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(b). (a). I n. I w. Figure 1. Typical ESR spectra of spin probe in NR:. Figure 4. ESR spectra of spin probe diffusing in NR irradiated with 300 kGy. The probe incorporation temperatures were: (a) 4 °C and (b) 24 °C. Spectra were measured at 19 °C. narrow (T > T g ) broad (T < T g )

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slide1

(b)

(a)

In

Iw

Figure 1. Typical ESR spectra of spin probe in NR:

Figure 4. ESR spectra of spin probe diffusing in NR irradiated with 300 kGy. The probe incorporation temperatures were: (a) 4 °C and (b) 24 °C. Spectra were measured at 19 °C.

  • narrow (T > Tg)
  • broad (T < Tg)
  • bimodal (T≈T5mT)

Figure 5. Schematic representation of the spin probe incorporation process at (a) 4 °C and (b) 37 °C in NR matrix

ESR - Spin Probe Method in Studying Crosslinked Elastomers:

an Effect of the Probe Incorporation Temperature

M. Didović1, D. Klepac1 and S.Valić1,2

1 University of Rijeka, School of Medicine, Braće Branchetta 20, Rijeka, 51000, Croatia

2 Rudjer Bošković Institute, Bijenička 54, Zagreb,10000, Croatia

Objective

Results

  • Toinvestigate the influence of the temperatureof spin probe incorporation process on theshape of ESR spectra.

Materials and Methods

  • natural rubber (NR) latex – 62 wt.% of dry matter
  • (The Rubber Research Institute of India)
  • spin probe:

4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl

EXPERIMENTAL

  • natural rubber latex containing 62 wt.% of dry matter was irradiated with different total irradiation doses of 200 kGy and 300 kGy
  • irradiated NR latex was deluted by ammonia solution (0.6 wt.%) up to 25 wt.% of solid content
  • ~1mm thick NR films were prepared by removing the liquid phase at room temperature
  • spin probe was incorporated in NR samples by swelling the samples in the probe solution at 4 °C, 16 °C, 24 °C and 37 °C. The solvent was toluene.
  • solvent was slowly removed by evaporation; all samples were then annealed at 60 °C for 72 hours
  • ESR spectra were recorded on Varian E-109 ESR spectrometer equipped with Bruker ER 041 XG microwave bridge and Bruker ER 4111 VT variable temperature unit

Figure 2. ESR spectra of spin probe diffusing in nonirradiated NR measured at -10 °C. The probe incorporation temperatures were: (a) 4 °C, (b) 24 °C and (c) 37 °C.

Figure 3. ESR spectra of spin probe diffusing in NR irradiated with 200 kGy measured at 0 °C. The probe incorporation temperatures were: (a) 16 °C and (b) 24 °C.

Table 1. Intensity ratios of the narrow (In) and broad (Iw) components of ESR spectra shown in Figures 2-4.

References

Conclusions

L. J. Berliner, Spin Labeling: Theory and Applications Vol 1. and Vol 2., Academic Press, 1976.

Z. Veksli, M Andreis, B. Rakvin, ESR spectroscopy for the study of polymer heterogeneity, Prog Polym. Sci. 25 (2000) 949-986.

  • the shape of ESR spectra of the spin probe in heterogeneous systems, as shown for NR, depends on the probe incorporation temperature
  • the increase of the probe incorporation temperature results in a higher amount of the broad component
  • higher probe incorporation temperature allows probe molecules to diffuse into the higher density regions of the matrix and consequently leads to the restriction in probe dynamics

17th European Symposium on Polymer Spectroscopy, September 9th to 12th, 2007 in Seggauberg, Austria