Small Molecule-Mediated Glass Transition of Acrylic Copolymers: Effect of Hydrogen Bonding Strength on Glass Transition Temperature

Poly(styrene-co-ethyl acrylate) [P(St-co-EA)] with different ratios of St/EA was mixed with the small molecule 4,4-thio-bis(6-tert-butyl-m-methyl phenol) (AO300) to investigate the influence of hydrogen bonding strength on the glass transition behavior. The glass transition temperature (T-g) linearly increased after adding AO300, and the slope value decreased with increased St/EA ratio. All lines could be extended to 62 degrees C, demonstrating that T-g of the small molecule in situ detected by the polymer chain was much higher than that by small molecule itself (29 degrees C). Fourier transform infrared spectroscopy analysis showed that the small molecules began to be self-associated at a concentration where the hydrogen bonded carbonyl ratio of the bulk polymer was approximately 0.5 and irrespective of the St/EA ratio. Above the critical loading, the mixture's T-g negatively deviated from the linearly extended lines because of self-association of the small molecules. The apparent T-g of AO300 was found to strongly depend on intermolecular hydrogen bonding number and strength. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 400-408