ABSTRACT
Polyurethane networks exhibiting hydrophilic elastic chains have been synthesized by stoichiometric end-linking reactions. The precursor polymers were efther poly(ethylene oxide) [PEO] or polydioxolane [PDXL], of known molecular welght, fitted at both chain ends with OH functions. Varlous plurifsocyanates [Desmodur] served as the antagonist reagents in these step growth crosslinking reactions.
An investigation of the crosslinking process was performed by following the rheological behavior of the reaction medium as end-linking proceeds. The storage G’ and loss G” moduli were measured at various stages of the reaction, over a wide range of oscillatory shear frequencies. Simultaneously, the Infrared The se kinetic and rheological data were accounted for on the basis of the Miller-Macosko simulation based on conditional probabilities. With stoichiometric systems the agreement is very good between the values of the gel point found and those calculated. It is confirmed that at the gel point, the storage and loss moduli are congruent, regardless of frequency, and that the variation of G’ and G” with ω is that observed by Winter and Chambon. This investigation was mixtures, especially those involving an excess of precursor.
