Synthesis and Properties of Azo-Based ABC Triblock Copolymers Owning Interaction and Composition Parameters That Influence Their Phase Behaviors

Abstract

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.

Characteristics and self‐assembly behaviors of photochromic triblock azo‐copolymers based on hard‐soft‐hard segments synthesized via RAFT process

“…(A,B)]. The thermal analysis collected in Table corresponded to our expectations and manifested similar trends to those in published literature …”

“…The M n values of the prepared macromolecular chain‐transfer agents and their related TBCs were determined via GPC and calculated from peak integration ratios in the 1 H NMR spectra or according to the equation reported in the literature . Both theoretical molecular weights ( M n (th)s) and M n ( 1 H NMR)s were in good agreement with M n (GPC)s. This observation was similar to that made by Rajasekhar et al and Zhao et al for azo‐type polymers .…”

“…The PCAEMA‐CTA macroinitiator was first synthesized by RAFT polymerization of the CAEMA monomer in the presence of the AIBN initiator and the CPDB starting chain transfer agent with molar feed ratio of (240 [CAEMA] 0 : 3 [CPDB] 0 : 1 [AIBN] 0 ) . A 50 ml Schlenk flask was filled with a mixture of CAEMA (6.5 g, 18.1 mmol), CPDB (50 mg, 0.2625 mmol), AIBN (12.4 mg, 0.0754 mmol) and 19.5 ml of anhydrous solvent (anisole).…”

“…Our previous work, Lee et al and He et al reported the preparation of series of azo‐based ABC triblock copolymers consisting of poly( n ‐butyl methacrylate) (PBMA) or poly(ethylene oxide) (PEO) as soft segments and poly(2‐[2‐(4‐cyano‐azobenzene‐4‐oxy)ethylene‐oxy]ethyl methacrylate) (PCAEMA), poly(6‐(4‐methoxy‐4′‐oxy‐azobenzene)hexyl methacrylate) (PMMAZO) or polymethacrylate (PMA) with a pendent cyanoterphenyl group as hard blocks using LFRP. In this article, we disclose the molecular design, synthesis and characterization of novel ABC‐type photochromic TBCs bearing azobenzene moieties in their side chains.…”

Formation and characteristics of starch‐based dual photo‐function composite hydrogel

“…Because the azobenzene‐based trans‐isomer can be converted to the cis‐one upon UV light irradiation and return to the trans‐isomer by visible light irradiation or in dark storage, azobenzene units are often used as the light‐responsive group. Such a strategy is widely employed to make polymer photo‐switchable .…”