**2. Heterogeneity of metal containing polyurethanes**

#### **2.1. Structural heterogeneity of PU according to X-ray data**

Formation of a polymer matrix in the presence of metal chelate compounds favours creation of a new hierarchy in structural organization of the polymer as compared with metal free system. This effect is caused by complex formation between metal chelate compound and functional groups of the forming polymer (Ying, 2002; Kozak et al., 2000).

Figure 1 represents the WAXS and Figure 2 presents SAXS intensity profiles of metal-free PU and PU modified with metal -diketonate. The asymmetric diffuse diffraction maxima (Figure 1) point on the amorphous structure of the metal-free and metal containing CPU and LPU. For the LPUs the short-range order parameter *d* (equation 1) is equal to 0.44 nm and don't depend on the metal chelate compound amount (table 1). For the CPU the Bragg's period (*d)* changes from 0.44 to 0.46 nm with increasing of the modifier amount from 0,5 to 5% wt.

The PU's SAXS profiles are characterized by the presence of one amorphous maximum with *qm* positions varying from 1,7 to 2,0 nm-1 (Figure 2). Such maximum points on the existence of changeover period of uniform electron density scattering elements and areas of uniform distribution of hard and flexible blocks in PU. The Bragg's period (*D*) falls from 3,7 to 3,1 nm with increasing of the modifiers amount from 0,5 to 5% wt. (table 1).

**Figure 1.** The WAXS intensity profiles of CPU (a) and LPU (b): metal-free (1), modified with 0,5% (2), 1% (3), 3% (4) и 5% (5) Eu(fod)3.

Bottom-Up Nanostructured Segmented Polyurethanes with Immobilized in situ Transition and Rare-Earth Metal Chelate Compounds – Polymer Topology – Structure and Properties Relationship 57


*2* θ - the diffraction maximum angular position, degrees;

56 Polyurethane

*The electron spectra* of the copper (2+) containing PU films and of copper (2+) chelate compounds solutions in dichloromethane (c = 10-2M) in the ultra-violet and visible region

*The quasi-elastic neutron scattering* (QENS) was recorded using the multi detector spectrometer "NURMEN" on the atomic reactor ВВР-М (The institute of the nuclear research of the NAS of Ukraine). The self-diffusion of chloform used as low molecular probe

Formation of a polymer matrix in the presence of metal chelate compounds favours creation of a new hierarchy in structural organization of the polymer as compared with metal free system. This effect is caused by complex formation between metal chelate compound and

Figure 1 represents the WAXS and Figure 2 presents SAXS intensity profiles of metal-free PU and PU modified with metal -diketonate. The asymmetric diffuse diffraction maxima (Figure 1) point on the amorphous structure of the metal-free and metal containing CPU and LPU. For the LPUs the short-range order parameter *d* (equation 1) is equal to 0.44 nm and don't depend on the metal chelate compound amount (table 1). For the CPU the Bragg's period (*d)*

The PU's SAXS profiles are characterized by the presence of one amorphous maximum with *qm* positions varying from 1,7 to 2,0 nm-1 (Figure 2). Such maximum points on the existence of changeover period of uniform electron density scattering elements and areas of uniform distribution of hard and flexible blocks in PU. The Bragg's period (*D*) falls from 3,7 to 3,1 nm

**Figure 1.** The WAXS intensity profiles of CPU (a) and LPU (b): metal-free (1), modified with 0,5% (2),

changes from 0.44 to 0.46 nm with increasing of the modifier amount from 0,5 to 5% wt.

were recorded using the spectrometer Specord UV-VIS.

**2. Heterogeneity of metal containing polyurethanes** 

**2.1. Structural heterogeneity of PU according to X-ray data** 

functional groups of the forming polymer (Ying, 2002; Kozak et al., 2000).

with increasing of the modifiers amount from 0,5 to 5% wt. (table 1).

liquid in swelled PU films was analyzed.

1% (3), 3% (4) и 5% (5) Eu(fod)3.

*d* – distance between PU atomic layers from WAXS, nm;

*qm -* value at maximum intensity of *I*(*q*) relationship, nm-1;

*D* - changeover period of uniform electronic density scattering elements from SAXS, nm.

