Stereocontrol using Lewis acids in radical polymerization

Abstract

The radical polymerization of various (meth)acrylamides in the presence of Lewis acids such as Yb(OTf)3 and Y(OTf)3 was carried out. The polymerization with Lewis acids led to highly isotactic polymers, while the polymers synthesized without Lewis acids were atactic or syndiotactic. The dependence of the polymer properties on the tacticity was also demonstrated.

Application of multivariate analysis of NMR spectra of poly(N-isopropylacrylamide) to assignment of stereostructures and prediction of tacticity distribution

“…13 C NMR spectra (100 MHz) were measured using an ECX400 spectrometer (JEOL Ltd), equipped with a 10-mm multinuclear direct detection probe (451 pulse (7.75 ms), pulse repetition ¼ 2.73 s, 5000 scans, with 1 H-broadband decoupling), in a mixed solvent (DMSO- …”

“…A composite of 1 H NMR (the methylene proton region; 1.18-1.80 p.p.m.) and 13 C NMR (the methine carbon region; 41.04-43.24 p.p.m.) spectra was used as the spectral vector in the matrix.…”

“…[8][9][10][11] The diad tacticities were easily determined from the 1 H NMR signals of the methylene groups in the main chain; the signals showed typical splitting as a result of diad stereostructures, as measured in deuterated dimethyl sulfoxide (DMSO-d 6 ) at 150 1C. [12][13][14][15] However, assignments, in terms of triad stereostructures, had not previously been made. We therefore assigned the 13 C NMR signals of the methine carbons in the main chain, at triad levels, by comparing the NMR spectra of poly(NIPAAm)s with a wide range of stereoregularities, such as isotactic, syndiotactic and heterotactic polymers, reported previously.…”

“…[12][13][14][15] However, assignments, in terms of triad stereostructures, had not previously been made. We therefore assigned the 13 C NMR signals of the methine carbons in the main chain, at triad levels, by comparing the NMR spectra of poly(NIPAAm)s with a wide range of stereoregularities, such as isotactic, syndiotactic and heterotactic polymers, reported previously. 10,16 The measurement conditions were optimized by mixing DMSO-d 6 with both D 2 O and 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (PenOH-F 8 ) at 100 1C.…”

“…[17][18][19][20][21][22][23] For example, principal component analysis (PCA) of 13 C NMR spectra of copolymers of methyl methacrylate and tert-butyl methacrylate, with various chemical compositions, the homopolymers of the two methacrylates, and blends of the homopolymers with various blend ratios extracted separately information of chemical composition and that of comonomer sequence. 23 Furthermore, chemical composition of the copolymers was successfully predicted by partial least-squares (PLS) regression of 13 C NMR spectra of the homopolymers of the two methacrylates, and the blends of the homopolymers. 23 Measurements of the 13 C NMR spectra of poly(NIPAAm)s to determine the triad tacticities require a large amount of sample, a long time, and use of a mixed solvent (DMSO-d 6 :D 2 O:PenOH-F 8 ¼ 75:10:15wt%).…”