Self-organized cross-linked phenolic thermosets: thermal and dynamic mechanical properties of novolac/block copolymer blends

We have recently demonstrated a concept to prepare self-organized spherical, cylindrical and lamellar nanostructures of phenolic thermosets by blending novolac and poly(2-vinylpyridine)-block-poly(isoprene), i.e. P2VP-block-PI, followed by thermal curing by hexamethyltetramine (HMTA) [Macromolecules 34 (2001) 3046]. In the present work, hydrogen bonding, dynamic mechanical properties and glass transition temperatures are investigated using Fourier transform infrared spectroscopy (FTIR), dynamic mechanical spectroscopy (DMA) and differential scanning calorimetry (DSC). Even after curing, FTIR shifts indicate hydrogen bonding between the hydroxyl groups of novolac and nitrogens of P2VP, thus promoting the self-organization. DMA shows that the storage E′ and loss moduli E″ do not change considerably as PI forms the spherical or cylindrical phases. A slightly larger drop takes place in the lamellar phase. In agreement with the self-organization, a separate glass transition temperature of PI is observed at ca. −62°C. Based on hydrogen bonds that tolerate the thermal curing and the possibility to tailor the self-organized morphologies, it is suggested that the properties of phenolic thermosets might be tailored in a systematic way, upon blending with proper block copolymers.