Solid‐state 13C NMR study on thermal dehydration process of poly(methacrylic acid)(PMAA)

Abstract

Thermal dehydration process of PMAA was investigated by solid-state 13 C NMR. For heat-treated PMAA at 150°C, at which the dehydration goes very slowly, we observed three 13 C peaks at 172, 178, and 187 ppm in the carboxyl group region. The peak at 172 ppm is due to the intramolecular cyclic anhydrides by comparing the reported value of 13 C chemical shift. The peaks at 178 and 187 ppm were assigned to regularly aligned free carboxylic acids and intermolecular acid dimers, respectively, from the 2D-exchange 13 C NMR spectra, 13 C chemical shift values and IR spectra. We concluded that by heat-treatment the rearrangement of intermolecular hydrogen bonding of the carboxylic acids in PMAA occurs firstly to form the regularly aligned acid dimers, and the dimers dissociated to be the regularly aligned free carboxylic acids at high temperatures. The adjacent free carboxyl acids dehydrate with each other, resulting in the formation of intramolecular anhydrides.

13C MAS NMR Study of Poly(methacrylic acid)–Polyether Complexes and Multilayers

“…The carbonyl peak at 179 ppm (Figure a,b) includes both the interpolymer hydrogen bonds of the complex (10.5 ppm) and the free COOH proton signals (9.5 ppm). This is not surprising as the 13 C peak at 180 ppm previously assigned as the complex overlaps with that assigned as the free carbonyl (178 ppm) …”

“…These labels are a combination of those used by Miyoshi et al . for the PEO–PMAA complex and Asano for the noncomplexed PMAA. The HETCOR spectra show that the dimer carbonyl at 187 ppm is correlated with the 1 H signal at 13 ppm assigned to the intra-PMAA cyclic dimers, for both polyether complexes (Figure a,b).…”

“…The inclusion of low glass transition ( T g ) polymers such as the polyethers, PEO or PVME, allows the formation of flexible free-standing films for sensor and device applications . PEO is known to induce order within the hydrogen bond structure of the poly(carboxylic acids). − This order can be detected in the solid-state 13 C NMR spectra where the broad 13 C carbonyl NMR resonance of the poly(carboxylic acid) , splits into two or three distinct resonances upon complexation to PEO. ,,, We have correlated this spectroscopic resolution to the stabilization and weakening of PMAA’s cyclic and open type dimers, respectively . This change in the intra-PMAA hydrogen bonding was also proposed to explain why PMAA–polyether bilayers are relatively thick and permeable relative to the other PMAA complexes.…”

Synthesis, Characterization, and Solid-State Properties of (CH2–CH2–C(COOH)2)n: A Highly Symmetrical, Semicrystalline Carbon-Chain Poly(carboxylic acid)

“…More attention was paid to peak 1, which corresponds to the -COOH functional groups, as it is made of three separate peaks (see Figure 6). As described independently by Fortier-McGill and Asano for polymethacrylic acid (PMAA), [31][32] the presence of multiple peaks for the carbonyl in carboxylic acid-containing polymers establishes the presence of local structural ordering. Based on the above NMR studies, the thinnest and most shielded peak (C in Figure 6) should correspond to the rigid regions in the polymer and therefore, due to PTD's semi-crystalline nature, to the crystal phase in the polymer.…”

“…Based on the above NMR studies, the thinnest and most shielded peak (C in Figure 6) should correspond to the rigid regions in the polymer and therefore, due to PTD's semi-crystalline nature, to the crystal phase in the polymer. [31][32] In order to unambiguously assign the three subpeaks in the carbonyl area to specific phases and chain arrangements, 13 indicates that all C(COOH) 2 subunits participate to cyclic dimers 33 and the very close fit for the 13 C NMR COOH peaks of DMAA and PTD, respectively, it seems reasonable to assume that the dimeric structure is also to be found in the crystalline fraction.…”