Supplementary information
The FTIR spectra for PEO, PVA-g-PLLA and their blends are shown in Figure S1.
Infrared spectroscopy is usually used to investigate the miscibility of polymer blends
through its sensibility to specific interactions. Therefore, in the systems investigated in
this work, the OH stretching ( 3500 cm-1), C=O stretching ( 1750 cm-1) and C-O
stretching ( 1150 cm-1) bands are of particular interest.
The C-O stretching band is very complex because in addition to the C-O bonds in PEO,
the C-O ester bonds of the L-lactide residues also absorb in this spectral region. The
absorption of both polymers makes not amenable this spectral region for a simple
spectral interpretation.
The C=O band of the pure PVA-g-PLLA copolymer shows a single and relatively broad
profile. The two components that could be expected in this spectral region,
corresponding to free and hydrogen bonded C=O groups, cannot be distinguished. This
feature can be attributed to the low relative intensity expected for the hydrogen bonded
C=O band. According to the composition of the copolymers (82 mol% LLA), there are
about 4 C=O groups per OH group. In addition, only a fraction of the OH groups
establishes hydrogen bonds with the C=O groups because the profile observed for the
OH stretching band indicates the presence of hydroxyl-hydroxyl multimers. For these
reasons, the contribution corresponding to the carbonyl groups establishing C=O···H-O
hydrogen bonds is much weaker than the contribution corresponding to the free C=O
groups, and the former is completely masked by the latter even in the pure PVA-gPLLA copolymer.
Nevertheless, the C=O band is observed to shift slightly to higher wavenumbers with
the addiotion of PEO. Table S1 lists the locations observed for the C=O stretching band
in pure PVA-g-PLLA and its blends with PEO. The shift to higher wavenumbers upon
addition of PEO can be explained considering the loss of intensity of the contribution
corresponding to hydrogen bonded C=O groups, that should be located in the lower
wavenumber range of this spectral region. Hence, the observed shift supports the
replacement of the C=O···H-O autoassociation interactions in pure PVA-g-PLLA by O-···H-O interassociation interactions upon addition of PEO.
Table S1. Location of the C=O stretching band for PVA-g-PLLA and its blends with
PEO.
System
Wavenumber (cm-1)
PVA-g-PLLA
1754
PEO/PVA-g-PLLA 20/80
1754
PEO/PVA-g-PLLA 50/50
1755
PEO/PVA-g-PLLA 70/30
1756
Finally, the OH stretching band is very well resolved and shows high sensitivity to the
variations in the interacting pattern occurring upon blending. For this reason, the OH
stretching band has been thoroughly analyzed in the body of the paper.
PVA-g-PLLA
PEO/PVA-g-PLLA 20/80
PEO/PVA-g-PLLA 50/50
PEO/PVA-g-PLLA 70/30
Absorbance
PEO
4000
3500
3000
2500
2000
1500
1000
-1
Wavenumber (cm )
Figure S1. FTIR spectra for PEO, PVA-g-PLLA and their blends.
500