Amphiphilic Graft Copolymers from End-Functionalized Starches: Synthesis, Characterization, Thin Film Preparation, and Small Molecule Loading

Abstract

End-functionalized macromolecular starch reagents, prepared by reductive amination, were grafted onto a urethane-linked polyester-based backbone using copper-catalyzed azide-alkyne cycloaddition (CuAAC) chemistry to produce novel amphiphilic hybrid graft copolymers. These copolymers represent the first examples of materials where the pendant chains derived from starch biopolymers have been incorporated into a host polymer by a grafting-to approach. The graft copolymers were prepared in good yields (63-90%) with high grafting efficiencies (66-98%). Rigorous quantitative spectroscopic analyses of both the macromolecular building blocks and the final graft copolymers provide a comprehensive analytical toolbox for deciphering the reaction chemistry. Due to the modular nature of both the urethane-linked polyester synthesis and the postpolymerization modification, the starch content of these novel hybrid graft copolymers was easily tuned from 28-53% (w/w). The uptake of two low molecular weight guest molecules into the hybrid polymer thin films was also studied. It was found that binding of 1-naphthol and pterostilbene correlated linearly with amount of starch present in the hybrid polymer. The newly synthesized graft copolymers were highly processable and thermally stable, therefore, opening up significant opportunities in film and coating applications. These results represent a proof-of-concept system for not only the construction of starch-containing copolymers, but also the loading of these novel polymeric materials with active agents.

Impact of starch content on protein adsorption characteristics in amphiphilic hybrid graft copolymers

“…Hybrid 53, like the other compositions, is insoluble in water and most organic solvents yet retains excellent film forming properties and thermal stability [29].…”

“…As reported previously, the ULPE-N3 backbone polymers used in these studies had M n~6 6K and PDI's of ~2 [29]. Azide and alkyne densities associated with the ULPE-N3 backbone polymers and starch reagents, respectively, were calculated using our published protocol [29].…”

“…Starch-based biomaterials are abundant in the literature yet most studies focus on blend characteristics or synthesizing functional starches using graftfrom [26][27][28] strategies. Recently, we reported a novel synthetic approach to hybrid amphiphilic graft copolymers that feature starch macromolecules as side chain moieties [29]. In our approach, starch macromolecular reagents are grafted-to an azide-containing urethane linked polyester (ULPE-N3) using copper-catalyzed azide-alkyne cycloaddition chemistry (CuAAC) to give amphiphilic copolymers.…”

“…2.2 Synthesis. All graft copolymers (including the PEG-containing polymers) and macromolecular reagents were synthesized using published procedures [29]. As reported previously, the ULPE-N3 backbone polymers used in these studies had M n~6 6K and PDI's of ~2 [29].…”

“…All graft copolymers (including the PEG-containing polymers) and macromolecular reagents were synthesized using published procedures [29]. As reported previously, the ULPE-N3 backbone polymers used in these studies had M n~6 6K and PDI's of ~2 [29]. Azide and alkyne densities associated with the ULPE-N3 backbone polymers and starch reagents, respectively, were calculated using our published protocol [29].…”