Low‐Temperature, Surface‐Mediated Foaming of Polymer Films

Abstract

nomethylpiperidine (AMP) solution, 0.4 M: 0.5 g of AMP are dissolved in 10 mL of THF and stored at 4 C for at least 1 h before use. Inside a cold room, amine-SBA-15 (1.0 g) is placed in a 15 mL peptide synthesis vessel and 10 mL of the CC solution is added. The mixture is incubated while shaking for 24 h at 4 C . Then, the solution is removed by filtration and the solid is rinsed with 30 mL portions of methanol, dichloromethane, and THF. The AMP solution (10 mL) is added to the amine±SBA-15 and incubated again for 24 h at 4 C while shaking. Afterward, the silica is washed as previously described and dried under vacuum. The same procedure is repeated to increase the generation (size) of the dendrimers attached to the SBA-15.Powder X-ray diffraction (XRD) was performed on a Bruker-AXS D8 powder diffractometer using Cu Ka radiation over a range of 0.8 to 10 2h. Transmission electron microscopy was performed on a JEOL 2010 microscope with a lanthanum hexaboride filament and an excitation voltage of 200 kV. TGA data were collected on a TG 209C Iris from Netzsch Instruments over a temperature range of 25 to 600 C using oxygen as a carrier gas and a temperature ramping rate of 10 C min ±1 . Mass spectra were aquired using MALDI-MS on an Applied Biosystems Voyager-DE STR Biospectrometry Workstation. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) spectra were recorded in linear ion mode with an Applied Biosystems Voyager DE-STR mass spectrometer (ABI, Framingham, MA). Positive ions were generated by using a nitrogen laser pulse (y = 337 nm, 20 Hz) and accelerated under 20 kV using delayed extraction (550 ns) before entering the time-of-flight mass spectrometer. Laser strength was adjusted to provide minimal fragmentation and optimal signal-to-noise ratio. An average of 200 laser shots was used for each spectrum, and data were processed with the accompanying Voyager software package. The sample was prepared using the overlayer method [18,19] with 2,4,6-trihydroxyacetophenone (THAP) as has been described previously [20]. The sample cocktail, approximately 1 lM dendrimer and 10 mg mL ±1 THAP solution in methanol, was spotted in 1 lL aliquots on top of a 100 mg mL ±1 THAP matrix bed. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) measurements were performed on a Perkin±Elmer Spectrum One FT-IR spectrometer. Nitrogen adsorption experiments were performed on a Micromeritics ASAP 2010 micropore system. Approximately 0.1 g of sample was degassed under vacuum at room temperature for 4 h, then at 60 C for 4 h, then at 100 C for 20 h before analysis. The mesopore size distribution was calculated from the adsorption branch of the isotherm using the Barret±Joyner±Halenda (BJH) method with a modified equation for the statistical film thickness [21,22] Polymer foams show tremendous promise over their dense analogs in terms of material, cost, weight, and waste reduction, as well as property enhancement, multiple functionality, and post-use recyclability. Here, we show for the first time that ul...

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