Well-Ordered Polymer Melts with 5 nm Lamellar Domains from Blends of a Disordered Block Copolymer and a Selectively Associating Homopolymer of Low or High Molar Mass

The use of short chain block copolymer melts as nanostructured templates with sub-10 nm domains is often limited by their low segregation strength (chi N). Since increasing molar mass to strengthen segregation also increases the interdomain spacing of block copolymer melts, it is more desirable to increase the Hory-Huggins segment-segment interaction parameter, chi, to produce strong segregation. We have recently shown that poly(oxyethylene-oxypropylene-oxyethylene) block copolymer melts can undergo disorder-to-order transition when blended with a selectively associating homopolymer that can hydrogen bond with one of the blocks. Here, we study the effect of the molar mass of poly(acrylic acid) in the range 1-13 times that of the copolymer on the segregation of a 6.5 kg/mol poly(oxyethylene-oxypropylene-oxyethylene) copolymer melt. The neat copolymer is disordered, and the addition of poly(acrylic acid) resulted in a well-ordered lamellar morphology with an interdomain spacing of 10 +/- 1.0 nm. Using small-angle and ultrasmall-angle X-ray scattering, we found that the blends remain well ordered at 80 degrees C over the entire range of homopolymer chain lengths. A small increase in the interdomain spacing of the lamellae and an order-order transition from lamellae-to-cylindrical morphology was observed in all blends as a function of increasing homopolymer concentration. The trends observed in experiments were validated by self-consistent field theoretical simulations.