ALTERNATING COPOLYMERIZATION THROUGH THE COMPLEXES OF CONJUGATED VINYL MONOMERS-ALKYLALUMINUM HALIDES

A vinyl monomer that has the nitrile or carbonyl group conjugated to t he C=C double bond, such as acrylonitrile, methyl acrylate, and methyl methacrylate, forms a complex with an alkylaluminum halide, and the c omplex resets spontaneously with a hydrocarbon monomer such as styrene , propylene, or ethylene, giving a high molecular weight copolymer. Th e copolymers always contain the two monomer units in 1:1 ratio. Thus s tyrene, copolymerized with methyl acrylate or methyl methacrylate in t he presence of ethylaluminum sesquichloride in homogeneous toluene sol ution, gives such an equimolar copolymer regardless of the initial mon omer compositions. The NMR spectra of these copolymers are distinctly different from those of the equimolar copolymers obtained with azobisi sobutyronitrile as initiator and have simpler and well separated patte rns. The copolymers and the corresponding radical copolymers appear to be amorphous, judged by their x-ray diffraction patterns and their di fferential thermal analyses. Their infrared spectra resemble each othe r very closely. Hence, the difference in the NMR spectra may be ascrib ed to the matter of the sequence distribution. The infrared spectrum o f ethylene-methyl acrylate copolymer shows no absorption near 720 cm.( -1) due to the methylene sequence arising from ethylene-ethylene linka ge. These experimental data lead to the inference that the equimolar c opolymers obtained in this work may have an alternating sequence.