**Table 2.** X-ray structural characteristic of LPU and CPU

**Figure 2.** The SAXS intensity profiles of CPU (a) and LPU (b): metal-free (1), modified with 0,5% (2), 1% (3), 3% (4) and 5% (5) Eu(fod)3.

Analysis according (Porod, 1982) of heterogeneity range (*lp*) and average diameter (*l1, l2*) of different scattering elements in CPU-0, CPU-Cr and CPU-Со indicate existence of two types of nanosize heterogeneities in the bulk of PU. The first one (with *l1* < *D* ) is inherent to segmented PU. The second one (with *l2* > *D*) is generated in the presence of transition metal chelate compound. We can define the latter structures as "metal chelate compound – polyurethane" complexes with polymer chains as macro ligands (Kozak et al., 2006; Nizelskii & Kozak, 2006) (Scheme 1).

Thus, the immobilization *in situ* of metal chelate compounds in polyurethane is accompanied with enrichment of polymer matrix with the nanosize heteroligand macro complexes of metal formed simultaneously with organic nanosize structures typical for metal-free polymer.

### **2.2. Dynamic heterogeneity of PU according to EPR data**

The structural heterogeneity of PU influences the local segmental mobility of macro chains, resulting in "dynamic heterogeneity" of the systems. The analysis of mobility of SP introduced into the polymer gives information concerning such heterogeneity.

Bottom-Up Nanostructured Segmented Polyurethanes with Immobilized in situ Transition and Rare-Earth Metal Chelate Compounds – Polymer Topology – Structure and Properties Relationship 59

7

**2**

T, K

**<sup>3</sup> <sup>1</sup>**

6

5

4

3

2 1

As a result of heating the equalizing of polymer segments mobility and "unfreezing" of "slow" SP rotation diffusion occurs. The correlation time decreases with the rise of temperature due to increasing of molecular mobility and "softening" of PU matrix. Figure 4

represents the relationship

thermal heating) (7).

0

0,5%wt. (2) and 5%wt. (3) of Er(acac)3.

10

20

30

40

\*1010, c

 *(Т)* for CPU.

B

**1mT**

**Figure 3.** The spectra of the TEMPO introduced in CPU+%Er(acac)3 at the various temperatures: 18 оС (1); 26 оС (2); 44 оС (3) ; 90 оС (4); 114 оС (5); 21 оС (30 min after thermal heating) (6); 18 оС (2 days after

280 300 320 340 360 380 400

**Figure 4.** The thermal dependence of correlation time of the TEMPO in CPU-0 (1), CPU, modified with

The PU's thermodynamic heterogeneity is closely associated with above discussed types of heterogeneities. The influence of the metal chelate compounds on the thermodynamic

**2.3. Thermodynamic heterogeneity of PU according to DSC data** 

1 CPU-0

2 CPU-0.5% Er(acac)3 3 CPU-5% Er(acac)3

Calculated values of are listed in the table 2. They characterize the hindered rotation of SP in PUs of different topology. The greater value of is, the harder rotation of the probe occurs in polymer matrix.


**Table 3.** The correlation time of TEMPO in CPUs and LPUs, modified with 1% of metal chelate compounds.

As it can be seen from the table 2, in CPU modified with 1%wt. Co(3+) and Cr(3+) chelate compounds the values of increase indicating reduction of SP mobility as compared with metal-free CPU. In the contrary, for CPUs modified with 1%wt. Cu(2+), Ni(2+) values of decrease as compared with metal-free CPU. This means that Co(3+) and Cr(3+) containing CPUs have more dense macro chain packing as compared with metal free CPU. Where as Cu(2+) and Ni(2+) containing CPUs possess looser macro chain packing. Similarly to (Lipatov et al., 2000), the effect we can relate to difference in metal chelate compounds electron configuration and symmetry. In addition, the influence of metal chelate compound on PU dynamic depends also on the polymer topology. For example, it can be seen the opposite influence of Cu(2+) chelate compounds on the macro chain mobility in LPU and CPU (Table2).

The analysis of SP EPR-spectrum shape and hyperfine splitting (HFS) gives additional information concerned probed medium. In PU matrices that contain metal chelate compounds the EPR spectra of SP have asymmetric shape (Figure 3). In all of the spectra occur essential increasing of central component and broadening of all components as compared with TEMPO spectrum in homogeneous glycerol matrix. In many spectra there is noticeable splitting of low-field and/or high-field components of SP spectrum.

