Synthesis of polyamide-imides with different monomer sequence and effect on transparency and thermal properties

Two novel series of polyamide-imides (PAIs) with different monomer sequence were prepared by two synthesis methods. First series of alternate polyamide-imides PAIs-2(a-e) were synthesized from polycondensation of diimide-diacids 1a-1c monomers with various aromatic diamines. Using the direct polycondensation of trimelletic acid chloride (TMAC) with aromatic diamines, second series of polyamide-imides PAIs-3(a-c) were prepared. The effect of monomer sequence on transparency and thermal properties of polymers is investigated. The transmittance at 550 nm (T-550) from the ultraviolet-visible (UV-vis) spectra of the PAIs was found in the range of 74-87%, greatly affected by the monomer sequence in the polymer repeating units. PAI-3a from TMAC exhibited high transparency of 87% and low coefficient of thermal expansion (CTE) of 25 ppm/degrees C. All co-polymers demonstrated good organosolubility and mechanical properties with initial moduli of 3.4-4.9 GPa, tensile strengths of 96-129 MPa and elongations at break of 3.0-5.2%. The glass transition temperatures (T-g) and 10% weight loss temperatures (T-10%) of PAIs in nitrogen were in the range of 291-330 degrees C and 489-501 degrees C, respectively