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 Molecular Weight M n, M w Nature of end-groups X,Y Composition n, m Nature of MAA-MMA copolymer block vs random MAA M = 86 Da MMA M = 100 Da

ESI-MS 3 ESI(+)-MS spectrum 2 distributions : [M + Na] + [M Na] + ∆ m/z 100 ∆ m/z 86 ∆ m/z 100 ∆ m/z 86 MMA MAA

ESI-MS 4 ESI(+)-MS spectrum M X, M Y unknown 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 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), ; Giordanengo, R. et al. Rapid Communication in Mass Spectrometry 2009, 23 (11) ; Giordanengo, R. et al. Analytica Chimica Acta 2009, 654, Na +

ESI-MS/MS 6 Neither water nor methanol losses in MS/MS spectra of precursor ion in the first column No MAA unit n = 0 - H 2 O - MeOH Only one loss of water Only one MAA/MAA pair 2 MAA units Only one loss of methanol Only one MAA/MMA pair 1 MMA unit m+1 = 1 m/z 499 (2 ; m+1)

ESI-MS/MS 7 M X + M Y = 204 Da m/z 689 m/z 771 m/z 753 m/z 739 m/z 735 m/z 721 m/z H 2 O - MeOH 2 consecutive losses of H 2 O 2 MAA-MAA pairs 4 MAA units 1 loss of H 2 O 2 losses of MeOH 1 MAA-MAA pair 2 MAA-MMA pairs 2 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 (M X + M Y ) 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 1590PMAA 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 (M n 3100 Da) Strong bias toward low mass oligomers for all acrylic polymers Wrong values of M n and M w Uncorrect MAA/MMA ratio M w (1+) 865 M w (2+) 1592 M w (1+) 612 M w (2+) 728

PMMA 1590PMAA 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

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/H 2 O 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,

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%). PMAAMethylated PMAA PMAAM w SEC M w MALDI M w SEC M w MALDI M w PGSE

No signal obtained before methylation After methylation Intense MALDI-MS signal M w 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 CopolymerCopolymer M n MALDI M n NMR M w MALDI M w PGSE M w calculated from M w MALDI M w calculated from M w PGSE MAA/MMA

Strategy 15 Derivatization of the copolymer for the end-group characterization

Methylation for end-group characterization 16 [M + Na] + (M X + M Y ) = 204 [M Na] + (M X + M Y ) = 220 [M + Na] + (M X + M Y ) = 204 [M Na] + (M X + M Y ) = 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) : Series FSeries A Series B Series D C+C+ C+C+ C+C+ C+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 C + C+C+ C+C+ Series DSeries C C+C+ C+C+ C+C+ Series FSeries E Methylation for end-group characterization

19 Application of the dissociation rules of PMMA homopolymers in positive mode ESI : m/z 827 Most intense fragment ions: Series A or B The two most intense fragment ions could be identified to Series A, revealing Y = H Na + A 0 : m/z 110 A 1 : m/z 210 A0A0 A1A1 Methylation for end-group characterization

Na + E 0 : m/z 209 E 1 : m/z 309 E 2 : m/z 409 E 3 : m/z 509 E 4 : m/z 609 Series E Validation of the nature of Y M Y = 1 Y = H 20 Application of the dissociation rules of PMMA homopolymers in positive mode ESI : m/z 827 Since Y = H, product ions D and E can be assigned Na + D 2 : m/z 265 D 3 : m/z 365 D 4 : m/z 465 D 5 : m/z 565 Series D Methylation for end-group characterization A0A0 A1A1

Na + Series F F 1 : m/z 381 F 2 : m/z 481 F 3 : m/z 581 Na + Series B B 0 : m/z 226 B 1 : m/z 326 Na + Series C C 1 : m/z 425 C 2 : m/z 525 C 3 : m/z 625 C 4 : m/z Application of the dissociation rules of PMMA homopolymers in positive mode ESI : M X + M Y = 204, with M Y = 1 → M X = 203 Based on M X = 203, product ions B, C and F can be identified Methylation for end-group characterization Validation of M X = 203

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 Methylation for end-group characterization

NMR analysis 23 Validation of the structure of the end-groups Proposed structure of X : NMR 1D ( 1 H, 13 C) and 2D (COSY, HSQC, HMBC, DOSY) analysis X end-group Natureδ 13 C (ppm)δ 1 H (ppm) ’ 2’ 3’ 4’ 5 CH 3 CH 2 CH 3 CH 2 CH CH 2 C(O) CH(SH)

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