The double bond in the unsaturated polyester and the double bond in the cross-linking agent polymerize to form an insoluble and infusible cross-linking network. The network contains two kinds of polymer molecular chain structures. The main body of the network is composed of random coils of unsaturated polyester molecular chains, and styrene copolymer molecular chains are interspersed among them to connect and fix the unsaturated polyester molecular chains to form a huge network. The average molecular weight of unsaturated polyester molecular chain in the network is 1000~3000. The average molecular weight of styrene copolymer molecular chain can reach 8000~14000. The average molecular weight of the entire network structure is 10,000~30,000. If the molecular weight of the network is less than 10000, it will directly affect the mechanical properties of the product, such as strength, elasticity and toughness.
Long life of unsaturated polyester resin cross-linked network During the curing process of unsaturated polyester resin cross-linked network, the polymerization process of the double bond of unsaturated polyester and styrene and the change of residual rate have certain characteristics. Experiments show that no matter whether the cross-linking network of polyester resin is perfect or not, some steric hindrance points where free radicals cannot be terminated will be generated, forming long-life free radicals. Due to the existence of long-life free radicals, the crosslinking reaction of unsaturated polyester resins can still proceed after curing.