Synthesis of a Block Copolymer of Butyl Acrylate with Vinylbutyl Ether Using the Triethylborane–Oxygen Initiating System in a Compensatory Manner

Abstract

The synthesis of a copolymer of butyl acrylate with vinyl butyl ether was carried out by a compensatory method in boiling vinyl butyl ether, at its excess, in the presence of triethyl boron isolated from the complex with hexamethylenediamine and an oxidizing agent. The resulting copolymer was used as a macroinitiator by adding a new portion of butyl acrylate to boiling vinyl butyl ether. Several samples of macroinitiators were obtained with different copolymerization times. As the formation of macromolecules upon copolymerization of butyl acrylate with vinyl butyl ether occurs along two centers of chain growth: oligomeric, formed due to the capture of initiating and growing radicals with a small number of copolymer units by boroxyl radicals, and one with low molecular weight, formed by conventional radical chain termination during initiation by alkyl and alkoxyl radicals, the composition of the isolated copolymer contains an oligomer and a low molecular weight copolymer. In the oligomeric fraction of the copolymer, there are more labile bonds with the boroxyl radical at the end of the chain than in the low molecular weight copolymer; as a result, the addition of butyl acrylate to the solution in vinyl butyl ether of the copolymer isolated from the reaction mixture leads to the formation of a block copolymer with a higher molecular weight, while the molecular weight increases after this, due to the addition of new copolymer units most of all to the oligomeric part of the sample. An increase in the molecular weight of the copolymer due to the grafting of new units predominantly onto the oligomer via a labile bond according to the reversible inhibition scheme leads to an increase in the mass of the samples and noticeable changes in the molecular weight distribution curve. If the sample synthesis time significantly exceeds the dosing time, the revealed effects are weaker, which is associated with the recombination of radicals formed according to the scheme of reversible inhibition, due to the usual radical termination. The presented data indicate that the copolymer of butyl acrylate with vinyl butyl ether synthesized in the presence of triethyl boron and an oxidizing agent during compensatory copolymerization in an excess of vinyl butyl ether is a macroinitiator of the block copolymerization of butyl acrylate with vinyl butyl ether, due to the labile bond of the terminal boroxyl radical.