Mixed-mode interpenetrating polymer networks from polymerizable eutectics†

Abstract

The preparation of interpenetrating polymer networks (IPNs) and semi-interpenetrating polymer networks (semi-IPNs) is reported via a solvent-free approach using a binary polymerizable eutectic. N-Isopropylacrylamide (NIPAM) and ε-caprolactone (CL) were mixed in various mole ratios to prepare viscous polymerizable liquids that were stable at room temperature, based on solid–liquid equilibrium phase diagrams from differential scanning calorimetry (DSC) data. The strong degree of association between NIPAM and CL within these mixtures was confirmed via 1D and 2D NMR spectroscopy. Using an appropriate UV photoinitiator and ring opening polymerization catalyst, the orthogonal polymerization (either in a sequential or simultaneous fashion) of each component within the eutectic was achieved, with enhanced reaction kinetics for the ring opening polymerization compared to a traditional solvent (DMSO). Through the incorporation of diacrylate and bis(carbonate) crosslinkers into the resin mixture, IPNs and semi-IPNs were realised in a one-pot two-step approach from polymerizable eutectics for the first time. These networks possessed thermoresponsive swelling behaviour in water, and retained their structural integrity in good solvents for both phases. This binary eutectic was also shown to be suitable as a resin for stereolithography 3D printing on a benchtop printer through the inclusion of a RAFT agent, achieving semi-IPN printed objects in a two-step approach.