KEY WORDSN-Isopropylacrylamide / Acrylamide / Trialkylaluminum / Isotactic Polymer / Stereospecific Polymerization / Protected Monomer / Isomerization / Stereoregularity of vinyl polymers often affects significantly their properties and functions, and thus stereospecific polymerization has been important from the view points of both polymer chemistry and industry. In vinyl polymerization ionic and coordination processes have been considered favorable for the stereocontrol, in which proper selection of initiators, catalysts, additives and solvents may provide us with a handle for controlling stereoregularity in a wide variety. For example, we have shown that highly isotactic, syndiotactic, and heterotactic polymethacrylates could be prepared in toluene by using several anionic initiators; tert-butylmagnesium bromide (t-BuMgBr) for isotactic polymerization 1, 2 tert-butyllithium (t-BuLi) / trialkylaluminum (R 3 Al) for syndiotactic one 3, 4 and t-BuLi / bis(2,6-di-tert-butylphenoxy)methylaluminum [MeAl(ODBP) 2 ] for heterotactic one. [5][6][7][8][9][10][11][12][13] Polymers of acrylamide and its derivatives including N-isopropylacrylamide (NIPAm) are widely used in industry, agriculture and medicine due to their remarkable properties including good biocompatibility and low toxicity. 14, 15 Electron-withdrawing nature of amide groups might provide the monomers with potential reactivity favorable for anionic polymerization. However, the presence of acidic hydrogen in acrylamide itself and monosubstituted acrylamide inhibits the anionic vinyl polymerization.Thus radical polymerization has been so far the only means to obtain the corresponding polymers with few exceptions such as hydrogentransfer polymerization of α-(aminomethyl)acrylates 16 and N-acryloylurea derivatives with potassium tertbutoxide or 1,8-diazabicyclo[5.4.0]undec-7-ene. [17][18][19][20][21] As a consequence, stereospecific anioic polymerization of acrylamide derivatives have only been known for N, N-disubstituted ones. 22-28 Nakahama and his coworkers have reported successful stereospecific anionic polymerization of N, N-diethylacrylamide (DEA) in tetrahydrofuran (THF) by careful selection of Lewis-acid additives and counter cations. A syndiotactic poly(DEA) was prepared with alkyllithium initiator [1,1-bis(4 -trimethylsilylphenyl)-3-methylpentyllithium]/diethylzinc (Et 2 Zn), an isotactic one with t-BuMgBr/Et 2 Zn, and a heterotactic one with diphenylmethylpotassium (Ph 2 CHK)/Et 2 Zn. [29][30][31][32][33][34] In 1996, Okamoto and his coworkers 35 reported the anionic polymerization of N, N-diphenylacrylamide with t-BuMgBr in toluene at −78 • C, which gave an isotactic polymer with m diad of 80%. More recently, they also found that, in radical polymerizations of acrylamide and its derivatives, rare-earth metal trifluoromethanesulfonates (triflates) as Lewis-acid additives promoted stereospecific polymerization and, in particular, isotactic poly(NIPAm)s with m diad content of 92% were obtained with lutetium and yttrium triflates in methanol at −20 • ...

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Abstract1H NMR chemical shifts of the protons in the vinyl groups of monomers are correlated with their reactivities in anionic, coordinated anionic, and cationic polymerizations. The relative reactivities of styrenes in anionic addition reactions with living polystyrene increase linearly with the chemical shift of the proton trans to the substituent (δH1). Only the plot for 2,4,6‐trimethylstyrene deviates very much from the linear relation because of the large steric hindrance. The relative reactivities of methacrylates in anionic copolymerizations increase with increasing chemical shifts of protons attached to the β‐carbon of methacrylates. In cationic polymerizations of styrenes, the relative reactivities decrease with increasing δH1. The relative reactivities in coordinated anionic polymerizations with Ti‐containing Ziegler initiators show a typical feature of cationic polymerization, and those with V‐containing initiators show a typical feature of anionic polymerization, indicating the importance of the coordination process in the propagation reaction with Ti‐containing initiator systems. From the results, it can be concluded that the chemical shifts of the protons attached to the β‐carbon of vinyl monomers can be used as a practical measure of the reactivity of vinyl monomers in ionic polymerizations and also as a tool for understanding the mechanism of polymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2134–2147, 2002

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