Synthesis of acrylonitrile-butyl acrylate copolymers under heterophase conditions: thermal behavior and melt rheology

Synthesis of copolymers of acrylonitrile with n-butylacrylate for obtaining precursors of carbon fibres suitable for melt processing has been investigated by heterophase polymerisation in water and in water-alcohol mixtures. It has been shown that precipitation polymerization in water leads to the formation of copolymers that are unable to transition to a viscous state, which is probably due to their high compositional heterogeneity.
The use of water-alcohol mixtures (water/isopropanol, water/ethanol) allows equalizing the solubility of polar and low-polar monomers, which increases the uniformity of the copolymer composition. The formulation parameters (water/alcohol ratio, concentration of initiator and molecular weight regulator) have been established to obtain copolymers with a given content of n-butyl acrylate units (10–15 mol.%) and a weight-average molecular weight in the range of (20–45)×10³ g/mol.
The thermal behavior and viscoelastic properties of copolymers, including mixtures with a plasticizer (ethylene or propylene carbonate), have been studied using differential scanning calorimetry and rheometry methods. Copolymers with Mw of about 20×10³ g/mol and BA content of about 15 mol.%, obtained in a water/isopropanol system, in combination with 10–15 wt.% ethylene carbonate, have been shown to be most effective in reducing melt viscosity.
It has been found that the behavior of copolymer melts produced by heterophase polymerization differs from that of similar copolymers produced by solution polymerization and requires higher temperatures or more plasticizer to achieve flowability.

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