A new morpholine-functionalised, trithiocarbonate-based RAFT agent, MPETTC, was synthesised with an overall yield of 80% and used to prepare a poly(glycerol monomethacrlyate) (PGMA) chain transfer agent. Subsequent chain extension with 2-hydroxypropyl methacrylate (HPMA) using a RAFT aqueous dispersion polymerisation formulation at pH 7.0 7.5 resulted in the formation of morpholine-functionalised PGMA-PHPMA diblock copolymer worms via polymerisation-induced selfassembly (PISA). These worms form soft, free-standing aqueous hydrogels at 15% w/w solids. Acidification causes protonation of the morpholine end-groups at pH 3, which increases the hydrophilic character of the PGMA stabiliser block.This causes a subtle change in the copolymer packing parameter which induces a worm-to-sphere morphological transition and hence leads to in situ degelation. This order-order transition was characterised by dynamic light scattering (DLS), transmission electron microscopy (TEM) and gel rheology studies. On returning to pH 7, regelation is observed at 15% w/w solids, indicating the reversible nature of the transition. However, such diblock copolymer worm gels remain intact when acidified in the presence of electrolyte, since the cationic surface charge arising from the protonated morpholine end-groups is screened under these conditions. Moreover, regelation is also observed in relatively acidic solution (pH < 2), because the excess acid acts as a salt under these conditions and so induces a sphere-to-worm transition.
The hydrogen bond interaction between water and imidazole was investigated with the matrix-isolation FTIR spectroscopy coupled to ab initio calculations performed with the RHF and MP2 methods and the parametrized DFT method with the B3LYP hybrid functional. The 6-31G** and 6-31++G** basis sets were used in the calculations. Evaluation of the accuracy of the three methods and the two basis sets was made for noncomplexed imidazole. All three of the methods gave geometries for imidazole in good agreement with the experimental structure. Also, all three levels of theory with both basis sets gave similarly accurate vibrational frequency predictions for monomeric imidazole with a best mean deviation for the DFT/B3LYP/ 6-31++G** method. The assignment of the matrix spectra of the two isomeric H-bond complex species, NsH‚‚‚OH 2 and N‚‚‚HsOH, was performed by comparison with the theoretically predicted IR frequencies and intensities and was further assisted by asymmetrical deuteration experiments. The MP2 and DFT methods employed with the basis set augmented with diffuse functions gave good predictions of the frequency shifts for the vibrational modes directly influenced by the H-bond interaction. For the other vibrational modes, the RHF method performed almost as equally well as the MP2 and DFT methods and we can conclude that this method can provide qualitative and quantitively reliable data on hydrogen-bonded systems.
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