Strong Screening Effect of Polyhedral Oligomeric Silsesquioxanes (POSS) Nanoparticles on Hydrogen Bonded Polymer Blends

In this study we used anionic living polymerization to prepare two different homopolymers: a poly(methyl methacrylate) (PMMA) and a PMMA derivative presenting polyhedral oligomeric silsesquioxane (PMA-POSS) units as its side chains. We then employed differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide-angle X-ray diffraction (WAXD) to investigate the miscibility and specific interactions of PMMA and PMA-POSS with three hydrogen bonding donor compounds: poly(vinyl phenol) (PVPh), phenolic resin, and bisphenol A (BPA). DSC revealed that all of the PVPh/PMMA, phenolic/PMMA, and BPA/PMMA blends exhibited a single glass transition temperature, characteristic of miscible systems; FTIR spectroscopic analyses revealed that such miscibility resulted from hydrogen bonding interactions between the C=O groups of PMMA and the OH groups of these three hydrogen bonding donor compounds. In contrast, all of the PVPh/PMA-POSS, phenolic/PMA-POSS, and BPA/PMA-POSS blends were immiscible: DSC revealed two glass transition temperatures arising from strong screening effects (FTIR spectroscopy) and high degrees of aggregation (WAXD) of the POSS nanoparticles. We propose that the value of the intramolecular screening effect () should be very close to 1 for all PMA-POSS blend systems when POSS nanoparticles appear as the side chains of PMMA, such that the OH groups of the hydrogen bonding donor compounds cannot interact with the C=O groups of PMA-POSS.