Caroline BARRERE. hydrophilic Poly(Ethylene Oxyde) hydrophobic Poly(Styrene) m X Y A wide range of...

Molecular weight determination of block copolymers by Pulsed Gradient Spin Echo NMR

Caroline BARRERE

hydrophilicPoly(Ethylene Oxyde)

hydrophobicPoly(Styrene)m

X Y

Block Copolymers PEO-b-PS

A wide range of applications (advanced nanomaterials, biocompatible drug delivery systems).

Properties depend on :- nature and size of block - end groups nature- molecular weight distribution (Mn, Mw).

16 October 2009 Journée RMN du grand Sud Est 2

Molecular weight determination methods


Advantages

Disadvantages

Mass Spectrometry MALDI-TOF

• Direct method.• Mn and Mw

estimation.

• Does not work with amphiphilic copolymers.

Steric Exclusion Chromatography

• Mn and Mw estimation.

• Indirect method.• Calibrated with

homopolymers.• Response depends on

the detection mode.• Weak adsorption.

PGSE NMR

• Homopolymers Mw determination .

• Calibration curve valid on any instrument.

• Indirect method.

To extend this method to PEO-b-PS copolymers.

Quantitative 1H NMR

• Direct method.• Mn

determination.

• End group signal identification.

• Only Mn determination.

Mw determination by PGSE NMR : Homopolymers

Stokes-Einstein equation for spherical particles in dilute solution :


D : Self diffusion coefficient

kB : Boltzmann constant

T : Temperature

η : Solvent viscosity

rH : Molecular hydrodynamic radius

6B

H

k TD

r

Mw determination by PGSE NMR : Homopolymers


à gradients de champ pulsés

Hahn Pulse sequence

RF

g

90°

180°

δ

γg

δ

γg t

τ τ

B0

Δ

Coding Decoding

Total phase shift=γgδ(z1-z2)(z1 - z2 ) = 0 maximum echo

(z1 - z2 ) ≠ 0 attenuated echo

3exp 2

0

gDII

D measurement

Intensity

g D (±3%)

DPS=2.869x10-8Mw-0.5539

DPEO=2.890x10-8Mw-0.5885

Mw determination by PGSE NMR : Homopolymers Flory’s law :

Calibration curves obtained for PEO and PS in dilute solution (3 mg mL-1 in CDCl3 at 300 K).


wMKD

Mw determination at ± 10%

Mazarin, M.; Viel, S. ; Allard-Breton, B. ;Thévand, A. ; Charles, L. Anal. Chem. 2006, 78, 2758-2764.

Samples caracterization

PEO-b-PS block copolymers synthesized from PEO 2000 and 5000 g.mol-1.

Impossible caracterization of amphiphilic copolymers by MALDI-ToF/MS Strategy : Hydrolysis in basic conditions .16 October 2009 Journée RMN du grand Sud Est 7

X Y Homopolymers analysis by MALDI-ToF/MS.

Girod, M.; Mazarin, M. ; Phan, T. N. T. ; Gigmes, D. ; Charles, L. J. Polym. Sci., Part A : Polym. Chem. 2009, 47, 3380-3390.

Mw determination by PGSE NMR : Block copolymers


1st Strategy : Using homopolymers calibration curves.

PGSEPEO

calibration curve

PS calibration

curve

#D

(x 10- 10 m2s-1)Mw

T (g mol-1)

Dev. (%)

MwT

(g mol-1)Dev. (%)

A1 1.474 7874 +2 13581 +76

A2 1.135 12276 -31 21770 +23

A3 1.077 13421 -30 23932 +24

A4 0.976 15865 -34 28588 +19

B1 1.384 8764 -7 15217 +61

B2 1.256 10335 +4 18131 +83

B3 1.102 12907 -12 22961 +56

B4 0.948 16669 -17 30131 +49

B5 0.875 19101 -32 34821 +23

Deviation greater than10% (Generaly admitted value for Mw determination by PGSE).

PEO calibration

curve

PS calibration

curve


An hydrodynamic model should be used in order to interpret diffusion data.

