| Thermosetting resins have been widely applied in human production and life,particularly in coatings,adhesions,electronics,and composite materials,et,al.,due to their excellent solvent resistance,heat resistance,and mechanical properties,et al.Traditionally,thermosetting resins are synthesized from petroleum-based starting materials.Nowdays,a lot of biomass-based thermosetting resins are being developed to aim to replace petroleum-based thermosetting resins because of continuous consumption of fossil energy and potential biological toxicity of petrochemical feedstock.Currently,a lot of investigations and industrial products of biomass-based thermosetting resins have been reported.Some commercial productions,including soybean-based and cashew phenol-based thermosetting resins,have been produced.However,compared with comprehensive properties of petroleum-based thermosetting resins,the biomass-based thermosetting resins performs poor.Thus,the current research focuses on improving the performance of thermosetting resin,such as high mechanical properties,good heat resistance,low flammability and degradability,et al.In this work,eugenol,stilbene and other biomass-based phenols were used as raw materials to build the chemical structure of thermosetting monomers.Firstly,the rigid-flexible integrated epoxy monomer was designed and synthesized.Through the adjustment of the rigid and flexible ratio,the structure-activity relationship between the micro-morphology and the macro-performance was investigated,the formation mechanism of the micro-phase structure was explored,and the system of thermosetting resins with high toughness was designed.Secondly,a thermosetting system possessing a ultra-high Tg,high strength,high modulus and low flammability was designed,which provides a good plastic sealing material for the third generation semiconductor SiC chip.Finally,the design of high-strength and degradable thermosetting system is discussed,and a new method to improve the atomic utilization efficiency of biomass raw materials is provided,which is supposed to be a new idea for the green and sustainable development of thermosetting resin.The main research contents and conclusions are as follows:1.In this part,eugenol was used as the starting material to prepare rigid-flexible integrated epoxy resin by click chemistry and reaction with epichlorohydrin(ECH).This structure can show the difference of solubility between chain segments.By adjusting the rigidity and flexibility of curing network structure,the micro-phase separation structure,the strength and toughness of curing epoxy resins can be adjusted,and the shape memory performance of the epoxy resin was also evaluated.Specifically speaking,two types of rigid-flexible integrated epoxy resins,diglycidyl ether of eugeno1-2-mercaptoethanol(DGEEM)and diglycidyl ether of vanillic alcohol(DGEVA),which possess similar rigid methoxy-substituted aromatic structures and different soft aliphatic chains in length,were prepared.Micro-morphology structures were tested by AFM,AFM nanomechanical mapping,and AFM-IR.Macro-properties were respectively characterized by tensile test and shape memory test.Results showed that a series of tunable micro-morphology structures including hard-phase-rich sea-island structure,bi-continuous structure,and soft-phase-rich sea-island structure were explored after cured with 4,4-methylenedianiline.The results from DMA show that Tg can be adjusted by rigid and flexible ratio of network structure in the range of 124.18-72.61?.Moreover,the shape memory mechanism for these SMEPs was concluded:phase separation structures are the base of these SMEPs,and soft phase acts as switching segments,which contributes to shape memory strain of the SMEPs.The optimal designed SMEPs(DGEEM50)with bi-continuous phase structure was prepared from this mechanism,which exhibit good mechanical properties and excellent shape memory performance(Rr and Rf>99%;and the ?m>30%).This part provides a new design idea and research method for the new high strain SMEPs.2.Micro-and nano-phase separation structure is an important factor affecting the macro-mechanical properties and solvent resistance of thermosetting resin.It is widely used in thermoplastic polyurethane system.However,the micro-phase separation caused by the chain segment heterogeneity of the framework itself in the high crosslinking density network of thermosetting resin is rarely reported,and the mechanism is unknown.There are two controversial theories in the academic circle:"crosslinking density" theory and "solubility parameter" theory.In this part,stilbestrol,with a special rigid conjugated structure,was used as raw