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Analytical strategy for the microstructural characterization of MAA-MMA copolymers
Rémi Giordanengo,(1) Stéphane Viel,(1) Manuel Hidalgo,(2)
Béatrice Allard-Breton,(2) André Thévand (1) and Laurence Charles (1)
(1) Aix-Marseille University – Marseille, France(2) ARKEMA – Centre de Recherche Rhônes-Alpes – Pierre-Bénite, France
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Copolymer Characterization
2
X
H3C
O OH
YH3C
OCH3O
mn
Molecular Weight
Mn , Mw
Nature of end-groupsX ,Y
Composition
n , m
Nature of MAA-MMA copolymerblock vs random
MAA
M = 86 Da
MMA
M = 100 Da
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499
513
527599
613
627699
713
727
ESI-MS
3
ESI(+)-MS spectrum
2 distributions : [M + Na]+
[M + 16 + Na]+
∆ m/z 100
∆ m/z 86
∆ m/z 100
∆ m/z 86
MMA MMA
MAA MAA
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ESI-MS
4
ESI(+)-MS spectrum
499
513527 599
613
627 699713
727685
413
427
327
313
MX, MYunknown
n, m ?
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ESI-MS/MS
MS/MS requested to determine the actual values of n and m
Dissociation rules of MAA-MMA copolymers in negative and positive mode ESI :
water elimination
methanol elimination
O OO
O O HO O
H
- 18 Da
- H2O
O OOO O H3CO O
H
- 32 Da
- CH3OH
Between two consecutive neutral MAA → MAA/MAA pair in the polymeric chain
Between neutral MAA and MMA→ MAA/MMA pair in the polymeric chain
The number of water and methanol losses is monitored to reveal the number and arrangement of MAA and MMA units in the selected precursor ion
Giordanengo, R. et al. Journal of the American Society for Mass Spectrometry 2009, 20 (1), 25-33 ; Giordanengo, R. et al. Rapid Communication in Mass Spectrometry 2009, 23 (11) 1552-1567 ; Giordanengo, R. et al. Analytica Chimica Acta 2009, 654, 49-58
Na+Na+
Na+Na+
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ESI-MS/MS
6
Neither water nor methanol losses in MS/MS spectra of
precursor ion in the first column
No MAA unitn = 0
- H2O
- MeOH
Only one loss of water
Only one MAA/MAA pair2 MAA units
Only one loss of methanol
Only one MAA/MMA pair1 MMA unit
m+1 = 1
m/z 499 (2 ; m+1)
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ESI-MS/MS
7
MX + MY = 204 Da
m/z 689
m/z 771
m/z 753
m/z 739
m/z 735
m/z 721
m/z 707- H2O
- MeOH
2 consecutive losses of H2O
2 MAA-MAA pairs4 MAA units
1 loss of H2O
2 losses of MeOH1 MAA-MAA pair
2 MAA-MMA pairs2 MMA units
Different dissociation routes from the same precursor ion
Random nature of the studied MAA-MMA copolymer
m/z 771 (4;2)
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Limitations of the ESI-MS/MS approach
8
Dissociation of MAA-MMA co-oligomer sodiated adducts allows :
To reach the co-monomeric composition of co-oligomers
To reveal the random nature of the studied MAA-MMA copolymer
To determine the sum of the end-group masses (MX + MY)
However :
The lack of specific fragmentation does not allow the end-groups to be structurally characterized (contrary to what is usually obtained in the case of homopolymers such as PMMA)
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Same phenomenon in ESI of constitutive homopolymers PMMA and PMAA
PMMA 1590 PMAA 1250
Signal only in the low m/z range indicating a strong bias toward low mass oligomers
Other ESI-MS Limitations
9
ESI-MS spectrum of the MAA-MMA copolymer :
Distribution parameters largely underestimated as compared to NMR data (Mn 3100 Da)
