NMR Studies of Polyethylene: Towards the Organization of Semi Crystalline Polymers

Transcription

1 NMR Studies of Polyethylene: Towards the Organization of Semi Crystalline Polymers Yefeng Yao, Robert Graf, Hans Wolfgang Spiess Max-Planck-Institute for Polymer Research, Mainz, Germany Leibniz Institut für Polymerforschung, Dresden, January 15th 2008

2 Line Width in 1 H NMR Spectra static dipolar broadening khz 30 khz MAS khz rigid solid HRMAS 4 3 khz soft matter Solution 5 0 khz isotropic molecular dynamics

3 Resolution Enhancement in NMR dipol-dipol coupling: H$ = R$ T$ 20, 20, i B 0 θ ij magic angle spinning: j space spin 1 $ 1 H ( 3cos 2 θ 1) γ γ ( 3$ I $ I $ I $ I ) r 3 ij 2 ij i j Z, i Z, j i j B 0 B 0 B 0 B 0 θ m θ θ m R$ 20, 0 ω R ω R ωr RF irradiation: -x y -y x -x y -y x -x y -y 0 T$ 20, (CRAMPS) τ τ 0 t C 2τ τ τ τ τ 2τ τ τ τ τ 2τ τ x -xy -y t C x -xy -y x -xy t H D,eff. (Recoupling) τ τ τ τ τ t 0 t R t R

4 Anisotropic NMR Interactions all-trans conformations crystalline gauche conformations non-crystalline ppm 1 H- 13 C dipolar couplings 13 C chemical shift anisotropy

5 Dipolar Sideband Pattern dipolar couplings: ReREDOR sideband pattern i j 1 2 D = μ h γ γ 4π r 2(3cos θij 1) i j H 0 T 3 ij 2,0 D ij = 20 khz D ij = 15 khz motional averaged t Saalwächter et al., Solid State NMR,22, 154 (2002). = ω/ω R D ij = 10 khz D ij = 5 khz

6 Chemical Shift Anisotropy Pattern 180 hopping axial rotation isotropic motion σ xx : ~50 ppm σ zz σ xx σ yy σ σ yy zz : ~34 ppm : ~15 ppm ppm ppm ppm Liu et al., J. Magn. Reson.,155, 15 (2002).

7 Morphology and Chain Dynamics in PE solution crystallized ultra high molecular weight PE crystalline non-crystalline ppm ω/ω R melt crystallized ultra high molecular weight PE crystalline non-crystalline ppm ω/ω R

8 13 C Chemical Shift Anisotropy crystalline non-crystalline solution crystallized more axial motion compatible with 180 jump more isotropic motion melt crystallized

9 Temperature Dependence solution crystallized UHMW-PE melt crystallized UHMW-PE D ij [khz] 9.1 T [K] 320 D ij [khz] ω/ω R ppm ω/ω R ppm

10 Observation and Analysis of Chain Translation Motion with 13 C NMR Experiments

11 Observation of Chain Translation saturate 13 C 13 C relaxation / chain diffusion acquisition t 0 t < 0

12 Time and Temperature Dependence SC-PE MC-PE SC-PE MC-PE exchange time [s] temperature [K]

13 Quantification of Chain Translation saturate 13 C 13 C relaxation / chain diffusion acquisition 1.0 relative intensity Intensities at short times are affected by T 1 relaxation Normalization needs the Intensity at infinit diffusion time t 1/2 [s 1/2 ]

14 Quantification of Chain Translation selective 13 C polarization chain diffusion acquisition relative intensity Intensities at short times are affected by T 1 relaxation Normalization needs the Intensity at infinit diffusion time t 1/2 [s 1/2 ] Non-exponential signal decay does not originate from T1 relxation

15 Determination of NMR Crystallinity 1.0 crystallinity C: relative intensity A + D t 1/2 1 - D t 1/2 C = 1 / (A+1) x-ray NMR MC 39% 46% t 1/2 [s 1/2 ] SC 74% 75% fiber 95% 90%

16 Chain Diffusion in Polyethylene 1.0 Diffusion Constant MC: m 2 s -1 relative intensity SC: m 2 s -1 Melt crystallized UHMW-PE Solution crystallized UHMW-PE t 1/2 [s 1/2 ]

17 Activation Energy of Chain Motion E A ~ 50 kj/mol ln(d) melt crystaliized solution crystallized /T [K -1 ]

18 Chain Diffusion vs Local Jump Rate MC-PE MC-PE from [Schnell 01a ] MC-PE from [Hu 99] ln v E a =50.3 kj/mol /T [K -1 ]

19 Variation of Lamellar Thickness relative intensity Fiber lamella-doubled SC solution crystallized (SC) t 1/2 [ s 1/2 ] Annealing lamellar, solution crystallized polyethylene close to the melting point leads to lamellar doubling. Rastogi et al, Macromolecules 30, 7880 (1997).

20 Variation of Lamellar Thickness relative intensity Fiber lamella-doubled SC solution crystallized (SC) t 1/2 [ s 1/2 ] Annealing lamellar, solution crystallized polyethylene close to the melting point leads to lamellar doubling. Rastogi et al, Macromolecules 30, 7880 (1997).

21 Variation of Lamellar Thickness relative intensity diffusion in the fiber sample 0.2 Fiber lamellar doubled SC ~ 100 nm solution crystallized (SC) 0.0 lamellar thickness t 1/2 [ s 1/2 ] Annealing lamellar, solution crystallized polyethylene close to the melting point leads to lamellar doubling. Rastogi et al, Macromolecules 30, 7880 (1997). time dependence of chain

22 Chain Diffusion in Drawn Samples relative intensity fiber draw ratio=30 draw ratio=5 undrawn t 1/2 [/s 1/2 ] Weak deformations do not change the local morphology Stronger deformations change the thickeness of crystalline layers

23 Conclusions Anisotropic NMR Interactions in SC-PE - highly restricted dynamics - almost temperature independent Observation of Chain Translation - local chain diffusion can be observed - (NMR) crystallinity can be determined - studies of local structure de/formation

24 Acknowledgements Max-Planck-Institut für Polymerforschung Dr. Yefeng Yao Prof. Dr. H.W. Spiess University of Eindhoven Prof. Dr. S. Rastogi Dr. D.R. Lippits