The Effect of Hofmeister Salts on the LCST Transition of Poly(2‐oxazoline)s with Varying Hydrophilicity

Bloksma, Meta M.; Bakker, Daniël J.; Weber, C.; Hoogenboom, Richard; Schubert, Ulrich S.

doi:10.1002/marc.200900843

Cited by 149 publications

(155 citation statements)

References 30 publications

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“…Those findings are in good agreement with previous observations for the LCST behavior of comb shaped pEtOx when compared to its linear analogue. 24,35 The formation of aggregates of pCPropOx with varying DP was investigated in further detail by dynamic light scattering (DLS) measurements at a concentration of 1 mg mL À1 at different temperatures. At a certain temperature the hydrodynamic radius (R h ) measured by DLS increases from the characteristic size of individual polymer chains (<10 nm) to the size of larger aggregates (>100 nm) (Figure 6a and ESI).…”

Section: ' Results and Discussionmentioning

confidence: 99%

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

et al. 2011

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There is a high potential for thermoresponsive polymers to be used in various applications, such as drug delivery systems 1À5 and separation processes, 6,7 and, therefore, these materials received significant attention over the last few years. Polymers that exhibit "lower critical solution temperature" (LCST) behavior are soluble in water below their LCST 3,7,8 due to effective hydration of the polymer based on hydrogen bonds between the polymer and the solvent. With increasing temperature, the hydrogen bonds are weakened resulting in dehydration when the LCST is reached. This entropically driven phase transition, i.e., release of water molecules, leads to a collapse of the hydrophobic polymer chains and the formation of aggregates. Therefore, the LCST can be tuned, e.g., by variation of the polymer side chains or by copolymerization with other monomers, as fully explored for the most widely studied thermo-responsive polymer, poly(N-isopropylacrylamide) [PNIPAM]. 3,6,9,10 Poly(2-oxazoline)s with methyl, ethyl, isopropyl, or n-propyl side chains are water-soluble and, except for the most hydrophilic poly(2-methyl-2-oxazoline) (pMeOx), show LCST behavior in water. 11,12 The cloud points (CP) of these poly(2-oxazoline)s increase with increasing hydrophilicity and depend on the degree of polymerization (DP) and concentration. 13À15 The CP can easily be tuned by copolymerization of various 2-oxazoline monomers, as well as by controlling the length and end groups. 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.Besides linear poly(2-oxazoline)s, we recently also reported comb polymers containing oligo(2-ethyl-2-oxazoline) (OEtOx) sidechains and a methacrylate (MA) backbone as thermo-responsive ABSTRACT: The synthesis and microwave-assisted living cationic ring-opening polymerization of 2-cyclopropyl-2-oxazoline is reported revealing the fastest polymerization for an aliphatic substituted 2-oxazoline to date, which is ascribed to the electron withdrawing effect of the cyclopropyl group. The poly(2-cyclopropyl-2-oxazoline) (pCPropOx) represents an alternative thermo-responsive poly(2-oxazoline) with a reversible critical temperature close to body temperature. The cloud point (CP) of the obtained pCPropOx in aqueous solution was evaluated i...

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Section: ' Results and Discussionmentioning

confidence: 99%

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

et al. 2011

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“…In a later study, these investigations were expanded to p i PrOx-stat-p n BuOx, which molecularly dissolved below the cloud point temperature in water and were incorporated into micellar nanoparticles of Pluronic F127 after increasing the solution temperature beyond their transition temperature [146]. Furthermore, copolymerizations with [147]. It was shown that the response to the addition of Hofmeister salts depended significantly on the (degree of) hydrophilicity of the polymers, but hardly on their architecture.…”

Section: S-galactosyl Substituents Namely (5oac·gal-s)etox and (5oacmentioning

confidence: 99%

Design Strategies for Functionalized Poly(2-oxazoline)s and Derived Materials

2013

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Abstract:The polymer class of poly(2-oxazoline)s currently is under intensive investigation due to the versatile properties that can be tailor-made by the variation and manipulation of the functional groups they bear. In particular their utilization in the biomedic(in)al field is the subject of numerous studies. Given the mechanism of the cationic ring-opening polymerization, a plethora of synthetic strategies exists for the preparation of poly(2-oxazoline)s with dedicated functionality patterns, comprising among others the functionalization by telechelic end-groups, the incorporation of substituted monomers into (co)poly(2-oxazoline)s, and polymeranalogous reactions. This review summarizes the current state-of-the-art of poly(2-oxazoline) preparation and showcases prominent examples of poly(2-oxazoline)-based materials, which are retraced to the desktop-planned synthetic strategy and the variability of their properties for dedicated applications.

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“…Furthermore, PEtOx can be salted out from aqueous solution by the addition of sodium chloride, leading to a decrease of the LCST, whereas the opposite effect is observed with tetrabutylammonium bromide [16]. A more extensive study on salting in and salting out effects of a range of Hofmeister ions on different thermoresponsive poly(2-alkyl-2-oxazoline)s was recently performed by Hoogenboom and Schubert [18]. In 1992 Kobayashi et al introduced poly(2-isopropyl-2-oxazoline) (PiPrOx) as a thermoresponsive polymer exhibiting a cloud point in the range from 36 to 39 °C [19].…”

Section: Thermoresponsive Poly(2-oxazoline)s In Aqueous Solutionmentioning

confidence: 99%

Bioinspired Poly(2-oxazoline)s

2011

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Poly(2-oxazoline)s are regarded as pseudopeptides, thus bioinspired polymers, due to their structural relationship to polypeptides. Materials and solution properties can be tuned by varying the side-chain (hydrophilic-hydrophobic, chiral, bioorganic, etc.), opening the way to advanced stimulus-responsive materials and complex colloidal structures. The bioinspired -smart‖ solution and aggregation behavior of poly(2-oxazoline)s in aqueous environments are discussed in this review.

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The Effect of Hofmeister Salts on the LCST Transition of Poly(2‐oxazoline)s with Varying Hydrophilicity

Cited by 149 publications

References 30 publications

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

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

Design Strategies for Functionalized Poly(2-oxazoline)s and Derived Materials

Bioinspired Poly(2-oxazoline)s

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