High Molecular Weight Uniform Polymers Encoding Octal Sequences by Passerini Iterative Exponential Growth

Sequence-defined polymers composed of a large pool of chemically distinct monomers (SDPs) have been pursued to achieve the structural and functional precisions exhibited by biopolymers in nonbiological environments. In contrast to the incremental growth of SDPs by sequential addition of individual monomers, the iterative exponential growth (IEG) method allows the synthesis of high molecular-weight SDPs, but their sequences have been composed mostly of binary monomers. Consequently, achieving high molecular-weight SDPs built with a large pool of monomers remains a challenge. Here we report the Passerini iterative exponential growth (P-IEG) approach that enables efficient synthesis of 128-mer uniform poly(hydroxybutyrate) (PHB), possessing 127 γ-acylamino cyclohexyl side groups (27 kDa, Đ = 1) and a 31-mer SDP, encoding an octal sequence composed of eight chemically distinct repeating units. Taking advantage of the combinatorial character of the Passerini three-component reaction involving an aldehyde, a carboxylic acid, and an isocyanide to form an acyloxy amide linkage, we simultaneously achieved the exponential chain growth through the convergence of bifunctional building blocks and side-chain implementation by selecting appropriate isocyanides as a third component. The P-IEG approach enabled the synthetic encoding of complex information, an octal sequence equivalent to a 93-bit binary code, into a 31-mer SDP. Our proposed P-IEG method could contribute to the synthesis of synthetic macromolecules with absolutely defined sequences of functionalities. These polymers could be used for the development of functional materials with properties not achievable by conventional polymers, including polymers storing digital information at higher density.