Preparation of poly(vinyl formal) of high acetalization

Abstract

Poly(vinyl alcohol) (PVA) can be dissolved in a non-aqueous medium in the presence of catalytic concentrations of C2H5ONO2.DMSO(EN-DMSO). Poly(vinyl formal) (PVF) of 90% acetalization was prepared by acid catalysed homogeneous formalization of PVA of molecular weight 14000 with paraformaldehyde. The formation of the formal was confirmed from the i.r. and 1H n.m.r. spectra. The molecular weight of the polymer was 104 000 as determined by g.p.c. The glass transition temperature (Tg), activation energy (E), order of reaction (n) and rate constant of melting (k) were computed from d.s.c. thermograms. Tg, E, n and k were found to be 52°C, 33.29 ± 0.71 kJmol-1, 0.82 ± 0.01 and 1.29 × 102 ± 1.11s-1, respectively. Thermal stabilities were checked by t.g.a. and d.t.g. The formal decomposed in three stages. The corresponding initial decomposition temperatures were found to be 300, 465 and above 500°C. A possible mechanism for the three-step thermal decomposition of PVF is proposed. © 1997 Elsevier Science Ltd.