In situ crosslinking of surface-initiated ring opening metathesis polymerization of polynorbornene for improved stability
By Fursule, Ishan A.; Abtahi, Ashkan; Jr, Charles B. Watkins; Graham, Kenneth R.; Berron, Brad J.
Published in Journal of Colloid and Interface Science
2018
Abstract
AbstractHypothesis In situ crosslinking is expected to increase the solvent stability of coatings formed by surface-initiated ring opening metathesis polymerization (SI ROMP). Solvent-associated degradation limits the utility of {SI} {ROMP} coatings. {SI} {ROMP} coatings have a unique capacity for post-functionalization through reaction of the unsaturated site on the polymer backbone. Any post-reaction scheme which requires a liquid solvent has the potential to degrade the coating and lower the thickness of the resulting film. Experiments We designed a macromolecular crosslinking group based on {PEG} dinorbornene. The {PEG} length is tailored to the expected mean chain to chain distance during surface-initiated polymerization. This crosslinking macromer is randomly copolymerized with norbornene through {SI} {ROMP} on a gold coated substrate. The solvent stability of polynorbornene coatings with and without {PEG} dinorbornene is quantitatively determined, and the mechanism of degradation is further supported through {XPS} and {AFM} analyses. Findings The addition of the 0.25 mol% {PEG} dinorbornene significantly increases the solvent stability of the {SI} {ROMP} coatings. The crosslinker presence in the more stable films is supported with observable {PEG} absorbances by {FTIR} and an increase in contact angle hysteresis when compared to non-crosslinked coatings. The oxidation of the {SI} {ROMP} coatings is supported by the observation of carbonyl oxygen in the polynorbornene coatings. The rapid loss of the non-crosslinked {SI} {ROMP} coating corresponds to nanoscale pitting across the surface and micron-scale regions of widespread film loss. The crosslinked coatings have uniform nanoscale pitting, but the crosslinked films show no evidence of micron-scale film damage. In all, the incorporation of minimal crosslinking content is a simple strategy for improving the solvent stability of {SI} {ROMP} coatings.