Suitable monoisocyanates which can be emnaphthylene'l4'diisocyanate ploycd in accordance with the present invention include naphthylenelsiqnsocyanate alkyl isocyanates wherein the alkyl group ranges from 1 i 'p to about, 18 carbon atoms, aryl isocyanates, e.g. phenyl f i 'duSocXanato dlphenyl methane and naphthyl isocyanates and optionally substituted by & 'f dnsocyanate