Synthesis and thin film characterization of poly(styrene-block-methyl methacrylate) containing an anthracene dimer photocleavable junction point

Telechelic high molecular weight polystyrene (PS-A) and poly(methyl methacrylate) (PMMA-A) containing anthracene end groups undergo end-coupling reaction in THF solution to form [4 + 4] anthracene photodimers upon exposure to UV irradiation at wavelengths greater than 300 nm. A mixture of products is obtained that include the coupled polystyrene homopolymer, P(S-AA-S), coupled PMMA homopolymer, P(MMA-AA-MMA), and the desired diblock copolymer, P(S-AA-MMA). The polymer concentration and molecular weights have a direct influence on the photoreaction kinetics but do not affect the molar ratio of the three polymeric products. P(S-AA-MMA), purified by extraction of the homopolymers with selective solvents, exhibits thermal cleavage of the junction points and reversion back to homopolymers at temperatures at or above 135degreesC. AFM images of thin films of P(S-AA-MMA) spin-coated onto passivated silicon substrates show a microphase-separated cylindrical microdomain morphology with the cylinders oriented normal to the surface.