Morphology evolution of multi-responsive ABA triblock copolymers containing photo-crosslinkable coumarin molecules

Abstract

Symmetric tri-block copolymer as P(DMAEMA-co-CuA)-b-PDMS-b-P(DMAEMA-co-CuA) was synthesized by atom transfer radical polymerization (ATRP) in which PDMS was used as bis-functionalized initiator. Moreover, PDMAEMA as multi-responsive hydrophilic segment was copolymerized with coumarin moieties as photocrosslinking agent. Variation of the ratio of hydrophilic/hydrophobic segments in block copolymers was resulted in different morphologies including snowman-like, hollow, spherical, and cubic structures where the morphology was affected by pH of media. The size of self-assembled tri-block copolymers was changed toward external stimuli including temperature, CO2 bubbling, and pH due to multi-responsivity of PDMAEMA block. The presence of photoactive coumarin molecules in hydrophilic PDMAEMA block was utilized for stabilizing the morphology in the self-assembled particles upon UV light irradiation (365 nm). Photocrosslinking of self-assembled particles by UV light-induced dimerization of coumarin molecules via [2π + 2π] cycloaddition reaction was investigated by spectroscopy and microscopy methods, and results indicated that morphology of the particles was stabilized after photocrosslinking. Also, the rate of coumarin dimerization was affected by its concentration, and size and morphology of the particles. According to the advantages of developed self-assembly system considering various UV-crosslinkable morphologies and multi-responsiveness, these structures have potential application in drug delivery systems for controlled release of doxorubicin (DOX).