Polymer Nanofibers Exhibiting Remarkable Activity in Driving the Living Polymerization under Visible Light and Reusability

Abstract Visible light‐driving syntheses have emerged as a powerful tool for organic synthesis and for the preparation of macromolecules under mild and environmentally benign conditions. However, precious but nonreusable photosensitizers or photocatalysts are often required to activate the reaction, limiting its practicality. Here, it is reported that poly(1,4‐diphenylbutadiyne) (PDPB) nanofibers exhibit remarkable activity in driving the living free radical polymerization under visible light. Moreover, PDPB nanofibers are very stable under irradiation of visible light and can be reused without appreciable loss of activity even after repeated cycling. The nanofiber will be a promising photocatalyst with excellent reusability and stability for the reactions driven by visible light.


Synthesis of S, S'-bis(α, α'-dimethyl-α''-acetic acid)-trithiocarbonate (BDMAT).
Carbon disulfide (13.77 g, 0.18 mol), chloroform (58.81 g, 0.45 mol), acetone (26.26 g, 0.45 mol), and tetrabutylammonium hydrogen sulfate (1.21 g, 3.6 mmol) were mixed with 12 mL of mineral ether in a 500 mL round bottom flask. NaOH solution (50%, 100.8 g) was added into the mixture for 1.0 h while maintaining the temperature at 25 o C. Then, the reaction was maintained at 22-25 o C for 10 h while being stirred with a magnetic stirrer. Water (90 mL) was added to dissolve the yellow solids, followed by adding hydrochloric acid (12 mL) to acidify the aqueous solution and yield crystalline solids. After filtration and washing three times by water, the crude compound was purified by recrystallization three times in mixture of acetone and mineral ether (4:1 v/v). Yield: 53%. The 1 H NMR result provided in Figure S1.

Synthesis of PDPB-NF4, PDPB-NF6 and PDPB6 [21a]
Sodium dodecyl sulphate (1.0 g) was dissolved in 2 mL of 0.3 M NaCl aqueous solution in a quartz tube. After slow agitation at 65 o C until the surfactant has completely dissolved to give a transparent and viscous micellar solution. The subsequent addition of cyclohexane containing monomer (1, 4-diphenylbutadiyne (DPB) (10% of mass)) and initiator benzoin methyl ether (BME) (5% of mass) in the micellar solution under stirring leads to a white unstable emulsion at 1000 rpm. A co-surfactant, pentanol-1 (300 μL), was then added to the mixture, which was then strongly vortexed for a few minutes. This led to a perfectly colourless, translucent, birefringent and stable gel: a hexagonal mesophase. The doped mesophases with the monomer and the initiator for polymerization were used as soft templates to synthesize polymer nanostructures induced by irradiation using an OSRAM ULTRA-VITALUX (100-300 W) lamp at a distance of 20 cm for one week for PDPB-NF4 and two weeks for PDPB-NF6. After reaction, the materials were extracted in water-ethanol mixture, centrifuged, and then washed several times to eliminate the surfactant, co-surfactant and salt. Similar photopolymerization route just without soft templates was carried out to synthetize PDPB powder (PDPB6).

General procedures for photo-induced living polyme rization catalyzed by various catalysts.
The polymerization ware conducted in a glass sealed tube, charged with water (3 mL), mo nomer (DMA, HEA, DPAA,) (1.5 mmol), BDMAT (4.23 mg, 0.015 mmol), and catalyst (3.0 mg). The mixture was deoxygenated by three freeze-pump-thaw cycles and sealed under vacuum. The mixture was then irradiated by OSRAM ULTRA-VITALUX (100-300 W) lamp at room temperature. After stop polymerization, catalyst was removed by centrifugation.
Polymers were obtained by precipitation and analyzed by 1 H NMR and GPC.

Redox potentials of BDMAT and various catalysts measured by cyclic voltammetry.
Samples (1 mg/mL in ethanol) were drop-casted onto the GC-electrode and then dried. The GC-electrode was immersed into the electrochemical cell containing acetonitrile with 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF 6 ). The compounds were electrochemically reduced prior to being oxidized between −2.0 V and +2.0 V at a scan rate of 100 mV/s.
Investigation of electron transfer mechanism using fluorescence quenching study.
A series of plastic tube containing PDPB-NF6 (at the same concentration of 0.125 mg/mL in EtOH) and quencher, MVCl 2 (varying concentrations from 0 to 3.89 mM). The mixture was degassed by N 2 for 20 min, then fluorescence properties were measured by fluorescence spectrometer.

General procedures for kinetic study of photo-induced living polymerization catalyzed
by PDPB-NF6.
The polymerization were conducted in a glass sealed tube, charged with water (3 mL

Photobleaching studies of eosin Y and catalysts.
The photobleaching experiments were conducted in a glass sealed tube, charged with eosin Y (1 × 10 -5 M) and catalysts (1 mg/mL) in DMF, respectively. The mixture was deoxygenated by three freeze-pump-thaw cycles and sealed under vacuum. The mixture was then irradiated by OSRAM ULTRA-VITALUX (100-300 W) at room temperature. Aliquots were withdrawn by syringe from the reaction mixture at predetermined interval times, and analyzed by UV-vis Spectroscopy.                  (g/mol) M n.GPC (Đ) [c] (g/mol)