Influence of azobenzene units on imidization kinetic of novel poly(ester amic acid)s and polymers properties before and after cyclodehydration

Abstract

In this article, the imidization reaction kinetic of novel poly(ester amic acid)s with azobenzene units as side groups was studied by dynamic experiments by means of differential scanning calorimetry. Polymers differ in the number of chromophore moieties in their repeating unit and position in which azobenzene group is attached to the polymer chain. The kinetic parameters of poly(ester amic acid)s conversion to poly(ester imide)s was compared with data calculated for parent polymer, that is, without azobenzene groups. For the first time to our knowledge, the imidization kinetic of polymers with side azobenzene groups was studied. Kinetic parameters, such as the activation energy and frequency factor were estimated with the by Ozawa model [ (E(O) and A(O)), respectively] and Kissinger model [(E(K) and A(K), respectively].The values of activation energy determined with both models were in the range 167.1-198.3 kJ/mol. The lowest activation energy of imidization reaction exhibited polymer in which azobenzene units were placed between amide linkages. Polymers were characterized by FTIR, 1 H-NMR, X-ray, and UV-vis methods. The glass transition temperature of resultant poly(ester imide)s was in the range of 217-237 C. The presence of chromophore units slightly decreased T g and significantly improved their solubility and optical properties.

Poly(amic acid)s and their poly(amide imide) counterparts containing azobenzene moieties: Characterization, imidization kinetics and photochromic properties

“…The T p can be associated with the location of the azobenzene group in the main chain. When the azobenzene chromophore was situated between the amide groups of the closing ring (PAA-1), the T p was lower than for the other poly(amic acid)s. Similar effect was observed in our previous work [26]. The imidization process was successfully completed below 250 C for PAA-1 and PAA-2, while in the case of PAA-3 it began in a higher temperature i.e., at 230 C and completed at 290 C.…”

“…The E and A parameters are higher for PAA-1 and PAA-3 than for PAA-2 in both cases. Moreover, they are higher (in particular E exceeded 200 kJ/ mol) than those reported recently for other polymers [13,26].…”

“…The largest differences in solubility between PAAs and PIs were observed for cyclohexanone and CHCl 3 . PAAs exhibited better solubility in these solvents than PIs, (PAA-2 was also soluble in THF), what could be associated with a less rigid polymer chain in comparison to the PIs [26]. The closure of the imide ring caused a deterioration of solubility of the poly(amide imide)s, which were only partially soluble or insoluble in these solvents.…”

“…Polymer code Viscosity a dL g À1 Solubility b NMP DMSO THF CHCl 3 Cyclohexanone investigated only in our previous works [13,26]. However, those results referred to the azopoly(amic acid)s containing the chromophores with non polar substituents only.…”

“…The last equation applies to the first-order kinetic reaction, which has almost exclusively been used to treat the imidization kinetics [26,35,36]. Typical dynamic DSC curves obtained at various heating rates for the studied poly(amic acid)s are depicted in Fig.…”