Polymer NMR spectroscopy. VII. The stereochemical configuration of polytrifluorochloroethylene

Abstract

The NMR spectrum of polytrifluorochloroethylene in 3,3′‐bistrifluoromethylbiphenyl solution at 150°C. consists of two doublets having unequal components. Those at lower field correspond to CF2 chain units, while those at higher field correspond to CFCL units. In the CF2 doublet, the weaker component (at lower field) is found to have half the area of the stronger (at higher field), for polymers prepared over a 120°C. range of polymerization temperatures. By comparison to the spectra of the model compounds meso‐ and dl‐CF2ClCFClCF2CFClCF2Cl, the peaks of which closely coincide with those of the polymer when both are compared at 150°C., it is concluded that of the two CF2 peaks in the polymer spectrum, the weaker one represents CF2 groups which are between monomer units in isotactic dyads whereas the stronger one represents CF2 groups which are between monomer units in syndiotactic dyads. It follows that in trifluorochloroethylene propagation, syndiotactic dyad formation is twice as probable as isotactic dyad formation. This preference for syndiotactic placement corresponds to an activation entropy for isotactic propagation 1.38 e.u. more negative than that for syndiotactic propagation; there is no difference in the activation enthalpies. This behavior is in contrast to that previously found for methyl methacrylate propagation; here, preference for syndiotactic placement is entirely dictated by a greater activation enthalpy for isotactic placement.

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

“…The spectra agree with what is expected for poly(CTFE-altiBuVE) copolymer and demonstrates that the system produced via •CF 3 radical initiation is alternating, as evidenced by the absence of any peaks in the -127 ppm range, indicative of CFCl groups in CTFE-CTFE dyads, in the 19 F NMR spectrum [16][17][18][19] .…”

NMR probe for combined homonuclear multiple pulse decoupling and magic angle spinning

“…The two peaks with relative intensity 2: 1, as expected, are separated by 23 x 10-6 , in agreement with solution spectra. 15 As a second example the improvement in resolution of the IH NMR spectrum of 4-4' dimethylbenzophenone is shown. Figure 8 is a spectrum using only the REV-8 sequence, and again the resolution does not make it possible to obtain chemical shift information.…”

Opening up the JCN toolbox

“…Regarding poly(CTFE‐ alt ‐P) copolymers, 19 F NMR characterizations demonstrated the alternance of the copolymer as also evidenced by the values of the corresponding reactivity ratios (Table 1): r p = 0 and r CTFE = 0.06 or 0.24 (at −35 and −78 °C, respectively) 10. Indeed, the signal centered at −127 ppm corresponding to the ‐CF 2 C F ClCF 2 CFCl‐diad is used as a good assessment of the deviation of the copolymer from alternating structure 17…”