The peculiarities observed are most likely the result of signal superposition of "fast" and "slow" probes located in polymer regions with different mobility. In conformity with above supposition the temperature increasing brings on enhancement of the SP EPR spectra isotropy (Figure 3). Initially asymmetric ESR spectrum becomes more isotropic while heating the sample. The spectrum components narrow and the intensity of central component diminishes.

As a result of heating the equalizing of polymer segments mobility and "unfreezing" of "slow" SP rotation diffusion occurs. The correlation time decreases with the rise of temperature due to increasing of molecular mobility and "softening" of PU matrix. Figure 4 represents the relationship  *(Т)* for CPU.

58 Polyurethane

in polymer matrix.

compounds.

CPU (Table2).

component diminishes.

**2.2. Dynamic heterogeneity of PU according to EPR data** 

The structural heterogeneity of PU influences the local segmental mobility of macro chains, resulting in "dynamic heterogeneity" of the systems. The analysis of mobility of SP

Calculated values of are listed in the table 2. They characterize the hindered rotation of SP in PUs of different topology. The greater value of is, the harder rotation of the probe occurs

As it can be seen from the table 2, in CPU modified with 1%wt. Co(3+) and Cr(3+) chelate compounds the values of increase indicating reduction of SP mobility as compared with metal-free CPU. In the contrary, for CPUs modified with 1%wt. Cu(2+), Ni(2+) values of decrease as compared with metal-free CPU. This means that Co(3+) and Cr(3+) containing CPUs have more dense macro chain packing as compared with metal free CPU. Where as Cu(2+) and Ni(2+) containing CPUs possess looser macro chain packing. Similarly to (Lipatov et al., 2000), the effect we can relate to difference in metal chelate compounds electron configuration and symmetry. In addition, the influence of metal chelate compound on PU dynamic depends also on the polymer topology. For example, it can be seen the opposite influence of Cu(2+) chelate compounds on the macro chain mobility in LPU and

The analysis of SP EPR-spectrum shape and hyperfine splitting (HFS) gives additional information concerned probed medium. In PU matrices that contain metal chelate compounds the EPR spectra of SP have asymmetric shape (Figure 3). In all of the spectra occur essential increasing of central component and broadening of all components as compared with TEMPO spectrum in homogeneous glycerol matrix. In many spectra there is

The peculiarities observed are most likely the result of signal superposition of "fast" and "slow" probes located in polymer regions with different mobility. In conformity with above supposition the temperature increasing brings on enhancement of the SP EPR spectra isotropy (Figure 3). Initially asymmetric ESR spectrum becomes more isotropic while heating the sample. The spectrum components narrow and the intensity of central

noticeable splitting of low-field and/or high-field components of SP spectrum.

System τ·10-10, c System τ·10-10, c CPU-0 45 LPU-0 48 CPU-1%Cu(eacac)2 43 LPU-1%Cu(eacac)2 69 CPU-1%Ni(acac)2 42 CPU-1%CuCd 45 CPU-1%Cr(acac)3 50 CPU-1%CuZn 32 CPU-1%Co(acac)3 49 CPU-1%CuNiCo 51 **Table 3.** The correlation time of TEMPO in CPUs and LPUs, modified with 1% of metal chelate

introduced into the polymer gives information concerning such heterogeneity.

**Figure 3.** The spectra of the TEMPO introduced in CPU+%Er(acac)3 at the various temperatures: 18 оС (1); 26 оС (2); 44 оС (3) ; 90 оС (4); 114 оС (5); 21 оС (30 min after thermal heating) (6); 18 оС (2 days after thermal heating) (7).

**Figure 4.** The thermal dependence of correlation time of the TEMPO in CPU-0 (1), CPU, modified with 0,5%wt. (2) and 5%wt. (3) of Er(acac)3.

#### **2.3. Thermodynamic heterogeneity of PU according to DSC data**

The PU's thermodynamic heterogeneity is closely associated with above discussed types of heterogeneities. The influence of the metal chelate compounds on the thermodynamic heterogeneity and thermo-physic properties of PUs was analyzed by DSC. Figure 5 illustrates the temperature dependences of specific heat capacity of CPUs modified with 0,5; 1; 3; 5%wt. of Cu(acac)2. The thermo-physic characteristics of copper-containing CPUs are given in Table 3.

