Preparation of Poly (ε-caprolactam-co-L-lactide) copolymers in bulk using organocatalysis

1. Introduction
Poly(ester-amide) copolymers are considered interesting targets because they combine outstanding thermal and mechanical properties
of polyamides with the biodegradation capacity of aliphatic polyesters.[1,2] However, obtaining an efficient method which involves the use
of organocatalyst and which works efficiently in the ring-opening polymerization (ROP) of both monomers is a challenging task.
In this work, ε-caprolactam and L-lactide have been copolymerized by a ring-opening process in the presence of two catalysts: a) a
Brønsted acid ionic liquid, i.e. 1-(4-sulfobutyl)−3-methylimidazolium hydrogen sulphate (BAIL) and b) a P4-t-Bu phosphazene superbase
(P4).
Preparation of Poly (ε-caprolactam-co-L-lactide) copolymers in bulk
using organocatalysis
Andere Basterretxea1,3, David Mecerreyes2, Olivier Coulembier 3, Haritz Sardon1
Methodology
Results and discussion
Conclusions
In conclusion, it was found that the homopolymerization of ε-caprolactam occurred more efficiently in the presence of P4 while the BAIL
was more effective for ROP of L-lactide monomer. Accordingly, at copolymers with high ε-caprolactam content P4 is more favorable that
BAIL while at low ε-Caprolactam the opposite trend is observed. In future, DSC analyses of the copolymers will be carried out to
determine the polymer crystallinity.
1 POLYMAT, University of the Basque Country (UPV/EHU), Joxe Mari Korta Center, Avda. Tolosa 72, 20018 Donostia-San Sebastian, Spain (andere.basterrechea@ehu.eus)
2 Ikerbasque, Basque Foundation for Science, E-48011 Bilbao (Spain)
3 Center of Innovation and Research in Materials and Polymers (CIRMAP), Laboratory of Polymeric and Composite Materials, University of Mons, Place du Parc 23, 7000
Mons, Belgium
Acknowledgements: This project receives funding from the European Community's Seventh Framework Programme under Grant Agreement n° 642671.
[1] H.-G. Elias, Macromolecules; Wiley-VCH: Weinheim, Chichester, 2006.
[2] Y. W. Zhi, X. Wei, K. X. Jin, C. L. Yao, X. W. Qian, J. X. Wei, Chin. Chem. Lett. 2008, 19, 241–244.
Figure 1. Monomer conversions (%) of CLA and LLA recorded
after 24, 48 and 72h with BAIL and P4 as catalysts.
Figure 3. Expansion of 1H NMR spectra representing both
homopolymers (A and C) and the P(ɛ-Caprolactam-co-L-Lactide)
copolymer synthesized using BAIL (B). The stars indicate the peaks
that correspond to the CLA-LA copolymer sequences.
ORGANOCATALYSTS
Phosphazene base
P4-t-Bu solution (P4)
1-(4-sulfobutyl)−3-
methylimidazolium
hydrogen sulphate (BAIL)
ɛ-Caprolactam L-Lactide (ɛ-Caprolactam-co-L-Lactide)1% CATALYST
Wavenumbers (cm-1)
Absorbance
-CO-NH2-
100/0
80/20
50/50
20/80
0/100
-COO-
0 24 48 72
0
20
40
60
80
100
120
CLA
LLA
Conv(%)
Time (h)
BAIL
P4
P4
BAIL
A) PCLA
B) (CLA-co-LA)
C) PLLA
When BAIL is used the conversion of L-lactide monomer is much faster than with P4, and on the contrary, ɛ-caprolactam monomer
conversion is much faster with P4 than with BAIL (Figure 1). FTIR spectroscopy successfully represents the carbonyl group of the ester
and the amide of copolymers with BAIL at different copolymer compositions (Figure 2). In 1H NMR spectra the stars indicate the peaks
related to the sequences given by transesterification reactions after ring-opening polymerization of ɛ-caprolactam when the
copolymerization occurs (Figure 3).
Figure 2. FTIR spectra expansion of the copolymers with
different compositions (CLA/LLA) obtained using BAIL as
catalyst.
CLA LLA
CLA-CLA CLA-CLA
CLA-LLA