Molecular Structure Design Of Bisphenol Compounds And Their Cross-linked Polymer Performance Study

Benzoxazine and epoxy resins are important thermosetting resin categories that are widely used in adhesives,coatings and composites owing to their excellent mechanical properties,thermal stability and solvent resistance.These two resins also have certain shortcomings,for example,the toughness of polybenzoxazine resins is significantly different from other resins,which seriously affects their application scope;a large number of epoxy resin waste products are difficult to recycle and degrade,posing profound environmental risks.Therefore,it is important to design cross-linked networks to give benzoxazine and epoxy resins excellent toughness and efficient decomposability,respectively.This paper focuses on the design of cross-linked network structures within thermosetting resins,by introducing flexible side chains in the benzoxazine copolymer in the resin to enhance toughness,and using dynamic covalent bonding in the epoxy monomer molecule to build a reversible dynamic covalent bonding system within the resin to form a decomposable recycling capability.Details of the research are as follows:In order to toughen benzoxazine resins,dodecyl chains were introduced into the benzoxazine structure in this paper to synthesise a benzoxazine with self-plasticising properties,bisphenol acid amide/dodecylamine type benzoxazine(DLA-la),which was copolymerised with a commercial benzoxazine,phenol/diaminodiphenylmethane type benzoxazine(PH-ddm),to prepare toughened polybenzoxazine resins.In this paper,we modulate the toughening effect of the resin by changing the self-plasticizing benzoxazine DLA-la component in the copolymerization system.Experimental results show that the DLA-la/PH-ddm copolymerisation does not produce phase separation in the molar ratio range of 20-80%,and when the DLA-la content is 70%,the elongation at break of the resulting copolymerised resin is 70% higher than that of the resin obtained by the native polymerisation,and the thermal stability can be maintained without significant.The present work shows that the synthesis of self-plasticising benzoxazines by molecular design and copolymerisation with brittle benzoxazines can achieve highly effective toughening effects,suggesting a new way to solve the problem of commercial benzoxazine toughening.In order to give the epoxy resin recyclable properties,this paper introduces an acetal dynamic covalent bond in the molecular structure of the epoxy monomer and a disulfide dynamic covalent bond in the molecular structure of the curing agent through molecular design,and constructs a double decomposable cross-linked network after curing to achieve the recyclable properties of the epoxy resin.The dynamic covalent bond within the epoxy monomer is an acetal structure,prepared by the aldol condensation reaction between p-hydroxybenzaldehyde and bis(trimethylolpropane);the dynamic covalent bond within the curing agent is a disulphide bond structure.After curing,the mixture forms a double decomposable cross-linked network structure with two dynamic covalent bonds: disulfide and acetal.Experimental results show that the cured epoxy resin can be completely degraded to a clear solution at 65°C in a mixture of hydrochloric acid and tetrahydrofuran in less than 8 minutes.By designing a doubly decomposable cross-linked network structure,this thesis solves the problem that epoxy resins are difficult to decompose and difficult to recycle,and the research results provide an effective solution for waste treatment of epoxy resin/carbon fiber composites,which has good potential for application.