Glass Transition Breadth and Self-Healing Character of Methacrylate/2-Ethylhexyl Acrylate (EHA) Random Copolymers: Different Trends with EHA Content for Methyl Methacrylate, Ethyl Methacrylate, and n-Butyl Methacrylate

Styrene (S)/2-ethylhexyl acrylate (EHA) random copolymers (p(S/EHA)) were previously reported to exhibit remarkable glass transition breadth (Tg breadth or ΔTg) and facile self-healing over a broad composition range. Here, we investigate whether similar effects can be achieved with other commercially relevant monomers in place of styrene. Three methacrylates were employed: methyl methacrylate (MMA), ethyl methacrylate (EMA), and n-butyl methacrylate (BMA). The methacrylate homopolymers exhibited ΔTg values several times that of polystyrene and exceeded the maximum ΔTg of p(S/EHA). The p(MMA/EHA) copolymers showed increasing ΔTg with increasing EHA content. In contrast, p(EMA/EHA) copolymers showed an invariance in ΔTg compared to PEMA, and p(BMA/EHA) copolymers showed decreasing ΔTg with increasing EHA. Copolymers of n-hexyl acrylate (nHA) with each methacrylate were also prepared. The incorporation of nHA into MMA and EMA copolymers led to little or no ΔTg enhancement, whereas p(BMA/nHA) copolymers exhibited decreasing ΔTg with increasing nHA. Both p(MMA/EHA) and p(BMA/EHA) copolymers exhibited generally larger ΔTg than the corresponding p(MMA/nHA) and p(BMA/nHA) systems. All tested methacrylate-based copolymers except for one, p(BMA/EHA) with 31 mol% EHA content, demonstrated “grudgingly” slow or incomplete, room-temperature self-healing over 100 h. These findings highlight the comonomer-dependent nature of ΔTg and self-healing when EHA is incorporated with methacrylates.