Study On Store-stability Of Poly(amic Acid)s And Hyperbranched Polyimide

Study on Store-Stability of Poly(amic acid)s and Hyperbranched Polyimide(Abstract}Aromatic polyimides are well-known as important high performance polymers due to their outstanding properties with high thermal stability, excellent mechanics, resist chemical and lower dielectric. Most commercialized aromatic polyimides are produced through a two-step method, which is composed of the preparation of polyamic acids as soluble precursors and the subsequent cyclization to form insoluble polyimides. Polyamic acids in solution are usually unstable in storage for long period because hydrolytic cleavage reaction readily takes place. Many methods have been studied to improve the stability. Recently, Hyperbranched polymers have attracted considerable attention owing to new physical and chemical properties caused by their unique structures. As compared to their linear analogues, hyperbranched polymers possess good solubility in organic solvents and lower viscosity. In addition, hyperbranched structures can be easily achieved by chemical modification of end groups. The two parts are included in the disstertation.A series of poly(amic acid)s based on pyromellitic dianhydride (PMDA), biphenylyl tetracarboxylic dianhydride (BPDA), thiodiphthalic dianhydride(TDPA) bis(dicarboxyphenoxy) benzene dianhydride (HQDPA) and oxydiphthalic dianhydride (ODPA) were prepared in different solvents. Two poly(amic acid)s, from PMDA with 4,4 ' -diaminodiphenyl methane or 4,4 ' -diamino-3,3 ' -dimethyl diphenyl methane, were gelating in N-methyl pyrrotone, and the others were solution. Store-stability of poly(amic acid)s were investigated in different condition such as temperature, gelating state, adding molecular sieve. Poiy(amic acid)s gel have better store-stability thanpoly(amic acid)s solutions. 4A molecular sieve can prevent poly(amic acid)s from depolymerization, and make it store for a long time. A series of novel ABx monomers were synthesized prepared and characterized. A series of hyperbranched aromatic polyimide with many with hydroxy, cyanobenzene, aromatic imide, aryl ester and alkyl ester end groups were synthesized successfully by self-polycondensation of the AB2 monomers and one-pot procedure. Their molecular structures were characterized by NMR, IR and elementary analysis. By gel permeation chromatography measurement (GPC), weight-average molecular weights (Mw) of hyperbranched aromatic bolyimides were found to be 5000-20000 and the very narrow molecular weight distributions were showed to be -1.00-1.60. By thermogravimetric (TG) and differential scanning calorimetry (DSC) measurements of the polymer, 10wt% thermal loss temperatures (T10) were observed to be above 200癈, and Tg values were 148-240 癈. Most of the polymers have good solubility in DMAc, THT, CHCI3 and ethanol The solution of the polymer showed lower intrinsic viscosity (0.08-0.20).