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New developments in bond‐forming initiation: Lewis acids accelerate spontaneous initiation of copolymerizations of olefins and dienes
Author(s) -
Hall H.K.,
Padias Anne Buyle,
Srisiri Warunee,
Mikhael Michael G.,
Wang Hua,
Chu Guobei
Publication year - 1995
Publication title -
macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 1022-1360
DOI - 10.1002/masy.19950950120
Subject(s) - lewis acids and bases , chemistry , polymer chemistry , copolymer , electrophile , lone pair , monomer , acrylonitrile , polymerization , styrene , cycloaddition , photochemistry , organic chemistry , catalysis , polymer , molecule
Lewis acids have long been known to influence the free radical propagation of donor‐acceptor olefin monomer pairs, changing random copolymers into strictly alternating ones, by complexing to the lone pair electrons of the acceptor monomer, and enhancing its electron‐poor character. This work reports that this same interaction enhances the rates of the spontaneous initiation in these systems. In agreement with earlier literature, we found that styrene‐acrylonitrile copolymerizations proceed readily in the presence of ZnCl 2 at 40° where no copolymerization occurs in the absence of the Lewis acid. p‐Methoxystyrene and isobutyl vinyl ether with AN gave more complicated results, due to competitive complexation of oxygen lone pairs with ZnCl 2 . Reaction of more electrophilic olefins with these donor monomers gave steadily increasing rates and a shift in product from spontaneous copolymer to inverse Diels‐Alder adduct (in the case of ester substituents) to cyclobutane. As for substituted diene monomers as the donor component, reactions of isoprene and 2,3‐dimethylbutadiene with AN are accelerated in the presence of ZnCl 2 and the Lewis acid affects the competition between the [4+2] cycloaddition and the copolymerization. All of these results are interpreted in the context of formation of Lewis‐acid complexed initiating diradicals by bond‐formation.