Multiarm Star‐Crosslinked Hydrogel: Polymer Network with Thermoresponsive Free‐End Chains Densely Connected to Crosslinking Points

• Published in: Macromolecular rapid communications. Vol. 42; no. 8; pp. e2000558 - n/a
• Main Authors: Ida, Shohei, Toda, Shogo, Oyama, Masatoshi, Takeshita, Hiroki, Kanaoka, Shokyoku
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.04.2021
• Subjects: Acrylamide; Addition polymerization; Bonding agents; Carbon; Chain transfer; Chemical synthesis; Compressive strength; Crosslinking; Free radical polymerization; Free radicals; Gels; Hydrogels; Mechanical properties; Molecular structure; Polyisopropyl acrylamide; Polymerization; Polymers; reversible addition–fragmentation chain transfer; Soft tissues; star polymers; stimuli‐sensitive polymers; star polymers; stimuli-sensitive polymers; hydrogels; reversible addition-fragmentation chain transfer; mechanical properties
• DOI: 10.1002/marc.202000558
• ISSN: 1022-1336

Soft tissue in biological system is a hydrogel with elaborate structure exhibiting repeatable dynamic function. In order to approach such sophisticated system, precise construction of a designed network with multi‐components is desired. This communication presents a novel hydrogel having highly dense stimuli‐responsive free‐end chains around crosslinking structure. A key molecule is a core‐crosslinked star‐shaped polymer with multiple thermoresponsive arms, which can be prepared by reversible addition–fragmentation chain transfer polymerization of divinyl crosslinker with poly(N‐isopropylacrylamide) (PNIPAAm) macro‐chain transfer agent and have a number of unreacted carbon–carbon double bonds in the core. These unreacted double bonds can be utilized as a crosslinker for poly(acrylamide) (PAAm) gel synthesis by free radical polymerization. The obtained gel contains homogeneously dispersed star PNIPAAms as crosslinking points and exhibits thermoresponsive swelling behavior in water depending on the star contents. In particular, the gel with low content of the star crosslinker shows localized responsive behavior with expansion and shrinkage of the star in one molecule. The mechanical properties of the star‐crosslinked gel are significantly high compared to the conventional PAAm gels particularly in compressive strength (≈9 MPa). Moreover, the star‐crosslinked gel has thermoresponsive mechanical toughening property. In order to approach a sophisticated system of biological soft tissue, precise construction of a network with multi‐components is desired. In this work, a novel hydrogel having highly dense thermoresponsive free‐end chains around crosslinking structure is designed utilizing core‐crosslinked star polymers as crosslinking points. The obtained gel exhibits unique mechanical properties and thermoresponsive behavior.