Hydrogen-Bonded Multilayers of Thermoresponsive Polymers

Abstract

Neutral temperature responsive polymers, such as poly(N-vinylcaprolactam) (PVCL) and poly(vinyl methyl ether) (PVME), were included in ultrathin films using layer-by-layer alternating adsorption of these polymers with poly(methacrylic acid) (PMAA) at low pH. The amounts of polymers adsorbed and ionization of carboxylic groups within a film were quantified using in situ FTIR-ATR (Fourier transform infrared spectroscopy by attenuated total reflection). The strength of interlayer adhesion provided through hydrogen-bonding interactions was inferred from the critical pH value (pHCR) and critical ionization (αCR) for multilayer decomposition which were pHCR 6.2, αCR 2% and pHCR 6.95, αCR 30% for PMAA/PVME and PMAA/PVCL films, respectively. When deposited onto porous support membranes, PMAA/PVME and PMAA/PVCL multilayers exhibited temperature-responsive changes in dye permeability. The transition occurred in a wide temperature range from 25 to 35 °C, reflecting lower cooperativity of the phase separation of PVME and PVCL chains included within the film. Finally, PMAA/PVME and PMAA/PVCL self-assembly was performed onto particulate substrates, producing capsules which hold promise as temperature-responsive containers for controlled delivery applications.