Effect of ZnCl₂ on the spontaneous copolymerization of methyl acrylate with substituted 1,3‐dienes

Abstract

The reactions of the mildly electron-poor olefin methyl acrylate (MA) with three electron-rich substituted hydrocarbon 1,3-dienes, namely 2,3-dimethyl-1,3-butadiene (DMB), 4-methyl-1,3-pentadiene (MPD) and isoprene (IP) were investigated in 1,2-dichloroethane in the presence of various amounts of zinc chloride at different temperatures. ZnC1, complexes with the ester group of MA and increases the MA's electron-poor character and therefore its tendency towards reactions with electron-rich dienes. In the absence of ZnCl,, no reaction occurs between the investigated dienes and MA under the used reaction conditions. Both alternating copolymers and [4+2] cycloadducts formed spontaneously in the presence of ZnC1, even at room temperature.The structure ofthe diene and its nucleophilicity control the product distribution.For the DMB and IP systems, raising the reaction temperature and increasing the ZnC1, concentration enhance the overall reaction rate and in most cases also favor the cycloaddition over the copolymerization. IP is less reactive than DMB. With MPD only copolymer is formed because the two terminal methyl groups retard the concerted [4+2] cycloaddition.These results are in agreement with a postulated mechanism involving competition between the formation of a n-allyl2-hexene-1,6-diradical, capable of initiating free radical copolymerization, and concerted [4+2] Diels-Alder cycloaddition.

A paradigm for the mechanisms and products of spontaneous polymerizations

“…In totally analogous fashion, on reacting 2,3‐dimethylbutadiene with acrylonitrile in the presence of zinc chloride as the Lewis acid, free radical copolymerization competed with concerted cycloadditions; higher rates were observed with than without Lewis acid 74. These reactions were also investigated using 1‐methylbutadiene, 1,1‐dimethylbutadiene, and indene as the dienes, acrylonitrile and methyl acrylate as the electrophilic olefin, and lithium perchlorate or zinc chloride as the Lewis acid (refs 75,7677…”

Tetrakis(pyridine)ruthenium Trans Complexes of Phenylcyanamide Ligands: Crystallography, Electronic Absorption Spectroscopy, and Cyclic Voltammetry

“…In this regard, the study of conductive organic polymeric and metallic coordination polymeric materials − holds great interest. Organic polymers, such as polyaniline and polythiophene, are of interest not only for their high conductivity (i.e., between 10 and 100 S cm -1 when doped) but also for their unique photonic and optical properties. Likewise, coordination polymers also hold promise as novel materials because of their magnetic, nonlinear optical, and conductive 4 properties.…”

“…Likewise, coordination polymers also hold promise as novel materials because of their magnetic, nonlinear optical, and conductive 4 properties. Development of such systems has been hampered by mediocre synthetic routes, which produce poorly defined, low molecular weight, insoluble, and often intractable products, and much work is currently directed toward developing strategies that will produce well-defined architectures. − …”

“…Development of such systems has been hampered by mediocre synthetic routes, which produce poorly defined, low molecular weight, insoluble, and often intractable products, and much work is currently directed toward developing strategies that will produce well-defined architectures. [2][3][4][5][6][7][8][9][10][11][12] We are attempting to construct conductive organic polymer chains that are cross-linked by cyanamide anion groups to a coordination complex: Conductivity within these linked systems will arise provided the polymer pπ orbitals and the metal dπ orbital are both symmetry and energy matched. Our extensive studies of mixedvalence dinuclear ruthenium complexes incorporating the 1,4dicyanamidobenzene dianion bridging ligand have shown that the magnitude of metal-metal coupling can be dramatically perturbed by the nature of either the inner or the outer coordination sphere.…”

Organic and polymer chemistry of electrophilic tri‐ and tetrasubstituted ethylenes

“…Zinc chloride also accelerated the copolymerization of acrylonitrile or methyl acrylate with 1,3‐dienes 102, 103. Catalysis with aluminum Lewis acids increased the reactivity of acrylonitrile or methyl acrylate, allowing copolymerization with a hydrocarbon macromonomer, but in this case the Lewis acid probably initiated not by enhancing the putative tetramethylene reactivity but instead through the oxidative decomposition of itself 104…”