Reversible addition–fragmentation
chain transfer polymerization
is employed for the preparation of a series of novel ABC-type azo
triblock copolymers (TBCs) consisting of poly(CAEMA), poly(BMA), and
poly(DOPAM) using AIBN as an initiator and anisole as a solvent. The
TBCs are characterized by means of 1H nuclear magnetic
resonance (NMR) and gel permeation chromatography (GPC). Their mesophase,
photoresponsive, and morphological behaviors are examined using differential
scanning calorimetry (DSC), optical polarizing microscopy (OPM), ultraviolet–visible
spectrophotometry (UV–vis), atomic force microscopy (AFM),
and grazing-incidence small-angle X-ray scattering (GISAXS). Molecular
weights and polydispersities (≤1.38) increase slightly with
the increase of the molar ratio of monomer to macroinitiator, confirming
a controlled/living radical polymerization. All TBCs demonstrated
endothermic and exothermic transition peaks corresponding to the smectic-to-nematic
and nematic-to-smectic phases. Thermal investigation revealed that
the TBCs containing 54 and 46 wt % of azo contents displayed batonnet
textures of smectic phase, while the TBC with low azo block fraction
of 39 wt % showed threaded texture of nematic phase. For TBC having
the lowest azo content of 31 wt %, neither liquid crystalline texture
is detected. TBC-2 with 46 wt % of azo block, 28 wt % of PBMA, and
26 wt % of PDOPAM produced a lamellar compared to TBC-1 and TBC-3
which formed a mixture of cylinder and lamellar morphologies. Contrastingly,
TBC-4 containing the highest PDOPAM volume ratio of 50 wt % generated
hexagonal cylinder-type morphology. All TBCs exhibited a reversible
trans–cis–trans photoisomerization behavior in chloroform
solution and in thin film under UV and visible light irradiation (or
dark storage) at varied intervals of time.