Bottom-Up Nanostructured Segmented Polyurethanes with Immobilized in situ Transition and Rare-Earth Metal Chelate Compounds – Polymer Topology – Structure and Properties Relationship 61

heterogeneity degree of CPU correlates with modifier amount in the system. This result

The segregation of metal containing micro crystals in CPU-5% Co and CPU-5%Cr was revealed in (Kozak et al., 2006):. Such unexpected segregation seemed unlikely due to homogeneous dispersion of metal chelate compound solution in reaction mixture (see 2.1) and coordination immobilization of metal chelate compounds in PU matrix. Nevertheless, the further X-ray study of CPU-5%Cu, LPU-5%Cu (fig. 6) and microscopy data (see 2.5) confirm partial segregation of metal-containing sites in PU matrices. This effect can be explained by different complex ability of segmented PU soft and hard components towards

The Scherer's equation (Stompel & Kercha, 2008) for the average diameter (*L*) of crystallite in amorphous media allows estimate dimensions of the particles in metal-containing PU.

height of diffraction angle in radians. The value of L is equal to 3 nm for CPU-1%Co, it is equal to 4 nm for CPU-1%Cr and it is equal to 10 nm in LPU-1%Eu. The evaluated

*L k λ* / ( ) *βcosθm* (9)

is the half-

= 1,54 Ǻ, *k* is the shape factor assigned to 0,9, *L* is the average

*<sup>m</sup>* is the Bragg's angle in degrees, and

3 CPU-0,5% Cu(acac)2 4 CPU-1% Cu(acac)2 5 CPU-3% Cu(acac)2 6 CPU-5% Cu(acac)2

1 Cu(acac)2 2 CPU-0

> > **2 1**

**2.4. The formation of ordered micro regions in metal containing PUs** 

metal chelate compound as well as by higher mobility of PU's soft component.

dimensions of the aggregates in copper containing PUs are ranged from 8 to 12 nm.

**0 5 10 15 20 25 30 35 40**

Segregation of the micro crystals detected via WAXS study has been also fixed by optical light transmission microscopy and by the scanning electron microscopy (SEM) (Figure 7). The micro crystals detected by optical microscopy are coloured like metal chelate compounds used as PU modifier. Such colouring indicates enrichment of the crystals with corresponding metal ions. The crystalline regions can be formed by the modifier itself and/or by complexes of modifier with PU chains as macro ligand. The last conclusion agrees

2, degree

agrees with X-ray data (section 2.1).

Here X-ray wavelength

Intensity, pulses

**Figure 6.** The WAXS diffractograms of the CPU-%Cu(acac)2 films.

diameter of the crystals in angstroms,

**Figure 5.** Temperature dependence of specific heat capacity for copper-containing CPU.


**Table 4.** The thermo-physical properties of copper-containing CPU.

It is evident from fig. 5 and table 3 that for the CPUs the specific heat capacity (̣ΔCp) grows with increasing of Cu (2+) chelate content from 0,5 to 5% wt. comparing with CPU‐0. In addition, the high temperature shifting of glass temperature (*Tg)* and the broadening of the temperature interval of glassing (̣*ΔT*) for CPU- 3%Cu and CPU-5%Cu are observed. The similar effect was discussed in (Lipatov et al., 1999) for CPUs, modified with 1%wt of various transition metals chelate compounds. That effect we can relate to formation of coordination bonds between functional groups of CPU and copper (2+) chelate compound.

Thus, growth of *Tg* and *ΔCp* values with increasing of Cu(acac)2 amount corresponds to rise of polymer segments with decreased mobility due to complexing.

The ratio of ΔCp(CPU-Сu) to ΔCp(CPU-0) allows estimate the degree of PU's thermodynamic heterogeneity (Bershtein. & Yegorov, 1990) and analyze the influence of metal chelate modifier content on this type of heterogeneity (table 3). As it can be seen the thermodynamic heterogeneity degree of CPU correlates with modifier amount in the system. This result agrees with X-ray data (section 2.1).

