Synthesis and characterization of segmented polyurethanes containing blocks of controlled molecular weight: 1. Materials preparation and characterization

C. L. Almeida Leni C. Akcelrud

A new method for segmented polyurethanes synthesis (SPU) was developed, in which segments of well-defined characteristics were prepared separately and coupled together in a further step. The soft segment was prepared from the reaction of commercially available anionic polyol-polyether, with an average molecular weight of 3800, and 1,6-hexamethylene diisocyanate. The molecular weight of these polymers varied acording to the NCO/OH ratio used in the synthesis, always greater than unity, providing -NCO end capped segments. The unreacted HDI was removed under vacuum (10-6-10-8mbar). The molecular weights of the soft segments, SS products, was determined by GPC analytical techniques. The hard segment was prepared from the reaction of the 1,6 hexamethylene diisocyanate and 1,4-butanediol, using a NCO/OH ratio equal to unity. These polymers were functionalized by the addition of an excess BDO after the reaction was completed, providing -OH terminated segments. The unreacted BDO was removed using a solvent. The molecular weights of the hard segments (HS products) was determined by MALDI (matrix assisted laser desorption), analytical techniques. The coupling of the soft with the hard segment (SPU products) was made in solution (DMF). The characterization of the SPU products was made by infrared, DSC, TGA, and mechanical analytical techniques. The SPU product characteristics were compared to those of a conventional polyurethane (PU), prepared by a prepolymer procedure.

Segmented polyurethane; synthesis; characterization

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