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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.

 

 

Group-Leader:

Fabian Rohden (FR)

 

Members:

Anastasia Weyrich (AW)

Stefan Zens (SZ)

Sebastian Jäger (SJ)

 

 

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

Solvent	Solubility of Product A3
H2O	good
THF	very good
CHCl3	very good
EtOH	very good
MeOH	good

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.

 

 

A10

Date: 16/07/15 – 17/07/15

Lab members: FR, AW

 

Preparation process:

A 20 mL snap-cap vial was loaded with 2.2750g (5.688 mmol, 1 eq.) PEG-400, 0.7388 g (5.679 mmol, 1 eq.) itaconic acid and capped with a pierced aluminium foil. 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 21 h. The brown-colored viscous liquid was cooled down to room temperature.

 

Visual Observations:

The brown-colored product was more viscous than A8 but less viscous than A7 and A9.

 

Analysis:

DSC

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

The T_g of A10 is -46.9 °C.

Figure 6:DSC- Plot of A10. The T_g of A10 is -46.9 °C.

 

 

 

Thermal polyesterification of itaconic acid (IA), polyethylene glycol 400 (PEG-400) and xylitol

 

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 and xylitol were pre-dried before use on a high vacuum line (< 10^-3 mbar) overnight.

 

 

A5

Date: 30/06/15 – 01/07/15

Lab members: FR, SJ, AW, SZ

 

Preparation process:

A 20 mL snap-cap vial was loaded with 0.997 g (2.491 mmol, 0.43 eq.) PEG-400, 0.3833 g (2.519 mmol, 0.44 eq.) xylitol, 0.7503 g (5.767 mmol, 1 eq.) itaconic acid and capped with a pierced aluminium foil. 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 17.5 h. The orange-colored gel was cooled down to room temperature.

 

Visual Observations:

The orange-colored product was a ductile gel. For a picture of A5 see appendix.

 

Analysis:

Solubility Tests

<tbody> </tbody>

Solvent	Solubility of Product A5
H2O	no
THF	no
Aceton	no
EtOH	no
MeOH	no

The gel wasn’t soluble in any solvent. Even by applying ultrasound no dissolving occurred. This is probably due to high cross linking with xylitol.

 

 

A6

Date: 30/06/15 – 01/07/15

Lab members: FR, SJ, AW, SZ

 

Preparation process:

A 20 mL snap-cap vial was loaded with 1.2775 g (3.194 mmol, 0.58 eq.) PEG-400, 0.2038 g (1.339 mmol, 0.25 eq.) xylitol, 0.7099 g (5.457 mmol, 1 eq.) itaconic acid and capped with a pierced aluminium foil. 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 17.5 h. The orange-colored viscous liquid was cooled down to room temperature.

 

Visual Observations:

The orange-colored product was a ductile gel. For a picture of A6 see appendix.

 

Analysis:

Solubility Tests

<tbody>

Solvent	Solubility of Product A6
H2O	no
THF	no
Aceton	no
EtOH	no
MeOH	no

The gel wasn’t soluble in any solvent. Even by applying ultrasound no dissolving occurred. This is probably due to high cross linking with xylitol.

 

 

A8 

Date: 16/07/15 – 17/07/15

Lab members: FR, AW

 

Preparation process:

A 20 mL snap-cap vial was loaded with 3.4567 g (8.642 mmol, 0.90 eq.) PEG-400, 0.0973 g (0.640 mmol, 0.067 eq.) xylitol, 1.2492 g (9.602 mmol, 1 eq.) itaconic acid and capped with a pierced aluminium foil. 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 21 h. The orange-colored viscous liquid was cooled down to room temperature.

 

Visual Observations:

The orange-colored product was a viscous liquid. A8 was less viscous than A10, A7 and A9.

 

Analysis:

DSC

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

The T_g of A8 is -44.8 °C. 

Figure 7:DSC- Plot of A8. The T_g of A8 is -44.8 °C.

 

 

A9

Date: 16/07/15 – 17/07/15

Lab members: FR, AW

 

Preparation process:

A 20 mL snap-cap vial was loaded with 1.5400 g (3.850 mmol, 0.95 eq.) PEG-400, 0.0205 g (0.135 mmol, 0.033 eq.) xylitol, 0.5257 g (4.041 mmol, 1 eq.) itaconic acid and capped with a pierced aluminium foil. 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 21 h. The brown-colored viscous liquid was cooled down to room temperature.

 

Visual Observations:

The brown-colored product was a viscous liquid. A9 was more viscous than A7, A10 and A8.

