**4. The influence of polymer topology and modifier content on the luminescent properties of segmented polyurethanes**

According to (Lobko et al., 2010) the PU matrix can intensify the photoluminescence of europium chelate compounds introduced into polymer *in situ*. Taking into account that immobilization *in situ* of metal chelate compounds in polymer matrix can influence both structure and properties of the hybrid system (Nizelskii & Kozak, 2006; Nizelskii et al., 2005) the investigation of rare-earth metal compounds in polymeric environment is a way for creation of new optically active materials.

LPUs and CPUs modified with Eu(3+) chelates when exposed in 365 nm UV-light demonstrate the intensive photoluminescence in red region. Figure 9 represents the luminescent spectra of LPU and CPU, modified with various amount of Eu(fod)3.

64 Polyurethane

System

\* the unbalanced wetting angles

ethylene glycol (EG) γЕG-air = 48,36 mN/m.

in LPU from 0,5 to 3%wt. lead to decreasing of both 1 and 2.

**luminescent properties of segmented polyurethanes** 

of the modifier's amount on the surface tension.

creation of new optically active materials.

photoluminescence measurements.

θ1 (the

"polymer-air" boundary)

Concentration of PU less polar groups that form the weak complexes with metal chelate compound at the "polymer-support" boundary can facilitate the partial segregation of metal containing centres at this boundary. That conclusion is consistent with microscopic data and

θ, degree γЕG-PU, mN/m

γ1 (the

CPU-0 55 65 38,06 34,50 10 3,56 CPU-1% Eu 53 64 38,74 34,67 11 4,07 CPU-3% Eu 51 66 39,39 33,95 15 5,44 CPU-5% Eu 56 64 37,70 34,77 8 2,93 LPU-0 58 70 37,00 32,45 12 4,55 LPU-1% Eu 61 67,5 35,95 33,43 6,5 2,52 LPU-3% Eu 67,5 73 33,43 31,25 5,5 2,18 LPU-5% Eu 59 74,5 36,63\* 30,64 15,5 5,99

θ1, θ2 – the wetting angles at the "polymer‐air" and the "polymer-support" boundaries, respectively, degree; γ1, γ2 – the surface at the "polymer‐air" and the "polymer-support" boundaries, respectively, mN/m;

**Table 5.** The contact wetting angle (θ) and surface tension () of PU films. The standard liquid is

Varying of the metal containing modifier amount (from 0,5 to 5% wt.) in CPU practically does not affect surface tension. In the contrary, change of metal chelate compound content

The difference of the tendency in changing of surface tension in LPU and CPU clearly depend on polymer topology. Different PU topology results in different segmental mobility of the polymer, that agrees with DRS data. This effect described detailed in Section 5 and Section 2.4. At that time we can't formulate the certain reason for non monotonous influence

According to (Lobko et al., 2010) the PU matrix can intensify the photoluminescence of europium chelate compounds introduced into polymer *in situ*. Taking into account that immobilization *in situ* of metal chelate compounds in polymer matrix can influence both structure and properties of the hybrid system (Nizelskii & Kozak, 2006; Nizelskii et al., 2005) the investigation of rare-earth metal compounds in polymeric environment is a way for

**4. The influence of polymer topology and modifier content on the** 

"polymer-air" boundary)

γ2 (the "polymersupport" boundary)

θ2 (the "polymersupport" boundary)

θ= θ2 –θ1, degree

= 1-2, mN/m

The luminescent spectra of europium containing PU are diffuse, while luminescence spectrum of Eu(fod)3 is enough well-resolved. According to (Poluectov et al., 1989) the luminescence spectra of europium *β*-diketonate solutions contain bands corresponding to the 5D0-7F*<sup>і</sup> -*transitions (where *і* = 0,1,2,3,4). The spectra of Eu *β*-diketonate in PU matrices demonstrate the intensive wide band of photoluminescence in the region of λ=610-635 nm (5D0-7F2-transition), narrow band λ=660 nm (5D0-7F3 –transition) and bands of 5D0-7F0, 1, 4 transitions (580, 600,700 nm, accordingly) of low-intensity. It is possible to explain the diffuse spectrum of luminescence of europium containing PU in the region of λ =610-635 nm by distortion of the Eu (3+) chelate geometry in PU due to complex "polymer-metal chelate compound" formation and due macroligand steric hindrances.

**Figure 9.** The spectra of luminescence of LPU *(a)* and CPU *(b)*, modified with europium chelate (λUV = 365 nm): (1) 0.5%; (2) 1%; (3) 5%.

The intensity of PU-Eu luminescence depends both on the europium chelate content and polymer topology. The luminescence intensity increases with increasing of europium chelate compound content. The luminescence intensities of 5D0 → 7F2 transition (λ=612nm) for LPU with 05%, 1% and 5%wt. of Eu(fod)3, correspond as 1:1,8:2,4. The relationship of luminescence intensity *vs.* modifier percentage in CPUs is linear (1:3,3:9,2). The CPU-Eu with low modifier content has the lower luminescent intensity as compared with LPU-Eu. Where as CPU-5%Eu luminescence intensity is 1,5 higher, than LPU-5% Eu luminescence intensity. Taking into account data of Sections 2, 3, 6 we can suppose that due to difference in PU topology this effect is associated with higher concentration of polymer photo transmitting sites near the modifier in CPU as compared with LPU.

The tetra coordinated Eu (3+) chelate compounds with different additional ligands in an external coordination sphere were used to analyse the influence of additional coordination 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+) compounds.

Bottom-Up Nanostructured Segmented Polyurethanes with Immobilized in situ Transition and Rare-Earth Metal Chelate Compounds – Polymer Topology – Structure and Properties Relationship 67

donor-acceptor complexes between aromatic fragments of PU and quasi-aromatic chelate

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

According to two-electrode method the direct current conductivity of PU can drastically change

CPU-5%Eu increases by one order as compared with CPU-0. In the presence of

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.

40oC System

102 103 104 105

f,Hz

**Figure 11.** Log-log plots of the imaginary part of complex electrical modulus M" *vs.* frequency for

1200 <sup>C</sup> 1000

CPU-0 1,78 10-12 1,310-11 LPU-0 4,6510-12 4.610-12 CPU-Cu 2,86 10-11 210-9 LPU-Cu 4,2510-11 3.810-11 CPU-Cu2Zn 2,47 10-9 0,710-8 LPU-Cu2Zn 1,5110-9 1.210-10 \*CPU2000-0 - 1\*10-10 \*CPU2000-Cu2Zn - 1\*10-7

*<sup>d</sup>* enlarges from 2 to 3 orders (fig. 13, table 5). DRS

a) dc, Sm/cm 20oC

dc for the

b) dc, Sm/cm 20oC

in the presence of some metal chelate compounds. At the room temperature

b) dc, Sm/cm

800 C C

rings of chelate compounds of rare-earth metals.

**5. Dielectric relaxation and conductivity** 

polyheteronuclear metal chelate compounds

a) dc, Sm/cm 20oC

\*CPU2000-Cu - 1\*10-9

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

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

600 C

10-2

M''

10-1

\* The PU films synthesized with PPG-2000

CPU–5%Eu at several temperatures

values are listed in Table 5.

System

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

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 Eu(fod)3 also is considerably lower.

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 donor-acceptor complexes between aromatic fragments of PU and quasi-aromatic chelate rings of chelate compounds of rare-earth metals.
