Self-Assembly of Ionizable “Clicked” P3HT‑<i>b</i>‑PMMA Copolymers: Ionic Bonding Group/Counterion Effects on Morphology

A novel methodology used to overcome the predominance of π–π interactions on the organization of rod–coil copolymer is reported in this paper. We demonstrated changes in the self-assembly morphology of poly­(3-hexylthiophene)-<i>b</i>-poly­(methyl methacrylate) (P3HT-<i>b</i>-PMMA) block copolymer BCP, by introducing an ionic group to the linking unit between the two blocks. A neutral polymer precursor was synthesized from ethynyl-terminated P3HT and azido-terminated PMMA via Huisgen’s 1,3-dipolar cycloaddition. Then two 1,2,3-triazolium-based block copolymers with different counteranions were obtained by a quaternization of 1,2,3-triazole groups with methyl iodide, and subsequent anion exchange was observed with a fluorinated salt, bis­(trifluoromethane) sulfonimide salt. Atomic force microscopy, modulated differential scanning calorimetry, and X-ray scattering were used to prove that the crystallization of the conjugated block is disrupted by the additional ionic interactions imposed to the system. The 1,2,3-triazolium-based BCP with iodide as the counterion exhibited highly organized well-defined fibrils, as the diblock phase segregation χ becomes predominant over the rod–rod interaction μ. When the more stable and larger NTf₂^– was used as counterion, P3HT phase was disrupted and no crystallization was observed. This methodology could be a useful strategy to open the range of nanomorphologies reachable with a semiconducting polymer for electronic or photovoltaic applications

Improved Solid Electrolyte Conductivity via Macromolecular Self-Assembly: From Linear to Star Comb-like P(S-<i>co</i>-BzMA)‑<i>b</i>‑POEGA Block Copolymers

Star block copolymer electrolytes with a lithium-ion conducting phase are investigated in the present work to assess the influence of this complex architecture compared to that of the linear one, on both, bulk morphology and ionic conductivity. For that purpose, the controlled synthesis of a series of poly(styrene-co-benzyl methacrylate)-b-poly[oligo(ethylene glycol) methyl ether acrylate] [P(S-co-BzMA)-b-POEGA] block copolymers (BCPs) by reversible addition–fragmentation transfer polymerization was performed from either a monofunctional or a tetrafunctional chain transfer agent containing trithiocarbonate groups. We emphasized how a small amount of styrene (6 mol %) drastically improved the control of the RAFT polymerization of benzyl methacrylate mediated by the tetrafunctional chain transfer agent. Transmission electron microscopy and small-angle X-ray scattering demonstrated a clear segregation of the BCPs in the presence of lithium salt. Interestingly, the star BCPs gave rise to highly ordered lamellar structures as compared to that of the linear analogues. Consequently, the reduced lamellae tortuosity of self-assembled star BCPs improved the lithium conductivity by more than 8 times at 30 °C for ∼30 wt % of the POEGA conductive phase

Controlling Water Content and Proton Conductivity through Copolymer Morphology

To investigate relationships between morphology and proton conductivity in ionic copolymer membranes, we have studied two series of fluorous copolymers bearing polystyrene grafts sulfonated from 0 to 100%. Small-angle X-ray and neutron scattering experiments reveal a disordered, partially phase-separated system consisting of fluorous domains in a partially sulfonated polystyrene matrix with aggregation of ion-rich domains within the matrix. The size of the fluorous domains depends on graft density, and their packing depends on the graft chain length. The spacing of the ion-rich domains is remarkably independent of either graft chain length or charge content. We find that the samples with lower graft density, which are partially crystalline, develop a less-ordered morphology with a lower degree of phase separation. The partially crystalline samples swell less and have a slightly lower conductivity at similar water content; the lower conductivity is attributed to a more tortuous conducting phase