. beta.-Hydrogen abstraction and regiospecific insertion in syndiotactic polymerization of styrene
Macromolecules, 1987•ACS Publications
E form Z form can be seen, the olefinic proton of the Z isomer resonates at lower field
thanthat of the E isomer. A similar tendency was also reported for trialkylsilyl-substituted
olefins. 7 Accordingly, the olefinic proton signals centered at 6.14 and 6.21 ppm in Figure 1
can be assigned to E and Z forms of monomer units incorporated in the polymer, respec-
tively. The estimated E: Z ratio was about 70: 30. Further information aboutthe microstructure
of poly (l) was provided by 13C NMR analysis. Figure 2 shows olefinic region of the proton …
thanthat of the E isomer. A similar tendency was also reported for trialkylsilyl-substituted
olefins. 7 Accordingly, the olefinic proton signals centered at 6.14 and 6.21 ppm in Figure 1
can be assigned to E and Z forms of monomer units incorporated in the polymer, respec-
tively. The estimated E: Z ratio was about 70: 30. Further information aboutthe microstructure
of poly (l) was provided by 13C NMR analysis. Figure 2 shows olefinic region of the proton …
E form Z form can be seen, the olefinic proton of the Z isomer resonates at lower field thanthat of the E isomer. A similar tendency was also reported for trialkylsilyl-substituted olefins. 7 Accordingly, the olefinic proton signals centered at 6.14 and 6.21 ppm in Figure 1 can be assigned to E and Z forms of monomer units incorporated in the polymer, respec-tively. The estimated E: Z ratio was about 70: 30. Further information aboutthe microstructure of poly (l) was provided by 13C NMR analysis. Figure 2 shows olefinic region of the proton-decoupled 13C NMR spectrum of the resulting polymer, where two pairs of olefinic carbons are observed. Detail assignments of the signals were carried out by comparing the chemicalshifts with those of the corresponding model compounds. They are summarized in Table II. Two major peaks at 146.4 and 131.1 ppm in Figure 2 can be assigned to carbons of 1, 4-1? configuration, and the other minor peaks at 148.5 and 127.8 ppm are attributable to those of 1, 4-Z form. Based on the as-sumption that nuclear Overhauser enhancement is equally effective to both carbons of isomeric forms, the E\Z ratio of monomer units in the polymer chain is estimated to be 67: 23 from relative intensities of the signals at 146.4 and 148.5 ppm, which agrees with the result of the NMR study. It should be noted that no other peaks which can be assigned to 1, 2-or 3, 4-structure were observed within the detection limits of our 13C NMR spectrometer. This is in contrast to the anionic polymerizations of butadiene and isoprene8, 9 where dangling vinyl structures were main components under the conditions employed here. Detail study of polymerization of this monomer and its deriva-
ACS Publications
以上显示的是最相近的搜索结果。 查看全部搜索结果