Supporting Information to
Influence of intermediate degradation products on the hydrolytic degradation of
poly[(rac-lactide)-co-glycolide] at the air-water interface
by Anne-Christin Schöne, Sandra Falkenhagen, Oksana Travkova, Burkhard Schulz, Karl
Kratz and Andreas Lendlein
For clarification, the water-insoluble (solid) OLGAs are abbreviated as s-OLGA-Mn and the
water-soluble (aqueous) products are shortened as aq-OLGA-x, whereby the x gives the
percentage amount of oligomer fragments which is solved in water, unless otherwise
specified.
Average-number molecular weight of water-insoluble s-OLGA after hydrolysis in different
media depending on degradation time period
Table S1. Average-number molecular weight Mn (g·mol-1, GPC, universal calibration)
distributions of water-insoluble s-OLGA after hydrolysis in different media at 70 °C
Media
8h
16 h
24 h
48 h
72 h
H2O
7000
6200
2900
2500
pH 3.0
7600
6800
5100
3500
3400
pH 9.5
7400
7400
4700
3200
3500
NaCl *
7500
5800
6800
2600
3100
PBS pH 7.4
7800
6400
6700
4900
5000
c ~ 0.4 mg·mL-1 in dimethylformamide (DMF)/50 mmol ammonium acetate with 0.005 wt-%
2,6-di-tert-butyl-4-methylphenol as internal standard
* physiologic saline solution
Gel permeation chromatography curves of PLGA and s-OLGA after hydrolysis in water
PLGA
s-OLGA-7000
s-OLGA-6200
s-OLGA-2900
s-OLGA-2500
0
5000
10000
15000
20000
-1
Mn [g·mol ]
Figure S1 GPC curves of water-insoluble s-OLGA after hydrolyses in water at 70 °C after
0 h, 16 h, 24 h, 48 h, and 72h (solvent: DMF; universal calibration)
1
1
H-NMR spectra of water-insoluble s-OLGA after hydrolysis in water
1
H-NMR: δ = 1.4 (C-COOH (f), lactic acid), δ = 1.56 (-CH3-, lactic acid), δ = 3.48, δ = 4.25
(-O-CH2-, initiator), δ = 4.8 (C-COOH (e), glycolic), δ = 4.90-5.05 (-CH2-, glycolic acid), δ =
5.1-5.3 (-CH-, lactic acid)
a)
c
DMF
a
e
b
f
d
s-OLGA-7500
s-OLGA-7000
s-OLGA-6200
s-OLGA-2900
s-OLGA-2500
b)
s-OLGA-6200
s-OLGA-7500
s-OLGA-8300
Figure S2 NMR spectra of water-insoluble s-OLGA after hydrolysis in water at 70 °C a) 1HNMR after 8 h, 16 h, 24 h, 48 h, and 72 h and b) 13C- NMR after 8 h and 24 h and PLGA
FTIR-spectroscopic measurement results of PLGA and water-insoluble s-OLGA
The IR spectra (Figure S3) illustrate all characteristic groups for PLGA: a broad peak around
3500 cm-1 is attributed to the OH stretch vibration, a triplet band between 2995 and 2881 cm -1
corresponding to CH3 and CH2 symmetric and asymmeric stretching with the additional band
2
at 1423 cm-1 for C-H stretching vibration; the main ester bands of the C=O stretching
vibration near 1750 cm-1, and the C-O-C asymmetric and symmetric stretching vibrations in
the range of 1184 – 1090cm-1, which have been identified on the IR spectra of all investigated
polymer samples of water-insoluble fraction. With the increasing hydrolysis degree the split
and the red-shift in C=O stretching vibration occurs showing the appearance of the carboxylic
groups and their coexistence with ester groups. The increase in the O-C=O deformation
vibration at 974 – 870cm-1 attributed to carboxylic group was detected indicating a gradual
hydrolysis of ester bonds with simultaneous generation of carboxyl end-groups. The split and
the blue-shift of C-O-C asymmetric stretching vibrations (1169 → 1184 cm-1) can be a sign of
particular cyclization of hydrolysis products in form of lactones.[55]
PLGA
s-OLGA-7500
s-OLGA-6200
s-OLGA-2900
2000
1800
1600
1400
1200
1000
800
600
-1
wavenumber (cm )
Figure S3: IR spectra of PLGA and three different s-OLGAs with different ratio of the
number of functional end-groups to the molecular weight
High-performance liquid chromatography measurements for water-soluble aq-OLGA
hydrolysis in water
The characterization of the two degradation products lactic acid and glycolic acid was
analyzed by Yoo et al.[16] under different conditions by liquid chromatography showing a
faster release of the glycolide compared to lactide. But it is still challenging to characterize
the intermediate degradation products – namely the oligomers of lactic acid and glycolic
acid.[56] Therefore, also other degradation fragments next to lactic acid and glycolic acid
cannot to be excluded from the degradation process.
