Thermo-Switchable Pressure-Sensitive Adhesives Based on Poly(N‑vinyl caprolactam) Non-Covalently Cross-Linked by Poly(ethylene glycol)

The properties of new hydrophilic pressure-sensitive adhesives (PSA) obtained by blending poly­(N-vinyl caprolactam) (PVCL) with short-molecular weight poly­(ethylene glycol) (PEG) were studied in aqueous media by a combination of several calorimetric and adhesion testing techniques. We found that the adhesive properties of the blends are the result of an extensive hydrogen bonding network formed between PVCL and PEG similar to the poly­(N-vinylpyrrolidone) (PVP)/PEG blends, except the extent of cross-linking is nearly 3 times higher in PVCL–PEG networks. Accordingly, we observed substantially higher peel adhesion in PVCL–PEG blends, which depends strongly on the amount of adsorbed water and the temperature. The adhesive properties of PVCL–PEG gels are considerably diminished when the amount of absorbed water exceeds 30% or at elevated temperature but can be easily recovered by drying or cooling the sample. The observed responsiveness of PVCL–PEG hydrogels in physiologically relevant temperature range makes them interesting candidates for industrial and biomedical applications as smart PSAs.