Synthesis & characterization of temperature- and pH- responsive nanostructures derived from block copolymers containing statistical copolymers of HEMA and DMAEMA
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Hydrogels containing of 2-dimethylaminoethyl methacrylate, DMAEMA, exhibit changes in their swelling properties in response to both pH and temperature. Accordingly, these materials are useful for a variety of applications, such as tissue scaffolds, responsive lenses, separations and drug delivery. The response of DMAEMAcontaining hydrogels can be tuned by copolymerization with other monomers, such as 2-hydroxyethyl methacrylate, HEMA. We have developed methodologies for the controlled synthesis of poly(HEMAco-DMAEMA), PHD, statistical copolymers with uniform composition distributions, controlled molecular weights, and narrow molecular weight distributions using controlled free-radical polymerization techniques, such as atom transfer radical polymerization and radical addition-fragmentation chain transfer polymerization. We have also investigated the controlled synthesis and characterization of amphiphilic block copolymers containing PHD statistical copolymers. These block copolymers microphase separate to form periodic nanostructures such as alternating lamellae, cylinders on a hexagonal lattice, or spheres on a body-centered cubic lattice, depending on the volume fraction of each block, the interblock segregation strength, and the choice of casting solvent. When swollen with water, these microphase-separated PHD-containing block copolymers form model hydrogels with uniform composition distributions. Model block copolymer hydrogels containing PHD statistical copolymers are responsive to changes in pH or temperature. The response of these model block copolymer hydrogels can be tuned by adjusting of the DMAEMA content within the PHD block. Moreover, the response can be tuned by changing the hydrophobic block. Specifically, the use of a glassy hydrophobic block, such as polystyrene or poly(tert-butyl acrylate) at temperatures below its glass transition temperature, resulted in the preservation of the original block copolymer morphology during swelling. In contrast, the use of a hydrophobic block that is rubbery during swelling, such as poly(methyl acrylate), enabled reversible morphological transformations.