Semi-rigid chains with strong attractive interactions can hardly crystallize. Strong intermolecular interactions slow down the relaxation of the randomly oriented backbones towards equilibrium crystalline structures. A way to weaken these interactions is to covalently attach alkyl side chains to the polymer backbones and prevent close contact sterically.
Poly(alkyl oxazoline)s show very rich side chain dependent properties both in bulk and in aqueous solutions. As the alkyl side chain length decreases, bulk crystallization is significantly hindered and was previously not observed for poly(ethyl oxazoline) (PEOX). We have shown that PEOX self-assemble into crystalline fibers in aqueous solutions when kept above the cloud point temperature (Tc) for long times (days to weeks). More interestingly, similar self-assembly was also observed below Tc where water is known to be a good solvent. The mechanism of self-assembly and the generality for other water soluble polymers will be discussed.