Supplementary Material for Chemical Communications
This journal is © The Royal Society of Chemistry 2003
Synthesis of polymers
The synthesis of the polymers by ring-opening polymerization follows work described in reference 7 of the original contribution.
Reagents. Silver cyanide (Across, 99 %), 3-amino-1-propanol (Across, 99 %), tert-butyl isocyanide (Fluka, ³ 98 %), sodium hydroxide (Riedel-de Haen, p.a.), formic acid (Across, 99 %), and formalin (Fluka, 36.5 % solution in water) were used without further purification. Methanol and diethyl ether were distilled. The stabilizer in benzyl chloride was removed by passing through an aluminum oxide column. Benzyl chloride and methyl tosylate were purified by distillation and stored under nitrogen at 0°. N,N-dimethylformamide (DMF) and 2-methyl-2-oxazoline were dried with CaH2, distilled, and stored under nitrogen at –18 °C. Concentrated hydrochloric acid was added to benzonitrile followed by preliminary drying with potassium carbonate. The solution was filtered, dried with phosphorous pentoxide, distilled, and stored under nitrogen at –18°.
Synthesis of 5,6-dihydro-4H-oxazine. In a two-necked round bottom flask, equipped with a reflux condenser, 0.011 mol silver cyanide, 0.221 mol tert-butyl isocyanide, and 0.221 mol 3-amino-1-propanol were mixed. The mixture was heated at 90 °C for 18 hr with stirring under nitrogen. After reaction the byproduct tert-butyl amine (b.p.: 46 °C) was distilled off under nitrogen. The product 5,6-dihydro-4H-oxazine was obtained in 70 % yield by destillation under reduced pressure (b.p. = 51-53 °C / 100 mbar).
1HNMR (CDCl3) d (ppm): 6.73 (-(-CH=N-CH2-CH2-CH2-O-)-, s), 3.08 (-(-CH=N-CH2-CH2-CH2-O-)-, t, J 5.9 Hz), 1.69 (-(-CH=N-CH2-CH2-CH2-O-)-, m), 3.90 (-(-CH=N-CH2-CH2-CH2-O-)-, t, J 5.5 Hz)
13CNMR (CDCl3) d (ppm): 149.5 (-(-CH=N-CH2-CH2-CH2-O-)-), 41.1 (-(-CH=N-CH2-CH2-CH2-O-)-), 22.1 (-(-CH=N-CH2-CH2-CH2-O-)-, 64.0 (-(-CH=N-CH2-CH2-CH2-O-)-)
Polymerization of 5,6-dihydro-4H-oxazine. A 10-mL-Schlenk tube was dried by heating under vacuum and backfilling with nitrogen three times. 2.5 mL 5,6-dihydro-4H-oxazine, 2.5 mL DMF and 0.443 mL methyl tosylate were placed in the Schlenk tube under nitrogen flow. After addition of the initiator a weak yellow coloration was observed. The Schlenk tube was heated at 80 °C for 24 hr and the reaction mixture changed its color to luminous yellow. The solution was diluted with methanol and precipitated in diethyl ether. Purification by reprecipitation was repeated twice and the pale yellow poly-N-formylpropylene imine (PFPI) was dried in vacuum. Yield: 95 %.
Polymerization of 2-methyl-2-oxazoline. A 10-mL-Schlenk tube was dried by heating under vacuum and backfilling with nitrogen three times. 20.0 mL 2-methyl-2-oxazoline, 40 mL benzonitrile and 3.28 mL benzyl chloride were placed in the Schlenk tube under nitrogen flow. The Schlenk tube was heated at 110 °C for 25 hr. The solution was diluted with methanol and precipitated in diethyl ether. Purification by reprecipitation was repeated twice and the poly-N-acetylethylene imine (PAEI) was dried in vacuum. Yield: 86 %.
