Journal of Polymer Science Part A:
Polymer Chemistry
A Novel Use of Ti-POSS as Initiator of L-lactide
Ring-Opening Polymerization
Orietta Monticellia*, Dario Cavalloa, Sergio Bocchinib, Alberto Fracheb, Fabio Carniatoc,
Alessandro Tonelottoa
a
Dipartimento di Chimica e Chimica Industriale, Università di Genova, via Dodecaneso, 31,
16146 Genova, Italy
b
Dipartimento di Scienza dei Materiali e Ingegneria Chimica, Politecnico di Torino - sede di
Alessandria, viale Teresa Michel, 5, 15121 Alessandria, Italy
c
Dipartimento di Scienze e Tecnologie Avanzate and Nano-SISTEMI Interdisciplinary
Centre, Università del Piemonte Orientale ‘A. Avogadro’, Viale Teresa Michel, 11, 15121
Alessandria, Italy
1
Experimental
Characterization
Fourier transform infrared spectroscopy spectra were recorded by a Bruker IFS66
spectrometer. The KBr pellet were prepared by mixing the sample with KBr powder
(around 1:100) and using a hydraulic press at the pressure of 10 tons. All the samples
were dried at 120 °C for 4 h under inert atmosphere and were scanned in the range
400-4000 cm-1 with nitrogen purge.
A Leica Stereoscan 440 scanning electron microscope equipped with a backscattered
electron detector was used to examine the Si distribution in PLA. The specimens were
submerged in liquid nitrogen for 30 min and fractured cryogenically. All samples
were thinly sputter-coated with carbon using a Polaron E5100 sputter coater.
Wide-angle X-ray diffraction was carried out on a Philips PW 1830 powder
diffractometer (Ni-filtered Cu KR radiation).
2
Intensity (a.u.)
(a)
(b)
3800
3300
2800
2300
1800
1300
800
300
Wavenumber (cm-1)
Figure 1. FTIR spectra of: (a) commercial PLLA, (b) PLA synthesized with Ti-POSS
at 130 °C for 24 h with [LLA]/[Ti] = 300 (entry 5 in Table 1)
The spectra of the commercial PLLA and of the polymer synthesized by using TiPOSS are very similar and, as reported in the following, show the typical peaks of
poly(lactide).
IR (KBr): 3012 cm-1 and 2964 cm-1 (-CH- stretch); 1760 cm-1 (-C=O- carbonyl); 1461
cm-1 and 1376 cm-1 (-CH- deformation); 1216 cm-1, 1136 cm-1, 1104 cm-1, 1055 cm-1
(-C-O- stretch); 879 cm-1 (-C-C- stretch).
3
60000
50000
Mn
40000
30000
20000
10000
0
0
20
40
60
80
100
Conversione (%)
Figure 2. Plot of Mn (employing polystyrene standards) for the synthesized PLA as a
function of conversion (130 °C and [LA]/[Ti] = 300) (circles) and theoretical Mn
calculated from the following formula: (MW of LA)  ([LA]/[Ti])  (Conversion)
(squares).
The values of the experimental and theoretical Mn are almost equal at low conversion,
while they tend to became different increasing the conversion, thus indicating the
occurrence of side reactions. Nevertheless, as the above difference is small, it is
possible to conclude that the ring opening polymerization is well controlled.
4
4 m
Figure 3. SEM micrograph by BS emission of PLA synthesized with Ti-POSS at 130
°C for 24 h with [LA]/[Ti] = 300 (entry 5, Table 1)
SEM investigation, coupled to EDS analysis, allowed to study the morphology of the
polymer prepared, paying specific attention to Si and Ti dispersion, i.e. POSS
distribution in the polymer matrix. Figure S4 shows the micrograph obtained by
backscattering emission (BS) of the sample synthesized at 130 °C for 24h with
[LA]/[Ti] = 300. No POSS aggregates have been observed on the sample surface,
while the elemental analysis has shown a uniform Si and Ti distribution without any
visible aggregates, thus evidencing a submicrometer POSS dispersion. Similar results
have also been obtained with the other samples.
5
(b)
(a)
Figure 4. DSC traces of: (a) commercial PLLA, (b) PLA synthesized at 130 °C for 24
h with [LA]/[Ti] = 300 (entry 5, Table 1)
6
14000
12000
Intensity (a.u.)
10000
8000
6000
4000
2000
0
6
9
12
15
18
21
2q (degrees)
Figure 5. X-ray diffraction pattern of PLA synthesized at 130 °C for 24 h with
[LA]/[Ti] = 300
7
Intensity (a.u.)
10
20
30
40
2q (degrees)
Figure 6. X-ray diffraction patterns of Ti-POSS
8