Tuning the LCST of poly(2-oxazoline)s by varying composition and molecular weight: alternatives to poly(N-isopropylacrylamide)?

Abstract

The cloud point of copolymers of 2-ethyl-2-oxazoline and 2-n-propyl-2-oxazoline could be tuned from 25 degrees C to 100 degrees C by varying molecular weight and composition; the reversibility and concentration dependence of the cloud points were evaluated to assess the potential of these copoly(2-oxazoline)s as alternatives to poly(N-isopropylacrylamide).

Poly(2-cyclopropyl-2-oxazoline): From Rate Acceleration by Cyclopropyl to Thermoresponsive Properties

“…The concentration dependence of the CP of the comb polymer follows the same trend as for linear pCPropOx (Figure 5b), which is in contrast to the concentration dependence of poly(2-oxazoline)s with different cloud points due to different side chains, such as pEtOx and pnPropOx. 15 This confirms that the side-chains shield the MA backbone and that only the OCPropOx side-chains interact with the aqueous environment, resulting in similar LCST behavior for the linear and comb pCPropOx. However, the CP's of the comb polymer are decreased by ∼10°C when compared to linear pCPropOx, which may be a result of the large number of ÀCH 3 end groups at the pendant side chains of the comb structure as well as the high local polymer concentration.…”

“…With the increase in concentration, the CP decreases in a nonlinear way and only a small decrease is observed when the concentration is increased from 10 to 30 mg mL À1 indicating that the CP at 30 mg mL À1 approaches the LCST value (Figure 5b). Both the DP and concentration dependence of the CP follow the same trend as for pnPropOx, 15 which is a consequence of the Type I FloryÀHuggins miscibility behavior that is characterized by a shift of the LCST toward lower polymer concentration when the polymer chain length is increased. 34 The CP of pCPropOx (30°C) lies in between the CP of pnPropOx (44°C) and piPropOx (27°C) (all 5 mg mL À1 and a DP of 100, ESI).…”

“…16À19 Poly(2-ethyl-2-oxazoline) (pEtOx) is known to only reveal a CP when the DP is above 100, since smaller polymer chains are soluble up to 100°C. 15 Poly(2-isopropyl-2-oxazoline) (piPropOx) is an interesting thermoresponsive polymer, since its CP is close to body-temperature, making it suitable for biomedical applications. 20 However, due to its semicrystallinity the thermo-responsiveness becomes irreversible after annealing above the LCST.…”

“…21À23 Poly(2-n-propyl-2-oxazoline) (pnPropOx) is amorphous but has a lower LCST of ∼24°C. 15 In addition, the rather low T g of ∼40°C, which decreases in the presence of water, makes it difficult to handle and to store the polymer at ambient temperature. Therefore, an alternative thermo-responsive poly(2-oxazoline) with a reversible critical temperature close to body temperature is desired.…”

Well-defined poly(N-isopropylacrylamide) with a bifunctional end-group: synthesis, characterization, and thermoresponsive properties

“…The bisalkynelinked PNIPAM that was designed as no end-group effect reference gave the smallest molecular weight dependence among the three series studied here. As mentioned above, previous studies of PNIPAM and other thermoresponsive polymers have demonstrated the LCST to be independent [32][33][34]45], directly dependent [10,26], or inversely dependent [17,[27][28][29][30][31]46,47] upon polymer molecular weight. LCSTs are expected to be decreased with increasing molecular weight on the basis of the changes in the polymer-solvent interaction [48,49].…”