Because copolymers are strongly amphiphilic, we assume a segregated conformation where the two blocks have no interactions.



2nd Strategy : spherical model


PSPEO

PSPEO

PSw

PSPEOw

PEO

PSw

PSPEOw

PEOcopo

MKMK

MKMKD

We obtained Dcalc=0.88Dexp The spherical model is not suitable.

Stokes-Einstein H

B

r

TkD

6

PSH

PEOHH rrr

Flory wMKD

General Stokes-Einstein equation:

Perrin’s works on ellipsoidal molecules diffusion :

With for a revolution ellipsoid.



Hs

B

rf

TkD

6

revolution

equatorial

r

r

2

2

32

0

11ln

1)(

1

D

D

f

prolate

prolates

r revolution

r equatorial

1arctan1)(

1 2

2

32

0

D

D

f

oblate

oblates

r revolution

r equatorial

Perrin, F., J. Phys. Radium, 1936, 1, 1-11

#Mw

T (g mol-1)

Dev. (%)

A1 12658 +64

A2 24489 +38

A3 28261 +47

A4 35190 +47

B1 12159 +29

B2 14799 +49

B3 20327 +38

B4 28297 +40

B5 35880 +27

exp)( copoprolateprolate DDMf


Prolate ellipsoïdal model :


PSH

PEOH

revolution rrr

biggestH

equatorial rr

PSH

PEOH

biggestH

revolution

equatorialprolate

rr

r

r

r

Expression of ρ :

3/20 revolutionH rr

Self diffusion coefficient of a sphere with the same volume (D0) :

00 6 Hr

kTD

)(0

prolates

prolate

fDD

Expression of Dprolate :

smallestbiggest

smallestbiggest

Tw

smallestsmallestTw

biggestbiggest

Tw

smallestsmallestTw

biggestbiggestprolate

MXKMXK

MXKMXKD

2

2

11ln

1

1

Deviation greater than 10%.

#Mw

T (g mol-1)

Dev. (%)

A1 9041 +17

A2 15762 -11

A3 17780 -8

A4 21681 -10

B1 8481 -10

B2 10599 +7

B3 14860 +1

B4 19840 -2

B5 23910 -15


Oblate ellipsoidal model :


exp)( copooblateoblate DDMf

PSH

PEOH

equatorial rrr

biggestH

revolution rr

biggestH

PSH

PEOH

revolution

equatorialoblate

r

rr

r

r

Expression of ρ :

3/20 revolutionH rr

Self diffusion coefficient of a sphere with the same volume (D0) :

00 6 Hr

kTD

biggestTw

biggestbiggestoblate MXKD

1arctan1

1 2

2

)(0

oblates

oblate

fDD

Expression of Doblate : The deviation is overall smaller than the 10% tipically obtained for homopolymers.The Oblate ellipsoidal model is valid to study these PEO-b-PS block copolymers.

Conclusion

Copolymers adopt a segregated conformation with no interactions between the two blocks.

Oblate ellipsoid modeled well the PEO-b-PS blocks copolymers conformation in dilute solution.


Barrère, C. ; Mazarin, M. ; Giordanengo, R. ; Phan, T. N. T. ; Thévand, A. ; Viel, S. ; Charles, L. Anal. Chem, 2009, 81, 8054-8060.

Advantages

Disadvantages

RMN PGSE

• Mw determination.• Fast.• Calibration curve

valid on any instrument.

• Indirect method.

• Only Mw.

Acknowledgements


Organizing committee

SACS team, LCP :Pr. Laurence Charles

CES team, ISM2 :Dr. Stéphane Viel

CROPS team, LCPDr. Trang NT. Phan

Spectropole :Privileged Access to the Instrumental Park(FEDER OBJ2142-3341)

ARKEMA®

(alcoxyamine)

Thank you for your attention.

Caroline BARRERE. hydrophilic Poly(Ethylene Oxyde) hydrophobic Poly(Styrene) m X Y A wide range of...

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