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

Abstract

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.

Nanoengineering Branched Star Polymer‐Based Formulations: Scope, Strategies, and Advances

“…In addition to the aforementioned advantages, star polymers offer the possibility of incorporating a much higher number of functional groups. This has implications in a wide variety of applications, ranging from thermoplastic elastomers, [ 24 ] polyelectrolytes, [ 25 ] polyionic liquids, [ 26 ] hydrogels, [ 27 ] wearable electronics, [ 28 ] and drug carriers. [ 29 ] One can construct topologically complex architectures by controlling a number of factors to alter their dimensions, morphologies, stability, and material properties, some of which will be touched upon in this review.…”

Structure–property correlation of crosslinked domain hydrogels exhibiting thermoresponsive mechanical toughening and hybridization with photoluminescent carbon dots

“…[19][20][21][22][23] Typical examples utilize phase separation of a thermoresponsive polymer such as PNIPAAm, which induces mechanical toughening above the transition temperature, and the incorporation of PNIPAAm chains as a free-end chain and microgel structure is effective. [24][25][26][27][28][29][30] Such topological control of thermoresponsive chains in a network would expand the applicability of the designed hydrogels, for example, if high dimensional stability and high clarity at the transition are imparted for a gel material.…”

Shrinking rates of polymer gels composed of star-shaped polymers of N-isopropylacrylamide and dimethylacrylamide copolymers: the effect of dimethylacrylamide on the crosslinking network

“…If we can construct a crosslinked network with the smallest polymer unit for which the structure is controlled at the molecular level, we may be able to explain macroscopic changes in polymer gels with respect to the behavior of polymer chains. 17,[20][21][22][23][24][25] In previous studies, we reported that star-shaped polymers obtained from living radical polymerization, which enables precise syntheses of polymers, can be combined under conditions appropriate for obtaining polymer gels with more homogeneous network structures than polymer networks obtained by conventional free radical polymerization. [26][27][28] Using living radical polymerization, star-shaped polymers consisting of block copolymers as well as random copolymers consisting of multiple monomers can be synthesized.…”

“…If we can construct a crosslinked network with the smallest polymer unit for which the structure is controlled at the molecular level, we may be able to explain macroscopic changes in polymer gels with respect to the behavior of polymer chains. 17,20–25…”