Strong bias toward low mass oligomers for all acrylic polymersWrong values of Mn and Mw
Uncorrect MAA/MMA ratio
Mw (1+) 865
Mw (2+) 1592
Mw (1+) 612
Mw (2+) 728
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PMMA 1590 PMAA 1250
10
MALDI-MS :
In contrast, MALDI-MS spectra of constitutive homopolymers PMMA and PMAA are more realistic
However, no signal obtained in MALDI for the MAA-MMA copolymers
Limitations in terms of Molecular Weight determination
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R
O
OH
Si CH N N
R
O
O
SiH2C N N
SiH2C N N CH3OH Si O H3C N N
H3C N N
R
O
O R
O
OCH3
N2
Strategy
11
End-group characterization :
Need for a homopolymer to allow the structure of X and Y end-groups to be reached by means of ESI-MS/MS
Molecular weight determination :
Need for a homopolymer to allow the distribution parameters to be obtained from MALDI-MS data
STRATEGY
Use of a methylation reaction to transform the MAA-MMA copolymers in PMMA homopolymers
~ 50 mg of MAA-MMA copolymer in 20 mL of a MeOH/H2O mixture (19/1, v/v)
(stirred 2h at room temperature) Addition of an excess of trimethylsilyldiazomethane (stirred 3h at room temperature) Drying at 30°C overnight
Experimental
Couvreur, L.; Lefay, C.; Belleney, J.; Charleux, B.; Guerret, O.; Magnet, S. Macromolecules 2003, 36, 8260-826
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Strategy
12
Derivatization of the copolymer for the distribution parameters
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Methylation of PMAA homopolymers
13
MALDI(+)-MS spectrum
PMAA 1700 methylated PMAA 1700
Methylation
- Complex MS spectrum due to the ability of PMAA to bind numerous Na+ cations.- High laser fluence (65%).
- A single PMMA distribution is obtained, indicating all acrylic acid functions of PMAA have been methylated.- Good signal-to-noise ratio is measured from low laser fluence (~ 40%).
PMAA Methylated PMAA
PMAA MwSEC Mw
MALDI MwSEC Mw
MALDI MwPGSE
1 1250 1132 1445 1231 1452
2 1700 1487 1966 1634 1701
3 3150 1951 3654 2579 2928
4 6600 4546 7664 5620 6311
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14
2000 3500 5000
400
800
No signal obtained before methylation
2000 4000 6000
600
200
1000
After methylation
Intense MALDI-MS signal
Mw can be determined by MALDI and PGSE NMR
Giordanengo, R.; Viel, S.; Hidalgo, M.; Allard-Breton, B.; Thevand, A.; Charles, L. Journal of the American Society for Mass Spectrometry 2009, submitted
Methylation for Molecular Weight determination
Methylated Copolymer Copolymer
MnMALDI Mn
NMR MwMALDI Mw
PGSEMw calculated from Mw
MALDI
Mw calculated from Mw
PGSE
MAA/MMA 3200 3150 4360 5170 41
10
48
70
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Strategy
15
Derivatization of the copolymer for the end-group characterization
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Methylation for end-group characterization
16
[M + Na]+ (MX + MY) = 204
[M + 16 + Na]+ (MX + MY) = 220
[M + Na]+ (MX + MY) = 204
[M + 16 + Na]+ (MX + MY) = 220
Methylation
MAA-MMA methylated MAA-MMA
After methylation :
ESI-MS simplified A single PMMA distribution is obtained indicating all MAA units have been methylated No modification of the end-groups during the methylation reaction
ESI(+)-MS :
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17
ESI(+)-MS/MS of the methylated MAA-MMA copolymer : m/z 827
Dissociation rules of PMMA homopolymers in positive mode ESI (1) :
XY
CO2CH3 CO2CH3 CO2CH3
n m.
XY
CO2CH3 CO2CH3 CO2CH3 CO2CH3
n m
XY
CO2CH3 CO2CH3 CO2CH3
n m.
