Homologous series of bottlebrush polymers were synthesized using a robust and efficient method, refined from previously published procedures combining ATRP, azide- alkyne click chemistry, and ROMP. The resulting bottlebrush polymers reach Ns~100 and Nb>1000, comparable to the largest values previously reported in the literature. The development of a macromonomer purification procedure utilizing flash chromatography using a gradient solvent system allowed for the facile and efficient purification of macromonomer, resulting in greater conversion than had been previously observed in this type of system[33].
By simplifying macromonomer purification and thereby improving the repeatability and conversion in the ROMP of macromonomers, the protocol described here enabled bottlebrushes with systematic and reproducible Nb (Tables 2.2, 2.3, and 2.4) to be made from polystyrene macromonomers with Ns=25 and 65. The procedure was not
affected significantly by deuterium labeling and allowed for matched pairs (same Nb and Ns) of bottlebrushes with PS and dPS side-chains. This provided the necessary contrast labeling for neutron scattering experiments to isolate the conformation of the backbone in a bottlebrush polymer and compare it to the overall object conformation (Chapter 3).
Another series of bottlebrushes were made using tert-butyl acrylate as the side chain monomer, and this was seen to reach even higher side-chain lengths of 40 and 95 repeat units and similar backbone lengths to the polystyrene bottlebrushes; This allows for study of the effect of side-chain chemistry and flexibility upon the bottlebrush behavior.
Through the hydrolysis of the tert-butyl ester it was also possible to transform the PtBA based brushes into ones with poly(acrylic acid) side-chains with >80% deprotection. This allows for the effect of pH and salt concentration upon a bottlebrush polymer to be examined using a series of thoroughly characterized polymers.
The development of this robust, modular, and accessible synthetic method also opens up opportunities for the creation of more complex bottlebrush structures (e.g.
polypeptide, block copolymer, or multivalent side-chains). Such bottlebrushes have been predicted to have very complex internal structures[60, 61] and the availability of the materials will enable experimental validation of theory to begin.
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Chapter 3