Chemical copolymerization method is mainly through the condensation reaction in the end of the main chain of polyorganosiloxane or side chain connected to the polyester resin, the formation of block, grafting or interpenetrating network copolymer, with the help of chemical bonds to make the two polarity of large polymer together. The method can improve the compatibility of the two phases, inhibit the migration of polysiloxane molecules to the surface, and make the silicone resin and polyester resin uniformly dispersed at the micro level. According to the type of raw materials, chemical copolymerization can be divided into monomer copolymerization modification and macromolecular copolymerization modification.
Monomer copolymerization modification method
The monomer copolymerization modification method is a method to prepare organosilicon modified polyester resin by first reacting organosilicon intermediate with polyols and then with polyacids.
Yang Jun et al. made organosilicon modified polyester by means of polycondensation reaction by partially replacing dialcohol with hydroxyl silicone oil of low molar weight. The synthesis principle of organosilicon modified polyester is as follows:
The results show that the molar weight of the polyester chain segment in the silicone modified polyester is higher than that of the polyester without hydroxyl silicone oil. Moreover, the molar weight of polyester chain segment increased with the increase of the amount of hydroxyl silicone oil. This is because in the presence of hydroxyl silicone oil, condensation reaction between carboxyl group and hydroxyl group occurs, as well as between some hydroxyl groups, so the molar weight of polyester chain segment increases. The content of organosilicon in the silicone modified polyester increases with the increase of the amount of hydroxy silicone oil, and reaches the limit when the molar fraction of hydroxy silicone oil is 617%. The silicone modified polyester prepared by this method has low surface energy and can be used as low surface energy additive or surfactant.
Macromolecular copolymerization modification
Macromolecular copolymerization is a method to prepare organosilicone modified polyester resin by condensation reaction with pre-made polyester resin containing C - OH group, starting from siloxane intermediate containing SiOH or SiOR.
Xu Zhenyu et al. synthesized organosilicone modified polyester resin by monomer copolymerization and macromolecular copolymerization. The results showed that the monomer copolymerization was more favorable for the reaction between silicone resin and polyester resin, and more silicon block copolymers were formed. The content of silicon components in the molecules was relatively small, and the compatibility with the system was better, which was more effective for reducing the glass transition temperature and melting viscosity of polyester. Silicone resin is easy to self-polymerize when using macromolecular copolymerization modification process route, and then the self-polymerized silicone resin is grafted to polyester resin, which makes the molar weight of the modified polyester become very large, thus affecting the content of silicon chain segment in the copolymer. Silicone modified polyester resin with low curing temperature, good heat resistance and mechanical properties can be prepared from alkoxy silicone resin and polyester containing hydroxyl group by one-step continuous process under acid catalysis.