Report No xxxx - Instytut Fizyki JÄ drowej PAN

SOLID-STATE NMR INVESTIGATION
OF LOCAL CHAIN DYNAMICS IN
POLYISOBUTYLENE/POLYPROPYLENE-CO-BUTENE BLENDS
Marcin Wachowicz 1,2 , Justyna E. Wolak 2 , Stefan Jurga 1 , Jeffery L. White 2
1 Institute of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland;
2 Department of Chemistry, Campus Box 8204, North Carolina State University, Raleigh, NC
27695, United States of America
Changes in local dynamics of polyisobutylene (PIB) upon blending with different poly-
(ethylene-co-1-butene) copolymers (PEB) were investigated by solid-state 2 H- and 129 Xe-
The pure PIB and 50/50 mixtures of PIB and PEB, where the butane
NMR methods.
monomer concentration in PEB copolymer was varied (23 or 66 wt %), were studied. The
blends were prepared by dissolution in toluene, solvent evaporation and vacuum drying [1].
The quadrupolar echo 2 H-NMR spectra for pure perdeuterated PIB (Fig. 1) and for two
PIB/PEB blends were acquired in the temperature range from 210 to 294 K. In the blend
samples only the PIB was perdeuterated. The line shapes contained the contribution from
methyl and methylene groups and at lower temperatures they were clearly distinguished due
to the different quadrupolar splittings. The deuteron line shape analysis demonstrated that the
molecular dynamics of PIB molecules (the conformational exchange along PIB backbone)
have the same character in all the samples investigated. However, the rate of molecular
dynamics of PIB chains is increased in the blends in comparison to the pure PIB as evidenced
by the shift of a temperature at which coalescence of the deuteron spectra occurs. The
difference between the coalescence temperatures of pure PIB and the blend containing the
highest butene monomer (PIB/PEB-66) content was ~10 K.
The 129 Xe-NMR experiments involved the investigation of Xe gas absorbed by the
polymer. The xenon chemical shift is sensitive to subtle changes in the electronic environment
and can be successfully utilized to probe the homogeneity of the blend. For the PIB/PEB-23
polymer two peaks were observed (Fig. 2b) corresponding to the chemical shifts of pure
polymers indicating phase separation. In contrast, PIB/PEB-66 blend was found to be
homogeneously mixed, as indicated by a single peak with an intermediate chemical
shift (Fig.2a)
2
Fig. 1. H-NMR spectra of pure
perdeuterated PIB.
129
Fig.2. Xe-NMR spectra of Xe gas absorbed in
(a) PIB/PEB-66 blend
and in (b) PIB/PEB-23 blend.
[1] Wolak J., Jia X., Gracz H., Stejskal E.O., White J.L., Wachowicz M., Jurga S.,
Macromolecules 36(13), 4844-4850
90