Polystyrene-block-poly(ethylene oxide) Bottlebrush Block Copolymer Morphology Transitions: Influence of Side Chain Length and Volume Fraction

Abstract

A systematic study was conducted to investigate the morphology transitions that occur in polystyrene-block-poly(ethylene oxide) (PS-b-PEO) bottlebrush block copolymers (BBCP) upon varying PEO volume fraction ( f PEO ) from 22% to 81%. A series of PS-b-PEO BBCPs with different PEO side chain lengths were prepared using ring-opening metathesis polymerization (ROMP) of PEO−norbornene (PEO-NB) (M n ∼ 0.75, 2.0, or 5.0 kg/mol) and PS−norbornene (PS-NB) (M n ∼ 3.5 kg/mol) macromonomers (MM). A map of f PEO versus side chain asymmetry (M n (PEO-NB)/ M n (PS-NB)) was constructed to describe the BBCP phase behavior. Symmetric and asymmetric lamellar morphologies were observed in the BBCPs over an exceptionally wide range of f PEO from 28% to 72%. At high f PEO , crystallization of PEO was evident. Temperaturecontrolled SAXS and WAXS revealed the presence of high order reflections arising from phase segregation above the PEO melting point. A microphase transition temperature T MST was observed over a temperature range of 150−180 °C. This temperature was relatively insensitive to both side chain length and volume fraction variations. The findings in this study provide insight into the rich phase behavior of this relatively new class of macromolecules and may lay the groundwork for their use as templates directing the fabrication of functional materials.

Manipulating the ABCs of self-assembly via low-χ block polymer design

“…S5.) Exposing L, S, and O to RuO 4 vapor results in unstained, slightly stained, and strongly stained domains, respectively, as deduced from literature results: PS is selectively stained in PLA/PS mixtures (28,29), and PEO is stained to a greater extent than PS (30,31). Surprisingly, the extent of staining and layer widths observed by transmission electron microscopy (TEM) are completely inconsistent with both the side-chain volume fractions measured by (Fig.…”

Recent progress in block copolymer crystallization

“…Each graft M n was varied over a range of f PEO = 0.22‐0.81. Gai et al . found that lamellar and cylindrical phase‐separated morphologies were observed dependent on f PEO though somewhat independent of M n PEO .…”

“…Here, blocks are tethered/constrained in ways different than the single tether; however, the crystallization behavior is related. Recent work has been focused on the morphologies of highly branched copolymers, such as graft copolymers, brush copolymers, and hyperbranched copolymers . For this review, we have focused only on highly branched BCP architectures (molecular schematics in Figure ) where polymer chains are involved in the crystallization process.…”

“…Brush copolymers of varying architectures were used to study the crystallization of PEO, PCL, and stereo PLLA/PDLA side chains . In one PEO study, a poly(norbornene) backbone was grafted with PS and PEO chains in a BCP type architecture where PS chains were grafted on one half while PEO chains were grafted on the other to form bottlebrush block copolymers (BBCP) . Each graft M n was varied over a range of f PEO = 0.22‐0.81.…”

“…Temperature‐controlled SAXS and WAXS 1D profiles of PS‐PEO BBCPs containing high volume fractions of PEO: f PEO = (A) 0.79 ( M n PS = 2k) (B) 0.81 ( M n PS = 5k) (C) 0.71 ( M n PS = 2k) and (D) 0.72 ( M n PS = 5k). (Reproduced from with permission from the American Chemical Society)…”