Correlation of linear viscoelastic behavior and molecular weight evolution in the bulk urethane polymerization

Bulk polymerization of urethane made from diphenylmethane 4, 4′ diisocyanate (MDI) and polyether macro diol was performed from size exclusion chromatography and viscoelastic studies. Coupling the viscoelastic characterization and the kinetic law showed that the viscoelastic behavior of the urethane system is only dependent of the degree of polymerization. The rheological study proved that low physical interactions can be found between the polyurethane chains. Furthermore, the critical molecular weight corresponding to a rheological maximum effect of these interactions was observed close to the value Mc = 2Me, characterizing the onset of the topological entanglement coupling. A qualitative explanation of this singular behavior was attempted from a hydrogen bonding point of view. On the other hand, the linear viscoelastic properties of polyurethane samples of different molecular weights were studied. The main viscoelastic parameters, ηo, and were determined. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2395–2406, 1997