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A Degradable Difunctional Initiator for ATRP That Responds to Hydrogen Peroxide
Lawrence Hill ; Hunter Sims ; Christopher Collins , et al. Polymers,2022,14(9):1733. DOI: 10.3390/polym14091733 PubMed ID: 35566902
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Abstract: Mid-chain degradable polymers can be prepared by atom transfer radical polymerization from difunctional initiators that include triggers for the desired stimuli. While many difunctional initiators can respond to reducing conditions, procedures to prepare difunctional initiators that respond to oxidizing conditions are significantly less available in the literature. Here, a difunctional initiator incorporating an oxidizable boronic ester trigger was synthesized over four steps using simple and scalable procedures. Methyl methacrylate was polymerized by atom transfer radical polymerization using this initiator, and the polymerization kinetics were consistent with a controlled polymerization. The polymer synthesized using the difunctional initiator was found to decrease in molecular weight by 58% in the presence of hydrogen peroxide, while a control experiment using poly(methyl methacrylate) without a degradable linkage showed a much smaller decrease in molecular weight of only 9%. These observed molecular weight decreases were consistent with cleavage of the difunctional initiator via a quinone methide shift and hydrolysis of the methyl ester pendent groups in both polymers, and both polymers increased in polydispersity after oxidative degradation.
Keywords: boronic ester ; degradable polymer ; difunctional initiator ; ATRP
Purchased from AmBeed: 138500-85-3
CAS No. : | 138500-85-3 | MDL No. : | MFCD02179493 |
Formula : | C13H18BBrO2 | Boiling Point : | No data available |
Linear Structure Formula : | (CH3)4C2O2BC6H4CH2Br | InChI Key : | CBUOGMOTDGNEAW-UHFFFAOYSA-N |
M.W : | 297.00 | Pubchem ID : | 3734506 |
Synonyms : |
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Signal Word: | Warning | Class: | |
Precautionary Statements: | P261-P301+P312-P302+P352-P304+P340-P305+P351+P338 | UN#: | |
Hazard Statements: | H302-H315-H319-H335 | Packing Group: | |
GHS Pictogram: |
* All experimental methods are cited from the reference, please refer to the original source for details. We do not guarantee the accuracy of the content in the reference.
Yield | Reaction Conditions | Operation in experiment |
---|---|---|
94% | With carbon tetrabromide; triphenylphosphine; In tetrahydrofuran; at 0 - 20℃; for 18h;Inert atmosphere; | 2-(4-(Bromomethyl)phenyl)-4,4,5,5-tetramethyl-l,3,2-dioxaborolane (3) The compound 2(1 eq, 5.72 mmol) was dissolved in THF (25 mL) followed by the addition of triphenylphosphine (2 eq, 11.4 mmol). The mixture was cooled to 0C with an ice bath then tetrabromomethane (2 eq, 11.4 mmol) was carefully added portion wise. The reaction was stirred at rt for 18h. The solution was poured into water (30 mL) and extracted 3 times (3 x 25 mL) with EtOAc. The combined organic extracts were dried, filtered and evaporated under vacuum. The compound was purified using column chromatography (silica gel, 99/1Hex/EtOAc) to afford the desired compound (Rf = 0.2) as a colourless solid (1.6 g, 94%). 1H-NMR (CDCI3, 600 MHz) delta 7.78 (d, J = 8.0 Hz, 2H), 7.38 (d, J = 8.0 Hz, 2H), 4.49 (s, 2H), 1.34 (s, 12H); 13C-NMR (CDC13, 150 MHz) delta 140.8, 135.3, 128.4, 84.0, 33.4, 25.0. |
92% | With carbon tetrabromide; triphenylphosphine; In tetrahydrofuran; at 20℃; for 4h;Cooling with ice; | 4-hydroxymethylphenylboronic acid, pinacol ester (1.08 g, 4.61 mmol) was dissolved in THF (20 ml) together with triphenylphosphine (2.42 g, 9.23mmol). The reaction mixture was cooled in an ice-water bath, and carbon tetrabromide (3.06 g, 9.23 mmol) was added portion wise. After stirring for 4 hours at room temperature, the reaction mixture was poured into water and extracted with ethyl acetate. The organic layer was combined and dried by sodium sulfate. After filtration, the solvent was evaporated, and the residue was purified by flash chromatography to give the product as a white solid (1.72 g, 92%). 1H NMR (300 MHz, CD2C12, delta): 7.62 (d, J = 6.0 Hz, 2H), 7.32 (d, J = 6.0 Hz, 2H), 4.58 (d, 2H), 1.34 (s, 9H); MS (ESI) m/z 297.0. |
