Study On Interpenetrating Hybrid And Rheological Properties Of PDMS-phenyl-substituted MDQ Silicon Resins

Polydimethylsiloxane(PDMS), used as a base polymer of liquid silicone rubber, issuch a kind of linear polysiloxane with methyl as side group and its main chain composedof alternating silicon and oxygen atoms.The poor mechanical property of silicone rubberwithout reinforcement is due to the weak intermolecular forces which is far worse thanorganic rubber’s. Therefore, silicone rubber has practical value after reinforcement. Thisthesis aims at preparing semi-interpenetrating polymer network(semi-IPN) using a liquidsilicone rubber instead of PDMS. The main researches contents, methods and conclusionsin this thesis are as follows:(1) Phenyl-substituted MDQ silicone resins were synthesized by cohydrolysis-condensation reaction initiating from tetraethoxysilane(TEOS), hexamethyldisiloxane(MM)and dimethoxydi-phenylsilane(DMDPS). FTIR and NMR were employed to characterizethe structures of silicone resins. The thermal stability, refractive index and relativemolecular mass(Mn) and relative molecular mass molecular weight distribution(MWD) ofthe synthesized resins were also investigated by thermal gravimetric analysis(TGA), Abberefractometer and gel permeation chromatography(GPC), respectively. In addition, thereaction conditions and the effects of several factors on the yield were also discussed.The results indicated that the product is phenyl-substituted MDQ silicon resins, andthe refractive index of silicone resins improves, relative molecular mass decreases slightlyand MWD become broader, the thermal stability of silicone resins rises in advance thenfalls with increasing the content of DMDPS in nitrogen(N2). The optimum conditions areas follows: using4wt%~6wt%ethanol as co-solvent, the dosage of catalyst is5wt%~8wt%,cohydrolysis temperature is30~40℃, cohydrolysis time is30~40min, polycondensationtemperature is70℃,polycondensation time is3~4h.(2) Hybrid materials were fabricated with PDMS and phenyl-substituted MDQsilicone resin catalyzed by tetramethylammonium hydroxide(TMAH). The microstructure,transparency and viscosity of hybrid material were investigated by transmission electronmicroscope(TEM),Ultraviolet-visible spectrophotometer and rotational viscometer,respectively. In addition, the rheological behavior of semi-IPN was studies using Haake Rheomix.The research result shows that hybrid materials represents semi-IPN structure, thetransmittance of semi-IPN decreases while viscosity increases as phenyl-substituted MDQsilicon resin content increases. In addition,Newtonian behavior can be observed in bothPDMS and semi-IPN at low shear rate. However, shear thinning behavior is observed insemi-IPN and PDMS when shear rate reached a critical value(γc). The γcvalues decreasewhen increasing the content of silicon resins and increased along with the raising tempera-ture. The relation of temperature and viscosity can be evaluated using theArrhenius model.Meanwhile, calculation results indicate that semi-IPN have higher activation energy thanPDMS.(3) siliconee elastomers were prepared with phenyl-MDQ silicone resin-PDMS semi-IPN as base polymer, crosslinked by alkoxy silane under the catalysis of organotin andtitanate. The effects of catalysts, cross-linking agents and the component ratios on theproperties of the elastomers were investigated. The thermostability, transmittance,mechanical properties, hardness, gel content and swelling ratio of elastomers were testedand characterized by TGA, Ultraviolet-visible spectrophotometer, electron universaltesting machines, Shore durometer and Soxhlet extractor, respectively.The results indicated that tack free time of elastomer were shorten with increasingof catalyst dosage and its optimum content is0.8%~1.0%by weight. Tensile strength andelongation at break increase at first but decrease finally with increase of cross-linkingagent and their optimum content is6%~8%by weight. With phenyl-substituted MDQsilicon resin content increasing, the hardness of elastomer increases and tack free timeprolong,while tensile strength and elongation at break firstly increased and then decreased.Its optimum content was30%by weight. Elastomers possessthe features of goodtransparency. Furthermore, the results of extraction test show that psychophysical bondingbetween phenyl-substituted MDQ silicon resins and PDMS network have formed.