Thermodynamic properties and morphology of 2D NBR/PEG-PPG-PEG networks

Abstract

2D binary polymer blends are an interesting tool to obtain nanostructured coatings combining the constituting polymers properties. However, the incompatibility of most polymer blends leads to phase separation and the difficulty to optimally combine their properties. Interpenetrating polymer networks (IPN) have been developed in 3D as a strategy to limit phase separation. In this work, the synthesis of 2D IPN was performed and their morphology was investigated depending on the cross-linking reaction parameters. For this, 2D mixed films based on nitrile-butadiene rubber (NBR) and poly(ethylene glycol)- block -poly(propylene glycol)- block -poly(ethylene glycol) (PEG-PPG-PEG) triblock copolymers were studied by coupling thermodynamic characterizations, microscopy observations and sum frequency generation (SFG) spectroscopy. A complete phase separation has first been evidenced in a large composition range and attributed to the very large difference in the polymers viscosities. Next, NBR and/or PEG-PPG-PEG networks formation within the mixtures was studied through a free radical cross-linking and/or an acid-catalyzed acetalization reaction, respectively. The synthesis of the NBR network or both polymer networks within the blends did not induce significant morphological changes in terms of complete phase separation, however the simultaneous cross-linking allowed to freeze the initial structure. In contrast, the formation of only the PEG-PPG-PEG network led to a significant reorganization of the NBR-richest mixed films, resulting in the miscibility of the copolymers. • Complete phase separation in a large composition range is attributed to the very large difference in the polymers viscosities. • Cross-linking of PEG-PPG-PEG within some mixtures leads to miscibility of the linear copolymers. • Simultaneous polymer cross-linking within mixtures allowed to freeze the initial structure.