Yield | Reaction Conditions | Operation in experiment |
---|---|---|
With potassium carbonate; In N,N-dimethyl-formamide; at 80℃; for 0.75h; | 2-(4-Bromomethyl-phenyl)-4,4,5,5-tetramethyl-[1 ,3,2]dioxaborolane (250 mg; 0.84 mmol), piperidine (94 mg; 1.1 mmol) and K2CO3 (140 mg; 1.01 mmol) in DMF (4 ml) are heated to <n="59"/>800C for 45 minutes. The reaction mixture is cooled to room temperature, diluted with TBME, filtered and evaporated to dryness to deliver the title compound as orange crystals. N 1 H-NMR (400MHz; DMSO-d6): 7.63 (d, 2H); 7.33 (d, 2H); 3.44 s, 2H); 2.31 (bs, 4H); 1.50 (m, 4H); 1.39 (m, 2H); 1.30 (s, 12H). MS (m/z) ES+: 302 (MH+). |
Yield | Reaction Conditions | Operation in experiment |
---|---|---|
82% | With cesium chloride; In N,N-dimethyl-formamide; at 60℃; for 0.75 - 0.833333h; | 6-(4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)benzyloxy)benzo[d]thiazole-2-carbonitrile (5) Compounds 3 (300 mg, 1.7 mmol) and 4 (505.7 mg, 1.7 mmol) were dissolved in 30 mL dry DMF prior to the addition of cesium chloride (610.25 mg, 1.87 mmol). The mixture was stirred at 60° C. for 45-50 min before it was allowed to cool to room temperature. 100 mL ethyl acetate was added to the reaction, and the organic phase was washed three times with deionized water. The aqueous layers were combined and washed three times with ethyl acetate. All of the organic layers were combined, washed twice with brine, dried over sodium sulfate, and concentrated. The crude material was purified on a silica column (90:10 hexanes:ethyl acetate, dry loaded) to give 547.4 mg (82percent) of the pure product. 1H NMR (400 MHz, CDCl3): delta 1.36 (1H, s), 5.21 (2H, s), 7.32 (1H, d, J=8.8 Hz), 7.40 (1H, s), 7.45 (2H, d, J=7.6 Hz), 7.86 (2H, d, J=7.2 Hz), 8.09 (1H, d, J=9.2). LRESI-MS: calculated for [C21H22BN2O3S]+393.1. found 393.1. |
Yield | Reaction Conditions | Operation in experiment |
---|---|---|
72% | To a solution of methyl 2-ethoxy-lH-benzo[d]imidazole-7-carboxylate (1.00 g, 4.54 mmol) in 2-propanol (15 ml) was added potassium carbonate (1.26 g, 9.08 mmol) and this was stirred at 30°C for 5 minutes. To this mixture were added 2-(4- (bromomethyl)phenyl)-4,4,5,5-tetramethyl-l,3,2-dioxaborolane (1.44 g, 4.77 mmol) and tetrabutylammonium iodide (0.084 g, 0.227 mmol) and the temperature was increased to 45°C. After stirring for 2.5 hours, another portion of 2-(4-(bromomethyl)phenyl)-4,4,5,5- tetramethyl-l,3,2-dioxaborolane (0.250 g, 0.842 mmol) was added and the reaction was stirred for an additional 18 hours. The reaction was cooled to RT and diluted with EtOAc (200 ml), and 0 (50 ml) was added. The layers were separated and the organic layer was washed with brine (50 ml), then dried over anhydrous sodium sulfate, filtered, and evaporated under reduced pressure. The residue was dissolved in DCM (10 ml) and injected on a 40-gram ISCO-type silica gel column pre-equilibrated with hexane and the title compound was purified by elution using a 0 to 60percent EtOAc/hexane gradient to provide the title compound as a yellow solid. (1.44 g, 3.31 mmol, 72percent yield). LC-MS (Method H): 1.42 min, [M + H]+= 437.2; H NMR (400 MHz, CDC13) delta ppm 7.73 (dd, 7=8.0, 1.0 Hz, 1 H) 7.67 (m, 7=8.2 Hz, 2 H) 7.53 (dd, 7=7.8, 1.2 Hz, 1 H) 7.16 (t, 7=7.8 Hz, 1 H) 6.96 (m, 7=8.2 Hz, 2 H) 5.63 (s, 2 H) 4.65 (q, 7=7.0 Hz, 2 H) 3.72 (s, 3 H) 1.46 (t, 7=7.0 Hz, 3 H) 1.31 (s, 12 H). |
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