Properties of copolymers of butyl acrylate with vinyl isobutyl ether obtained using the triethylborane - oxygen system by the compensating method

The synthesis of copolymers of butyl acrylate with vinyl isobutyl ether was carried out by adding the active monomer to the excess of the comonomer when boiling in the presence of triethylborane. An organoelement co-initiator was isolated from a complex with hexamethylenediamine in a solution of vinyl butyl ether, with addition of methacrylic acid in an amount proportional to the amount of amine in moles, together with butyl acrylate. As a co-initiator of triethylborane, air oxygen was present in the reaction mixture at boiling of the vinyl butyl ether. The introduction of butyl acrylate was completed within 20 minutes. After that, the process was stopped (in the first series of samples), or else the reaction mixture was thermostated for another 40 minutes (in the second series of samples). At the end of polymerization, the liquid fraction was distilled off. The copolymer samples were isolated by removing the monomers under vacuum, and their conversion was evaluated gravimetrically by the dry residue. Molecular weight parameters for the samples were determined by gel permeation chromatography. The composition of the copolymers was determined by IR spectroscopy using a calibration graph based on the area of the characteristic peak. The obtained data suggest that during the copolymerization of butyl acrylate with vinyl isobutyl ether, a macromolecular chain is formed along two centers: oligomeric and low-molecular. The formation of an oligomer along with a low-molecular polymer, usually formed under such conditions at traditional radical initiation, is explained by the presence of boroxyl radicals in the reaction mixture, which are known in the oxidation of trialkylboranes. Due to the interaction of the latter with initiating R• or RO• radicals, which are also observed during the oxidation of trialkylboranes, or with oligomeric growing radicals, a growth center of the polymer chain is formed by the mechanism of reversible inhibition with a very low degree of polymerization. Continued thermostating of the reaction mixture after dosing butyl acrylate with methacrylic acid leads to a shift in the oligomeric mode in the direction of increasing the value of molecular weight; accordingly, Mn increases and Mw/Mn decreases. This occurs because the copolymerization process continues in the absence of the initiator due to the reversible inhibition reaction. The time-dependent conversion rate is characterized by an abrupt decrease in the conversion rate by 40-60 %, which is also associated with the transition of the method of forming macromolecules with the predominantly high-speed bimolecular break to a process following the reversible inhibition mechanism according to the scheme, which runs at a much lower rate. The composition of the copolymers is characterized by a slightly higher equimolar content of acrylate, with a higher value of the relative activity of vinyl isobutyl ether, paired with butyl acrylate during copolymerization (rBA = 1.45 ± 0.07; rVBE ≈ 0; rBA = 5.2 ± 1.5; rViBE ≈ 0).