Synthesis methods of fluorinated polyurethanes. 1. Effects on the thermal and dynamic-mechanical behaviours

Fluorinated polyurethanes (FPUs) were synthesised from 4,4′-methylenebis(phenylisocyanate) (MDI), 1,4-butandiol (BDO), as a chain-extender, and soft perfluoropolyetheric block (ZDOLTX), by a two-step polymerisation technique, following specific procedures to obtain chains with a regular-segmented structure or polymers characterised by having high hard (MDI–BDO) segment polydispersity. Calorimetric and dynamic mechanical data, reported in this first part of our work, show that, independently of the synthesis method, the polymers are always characterised by a heterogeneous structure. This is true not only at molecular level but also at a macroscopic scale, in which the continuous soft phase contains different populations of crystalline hard domains. However, the crystallinity degree decreases on increasing the weight fraction of the soft phase. The so-called ‘regular synthesis’ seems to favour the MDI–BDO–MDI sequence, which is the largest constitutive part of the hard phase, but the macrostructure is less regular than that present in the other FPUs