Glass Transition Breadths and Composition Profiles of Weakly, Moderately, and Strongly Segregating Gradient Copolymers: Experimental Results and Calculations from Self-Consistent Mean-Field Theory

• Published in: Macromolecules 2009-10, Vol.42 (20), p.7863-7876
• Main Authors: Mok, Michelle M, Kim, Jungki, Wong, Christopher L. H, Marrou, Stephen R, Woo, Dong Jin, Dettmer, Christine M, Nguyen, SonBinh T, Ellison, Christopher J, Shull, Kenneth R, Torkelson, John M
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Thermal and thermodynamic properties
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma9009802

Gradient copolymers are prepared from comonomer systems with a range of segregation strengths and homopolymer glass transition temperature (T g) differences to explore the breadths that can be achieved by their single, continuous glass transition regions compared to random and block copolymers. A variety of chain architectures are synthesized using semibatch nitroxide-mediated controlled radical polymerization, including linear gradients, sigmoidal gradients, blocky gradients, and blocky random cases. The derivative of the differential scanning calorimetry heat curve is used to extract T g breadths (ΔT gs). For the first time, these T g breadths are compared against values derived from nanophase separation levels predicted by self-consistent mean-field theory and found to be in good accord. In moderately segregating systems (styrene (S)/n-butyl acrylate and S/tert-butyl acrylate), ΔT g may be tuned dramatically via gradient structure and molecular weight; e.g., a T g breadth exceeding 100 °C, or >65% of the homopolymer T g difference, is obtained with a sigmoidal gradient copolymer of S/n-butyl acrylate. In the very weakly segregating system (S/n-butyl methacrylate), ΔT g remains narrow (