(439a) Supramolecular Soft Material Formation through Polyelectrolyte-Templated Polymerization

Template polymerization (i.e., polymerization that involves electrostatic, hydrophobic and/or hydrogen bonding association of growing polymer chains with macromolecular templates) has been used to direct supramolecular assembly of diverse soft materials, ranging from nanoparticles to macroscopic gels. To demonstrate the functionality of this technique, we describe three examples of its application from our lab: (1) formation of custom-shaped polyelectrolyte complexes (PECs) through photodirected assembly; (2) use of these PECs as templates for directing the shapes of other supramolecular materials; and (3) assembly of narrowly dispersed PEC nanoparticles. PECs with customized 3-D shapes and either microscale or macroscopic dimensions assemble when an anionic monomer is photolithographically polymerized in the presence of a polycation (which generates PECs with shapes directed by the photoirradiation pattern). These custom-shaped PECs have stimulus-responsive properties (e.g., they can fold, unfold, or dissolve upon changes in pH or ionic strength) and can serve as structure-directing templates for other materials. To illustrate this templating functionality, we show how these PECs can direct the shapes of thermoreversible gels. Here, agarose (a model thermogelling polymer) is added to the anionic monomer/polycation/photoinitiator precursor solutions and gels them. On photopatterning these gelled mixtures, which produces custom-shaped PECs inside the gels, the hydrogels surrounding the PECs are melted via heating and washed away. The agarose inside the PECs, however, remains in place, and (upon returning to room temperature) forms interpenetrating networks of ionically bonded PECs and hydrogen-bonded agarose. The dissolution of the PEC templates at high ionic strengths then generates agarose gels with customized shapes that match those of their sacrificial PEC templates. Finally, we show how template polymerization (with the same anionic monomer/polycation system) can produce self-assembled colloidal PEC particles with highly tunable size and narrow size distributions. By varying the precursor solution compositions, narrowly dispersed particles ranging from 20 to 400 nm in diameter can be prepared by this approach. Collectively, these examples show template polymerization to be a versatile tool for directing the assembly of soft materials with tailored sizes and shapes.