Effect of Gradient Sequencing on Copolymer Order–Disorder Transitions: Phase Behavior of Styrene/n-Butyl Acrylate Block and Gradient Copolymers

• Published in: Macromolecules Vol. 44; no. 15; pp. 6220 - 6226
• Main Authors: Mok, Michelle M, Ellison, Christopher J, Torkelson, John M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 09.08.2011
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Thermal and thermodynamic properties; Viscoelasticity; Structure effect; Domain structure; Phase diagram; Diblock copolymer; Temperature effect; Gradient copolymer; Order disorder transformation; Experimental study; Butyl acrylate copolymer; Styrene copolymer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma201080n

We investigate the effect of gradient sequence distribution in copolymers on order–disorder transitions, using rheometry and small-angle X-ray scattering to compare the phase behavior of styrene/n-butyl acrylate (S/nBA) block and gradient copolymers. Relative to block sequencing, gradient sequencing increases the molecular weight necessary to induce phase segregation by over 3-fold, directly consistent with previous predictions from theory. Results also suggest the existence of both upper and lower order–disorder transitions in a higher molecular weight S/nBA gradient copolymer, made accessible by the shift in order–disorder temperatures from gradient sequencing. The combination of transitions is speculated to be inaccessible in S/nBA block copolymer systems due to their overlap at even modest molecular weights and also their location on the phase diagram relative to the polystyrene glass transition temperature. Finally, we discuss the potential impacts of polydispersity and chain-to-chain monomer sequence variation on gradient copolymer phase segregation.