Poly(vinyl acetal)s containing electron-donor groups: Synthesis in homogeneous phase and their thermal properties

The condensation reaction of 1-Naphthaldehyde (NA), 9-Anthraldehyde (ANTA), 9-Ethyl-3-carbazolecarboxaldehyde (ECZA) with poly(vinyl alcohol) (PVA) to give poly(vinyl acetal)s (PVAcs) was studied in detail using N-methyl-2-pyrrolidone (NMP) as solvent for PVA and PVAcs. PVAcs having various degrees of acetalization were obtained. The acetalization reaction under a variety of conditions gave at best a poly[2-(1-naphthyl)-1,3-dioxan-4,6-diylmethylene] (PNA) with 78% acetalization, poly[2-(9-anthryl)-1,3-dioxan-4,6-diylmethylene] (PANTA) with 70% acetalization and poly[2-(9-ethyl-3-carbazolyl)-1,3-dioxan-4,6-diylmethylene] (PECZA) with 48% acetalization. The extent of modification of the polymers was determined by 1H NMR. PVAcs were characterised by IR spectroscopy and 1H and 13C NMR. The glass transition temperatures of PVAcs, determined by DSC, increased linearly as vinyl acetal units increased. Thermal degradation of PVAcs was studied using differential thermal analysis (DTA) and thermogravimetry (TGA) under dynamic conditions in nitrogen. The content of hydroxyl groups had an effect on the thermal stability of PANTAs, the thermal stability of PANTAs decreased as vinyl alcohol units increased. The apparent activation energy of the decomposition was determined by the Kissinger and Flynn-Wall methods which agree well. FTIR (Fourier transform infrared) spectroscopic analysis of the degraded PVAcs showed evidence for elimination of hydroxyl and cyclic acetal groups and the formation of dienes.