A-Fluorostyrenes

Bromofluoro compounds are themselves useful starting materials for the preparation of monofluorinated compounds. For example, reduction of 1-bromo-2-fluorocyclododecanes with tributyltin hydride gives fluorocyclododecane, while other methods to produce this compound have been unsuccessful.15 The elimination of hydrogen bromide from vicinal bromofluorides also gives vinyl fluorides in good yields,10 16 as is illustrated by the recent synthesis of several substituted a-fluorostyrenes for studies related to [4+2]-cycloadditions.17... 

Tetrakis(triphenylphosphine)palladiuin(0)-copper(l) iodide. 18,349-350 20,369 Coupling reactions. a-Fluorovinylstannanes are a source of a-fluorostyrenes by virtue of their capacity of partaking in the Stille coupling. A synthesis of (Z)-alkenes is based on the Pd(0)-catalyzed exchange of alkenyl tellurides or selenides with zinc followed by the Negishi coupling. ... 

Coupling of organotins with unsaturated halides. Functionalized reagents are widely applicable for the coupling such that a-fluorostyrenes, a-arylacrylic esters, and cinnamyl amines are readily obtained. 

Polyfluorostyrenes are described in many publications. A -fluorostyrene can be formed by a cationic mechanism. The material softens at 240-260 °C. An a,, jff -trifluorostyrene can be polymerized by a free-radical mechanism to yield an amorphous polymer that softens at 240 Ring-substimted styrenes apparently polymerize similarly to styrene. Isotacticpoly(o-fluorostyrene) melts at 265 °C. It forms by polymerization with Ziegler-Natta catalysts. The meta analog, however, polymerized under the same conditions, yields an amorphous material. 

SYNTHESIS AND NMR CHARACTERIZATION OF COPOLYMERS OF a-FLUOROSTYRENE WITH METHYL ACRYLATE... 

We have recently found that pure a-fluorostyrene can be polymerized by the conventional free radical method and that poly-(a-fluorostyrene) solutions can be stabilized by weak or highly hindered bases. This finding enabled us to investigate the microstructure of poly(a-fluorostyrene) by C-NMR spectroscopy. 

This study has been extended to copolymers of a-fluorostyrene with methyl acrylate because of our interest in the cotacticity of statistical and alternating copolymers of styrene and substituted styrenes with acrylates and methacrylates. The present paper covers the 300 MHz 20 MHz C- and 282 MHz F-NMR studies of... 

Gel permeation chromotograms of some of the polymers were measured with a Waters Association Model 440 Gel Permeation Chromatograph equipped with an absorbance detector. Tetrahydrofuran (THF) was used as a solvent and a calibration based on polyisobutylene standards was u ed. The approximate number and weight averages are Mj =136,000 and M =296,000 for the copolymer having 19.6 mole % a-fluorostyrene Hn=60,200 and 1 =98,000 for th copolymer having 48.1 mole % a-fluorostyrene and 1 =16,400 and M =24,800 for poly-(a-fluorostyrene). A similar poly(a-fluorostyrene) sample that was analyzed earlier using a polystyrene calibration had Mj =4,900 and M =10,400 ... 

Based on Q and e values of 0.45 and +0.64 for methyl acrylate , Q and e values for a-fluorostyrene, were calculated to be 0.9 and -0.7, respectively. This indicates that a-fluorostyrene, although slightly less reactive than styrene, behaves as a relatively strong electron donor, comparable to styrene Itself. This is interesting since vinyl fluoride is a strong electron acceptor. Table II compares the Q and e values of some relevant substituted ethylenes with those of a-fluorostyrene. 

Fig. 4. Copol3nnerization diagram for the a-fluorostyrene/ methyl acrylate system.

Table III lists calculated MA-centered triad fractions, F, Fg and Fq values used in this determination. Figure 6 shows plots of the left-hand parts (L.H.P.) of Eqs. 1-3 vs. (F ms+ SHM)/ SMS The plots are linear and their slopes and intercepts define a O g value of 0.47. This suggests that MS and SM placements in the copolymers have nearly equal probabilities of being coisotactic or cosyndio-tactic. Since poly(methyl acrylate)and poly(a-fluorostyrene) have been shown to have random stereosequence distributions when prepared by free radical initiated polymerizations, the copolymers may be considered to have atactic stereosequence structures.

Figures 7A, 7B and 8A show 20 MHz C-NMR spectra of several methyl acrylate-a-fluorostyrene copolymers in GDCI3 solution at room temperature. Many of the resonances evident in these spectra are sources of microstructure information.

MHz C-NMR spectra of an a-fluorostyrene-methyl acrylate copolymer containing 48 1 mole percent ot-fluorostyrene. Spectrum A is of a freshly prepared solution in CDCI3 Spectrum B is of the solution after standing for 12 days at room temperature. 

The quaternary aromatic carbon resonance of the copolymers (6q=140.8 ppm) is observed as a group of four resonances, the relative intensities of which are influenced by C-F couplings, by sequence distribution effects and probably also by stereosequence distribution effects. In the spectrum of poly(a-fluorostyrene), this resonance region contains two strong signals separated by 28 Hz (1.4 ppm), which corresponds to for this polymer. The... 

Fig, 9. Quaternary aromatic carbon resonance of an a-fluoro-styrene-methyl acrylate copolymer containing 48 mole percent a-fluorostyrene. Assignments for the various regions are given in Table IV,... 

Aromatic Carbon Resonances of a-Fluorostyrene-Methy1 Acrylate Copolymers... 

Fig. 12. Infrared spectra of (A) a methyl acrylate-a-fluorostyrene copolymer containing 40.1 mole percent a-fluorostyrene and (B) the same copolymer after spontaneous degradation ii CHCI3 solution.

Fig. 13. Glass transition temperatures (Tg) of poly-a-fluoro-styrene, poly(methyl acrylate) and methyl acrylate-a-fluorostyrene copolymers as a function of a-fluoro-styrene content (weight percent).

Stabilization and NMR spectra of poly(a-fluorostyrene), Makromol Chem., Rapid Commun. 3 421 (1982). 

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