Coatings based on polyurethane chemistry. Concept of hard clusters in the interpretation of properties of polyurethane and polyurethane acrylate networks

Abstract

Polyurethane (PU) and polyurethane acrylate (PUA) networks based on hydroxyl‐terminated poycaprolactone (PCL), m‐tetramethylene diisocyanate (m‐TMXDI), trimethylolpropane (TMP) for PU or hydroxyethyl methacrylate (HEMA) for PUA, have been synthesized with various molar masses of PCL, various molar ratios and consequently with various crosslink densities. PUA can be considered as one‐component systems. Even when thermodynamics driven segregation does not occur, the distribution of crosslinks in networks is topologically non uniform. The concept of hard cluster crosslinks, which are represented by structures of chemically 〈〈hard〉〉 units: diisocyanate linked to TMP in the case of PU networks, and microgel‐like polymerized polyacrylate chains in the case of PUA networks, is very useful to explain Tg and equilibrium modulus variations.