The link between the mechanical properties produced by thermal imidization of poly-(p,p′-diphenylenoxy)pyromellitic amic acid and the reaction conditions

Reaction Modeling of the Multistep Synthesis of Polyamic Acid from Pyromellitic Dianhydride and Oxydianiline

“…-OCNOO•' (3) where Ao is the amine end on diamine monomer, AR is the amine end on polymer, B is the anhydride end, C is the favored conformer of amide link, Cx is the unfavored conformer of amide link, D is the imide link, E is the Since the thermal conversion imidization is characteristic of an initially fast reaction followed by a much slower one (Kreuz et al, 1966), the existence of a transformation between conformers of polyamic acid has been postulated. This postulation is based on the assumption that all polyamic acids are kinetically nonequivalent (Kreuz et al, 1966;Tsapovetskii and Laius, 1982;Korshak et al, 1981;Laius and Tsapovetskii, 1980). They can be present in two different conformations (relative position of the -OH and -NH in the amide link) and the exchange between conformations is possible.…”

“…A MWD with polydispersity higher than 2 for a polycondensation polymer can be attributed to an inhomogeneous environment caused by the imbalance between the chemical reaction rate and the rate of diffusive mixing (Kilkson, 1968(Kilkson, ,1964. This imbalance has been found to have resulted in poor selectivity in many organic reactions (Korshak et al, 1981; Bourne et al, 1981;Kilkson, 1964Kilkson, ,1968. Although the overall amount of PMDA added into ODA solution does not exceed the unity of the stoichiometric point, the immediate neighborhood of dissolved PMDA is inevitably rich in PMDA causing a concentration gradient of ODA.…”