Molecular Structure Study Of The Self-crosslinking Unsaturated Polyester And The Investigation Of The Resin Synthesis And Its Curing Properties

The unsaturated polyester is one of the most commonly used thermosetting resins,which can be cured through radical copolymerization with the volatile crosslinkingmonomers. But the volatile crosslinking monomers will cause the environmentpollution problems in the curing process. Self-crosslinkable unsaturated polyester canbe cured through the reaction of the radical homopolymerization of vinyl doublebonds in the unsaturated polyester molecular chain or the reaction between vinyldouble bonds and other functional groups, turning into crosslinking cured resinwithout the exist of the crosslinking monomers. So when the self-crosslinkableunsaturated polyester is used in the plastic industry, the problems of environmentpollution from volatilization of the crosslinking monomers can be effectively solved.In this paper, two kinds of self-crosslinkable unsaturated polyesters weredesigned and prepared: the self-crosslinkable unsaturated polyester with pendanthydroxyl group; the self-crosslinkable unsaturated polyester with vinyl double bondsat the end of the chain. Meanwhile, the reaction mechanism of synthesis, the reactionmechanism of crosslinking, curing process and thermal properties of the cured resinswere studied.The main experimental results are as follows:1、 A series of unsaturated polyesters (IG-UP) with pendant hydroxyl groupswere synthesized used itaconic anhydride and glycidol as raw materials. The mole ratios of the raw materials were1:2,2:3and3:4, respectively. Fourier transforminfrared spectroscopy (FT-IR) and Nuclear magnetic resonance hydrogen (1H-NMR)were used to characterize the molecular structure of the self-crosslinkable unsaturatedpolyesters (IG-UP) and helped to explore the systhesis reaction mechanism of theresin.2、 The series of unsaturated polyesters (IG-UP) were successfullyself-crosslinked after heated at145°C for2h, at160°C for2h, and at180°C for4h.Two crosslinking reactions were existed in the curing process: one was additionreaction of hydroxyl groups (-OH) with vinyl double bonds (C=C); the other wasring-opening addition reaction of the epoxy ring with hydroxyl (-OH). Compared withthe cured self-crosslinkable resin which was synthesized with maleic anhydride andglycidol as raw materials, the cured IG-UP shew good heat resistance.3、 A self-crosslinkable unsaturated polyester with vinyl double bonds at the endof the chain (EA-UP) was synthesized with the molar ratio of ERL-4221to acrylicacid as1:2. With the existence of the initiator BPO, EA-UP could be cured throughthe radical homopolymerization of vinyl double bonds when heated at90°C for30min and at120°C for2h. Without the existence of the initiator BPO, EA-UP could becured through the addition reaction of hydroxyl groups (-OH) and vinyl double bonds(C=C) when heated at145°C for1h and at160°C for3h. The EA-UP after curing hada good stretch.4、 Another self-crosslinkable unsaturated polyester with vinyl double bonds atthe end of the chain (TGG-UP) was synthesized with the molar ratio of trimelliticanhydride to glycol to acrylic acid as1:3:3. Without the existence of the initiator BPO,TGG-UP could not be cured when heated. However, with the existence of the BPO,TGG-UP could successfully be cured when heated at100°C for30min, at140°C for3h. Compared with the cured EA-UP, the cured TGG-UP shew good heat resistance.The TGG-UP after curing had a good stretch.