Abstract
The ability to tune the behavior of temperature-responsive polymers and self-assembled nanostructures has attracted significant interest in recent years, particularly in regard to their use in biotechnological applications. Herein, well-defined poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA)-based core–shell particles were prepared by RAFT-mediated emulsion polymerization, which displayed a lower-critical solution temperature (LCST) phase transition in aqueous media. The tertiary amine groups of PDEAEMA units were then utilized as functional handles to modify the core-forming block chemistry via a postpolymerization betainization approach for tuning both the cloud-point temperature (TCP) and flocculation temperature (TCFT) of these particles. In particular, four different sulfonate salts were explored aiming to investigate the effect of the carbon chain length and the presence of hydroxyl functionalities alongside the carbon spacer on the particle’s thermoresponsiveness. In all cases, it was possible to regulate both TCP and TCFT of these nanoparticles upon varying the degree of betainization. Although TCP was found to be dependent on the type of betainization reagent utilized, it only significantly increased for particles betainized using sodium 3-chloro-2-hydroxy-1-propanesulfonate, while varying the aliphatic chain length of the sulfobetaine only provided limited temperature variation. In comparison, the onset of flocculation for betainized particles varied over a much broader temperature range when varying the degree of betainization with no real correlation identified between TCFT and the sulfobetaine structure. Moreover, experimental results were shown to partially correlate to computational oligomer hydrophobicity calculations. Overall, the innovative postpolymerization betainization approach utilizing various sulfonate salts reported herein provides a straightforward methodology for modifying the thermoresponsive behavior of soft polymeric particles with potential applications in drug delivery, sensing, and oil/lubricant viscosity modification.
Highlights
IntroductionStimuli-responsive (or “smart”) polymers exhibit a change in their physical and/or chemical properties in response to an externally applied stimulus.[1−4] This interesting class of macromolecules has attracted a huge amount of attention within the literature over the past few decades, resulting in numerous examples of polymers and self-assembled nanostructures that respond to a variety of stimuli, including temperature,[5−9] pH,− light,[13−16] oxidants/reductants,[17−19] or enzymes.[20−22] These external stimuli typically induce detectable micro- or nanoscale changes, which often result in significant variations in the macroscopic properties of the polymer, such as its shape, solubility, or mechanical properties.[1−4] Due to the vast array of external stimuli that can induce a response, stimuli-responsive materials have come to be utilized in numerous applications, including drug delivery,[23,24] interactive coatings,[25,26] tissue engineering,[27,28] and protein purification.[29,30]While a wide range of polymers and nanostructures that respond to external stimuli have been reported to date, perhaps the most widely studied and best understood examples typically entail thermoresponsive polymers.[1−4] In this case, thermoresponsive polymers will undergo a reversible change in solubility at a specific temperature, known as critical solution temperature (CST)
Form the Cross-Linked PDMAPS18-b-P(DEAEMA675-co-EGDMA6) P1 Nanoparticles broadly used to classify thermoresponsive polymers into one of two categories, depending on whether they exhibit a lowercritical solution temperature (LCST) or an upper-critical solution temperature (UCST).[34−37] LCST behavior corresponds to demixing of the polymer from solution above a critical temperature, whereas UCST behavior corresponds to an improved miscibility of the polymer with the solvent above a critical temperature.[34−37] To date, a vast majority of literature examples utilizing temperature-sensitive polymers have focused on LCST-type phase transitions in aqueous media, with this disparity most commonly justified on the grounds that UCST behavior is rather sensitive to even small variations in pH, ionic strength, andpolymer composition, including end-group functionality.[34,35,38,39]
Using the poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) units as functional handles, the core of the originally obtained particles was subsequently modified via a postpolymerization betainization approach employing a series of sulfonate salts of varying nature and hydrophilicity
Summary
Stimuli-responsive (or “smart”) polymers exhibit a change in their physical and/or chemical properties in response to an externally applied stimulus.[1−4] This interesting class of macromolecules has attracted a huge amount of attention within the literature over the past few decades, resulting in numerous examples of polymers and self-assembled nanostructures that respond to a variety of stimuli, including temperature,[5−9] pH,− light,[13−16] oxidants/reductants,[17−19] or enzymes.[20−22] These external stimuli typically induce detectable micro- or nanoscale changes, which often result in significant variations in the macroscopic properties of the polymer, such as its shape, solubility, or mechanical properties.[1−4] Due to the vast array of external stimuli that can induce a response, stimuli-responsive materials have come to be utilized in numerous applications, including drug delivery,[23,24] interactive coatings,[25,26] tissue engineering,[27,28] and protein purification.[29,30]While a wide range of polymers and nanostructures that respond to external stimuli have been reported to date, perhaps the most widely studied and best understood examples typically entail thermoresponsive polymers.[1−4] In this case, thermoresponsive polymers will undergo a reversible change in solubility at a specific temperature, known as critical solution temperature (CST). This interest in the use of LCST-type thermoresponsive polymers in aqueous solution can further be justified on the grounds that they can be regarded as simplified mimics of biological systems, which has driven studies into potential biomedical applications.[37,40,41] For instance, one of the most extensively studied thermoresponsive polymers, poly(N-isopropylacrylamide) (PNIPAAm), and PNIPAAm-based assemblies have been widely explored in a range of biomedical applications such as drug carriers, enzyme mimics, and biosensors.[42−44] the LCST of PNIPAAm is commonly reported to be approximately 32 °C, which can be a potential issue as it is below that of physiological temperature.[45,46] there is substantial research interest in being able to accurately tune the LCST of thermoresponsive polymers, in an effort to better control their thermoresponsive behavior and broaden their potential range of applications
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
