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Synthesis of prepolymers and characterization

Thermal polyesterification of itaconic acid (IA), polyethylene glycol 400

Polymers were prepared in dependence on the experimental procedures of Barrett et al.^[1]

The procedure requires exact masses. Therefore an analytical balance (4 decimal places) was used and if not otherwise stated PEG as well as itaconic acid were pre-dried before use on a high vacuum line (< 10^-3 mbar) overnight.

To avoid contamination with oxygen during the reaction and to remove produced water, common Schlenk technique was applied. As inert gas argon was used.

A1

Date: 02/06/15 – 03/06/15

Lab members: AW, SZ

Preparation process:

A 50 mL Schlenk flask was loaded with 1.213 g (3.033 mmol, 1 eq.) PEG-400 and 0.395 g (3.032 mmol, 1 eq.) itaconic acid and flushed with argon. Within 20 minutes the mixture was heated up to 100 °C with an oil bath and stirred under argon atmosphere. As a colorless melt had formed the vacuum was applied (3·10^-2 mbar) and the mixture was stirred at 100 °C for 17 h. The slightly yellow viscous liquid was cooled down to room temperature. 

For a picture of A1 see appendix.

Analysis:

No further analyses were performed.

A2

Date: 09/06/15 – 10/06/15

Lab members: FR, SJ

Preparation process:

A 25 mL Schlenk tube was loaded with 2.169 g (5.422 mmol, 1 eq.) PEG-400, 0.705 g (5.420 mmol, 1 eq.) itaconic acid and capped with a septum. Within an hour the mixture was heated up to 145 °C with an oil bath and stirred under argon atmosphere. As a colorless melt had formed the vacuum was applied (< 10^-3 mbar) and the mixture was stirred at 145 °C for 24 h. The slightly yellow viscous liquid was cooled down to room temperature.

For a picture of A2 see appendix.

Visual Observations:

During the reaction itaconic acid recrystallised on the flask surface which wasn’t dipped into the oil bath. Therefore the ratio between itaconic acid and PEG-400 has changed.

Analysis:

The product was analyzed by differential scanning calorimetry DSC to identify the glass transition (T_g) temperature.

The T_g of A2 is -4.7 °C.

Figure 1: DSC- Plot of A2. The T_g of A2 is -4.7 °C

A3

Date: 11/06/15 – 12/06/15

Lab members: FR, SJ, AW, SZ

Preparation process:

A 10 mL Schlenk tube was loaded with 2.675 g (6.688 mmol, 1 eq.) PEG-400, 0.869 g (6.679 mmol, 1 eq.) itaconic acid and capped with a septum. The mixture was heated up to 145 °C with an oil bath on air. No vacuum was applied and the mixture was stirred on air at 145 °C for 24 h. The orange-colored viscous liquid was cooled down to room temperature.

Visual Observations:

The orange-colored product was more viscous than A1 and A2. For a picture of A3 see appendix.

Analysis:

DSC

The product was analyzed by differential scanning calorimetry DSC to identify the glass transition (T_g) temperature.

The T_g of A3 is -45.8 °C.

Figure 2: DSC- Plot of A3. The T_g of A3 is -45.8 °C

¹H-NMR

The product was analyzed by ¹H-NMR to ensure that double bonds are still intact in the product.

Figure 3 shows the spectrum with an enlargement of the olefin region.

Figure 3: ¹H-NMR (300 MHz) of A3 in CDCl₃

Solubility Tests

The solubility of product A3 increases with hydrophobicity of the solvent. But it is still good soluble in water and methanol. This indicates that alkene cross linking during the synthesis not occurred. And the polymer is linear shaped.

A4

Date: 11/06/15 – 12/06/15

Lab members: FR, SJ, AW, SZ

Preparation process:

A 20 mL snap-cap vial was loaded with 1.912 g (4.779 mmol, 1 eq.) PEG-400, 0.622 g (4.781 mmol, 1 eq.) itaconic acid and capped with a septum. The snap-cap vial was flushed with argon for 5 minutes and heated up to 145 °C with an oil bath. The snap-cap vial was almost complete dipped into the oil bath to avoid crystallization on the cold glass surface. The formed colorless melt was then stirred under slight vacuum for 24 h. Afterwards the orange-colored viscous liquid was cooled down to room temperature.

Visual Observations:

The orange-colored product was more viscous than A1 and A2. Viscosity and colour were comparable with A3. For a picture of A4 see appendix.

Analysis:

DSC

The product was analyzed by differential scanning calorimetry DSC to identify the glass transition (T_g) temperature.

The T_g of A3 is -49.1 °C.

Figure 4: DSC- Plot of A4. The T_g of A4 is -49.1 °C

¹H-NMR

The product was analyzed by ¹H-NMR to ensure that double bonds are still intact in the product.

Figure 5 shows the spectrum with an enlargement of the olefin region.

Figure 5: ¹H-NMR (300 MHz) of A4 in CDCl₃.