Polyphenoxy Radicals: Synthesis and Homo-Polymerization of 2-(3,5-Dl- t -Butyl-4-Hydroxyphenyl)Isobutyl Methacrylate
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POLYPHENOXY RADICALS: SYNTHESIS AND HOMOPOLYMERIZATION OF 2-(3,5-DI-t-BUTYL-4HYDROXYPHENYL)ISOBUTYL METHACRYLATE RAVINDRA B. UPASANI,a,b LONG Y. CHIANGa,* AND D. P. GOSHORNa a
Corporate Research Laboratories, Exxon Research and Engineering Company,
Annandale, New Jersey 08801 b Department of Physics, Princeton University, Princeton, New Jersey 08544
ABSTRACT We evaluated the chemical stability of various polyphenoxy radicals prepared through the modified synthetic methods. The monomeric 3,5-di-t-butyl-4hydroxyphenyl derivatized olefins and methacrylates were prepared in a multistep synthesis starting from 2,6-di-t-butylphenol. These monomers were polymerized in the presence of radical initiators at the refluxing temperature of aromatic solvents under an inert atmosphere. The most stable polyradicals were found to be highly hindered poly(DBPM) radicals. INTRODUCTION Stable polyradicals can be utilized as precursors for the preparation of potential organic ferromagnetic materials. They can be hydrazyl, nitroxyl, phenoxyl, triarylmethyl, and diaryl carbene radicals. These radicals can be stabilized by a high degree of resonance and adjacent highly hindered t-butyl groups. The stabilization significantly decreases their reactivity toward radical coupling with bond formation. A number of polyphenoxy radicals have been synthesized and reviewed. 1 Generally, polyphenoxy radicals can be prepared by an oxidative reaction on the phenol moiety of polyalkenylphenols. The method of polymerization was found to depend heavily on the structure of monomers. 2 ,3,4 In the case of 2,6-di-t -butyl-4vinyl phenol, the polymerization was most efficiently carried out by a cationic mechanism to give a benzyl hydrogen containing poly(2,6-di-t -butyl)phenols. The radicals derived from these polyphenols are not chemically stable and themselves may undergo disproportionation to result quinonemethide formation. 2 5 To stabilize this type of polyphenoxy radicals the removal of benzyl hydrogen is desirable. This can be achieved by replacing it with a methyl group. However, the resulting 2,6-di-t butyl-4-isopropenyl phenol can not be polymerized easily. 2 ,6 Therefore, we modified the structure of 2,6-di-t -butyl-4-isopropenyl phenol monomer to move the polymerizable olefin away from the hindered moiety of molecules. Mat. Res. Soc. Symp. Proc. Vol. 173. c1990 Materials Research Society
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Here we report the synthesis of 3,5-di-t-butyl-4-hydroxy-phenyl derivatized olefins and methacrylates and their polymers. The most stable polyradicals were found to be highly hindered poly(DBPM) radicals.
X
Cationic or Free Radical Polymerization OR2
OR2
1: R1 = R2 = H 2: R 1 =Me, R2 =H 3: R1 = Me, R2 = Ac
4: R 1 = R2 = H 5: R 1 =Me, R2 =H 6: R 1 = Me, R2 = Ac
Scheme 1
RESULTS AND
DISCUSSION
3,5-di-t -butyl-4-hydroxystyrene (1) was synthesized according to the literature method 6 starting from 2,6-di-t -butylphenol. As shown in Scheme 1, the polymerization reaction of 1 was carried out by an cationic method in the presence of BF 3 -Et 2 O in methyl
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