Hyperbranched polyester as a crosslinker in polyurethane formation: real-time monitoring using in situ FTIR

Abstract

Hyperbranched polymers find applications in many fields such as biomedical, catalysis, commercial coatings, etc., owing to their many advantages such as ease of synthesis, more number of end functional groups, and low solution/melt viscosity. In our study, a previously unreported synthesis of A2 + AB2 type hyperbranched polyester (HBP) of three different generations (HBP-G1 to HBP-G3) using phenyl dichlorophosphate as a core and 2,2-dimethylol propionic acid as a monomer was carried out, and characterized using spectral, physical and thermal analyses. In situ FTIR was used to study the one-shot curing reaction between hexamethylene diisocyanate, polyethylene glycol and HBP-G3 at 60 °C for two different NCO/OH ratios (1.2316 and 2.1042). Lower NCO/OH ratio (1.2316) was found to obey the second order, thereby indicating the occurrence of primary reaction between –OH and –NCO groups, whereas higher NCO/OH ratio (2.1042) follows third order due to auto-catalytic effect of urethane resulting from its reaction with excess isocyanate group. Non-isothermal curing kinetics of PU formation using in situ FTIR was accomplished to determine the percentage of urethane content formed using Factor Analysis program for the first time. Based on the above data, further curing kinetics studies were carried out at three different isothermal (70, 90, and 110 °C) temperatures for lower NCO/OH ratio sample to extract its thermodynamic parameters.