#### **2.4. The formation of ordered micro regions in metal containing PUs**

60 Polyurethane

given in Table 3.

heterogeneity and thermo-physic properties of PUs was analyzed by DSC. Figure 5 illustrates the temperature dependences of specific heat capacity of CPUs modified with 0,5; 1; 3; 5%wt. of Cu(acac)2. The thermo-physic characteristics of copper-containing CPUs are

220 240 260 280 300 320 340 360 380 400

T,K

**Figure 5.** Temperature dependence of specific heat capacity for copper-containing CPU.

CPU-0 258 18 0,25 1 CPU-0,5%Cu(acac)2 256 16 0,38 1,52 CPU-1%Cu(acac)2 258 18 0,43 1,72 CPU-3%Cu(acac)2 260 21 0,50 2,00 CPU-5%Cu(acac)2 271 20 0,55 2,20

It is evident from fig. 5 and table 3 that for the CPUs the specific heat capacity (̣ΔCp) grows with increasing of Cu (2+) chelate content from 0,5 to 5% wt. comparing with CPU‐0. In addition, the high temperature shifting of glass temperature (*Tg)* and the broadening of the temperature interval of glassing (̣*ΔT*) for CPU- 3%Cu and CPU-5%Cu are observed. The similar effect was discussed in (Lipatov et al., 1999) for CPUs, modified with 1%wt of various transition metals chelate compounds. That effect we can relate to formation of coordination bonds between functional groups of CPU and copper (2+) chelate compound.

Thus, growth of *Tg* and *ΔCp* values with increasing of Cu(acac)2 amount corresponds to rise

The ratio of ΔCp(CPU-Сu) to ΔCp(CPU-0) allows estimate the degree of PU's thermodynamic heterogeneity (Bershtein. & Yegorov, 1990) and analyze the influence of metal chelate modifier content on this type of heterogeneity (table 3). As it can be seen the thermodynamic

System *Tg*, K ΔT, K *Cp* , J/ (g·K)

**Table 4.** The thermo-physical properties of copper-containing CPU.

of polymer segments with decreased mobility due to complexing.

1 СPU-0

2 СPU-0,5% Cu(acac)2 3 СPU-1% Cu(acac)2 4 СPU-3% Cu(acac)2 5 СPU-5% Cu(acac)2

> 0 ( ) ( ) *p CPU Сu p CPU*

 

*C C*

 

0,9

1,2

1,5

1,8

Cp, J/(g·K)

2,1

2,4

The segregation of metal containing micro crystals in CPU-5% Co and CPU-5%Cr was revealed in (Kozak et al., 2006):. Such unexpected segregation seemed unlikely due to homogeneous dispersion of metal chelate compound solution in reaction mixture (see 2.1) and coordination immobilization of metal chelate compounds in PU matrix. Nevertheless, the further X-ray study of CPU-5%Cu, LPU-5%Cu (fig. 6) and microscopy data (see 2.5) confirm partial segregation of metal-containing sites in PU matrices. This effect can be explained by different complex ability of segmented PU soft and hard components towards metal chelate compound as well as by higher mobility of PU's soft component.

The Scherer's equation (Stompel & Kercha, 2008) for the average diameter (*L*) of crystallite in amorphous media allows estimate dimensions of the particles in metal-containing PU.

$$L = k\lambda \;/\; \left(\beta \cos \theta\_m\right) \tag{9}$$

Here X-ray wavelength = 1,54 Ǻ, *k* is the shape factor assigned to 0,9, *L* is the average diameter of the crystals in angstroms, *<sup>m</sup>* is the Bragg's angle in degrees, and is the halfheight of diffraction angle in radians. The value of L is equal to 3 nm for CPU-1%Co, it is equal to 4 nm for CPU-1%Cr and it is equal to 10 nm in LPU-1%Eu. The evaluated dimensions of the aggregates in copper containing PUs are ranged from 8 to 12 nm.

**Figure 6.** The WAXS diffractograms of the CPU-%Cu(acac)2 films.

Segregation of the micro crystals detected via WAXS study has been also fixed by optical light transmission microscopy and by the scanning electron microscopy (SEM) (Figure 7). The micro crystals detected by optical microscopy are coloured like metal chelate compounds used as PU modifier. Such colouring indicates enrichment of the crystals with corresponding metal ions. The crystalline regions can be formed by the modifier itself and/or by complexes of modifier with PU chains as macro ligand. The last conclusion agrees

with the X-ray data that register several discrete peaks in Cu(2+), Cr(3+) and Co(3+) containing PUs (Figure 6).

