The radical polymeriza6on of a-(alkoxymethyl)acrylates in the presence of a catalytic amount of scandium trifluoromethanesulfonate [initiator: (i-PrOCO 2) 2 , temp.: 30'C] proceeds in an isotactic specific manner (m'"70%), whereas the syndiotactic (r'"70%) and atactic polymers were obtained during the radical polymerization with a catalytic amount of zinc bromide and without metal salts, respectively. The achievement of opposite sense of stereoregularity (isotactic and syndiotactic) by choosing Lewis acid catalysts during the radical polymerization of a-(alkoxymethyl)acrylates was attained to some extent. KEY WORDS Stereospecific Polymerization/ Radical Polymerization I Scandium Trifluoromethanesulfonate / a-(Alkoxymethyl)acrylate / Isotactic Polymer/ Lewis Acid/
The stereospecific radical polymerization of methyl and benzyl α-(methoxymethyl)acrylates
was performed in the presence of Lewis acids, such as ZnBr2 and Sc(OTf)3. The stereochemistry of the
polymerization was significantly affected by the coordination of the Lewis acids to the polar groups of
the monomer and polymer. The polymerization systems in the presence of ZnBr2 and Sc(OTf)3 produced
syndiotactic- and isotactic-rich polymers, respectively, showing different ESR signals. When amino alcohols
were added to the polymerization system with ZnBr2, heterotactic-rich polymers were obtained. Therefore,
syndiotactic-, isotactic-, and heterotactic-rich polymers can be synthesized by the radical method in the
presence of a catalytic amount of ZnBr2, Sc(OTf)3, and the ZnBr2−amino alcohol complex, respectively,
without changing the other polymerization conditions, although an atactic polymer was produced in the
absence of a Lewis acid. The detailed tacticity (tetrad) of the obtained polymer was estimated by 13C
NMR analysis of the main-chain methylene carbon.
Stereospecific polymerization and asymmetric oligomerization of allylsilanes were investigated by using C2‐ and Cs‐ symmetric zirconocene catalysts. Isotactic and syndiotactic poly(allylsilane)s were produced with rac‐ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl)zirconium dichloride (1) and diphenylmethylene(η5‐cyclopentadienyl)(η5‐fluorenyl)zirconium dichloride (6), respectively. Bulky allylsilanes afforded optically active oligomers in the reactions using optically active ethylenebis(4,5,6,7‐tetrahydro‐1‐indenyl)zirconium and ‐hafnium complexes.
The stereospecific radical polymerization of R-(alkoxymethyl)acrylatessbenzyl R-(methoxymethyl)acrylate, benzyl R-(ethoxymethyl)acrylate, and ethyl R-(ethoxymethyl)acrylatesin the presence of a catalytic amount of zinc halides (ZnCl2 and ZnBr2) was attained, and the obtained polymers had very different tacticities, rich in syndiotacticity (up to r ) 0.71), from that prepared in the absence of a zinc salt (atactic). In contrast, no change was observed in the stereoregularity of the polymethacrylates radically obtained in the presence of ZnBr2 as an additive. The coordination of zinc salts to polar R-substituents on the ω-end of the propagating polymer and the monomer must play an important part in this system.
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