Synthesis of polymer-grafted thermally reduced graphene oxide by RAFT polymerization and their effects on properties of cured unsaturated polyester resins. I. Synthesis of polymer-grafted thermally reduced graphene oxide by RAFT polymerization

Abstract

The polymer-grafted thermally reduced graphene oxide (TRGO) as low-profile additive (LPA) for unsaturated polyester resins (UP) was synthesized by simultaneous coupling reaction and reversible addition-fragmentation chain transfer (RAFT) process. Z functionalized S-Benzyl S'-trimethoxysilylpropyltrithiocarbonate (BTPT) was used as couplable RAFT chain transfer agent to prepare the TRGO-polymer, where the grafted polymer was made from poly(butyl acrylate)-b-poly(methyl acrylate-co-glycidyl methacrylate) (designated as TRGO-g-PBA-b-P(MA-co-GMA)). For the six TRGO-polymer, abbreviated as TRGO-Gx-yK (x = 10 or 20; y = 8, 17, or 30), the initial molar composition of GMA incorporated in exterior grafted polymer was set at 10 or 20 mol%, molecular weights (M_n) of grafted polymer were controlled at nominal values of 8000, 17000, and 30000 g/mol, the molar grafting ratio (G_p) was 15.6 to 216 μmol polymer chain/g TRGO, and the molar grafting ratio of epoxy group in GMA residue (G_p,GMA) was 154 to 1490 μmol epoxy group/g TRGO. G_p and G_p,GMA were lower for TRGO-polymer with a higher nominal M_n for the grafted polymer chain, which was ascribed to the more noticeable shielding effect for a longer grafted polymer chain on TGRO during synthesis. The number of stacked layers (N) from XRD measurements was 143.2, 14.3, and 6.9 for graphite, GO, and TRGO, respectively. For polymer-grafted TRGO, N decreased to 3.8–6.9. Either increasing M_n or increasing GMA composition in the exterior grafted polymer on TRGO led to a smaller N. Higher G_p, lower N, or higher G_p,GMA would enhance miscibility for styrene/UP/TRGO-polymer system during cure due to better dispersion and interfacial adhesion.