Alkaline hydrolysis of PFPI. 1.03 g PFPI and 0.80 g sodium hydroxide were dissolved in a mixture of 6.5 mL water and 6.5 mL methanol. The solution was purged with nitrogen and heated to 95 °C for 3 hr. The precipitate was filtered and washed with water. The crude product was dissolved in methanol and precipitated in diethyl ether. This procedure was repeated twice and the white polypropylene imine was dried in vacuum. Yield: 49 %.
Alkaline hydrolysis of PAEI. 5.00 g PAEI and 4.68 g sodium hydroxide were dissolved in 50 mL water. The solution was purged with nitrogen and heated to 95 °C for 40 hr. The precipitate was filtered and washed with water to pH of 8-9. For purification the crude product was dissolved in hot water and precipitated by cooling down the aqueous solution. This procedure was repeated once and the white polyethylene imine was dried in vacuum. Yield: 60 %.
Reductive methylation of PAEI or PFPI. 1.00 g of polymer was dissolved in a mixture of 5 mL formalin and 10 mL formic acid. The solution was refluxed at 105 °C for 48 hr and then distilled under reduced pressure. 15 mL concentrated hydrochloric acid were added to the residue. This solution was again distilled under reduced pressure. The crude hydrochloride of the methylated polymer was dissolved in water and neutralized by passing through a column of an anion exchange resin (Dowex 1x2-400 converted to OH- form). The neutralized solution was lyophilized. Yield for PMEI: 97 %. Yield for PMPI: 68 %.
Titration of the polyamines.
A general procedure was as follows. 50 mL of a polyamine solution (c = 8.6×10-4mol amino groups / l) was kept at 25°C and titrated with 0.01 M hydrochloric acid (Fixanal solution). The pH was measured with a digital pH-meter, which was calibrated at pH = 4 and pH = 7 with standard buffers. After addition of acid, the pH was constant only after several minutes of equilibration time.
Kinetic investigations of silica condensation
Investigation on the kinetics of the silicic acid condensation in the presence of polyamines was performed by the molybdate method, introduced by Alexander (ref. 14 of the original contribution). After addition of a molybdate solution, the yellow molybdosilicate [SiMo12O40]8- is formed from monomeric and dimeric silicic acid. The absorption of this anion is measured at a wavelength of 400 nm. The decrease of the absorption with time reflects the decrease in the concentrations of monomeric and dimeric silicic acid due to the condensation reactions. Due to the chemical equilibria between silicic acid and molybdate as well as between monomeric, dimeric and oligomeric silicic acids, it is important to adhere to a strictly defined protocol with a constant reaction time for the formation of the molybdosilicate.
Polyamine solutions were prepared by dissolving the amine in 10-5 M hydrochloric acid so that the amine concentration was 10 mg/L. The silicic acid solution was prepared by hydrolysis of tetramethoxysilane in the stochiometric amount of 0.01 M hydrochloric acid.
To the freshly prepared silicic acid solution the solution containing the amine was added so that the initial silicic acid concentration was 0.16 M. At regular intervals, samples were drawn from this mixture to monitor the progress of the condensation reaction. The samples were diluted to an appropriate silicic acid concentration and then added to the acidic molybdate solution. After exactly 10 minutes of reaction time for the formation of the molybdosilicate, the absorbance of the yellow solution was measured.
The pH value of the reaction mixtures containing polyamines decreased within the first 50 minutes of the condensation and then remained constant. Table 1 shows the initial and final pH values for the different amines. Reaction mixtures containing amines that show a stronger accelerating effect on the condensation have a higher final pH.
Table 1. Initial and final pH values of the reaction mixtures containing the different amines.
pH / amine / pH / Amine4.3 → 4.3 / w/o amine / 5.0 → 4.2 / PMPI
4.8 → 4.4 / Branched PEI / 4.9 → 4.4 / linear PPI
4.8 → 4.3 / PMEI / 6.0 → 4.8 / hexaazadocosane
5.5 → 4.8 / linear PEI / 5.9 → 6.0 / 1,3-diaminopropane
5.9 → 5.9 / diaminoethane