Given that it breaks down somewhere, why doesn't it liquefy? This does not require any advanced chemistry; think about the polymer structure and structure of a solid polymer.

Polyacrylonitrile is commonly used as fiber reinforcements in composites, including in concrete and in polymer matrices (more on composites really soon). It is susceptible to hydrolysis, but it doesn't really break down into a liquid like a hydrolysis-susceptible polyester