Research article

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A series of homo- and copolyimides based on mixed thioetherdiphthalic anhydride isomers (mixed-TDPA) were synthesized with several kinds of aromatic diamines. The properties of these polyimides were characterized by glass transition temperature (T_g), thermal decomposition temperature, and melt processability. A series of copolyimides were prepared to achieve high T_g concurrently with melt processability by means of selecting appropriate diamines and their composition in the copolyimides. As a result, we obtained rheological information for a series of polyimide resins as a function of temperature, time and shear rate. It is found that the processability (e.g., melt viscosity of polyimides) and ultimate product properties (e.g., T_g of polyimides) can be systematically varied by changing the variety and composition of the aromatic diamines. It has been demonstrated that the incorporation of meta- or flexible diamines improve the melt processability of polyimides significantly. Meanwhile, T_g of copolyimides from dual-diamines can be predicted and regulated. Accordingly, copolyimides from 1,3-phenylenediamine (m-PDA) and 3,4’-oxydianiline (3,4’-ODA) were obtained with higher T_g and lower melt viscosity. Such correlations of chemical structures and rheological behavior provide the necessary database for tailor-making new polyimide systems with desirable processability and physical properties.