is formed as follows r 1 nco r 2 oh u2192 r 1 nhcoor 2 the organic polyisocyanates which may be employed for the u201c a side u201d component include aromatic aliphatic and cycloaliphatic polyisocyanates and combinations thereof representative of these types are the diisocyanates such as m phenylene diisocyanate 2 4 toluene diisocyanate 2 6 toluene diisocyanate mixtures of 2 4 and 2 6 toluene diisocyanate hexamethylene diisocyanate tetramethylene diisocyanate cyclohexane 1 4 diisocyanate hexahydrotoluene diisocyanate and isomers naphthalene 1 5 diisocyanate 1 methoxyphenyl 2 4 diisocyanate 2 2 u2032 2 4 u2032 and 4 4 u2032 diphenylmethane diisocyanate 4 4 u2032 biphenylene diisocyanate 3 3 u2032 dimethoxy 4 4 u2032 biphenyl diisocyanate and 3 3 u2032 dimethydiphenylmethane 4 4 u2032 diisocyanate thetriisocyanates such as 4 4 u2032 4 u2033 triphenylmethane triisocyanate and toluene 2 4 6 triisocyanate and the tetraisocyanates such as 4 4 u2032 dimethyldiphenylmethane 2 2 u2032 5 5 u2032 tetraisocyanate and polymericpolyisocyanates such as polymethylene polyphenylene polyisocyanate especially useful die to their availability and properties are 4 4 u2032 diphenylmethane diisocyanate and polymethylene polyphenylene polyisocyanate also used are the easily accessible optionally uretonimine carbodiimide and urethane group containing aromatic di and polyisocyanates such as 2 2 u2032 2 4 u2032 4 4 u2032 diphenylmethane diisocyanate mdi as well as any desired mixtures of these isomers and mixtures of 2 2 u2032 2 4 4 4 u2032 diphenylmethane diisocyanate and polyphenyl polymethylene polyisocyanates crude mdi the b side resin component contains a hydroxy functional.