 

Analysis:

DSC

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

The T_g of A9 is -44.4 °C.

Figure 8:DSC- Plot of A9. The T_g of A9 is -44.4 °C.

 

 

 

Thermal polyesterification of itaconic acid (IA) and polyethylene glycol 200 (PEG-200)

 

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.

 

 

A7

Date: 16/07/15 – 17/07/15

Lab members: FR, AW

 

Preparation process:

A 20 mL snap-cap vial was loaded with 3.0745 g (15.373 mmol, 1 eq.) PEG-200, 2.000 g (15.373 mmol, 1 eq.) itaconic acid and capped with a pierced aluminium foil. 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 21 h. The orange-colored viscous liquid was cooled down to room temperature.

 

Visual Observations:

The orange-colored product was a viscous liquid.

 

Analysis:

DSC

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

The T_g of A7 is -37.1 °C.

Figure 9:DSC- Plot of A7. The T_g of A7 is -37.1 °C.

 

 

A11

Date: 28/07/15 – 30/07/15

Lab members: FR, SJ

 

Preparation process:

A 20 mL snap-cap vial was loaded with 12.3079 g (61.540 mmol, 1 eq.) PEG-200, 8.0030 g (61.514 mmol, 1 eq.) itaconic acid and capped with a pierced aluminium foil. 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 42 h. The orange-colored viscous liquid was cooled down to room temperature.

 

Visual Observations:

On the surface of the orange-colored viscous liquid a rigid gel has formed. For a picture of A11 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 A11 is -37.4 °C.

Figure 10: DSC- Plot of A11. The T_g of A11 is -37.4 °C.

 

 

A12

Date: 28/07/15 – 30/07/15

Lab members: FR, SJ

 

Preparation process:

A 20 mL snap-cap vial was loaded with 12.2955 g (61.478 mmol, 1 eq.) PEG-200 and 8.0025 g (61.511 mmol, 1 eq.) itaconic acid. For this experiment itaconic acid wasn’t pre-dried under high vacuum. The vial was capped with a pierced aluminium foil and 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 42 h. The orange-colored viscous liquid was cooled down to room temperature.

 

Visual Observations:

On the surface of the orange-colored viscous liquid a rigid gel has formed. For a picture of A12 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 A12 is -37.1 °C.

Figure 11:DSC- Plot of A12. The T_g of A12 is -37.1 °C.

 

 

A13

Date: 12/08/15 – 13/08/15

Lab members: SJ

 

Preparation process:

A 500 mL round bottom flask was loaded with 90.88 g (454.4 mmol, 1 eq.) PEG-200 and 59.12 g (454.4 mmol, 1 eq.) itaconic acid. For this experiment itaconic acid wasn’t pre-dried under high vacuum. The flask was capped with a pierced aluminium foil and 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 over night. The orange-colored viscous liquid was cooled down to room temperature.

 

Visual Observations:

At 143 °C IA was completely dissolved and a slightly yellow melt has formed. The produced water condensed partially on the wall of the flask. For a picture of A13 during and after synthesis 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 A13 is - 40.8 °C.

Figure 12: DSC- Plot of A13. The T_g of A13 is -40.8 °C.

 

 

A15

Date: 18/08/15 – 19/08/15

Lab members: SJ, AW, SZ

 

Preparation process:

A 1 L round bottom flask was loaded with 302.9 g (1.51 mol, 1 eq.) PEG-200 and 197.0 g (1.51 mol, 1 eq.) itaconic acid. For this experiment itaconic acid wasn’t pre-dried under high vacuum. The flask was capped with a pierced aluminium foil and 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 31 h. The orange-colored viscous liquid was cooled down to room temperature.

 

Visual Observations:

After 24 h a viscous orange-colored liquid has formed. The loss of mass during synthesis doesn’t correspond to the calculated mass loss due to produced and evaporated water (2 eq. water by high conversion). A sample for DSC analysis was taken and the mixture was stirred for 7 h. Afterwards another sample for DSC analysis was taken. For a picture of A15 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 A15 after 24 h at 145 °C is -39.9 °C.

The T_g of A15 after 31 h at 145 °C is -37.9 °C.

Figure 13: DSC- Plot of A15 after 24 h at 145 °C. The T_g of A15 is -39.9 °C.

 

Figure 14: DSC- Plot of A15 after 31 h at 145 °C. The T_g of A15 is -37.9 °C.

 

 

 

Thermal polyesterification of itaconic acid (IA) and ethylene glycol (EG)

 

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 EG as well as itaconic acid were pre-dried before use on a high vacuum line (< 10^-3 mbar) overnight.

