Solvent effects on chain structure and conformation of poly(amic acids) and their crystallosolvate formation

Abstract

Poly(amic acids) (PAAs) were prepared from pyromellitic dianhydride (PMDA) and diamines such as 2,2'-difluoro-, 3,3 '-difluoro-and 2,2'-dichloro-4,4'-methylenedianiline. These PAAs form liquid crystals in N-methyl-2-pyrrolidone (NMP) solution, in addition to the PMDA/4,4'methylenedianiline (MDA) system reported previously. NMP was the only solvent in which liquid crystals were formed. The "liquid crystal" was shown to be a polymer crystallosolvate (PCS) of PAA and NMP. ' H NMR spectroscopy revealed that PAAs derived from PMDA contain isophthalamide and terephthalamide repeating units in nearly equal proportion, which varies slightly between samples prepared in NMP and dimethylacetamide (DMAc). WAXS showed that the PAA from PMDA/MDA is non-crystalline but forms a liquid crystalline state in NMP solution. The rate of crystallization is, however, vastly different between samples prepared in different solvents. This was attributed to their difference in chain conformation, which has to be an extended one for PCS formation. The morphologies of PCS are given, and limitations in PCS formation are discussed in terms of PAA structure and solvent.

Kinetic and mechanistic investigations of the formation of polyimides under homogeneous conditions

“…Since both acid and amide functional groups belong to the same molecule, many kinetic studies have been analyzed using the first-order kinetic equation:1'2 [33][34][35][36][37] ln(l -p) = -kt (14) where p is the degree of imidization, k is a rate constant, and t is the reaction time.…”

Effect of the solvent type and polymerization conditions on the curing kinetics, thermal and viscoelastic performance of poly(amide-imide) resins

“…has found that terephtalic conformation is thermodynamically more stable than the isophtalic one due to the stronger ability to build the hydrogen bonds with NMP and, thereof, reacts at higher temperatures. Moreover, the ratio of tere-to isophtalic isomers in NMP solution is 3 to 1 found by NMR analysis whereas in dimethylacetamide (DMAc) this ratio was found to be lower (1 to 1) [28]. Since MI used as solvent in this work is hardly able to solvate PAAc through the hydrogen bonding, formation of the low-energy isophtalic-conformation is preferable and causes the lowering the reaction temperature and activation energy.…”

Formation of Macrovoid-Free PMDA-MDA Polyimide Membranes Using a Gelation/Non-Solvent-Induced Phase Separation Method for Organic Solvent Nanofiltration

“…Thus, polymer and solvent must be paired in advance. Despite this, there still exist many bi- or tricomponent dope systems that can form physical gels such as polyamic acid (PAA)/ N -methyl pyrrolidone (NMP), − poly­(acrylonitrile- co -acrylic acid)/ N , N -dimethylformamide/H 2 O, polyethersulphone/dimethylacetamide/H 2 O, poly­(2,6-dimethyl-1,4-phenylene oxide)/ethanol, methylcellulose/H 2 O, and so on. In this study, we select PAA because its corresponding polyimide (PI) has high thermal stability, good mechanical strength, and strong solvent-resistance. ,− …”

“…The idea is to induce gelation of the PAA dope to inhibit the formation of macrovoids during NIPs. PMDA-MDA PAA is selected instead of PMDA-ODA PAA because PMDA-MDA PAA/NMP solution could gelatinize at T < 45 °C. − TiO 2 nanoparticles are added to the dope for two reasons. First, membranes with more open-pore structures can form because the hydrophilic TiO 2 particle promotes water diffusion into dope. − Second, TiO 2 particles tend to conjoin with polymer chains by self-assembly to accelerate gelation process .…”