Y
CO2CH3
mX
CO2CH3 CO2CH3
n.Y
CO2CH3 CO2CH3
m.X
CO2CH3
n
Series F Series A Series B Series D
-CO2CH3 -CO2CH3
C+
C+
C+
C+C
+
C+
C+
Methylation for end-group characterization
Jackson, A. T.; Yates, H. T.; Scrivens, J. H.; Critchley, G.; Brown, J.; Green, M. R.; Bateman, R. H. Rapid Communications in Mass Spectrometry 1996, 10, 1668 ; Jackson, A. T.; Yates, H. T.; Scrivens, J. H.; Green, M. R.; Bateman, R. H. Journal of the American Society for Mass Spectrometry 1997, 8, 1206
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18
ESI(+)-MS/MS of the methylated MAA-MMA copolymer :
Dissociation rules of PMMA homopolymers in positive mode ESI (2) :
Jackson, A. T.; Yates, H. T.; Scrivens, J. H.; Critchley, G.; Brown, J.; Green, M. R.; Bateman, R. H. Rapid Communications in Mass Spectrometry 1996, 10, 1668 ; Jackson, A. T.; Yates, H. T.; Scrivens, J. H.; Green, M. R.; Bateman, R. H. Journal of the American Society for Mass Spectrometry 1997, 8, 1206
X
CO2CH3
n
CO2CH3 C+
Y
CO2CH3
m
C+
X
CO2CH3
nH3CO2C
Y
CO2CH3
Hm
CO2CH3 C+
Series DSeries C
- HCO2CH3
Y
CO2CH3 CO2CH3 CO2CH3
mC
+X
CO2CH3
n
C+
- HCO2CH3
X
CO2CH3
n
CO2CH3 H
H3CO2C
CO2CH3 CO2CH3
YmC
+
Series F Series E
Methylation for end-group characterization
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19
Application of the dissociation rules of PMMA homopolymers in positive mode ESI :
m/z 827Most intense fragment ions:
Series A or B
The two most intense fragment ions could be identified to Series A,
revealing Y = H
H
CO2CH3 CO2CH3
m.Na+
A0 : m/z 110
A1 : m/z 210
A0A1
Methylation for end-group characterization
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H
CO2CH3
m Na+
E0 : m/z 209
E1 : m/z 309
E2 : m/z 409
E3 : m/z 509
E4 : m/z 609
Series E
H
CO2CH3 CO2CH3 CO2CH3
mValidation of the nature of Y
MY = 1
Y = H
20
Application of the dissociation rules of PMMA homopolymers in positive mode ESI :
m/z 827Since Y = H, product ions D
and E can be assigned
Na+
D2 : m/z 265
D3 : m/z 365
D4 : m/z 465
D5 : m/z 565
Series D
Methylation for end-group characterization
A0A1
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Na+
Series F
F1 : m/z 381
F2 : m/z 481
F3 : m/z 581
X
CO2CH3
nNa+
X
CO2CH3 CO2CH3
n.
Series B
B0 : m/z 226
B1 : m/z 326
Na+
Series C
C1 : m/z 425
C2 : m/z 525
C3 : m/z 625
C4 : m/z 725
X
CO2CH3
n
CO2CH3
21
Application of the dissociation rules of PMMA homopolymers in positive mode ESI :
MX + MY = 204, with MY = 1 → MX = 203
Based on MX = 203, product ions B, C and F can be identified
Methylation for end-group characterization
Validation of
MX = 203
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Na+Na+
Na+
Use of a sulfurated agent during the copolymer synthesis,
2-ethylhexyl thioglycolate (M = 204 Da)
2 additionnal product ions detected at m/z 715 et m/z 683 allow to validate the structure proposed for X
22
Proposed structure for X
715
683
Methylation for end-group characterization
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NMR analysis
23
Validation of the structure of the end-groups
Proposed structure of X :
NMR 1D (1H, 13C) and 2D (COSY, HSQC, HMBC, DOSY) analysis
O O
HS MAA-MMA
1
2
3
4
1'
2'
3' 4'
5
6
X end-group Nature δ13C (ppm) δ1H (ppm)
1
2
3
4
1’
2’
3’
4’
5
CH3
CH2
CH2
CH2
CH3
CH2
CH
CH2
C(O)
14.6
24.0
30.0
31.4
11.4
24.7
40.0
68.3
172.0
0.96
1.38
1.37
1.40
0.98
1.45
1.65
4.10
-
6 CH(SH) 35.5 3.27
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Conclusion
24
Methylation of MAA-MMA copolymer allow :
A complete microstructural characterization (validated by NMR anlysis)
The distribution parameters to be determined (with the help of NMR data)
This derivatization strategy can be envisaged for any copolymer :
Not amenable to MALDI
Which can be transformed into a homopolymer
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Acknowledgments
25
The organisation committee
The French Society for Mass Spectrometry
The Spectropôle, analytical facility of Aix-Marseille University, for the special access to the instruments
ARKEMA, for the financial support
SACS and C&S members
Thank you for your attention