Uncatalyzed urethane forming reaction of 1,3-xylylene diisocyanate with aliphatic alcohols of varying chain lengths and polyols

Abstract

In this article, we report a detailed study on the kinetics of the reaction of 1,3-xylylene diisocyanate (1,3-XDI) with alcohols of varying alkyl chain lengths and with low molecular weight polyols such as monomethoxylated polyethylene glycol (mPEG) and polytetrahydrofuran (PTHF) in toluene, in the absence of a catalyst. It was found that the pseudo-firstorder rate coefficient increased with the increasing alkyl chain length (k1,app was found to be 0.0166 and 0.0341 min–1 for 1-propanol and 1-hexanol, respectively) and the reactivities of the 1,3-xylyene diisocyanate towards the alcohols and polyols are between those of the aromatic and alkyl isocyanates. The activation energies were also determined and were found to vary from 25.6 to 38.6 kJ/mol (from 1-propanol to 1-hexanol). According to further kinetic studies, the rate coefficients k1,app and k2,app for the reaction of 1,3-XDI with PTHF were determined to be (1.13±0.01)・10–2 and (1.28±0.01)・10–2 min–1, respectively. It was also found that the rate constants did not depend significantly on the length of the polymer chain. However, significantly lower rate coefficients were obtained for the 1,3-XDI-mPEG reaction (k1,app = (2.64±0.03)・10–3 min–1 and k2,app = (2.45±0.03)・10–3 min–1). Besides, the dependence of the pseudo-first-order rate coefficient on the concentration of the alcohols was also studied, and based on these findings a reaction mechanism is proposed.

Keywords

• polymer synthesis, molecular engineering
• xylylene diisocyanate
• kinetics
• aliphatic alcohols
• polyether polyols