(663b) Order-Disorder Transitions in Strongly-Segregated Block Copolymers

Leibler's seminal work, the mean field treatment on the block copolymer thermodynamics near the order-disorder transition has given valuable understandings on this subject, but it assumes an infinitely large degree of polymerization (N) with an infinitesimally small Flory-Huggins interaction parameter (χ). All experimentally accessible block copolymer compounds have N and χ far from these limits. The correction of mean field theory with the fluctuation effect from finite N near ODT has been attempted, but it is still not successful. We have investigated the thermodynamics of poly(1,4-isoprene-b-DL-lactide) diblock copolymers near the ODT with small N and relatively large χ using small angle X-ray scattering (SAXS), dynamic mechanical spectroscopy (DMS), and differential scanning calorimetry (DSC) techniques. These studies provide fresh insights into the role of fluctuations on the state of segregation and ordering kinetics in symmetric and asymmetric diblock copolymers, prompting new questions regarding the application of mean-field and fluctuation corrected theories to block copolymer melts with finite molecular weights.