In this paper, we examine a new block copolymer architecture-cyclic block copolymers. The physical behavior of cyclic polymers, both in solution1 and in the bulk,2-3 has been the subject of continual research. Current issues concern their dynamics4-5 and topological characteristics.6-9 Due to the challenges present in the synthesis of cyclic polymers,10 the morphology of microphase-separated cyclic block copolymer systems has not been investigated previously. Recently, however, well-characterized cyclic polystyrene-poly(2-vinylpyridine) (PS-P2VP) and polystyrene-poly(dimethylsiloxane) (PS-PDMS) block copolymers have been synthesized from their linear triblock precursors.11-13 The morphology of these microphase-separated systems is the topic of the present study.The focus of our study is to probe the effect of loops versus bridges on the morphological characteristics of microphase-separated block copolymer systems. Cyclic A-B diblocks only assume doubly-looped chain conformations in the microphase-separated state, while their linear A-B-A triblock precursors are looped and bridged. We anticipate this difference to be manifest in the relative spacings of their respective microlattices. The microstructural characteristics of these systems are examined through transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) of systems exhibiting varying degrees of quench into the microphase-separated state. These observations are then compared to our theoretical predictions.Cyclic PS-P2VP and PS-PDMS were prepared by end-coupling their linear triblock precursors bis-anionic LiP2VP-PS-P2VPLi and LiPDMS-PS-PDMSLi with l,4-bis(bromomethyl)benzene and Cl2Si(CH3)2, respectively. The details of the synthesis of the precursor triblocks, coupling reactions, and characterization of the block copolymers are given elsewhere.11-13 The molecular characteristics of the cyclic diblock and linear triblock precursors used in this study are shown in
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