Brad S. Lokitz

RAFT-synthesized diblock and triblock copolymers: thermally-induced supramolecular assembly in aqueous media

This review highlights recent advances in the synthesis of functional, temperature-responsive, water-soluble block copolymers, including particular focus on the results obtained by employing reversible addition–fragmentation chain transfer (RAFT) polymerization. The applicability of the RAFT process for the polymerization of functional monomers under a diverse range of experimental conditions has facilitated the synthesis of water-soluble (co)polymers that were previously inaccessible. Unprecedented control afforded by RAFT in homogeneous aqueous media allows well-defined polymeric systems to be prepared without stringent purification techniques and under increasingly “green” conditions while maintaining the ability to tailor many of the macromolecular characteristics (molecular weight, chain topology, copolymer composition, functionality, etc.) that affect self-assembly in solution. Block copolymer formation and postpolymerization modification utilizing crosslinking and copper-catalyzed azide–alkyne “click” chemistry are described, with attention being paid to their ability to control copolymer structure for subsequent self-assembly in response to changes in temperature.

Chiroptical Properties of Homopolymers and Block Copolymers Synthesized From the Enantiomeric Monomers N-acryloyl-L-alanine and N-acryloyl-D-alanine Using Aqueous RAFT Polymerization

Chiral homo- and block copolymers based on the enantiomeric monomers N-acryloyl-l-alanine (ALAL) and N-acryloyl-d-alanine (ADAL) were prepared directly in water using controlled reversible addition–fragmentation chain transfer (RAFT) polymerization. The polymerization of the chiral monomers proceeded in a controlled fashion producing the respective homopolymers, block copolymers, and a statistical copolymer with targeted molecular weights and narrow molecular weight distributions. The chiroptical activity of these biomimetic polymers and their analogous model compounds was investigated using circular dichroism (CD). P(ALAL) and P(ADAL) were shown to be optically active exhibiting mirror image CD spectra. In addition, statistical and enantiomeric block copolymers prepared at 1:1 stochiometric ratios exhibited virtually no optical activity.