Studies of the Preparation and Characterization of Polyamic Acid Esters

In the present paper, the synthesis and imidization kinetic studies of polyamic acid esters have been made. Pyromellitic dianhydride (PMDA) diester monomers have been synthesized from the ring-opening reaction of PMDA and aliphatic alcohols such as methanol, ethanol, isopropanol, n-butanol, t-butanol, and 2-hydroxyethyl methacrylate. Polyamic acid esters have been synthesized from the direct polycondesation of 4,4'-oxydianiline and PMDA based diester monomers at room temperature using dicyclohexyl carbodiimide (DCC) or diphenyl (2,3-dihydro-2-thioxo-3-benzoxazolyl)-phos-phonate (DTBP) as an activation agent. When DCC was used as the activating agent. low molecular weight polyamic acid esters that are soluble in methanol were obtained. When DTBP was employed, however, high molecular weight polyamic acid esters whose inherent viscosity values were larger than 0.3 dl/g were synthesized. Furthermore. imidization kinetics of polyamic acid esters were studied by performing the dynamic thermogravimetric analysis (TGA) at a constant heating rate of 10℃/min. The activation energy and Arrhenius pre-exponential factor were calculated from the TGA thermograms. The imidization of polyamic acid esters was effected by the chemical structure of the diester monomers such as the size and bulkiness of alkyl groups of the diester monomers. Activation energy values for the imidization reaction increased from 83 KJ/mol to 169 KJ/mol with decreasing the size of the alkyl groups of polyamic acid esters.

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