Comparison of the Lamellar Morphology of Microphase-Separated Cyclic Block Copolymers and Their Linear Precursors

Abstract

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

Cyclic polymers: Synthetic strategies and physical properties

“…From another pair of cyclic DBCPs and triblock precursor, a Ds c /Ds l ratio around 0.93 6 0.02 was reported (see below). 305 When the Ds c of the cyclic PS-PI DBCP was compared to an analogous linear PS-PI DBCP, 306 a Ds c /Ds l ratio of 0.61 was found in agreement with theoretical calculations. 307 An enormous body of morphological studies was elaborated from a pair of cyclic and linear PS-PI DBCPs composed of $ 290 styrene and 110 isoprene units.…”

“…Almost all authors who worked on syntheses and characterization of cyclic DBCPs 75,80,81,83,91,[93][94][95][300][301][302][303][304][305] were interested in the phenomenon of phase separation. It is long known that nearly all polymers of different structure (even if the difference is small, e.g., polyethylene/polypropylene) are not miscible in the melt, because the entropy of mixing is too low.…”

“…TEM and SAXS measurements revealed a ratio of domain spacings Ds c /Ds l around 0.91 in analogy to other PS-DBCPs. 305 From cyclic PS-PDMS diblock copolymers, the following results were reported. 79,305 A cyclic DBCP and its triblock precursor having M w s around 45 kDa were compared in cyclohexane at temperatures in the range of 12-30 C. 79 By static and dynamic light scattering measurements no significant conformational changes were detectable for the cyclic DBCP.…”

“…305 From cyclic PS-PDMS diblock copolymers, the following results were reported. 79,305 A cyclic DBCP and its triblock precursor having M w s around 45 kDa were compared in cyclohexane at temperatures in the range of 12-30 C. 79 By static and dynamic light scattering measurements no significant conformational changes were detectable for the cyclic DBCP. Yet, when the solution of triblock copolymer was cooled below 21 C, a rapid aggregation and micelle formation was observed as indicated by a change of the second virial coefficient, a change of R g and a change of the intensity auto acceleration funnels.…”

Synthesis and characterization of macrocyclic vinyl aromatic polymers

“…The characterization of these novel block copolymers was carried out with the aforementioned methods and in two cases by electron microscopy as well. 52 …”