Poly(ester-urethanes) derived from poly(ε-caprolactone) macrodiols: Effect of the molar ratios using design of experiments, synthesis, and characterization

In this study, a randomized complete block design was established to compare three different molar ratios and assess their influence on various properties of a series of poly(ester-urethane)s (PEUs). Different molar ratios of 1,6-hexamethylene diisocyanate (HDI) to α,ω-hydroxy telechelic poly(ε-caprolactone) (HOPCLOH) (also called macrodiol) were investigated: 1.14:1, 1.05:1 and 1:1. The results showed that the 1.14:1 molar ratio produced PEUs with a high number-average molar mass (<i>M</i>_n), the lowest residual hydroxyl content, and the highest urethane formation. Additionally, a significant decrease was observed in the enthalpy of fusion (Δ<i>H</i>_m) of the soft segment for the 1.14:1 and 1.05:1 molar ratios, suggesting the presence of physical crosslinking between ester and urethane groups. Several significant correlations between the mechanical properties and <i>M</i>_n were identified. The chemical nature of the PEUs was confirmed by different analytical techniques.