Synthesis And Properties Of Organosilicon Materials Via Aza-Michael Reaction

Organosilicon materials are a class of synthetic materials in which at least one organic group directly attaches to silicon atom.They are one of the fastest growing element-organic materials.Organosilicon materials exhibit unique properties,such as high and low temperature resistance,aging resistance,weather resistance,electrical insulation and biocompatibility.Organosilicon materials,including silane coupling agents,silicone oils,silicone rubber and silicone resins,have been widely used in aerospace,electrical industry,construction,automobile manufacturing,textiles,medical treatment and daily chemical industry.Generally,the main way to prepare and functionalize organosilicon materials is the hydrosilylation reaction.The unavoidable drawback is that it requires expensive catalysts,which will increase the cost of production.The catalyst can be easily poisoned and lost activity when touch some elements,such as N,P,S.Besides,side reactions are always existing,which requires tedious product purification.Thus,a simple and efficient way is in great need to prepare and functionalize organosilicon materialsAza-Michael reaction is a kind of conjugate addition from amino compounds and?,?-unsaturated olefin.The atom utilization rates reach 100%,so it is an atom economy reaction.Aza-Michael reaction benefits from mild reaction conditions,favorable reaction rates,high conversions and functional group tolerance.Besides,it is catalyst-free and has been widely used in drug synthesis,preparation of natural products,construction and functionalization of polymers.In this thesis,aza-Michael reaction was proposed as a valuable way to synthesize organosilicon materials.The main contents are as follows:1.Functional alkoxysilanes were prepared from 3-aminopropyltriethoxysilane and[3-(1-piperazinyl)propyl]methyldimethoxysilane with varies kinds of electron-deficient alkenes via aza-Michael reaction under mild reaction conditions without any catalysts.The yield was very high,and a wide range of functional groups could be tolerated in this methodology to form monofunctional or multifunctional alkoxysilanes.The reactivity of amino-alkoxysilanes and ?,?-unsaturated olefin was discussed.The effects of concentration,temperature and the structure of olefin on the selectivity were investigated,which provides references for the preparation of functional organosilicon materials.Aza-Michael reaction seems to be an impressive choice to functional alkoxysilanes.2.Aza-Michael reaction was proposed as a novel way to cure silicone rubber.High-molecular-weight poly((piperazinylpropyl)methylsiloxane-co-dimethylsiloxane)was synthesized as base gum,oligo[(acryloxypropyl)methylsiloxane-co-dimethyl siloxane]was prepared as crossliner,and silicone rubber was cured by aza-Michael addition of piperazine and acryl goup.The crosslinking mechanism was validated by solid-state 13C NMR spectroscopy.The curing process was analyzed by cure-curves performed by rheometry.The effects of various factors,such as post-cure temperature and time,crosslinker and filler amounts,molecular weight,and piperazine group content,on the mechanical properties of the novel silicone rubber were investigated in detail.Vulcanizate with tensile and tear strengths of 11.43 MPa and 30.72 kN/m,respectively,was obtained.The cure was free of catalysts,and the cure temperature is not too high(120 0C).Our method yielded silicone rubber of high strength and stable dimension.The synthesized silicone rubber also exhibited favorable thermal stability,low temperature performance,and hydrophobic property,as characterized by Thermogravimetric Analysis,Differential Scanning Calorimetry and static contact-angle analysis.3.Base gums with new structures were prepared to improve the modulus of silicone ruuber.High-molecular-weight poly[(aminopropyl)methylsiloxane-co-dimethylsiloxane]and poly[(aminoethylaminopropyl)methylsiloxane-co-dimethyl siloxane]were synthesized as base gums.These materials were crosslinked with oligo[(acryloxypropyl)methylsiloxane-co-dimethylsiloxane]via aza-Michael reaction to produce novel silicone rubbers.Diaddition and triaddition reactions occurred between the aminopropyl groups and the aminoethylaminopropyl groups with the arcyl groups of crosslinkers.This led the higher modulus of novel silicone rubbers prepared via "tension spring-type crosslinking" compared with that of the silicone rubber prepared from poly[(piperazinylpropyl)methylsiloxane-co-dimethylsiloxane]via monoaddition reaction.Crosslinking mechanism was proven by solid-state 13C NMR and Fourier transform infrared spectroscopy.Curing characteristics were measured through cure curves conducted on rheometry.The postcure conditions and the ratio of crosslinkers used were investigated in detail.Analysis of mechanical properties showed that tension spring-type crosslinking improved the modulus of silicone rubber.The modulus at 100%strain increased from 1.31 MPa of cured poly[(piperazinylpropyl)methylsiloxane-co-dimethylsiloxane]to 2.18 MPa of cured poly[(aminopropyl)methylsiloxane-co-dimethylsiloxane]and or 2.55 MPa of cured poly[(aminoethylaminopropyl)methylsiloxane-co-dimethylsiloxane].4.Nucleobase-functionalized polysiloxanes were synthesized via aza-Michael reaction for the first time.Adenine or thymine reacted with excess 1,4-butanediol diacrylate to form adenine or thymine acrylic derivatives,which contained double bonds and could further react with poly[(piperazinylpropyl)methylsiloxane-co-dimethylsiloxane]to prepare adenine-or thymine-containing polysiloxanes(A-PDMS or T-PDMS).Their chemical structures were characterized by NMR and GPC.This method avoids the protection and deprotection process of traditional hydrosilylation reaction,and provides a simple and efficient way to prepare nitrogen-containing polysiloxanes.The starting materials were low viscosity liquids,while A-PDMS or T-PDMS were solid state,and exhibited stree/strain relationships consistent with elastomers.The analysis of variable temperature FT-IR spectra shows that the state changes were caused by hydrogen bonding assembly of A-A or T-T.Upon blending,the two polysiloxanes associated into a thermodynamically stable complex,which was physically cross-linked through hydrogen bonding recognition between A-T pairing.This blending supramolecular elastomer exhibit better mechanical properties than that of A-PDMS or T-PDMS,because complementary hydrogen bonding of A-T is stronger than A-A/T-T self-association.In addition,the mechanical properties of the blending supramolecular elastomer could be detailedly adjusted by the content of the two nucleobases.