 

 

A14

Date: 12/08/15 – 13/08/15

Lab members: SJ

 

Preparation process:

A 20 mL snap-cap vial was loaded with 1.6155 g (26.027 mmol, 1 eq.) EG and 3.3853 g (26.021 mmol, 1 eq.) itaconic acid. For this experiment itaconic acid wasn’t pre-dried under high vacuum. The vial was capped with a pierced aluminium foil and 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 over night.

 

Visual Observations:

During the reaction a film of ethylene glycol condensed on the vial wall. This is due to the boiling point of EG (197 °C). In this way the exact IA/EG ratio could be changed. The yellow-colored polymer is a rigid gel and not applicable for 3D printing. For a picture of A14 see appendix.

 

 

 

Analysis of the prepolymers with GPC

 

The prepolymers A10, A12, A13 and A15 were additionally analyzed by GPC (Gel permeation chromatography) to detect the average molar mass.

 

Method:

The metering was performed with the PSS Suprema HS column connect to a RID detector. NaNO₃ (0.1 mol/l) was used as eluent by a flow rate of 1 ml/min and polyacrylic acid as polymerstandard for the calibration.

 

Results:

All assays were smaller than the smallest polymerstandard of 1250 g/mol. Therefor the average molar mass was not definable.

Overlaying the assays allows the comparison of the different prepolymers. Thereby, one can see that the polymers A 12, A13 and A15 are very similar and only A10 has a different curve. This reflect the composition of the prepolymers. While A10 is out of PEG 400 and IA, the prepolymers A12-A15 are out of PEG 200 and IA.

Figure 15: GPC-Plot of A10 (light blue), A12 (blue), A13 (yellow) and A15 (black).

 

 

 

Curing of prepolymers

 

Prepolymers were mixed with different amounts of Ciba® DAROCUR 1173 photoinitiator and streaked on microscope glass slides. The slides were placed for different periods of time under UV-light 254 nm.

For pictures of the cured prepolymers see appendix.

<tbody> </tbody>

Prepolymer/ sample	Photoinitiator [wt-%]	Curing time (254 nm)
		5 min	10 min	15 min
PEG-400	1
A2	1
A3	2.3	-	-	currugation, soft
A4	1.8	-	-	currugation, soft
A7	2	-	-	solid
A8	2	-	-	gel
A9	2	-	-	gel
A10	2	-	-	gel
A11	0	currugation, soft	currugation, soft	currugation, soft
A11	0.5	currugated skin	currugated skin	currugated skin
A11	1	currugated skin	currugated skin	currugated skin
A11	2	currugated skin	currugated skin	currugated skin
A11	4	almost solid, plain	plain solid	plain solid
A11	9	plain solid	plain solid	plain solid
A12	0	currugation, soft	currugation, soft	currugation, soft
A12	0.5	plain skin	plain skin	plain skin
A12	1	plain skin	plain skin	plain skin
A12	2	plain skin	plain skin	plain skin
A12	4	almost solid, plain	plain solid	plain solid
A12	9	plain solid	plain solid	plain solid

By UV-curing of A8 on a polystyrene petri dish an interesting effect was observed. The hydrophilic hydroxyl groups of xylitol lead to formation of prepolymer drops due to the hydrophobic polystyrene surface of the petri dish. This effect is interesting because it could prevent adhesion of the polymer on the basin of the 3D printer during UV curing. Unfortunately A8 doesn’t cured by UV light, even not with 6 % DAROCUR 1173. For a picture see appendix.

 

 

 

References:

[1]        Barrett et al., Macromolecules 2010, 43, 9660-9667.

 

 

 

Appendix

 

Pictures of prepolymers during and after synthesis

 

Figure 16: From left to right A1 – A4 after synthesis

 

Figure 17: A5 and A6 after synthesis.

 

Figure 18: From left to right A12 – A11 after synthesis.

 

Figure 19: A13 and A14 during (left) and after synthesis (right).

 

Figure 20: A15 during heating up. At 131 °C no melt has formed and the white itaconic acid can be seen.

 

 

 

Pictures of cured prepolymers

 

Figure 21: UV-curing of A3 and A4 after 15 min.

 

Figure 22: UV-curing of A11 after 5, 10 and 15 min.

 

Figure 23: UV-curing of A12 after 5 and 10 min.

 

Figure 24: UV-curing of A8 and A15 on glass and on a polystyrene petri dish after 5 min 254 nm. 6 % DAROCURE 1173 was used.