Stimuli‐responsive reversible physical networks. I. Synthesis and physical network properties of amphiphilic block and random copolymers with long alkyl chains by living cationic polymerization

Abstract

The living cationic polymerization of octadecyl vinyl ether (ODVE) was achieved with an 1-(isobutoxy)ethyl acetate [CH 3 CH(OiBu)OCOCH 3 ]/EtAlCl 2 initiating system in hexane in the presence of an added weak Lewis base at 30°C. In contrast to conventional polymers, poly(octadecyl vinyl ether) underwent upper-critical-solution-temperature-type phase separation in various solvents, such as hexane, toluene, CH 2 Cl 2 , and tetrahydrofuran, because of the crystallization of octadecyl chains. Amphiphilic block and random copolymers with crystallizable substituents of ODVE and 2-methoxyethyl vinyl ether (MOVE) were synthesized via living cationic polymerization under similar conditions. Aqueous solutions of the copolymers yielded physical gels upon cooling because of strong interactions between ODVE units, regardless of the copolymer structure. The product gels, however, exhibited different viscoelastic properties: A 20 wt % solution of a block copolymer (400/20 MOVE/ODVE) became a soft physical gel that behaved like a typical gel, whereas the corresponding random copolymer gave a transparent but stiff gel with a certain relaxation time. Differential scanning calorimetry analysis confirmed that the crystalline-amorphous transition of the octadecyl chains was a key step for inducing such physical gelation.

Thermogelation of amphiphilic poly(asparagine) derivatives

“…Poly( N ‐isopropylacrylamide) (PNIPAAm) is known as one of the representative thermoresponsive polymers, and its aqueous solution shows a reversible and rapid LCST‐type phase separation around body temperature (32°C) due to the hydration–dehydration change in the polymer chain 21–23. Besides PNIPAAm and its copolymers, poly(vinyl ether)s,24, 25 poly(2‐isopropyl‐2‐oxazoline),26 poly( N ‐vinylalkylamide)s,27 and poly (phosphazene)s28 were developed as thermoresponsive polymers. However, lack of biodegradability and biocompatibility restricts their potential applications in biomedical fields.…”

“…Among the stimuli‐responsive polymer gelations, sol–gel transition via physical association is beneficial due to the rapid transformation from a liquid form at room temperature to a gel state at the physiological temperature without any additives,31–33 while the crosslinking by chemical reagents is often harmful to the human body. Most of the polymers showing the sol–gel transition in water are block and graft copolymers: poly(ethylene glycol)‐ block ‐poly(propylene glycol) ‐block ‐poly(ethylene glycol) (PEG‐PPG‐PEG; Pluronic),34 block copolymers of poly(vinyl ether)s,24, 25 triblock copolymer of poly( dl ‐lactic acid‐ co ‐glycolic acid) (PLGA) and PEG,35 poly(phosphazene)‐ graft ‐PEG,28 and chitosan‐ graft ‐PEG 36. Aoshima et al .…”

Complex amphiphilic networks derived from diamine‐terminated poly(ethylene glycol) and benzylic chloride‐functionalized hyperbranched fluoropolymers

“…Recently, amphiphilic copolymers, whether as micelles, hybrids, or networks, have attracted attention because of their interesting properties and significant applications 1–14. These systems are composed of at least two types of covalently‐attached polymer building blocks varying widely in their hydrophilicity (and possibly also in architecture).…”

Chemoenzymatic Synthesis of H-shaped Amphiphilic Pentablock Copolymer and Its Self-assembly Behavior

“…[1][2][3][4] Some synthetic routes have been exploited to synthesize amphiphilic block copolymers, including living anionic polymerization, 5-7 cationic polymerization, [8][9][10] and the controlled/ ''living'' radical polymerization and so forth. [11][12][13] Among these methods reported, living radical polymerization (LRP), which exemplifies stable free radical polymerization (SFRP), 14,15 atom transfer radical polymerization (ATRP), [16][17][18] and reversible addition-fragmentation transfer polymerization (RAFT), [19][20][21] has become preferred to others lying in its accurate control of molecular weight, polydispersity, and chain-end functionality.…”