Water uptake of poly(2-N-alkyl-2-oxazoline)s: influence of crystallinity and hydrogen-bonding on the mechanical properties

Poly(2-oxazoline)s are suitable materials to study structure–property relationships as their preparation by a living cationic ring-opening polymerization procedure and the relatively facile monomer synthesis allow accurate control over the molecular structure. In this contribution, the number of carbon atoms in the linear side-chain is systematically varied from a short methyl- to a long nonyl-group. As some of the materials are known to be hygroscopic, the effect of water uptake on the mechanical properties is investigated in detail. The combination of water uptake measurements, FT-IR spectroscopy and indentation revealed that only the samples with very short side-chains show significant hygroscopicity, while samples with longer side-chains exhibit crystalline behavior. Furthermore, depending on the polymer structure, it could be differentiated between side-chain and main-chain crystallinity.