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

Abstract

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