Pyrene-functionalized polystyrene: Thermodynamic and dynamic properties of the glass transition in the bulk and under confinement

Polystyrene (PS) samples functionalized with 1-pyrenebutyl methacrylate randomly distributed in between styrene units, were developed through means of free-radical copolymerization at three pyrene weight concentrations (0.8%, 1.8%, and 11.5%) and compared to neat PS. The pyrene end of the 1-pyrenebutyl methacrylate monomers can be employed as a fluorescent dye to monitor the segmental dynamics of the main polymer chain. For that purpose, thin films were developed by means of spin-coating on Si substrates in thicknesses ranging from 15 to 300 nm and examined via fluorimetry and ellipsometry to obtain information about their thermodynamic glass transition temperature under confinement. To compare with bulk properties, the calorimetric glass transition temperature was identified by means of Differential Scanning Calorimetry. Finally, the glass transition properties in a dynamic environment (segmental relaxation) were analyzed by Broadband Dielectric Spectroscopy, employing a Phecos temperature system with an integrated dielectric cell and an Alpha-A frequency analyzer, all provided by Novocontrol Technologies, Germany. The experiments were done in the temperature and frequency ranges of 30 – 190 ^oC and 10^-1 – 10⁶ Hz, respectively.