Microphase Separation and Crystallization in H‑Bonding End-Functionalized Polyethylenes

Well-defined, crystalline, low molar mass polyethylene PE_<i>x</i> (where <i>x</i> is the molar mass 1300 and 2200 g mol^–1) bearing thymine (Thy) or 2,6-diaminotriazine (DAT) end groups have been synthesized from amino-terminated PE. Either double-layer or monolayer solid-state morphologies were attained depending on the nature of the end-group(s). PE₁₃₀₀-NH₂, PE₁₃₀₀-DAT, and the equimolar blend PE₁₃₀₀-Thy/DAT-PE₁₃₀₀ all organized into double-layer structures composed of extended PE chains sandwiched between H-bonding chain-ends. The double-layered morphology arose from the microphase separation of the polar end-groups and the nonpolar PE chains and was frozen by the crystallization of the PE domains. The regularity of the PE lamellar stacking was higher for the stronger and more directional associated pair Thy/DAT compared with samples of either PE-NH₂ or PE-DAT. For PE₁₃₀₀-Thy, the mesoscopic organization was driven by the crystallization of Thy domains prior to crystallization of the PE chains, forcing the small proportion of nonfunctionalized PE chains to segregate and crystallize separately to the PE-Thy chains. The confinement of PE chains between Thy domains lead to a conventional monolayer form in which extended PE chains were interdigitated. The volume fraction of Thy or DAT end-groups was a key parameter in the organization in all these systems: the PE crystallinity was higher with longer PE chains (i.e., a low volume fraction of Thy or DAT units), but the mesoscopic organization of the supramolecular PE was less regular

Direct Route to Well-Defined Poly(ionic liquid)s by Controlled Radical Polymerization in Water

The precision synthesis of poly­(ionic liquid)­s (PILs) in water is achieved for the first time by the cobalt-mediated radical polymerization (CMRP) of <i>N</i>-vinyl-3-alkylimidazolium-type monomers following two distinct protocols. The first involves the CMRP of various 1-vinyl-3-alkylimidazolium bromides conducted in water in the presence of an alkyl–cobalt­(III) complex acting as a monocomponent initiator and mediating agent. Excellent control over molar mass and dispersity is achieved at 30 °C. Polymerizations are complete in a few hours, and PIL chain-end fidelity is demonstrated up to high monomer conversions. The second route uses the commercially available bis­(acetylacetonato)­cobalt­(II) (Co­(acac)₂) in conjunction with a simple hydroperoxide initiator (<i>tert</i>-butyl hydroperoxide) at 30, 40, and 50 °C in water, facilitating the scaling-up of the technology. Both routes prove robust and straightforward, opening new perspectives onto the tailored synthesis of PILs under mild experimental conditions in water

Completely Miscible Polyethylene Nanocomposites

A route to fully miscible polyethylene (PE) nanocomposites has been established based on polymer-brush-coated nanoparticles. These nanoparticles can be mixed with PE at any ratio, with homogeneous dispersion, and without aggregation. This allowed a first systematic study of the thermomechanical properties of PE nanocomposites without interference from aggregation effects. We observe that the storage modulus in the semicrystalline state and the softening temperature increase significantly with increasing nanoparticle content, whereas the melt viscosity is unaltered by the presence of nanoparticles. We show that the complete miscibility with the semicrystalline polymer matrix and the improvement of thermomechanical properties in the solid state is caused by the PE-coated nanoparticles being nucleating agents for the crystallization of PE. This provides a general route to fully miscibility nanocomposites with semicrystalline polymers