Kazuki Sada's research while affiliated with Hokkaido University and other places

The enumeration of structural isomers of organic molecules using programs capable of enumerating all structural isomers for a given molecular formula has been expanding the chemical library. Here, we report the development of the program (PolyENU) that completely enumerates polymer structural isomers. PolyENU program enumerates all isomers of the repeating unit defined by a molecular formula and a functional group constituting the polymer structure. From the repeating unit of nylon 6 (C6H11NO and an amide group), 387 polymer isomers were generated by PolyENU. The enumerated polymer library includes common organic polymers such as nylon 6, polyleucine, poly(2-isopropyl-oxazoline), and poly(N-propylacrylamide), as well as many unexplored polymers. The enumeration of nylon n (n = 3-10) yielded 36,505 polymers within 44 minutes. These results clearly indicate that PolyENU expands polymer chemical space and contributes to diversity in polymer science.

High crystallinity and low solubility are inherent characteristics of polyamides. Research efforts have primarily focused on exploring their bulk properties as fibers, with less emphasis on their solution properties. Herein, we report on the synthesis and properties of soft and soluble N-methylated nylons as a novel class of soft polymer matter. Surprisingly, N-methylated nylons have scarcely been reported and are almost not registered with CAS SciFindern, while their unit structure is very simple. The N-methylation of nylons resulted in softness and high solubility by eliminating hydrogen bonds between polymer backbones and generating two conformers (cis and trans) of the tertiary amide group. Remarkably, some of them exhibit lower critical solution temperature (LCST)-type phase separation in water. By manipulating the carbon number within polymer backbones, we have found that the quantitative hydrophilic/hydrophobic balance for LCST is its unit formula per amide group equal to C6H11NO, which aligns with typical LCST polymers like poly(N-isopropylacrylamide) (PNIPAM). Despite the structural similarity to PNIPAM, polymer scientists have never found LCST-type behavior of N-methylated nylons during over 50 years of soft polymer matter research. The long-standing assumption that polyamides are inherently rigid and cannot exhibit softness and solubility has impeded their application to soft polymer matter.

Molecular design of LCST-type phase separation in water has been widely accepted as desolvation of water-soluble amphiphilic polymers with a small alkyl group triggered by heat. However, for organic media,...

Commercially available poly(4-hydroxylstyrene) was introduced as a new LCST (lower critical solution temperature)-type thermo-responsive polymer at ambient temperature. The LCST-type phase separation was designed by control of the solvation and...