material to design and synthesize a rigid stilbestrol allyl compound(RAE).Through the photo-thermal double curing reaction of click chemistry,the micro phase separation structure of glass transition and chain segment movement of thermosetting resin is tracked,so as to explore the formation mechanism of the micro-phase separation structure of thermosetting resin.Specifically,the micro-phase structures were characterized by AFM,AFM nanomechanics and AFM-IR.The macro-properties were characterized by thermal properties,thermomechanical properties and mechanical properties.The results show that during the UV-curing process,the AFM phase diagram shows a homogeneous network structures,and after thermal-curing,the AFM phase diagram showed a heterogeneous nanostructure.Therefore,the movement of rigid and flexible segments and the rearrangement of segments are the main mechanism of the formation of micro phase structure;the change of local crosslinking density caused by exothermic reaction is not the main reason.In the process of research,we also found that RAE has fluorescence performance because of its unique stilbene structure,and its potential application in anti-counterfeiting and detection has been investigated,which solves the problem of difficult identification and inconvenient identification of traditional photoresist.3.In the rapid development of electronic and electrical industry,especially in the field of the third generation semiconductor chip(SiC),the packaging materials with high Tg,high strength,high modulus and low flammability are in urgent need.In this part,stilbene was used as raw material to prepare rigid epoxy resin with three function epoxy groups.This kind of structure can give thermosetting resin high crosslinking density and rigid chain segments,resulting in high Tg and good mechanical properties.At the same time,conjugated structure is conducive to the carbonization of thermosetting resin and achieve the preparation of epoxy resin with low flammability.Specifically speaking,a resveratrol-based epoxy resin(REEP)with well-designed chemical structures possessing trifunctional epoxy groups and rigid conjugate structures was prepared through the one-pot method and was then cured by methyl hexahydrophthalic anhydride(MeHHPA).The conventional petroleum-based epoxy resin(DGEBA)was cured by the same kind of curing agent.Results showed that Tg of REEP/MeHHPA was up to 210.8?,much higher than that of DGEBA/MeHHPA(only 146.5?).The tensile strength and modulus of REEP/MeHHPA were 73.5 MPa and 3.0 GPa,respectively.More importantly,REEP/MeHHPA exhibited exceptional low permittivity and low flammability with high char yield of 19.0%(800?).Therefore,the resveratrol-based epoxy resin could be a promising candidate for DGEBA and has great potential application in electronics and microelectronics industry,particularly in the third generation semiconductor SiC chip.4.Designing a fully biobased monomer to build a series of degradable thermosets is of great significance for sustainable development and environmental protection.In second part,the biomass content of resveratrol allyl ether(RAE)is only 64.7%,and toxic compounds(such as allyl bromide)need to be used in the synthesis process.In this part,a fully biomass content monomer(EUIT)was designed and synthesized from itaconic acid(IA)and eugenol(EU).The thiol-ene crosslinked polymers(TCPs)were prepared by changing the degree of thiol functionality from 2 to 4 via VOC-free thiol-ene click reaction.And thermal,thermomechanical,and mechanical properties of these TCPs were respectively investigated.The results showed that EUIT/4SH possessed the best comprehensive properties,that is,glass-transition temperature(Tg)was up to 74.0?,mechanical properties including tensile strength and modulus were respectively 58.6 MPa and 1.5 GPa,which were the maximum values compared with reported investigations.Besides,these TCPs exhibited good degradable properties because of the inherent functional groups of ester groups in EUIT.Thus,this study provides a new method to prepare a fully biobased monomer and to produce a series of degradable thermosets which are expected to be advanced biomedical materials and flexible electronics materials,etc.Therefore,starting from biomass-based phenol,aiming at designing high-performance thermosetting resin system,this paper synthesized a variety of functional monomers,achieved the design of high-performance thermosetting system such as high toughness,high strength and high Tg,and provided important basic data and basic methods for the basic research of biomass-based thermosetting resins. |
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