Synthesis And Investigation Of Coating Properties Of Novel Poly (Amide-Imide)

The main function of coating is to protect the substrate. It provides a theoretical basis for comprehensive understanding of paints along with the development of organic chemistry, polymer chemistry and materials science and engineering. In addition, the development of polymerization process offers technical basis to synthesize various organic coatings. Currently, polymer polyester, polyurethane, polyimide, polyester-imide, polyamide-imide are used in many aspects. On account of fire prevention, insulation, electromagnetic shielding function properties, special coatings are widely used in fire prevention, electronics, machinery and other applications. Industry divides coating into different levels according to the different temperature of heat-resistance, the heat-resistant temperature below 180 ℃ are called the general coatings, the heat-resistance temperature over 180℃ are called high-temperature coatings. Polyamide-imide coating with high heat-resistant temperature and excellent insulation property is used to protect the motor and motor winding wire.The water absorption of traditional PAI is obvious and the decomposition temperature needs to be improved. We synthesized novel PAI by adding Pyromellitic dianhydride(PMDA) into reaction system. The glass transition temperature and decomposition temperature were raised, water absorption was reduced, at the same time, the optical performanc and mechanical properties were also outstanding.this article took Trimellitic anhydride(TMA), Pyromellitic dianhydride(PMDA), 4,4’—diphenyl methane diisocyanate(MDI) as monomers, N- methylpyrrolidone(NMP) and xylene as mixed solvent, deionized water was coagulation bath and made use of "one-step" method to prepare novel polyamide-imide(PAI). By comparing the inherent viscosity of synthetic PAIs, we obtained the optimum process to synthesize polyamide-imide polymer. The reaction temperature was 140℃, reaction time was 6h, and adding TMA and PMDA firstly, then putting MDI into reaction system, the ratio of acid anhydride and MDI was 1: 1.05.With PMDA content increasing, the anhydride content in reaction system was also increasing. The glass transition temperature of PAI improved from 285 ℃ to 308 ℃, decomposition temperature was rising too, this phenomenon can be attributed to the increasing proportion of imide ring. Furthermore, PAI films showed excellent resistance to ultraviolet light. There was almost no light transmit in the range of 200 nm to 400 nm. What’s more, with the increasing content of PMDA, the light transmission of PAI films had a certain upgrade in 400nm-600 nm region. PAI films showed some surface wrinkles and became dark in color after treatment in muffle furnace, the original weight before heat treatment was 0.107 g and the weight became 0.089 g after 24 h heat treatment under 300℃, it declined rapidly in initial 6 hours and the mass loss is 16.8%, This result matched with TGA test. The reasons that weight loss were NMP solvent evaporation under high temperature and decomposition of small molecules. While the film weight reduced, the hardness of PAI film did not change, the hardness was still 5H. The electrical test resultes showed that the loss tangent of PAI films were 10-3, this outcome indicated the dielectric loss was very small. The conductivity was 10-6S/cm. From these results, we could conclude that PAI films have excellent insulation property.After storing 90 days under 100 ℃, PAI solution became darker after comparing with PAI solutions stored under-10℃ and 25℃, in addition, under 25℃ and-10℃ condition, the inherent viscosity of PAI solution presented no clear difference with the newly synthesized PAI solution, however, the inherent viscosity of PAI-5 solution was significantly raised under 100℃. This was because under high temperature, the molecular chain mobility enhanced and reaction groups were more active, leading to further polycondensation reaction occured, at last, the molecular weight increased as well as viscosity promoted,the tensile strength of PAI films also increased. According to IR spectroscopy test, the absortion peaks of PAI groups were not altered after 90 days.