posted on 2024-04-23, 19:05authored byPiotr Mocny, Ting-Chih Lin, Rohan Parekh, Yuqi Zhao, Marek Czarnota, Mateusz Urbańczyk, Carmel Majidi, Krzysztof Matyjaszewski
Poly(vinylidene fluoride) (PVDF) shows excellent chemical
and thermal
resistance and displays high dielectric strength and unique piezoelectricity,
which are enabling for applications in membranes, electric insulators,
sensors, or power generators. However, its low polarity and lack of
functional groups limit wider applications. While inert, PVDF has
been modified by grafting polymer chains by atom transfer radical
polymerization (ATRP), albeit via an unclear mechanism, given the
strong C–F bonds. Herein, we applied eosin Y and green-light-mediated
ATRP to modify PVDF-based materials. The method gave nearly quantitative
(meth)acrylate monomer conversions within 2 h without deoxygenation
and without the formation of unattached homopolymers, as confirmed
by control experiments and DOSY NMR measurements. The gamma distribution
model that accounts for broadly dispersed polymers in DOSY experiments
was essential and serves as a powerful tool for the analysis of PVDF.
The NMR analysis of poly(methyl acrylate) graft chain-ends on PVDF-CTFE
(statistical copolymer with chlorotrifluoroethylene) was carried out
successfully for the first time and showed up to 23 grafts per PVDF-CTFE
chain. The grafting density was tunable depending on the solvent composition
and light intensity during the grafting. The initiation proceeded
either from the C–Cl sites of PVDF-CTFE or via unsaturations
in the PVDF backbones. The dehydrofluorinated PVDF was 20 times more
active than saturated PVDF during the grafting. The method was successfully
applied to modify PVDF, PVDF-HFP, and Viton A401C. The obtained PVDF-CTFE-g-PnBMA materials were investigated in more detail. They
featured slightly lower crystallinity than PVDF-CTFE (12–18
vs 24.3%) and had greatly improved mechanical performance: Young’s
moduli of up to 488 MPa, ductility of 316%, and toughness of 46 ×
106 J/m3.