Synthesis of well-defined PMMA-b-PDMS-b-PMMA triblock copolymer and study of its self-assembly behaviors in epoxy resin

Abstract

PMMA- b -PDMS- b -PMMA block copolymers can mediate different reaction-induced microphase separation mechanism with different curing agents and formed ordered nanospheres. • A mild condition to conduct chain extension of Br-PDMS-Br with MMA via effective SARA ATRP was demonstrated and obtained a well-defined PMMA- b -PDMS- b -PMMA tBCP. • Then the tBCP shows its good compatibility with respect to epoxy resin, owing to the presence of compatible PMMA segments. • Through in-situ SAXS measurements, we found the tBCP underwent reaction-induced microphase separation (RIMPS) mechanism cured by 4,4′-methylenedianiline (MD) but self-assembly (SA) mechanism cured by phenol novolacs (PN). • We inspected the interesting mechanism variations, compatibility, and microphase morphology by using FT-IR, DSC, TGA, TEM, and SAXS of the obtaining MD- and PN-cured composites, mainly including nanospheres morphology in approximately 30 nm. With the evolutions of reversible deactivation radical polymerizations (RDRPs), including atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP), one technique can be noted that supplemental activator and reducing agent (SARA) ATRP can conduct controlled/living radical polymerization fashion with a ppm level of catalyst. In addition, polydimethylsiloxane (PDMS) has wide ranges of applications in surfactants, sealants, and impact-relief materials. In this study, we first prepared a well-defined PDMS ended with α,ω-isobutyryl bromide (i.e., Br-PDMS-Br) macroinitiator (MI). Then chain extension of Br-PDMS-Br with methyl methacrylate (MMA) via SARA ATRP was conducted. Mild chain extension conditions were demonstrated and we successfully achieved controlled/living radical polymerization. A well-defined PMMA- b -PDMS- b -PMMA tBCP (named as ABA: M n, GPC = 49770; PDI = 1.44) comprising two external epoxy-philic blocks and a middle soft block was thus acquired. The ABA was further blended with diglycidyl ether of bisphenol-A (DGEBA) epoxy monomer and two crosslinkers of 4,4′-methylenedianiline (MD)/phenol novolacs (PN) to construct nanostructures driven by curing reactions. The cured epoxy thermoset (ET)/ABA composites showed good thermal properties and well-compatible behaviors (i.e, T g = ca. 100 °C and T (5 wt% loss) = ca. 270–335 °C) characterized by the measurements of differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). We further analyzed the two composite systems by utilizing Fourier transform infrared spectroscopy (FT-IR), (in-situ) small-angle X-ray scattering (SAXS), and transmission electron microscope (TEM). With different curing agent, interestingly, we observed a reaction-induced microphase separation (RIMPS) mechanism in MD-cured system but a self-assembly (SA) mechanism in PN-cured system. Furthermore, the PN-cured composites can create ordered nanospheres in a range of 27–41 nm.