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

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

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

ESI-MS

4

ESI(+)-MS spectrum

499

513527 599

613

627 699713

727685

413

427

327

313

MX, MYunknown

n, m ?

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+

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)

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)

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)

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

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

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

Strategy

12

Derivatization of the copolymer for the distribution parameters

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

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

Strategy

15

Derivatization of the copolymer for the end-group characterization

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 :

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

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

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

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

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

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

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

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

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