Polymer chemists have long tried to replicate Nature’s remarkable ability to make macromolecules of defined length, sequence, and chirality. Many new synthetic approaches have attempted to access precisely defined and diversely functionalized uniform macromolecules in useful quantities. Living statistical polymerization methods can yield polymers with precise nanoscale structures on kilogram scales, but these methods lack absolute mass control, sequence control, and stereocontrol. Solid-phase syntheses provide an extremely valuable tool for the synthesis of macromolecules with absolute structural control. However, these methods require large excesses of reagents in each step and are not yet amenable for the synthesis of polymers in a readily scalable way<br/>We are advancing a promising alternative synthetic strategy called Iterative Exponential Growth (IEG) wherein doubly protected molecules of length L undergo cycles of orthogonal activations and couplings to yield macromolecules with length L x (2^n) cycles. Though IEG is limited to repetitive or palindromic sequences, we have used it to make unimolecular, fully sequence-controlled and stereo-controlled polymers on multigram scales.<br/>Through synthetic modification of base monomers of varying lengths, we can install many functionalities such as alcohols, electron rich and poor aromatics, free amines, and primary alkenes etc. A vast number of sequences and topologies that can be made using this system. For instance, using sequential thiol-ene click chemistry, we have synthesized unimolecular block copolymers (BCPs) of up to 12.1 kDA on a gram scale in under a week. BCPs of decane-based side chains and either triethyleneglycol- or thioglycerol-based side chains phase-segregate into hexagonal cylinder morphologies. In addition, we have found that inducing differences in tacticity, stereoisomers of these discrete block copolymers will phase-segregate differently. It is our hope that by using our IEG system, we will elucidate the structure-property relationships that will guide the design of next-generation polymeric materials.

Iterative exponential growth synthesis of perfect triazole-based polymers

255th National Meeting (2018)

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