**5. Dielectric relaxation and conductivity**

66 Polyurethane

compounds.

(3); Eu(fod)3 (4)

Eu(fod)3 also is considerably lower.

of europium chelate compounds on the intensity of their luminescence. The fig. 10, a illustrates the luminescent spectra of isolated Eu (3+) chelate compounds. The fig. 10, b represents the spectra of luminescence of CPU films, modified with 1%wt. of Eu (3+)

**Figure 10.** The luminescence spectra (λex. = 365 nm) of the europium (3+) chelate compounds (a) and of CPU films with 1%wt. of these chelate compounds (b): Eu(TTA)3phen (1); Eu(TTA)3ТРРО (2); Eu(TTA)3

(a) (b)

As it can be seen the luminescence of Eu (3+) chelate compounds introduced into PU matrix (only 1%wt.) is more intensive than luminescence of isolated metal chelate compounds (100% wt). In addition, the intensity of luminescence of tetra coordinated Eu(3+) chelate compounds (Eu(TTA)3phen and Eu(TTA)3TPPO) both isolated and introduced into CPU matrix, considerably exceeds such intensity for 3-coordinated Eu(3+) chelate compound Eu(TTA)3 that does not contain additional ligands The intensity of photoluminescence of

Estimation of Eu (3+) environment symmetry in various complexes via the coefficient of asymmetry (*η*) defined as ratio of intensity of 5D0 → 7F2 –transition to intensity of 5D0 → 7F1 transition. (Haopeng et al., 2008) shows that the greatest coefficient of asymmetry (*η* = 9) has CPU-1%Eu(TTA)3phen characterized by the greatest intensity of luminescence. Consequently, the presence of additional ligand in the external coordination sphere of Eu (3+) favours increasing of luminescence intensity. Then increasing of Eu-chelate compounds luminescence intensity in PU can be explained in particular by additional coordination of lanthanide ion with the functional groups of PU and/or by formation of The dielectric properties of PU were studied by broad band DRS measurements in wide range of temperature (-40 to 120 oC). The data are analyzed within the various formalisms. The direct current conductivity was both measured using two-electrode method and was estimated using DRS complex electric resistance dс =d/(ARdc) and Z"(Z') isotherms (Cole-Cole diagram). Figure 11-13 illustrate obtained dielectric spectra. Calculated conductivity values are listed in Table 5.

According to two-electrode method the direct current conductivity of PU can drastically change in the presence of some metal chelate compounds. At the room temperature dc for the CPU-5%Eu increases by one order as compared with CPU-0. In the presence of polyheteronuclear metal chelate compounds *<sup>d</sup>* enlarges from 2 to 3 orders (fig. 13, table 5). DRS analysis of complex dielectric permittivity as well as complex admittance σ\*, complex electrical modulus М\* and impedances Z', Z" allows reveal the nature of the observed conductivity.


\* The PU films synthesized with PPG-2000

a) dc measured using two-electrode method and b) dc obtained using DRS data

**Table 6.** PUs conductivity at a direct current

**Figure 11.** Log-log plots of the imaginary part of complex electrical modulus M" *vs.* frequency for CPU–5%Eu at several temperatures

Bottom-Up Nanostructured Segmented Polyurethanes with Immobilized in situ Transition and Rare-Earth Metal Chelate Compounds – Polymer Topology – Structure and Properties Relationship 69

2 max

*τ*

metal-containing PU are linear indicating the Arrhenius-type of temperature dependence of

Decreasing of max value with the increasing of Eu(3+) content in PU confirm increasing of macro chains mobility in metal-containing CPU (Kozak et al., 2006). The activation energy of conductivity relaxation for CPU-0, CPU-0,5%Eu, CPU-1%, CPU-5% are approximately similar. Experimental dependences of logdc vs. 1/T are non-Arrenius both for PU-0 and metal containing PUs. It fit the theoretical curves of Vogel–Tamman-Fulcher (VTF) equation σdc=σoexp(-B/(T-To) (fig. 13) indicating influence of the PU free volume on charge transport. The results obtained give evidence of significant influence of structural organization in the

As it can be seen PU's direct current (σdc) conductivity grows with increasing of temperature and that is characteristic to ionic conductivity. The metal ion participation as current carrier is unlikely because to small amounts of metal ion in the modified PUs (~ 0.025-0.25% wt.). That fact and coordination immobilization of the modifiers in polymer makes unlikely increasing of the conductivity due to the metal chelate compound conductive properties. On the other hand ionic mechanism of conductivity and adequate amount of protons presented in PU matrix as well as observed increasing of polymer chain mobility in modified PU

Comparison of direct current conductivity of CPU based on PPG-2000 with conductivity of CPU based on PPG-1000 shows increasing of conductivity at the direct current of such system up to 10-7Sm/sm at the 40оС due "softening" of PU. Nevertheless it can be seen that conductivity level of maximum soft LPU is at least one order lower then conductivity of CPU.

