Abstract
A series of amphiphilic poly(3-hexylthiophene-b-hydroxystyrene) (P3HT-PHS) diblock and poly(hydroxystyrene-b-3-hexylthiophene-b-hydroxystyrene) (PHS-P3HT-PHS) triblock copolymers with various compositions were synthesized via coupling reaction between aldehyde end-functionalized P3HT and precursor polymer anion of PHS as well as the following analogous chemistry. The morphologies, the crystallinity of P3HT and the optical properties of bulk samples and thin films of these copolymers under various thermal treatments were investigated. The strong interaction between polyhydroxystyrene repeat units through hydrogen bonding and high glass transition temperature of PHS were shown to significantly affect the microphase separation behaviors and crystallinity of P3HT of these block copolymers, making the self-assembly behavior very different from most P3HT based rod-coil block copolymers. For P3HT-PHS diblock copolymers, different form most other P3HT based rod-coil block copolymers that formed fibrillar or lamellar structure with low coil volume fraction, bulk samples formed not only fibers and lamellar structures but also cylindrical structure due to the strong hydrogen bonding between PHS. Well ordered fibers were observed for spin coated thin films of diblock copolymers on glass substrate before annealing and showed enhanced absorption at long wavelength. However, no organized microphase separated morphologies were observed for both bulk samples and thin films of triblock copolymers, probably due to the strong interaction between PHS segments and physical crosslink effect to prevent the packing of P3HT. For bulk samples, Crystallinity of (100) plane of P3HT increased after thermal annealing, but still weaker than pristine P3HT. In thin films, annealing improved the crystallinity of P3HT with the annealing temperatures below Tg of PHS, but worsened the crystallinity when the annealing temperature was above Tg of PHS. These effects might due to the strong interaction of hydrogen bonding between PHS segments that prevented ordered packing of P3HT chains. In both bulk samples and thin films, diblock copolymers showed more well ordered microstructures than triblock copolymers, and the crystallinity of diblock copolymers were better than triblock copolymers, as a result that the strong interaction of hydrogen bonding of PHS significantly affect the morphology and crystallinity of block copolymers.
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