Fabrication of thermally cross-linked poly(methacrylic acid)-based sponges with nanolayered structures and their degradation

Water-insoluble poly(methacrylic acid) (poly(MAAc)) sponges with nanolayered structures were fabricated via thermal cross-linking with poly(vinyl alcohol) (PVA). The cross-linked water-insoluble sponges contained up to 75 wt% poly(MAAc) when the molecular weight of PVA and the cross-linking time were adjusted appropriately. After immersion in a NaClO·5H2O aqueous solution for 24 h, all poly(MAAc)/PVA_50 wt% sponges with different PVA molecular weights were completely dissolved, and their residual weights were approximately 0%. The molar ratio of NaClO·5H2O was 3.6 times that of the vinyl alcohol units in the sponges. The molecular weight (Mn) and molecular weight distribution (Mw/Mn) of poly(MAAc) observed after immersion in the NaClO·5H2O aqueous solution were similar to those of the original poly(MAAc) (Mn: 46200 g/mol, Mw/Mn: 1.65). In contrast, the gel permeation chromatography (GPC) curves for PVA were shifted to lower molecular weights with increasing NaClO·5H2O concentrations. These results suggested that only the PVA in the poly(MAAc)/PVA sponges was decomposed. Multilayer films of poly(MAAc)/PVA with different physicochemical properties were also fabricated. The first and third layers were made of a poly(MAAc)/PVA_10wt% film, and the second layer was made of a poly(MAAc)/PVA _50wt% sponge.