Bottom-Up Nanostructured Segmented Polyurethanes with Immobilized in situ Transition and Rare-Earth Metal Chelate Compounds – Polymer Topology – Structure and Properties Relationship 63

Figure 8 illustrates the typical differences in surfaces of PU films. As it can be seen, at surface formed at the boundary "polymer-support" (fig. 8*, a*) the size and quantity of crystals are larger. Where as, at surface formed at the "polymer-air" boundary (fig. 8, *b*) the size and quantity of crystals are significantly smaller. For example, the mean size of crystals

Detailed analysis of PUs surface properties depending on the boundary nature can give

The presence of metal chelate compounds in reaction mixture can influence the surface tension of the formed polyurethane. In (Lipatov, 1997) the surface properties were studied of PU with metal ions introduced through in four different ways. There are filling, metal ion cross-linking, metal ion chain-extending and diffusion of metal chelate compound from its solution to polymer being formed earlier. It has been shown that the surface properties of metal containing PU depend on metal quantity much less than on the way of metal chelate compound introduction in polymer. For example, the γsg of PU filled with Cr(acac)3 (0.18% wt.) changes up to 8 mN/m. On the contrary the γsg of Pb (15% wt) cross-linked PU

Obviously, the PU's surface structure depends on the boundary "polymer-support" or "polymer-air". Data of ESCA and IR-spectroscopy by (Lipatova et al., 1987; Lipatova & Alexeeva, 1988) point on possibility of the chemical unequivalenсe of the polymer surfaces formed at the different boundaries. In addition in (Kozak et al., 2010) it was observed substantial difference in luminescence intensity at different surfaces of the PU films modified with europium (3+) chelate compounds. Therefore, the surface properties of europium containing LPU and CPU were compared for surfaces formed at the "polymerair" and "polymer-support" boundary using measurement of contact wetting angle. The

The values of surface tension of metal containing PU obtained using Wilgelmy method(with water as wetting liquid) (Lipatov et al., 1997) are consistent with values of the surface tension calculated using measurement of contact wetting angle (Table 5) of standard liquid.

The wetting angles at the "polymer-air" boundary for all of CPU and LPU are from 5.5 to 15.5 degrees less than the wetting angles at the "polymer-support" boundary (table 4). The difference between relative values of surface tension (1-2) takes values from 2.18 to 5.59 mN/m. As it is known, the higher compound polarity is the greater surface energy and surface tension it possesses. Obtained results allow conclude that PU surface formed at the "polymer-air" boundary is enriched with more polar groups (e.g. urethane ) and PU surface formed at the "polymer-support" boundary is enriched with less polar groups (e.g. glycol

in LPU-1%Eu changes from the one surface to another from 20 μm to 0,5 μm.

**3. Influence of metal chelate modifiers on surface properties of** 

changes up to 0.3 mN/m as compared with metal free PU.

data obtained are listed in the table 4.

segments).

additional information.

**polyurethanes** 

**Figure 7.** The optical microscopy (a, b) and SEM microscopy micro images of the LPU-0,5%Cu(acac)2 (in polarized light) (a), LPU-5%Cu(acac)2 (b) and CPU-5%Cr(acac)3.

Optical microscopy allows obtain information concerning two surfaces of one PU film. One of them formed on the boundary "polymer-support" (the PU's surface formed on the Teflon support) and another formed on the boundary "polymer-air" (the PU's surface formed on the air).

**Figure 8.** Micro images of LPU-1%Eu(fod)3 (a,b) and CPU-1%Cr(acac)3 (c, d) surfaces formed at the "polymer-air" boundary (а, c) and the "polymer- support" boundary (b, d).

Figure 8 illustrates the typical differences in surfaces of PU films. As it can be seen, at surface formed at the boundary "polymer-support" (fig. 8*, a*) the size and quantity of crystals are larger. Where as, at surface formed at the "polymer-air" boundary (fig. 8, *b*) the size and quantity of crystals are significantly smaller. For example, the mean size of crystals in LPU-1%Eu changes from the one surface to another from 20 μm to 0,5 μm.

Detailed analysis of PUs surface properties depending on the boundary nature can give additional information.
