The ability of bottlebrush block copolymers (BBCPs) to self-assemble into ordered large periodic structures could greatly expand the scope of photonic and membrane technologies. In this paper, we describe a two-step synthesis of poly(l-lactide)-b-polystyrene (PLLA-b-PS) BBCPs and their rapid thin-film self-assembly. PLLA chains were grown from exo-5-norbornene-2-methanol via ring-opening polymerization (ROP) of l-lactide to produce norbornene-terminated PLLA. Norbonene-terminated PS was prepared using anionic polymerization followed by a termination reaction with exo-5-norbornene-2-carbonyl chloride. PLLA-b-PS BBCPs were prepared from these two norbornenyl macromonomers by a one-pot sequential ring opening metathesis polymerization (ROMP). PLLA-b-PS BBCPs thin-films exhibited cylindrical and lamellar morphologies depending on the relative block volume fractions, with domain sizes of 46–58 nm and periodicities of 70–102 nm. Additionally, nanoporous templates were produced by the selective etching of PLLA blocks from ordered structures. The findings described in this work provide further insight into the controlled synthesis of BBCPs leading to various possible morphologies for applications requiring large periodicities. Moreover, the rapid thin film patterning strategy demonstrated (>5 min) highlights the advantages of using PLLA-b-PS BBCP materials beyond their linear BCP analogues in terms of both dimensions achievable and reduced processing time.
Abstract
A method is given for the quantitative determination of sodium lauryl sulfate in liquid, frozen, powdered, or flake-dried egg white. The egg white is dissolved in water and the protein is precipitated with ethanol and filtered off. The filtrate is evaporated, the residue is dissolved in water, and the pH is adjusted to 5.0. Total alkyl sulfates are titrated with standard benzethonium chloride solution in the presence of chloroform with bromphenol blue indicator. Results are calculated as sodium lauryl sulfate. The formation of the bromphenol bluebenzethonium chloride complex, when excess benzethonium chloride is present, is taken as the end point. The blue-green complex is soluble in the chloroform. Overall recoveries of sodium lauryl sulfate from egg whites ranged from 94 to 100%. Collaborative study of the method is recommended.
Magnetic susceptibility measurements have shown that the chromium atoms in the toluene–chromyl chloride complex are tetravalent. The structure of the complex and the reaction mechanism are discussed. Spectroscopic evidence has been found of the initial formation of a π-complex. The products of reaction of chromyl chloride and ethylbenzene, isopropylbenzene, tetralin, and indane have been determined.
Precise Synthesis and Thin Film Self-Assembly of PLLA-b-PS Bottlebrush Block Copolymers