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, Croatia2 Rudjer Bošković Institute, Bijenička 54, Zagreb,10000, Croatia

spin probe:

EXPERIMENTAL

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

Objective

. N

OH

O

natural rubber (NR) latex – 62 wt.% of dry matter

(The Rubber Research Institute of India)

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

To investigate the influence of the temperature of spin probe incorporation process on the shape of ESR spectra.

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

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.

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

(a) (b)

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.

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.

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.

Sample

Temperature of

measurement / ºC

Temperature of probe

incorporation / ºC

In/Iw

NR 0 kGy -10

4 1.61

24 1.35

37 1.15

NR 200 kGy 016 2.47

24 2.32

NR 300 kGy 194 20.9

24 15.1

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

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

a) narrow (T > Tg)b)broad (T < Tg)c) bimodal (T≈T5mT)

Iw

In

Materials and Methods

References Conclusions

Results

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