Preparation And Properties Of Thermoreversible Cross-linked Polymers Based On Dynamic Bonds

Thermosetting polymers are widely used in production and life due to the advantages of low processing viscosity,good dimensional stability and easy adjustment of chemical structure.However,due to the limitation of the cross-linked network,thermosetting polymers do not have thermoplastic reprocessing properties,and their recycling has always been a major problem in the field of polymers.To this end,in this study,dynamic bonds were introduced into the polymer cross-linked network to prepare thermoreversible cross-linked polymers with excellent mechanical properties and thermoplastic reprocessing.The main research contents of this paper are as follows:(1)Using commercially available epoxidized natural rubber(ENR)as the matrix,using dicarboxylic acid dicyclopentadienedicarboxylic acid(DCPDCA)containing Diels-Alder(DA)adduct structure as the crosslinking agent,through the carboxyl group and The ring-opening reaction of epoxy groups constructs multiple thermally reversible cross-linked networks containing DA adduct structures/β-hydroxyester bonds/hydrogen bonds.The mixing and dispersing properties of DCPDCA in ENR matrix,masterbatch formulation,cross-linking activity,mechanical properties and thermoplastic reprocessing properties of cross-linked rubber samples were investigated.The results show that DCPDCA has good compatibility with ENR and can effectively crosslink ENR;the tensile strength of DCPDCA crosslinked ENR rubber reaches 8.2 MPa,and the elongation at break reaches 425%;the rubber is heated at 180 ℃ to produce viscous flow,and repeated heating After pressing for three times,the tensile strength still reaches 6.7 MPa,and the tensile strength recovery rate is 82%.(2)The carbon black reinforced DCPDCA cross-linked ENR rubber was prepared,and it was found that when the carbon black filling amount was 50 phr and the DCPDCA dosage was 2 phr,the tensile strength of the rubber sample reached 15.4 MPa,and the elongation at break reached386%;After three times of thermoplastic processing,the tensile strength is11.4 MPa,and the tensile strength recovery rate is 74%;After repeated hot pressing for three times,the crosslinking density of the carbon black reinforced DCPDCA crosslinked ENR rubber decreased slightly,and the pyrolysis temperature did not change significantly.(3)Using epoxidized low-density polyethylene(ELDPE)as a matrix,a thermally reversible cross-linked low-density polyethylene based on β-hydroxyester bond was prepared by the reaction between the epoxy group of ELDPE and the carboxyl group of sebacic acid(SA).Ethylene(TRCLDPE),and then adding TRCLDPE to ordinary LDPE to prepare LDPE/TRCLDPE blended materials.The compatibility and crosslinking activity of SA and ELDPE,the effect of SA dosage on the mechanical properties of TRCLDPE,the crystallization properties of LDPE/TRCLDPE blends,and the mechanical properties and thermoplastic processability of the blends at room temperature and high temperature were investigated.The results show that SA has good compatibility with ELDPE and can crosslink ELDPE;when the molar ratio of carboxyl group/epoxy group is 0.1,the elastic modulus of TRCLDPE reaches 105 MPa,and the tensile strength reaches 18.1 MPa;LDPE/TRCLDPE The blend can form a eutectic,and its mechanical properties are significantly better than LDPE.At room temperature,the yield strength increases from 9.1 MPa to 11.4MPa,and at 60 ℃,the yield strength increases from 4 MPa to 5.2 MPa.At80 ℃,the yield strength of the sample increases The strength increased from 2.1 MPa to 3.2 MPa,and the yield strength increased from 0.7 MPa to 1.7 MPa at 100 ℃.