|
The Shull Group |
||||
60. "Origins of mechanical strength and elasticity in thermally reversible, acrylic triblock copolymer gels" Drzal, P.L.; Shull, K.R., Macromolecules, 36, 2000 (2003).
Thermoreversible gels were formed by dissolving a poly(Me methacrylate)-poly(tert-Bu acrylate)-poly(Me methacrylate) triblock copolymer in a variety of alcs., including ethanol, 1-butanol, 2-ethylhexanol, and 1-octanol. The gels exhibit an ideal and reversible solid/liq. transition in each of these solvents, behaving as strong elastic solids at room temp. and as freely flowing liqs. above the gel transition. The time-dependent elastic properties of the gels are governed by two transition temps. The first transition is the crit. micelle temp. (cmt) near 60 DegC, below which the PMMA blocks aggregate to form a phys. cross-linked network. As the gels are cooled to room temp., differential scanning calorimetry (DSC) reveals a second transition where the PMMA domains undergo a glass transition. The glass transition temp. of the PMMA domains increases when the gels are aged at room temp. Time-temp. superposition can be applied below the cmt to give master curves describing the relaxation behavior of the gels in the vicinity of the glass transition of the PMMA domains. These relaxation times increase by 1 decade for every 8 K decrease in temp., a result that is consistent with previous measurements of polymer relaxations in the vicinity of the glass transition temp.