Analysis of chemical structure of fluoro-containing copolyamic acid methyl esters and its effect on the thermal imidization process

Copolyamic acid methyl esters were directly synthesized from 2,5-dicarbomethoxy terephthalic acid (p-PMDE) and 4,4′-oxydianiline (ODA) and fluoro-containing diamines using phenyl phosphonic dichloride. The average sequence lengths of the copolyamic acid methyl esters were controlled by stoichiometric unbalance and monitored by proton nuclear magnetic resonance spectroscopy (1H-NMR). The effect of chemical structure of copolyamic methyl esters on thermal cyclization to the corresponding copolyimides was studied by differential scanning calorimetry and on thermal properties and solubility by thermogravimetry and solubility testing. The maximum imidization temperatures of the copolyamic acid methyl esters were between those of the homopolymers. The short sequence length of the fluoro-containing moiety of the copolyamic methyl esters made the copolyimide more soluble in organic solvents. The average sequence length of the copolymer did not affect the thermal properties of the corresponding copolyimide in this system.