Near-Model Amphiphilic Polymer Conetworks Based on\nFour-Arm Stars of Poly(vinylidene fluoride) and Poly(ethylene glycol):\nSynthesis and Characterization

Abstract

Amphiphilic polymer conetworks (APCN)\nwere prepared in <i>N</i>,<i>N</i>-dimethyl­formamide\n(DMF) by the interconnection of four-arm star poly­(vinylidene fluoride)\n(PVDF, <i>M</i>_n = 8800 Da) end-functionalized\nwith benzaldehyde groups and four-arm star poly­(ethylene glycol) (PEG, <i>M</i>_n = 10 kDa) end-functionalized with benzaacyl­hydrazide\ngroups. The PVDF stars were prepared via the reversible addition–fragmentation\nchain transfer polymerization of vinylidene fluoride using a tetraxanthate\nchain transfer agent. Equilibrium swelling of the APCNs in various\nsolvents was dependent on the compatibility of the APCN components\nwith the solvent, with the degrees of swelling (DS) varying from 22\nin DMF (a good solvent for both PEG and PVDF), down to 8 in water\n(a good and selective solvent for PEG), and even down to 3 in diethyl\nether (a nonsolvent for both polymers). Characterization of the conetworks\nin D₂O using small-angle neutron scattering (SANS) indicated\nphase separation at the nanoscale, as evidenced by a (broad) correlation\npeak, consistent with a 19 nm spacing between the formed PVDF-based\nhydrophobic clusters of ∼10 nm diameter and an aggregation\nnumber of ca. 50 (growing in size with PVDF content). This behavior\nwas independent of temperature from 25 to 70 °C and slightly\ndependent on deviations (±ca. 50 mol %) from the PVDF: PEG stoichiometry.\nConetwork characterization in the bulk using atomic force microscopy\n(AFM) revealed a domain spacing of 14 ± 6 nm, in good agreement\nwith the spacing of 11 nm calculated from the SANS results above (19\nnm) but also taking into account the DS in D₂O (5.5). Annealing\nthe conetworks at 200 °C, a temperature above the melting point\nof PVDF, did not improve the morphological order in the AFM images.\nFinally, APCNs prepared in the room temperature ionic liquid binary mixture lithium\nbis­(trifluoro­methane­sulfonyl)­imide:1-ethyl-3-methyl­imidazolium\nbis­(trifluoro­methane­sulfonyl)­imide (1:9 molar ratio) exhibited\nan electrochemical stability up to 4.3 V and a good room temperature\nion conductivity of 0.6 mS cm^–1.