S. Haseebuddin et al., CROSS-LINK DENSITY OF OLIGOURETHANE DIOLS CURED WITH AMINO RESIN AT DIFFERENT TEMPERATURES, Polymer international, 44(4), 1997, pp. 453-460
Oligourethane diols were crosslinked with melamine formaldehyde (N, N,
N',N',N'',N''-hexakis (butoxymethyl)-2,4,6-triamino-1,3,5-triazine). T
heir films were wetted with dichloromethane and the increase in dimens
ions of the swollen film under equilibrium swelling conditions was use
d to calculate crosslink density by using the Flory-Rehner equation. T
he molar mass between two crosslinks (M) over bar c was also determine
d. The crosslink density of the coating is found to be influenced by a
trans-etherification reaction as well as by self-condensation of the
crosslinker. In formulations containing primary hydroxylated diol a ma
jor part of the crosslinker is consumed in a trans-etherification reac
tion, whereas a part of the crosslinker undergoes self-condensation in
formulations containing secondary hydroxylated diols. The aromatic na
ture of 4-methyl-m-phenylene diisocyanate (TDI) imparts rigidity while
the aliphatic nature of to-1-(isocyanatomethyl)-1,3,3-trimethylcycloh
exane (IPDI) results in flexibility of the backbone. The formulations
containing 30% crosslinker and cured at 140 degrees C for 20 min are f
ound to undergo completion of the major part of the reaction, indicati
ng ideal conditions for their crosslinking from a commercial point of
view.