Characterization of polyurethane network chains by gel permeation chromatography

Abstract Starting materials, prepolymers, chain‐extended oligomers, and polyurethane network chains were characterized by gel permeation chromatography in order to make clear the change of molecular distribution in the formation of polyurethane networks. The polyurethane networks were prepared from poly(oxypropylene)glycol (PPG 1000, Mn = 997, Mw/Mn = 1.04), 2,4‐tolylene diisocyanate, and 1,4‐butanediol by the prepolymer method. Polyurethane networks were degraded by the amine degradation method, by which allophanate groups as crosslinking sites were decomposed selectively. The prepolymer had four species. The polydispersity index of the prepolymer (Mw/Mn) was about 2, that is, the most probable distribution. The product of the chain‐extending reaction of prepolymer with BD had five species. The molecular‐weight distribution of this product was narrower than that of the prepolymer. The polydispersity of the interstitial chains between crosslinking sites was also narrower than that of the chain‐extended product. The polyaddition mechanism in the formation of PPG–TDI–BD polyurethane networks was discussed.