Glass transition breadths and composition profiles of weakly, moderately, and strongly segregating gradient copolymers: experimental results and calculations from self-consistent mean-field theory

Michelle M. Mok, Jungki Kim, Christopher L H Wong, Stephen R. Marrou, Dong Jin Woo, Christine M. Dettmer, Sonbinh T. Nguyen, Christopher J. Ellison, Kenneth R. Shull, John M. Torkelson

Research output: Contribution to journalArticle

71 Scopus citations

Abstract

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 (<40% of the homopolymer T g difference), regardless of gradient design. In strongly segregating systems (S/4-vinylpyridine and S/4-acetoxystyrene (AS)), ΔT gs are observed spanning 70-80% of the homopolymer T g difference. Smallangle X-ray scattering applied to S/AS materials demonstrates a range of temperature-sensitive scattering intensities consistent with the level of segregation observed through their ΔT gs.

Original languageEnglish (US)
Pages (from-to)7863-7876
Number of pages14
JournalMacromolecules
Volume42
Issue number20
DOIs
StatePublished - Oct 27 2009

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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