Abstract
The microphase-separated morphologies of a series of four poly[styrene-b-(d-styrene-grad-isoprene)-b-isoprene] tapered block copolymers have been explored in this work with small-angle neutron scattering (SANS) and transmission electron microscopy (TEM). Each of the copolymers consists of two pure end blocks and a selectively deuterated statistical middle block, across which exists a composition gradient. The middle-block fraction varies from 10 to 40 wt% in this series. All four materials are found to exhibit ordered lamellar morphologies, in which the microdomain periodicities do not differ significantly from that of the corresponding poly(styrene-b-isoprene) diblock copolymer of equal molecular weight (M=200 kDa). These results are compared with predictions from recent theoretical developments. In contrast, a 100 kDa poly[styrene-b-(styrene-ran-isoprene)-b-isoprene] triblock copolymer, possessing a 40 wt% statistical (random) middle block with an average composition of 50 wt% styrene, is observed to order into a lamellar-spherical three-microphase morphology upon block segregation
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