A series of non-ionic poly(glycerol monomethacrylate)–poly(2-hydroxypropyl methacrylate) (PGMA–PHPMA) diblock copolymer vesicles has been prepared by reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of HPMA at 70 °C at low pH using a carboxylic acid-based chain transfer agent. The degree of polymerization (DP) of the PGMA block was fixed at 43, and the DP of the PHPMA block was systematically varied from 175 to 250 in order to target vesicle phase space. Based on our recent work describing the analogous PGMA–PHPMA diblock copolymer worms [LovettJ. R.LovettJ. R.25418214Angew. Chem.20155412791283], such diblock copolymer vesicles were expected to undergo an order–order morphological transition via ionization of the carboxylic acid end-group on switching the solution pH. Indeed, irreversible vesicle-to-sphere and vesicle-to-worm transitions were observed for PHPMA DPs of 175 and 200, respectively, as judged by turbidimetry, transmission electron microscopy (TEM), and dynamic light scattering (DLS) studies. However, such morphological transitions are surprisingly slow, with relatively long time scales (hours) being required at 20 °C. Moreover, no order–order morphological transitions were observed for vesicles comprising longer membrane-forming blocks (e.g., PGMA43–PHPMA225–250) on raising the pH from pH 3.5 to pH 6.0. However, in such cases the application of a dual stimulus comprising the same pH switch immediately followed by cooling from 20 to 5 °C, induces an irreversible vesicle-to-sphere transition. Finally, TEM and DLS studies conducted in the presence of 100 mM KCl demonstrated that the pH-responsive behavior arising from end-group ionization could be suppressed in the presence of added electrolyte. This is because charge screening suppresses the subtle change in the packing parameter required to drive the morphological transition.

A poly(glycerol monomethacrylate) (PGMA) chain transfer agent is chain-extended by reversible addition–fragmentation chain transfer (RAFT) statistical copolymerization of 2-hydroxypropyl methacrylate (HPMA) with glycidyl methacrylate (GlyMA) in concentrated aqueous solution via polymerization-induced self-assembly (PISA). A series of five free-standing worm gels is prepared by fixing the overall degree of polymerization of the core-forming block at 144 while varying its GlyMA content from 0 to 20 mol %. 1H NMR kinetics indicated that GlyMA is consumed much faster than HPMA, producing a GlyMA-rich sequence close to the PGMA stabilizer block. Temperature-dependent oscillatory rheological studies indicate that increasing the GlyMA content leads to progressively less thermoresponsive worm gels, with no degelation on cooling being observed for worms containing 20 mol % GlyMA. The epoxy groups in the GlyMA residues can be ring-opened using 3-aminopropyltriethoxysilane (APTES) in order to prepare core cross-linked worms via hydrolysis-condensation with the siloxane groups and/or hydroxyl groups on the HPMA residues. Perhaps surprisingly, 1H NMR analysis indicates that the epoxy–amine reaction and the intermolecular cross-linking occur on similar time scales. Cross-linking leads to stiffer worm gels that do not undergo degelation upon cooling. Dynamic light scattering studies and TEM analyses conducted on linear worms exposed to either methanol (a good solvent for both blocks) or anionic surfactant result in immediate worm dissociation. In contrast, cross-linked worms remain intact under such conditions, provided that the worm cores comprise at least 10 mol % GlyMA.

Protonation of [Co(q-C5Me5)(C2H4){ P ( p -t ~l y l ) ~) ] affords the ethyl cation [Co(q-C5Me5)Et{ P ( p -t ~l y l ) ~) ] + in which there is a strong three-centre interaction between the metal and a (3-C-H, as indicated by 1H and 13C n.m.r. and by a single crystal X-ray diffraction study of the tetrafluoroborate salt.

The reaction of [(η5-C5Me5)Co(η4-1,5-cyclooctadiene)] with HBF4·Me2O affords, at room temperature, an agostic η3-cyclooctenyl complex which undergoes a facile ring opening to afford anti-[(η5-C5Me5)Co(η5-1-propylpentadienyl)]BF4.