Structure, dynamics and interactions of complex sol-gel hybrid materials through SSNMR and DSC: part I, bynary systems based on PE-PEG block copolymer, PHS and Silica

This paper is the first part of a combined DSC and solid-state NMR study aimed at understanding the dynamic, morphological and interaction properties of three-component organic-inorganic hybrid coatings exhibiting interesting barrier properties against oxygen diffusion, obtained by sol-gel processes starting from triethoxysilane-terminated polyethylene-b-poly(ethylene glycol) copolymer (PE-PEGSi), poly(4-hydroxystyrene) (PHS), and tetraethoxysilane (TEOS). This paper reports the results of the study of the corresponding simpler two-component hybrids, which, beside the interest of these systems by themselves, was necessary for unravelling the characterization of the complex three-component systems. The phase, dynamic and interaction properties of binary systems PE-PEG/SiO2, PHS/SiO2, and PE-PEG/PHS have been here investigated and compared with those of the single components. Evidences of the occurrence of hydrogen-bonds between PHS and both silica and PEG have been obtained. The interaction with silica and PHS seems to strongly inhibit the crystallization of PEG segments but to not prevent PE from segregating into crystalline domains. Moreover a noticeable mobility of the amorphous PEG phase and the presence of mobile isolated or loosely packed PE segments in all-trans conformations have been highlighted in PE-PEG/SiO2 hybrids. The structural and phase behaviour of PHS results to be strongly affected by the presence of either silica or PEG. In PHS/SiO2 hybrids a two-state model with PHS chains either tightly- or loosely-bound to silica domains has been proposed, while in PE-PEG/PHS blends the presence of a PEG-PHS miscible amorphous phase has been observed.