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Synthesis of Stereoblock Polypropylene by Change of Temperature in Living Polymerization
Zhengguo Cai,Yuushou Nakayama,Takeshi Shiono 한국고분자학회 2010 Macromolecular Research Vol.18 No.8
[t-BuNSiMe2(3,6-t-Bu2Flu)]TiMe2 (1) combined with trialkylaluminum-free modified methylaluminoxane (dMMAO) was used to induce the living polymerization of propylene in toluene at -20, 0, and 25 oC with control of the syndiospecificity. After the first polymerization at -20 oC, the same amounts of propylene were added at 25 oC for the second polymerization. The resulting PP was syndiotactic-rich (rr = 0.75), the value of which is the arithmetical average ((0.89 + 0.60)/2 = 0.745) of those produced at -20 and 25 oC. These results indicate the formation of the expected syndiotactic-atactic di-stereoblock PP.
Nath Dilip Chandra Deb,Fellows Christopher M.,Shiono Takeshi The Polymer Society of Korea 2006 Macromolecular Research Vol.14 No.3
The kinetic features of polymerization with an active site comprising cobalt dihalides ($CoX_2$, where X=Cl, Br, I) activated by methylaluminoxane (MAO) were investigated in 1,3-butadiene polymerization. The catalytic system exhibited the characteristic features of living polymerization. The initiation ($k_i$) and propagation ($k_p$) rate coefficients were estimated using the kinetic model for slow initiation previously reported by Shiono et al. The energy of activation fur the propagation reaction was calculated to be 27-30 $kJmol^{-1}$. The marked changes in reaction rate observed with different halides could be adequately described in terms of variations in the initiation process, with the same Arrhenius curve fitting propagation rate coeffcients estimated from all three halides, suggesting that the halide does not participate in the growing chain end.