Abstract
Novel regular‐network polyurethane films were prepared from polyols of phloroglucinol (1), 2,4,2′,4′‐tetrahydroxybenzophenone (2) or glycerol (3), and diisocyanates of hexamethylene diisocyanate (6), 4,4′‐diphenylmethane diisocyanate (4,4′‐methylenebis(1,4‐phenylene) diisocyante (5)) or p‐phenylene diisocyanate (4). Prepolymers prepared by solution polyaddition were cast and successively post‐polymerized at various temperatures between 60 and 160°C for 1 h to form networks. The resultant films were transparent, flexible and insoluble. Heat distortion temperatures (T~h~) of the polyurethane films increased with increasing post‐polymerization temperature. The highest T~h~ values obtained are 52, 58, 61, 69, 99, 122, 122 and 151°C for 1/5, 3/5, 2/5, 3/6, 2/4, 1/6, 1/4 and 2/6, respectively. The densities of polyurethane films also increased with increasing post‐polymerization temperature, which is comparable with an increase of T~h~. The X‐ray diffraction patterns of films showed two diffraction peaks, suggesting some ordered structure due to the regular networks. The network polyurethane film showed higher T~h~ and tensile strength compared with the corresponding network polyester film, suggesting an effect of intermolecular hydrogen bonding. All films started to decompose at a temperature around 120°C due to the decomposition of unreacted terminal isocyanate groups. The thermal stability of a network polyurethane film could be remarkably enhanced by capping the unreacted terminal isocyanate group with phenol.