Synthesis and Thermal Properties of Polythioetherimides Derived from 4,4'-[p-Thiobis(phenylenesulfanyl)]Diphthalic Anhydride and Various Aromatic Diamines

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Abstract
An asymmetrical aromatic diamine, 1-(4'-aminophenoxy)-4-(4'-aminophenylenesulfanyl) benzene (OSDA) was synthesized. A series of polythioetherimides (PTEIs) were prepared from a thioether-bridged aromatic dianhydride 4,4'-[ p-thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA) and various aromatic diamines having ether or thioether linkages between phenylene rings by a two-step polycondensation procedure via their soluble poly(amic acid) (PAA) precursors. Medium to high molecular weight PAAs were obtained with inherent viscosities near or higher than 1.0 dL g-1, which is high enough to afford flexible and tough PTEI films except for PI-2 (3SDEA-134APB) and PI-6 (3SDEA- m2SPDA) derived from meta-ether-substituted diamines. PI-2 and PI-6 showed some extent of crystallinity compared to the amorphous natures of the other polymers. The PTEI films exhibit good resistance to organic solvents except for PI-3 (3SDEA-133APB), which is soluble in N-methyl-2-pyrrolidinone (NMP) and sulfuric acid at room temperature. The PTEI films show good thermal stability with the 5% weight loss temperatures being above 480°C both in nitrogen and in air. The glass transition temperatures of the PTEIs are in the range of 155—191°C, which are lower than those of the commercial polyetherimides due to their plural thioether linkages in the main chains.