Stereospecific sequential block copolymerizations of styrene and 1,3‐butadiene with a C₅Me₅TiMe₃/B(C₆F₅)₃/Al(oct)₃ catalyst

Abstract

This article reports a new methodology for preparing highly stereoregular styrene (ST)/1,3-butadiene (BD) block copolymers, composed of syndiotactic polystyrene (syn-PS) segments chemically bonded with cis-polybutadiene (cis-PB) segments, through a stereospecific sequential block copolymerization of ST with BD in the presence of a C 5 Me 5 TiMe 3 /B(C 6 F 5 ) 3 /Al(oct) 3 catalyst. The first polymerization step, conducted in toluene at Ϫ25°C, was attributed to the syndiospecific living polymerization of ST. The second step, conducted at Ϫ40°C, was attributed to the cis-specific living polymerization of BD. The livingness of the whole polymerization system was confirmed through a linear increase in the weight-average molecular weights of the copolymers versus the polymer yields in both steps, whereas the molar mass distributions remained constant. The profound cross reactivity of the styrenic-end-group active species with BD toward ST led to the production of syn-PS-b-cis-PB copolymers with extremely high block efficiencies. Because of the presence of crystallizable syn-PS segments, this copolymer exhibited high melting temperatures (up to 270°C), which were remarkably different from those of the corresponding anionic ST-BD copolymers, for which no melting temperatures were observed. Scanning electron microscopy pictures of a binary syn-PS/cis-PB blend with or without the addition of the syn-PS-b-cis-PB copolymers proved that it could be used as an effective compatibilizer for noncompatibilized syn-PS/cis-PB binary blends.

Synthesis and characterization of graft copolymers of syndiotactic polystyrene with polybutadiene and 4‐methylstyrene

“…The strong and sharp peak appearing at 145.9 ppm confirmed that the graft copolymers were highly syndiotactic 12, 13. Figure 4(A) shows the peaks at 21.4 ppm derived from methyl carbon in MS.…”

“…Figure 4(B–D) reveals during the anionic grafting reaction a qualitative decrease in the peak intensity at 21.4 ppm and a corresponding qualitative increase in the peak intensity of the PB units at 27.5 ppm. This peak proved that PB was highly cis‐1,4 12, 13. If the grafting reaction had been complete, the 13 C‐NMR peak at 21.4 ppm should have disappeared completely, and the intensity of the peak at 27.5 ppm should have reached its maximum.…”

“…Moreover, the addition of excess amounts of PB led to poly(sPSMS-g-PB) in good yields without any difficulty. The synthesis of graft copolymers of sPSMS and PB by the reaction of the CH 3 group of MS with n-BuLi was successfully conducted and could be proven by 13 C-NMR as follows. The excess PB was removed by Soxhlet extraction with pentane to ensure that excess PB would not interfere with 13 C-NMR.…”

“…In this study, the method of synthesizing a graft copolymer of sPS and PB (a commercial elastomer) via an n ‐butyl lithium ( n ‐BuLi) reaction was investigated. Many researchers have reported the copolymerization of sPS with low‐molar‐mass butadiene12–14 or isoprene monomers,4, 10, 11, 15 whereas in this article, we report the grafting reactions of sPS and high‐molar‐mass PB (Scheme ). The combination of metallocene copolymerization and grafting reaction procedures for the preparation of the graft copolymers is illustrated.…”

“…Their polymorphic behaviors were studied with X‐ray diffraction, and the results illustrated successful approaches to sPS modification through the use of the aforementioned graft copolymers as compatibilizers. Recently, Ban et al12, 13 investigated poly(syndiotactic polystyrene‐ b ‐ cis ‐butadiene), which was synthesized by the blocking of butadiene monomer to sPS chains for effective compatibilization of an immiscible blend of sPS and cis ‐polybutadiene ( cis ‐PB). Their block copolymer, poly(syndiotactic polystyrene‐ b ‐butadiene), was produced from the reaction with butadiene monomer.…”