Studies On Synthesis Mechanism,Kinetics And Application Of Episulfide Model Compounds

Episulfide resins,whose structure is similar to that of epoxy resins,refer to a type of compounds containing episulfide groups(three-membered ring with a sulfur atom)in the structure.Episulfide resins could react with curing agents,obtaining thermosetting resins with three-dimensional networks.The cured products present lots of good performance,such as excellent chemical resistance,adhesion,heat resistance,mechanical properties,electrical properties and dimensional stability.They have been widely applied in many fields such as adhesives,protective coatings,and composite matrix resins.Compared with epoxy resins,episulfide resins have their unique features.Firstly,as episulfide group has a greater bond length,a larger bond angle and a smaller tensile energy,it is easier for episulfide group to perform a ring-opening reaction than epoxy group and the reactivity between episulfide group and curing agents;secondly,sulfhydryl group,which is generated after the ring-opening of episulfide group,has a higher reactivity(such as an amine-catalyzed curing reaction)and more designability(such as a click reaction)than hydroxy group which is formed after ring-opening of epoxy group,bringing a insightful future for the curing reaction,molecular structure design and application fields.Therefore,episulfide resins have attracted the researcher's widespread concern.To date,there are few reports on the synthesis and curing reaction of episulfide resin and two issues are focused.One is pure episulfide resin couldn't be obtained when they are simply synthesized from epoxy resin and only 70%conversion could be achieved.The other issue is that few researches on the curing behavior of pure episulfide resin have yet been reported.To address these issues,our works were carried out on the synthesis,curing behavior and applications of pure episulfide resin.Firstly,based on the reaction mechanism of preparing episulfide resin from epoxy resin,model compound benzyl glycidyl ether(BGE)was employed to react with potassium thiocyanate to get benzyl-dithiocyclohexyl sulfide(BTE).The differences on the efficiency of ring-opening reactions,the formation and transformation of intermediate products between the method of microwave enhanced low temperature thermal reaction and thermal method were thoroughly investigated.Pure BTE could be successfully synthesized by controlling reaction conditions.Furthermore,curing behaviors of BTE and two typical amine curing agent(aliphatic amine and arylamine)were studied systematically and the kinetic parameters were calculated.Then,because of the low-temperature curing features of episulfide compounds,trifunctional episulfide resins(TFESs)were designed and prepared.The TFESs could be cured in relatively low temperature and be used in relatively high temperature because of the advantages of low reaction temperature of episulfide and the high crosslink density.Finally,by taking the advantage of the thiol groups formed from ring-opening reaction of episulfide groups,we designed and prepared special thiol-vinyl compounds,which were promising in the application of UV curing acrylic adhesive.The problem of oxygen inhibition normally found in the field of UV curing was solved by using the click chemistry between thiol groups and vinyl groups.In this thesis,firstly,BGE was employed for the synthesis of episulfide resin through MWTP with the reaction temperature of 45 ?for 2 h and a following room temperature for 15 days.The efficiency of the ring opening reaction of polar epoxy ring increased obviously under the microwave.The conversion of the polar five-membered ring into a three-membered sulfur ring could be accelerated without increasing the reaction temperature.The increase of the conversion rate could be achieved by combining low-temperature closed-loop process.Meanwhile,the reaction process of MWTP and simple thermal reaction was studied for comparasion via FTIR tracing method.The change of epoxy initiator,intermediate products of five-membered ring,and episulfide compound during the reaction and the following 15 days were characterized in detail.It was found that microwaves played a significant role in accelerating the ring-opening of epoxy groups and the transformation of the metacyclic transition state.It is a simple method to get a high conversion of pure paracyclic sulfur model compounds which spares the need of catalyst or column separation.Next,the curing behaviors of BGE,BTE with the low-temperature reacting aliphatic amine(polyetheramine,D230)and the high temperature reaction aromatic amines(4,4'-diaminodiphenylmethane,DDM)as curing agents were studied.Four systems of BGE/D230,BTE/D230,BGE/DDM,and BTE/DDM were set.Basic data of the curing reaction of episulfide groups were obtained by the analysis of dynamic parameters and were further used for simulation of each system dynamic formulations.Results were as follows.For the curing behaviors of the BTE/D230 and BGE/D230 systems,the enthalpy of the former is 313 J/g,which of the latter is 97 J/g;the activation energy is 58.7 kJ/mol and 54.3 kJ/mol;the pre-exponential factor is 1.28×107 and 6.93×105;the reaction order m and n is 0.0512,1.432 and 0.19,1.236.Both systems fit the SB model,no evident self-catalyzation was detected.The initial curing temperature,peak temperature,final curing temperature of BTE/D230 all show a 30-50°C reduction compared with BGE/D230.For the curing behaviors of the BGE/DDM and BTE/DDM systems,the enthalpy of the former is 455.6 J/g,which of the latter is 151.1 J/g;the activation energy is 58.9 kJ/mol and 68.5 kJ/mol;the pre-exponential factor is 3.72×106 and 1.78×108;the reaction order m and n is 0.742,1.49 and 0.0295,1.248;both systems fit the SB model,BGE/DDM shows evident self-catalyzation effect.Thirdly,a rigid trifunctional epoxy resin was designed and prepared in order to achieve a resin system with both low curing temperature and heat resistance simultaneously.4-(3,3-Diamino-7-hydroxy-2,4,4-trimethyl-2H-1-phenylpyran-2-yl)-1 was prepared by reacting resorcinol with acetone.TFEP was synthesized from TMBPBTH.Then TFES was synthesized by using MWTP according to the synthesis section.Using DDM and DMDC as curing agents,DSC was used to study the curing behaviors of TFEP/DMDC,TFES/DMDC,TFEP/DDM and TFES/DDM four systems.DMA was used to study the glass transition temperature of the cured resin.The results indicated that the initial curing temperature,peak temperature,final suring temperature of TFEP/DMDC and TFES/DMDC is 39 ?,17?;102 ?,95 ?;145 ?,105 ?.The initial curing temperature,peak temperature,final suring temperature of TFEP/DDM and TFES/DDM is 74.3 ?,37.2 ?;137.4 ?,97.1 ?;180.2 ?,150.7 ?.When DMDC was used as curing agent,the curing temperature of TFES is 20 ? lower than that of TFEP.When DDM was used as curing agent,the curing temperature of TFES is 30-40 ? lower than that of TFEP.The Tgof the cured resin of TFEP/DMDC and TFES/DMDC is 217 ? and 198 ?;The Tgof the cured resin of TFEP/DDM and TFES/DDM is 262 ? and 243?.The TFES did not show a dramatic reduction in Tg while maintained good heat resistance even under low curing temperature.Finally,an oxygen-resistant UV curable acrylate adhesive was achieved by introducing the eugenol-episulfide resin into the UV-curable acrylate system.The oxygen-resistant UV curable acrylate adhesives solved the scientific and technical problems in the field.The eugenol episulfide resin was first synthesized,and was further subjected to n-butylamine for chain extension reaction to prepare an oligomer containing both mercapto groups and vinyl groups(EUES-Butyl Amine-EUES,ESBAES).The effects of ESBAES on four UV-curable acrylate systems,Polycarbonate urethane acrylate resin,isobornyl acrylate,hydroxyethyl acrylate,are studied.Photoinitiator 184 was used as initiator for all systems.The results show that the addition of ESBAES to the acrylate light-cured adhesive could easily reach surface dry,surface dry energy reduced from 3000 mJ/cm2 to 500 mJ/cm2,when the content of ESBAES increased from 5%to 20%.Further more,the introducion of ESBAES did not affect the curing depth and adhesive performance of the UV adhesive.