Modular Synthesis and Patterning of High-Stiffness Networks by Postpolymerization Functionalization with Iron-Catechol Complexes

Declan P Shannon; Joshua D Moon; Christopher W Barney; Nairiti J Sinha; Kai-Chieh Yang; Seamus D Jones; Ronnie V Garcia; Matthew E Helgeson; Rachel A Segalman; Megan T Valentine; Craig J Hawker

doi:10.1021/acs.macromol.2c02561

Modular Synthesis and Patterning of High-Stiffness Networks by Postpolymerization Functionalization with Iron-Catechol Complexes

Macromolecules. 2023 Mar 15;56(6):2268-2276. doi: 10.1021/acs.macromol.2c02561. eCollection 2023 Mar 28.

Authors

Declan P Shannon^{1

2}, Joshua D Moon^{1

3}, Christopher W Barney^{3

4

2}, Nairiti J Sinha^{3

2}, Kai-Chieh Yang³, Seamus D Jones³, Ronnie V Garcia⁵, Matthew E Helgeson^{3

2}, Rachel A Segalman^{1

3

5

2}, Megan T Valentine^{4

2}, Craig J Hawker^{1

5

2}

Affiliations

¹ Materials Department, University of California Santa Barbara, Santa Barbara, California 93106-5050, United States.
² Materials Research Laboratory, University of California Santa Barbara, Santa Barbara, California 93106-5121, United States.
³ Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, California 93106-5080, United States.
⁴ Department of Mechanical Engineering, University of California, Santa Barbara, Santa Barbara, California 93106-5070, United States.
⁵ Department of Chemistry & Biochemistry, University of California Santa Barbara, Santa Barbara, California 93106-9510, United States.

Abstract

Bioinspired iron-catechol cross-links have shown remarkable success in increasing the mechanical properties of polymer networks, in part due to clustering of Fe³⁺-catechol domains which act as secondary network reinforcing sites. We report a versatile synthetic procedure to prepare modular PEG-acrylate networks with independently tunable covalent bis(acrylate) and supramolecular Fe³⁺-catechol cross-linking. Initial control of network structure is achieved through radical polymerization and cross-linking, followed by postpolymerization incorporation of catechol units via quantitative active ester chemistry and subsequent complexation with iron salts. By tuning the ratio of each building block, dual cross-linked networks reinforced by clustered iron-catechol domains are prepared and exhibit a wide range of properties (Young's moduli up to ∼245 MPa), well beyond the values achieved through purely covalent cross-linking. This stepwise approach to mixed covalent and metal-ligand cross-linked networks also permits local patterning of PEG-based films through masking techniques forming distinct hard, soft, and gradient regions.