The Relationship Between Sustitution Structure And The De-Crosslinking Temperature Of Thermal Reversible Crosslinking Agent

Currently, the carboxylate salts from dicyclopentadiene (DCPD) system have been used for the preparation of thermal reversible covalent crosslinking polymer. However, side reactions occur easily, due to the high temperature in the re-crosslinking of the polymers. Reversible crosslinking of polymers is related to the structure of crosslinking agents. Therefore, an ideal way to solve above problems is reducing the de-dimerizing temperature of thermal reversible cross-linking agents, and hence the de-crosslinking temperature.DCPD derivatives themselves have thermal reversible characteristics of dimerizmg/de-dimerizing, so the de-dimerizing temperatures of crosslinking agents with different structure weres investigated in this paper. After DCPD was substituted by alkyl for offering electronic effect and space steric effect, and then synthetized sodium salts, carboxylic acid and esterifying products, the de-dimerizing temperatures of compounds from different structures were investigated, expecting to reduce the de-dimerizing temperature. The main task focused on the synthesis and characterization of DCPD derivatives, and the investigation on de-dimerizing temperatures of carboxylic acid, sodium salts and ester products. The details are as follows:1. Dicyclopentadiene dicarboxylic acid (DCPDCA), dimethyl dicyclopentadiene dicarboxylic acid (DMCPDCA), diethyl dicyclopentadiene dicarboxylic acid DECPDCA) and the corredponding sodium salts were synthesized, with emphasis on the synthetic reaction condition of DECPDCA, and the characterization of structure of DECPDCA by elemental analysis, MS,’H-NMR, DSC, UV and IR. The results showed that the molecular weight of DECPDCA was276.0, there was C=C, carboxyl and ethyl in the structure, and conjugate existed between-COOH and C=C, and there were many isomers.2. The carboxyl reaction of isopropyl cyclopentadiene sodium (IPCPDNa) and dry ice was investigated. DSC curves of the synthesized carboxylic acid indicated that de-dimerizing temperature of DIPCPDCA was143.2℃, which was15.7℃lower than DECPDCA. The reaction of tetramethyl cyclopentadiene (TMCPD) and sodium was studied, with THF as solvent. When heated from10℃to65℃, the tetramethyl cyclopentadiene sodium (TMCPDNa) was failed to be obtained. The reason may be that reacting activity of hydrogen from TMCPD is too low, and souium and TMCPD cannot react in inspected condition.3. The de-dimerizing temperatures of DCPDCA, DMCPDCA, DECPDCA and the corresponding sodium salts were compared. The results showed that the de-dimerizing temperatures were followed by TDECPDCA<TDMCPDCA<TDCPDCA and the de-dimerizing temperature of sodium salts was lower than the corresponding carboxylic acid.4. Esterifying products between sodium salts and a,a’-dichloro-p-xylene (DCX) were characterized by IR, GPC and DSC. IR spectra indicated that-COO-existed at1705cm-1due to the ester group and the number-average molecular weight (Mn) of polymers were1160,2065and1145by GPC, which proved esterified reaction happened. DSC curves indicated de-dimerizing temperatures were at174℃,170℃and157℃, and showed that the de-dimerizing temperatures were reduced in turn; and carboxylic acid, sodium salts and esterified products, substituted by the same group, the de-dimerizing temperature was followed by Testerified products<Tsodium salts<Tcarboxylic acid.