Systematic Order-Made Synthesis of Sequence-Defined Polyurethanes with Length, Types, and Topologies

Abstract

Polyurethanes are industrially and academically important as soft materials. They are conventionally synthesized by a process based on step-growth polymerization; thus, molecular weight and structural control are impossible. However, the development of a synthetic strategy for polyurethanes remains a big challenge in designing soft materials. Herein, we demonstrate a synthetic methodology for generating polyurethanes with selectable lengths and termini characteristics. The multistep synthetic process offered the systematic synthesis of high-molecular weight, regioregular, and α,ω-urethane telechelics. Various oligomers with order-made repeating units revealed the effective length of the polymer properties. To demonstrate the scope of our methodology, it was also applied to the synthesis of block co-oligomers, three-armed star oligomers, and miktoarm star co-oligomers. Thus, our method allows the synthesis of high-molecular-weight oligomers with complete structural and molecular weight control, which is of enormous value to materials science; particularly the study and application of structure−property relationships in polyurethanes.

Iterative Click-Addition Process for Urethane-based 1st-5th Dendrons

“…SEC does not provide absolute MW values for polymers without using internal standard and represented as a relative value based on hydrodynamic volume. The M n SEC values of polyurethane-based SDPs were 130%–141% compared with the absolute MW values . This indicates that the polyurethanes and dendrons (1st-4th-generations) have a higher hydrodynamic radius than the coiled segments in polystyrene (Table ).…”

“…Various methods for synthesizing sequence-defined polymers (SDPs) that involve the elegant combination of addition, substitution, and elimination reactions have been developed. − For instance, we have recently reported the precise synthesis of polyurethane-based SDPs involving facile control of the number of urethane groups using an iterative click addition reaction process (iCAP) in which nucleophilic addition and thiol–ene reactions are alternately repeated to form urethane repeating groups . This method allows each reaction to proceed quantitatively, enabling purification by simple reprecipitation.…”

Tailored Polyurethane Synthesis from AB-Type Monomers

“…Compared with the defined polymer synthesis on chain polymerization, sequence control on step polymerization has not progressed so far, probably because of the difficulty of controlling the latter. − Meanwhile, one of the most produced polymers in industries is polyurethane, which is typically prepared by step polymerization using a diol and a diisocyanate as monomers (Figure A). − Since the polymerization based on such AA plus BB-type monomers provides always a simple repeating pattern consisting of AA-BB repeating units, the idea of sequence does not make much sense. To implement a more sophisticated polyurethane backbone design, multiple approaches have been reported, such as ring-opening polymerization (ROP) of cyclic monomers or one-by-one monomer addition to synthesize oligomer species. − However, those methods often face inevitable limitations on their versatility caused by the taxing synthetic process, and highly defined structures have been achieved only for oligomers, not polymers. Considering the importance of polyurethane as a worldwide material with a wide range of industrial applications, the development of new polyurethane synthetic methods has been highly desirable, which enables defined primary structure construction by an easy and versatile process (ideally applicable for industrial production).…”