Abstract
Amphiphilic temperature and photoresponsive linear-dendritic block copolymers comprising second generation acetonide-2,2-bis-methylolpropionic acid (bis-MPA)-based polyester dendron and linear poly(N-isopropyl acrylamide) (PNIPAM) linked by an azobenzene unit were synthesized using ATRP followed by click chemistry. Precursor linear PNIPAM was prepared from an azide-functionalized azobenzene containing ATRP initiator. Two polymers obtained by varying the chain length of PNIPAM block showed different morphologies and LCST values in aqueous solution. Complete change in morphology of the two polymers into large spherical aggregates and nanotubes, respectively, was observed upon heating the micellar solution above LCST. Azobenzene unit was found to undergo trans-cis photoisomerization in the assemblies and caused change in the microenvironment of encapsulated hydrophobic dye without any release. Acetonide groups on the dendron were deprotected to afford hydroxylated polymer that showed well-defined morphologies above the LCST and after heating-cooling cycle while significant dye encapsulation was seen only above LCST.
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