Study on the synthesis of urethane oligomers as intermediate products for the production of linear polyurethanes

On the basis of kinetic scheme for step-growth polyaddition, a method was developed for the synthesis of urethane oligomers and linear polyurethanes with isocyanate and hydroxyl end groups arranged alternately 3,4-TDI, 2,6-TDI and 1,4-butanediol were used as the feedstock materials and the polymerisation process was carried out in a tetrahydrofuran solution at constant concentration. Complex mixtures of diisocyanate and hydroxyl compounds were obtained, which were then utilised as parent materials at further stages of the process. The mixtures of urethane oligomers were produced where the molecular weights were gradually higher and the molecular weight distribution was wider and wider. However, the chemical composition was pre-defined as resulted from the reaction stoichiometry. The products were subjected to structural investigation. The following analytical procedures were especially useful in the analysis of the linear polyurethanes obtained: gel-permeation chromatography and mass spectroscopy, which employed gentle excitation due to electro-spraying. These methods made it possible to identify oligomers, which were formed at the successive stages of step-growth polyaddition. The findings made a basis for the discussion of the technological aspects of the polymerisation method developed. (C) 2000 Elsevier Science Ltd. All rights reserved.