Synthesis of Star Polymers with Epoxide-Containing Highly Branched Cores by Low-Catalyst Concentration Atom Transfer Radical Polymerization and Post-Polymerization Modifications

Abstract

Star polymers were synthesized by atom transfer radical polymerization (ATRP) using a "core first" approach. Multibrominated, highly branched functional polymers were first synthesized by copolymerizing an epoxide-containing monomer, glycidyl methacrylate (GMA), with divinyl crosslinkers, ethylene glycol dimethacrylate or the reductively degradable bis(2-methacryloyloxyethyl) disulfide, in the presence of an efficient chain transfer agent, CBr 4 . Multiple alkyl bromide chain end groups were present in the branched polymers, which were successfully used as multifunctional macroinitiators, from which both polyacrylateand polymethacrylate-type arms were grown under low catalyst concentration ATRP conditions. Due to the ability of epoxides to reduce Cu II to Cu I complexes, the low catalyst-concentration ATRP chain extensions were performed in the absence of any externally added reducing agents. The cores of the obtained stars, contained numerous epoxide functionalities, originating from GMA, and were efficiently modified using reactions with a variety of tertiary aliphatic amines to afford star polymers with hydrophilic, cationic cores. Ring-opening of the oxirane rings in polyGMA with a pyridine derivative, nicotinamide, in

Cationic branched polymers for cellular delivery of negatively charged cargo

“…We recently reported kinetics for reactions between epoxide and amines in linear polyGMA, providing insight as to the efficiency of these reactions. 43 Modification of hb-polyGMA EST -Br x with DMBA was completed at a similar rate to other studied amines, particularly DMEA (Figure 1). The multiple end groups in the branched polymers (originally alkyl bromide) are likely converted to ammonium groups under the reaction conditions, i.e., in the presence of nucleophilic amines, although some HBr elimination leading to the formation of carbon-carbon double bonds is also feasible due to the pronounced basicity of the utilized amines.…”

“…Hb-polyGMA EST -Br x and hb-polyGMA DS -Br x were also modified with DMEA under similar conditions as previously reported 43 to produce polymers with hydroxyethylammonium salt repeat units (hb-polyHOEAmm EST -Z x and hb-polyHOEAmm DS -Z x , respectively).…”

“…Epoxide protons are denoted by “e.” Kinetics of epoxide transformations using both DMBA and DMEA (right). Data shown for DMEA is for linear polyGMA, adapted from ref 43 .…”

“…One particularly interesting chain transfer agent is CBr 4 because the chain transfer reactions afford alkyl bromide chain ends, which can be employed in further functionalizations, including nucleophilic substitutions and chain extension reactions under ATRP conditions. 41-43 This approach allows for the generation of polymers that not only have functional groups at the chain ends directly originating from the transfer agent, but also functional groups at the branching points introduced with the crosslinker (e.g., degradable functionalities), 41, 43, 44 and backbone functionalities derived from the monomer(s) (e.g., reactive pendant groups).…”

“…Some synthetically useful examples of these transformations within the scope of polymer chemistry include the synthesis of polymers with pendant azide groups, 50 polymers functionalized via thiol “click” reactions, 51 as well as star polymers with cationic, hydrophilic cores. 43 …”