کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
9614543 | 48541 | 2005 | 8 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Binary cerium(IV) tert-butoxides-dialkylmagnesium systems: Radical versus coordinative polymerization of styrene
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
مهندسی شیمی
کاتالیزور
پیش نمایش صفحه اول مقاله
چکیده انگلیسی
Combinations of a dialkylmagnesium and a cerium tert-butoxide complex have been explored for styrene polymerization. Cerium(IV) precursors, equivalently Ce(OtBu)4(THF)x (1) or Ce3(OtBu)10O (2), when associated to 5 or more equivalents of n-butylethylmagnesium (BEM), oligomerize styrene in a controlled way with activities ranging from 10 to 1000 mol St mol Ceâ1 hâ1 at 25 and 105 °C, respectively. Effective chain transfer to BEM takes place in the course of polymerization, as evidenced by the decrease of the molecular weight of polystyrene with increasing amounts of BEM, eventually yielding Et and n-Bu end-capped oligostyrenes (identified by MALDI-TOF-MS) with Mn = 650-7400 g molâ1 and Mw/Mn = 1.3-2.5. ESR analyses established the formation of butyl and/or styryl radicals from these binary systems. The use of phenothiazine as a radical inhibitor did not inhibit completely the polymerization of styrene but significantly decreased the polymer yields. Therefore, the polymerization of styrene is proposed to arise from two different, concomitant pathways, which both enable effective transfer of growing polystyryl chains to dialkylmagnesium species: (i) radical polymerization initiated by free radicals generated from the redox-active metal precursors, as the major pathway, and (ii) coordination/insertion polymerization based on in situ produced Ce(III)- and/or Ce(IV)-alkyl species.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Molecular Catalysis A: Chemical - Volume 238, Issues 1â2, 1 September 2005, Pages 207-214
Journal: Journal of Molecular Catalysis A: Chemical - Volume 238, Issues 1â2, 1 September 2005, Pages 207-214
نویسندگان
Yann Sarazin, Thomas Chenal, André Mortreux, Hervé Vezin, Jean-François Carpentier,