Multinuclear Magnetic Resonance and DFT Studies of the Poly(chlorotrifluoroethylene-alt-ethyl vinyl ether) Copolymers

Abstract

Chlorotrifluoroethylene (CTFE) and ethyl vinyl ether (EVE) were reacted under radical conditions to produce the poly(CTFE-co-EVE) alternating copolymer, and a full 13 C, 1 H, and 19 F NMR structural interpretation is offered. All spectra were characterized by broad signals resulting from the overlapping of different chemical shifts. This observation was rationalized by considering a complex mixture of diastereomerically related compounds, hence allowing an average assignment to be determined. A density functional theory (DFT) computational study of the isotropic magnetic shieldings with the GIAO and CSGT methods was performed to explore the diasteriomeric relationships between the single building blocks and their mutual influences along the polymer chain. The calculated results totally support the assignment of the experimental chemical shifts of two diasteriomeric sets of resonances indicating chiral center inversion, and not spin-spin J coupling interactions, as the main cause of spectral complexity. 13 C, and 19 F NMR spectra, obstructing the determination of 1 H-19 F coupling constants and detailed structure of the copolymer. Furthermore, few detailed analyses using multinuclear 19 F, 13

Radical copolymerisation of chlorotrifluoroethylene with isobutyl vinyl ether initiated by the persistent perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical

“…The molecular weights determined by 19 F NMR also show the expected decrease in molecular weight with increase in initiator concentration, with the trend being nearly linear in the region of 1% to 10% initiator (with Mn ranging from 340000 to 122000 g•mol -1…”

“…The five peaks present in the 19 Both signals are broad arising from the presence of two types of asymmetric carbons leading to two diastereoisomers, which makes these protons anisochronous (i.e. nonequivalent).…”

“…The literature 10,13 indicates that, if the polymerisation occurs in a regioselective way via path 1a, there should be only one 19 F NMR signal for CF 3 , centered at -63 ppm.…”

“…If such a product did exist there should be 19 F NMR signals at around -175 ppm. Since no such signals are detected, this reaction did not occur and the unexpected 19 F NMR signals for CF 3 observed in the 19 F NMR spectrum for 20% PPFR cannot be due to incorporation of the PPFR elimination product into the polymer.…”

“…4,8,9 Recently Patil et al 10 utilised the persistent perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical (abbreviated as PPFR 11 , structure shown in Figure 1) to generate •CF 3 radicals for polymerisation initiation. The resulting CF 3 end groups were used in 19 F NMR spectroscopy for the determination of average molecular weights of VDF copolymers. The technique provides M n values closer to the true molecular weight of the copolymers than SEC.…”