Patricia R. Bachler

Hyperbranched polymers via RAFT self-condensing vinyl polymerization

RAFT-mediated self-condensing vinyl polymerization is a promising synthetic tool to create well-defined hyperbranched polymers. The functional group tolerance of RAFT, as well as the inherent ability to install readily functionalizable end groups, allow for formation of highly functionalized materials with unique properties. Due to the controlled nature of RAFT, it is possible to synthesize polymers with predetermined branching frequencies, resulting in materials with tunable properties and readily tailored macromolecular structure. This minireview gives an overview of this emerging field, emphasizing structural variety, monomer functionality, and post-polymerization modifications that have been employed to prepare previously inaccessible materials.

Hyperbranched Poly(N-(2-hydroxypropyl) methacrylamide) via RAFT Self-Condensing Vinyl Polymerization

We report the first synthesis of hyperbranched poly(N-(2-hydroxypropyl) methacrylamide) (HB-PHPMA) using reversible addition–fragmentation chain transfer (RAFT) self-condensing vinyl polymerization (SCVP). The synthesis of these complex, well-defined architectures involved the copolymerization of HPMA with a chain transfer monomer (CTM). The polymerization kinetics, as well as the effects of initiator concentration and the ratio of monomer to CTM were studied. The resulting polymers show high molecular weights and controlled branching frequencies. Due to their inherent amphiphilic nature, these hyperbranched structures self-assemble into aggregates in water. Additionally, we determined the cloud point of the HB-PHPMA to be in the range of sub-ambient temperature to 40 °C. This approach provides access to a new class of thermoresponsive PHPMA polymers with potential to be used in drug delivery and other biological applications.

Aminobisphosphonate Polymers via RAFT and a Multicomponent Kabachnik–Fields Reaction

Polyacrylamides containing pendant aminobisphosphonate groups are synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization and a multicomponent postpolymerization functionalization reaction. A Moedritzer-Irani reaction installs the phosphonic acid groups on well-defined, RAFT-generated polymers bearing a pendant amine. An alternate route to the same materials is developed utilizing a three-component Kabachnik-Fields reaction and subsequent dealkylation. Kinetics of the RAFT polymerization of the polymer precursor are studied. Successful functionalization is demonstrated by NMR and FTIR spectroscopy and elemental analysis of the final polymers.

Functional precision polymers via ADMET polymerization

Acyclic diene metathesis (ADMET) polymerization is a powerful and versatile technique for creating precision polymers. Specialized and well-defined materials, as well as improved understanding of structure–property relationships, can be achieved by ADMET polymerization of designed symmetrical monomer structures. The introduction of functional groups into ADMET polymers, from polar groups to biodegradable moieties, has resulted in an array of precision functional materials with distinct properties and interesting applications.Graphical abstract

Modular segmented hyperbranched copolymers

Modular segmented hyperbranched polymers, amenable to facile post-polymerization functionalization, were created via two distinct approaches. Self-condensing vinyl polymerization via reversible addition–fragmentation chain transfer (RAFT) polymerization and RAFT polymerization with a divinyl comonomer were employed to create well-defined highly branched materials containing activated esters amenable to highly efficient functionalization in a modular manner.