Characteristics of concentrated polyurethane solutions
It has been demonstrated on the example of concentrated solutions in ethyl acetate of segmented PUR — prepared from poly(ethylenebutylene adipate), diethylene glycol and tolylene diisocyanate — that dissolution is hampered by an increase in the rigid-segment content. It has also been found that agents blocking NCO groups (methanol, 3-methylpyrazol) have no effect on the decomposition of crosslinking and branching biuret and allophanate groups present in PUR; thus these are not the groups responsible for the observed decrease with time of the viscosity of concentrated PUR solutions. The presence of free (non-blocked) NCO groups is the cause of a spontaneous increase in the vis co sity of PUR solutions during their storage. The presence of a tin-catalyst used during the PUR synthesis (dibutyltin dilaurate) causes a considerable (up to 50% decrease of the viscosity of solutions under study.
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