The amount of lactic acid in the water-soluble fraction increased about 50 times from a
degradation time of 24 h to 72 h (Table S2), which nevertheless just suggests that at the
beginning of the degradation the amount of produced acid is negligible comparing to further
3
hydrolysis products, and while increasing in the absolute mass the relative content remains
unchanged.
Table S2: Lactic acid area, lactic acid rel. area and amount of lactic acid of partly degraded sOLGA samples determined by high performance liquid chromatography
Area of lactic acid
Rel. area of Lactic
Amount lactic acid
Sample ID
[µRIU·min]
acid [%]
[g·L-1]
s-OLGA-7
0.04
21.3
0.04
s-OLGA-32
1.01
27.6
0.92
s-OLGA-57
2.19
28.6
2.00
a)
The area and rel. area of lactic acid, respectively, refer to the integral of the peak corresponding to the
lactic acid
Molecular weight of PLGA and water-insoluble s-OLGA after hydrolysis in different media
determined by GPC and OH-group titration
Gel permeations chromatography (GPC) The determination of the number molecular weight
(Mn) by GPC investigations was performed using 50 mmol ammonium acetate in N,Ndimethylformamide at 35 °C as eluent with a flow rate of 0.25 mL·min-1 and 0.005 wt-% 2,6di-tert-butyl-4-methylphenol as internal standard for all samples. The system was equipped
with 250 mm x 4.6 mm GRAM gel columns, 3 and 3 x 102 nm porosity, 10 µm particle size
(Polymer Standard-Service GmbH, Mainz, Germany, PSS), a degasser (ERC-3315,
Riemerling, Germany), a gradient pump PU 980 and an automatic injector AS-851 (both
Jasco, Tokyo, Japan). Three detectors were used: a multi wavelength detector MD-910 (270
nm), a RI-930 (both Jasco) and the viscosimeter n-1001 (WGE, Dr. Bures, Dallgow,
Germany), which were combined by a split. All molecular weights were determined using a
universal calibration with polystyrene standards (PSS).
End-group titration The content of carboxyl groups (COOH-value) and or hydroxyl groups
(OH-value) were determined as the acid number (mgKOH/gpolymer) or respectively the hydroxyl
number (mgKOH/gpolymer) by potentiometric titration of the copolymers dissolved in
dimethylformamide (DMF, Merck), with 0.1 N-tetrabutylammonium hydroxide (Merck). The
titrations were performed with the titrator DMS Titrino 716 (Metrohm, Schwizerland) and a
Solvotrode with LiCl (sat.) in ethanol. The carboxyl groups were directly titrated but the
determination of the hydroxyl groups is based on the esterification of the OH-groups with
4
acetic anhydride (abundantly, Sigma-Aldrich) in presence of N-methylimidazole (SigmaAldrich) as catalyst at ambient temperature and by back titration.
Table S3 Average-number molecular weight Mn (g·mol-1) determined by GPC (universal
calibration) and OH-group titration of PLGA and water-insoluble s-OLGA after hydrolysis in
water at 70 °C for different time periods. Sample ID are abbreviated as s-OLGA-degradation
time in h
OH-value
[g∙mol-1]
GPC
[g∙mol-1]
10000
4200
s-OLGA-8h
7200
4500
s-OLGA-24h
4400*
3800
Sample ID
PLGA
#
s-OLGA-48h
2300*
3100
* Determined by taking into account the COOH-value determined for s-OLGA-24h (28.6
mg∙g-1) and s-OLGA-48h (35.0 mg∙g-1), respectively
# The time refers to the correlated degradation time
Brewster angle microscopy images of PLGA and s-OLGA
a) PLGA
b) s-OLGA-7500
c) s-OLGA-2900
100 µm
Figure S4: BAM images in dependence on the grade of PLGA hydrolysis recorded at room
temperature on a pure water subphase at a)  = 11.0 mNm-1, b)  = 12.8 mNm-1, c)  =
9.8 mNm-1 (s-OLGA-7500 and s-OLGA-2900 are degraded for 8 h and 48 h, respectively)
5