALSR adhesive containing HMQ-g-TPGDA to PC、PA66 and Al had good water resistance,among them,the water resistance of ALSR adhesive to PC was the best.The tensile shear strength of ALSR adhesive to PC still reached 2.45 MPa after immersing in boiling water at 100℃for 8 h.The test of mechanical properties and ATR-FTIR spectra showed that ALSR adhesive matrix had excellent water resistance.The mechanical properties of ALSR adhesive decreased by less than 6%after being immersed at 100℃for 8 h,and the structure was almost unchanged. |
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