Glass (T-g) and Stimuli-Responsive (T-SR) Transitions in Random Copolymers

Fang Liu, University of Southern Mississippi
William L. Jarrett, University of Southern Mississippi
Marek W. Urban, University of Southern Mississippi

Abstract

In an effort to elucidate the origin of stimuli-responsive (T-SR) transitions and correlate them to the glass transition temperature (T-g), poly(N-acryloyl-N'-propylpiperazine-co-2-ethoxyethyl methacrylate) (p(Acr-NPP/EEMA)), poly(N-vinylcaprolactam-co-n-butyl acrylatc) (p(VCl/nBA)), poly(N-isopropyl methacrylamide-co-n-butyl acrylate) (p(NIPMAm/nBA)), and poly(2-(N,N'-dimethylamino)ethyl methacrylate-co-n-butyl acrylate) (p(DMAEMA/nBA)) colloidal dispersions were synthesized, which upon coalescence form solid films. These studies showed that molecular rearrangements responsible for the T-SR transitions are attributed to the backbone buckling and collapse of stimuli-responsive components. Based on empirical data, the relationship between T-g and T-SR was established: log(V-1/V-2) = (P-1(T-SR - T-g))/(P-2 + (T-SR - T-g)), where the V-1 and V-2 are the copolymer total volumes below and above the T-SR, respectively, Tg is the glass transition temperature of the copolymer, and P-1 and P-2 are the fraction of the free volume (f(free)) at T-g (P-1) and (T-g.midpoint - T-SR)(50/50)) for each random copolymer (P-2), respectively. This relationship can be utilized to predict the total volume changes as a function of T-SR - T-g for different copolymer compositions. To our best knowledge, this is the first study that provides the relationship between the T-SR, T-g, free volume, chain mobility, and dimensional changes in stimuli-responsive random copolymer networks.