The Effect of Segregation Strength on Network Formation in ABC Triblocks

The effects of segregation strength on network phases were investigated in linear poly(isoprene-$b$-styrene-$b$-ethylene oxide) triblocks with various molecular weights. Morphological behavior at higher molecular weights indicated that network long-range order decreased as the polymer molecular weight increased. The signature Q$^{230}$ and O$^{70}$ X-ray scattering patterns were retained in the lowest molecular weight specimens, while the highest molecular weight data were ambiguous, displaying broad peaks at approximately q* and 2q*. TEM results on these materials showed network-like structures with reduced long-range order. It is unclear whether the highest molecular weight structures represent poorly ordered versions of equilibrium networks or kinetically trapped metastable states. Interestingly, this effect was specific to triply-periodic structures, as lamellar samples of comparable molecular weights displayed excellent long-range order. The reduced organization of the networks likely arises from a decrease in coordinated chain motion as a result of the different diffusion mechanisms available to lamellar versus triply-periodic microstructures.