This document summarizes research on the bulk copolymerization of L-lactide (LLA) and ε-caprolactone (CL) catalyzed by the organocatalyst dibenzoylmethane (DBM), which allows for the metal-free synthesis of random copolyesters. The researchers achieved good control over the ring-opening copolymerization as indicated by linear increases in molecular weight with conversion and dispersities below 1.5. NMR spectroscopy and thermal analysis confirmed the formation of random copolymers with compositions matching initial monomer feed ratios and a single glass transition temperature. A bifunctional cooperative mechanism is proposed for the DBM-catalyzed copolymer

1. European Joint Doctorate in Sustainable
Organocatalysis and Polymers “SUSPOL”
Bulk copolymerization of L-lactide with ε-caprolactone catalyzed
by an organocatalyst: Toward a metal-free random-like
copolymerLeila MEZZASALMA1,2, Daniel TATON2, Olivier COULEMBIER*1
Leila.Mezzasalma@umons.ac.be
1 Laboratory of Polymeric and Composite Materials, Center of Innovation and Research in Materials and Polymers (CIRMAP), University of Mons, Place du Parc 23, 7000 Mons, Belgium
2 Laboratoire de Chimie des Polymères Organiques (LCPO), CNRS, ENSCBP University of Bordeaux, UMR 5629, 16 av. Pey Berlan 33607 Pessac, France.
The authors thank the “European Joint Doctorate in Sustainable and
Organocatalyzed Polymers SUSPOL-EJD” project for the financial
support (Grant Agreement no. 642671). And Dr. Julien De Winter for
MALDI-MS analyses.
LL = CL =
L = Biocomptatible
Biodegradable
Applications
Biomedicals1
Packaging2
Coating
Dibenzoylmethane
(DBM)
METAL-FREE CATALYSTS, LESS TOXIC3,4
SYNTHESIS OF COPOLYESTERS BY METAL-FREE RING-OPENING
COPOLYMERIZATION (ROCP) IN BULK
CL-LA CCL
24h
48h
51h
70h
72h
-36% -15%
-52%-72%
-78% -66%
-91% -90%
-94% -93%
1H NMR spectra
rLA = 1.8 rCL = 0.1
Evolution of uncorrected Mn,SEC of crude copolymers (●)
and Đ (x) with total monomer conversion. Polystyrene
calibration in THF/NEt3 .
Acceptable level of control:
 Mn=f(CTOT)
 Dispersity (Đ) < 1.5
Χ Mn,NMR< Mn,th
[15/15/1.5/1]
[LLA]0/[CL]0/[DBM]0/[I]0
 CL:LA composition in the final copolymer (51:49)
a
L =
LL =
CL =
*
xb
Absence of the peak CL-L-CL at 170.8 ppm ( no
transesterifications)
1H (a) and 13C (b) NMR spectra of purified final copolymer obtained from
BnOH (CDCl3 ,r.t., 500 MHz) *Stereoirregular PLLA
3127 g.mol-1
m/z
2000 3000 4000 50001400
13
10
14
1012
12
13
9
3000 3100 3200 3300
Δm/
z= 30 Δm/z=
114
Δm/z=
144
m/z
DPTOT=23
DPTOT=24
DPTOT=22
[30/1.5/1]
[M]0/[DBM]0/[I]0
MALDI-MS spectrum of pure random copolymer initiated by Bu(OH)2 obtained
after 48h of reaction (CL-LA= 70 %, CCL= 54 %, Mn,sec=3850 g.mol-1, Đ = 1.38)
 Gaussian like distribution
Hydrophilic PEG1000
Hydrophobic P(LA-co-CL)
Picture of P(LA-ran-CL)
initiated (a) by BnOH
(b) by PEG1000 (10mg.mL-1)
a b
 Water dispersible
SEC traces
PEG
COPOLYMER STRUCTURE FROM
GRADIENT TO RANDOM
 Quasi equal
incorporation of
both monomers
in the copolymer
backbone
 Presence of heterodiads (38%) and -triads
Temperature (°C)
HeatFlow(W.g-1)
Exo up
Tg= -19 °C
DSC analyses of the purified final copolymer initiated by BnOH (-70°C to
200°C at a heating and cooling rate of 10°C/min under N2)
 Only one Tg
DBM
PROPOSED MECHANISM
Bifunctional cooperative mechanism
2nd catalyst
Structure
not shown
*
x
L =
LL =
CL =
a
b
Good control over the ROcP
 Mn=f(CTOT)
 ln([M]0/[M])= f(t)
 Dispersity (Đ) < 1.25
 Mn,NMR ≈ Mn,th
SEC traces of crude copolymers
Evolution of uncorrected Mn,SEC of crude copolymers (●) and Đ (x)
with total monomer conversion. Polystyrene calibration in THF/NEt3
Semi-logarithmic kinetic plot for LLA and CL
copolymerization using BA as catalyst in bulk at 155°C
[25/25/2.5/1]
[LLA]0 /[CL]0/[2nd cata]0/[I]0
1H (a) and 13C (b) NMR spectra of purified final copolymer obtained from
Bu(OH)2 (CDCl3 ,r.t., 500 MHz) *Stereoirregular PLLA
 CL:LA composition in the final copolymer (50:50)
 Absence of the peak CL-L-CL at 170.8 ppm
 Presence of heterodiads (44%) and -triads
Reactivity ratios
rLA = 1.7 rCL = 1.4
2nd
catalyst
RANDOM COPOLYMER
Reactivity
ratios
CONCLUSIONS & OUTLOOKS
Dibenzoylmethane
Acceptable level of control over the
ROcP of L-LA and ε-CL at 155°C.
Copolymer structure from gradient
to random on the basis of kinetic
investigations, NMR, thermal and
MALDI ToF analyses
Demonstration of the versatility
of DBM catalyst using different
initiators for the ROcP
A bifunctional cooperative
mechanism is proposed to operate
2nd catalyst
Very good control over the ROcP
of L-LA and ε-CL at 155°C
Obtention of random copolymer
Try to obtain high molar masses
Computational calcultations are
undergoing
Try to boost the kinetic
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CTOT