New Thermal Transitions in Temperature and pH Responsive Polymeric Films

摘要

While it is well established that polymers exhibit α, β, crystallization, and melting thermal relaxations, the presence of stimuli- responsive components, in particular those units which exhibit lower critical solution temperature (TLCST) in solutions, result in more complex thermal responses. Recently, we have reported1 that poly((N-(DL)-(1- hydroxymethyl) propylmethyacrylamide/n butyl acrylate) (p(DL- HMPMA/nBA)) solid films exhibit a 18.5 % shrinkage at the 27-37 °C range which resulted from the collapse of hydrophobic segments and buckling of the polymer backbone. These studies have also shown that in order to develop stimuli-responsive solid state films, the presence of the low T_g (α transition) components, such as nBA (T_g of p(nBA) ~ ～ 46 °C),, may be required to facilitate sufficient free volume necessary for remodeling of network components. Along the same theme, poly(2-(N, N-dimethylamino) ethyl methacrylate/n-butyl acrylate) (p(DMAEMA/nBA)) and poly(N-acryloyl-N'-propylpiperazine /2- Ethoxyethyl Methacrylate) (p(AcrNPP/EEMA)) copolymer films were prepared and exhibit dual pH and temperature-responsiveness.3 These studies showed that solid p(DMAEMA/nBA) and p(AcrNPP/EEMA) films also exhibit a 29.6 %3 and 16.1 % volume decrease, respectively, above the endothermic transition that is above the T_g of the copolymers. During the course of these studies we noted that thermal transitions in continuous films containing stimuli-responsive components such as DL-HMPMA, DMAEMA, or AcrNPP are significantly different from those detected in non-stimuli-responsive copolymer films.