**6. "Metal chelate compound - polymer" complexing and formation of the** 

Mutual influence of metal chelate compound and polymer matrix due to complex formation is a decisive reason of observed changes of structural, dynamic, relaxation etc. characteristics of the metal contained PU. The complexing of metal chelate compounds with

**6.1. The complexing of the metal chelate compound with PU matrix according to** 

The electron spectroscopy allows analyse both character of complexing of metal chelate compound with the polymer matrix and state of metal chelate compound in PU. The electron spectra of transition and rare-earth metal chelate compound in PU indicate presence of the band of *d-d*-transitions for the transition metal chelate compound introduced into PU (fig.14) and band of π-π-transitions for the rare-earth metal chelate compounds

**additional network of coordination bonds in metal containing PU** 

PU matrix was analysed using electron spectroscopy and EPR.

**the electron spectroscopy** 

allows us to suppose proton participation in the process of charge transport.

max

*πf* ) in log scale *vs.* 1/T (fig. 12) for

Experimental dependences of relaxation time ( <sup>1</sup>

modified PU on its conductivity level.

*τmax*.

**Figure 12.** The thermal dependence of the relaxation time (τmax) for the CPU with various content of Eu (3+) chelate compound.

**Figure 13.** The logdc vs. 1/T for CPU: (a) CPU with various length of flexible component: CPU (PPG-2000) – 1%Cu2Zn (1); CPU (PPG-1000) – 1% Cu(eacac)2 (2); CPU (PPG-2000) – 1% Cu(eacac)2 (3); CPU (PPG-2000) – 0 (4); CPU (PPG-1000) – 0 (5) and (b) CPU-0 (1) and CPU-Cu2Zn formed in the presence of various solvents: 1, 4-dioxane (2); dichloromethane (3) and DMFA (4).

The curves on the fig. 11 have well defined maxima in temperature region of 60 to 120oC. According to (Pathmanatham & Johari, 1990; Kyritsis & Pissis, 1997) these maxima correspond to conductivity relaxation. Increasing of temperature is accompanied with shift of conductivity relaxation maxima to higher frequencies (fig. 11). The fact concerned to increasing of segmental mobility in PU. The metal chelate compounds introduction and increasing of their content in the system result in increasing of PU segmental mobility.

Experimental dependences of relaxation time ( <sup>1</sup> 2 max max *τ πf* ) in log scale *vs.* 1/T (fig. 12) for metal-containing PU are linear indicating the Arrhenius-type of temperature dependence of *τmax*.

68 Polyurethane

120 110 100 90 80 70

T,C0

0,5% Eu(fod)3

1% Eu(fod)3

1000/T,K-1

**Figure 12.** The thermal dependence of the relaxation time (τmax) for the CPU with various content of

1

lgdc(S/cm)


1000/T,K-1

presence of various solvents: 1, 4-dioxane (2); dichloromethane (3) and DMFA (4).

**Figure 13.** The logdc vs. 1/T for CPU: (a) CPU with various length of flexible component: CPU (PPG-2000) – 1%Cu2Zn (1); CPU (PPG-1000) – 1% Cu(eacac)2 (2); CPU (PPG-2000) – 1% Cu(eacac)2 (3); CPU (PPG-2000) – 0 (4); CPU (PPG-1000) – 0 (5) and (b) CPU-0 (1) and CPU-Cu2Zn formed in the

The curves on the fig. 11 have well defined maxima in temperature region of 60 to 120oC. According to (Pathmanatham & Johari, 1990; Kyritsis & Pissis, 1997) these maxima correspond to conductivity relaxation. Increasing of temperature is accompanied with shift of conductivity relaxation maxima to higher frequencies (fig. 11). The fact concerned to increasing of segmental mobility in PU. The metal chelate compounds introduction and increasing of their content in the system result in increasing of PU segmental

2,6 2,8 3,0

0% Eu(fod)3

10-4

2,5 3,0

Eu (3+) chelate compound.


mobility.




lg

dc, S/c

m



10-3

10-4

4

3 2

1

2,4 2,6 2,8 3,0 3,2 3,4

1000/T(K-1 )

5% Eu(fod)3

10-3

Decreasing of max value with the increasing of Eu(3+) content in PU confirm increasing of macro chains mobility in metal-containing CPU (Kozak et al., 2006). The activation energy of conductivity relaxation for CPU-0, CPU-0,5%Eu, CPU-1%, CPU-5% are approximately similar. Experimental dependences of logdc vs. 1/T are non-Arrenius both for PU-0 and metal containing PUs. It fit the theoretical curves of Vogel–Tamman-Fulcher (VTF) equation σdc=σoexp(-B/(T-To) (fig. 13) indicating influence of the PU free volume on charge transport. The results obtained give evidence of significant influence of structural organization in the modified PU on its conductivity level.

As it can be seen PU's direct current (σdc) conductivity grows with increasing of temperature and that is characteristic to ionic conductivity. The metal ion participation as current carrier is unlikely because to small amounts of metal ion in the modified PUs (~ 0.025-0.25% wt.). That fact and coordination immobilization of the modifiers in polymer makes unlikely increasing of the conductivity due to the metal chelate compound conductive properties. On the other hand ionic mechanism of conductivity and adequate amount of protons presented in PU matrix as well as observed increasing of polymer chain mobility in modified PU allows us to suppose proton participation in the process of charge transport.

Comparison of direct current conductivity of CPU based on PPG-2000 with conductivity of CPU based on PPG-1000 shows increasing of conductivity at the direct current of such system up to 10-7Sm/sm at the 40оС due "softening" of PU. Nevertheless it can be seen that conductivity level of maximum soft LPU is at least one order lower then conductivity of CPU.
