Rational Design and Preparation of Epoxy/polysiloxane Heterogeneous Networks for Achieving Excellent Damping Properties

Author:Li Yan

Supervisor:zhang jun ying cheng zuo

Database:Doctor

Degree Year:2018

Download:201

Pages:164

Size:15232K

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Damping materials are effectively used in reducing vibration,sound and noise by absorbing or dissipating external energy,such as,weapon,transportation,electronic device,construction,and other fields.In this regard,damping polymers have attracted much attention due to their lightweight structure,excellent damping,good processing,and designing properties.In fact,the use of damping polymers in damping systems is an irreplaceable strategy to turn unwanted kinetic energy into heat energy,which is dissipated through the viscoelastic of polymer.However,most traditional polymers suffer from the limitation of relatively narrow damping temperature ranges,only 20~30 ℃C(tan δ≥0.3),generally,which is unfavorable for practical applications.Therefore,broadening the damping temperature range of polymers is currently a hot potato.So far,polymer blending,copolymer and interpenetrating polymer networks(IPNs),are successfully used in broadening the effective damping temperature by combining two polymers(one of them has a high glass transition temperature(Tg),and the other has a low Tg)to form specific phase structure.Nonetheless,the huge difference between two Tg will result in highly incompatibility,and thus lead to uncontrollable phase structure.Thus,the damping temperature ranges from ultralow to ultrahigh are rarely.Here,the polysiloxane is regarded as one of the shining stars in the fields of low temperature due to its extremely low Tg(-123℃).However,the backbone of polysiloxane is too flexible to provide high internal friction(which is the source of damping capacity),so the tan δ value is hard to reach 0.3.Meanwhile,epoxy resin is regarded as one of the best candidates in the fields of damping property due to its high damping capacity(the value of tan δis usually higher than 1.0).Thus,epoxy/polysiloxane materials may possess the highest potential as an excellent ultralow-temperature and wide damping temperature range materials.However,they have not yet achieved their potential application due to the highly incompatibility of polysiloxane and epoxy resin.Once the two components are mixed together,the macro-separation will occur,which will result in two separately narrow damping regions.Having all these in mind,a novel high purity dual-functional epoxy monomer,diglycidyl ether of 4,4’-diallyl-bisphenol-A(DADGEBA),is deliberately designed.The structure of DADGEBA was confirmed by infrared spectroscopy FTIR,ESI-MS,and 1H-NMR.Thereafter,a series of fishbone-shaped epoxy/polysiloxane materials were constructed by polymerizing DADGEBA with methyl phenyl polysiloxane.The optimum synthesis condition was confirmed by Real-time FTIR.Moreover,the structure of fishbone-shaped epoxy/polysiloxane materials was confirmed by FTIR,1H-NMR,29Si-NMR,and GPC.The results showed that the backbone of fishbone-shaped epoxy/polysilxoane materials contains not only flexible polysiloxane and but also rigid epoxy part.Furthermore,the fishbone-shaped epoxy/polysilxoane material showed excellent viscosity and solubility properties.Second,we prepared a series of fishbone-shaped three-dimensional networks by using Jeffamine D230 as curing agent.The curing behavior and curing degree were investigated by DSC and FTIR,respectively.The relationships of morphology and damping property were systematically explained by DMA and SEM.The results showed that there is no distinct phase separation between polysiloxane and epoxy at 1 μm scale.However,the broader of peak half-width showed their stricture was heterogeneous structure.Therefore,the unique architecture and heterogeneous structures endowed the cured fishbone-shaped epoxy/polysilxoane material excellent damping properties,from-54 ℃ to-1 ℃ and tan δ≥0.3.Furthermore,the damping temperature range can be tuned by adjusting the content of polysiloxane.Moreover,in contrast to the traditional epoxy/polysiloxane materials,the cured fishbone-shaped epoxy/polysilxoane material takes full advantage of the cooperative effect of epoxy and polysiloxane exhibiting excellent damping properties(tan δ≥0.3)at temperatures near the Tg of the polysiloxane.In addition,TGA,water contact and mechanical property showed that the cured fishbone-shaped epoxy/polysilxoane materials possessed good thermal stability,surface hydrophobicity and tensile strength.Third,a new epoxy/polysiloxane monomer(SH-EP)was designed by thiol-ene click reaction of DADGEBA and trimethoxysilylpropanethiol(γ-SH).Based on its structure,a series of ’forced’ intermixing epoxy/polysiloxane networks were prepared by a combination of epoxy-amine curing reaction and polysiloxane hydrolysis condensation reaction under dry toluene conditions in a one-pot synthesis.The FTIR,1H-NMR and 29Si-NMR demonstrated that epoxy and polysiloxane networks are formed simultaneously.The relationship of structure and property is systematically investigated by FTIR,Rheometer,SEM,and DMA analysis.Both qualitative(SEM)and quantitative(the degree of segregation)analyses indicated that the smaller the phase domain size,the stronger interaction between polysiloxane and epoxy,and the better synergistic effect.Moreover,the epoxy and polysiloxane networks can be driven to closely interpenetrate by their intrinsic motive force derived from the ’forced’sites in SH-EP,which in turn,may easily give rise to nanoscale bi-continuous morphology.Besides,the gelation time is systematically controlled by varying the polysiloxane contents and pre-curing temperature.By tuning gelation time,the extent of phase mixing and the degree of phase separation can be further regulated.The result is striking:for the first time,this highly incompatible epoxy/polysiloxane intermixing networks exhibit ultralow-temperature damping properties(tan 80.3)over a very broad temperature range of 217 ℃(from-114 ℃ to 103 ℃).Moreover,when the frequency increased,the Tg slightly shifts to higher temperature and the damping temperature range becomes broader.In addition,the nanoscale phase separation also endowed the ’forced’ intermixing epoxy/polysiloxane networks excellent thermal stability and surface hydrophobicity properties.Finally,a dimethyl-fishbone-shaped epoxy/polysiloxane material(Si-EP)was firstly synthesized by the hydrosilylation reaction between DADGEBA and hydride terminated poly(dimethylsiloxane)(PDMS-H).The structure of Si-EP was confirmed by FTIR,1H-NMR and 29Si-NMR.After that,we facilely prepared a series of epoxy/polysiloxane hybrid polymer networks(HPNs)by blending Si-EP,a commercial epoxy-functionalized polysiloxane monomer(SEP),methyl-5-norbornene-2,3-dicarboxylic anhydride(MNA),and N,N-Dimethylbenzylamine(BDMA)together followed by a one-pot curing process.SEM,DMA and SAXS analysis showed that these epoxy/polysiloxane HPNs possessed nanoscale heterogeneity,which,in turn,provide these HPNs excellent low-temperature damping properties(from-93 to 52 ℃,as large as 145.2 ℃).Furthermore,the damping temperature range of HPNs is more than two times that of cured SEP and more than five times that of cured Si-EP.Besides,the mechanisms of formation of nanoscale heterogeneous structure were systematically investigated by thermodynamics and kinetic.The present result provides a feasible method to design high damping materials by the fabrication of nanoscale heterogeneous HPNs.In addition,TGA also showed that these HPNs have good thermal stabilities.