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Abstract
A series of smart hydrogels based on dual stimuli responsive star-block copolymers responding to pH and temperature were prepared via atom transfer radical polymerization (ATRP) employing the core-first method. They consist of poly(2-(dimethylamino)ethyl methacrylate) (PDMA) inner blocks and outer blocks comprised of poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA). The aggregation behavior of these block copolymer stars is analyzed by dependence on block length and arm number. The dual stimuli responsiveness of the stars is demonstrated by turbidity as well as dynamic light scattering on dilute aqueous solution, and the gelation behavior of concentrated aqueous solutions is studied by rheology. Above the transition temperature of the PDEGMA outer blocks the stars form flower-like aggregates in dilute solution or free-standing gels at higher concentrations. When the temperature is increased further above the transition temperature of the PDMA inner block, the aggregates start to contract and a weakening was observed for soft gels, whereas for strong gels no influence on the moduli was detected. The behavior is controlled by both concentration and pH value. In addition, we show that the minimum polymer concentration for gel formation can be lowered by quaternizing the inner block of the stars, but a second response to stimuli is lost during the procedure.
Highlights
Hydrogels are three-dimensional hydrophilic networks that can bind a large amount of water or biological fluid.[1,2] Stimuli responsive hydrogels, i.e., hydrogels responding with a large property change on small variations in their physical and/or chemical environment, have gathered much interest for their use as biomaterials, with applications such as controlled drug release, cell carriers and tissue engineering.[1,2,3,4,5] In general, hydrogels can be classified into two categories depending on their cross-linking method: chemical or physical
Synthesis and molecular characterization of star-block copolymers We have synthesized star-shaped block copolymers consisting of a poly(2-(dimethylamino)ethyl methacrylate) (PDMA) inner block and a poly(di(ethylene glycol) methyl ether methacrylate) (PDEGMA) outer block
The trace of the precursor is monomodal with a narrow distribution (PDI 1⁄4 1.13) while the block copolymer shows a small shoulder at higher elution volume but still has
Summary
Hydrogels are three-dimensional hydrophilic networks that can bind a large amount of water or biological fluid.[1,2] Stimuli responsive hydrogels, i.e., hydrogels responding with a large property change on small variations in their physical and/or chemical environment, have gathered much interest for their use as biomaterials, with applications such as controlled drug release, cell carriers and tissue engineering.[1,2,3,4,5] In general, hydrogels can be classified into two categories depending on their cross-linking method: chemical or physical. Scheme 1 Aggregation and network formation of dual temperature and pH responsive star-block copolymers in dependence on concentration.
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