Synthesis and Properties of Linear Polymer,Flame Retardant and Self-Healing Epoxy Resins Based on Phosphazenes

Author:Zhou Li Sheng

Supervisor:zhang guang cheng


Degree Year:2018





Polyphosphazenes and cyclotriphosphazenes are compounds with a backbone of alternating phosphorus and nitrogen atoms,and have two adjustable organic side groups on the backbone,these compounds generally with excellent properties such as heat resistance,flame retardant,chemical resistance,radiation resistance,et al.Furthermore,numerous of nucleophiles can be connected with phosphorus atoms as side groups,making polyphoshanzenes and cyclotriphosphazenes with a variety of properties,which make these materials of great theoretical significance and application value.A series of new structural and functional materials can be obtained by substitution reaction of polydichlorophosphazene(PDCP)with different side groups,but the synthesis and preservation conditions of PDCP are very harsh.Therefore,how to prepare PDCP with high molecular weight,good linearity and solubility still a problem to be solved.The exploration of the relationship of structures and properties for linear polyphosphazenes is very important.In addition,to improve the flame-retardant property of epoxy resin while maintaining mechanical properties,heat-resisting and process performance is still facing many difficulties,synthesis of high molecular weight flame retardants or neotype epoxy resins contain cyclotriphosphazene structures could be effective methods.And the preparation of self-healing and flame-retardant cyclotriphosphazene-containing epoxy resin based on dynamic covalent disulfide bonds is of great theoretical significance and application value.By considering all of the above aspects,this dissertation focuses on the study of synthesis of macromolecule linear polydichlorophosphazene,relationship between structure and performance of substituted polyphosphazenes,preparation and performance study of flame-retarded epoxy resin with high molecular weight cyclotriphosphazene halogen-free flame retardant,synthesis and performance study of multifunctional epoxy resin contains cyclotriphosphazene,and design of a self-healing and flame-retardant cyclotriphosphazene-containing epoxy resin based on disulfide bonds,the major contents and results are as follows:(1)Firstly,by comparing the appearance and yield of linear PDCP prepared by three different synthetic methods of PDCP,one-pot,solution polymerization and thermal ring-opening polymerization,melt polymerization of hexachlorocyclotriphosphazene(HCCP)in vacuum was selected for further investigation.Then,effects of different parameters including purity of HCCP,polymerization temperature,polymerization time,type and concentration of catalyst on the properties of the final polymers were investigated in order to screen out proper polymerization process that can obtain linear PDCP with high molecular weight and good solubility.Finally,the selected polymerization process as follows,monomer HCCP was purified by recrystallized for two times and vacuum sublimated once,the purified HCCP and anhydrous AlCl3(mole fraction is 0.17%)were placed in a glass tube and sealed under Schlenk line,then the sealed glass tube was put into a muffle furnace for melt polymerization at 250-260℃for12-17 h,the yield of soluble PDCP was more than 80%,and the molecular weight was up to106.(2)On the basis of the preparation of PDCP,ethoxy,phenoxy,2,2,2-trifluoroethoxy,2,2,3,3,4,4,5,5-octafluoropentoxy,aniline and p-trifluoroethoxyaniline reacted with PDCP as nucleophiles,respectively,to obtain six mono-substituted and two mixed-substituted polyphosphazenes.The thermal and hydrophilic properties of these polymers were measured by DSC,TGA and WCA(water contact angles),then the relationship between the substituent and properties of polymers were studied.According to the results,alkoxy substituted polymers,especially polyfluoroalkoxyphosphazenes have excellent low temperature resistance with Tg values below-60℃,while aryloxy substituted polyphosphazenes have good thermal stabilities.The WCA results indicating that products with fluorine-containing side groups were hydrophobic,ethoxy and phenoxy substituted products were hydrophilic.Moreover,two polyarylaminophosphazenes both showed lower flexibility at low temperature and poor thermal stability,but the different properties between these two polymers suggesting that the properties of polyphosphazenes could also be changed by connection with side groups indirectly,even with an aromatic spacer.(3)Anα-hydroxyphosphonate cyclotriphosphazene compound HDHPCP was synthesized by two steps from HCCP,the molecular weight is 1690.3 g/mol,then it was blended into diglycidyl ether of bisphenol A and cured with 4,4’-diaminodiphenyl methane to prepare flame-retardant epoxy resin(EP).HDHPCP has a good compatibility with EP,with the increase of HDHPCP content in EP,Tg values and thermal stabilities of EP/HDHPCP composites decreased gradually.On the contrary,the flame retardancy of EP was remarkably improved with the addition of HDHPCP,for EP/HDHPCP composite with 20 wt%HDHPCP,the LOI value is30.7%and reaches UL-94 V-0 rating,which demonstrated good flame retardancy.As for the mechanical properties,the flexural strength decreased while the impact strength improved with the HDHPCP content increasing,this meaning that the addition of HDHPCP makes no significant negative effect on mechanical properties of EP and has toughening effect.(4)A novel multi-functional epoxy resin hexa-(4-glycidyl methyl-phenoxy)-cyclotriphosphazene,HGPCP,which with a core structure of cyclotriphosphazene,was synthesized.The epoxy value of HGPCP is 0.50 eq/100g,the epoxy equivalent is 201.7 g/eq and molecular weight is 1210.1 g/mol.Three common epoxy hardeners DDM,DDS and2E4MZ were selected to cure HGPCP,according to the FTIR and DSC results these hardeners can cure HGPCP successfully.The obtained curing systems HGPCP/DDM,HGPCP/DDS and HGPCP/2E4MZ have good heat resistance and thermostability,with Tg values of 191℃,196℃and 186℃,respectively.The char residues of HGPCP/DDM,HGPCP/DDS and HGPCP/2E4MZ are 53.2%,45.4%and 52.9%.The mechanical properties of these three cured epoxy resin systems have no obvious difference compared with DGEBA/DDM,but due to the higher crosslink densities HGPCP/DDM,HGPCP/DDS and HGPCP/2E4MZ have lower toughness than DGEBA/DDM.Furthermore,HGPCP/DDM,HGPCP/DDS and HGPCP/2E4MZ all have excellent flame retardant with LOI values of 32.5%,35.4%and 34.2%,respectively,and reache UL-94 V-0 flammability rating.(5)A bifunctional cyclolinear cyclotriphosphazene-based epoxy resin(CTP-EP)was successfully synthesized and characterized,then disulfide-containing aromatic diamine 4,4’-dithiodianiline(DTDA)was selected as hardener to form a new epoxy vitrimer,CTP-EP/DTDA.The dynamic covalent bond disulfides endow the epoxy resin with reversible cross-linkages,this reversibly cross-linked epoxy system combines the features of thermosets and thermoplastics.It behaves as a thermoset at ambient conditions yet can be quickly reprocessed or repaired at high temperature by hot-pressing like a thermoplastic.The multiple self-healing ability was measured by tensile strength,under appropriate hot-pressing condition,this vitrimer system can be reshaped for many times with high healing efficiency,which is attributed to the radical-mediated aromatic disulfide exchange mechanism.In addition,this newly obtained epoxy system also possesses good thermal stability and excellent flame retardancy with LOI value 30.4%,and a flammability rating of UL-94 V-0.The multifunctional epoxy vitrimer prepared in this study has potential applications in the aircraft and automotive industries takes into account the environment and human health.