Unique ordering of gradient copolymers: Analysis, consequences and applications

Gradient copolymers are a type of linear copolymer where the distribution of comonomers varies smoothly over the entire chain, from mostly A monomer to mostly B monomer. Theoretical works have predicted that gradient copolymers phase segregate to give sinusoidal composition profiles spanning a wide range of compositions. The specific range of compositional amplitudes is expected to increase gradually with increasing chi N compared to block copolymers. This suggests that gradient copolymers should exhibit behavior akin to block copolymers, due to their phase segregation properties, as well as to nanoheterogeneous materials, due to the sampling of wide ranges of compositions. This work investigates analysis techniques used for these classes of materials for studying phase segregation in neat gradient copolymers, specifically evaluating the effects of polymer chain architecture, such as molecular weight, copolymer species and gradient design. Controlled radical polymerization was used to prepare gradient copolymers with controlled chain architectures.;To evaluate their nanoheterogeneity, techniques established for investigation of glass transitions were applied to study relaxation breadths in gradient copolymers. Single glass transition regions of considerable breadth were found; these breadths were extremely sensitive to details of chain architecture in systems of moderate segregation strength. Experimental results were compared to predictions from mean-field theory and found to be in good agreement, providing strong support for the formation of sinusoidal composition profiles.;To evaluate gradient copolymer phase segregation properties, techniques established for studying block copolymer phase segregation were applied to investigate their behavior as a function of temperature. Samples of intermediate phase segregation exhibited temperaturedependent behavior over extended temperature ranges, supporting predictions that gradient copolymers exhibit gradually changing composition amplitudes with respect to chiN. We also demonstrated the potential for critical point shifting through gradient sequence distribution, bringing to light a new degree of freedom for phase transition design; in fact, the extremely rare combination of both upper and lower critical ordering transitions was observed in one comonomer system. Finally, gradient copolymers thin films were demonstrated to phase segregate into island and hole structures, but with much larger features than those of block copolymers, consistent with their lower driving force to phase segregate.