Gelation Behavior of Poly(ethylene glycol) and Polycaprolactone Triblock and Multiblock Copolymer Aqueous Solutions

Abstract

We reported aqueous solutions of poly(caprolactone-b-ethylene glycol-b-caprolactone) (PCL−PEG−PCL) that underwent sol−gel−sol transition as the temperature increased (Macromolecules 2005, 38, 5260−5265). However, when the triblock copolymer aqueous solution (20 wt %), initially as a sol phase, was left at room temperature (20 °C), it turned into an opaque gel in 1 h. The crystallization of the PCL−PEG−PCL triblock copolymer in water was suggested to be responsible for such a kinetic aspect of the phase transition. In addition, PEG/PCL multiblock copolymers were synthesized by coupling the triblock copolymers using terephthaloyl chloride. Even though both PCL−PEG−PCL triblock and PEG/PCL multiblock copolymer aqueous solutions (20 wt %) instantaneously undergo a sol-to-gel transition upon injection into 37 °C water and their thermogels show a maximum modulus at around body temperature (35−42 °C), the multiblock copolymer shows a pronounced sol phase stability at room temperature. The fundamental difference in such phase behavior between triblock and multiblock copolymers seems to lie in their ability to form micelles at low temperature and high crystallizability of the low molecular weight PCL.

Injectable Biodegradable Hydrogels

“…The isotactic arrangement in PLLA induced strong aggregation of the PEG/PLLA multiblock. In contrast with the sol-to-gel transition behavior of the PCL-PEG-PCL (1 000-1 000-1 000) multiblock copolymer, [34] the PCL-PEG-PCL multiblock copolymer, with a higher molecular weight of both PEG and PCL, exhibited a gel-to-sol transition upon heating. [37] In addition, multiblock copolymers of PEG-sebacate (PEG-SA) were synthesized by simple condensation polymerization.…”

“…The gelation mechanism was attributed to crystallization of the multiblock copolymer. [34] The multiblock topology affected the gelation behavior of other copolymer hydrogels. A series of PEG/PLLA alternating multiblock copolymers was synthesized by coupling PEG (MW ¼ 600) to PLLA (MW ¼ 1 100-1 500) using succinic anhydride.…”

Thermosensitive Self-Assembling Block Copolymers as Drug Delivery Systems

“…Additionally, these multiblock copolymer solutions were stable as a transparent solution at room temperature, providing practical convenience during drug formulation [95].…”

“…When the same gel was heated up to 50 °C for 30 s and a quickly quenching in an ice bath, it reversibly became a transparent free-flowing sol and when this transparent sol was injected into 37 °C water, it instantaneously became a gel. Thus, different mechanisms occur when opaque gels are formed at 20 °C (low-temperature gel) or for thermogels formed at 37 °C [95].…”

“…Terephthaloyl chloride (0.694 g, 3.3 mmol) and triethylamine (1.41 mL, 10.12 mmol) were added to the reaction mixtures and stirred at 60 °C for 24 h. The product was isolated by precipitation into diethyl ether, then the polymer was redissolved in 30 mL of methylene chloride, filtered, and precipitated by slowly adding diethyl ether. The residual solvent was removed under vacuum [95,[99][100][101]. Figure 4.…”