‘Spider-like’ POSS in NIPU webs: enhanced thermal stability and unique swelling behavior

Abstract

PEO-based non-isocyanate polyhydroxyurethane (NIPU, PHU) networks physically modified with octa(3-hydroxy-3-methylbutyldimethylsiloxy)POSS (8OHPOSS) were synthesized via one-pot one-step approach. POSS was introduced into the polymer matrix in the amount of 1–10 wt%. Polar hydroxyls on the vertex groups of POSS allowed for uniform dispersion even up to high loadings (10 wt%). Composites exhibit enhanced thermal stability in comparison to the pristine matrix. FTIR analysis confirmed that POSS strengthens the hydrogen bonding in the material. Upon POSS introduction, plasticization was observed with a peculiar trend change at POSS loadings over 5 wt%. Glass transition temperature of highly crystalline 8OHPOSS was measured and reported to be at around 3 °C. NIPUs at hand exhibit high water absorption (around 200 wt%) typical for hydrogels. Swelling studies show that 8OHPOSS enhances PHUs hydrogels absorption capacity in phosphate-buffered saline (PBS). Higher absorption capacity in PBS solution in comparison to distilled water is an uncommon phenomenon in hydrogels.

Examining the Water–Polymer Interactions in Non-Isocyanate Polyurethane/Polyhedral Oligomeric Silsesquioxane Hybrid Hydrogels

“…NIPU networks at hand upon immersion in an aqueous medium exhibit water absorption in the range typical for hydrogels, and we have observed this kind of behavior in our previous work [56]. To study polymer-water interactions in such a system in detail, the changes in physicochemical properties of the NIPUs were monitored as a function of the environmental relative humidity (water vapor absorption).…”

“…Taking also into account that there is no significant change in the energetic parameters and it may be concluded that 8OHPOSS does not hinder access of water to hydration sites and it does not “block” any of them. Although in [ 56 ] we observed some attachment of POSS on the polymer chain by hydrogen bonds, this does not hinder the attachment of the more mobile and more polar water molecules to access the hydration sites. The obtained values of monolayer capacity are around 14 g per 100 g of dry material, which is more than 25 times higher than in cellulose-based hydrogels studied by Filip et al [ 72 ], 3.5 times higher than for acrylate hydrogels reported by Ferrer et al [ 73 ], and 1.5 times the value reported for polyacrylamide-based superporous hydrogel composites reported by Mittal et al [ 74 ].…”

“…The materials studied in this work, i.e., a series of NIPUs networks physically modified with octa(3-hydroxy-3-methylbutyldimethylsiloxy)POSS (8OHPOSS), are the same as those described in Ref. [ 56 ]. Their synthesis, structure, and micromorphology are described in detail in this previous publication.…”

“…In a previous article, we studied hydrophilic NIPU networks physically modified with octa(3-hydroxy-3-methylbutyldimethylsiloxy)POSS (8OHPOSS) with respect to their morphology, hydrogen bonding, and glass transition in a dry state [ 56 ]. We found in this previous work that POSS disperse excellently in the NIPU network, possibly thanks to the affinity of the hydroxyl groups on POSS vertices with the polymeric chain.…”

“…POSS is a promising additive in biomaterials [ 57 ] and, therefore, its influence on water–polymer interactions is paramount from the point of view of applications. In the work at hand, we extend the research on the very same materials [ 56 ] to their hydration properties in humid environments. Polymer–water interactions are studied by conditioning materials in a range of progressively increasing relative humidity environments.…”