Synthesis of well-defined PCL-b-PnBA-b-PMMA ABC-type triblock copolymers: toward the construction of nanostructures in epoxy thermosets

In this study we prepared a novel triblock copolymer (tBCP) through ring-opening polymerization (ROP) with ε-caprolactone (ε-CL) and two specific atom transfer radical polymerizations (ATRPs), with n-butyl acrylate (nBA) and methyl methacrylate (MMA), respectively (herein, a supplemental activator and reducing agent and halogen-exchange ATRPs were employed). These chain-extending polymerizations were chosen to achieve controlled/living polymerization. This strategy afforded a well-defined ABC-type PCL-b-PnBA-b-PMMA tBCP (Mn, GPC = 56 600; PDI = 1.18) comprising two external miscible blocks with an epoxy monomer and a middle soft block. After curing with the diglycidyl ether of bisphenol-A and 4,4′-methylenedianiline, the miscibility of the resulting epoxy thermoset (ET)/tBCP composites was examined using Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. On further examining the ET/tBCP microstructures using transmission electron microscopy and small-angle X-ray scattering, we observed transitions with a long range order—from lamellar to core/shell cylinder to short core/shell cylinder morphologies—upon increasing the amount of ET. The domain sizes obtained after the curing reaction were in the range of approximately 30–60 nm.