Aggregative behavior of AB and ABC block copolymers in the solid phase and in a nonselective solvent

Abstract

Effects of the amount of chemically dissimilar blocks (two or three) and their polarity on the aggregative behavior of АВ and АВС linear block copolymers of various compositions that are based on polystyrene, poly(n-butyl acrylate), and either poly(acrylic acid) or poly(tert-butyl acrylate) in bulk and in the nonselective solvent DMF are studied via differential scanning calorimetry and dynamic light scattering. АВ block copolymers composed of two chemically dissimilar blocks in the diluted solution in DMF are fully dispersed into macromolecular coils. However, the simultaneous incorporation of three incompatible blocks of different polarities (polystyrene, poly(acrylic acid), and poly(n-butyl acrylate)) into the copolymer is accompanied by a well-defined segregation of blocks in the nonselective solvent, regardless of the composition of the block copolymer and the length and sequence of blocks. This phenomenon makes itself evident as the formation of intermacromolecular aggregates in diluted solutions with a mean hydrodynamic radius of 60–120 nm that are stable in the range 10–60°C. A decrease in the level of the thermodynamic incompatibility of blocks (replacement of a poly(acrylic acid) polar block with a less polar poly(tert-butyl acrylate) block) or the selective improvement of solvent quality with respect to the polar block (the addition of LiBr to DMF) suppresses the segregation of blocks and may lead to the formation of a molecularly dispersed solution of the block copolymer.