Precision polymerization has enabled the synthesis of polymers with well-defined primary structures; however, the precise control and analysis of polymer network structures remain challenging because of their inherent heterogeneity and insolubility. This review summarizes our recent studies on precision polymerization systems beyond conventional classifications based on active species and polymerization mechanisms, and their application to advanced polymer networks. Particular emphasis is placed on mechanistic transformation through RAFT terminals, interconvertible radical/cationic living polymerization, precise synthesis of branched poly(vinyl alcohol)s, selectively degradable polymer networks, and controlled/living click polymerization. In particular, degradable branching points and active-species transformation have enabled the design of analyzable and structurally controlled network polymers. These studies demonstrate that integrating precise polymer synthesis with controllable and analyzable network architectures provides a promising strategy for the development of advanced functional and sustainable polymer materials.

Free radical copolymerization of glycidyl methacrylate (GMA) and 2-hydroxyethyl methacrylate (HEMA) was conducted in tetrahydrofuran (THF) using 2,2’-azobisisobutyronitrile (AIBN) as a radical initiator. The copolymerization proceeded smoothly to give the corresponding copolymers (P(GMA-HEMA)) in high yields. The compositions of the resulting copolymers were almost the same as the monomer feed ratios. The epoxy group of the copolymers was converted efficiently to five-membered cyclic carbonate group by CO2 incorporation reaction using dicyclohexylammonium iodide (DCAI) to give copolymers bearing cyclic carbonate pendant group (P(MA5CC-HEMA)). The copolymers consisting of equimolar amounts of MA5CC and HEMA units were crosslinked with hexamethylenediamine (HMDA) or 1,3-bis(aminomethyl)cyclohexane (1,3-BAC) to form networked polymers by ring-opening hydroxyurethane formation reaction. In addition, the copolymer was cross-linked with hexamethylene diisocyanate (HMDI) by tin-catalyzed addition reaction of the hydroxy group of HEMA unit to afford network polymer.

PVA/β-CyD vinylon thin films were prepared by formalizing PVA (poly(vinyl alcohol)) in the presence of β-CyD (β-cyclodextrin). PVA/β-CyD vinylon thin films were prepared by coating a 15 wt% PVA aqueous solution containing β-CyD and formalin adjusted to pH 1 on a corona treated PET film with a solution height of 225 μm, and then standing in a 60 °C thermostatic bath for 24 h. The obtained PVA/β-CyD vinylon thin films were subjected to solid-state 13C NMR, water contact angle, surface friction coefficient, and tensile strength measurements. It was found from NMR measurements that β-CyD components are disproportionately abundant on the polar surface of the films. By the introduction of β-CyD component, the film quality of the PVA/β-CyD vinylon thin film became thicker and stiffer, the elongation decreased, the strength increased, the wettability decreased, and the friction coefficient increased.

An aqueous solution of mechanically disintegrated cellulose nanofiber (CNF) was stirred at room temperature for 1 h in the presence of water glass (WG) at a CNF/SiO2 ratio of 11.1/88.9. After stirring, a relatively transparent polymer hybrid was obtained by standing at 40°C for 10 days and drying under reduced pressure at 60°C for 48 h. The weight loss temperature (Td10) of the obtained polymer hybrid increased by 10% compared with that of the raw CNF, indicating that the polymer hybridization improved heat resistance. On the other hand, an aqueous solution of chemically disintegrated cellulose nanofiber (TOCNF) prepared by 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) oxidation in the presence of WG at a TOCNF/SiO2 ratio of 90.0/10.0 generated a relatively transparent polymer hybrid by stirring the solution at room temperature for 1 h, standing at 40°C for 10 days, and drying under reduced pressure at 60°C for 48 h. When polymer hybridization was performed using TOCNF, increasing the amount of WG used resulted in an increase in Td10, indicating a tendency for the improved heat resistance by the polymer hybridization.

A poly(allylamine) (PAA) hydrogel cross-linked with thiourea units was synthesized from PAA and CS2, and its ability to immobilize various pH indicators and a universal indicator was investigated. Owing to its cationic nature in water, the PAA hydrogel effectively immobilized anionic dyes through ionic interactions. All four tested pH indicators were successfully immobilized and exhibited reversible, indicator-specific color changes in aqueous media. The immobilization capacity varied depending on dye acidity and charge, demonstrating selective uptake of anionic dyes. The universal indicator containing multiple dyes was also immobilized, and the resulting hydrogel showed continuous color transitions over pH 3–9. MALDI-TOF MS analysis confirmed the incorporation of all dye components. Further, the universal indicator–loaded hydrogel showed acid-induced swelling, indicating coupled optical and mechanical responses. These results highlight the potential of PAA hydrogels as simple, reusable pH sensors and versatile stimuli-responsive devices.