科研之友
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摘要
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 (Delta T(g)s). 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. fit moderately segregating systems (styrene (S)/n-butyl acrylate and S/tert-butyl acrylate), Delta T(g) may be tuned dramatically via gradient structure and molecular weight; e.g., a T(g) breadth exceeding 100 degrees 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), Delta T(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)), Delta T(g)s are observed spanning 70-80% of the homopolymer T(g) difference. Small-angle X-ray scattering applied to S/AS materials demonstrates a range of temperature-senstitive scattering intensities consistent with the level of segregation observed through their Delta T(g)s.
- 出版日期2009-10-27
- 单位西北大学
