New Thermal Transitions in Stimuli-Responsive Copolymer Films

Authors

Fang Liu, University of Southern Mississippi
Marek W. Urban, University of Southern MississippiFollow

Document Type

Article

Publication Date

2-24-2009

School

Polymer Science and Engineering

Abstract

These studies report for the first time new thermal relaxations in stimuli-responsive solid-phase copolymers detected by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). When 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and n-butyl acrylate (nBA) monomers were copolymerized into colloidal dispersions and allowed to coalesce to form solid continuous films, in addition to the glass-transition temperature (T_g), which follows the Fox equation for random copolymers, a new composition-sensitive endothermic stimuli-responsive transition (T_SR) was observed. The T_SR transition changes with the composition of the stimuli-responsive component of the copolymer, the temperature, and the rate of temperature change. On the basis of the experimental data, the following relationship was established: 1/T_SR = w₁/T_binary + w₂/T or 1/T_SR = w₁(1/T_binary − 1/T) + 1/T, where T_SR is the temperature of the stimuli-responsive transition, T_binary is the temperature of the stimuli-responsive homopolymer in a binary polymer−water equilibrium, w₁ and w₂ (w₂ = 1 − w₁) are weight fractions of each component of the copolymer, and T is the film-formation temperature. This relationship allows us to predict T_SR transitions in stimuli-responsive solid copolymers. The enthalpic (ΔH) components of the T_g and T_SR transitions determined from DSC measurements are 122 kcal/mol for T_g and 199 kcal/mol for T_SR, which are part of the total energy, ΔE_tot, of the system. The calculated values of the ΔE_tot obtained using computer modeling simulations (168 kcal/mol for T_g and 223 kcal/mol for T_SR, respectively) are in good agreement with the experimental data, and the energy difference is attributed to the inclusion of the entropic components in ΔE_tot calculations.

Publication Title

Macromolecules

Volume

42

Issue

6

First Page

2161

Last Page

2167

Recommended Citation

Liu, F., Urban, M. W. (2009). New Thermal Transitions in Stimuli-Responsive Copolymer Films. Macromolecules, 42(6), 2161-2167.
Available at: https://aquila.usm.edu/fac_pubs/12713