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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 (� N). Since increasing molar mass to strengthen segregation also increases the interdomain spacing of block copolymer melts, it is more desirable to increase the Flory-Huggins segment-segment interaction parameter, � , 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 °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.