Fluoroalkyl Pentacarbonylmanganese(I) Complexes as Initiators for the Radical (co)Polymerization of Fluoromonomers

Abstract

The use of [Mn(R_F)(CO)₅] (R_F = CF₃, CHF₂, CH₂CF_3, COCF₂CH₃) to initiate the radical polymerization of vinylidene fluoride (F₂C=CH₂, VDF) and the radical alternating copolymerization of vinyl acetate (CH₂=CHOOCCH₃, VAc) with <i>tert</i>-butyl 2-(trifluoromethyl)acrylate (MAF-TBE) by generating primary R_F^• radicals is presented. Three different initiating methods with [Mn(CF₃)(CO)₅] (thermal at ca. 100 °C, visible light and UV irradiations) are described and compared. Fair (60%) to satisfactory (74%) polyvinylidene fluoride (PVDF) yields were obtained from the visible light and UV activations, respectively. Molar masses of PVDF reaching 53,000 g·mol^-1 were produced from the visible light initiation after 4 h. However, the use of [Mn(CHF₂)(CO)₅] and [Mn(CH₂CF₃)(CO)₅] as radical initiators produced PVDF in a very low yield (0 to 7%) by both thermal and photochemical initiations, while [Mn(COCF₂CH₃)(CO)₅] led to the formation of PVDF in a moderate yield (7% to 23%). Nevertheless, complexes [Mn(CH₂CF₃)(CO)₅] and [Mn(COCHF₂)(CO)₅] efficiently initiated the alternating VAc/MAF-TBE copolymerization. All synthesized polymers were characterized by ¹H and ¹⁹F NMR spectroscopy, which proves the formation of the expected PVDF or poly(VAc-<i>alt</i>-MAF-TBE) and showing the chaining defects and the end-groups in the case of PVDF. The kinetics of VDF homopolymerization showed a linear ln[M]₀/[M] versus time relationship, but a decrease of molar masses vs. VDF conversion was noted in all cases, which shows the absence of control. These PVDFs were rather thermally stable in air (up to 410 °C), especially for those having the highest molar masses. The melting points ranged from 164 to 175 °C while the degree of crystallinity varied from 44% to 53%.