Thermal stability of polystyrene- b-poly(ethylene/propylene) diblock copolymer micelles in paraffinic solvents

• Published in: Polymer (Guilford) 1989-11, Vol.30 (11), p.2038-2046
• Main Authors: Schouten, M., Dorrepaal, J., Stassen, W.J.M., Vlak, W.A.H.M., Mortensen, K.
• Format: Article
• Language: English
• Subjects: Applied sciences; diblock copolymers; Exact sciences and technology; micelles; Organic polymers; Physicochemistry of polymers; Properties and characterization; small-angle neutron scattering; Solution and gel properties; thermal stability
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/0032-3861(89)90291-7

The micelles formed by a polystyrene- b-poly(ethylene/propylene) diblock copolymer in two paraffinic solvents have been investigated with small-angle neutron scattering. At room temperature, the micelles consist of a core composed of insoluble polystyrene blocks surrounded by a well solubilized layer of ethylene/propylene chains. At polymer concentrations as low as 0.5% by weight, these micelles interact strongly, resulting in a ‘fluid-like‘ distribution of the micelles over the solution volume. For a 1% concentration in n-dodecane the degree of intermicellar interaction diminishes dramatically when the temperature is raised from 100 to 140°C. Above 100°C the micelles start to decrease in size gradually, their total number, however, remaining the same. In combination with nuclear magnetic resonance and viscometry, neutron scattering suggests that it is only at elevated temperatures that polymer molecules are able to leave the micelle and enter the solution as individual molecules. It is discussed how this explains the sharp viscosity drop of these polymer solutions around 80°C.