Structural Characterization of Novel Styrene−Butadiene Block Copolymers Containing Syndiotactic Styrene Homosequences

Abstract

Samples of poly(syndiotactic styrene-co-butadiene) (sPS-B) have been prepared using methylalumoxane (MAO) activated CpTiCl3 under a range of experimental conditions. Copolymerization activities were low (24-36 kg mol -1 of cat. h -1 ) and nearly constant over the range of polymerization temperatures investigated (25-70 °C). Eight sPS-B samples were synthesized at 25 °C with styrene molar fractions (xs) covering a full range of compositions (xs ) 0.15-0.92). The copolymer samples were characterized by solution and solid state 13 C NMR spectroscopy, X-ray powder diffraction analysis, and thermal (DSC) analysis. The 13 C NMR analysis of the copolymer microstructure suggests that the butadiene homosequences are primarily cis-1,4 and the styrene segments are syndiotactic. However, some 1,2-and trans-1,4-butadiene units are occasionally formed during the polymerization process. The 13 C NMR resonances diagnostic of the monomer triads comprising styrene units (SSB, SBS, BBS, BSB, and SSS) were assigned and the average styrene block lengths (nS) calculated. Copolymer samples in which nS > 9 are crystalline due to the syndiotactic polystyrene segments detected in the δ-toluene clathrate form with melting points in the range 205-230 °C. Syndiotactic polystyrene segments with shorter styrene block lengths are amorphous and partially included in the poly(butadiene) rubber domains. TEM images of sample 13 (xS ) 0.37, nS ) 8.8) show the presence of small sPS fibers.

A Lutetium Allyl Complex That Bears a Pyridyl‐Functionalized Cyclopentadienyl Ligand: Dual Catalysis on Highly Syndiospecific and cis‐1,4‐Selective (Co)Polymerizations of Styrene and Butadiene

“…That the polymerization was living could be further confirmed by adding another 500 equiv of BD to a 100 % conversion BD (500 equiv) polymerization system; a total 100 % conversion was achieved to give PBD with doubled molecular weight ( Table 1, run 8). When the polymerization was performed in chlorobenzene instead of nonpolar toluene, the system showed decreased catalytic activity; to our delight, a perfect cis-1,4-regulated (99 %) PBD was obtained (Table 1, run 9), which could be evidenced by the very strong and sharp singlet appearing at d = 27.42 ppm in the 13 C NMR spectrum ( Figure 5 in the Supporting Information), and correspondingly a much lower glass transition temperature appeared at À109 8C in the DSC curve.…”

“…[13][14][15][16] These copolymers were characterized by 1 H NMR spectroscopy to determine the styrene molar fraction (x S ) in the copolymers. As shown in Figure 2, the peaks appearing at d = 6.52-7.05 ppm were assigned to phenyl protons in the Table 1.…”

“…The microstructures of these copolymers were characterized by 13 C NMR spectroscopy analyses. The representative spectrum of a butadiene-styrene copolymer with a moderate styrene content of 39.0 mol % is provided in Figure 4a ( Table 2, run 4).…”

“…[13][14][15][16] The 13 C NMR spectra of the other copolymers obtained with different styrene contents showed similar topologies. Meanwhile the cis-1,4 tacticity of the PBD segments remained unchanged (95.1-95.5 %) in all copolymers, which were not affected by varying the styrene content.…”

“…Although the copolymerization of styrene with butadiene or isoprene has been achieved by using some titanium and rare-earth-metal-based catalyst systems, [13][14][15][16] the problems such as low activity, or low styrene incorporation rate, or high trans-1,4-(or 1,2-or 3,4-) polydiene segments as well as relatively low molecular weights accompanied by broad molecular weight distributions (the presence of homopolymers) have not been well resolved. Therefore highly specific selective styrene-butadiene copolymerization has remained as a promising but challenging subject for academic and industrial fields.…”