1. Contribution from the Matson group.
The Synthesis of Bottlebrush Polymers: Grafting-From vs. Transfer-To
Karen Tran, Scott Radzinski, Jeffrey Foster, Samantha Scannelli, John Matson
Bottlebrush polymers are becoming much more relevant to the polymer
industry due to their structures, shape persistence, nanoscopic dimensions, and
unique mechanical and rheological properties. [1]
They differ from linear polymers in a
sense that they do not interact via chain entanglements, rather they are encompassed
with polymeric side-chains grafted to a polymer backbone. Because of the grafting
density and steric repulsion between polymeric neighbors, the backbone is able to
adopt a chain-extended conformation. The size and shape of bottlebrush polymers
also allows for the in vivo delivery of therapeutic agents.
Bottlebrush polymers can be prepared in one of four approaches: the grafting-
from strategy, the grafting-to methodology, the grafting-through or macromonomer
(MM) approach, or the transfer-to approach. The transfer-to approach is a mix of the
grafting-from and grafting-to; polymeric radicals will detach from the bottlebrush
backbone and propagate freely in solution while eventually returning to the backbone
through a chain-transfer reaction with a pendant chain-transfer agent (CTA). The
transfer-to approach is used for bottlebrush polymers with lower dispersities and higher
possible conversions compared to usual RAFT grafting-from methods while the
grafting-from strategy is used to synthesize bottlebrush polymers with relatively higher
molecular weights.
Chain transfer agents were synthesized and polymerized to form the backbone
polymer to perform transfer-to and grafting-from polymerizations. The two techniques
will then be compared using size exclusion chromatography (SEC) and nuclear
magnetic resonance spectroscopy (NMR) to highlight the differences.
[1] S. C. Radzinski, J. C. Foster and J. B. Matson, Polymer Chemistry 2015, 6, 5643-
5652.