* Corresponding authors
a Guangzhou Institute of Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China
b Key Laboratory of Cellulose and Lignocellulosics Chemistry, Chinese Academy of Sciences, Guangzhou 510650, China
c University of Chinese Academy of Sciences, Beijing 100049, China
Bisphenol A and bis(p-chlorophenyl) sulfone (Hallochem Pharma Co. Ltd, China), methanol (Merck), dimethylacetamide (DMA, 99%, Merck) were used without any purification. Dichloromethane (99%, Aldrich), chloroform (+99%, Aldrich), acryloyl chloride (+97%, Merck), methacryloyl chloride (+97%, Merck) were used as received. 2,2-Dimethoxy-2-phenylacetophenone (DMPA, 99%, Across) was also used without any additional treatment.
1H NMR spectra of 5–10% (w/w) solutions of the intermediates and final polymers in CDCl3 with Si(CH3)4 as an internal standard were recorded at room temperature at 250 MHz on a Bruker DPX 250 spectrometer. Fourier transform infrared-Attenuated Total Reflectance (FTIR-ATR) spectra were recorded on a Perkin-Elmer FT-IR Spectrum One B spectrometer with a Universal ATR accessory equipped with a single reflection diamond crystal. Solid oligomers were placed over the ATR crystal and maximum pressure was applied using the slip-clutch mechanism. Differential scanning calorimetry (DSC) was performed on a Perkin-Elmer Diamond DSC. Molecular weights and polydispersities of the linear oligomers were measured by gel permeation chromatography (GPC) employing an Agilent 1100 instrument equipped with a differential refractometer with tetrahydrofuran as the eluent at a flow rate of 0.3 mL min−1 at 30 °C. Molecular weights were determined using polystyrene standards. Thermal gravimetric analysis (TGA) was performed on Perkin–Elmer Diamond TA/TGA with a heating rate of 10 °C min under nitrogen flow.
Preparation of the oligomers
General procedure for the synthesis of polysulfone oligomer
Bisphenol A (40 g, 175 mmol), bis(p-chlorophenyl) sulfone (25.16 g, 87.6 mmol) and dried potassium carbonate (25.39 g, 183.6 mmol) were added to 400 mL DMA (dimethyl acetamide) and 50 mL toluene in a 2000 mL, 2 necked round bottom flask, fitted with a condenser, nitrogen inlet, a Dean and Stark trap and an overhead mechanical stirrer. The reaction mixture was heated under reflux at 150 °C for 4 h with water removal. The reaction was stopped after about 2 h and cooled to room temperature. The solution was filtered to remove most of the salts and poured into a mixture of methanol andwater (4:1). The precipitated polymer was filtered, and washed several times with water in order to remove the remaining salts and impurities. Finally, the polymer was washed with methanol and dried in a vacuum oven at 60 °C for about 12 h to give PSU-2000 oligomer (42.2 g).
IR (ATR, cm−1): 3435 (-OH), 3200–3000 (Ar), 2975 (-CH3 sym-), 2945 (-CH3 asym-), 1322 and 1293 (O=S=O asym-), 1240 (C-O-C), 1175 and 1151 (O=S=O sym-) and 1014 (Ar).
1H NMR (CDCl3, ppm): δ = 7.85 (16H), 7.26 (16H), 7.07 (4H), 7.00 (16H), 6.94 (16H), 6.75 (4H), 1.69 CMe2 (30H).
A similar procedure using appropriate ratios of the monomers was used for the synthesis of PSU-4000.
Synthesis of polysulfone diacrylate (PSU-DA)
PSU-2000 (5 g, 2.86 mmol) was added to 20 mL CH2Cl2 in a 50 mL, two necked round bottomed flask fitted with a condenser and argon inlet. The flask was placed in an ice bath and the contents stirred for about 5 min. Excess triethylamine (Et3N) 2.0 mL was added followed by excess acryloyl chloride (1.15 mL, 14.3 mmol) dissolved in 5 mL CH2Cl2 which was added slowly to the reaction flask over a 10 min period. The reaction mixture was stirred for 24 h then filtered to remove the salts formed and poured into methanol to precipitate the acrylate oligomer. The precipitated oligomer was filtered and washed several times with water to remove the remaining salts and impurities. Finally, the polymer was washed with methanol and dried in a vacuum oven at room temperature for about 12 h to give PSU-DA-2000 macromonomer (5 g).
IR (ATR, cm−1): 3200–3000 (Ar), 2968 (-CH3 sym-), 2875 (-CH3 asym-), 1739 (-C=O), 1322 and 1293 (O=S=O asym-), 1238 (C-O-C), 1175 and 1151 (O=S=O sym-) and 1014 (Ar).
1H NMR (CDCl3, ppm): δ = 7.76 (16H), 7.16 (16H), 7.02 (4H), 6.94 (16H), 6.86 (16H), 6.84 (4H), 6.53–6.51 (2H) and 6.24–6.22 (2H) (CH2=), 5.94–5.92 (2H) (=CH-), 1.62 CMe2 (30H).
The same procedure was applied for the synthesis of PSU-DA-4000.
Synthesis of polysulfone dimethacrylate (PSU-DM)
For the preparation of PSU-DM-2000, a similar procedure as described for the synthesis of acrylate functional macromonomers was followed with methacryloyl chloride.
IR (ATR, cm−1): 3200–3000 (Ar), 2969 (-CH3 sym-), 2875 (-CH3 asym-), 1735 (-C=O), 1323 and 1295 (O=S=O asym-), 1243 (C-O-C), 1175 and 1151 (O=S=O sym-) and 1014 (Ar).
1H NMR (CDCl3, ppm): δ = 7.78 (16H), 7.17 (16H), 6.94 (16H), 6.87 (16H), 6.26 (2H) and 5.76 (2H), 1.98 (C=-Me) (6H), 1.63 CMe2 (30H).
Preparation of Photo-curable formulations
Formulations containing macromonomers (0.003 g) and DMPA (2 mol %) in 250 µL chloroform were prepared from appropriate stock solutions. The mixture was then dropped onto an aluminum pan and the solvent allowed to evaporate completely. The film samples were placed into the sample cell of photo-DSC instrument.
The photo-differential scanning calorimetry (Photo-DSC) measurements were carried out by means of a modified Perkin-Elmer Diamond DSC equipped with a high pressure mercury arc lamp (320–500 nm). A uniform UV light intensity was delivered across the DSC cell to the sample and reference pans. The intensity of the light was measured as 53 mW cm−2 by a UV radiometer capable of broad UV range coverage. The mass of the sample was 3 mg, and the measurements were carried out in an isothermal mode at 30 °C under a nitrogen flow of 20 mL min−1. The heat liberated in the polymerization was directly proportional to the number of acrylate groups reacted in the system. By integrating the area under the exothermic peak, the conversion of the acrylate groups (C) or the extent of the reaction was determined according to Equation 1:
where ΔHt is the reaction heat evolved at time t and ΔH0theory is the theoretical heat for complete conversion. ΔH0theory = 86 kJ mol−1 for an acrylic double bond . The rate of polymerization (Rp) is directly related to the heat flow (dH/dt) by Equation 2: