Effect of Structure on Cationic Initiation Efficiency of a Carbocatonic/ATRP Dual Initiator

详细信息    查看全文

• 作者：Yaling Zhu ; Robson F. Storey
• 刊名：Macromolecules
• 出版年：2012
• 出版时间：February 14, 2012
• 年：2012
• 卷：45
• 期：3
• 页码：1217-1221
• 全文大小：258K
• 年卷期：v.45,no.3(February 14, 2012)
• ISSN：1520-5835

文摘

The dual initiator, 3,3,5,5,7-pentamethyl-7-chlorooctyl 2-bromo-2-methylpropionate (IB₃BMP), possessing initiating sites for both living carbocationic polymerization (LCP) and atom transfer radical polymerization (ATRP), was synthesized to overcome the low initiation efficiency of previously reported dual initiators such as 3,3,5-trimethyl-5-chlorohexyl 2-bromo-2-methylpropionate (IB₂BMP). Low initiation efficiency of the latter and similar initiators has been attributed to complexation between the Lewis acid polymerization catalyst and the ester carbonyl group of the initiator. IB₃BMP was synthesized by reacting IB₂BMP with 2-methallyltrimethylsilane at low temperature, followed by hydrochlorination. IB₃BMP, which differs from IB₂BMP by the inclusion of one additional isobutylene (IB) repeating unit, showed quantitative initiation efficiency (I_eff 1) in TiCl₄-co-initiated LCP of IB under various reaction conditions, including low temperature (鈭?0 掳C) and low monomer/initiator ratios (48鈥?64). I_eff and polydispersity index of the resulting polyisobutylenes were identical to those obtained with the commonly used, monofunctional cationic initiators 2-chloro-2,4,4-trimethylpentane (TMPCl) and 2-chloro-2,4,4,6,6-pentamethylheptane (PMHCl). The superiority of IB₃BMP compared to IB₂BMP in carbocationic initiation was attributed to increased separation between the tert-chloride initiating site and the TiCl₄:carbonyl complex at the ATRP initiating site. A PIB macroinitiator prepared from IB₃BMP was used to initiate ATRP of methyl acrylate. Efficiency of radical initiation was quantitative, the targeted poly(methyl acrylate) block length was obtained, and the resulting block copolymer possessed narrow polydispersity.