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
Line Width in 1 H NMR Spectra static dipolar broadening 60 40 20 0-20 -40-60 khz 30 khz MAS 20 10 0 khz rigid solid HRMAS 4 3 khz soft matter Solution 5 0 khz isotropic molecular dynamics
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
Anisotropic NMR Interactions all-trans conformations crystalline gauche conformations non-crystalline 36 34 32 30 28 ppm 1 H- 13 C dipolar couplings 13 C chemical shift anisotropy
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). = -8-6 -4-2 0 2 4 6 8 ω/ω R D ij = 10 khz D ij = 5 khz
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 60 40 20 0 ppm 60 40 20 0 ppm 60 40 20 0 ppm Liu et al., J. Magn. Reson.,155, 15 (2002).
Morphology and Chain Dynamics in PE solution crystallized ultra high molecular weight PE crystalline non-crystalline 36 34 32 30 28 ppm -6-4 -2 0 2 4 6 ω/ω R melt crystallized ultra high molecular weight PE crystalline non-crystalline 36 34 32 30 28 ppm -6-4 -2 0 2 4 6 ω/ω R
13 C Chemical Shift Anisotropy crystalline non-crystalline solution crystallized more axial motion compatible with 180 jump more isotropic motion melt crystallized
Temperature Dependence solution crystallized UHMW-PE melt crystallized UHMW-PE D ij [khz] 9.1 T [K] 320 D ij [khz] 6.3 8.9 340 5.6 8.8 360 5.0-8 -4 0 4 8 ω/ω R 60 40 20 0 ppm -8-4 0 4 8 ω/ω R 60 40 20 0 ppm
Observation and Analysis of Chain Translation Motion with 13 C NMR Experiments
Observation of Chain Translation saturate 13 C 13 C relaxation / chain diffusion acquisition t 0 t < 0
Time and Temperature Dependence SC-PE MC-PE SC-PE MC-PE exchange time [s] 40 20 10 5 2 0.8 temperature [K] 360 350 340 330 320 310
Quantification of Chain Translation saturate 13 C 13 C relaxation / chain diffusion acquisition 1.0 relative intensity 0.8 0.6 0.4 0.2 Intensities at short times are affected by T 1 relaxation Normalization needs the Intensity at infinit diffusion time. 0.0 0 5 10 15 20 25 30 35 40 t 1/2 [s 1/2 ]
Quantification of Chain Translation selective 13 C polarization chain diffusion acquisition relative intensity 1.0 0.8 0.6 0.4 0.2 Intensities at short times are affected by T 1 relaxation Normalization needs the Intensity at infinit diffusion time. 0.0 0 5 10 15 20 25 30 35 40 t 1/2 [s 1/2 ] Non-exponential signal decay does not originate from T1 relxation
Determination of NMR Crystallinity 1.0 crystallinity C: relative intensity 0.8 0.6 0.4 0.2 A + D t 1/2 1 - D t 1/2 C = 1 / (A+1) x-ray NMR MC 39% 46% 0.0 0 5 10 15 20 25 30 35 40 t 1/2 [s 1/2 ] SC 74% 75% fiber 95% 90%
Chain Diffusion in Polyethylene 1.0 Diffusion Constant MC: 1.8 10-19 m 2 s -1 relative intensity 0.8 0.6 0.4 0.2 SC: 3.7 10-18 m 2 s -1 Melt crystallized UHMW-PE Solution crystallized UHMW-PE 0.0 0 5 10 15 20 25 30 t 1/2 [s 1/2 ]
Activation Energy of Chain Motion -39-40 -41-42 E A ~ 50 kj/mol ln(d) -43-44 -45-46 melt crystaliized solution crystallized 2.8 3.0 3.2 3.4 1000/T [K -1 ]
Chain Diffusion vs Local Jump Rate 12 10 8 MC-PE MC-PE from [Schnell 01a ] MC-PE from [Hu 99] ln v 6 4 2 0 E a =50.3 kj/mol 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 1000/T [K -1 ]
Variation of Lamellar Thickness relative intensity 1.0 0.8 0.6 0.4 0.2 Fiber lamella-doubled SC solution crystallized (SC) 0.0 0 5 10 15 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).
Variation of Lamellar Thickness relative intensity 1.0 0.8 0.6 0.4 0.2 Fiber lamella-doubled SC solution crystallized (SC) 0.0 0 5 10 15 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).
Variation of Lamellar Thickness relative intensity 1.0 0.8 0.6 0.4 diffusion in the fiber sample 0.2 Fiber lamellar doubled SC ~ 100 nm solution crystallized (SC) 0.0 lamellar thickness. 0 5 10 15 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
Chain Diffusion in Drawn Samples relative intensity 1.0 0.8 0.6 0.4 0.2 0.0 fiber draw ratio=30 draw ratio=5 undrawn 0 5 10 15 t 1/2 [/s 1/2 ] Weak deformations do not change the local morphology Stronger deformations change the thickeness of crystalline layers
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
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