H-bonding tuned phase transitions of a strong microphase-separated polydimethylsiloxane-b-poly(2-vinylpyridine) block copolymer

Abstract

The phase behaviors of a polydimethylsiloxane-b-poly(2-vinylpyridine) block copolymer (PDMS-b-P2VP, DV) tuned by the supramolecular self-assembly approach with the 1-pyrenebutyric acid (PBA) as additive were investigated. The PDMS-b-P2VP block copolymer (D10kV12.5k, the molecular weight of the PDMS and P2VP were 10000 and 12500 g mol−1, respectively) with volume fraction of P2VP (fP2VP) 52% exhibited hexagonally perforated layer (HPL) morphology after dried from the solution, and the nanostructure transformed to gyroid structure after thermal annealing above 140 oC, which were indicated by the small-angle X-ray diffraction (SAXS) and transmission electron microscopy (TEM) results. Through solution blending method, a series of H-bonding supramolecular complexes of PDMS-b-P2VP with PBA were fabricated. The Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) experiments demonstrated that the PBA molecules uniformly interacted with P2VP through H-bonding and the glass transition temperature of P2VP(PBA)x decreased with the increase of the mole ratio (x) of PBA/2VP. Due to the increase of the volume fraction of P2VP(PBA)x and that of the stretching extent of the P2VP backbone as the x value increased, the microphase-separated nanostructures transformed from HPL to hexagonally packed cylinder (HEX), then to body centered cubic (BCC) structure and then to disordered spheres morphologies. When the PDMS-b-P2VP(PBA)x complexes were heated above 120 oC, the H-bonding between the P2VP and PBA was broken and the PBA became compatible within both PDMS and P2VP domains and thus the nanostructure of the PDMS-b-P2VP(PBA)x complexes transformed accordingly. Therefore, a variety of the nanostructures and structural transformations were induced by the H-bonding formation and disassociation based on one block copolymer.