**3. Reactions of aromatic isocyanates and urethane prepolymers with coordination compounds of iron (III)**

Further studies established that similar structural units could be formed even in the polyurethane matrix itself as a result of its modification with metal complexes synthesized for this purpose. A characteristic feature of these coordination compounds is the presence of chloride-bridged metal ions in their structure. One of such crosslinking metal complex system was prepared by the reaction of iron chloride (FeCl3) with ethanolamine (EA). It was found that reactions involving aromatic isocyanates and EA in the coordination sphere of the iron ion (III) led to the formation of azoaromatic compounds shown in figure 2.

Serrano & Oriol, 1995).

polyurethanes.

macrochain.

However, this approach is seriously limited and cannot be used for the creation of stacked metal-coordinated fragments in a disordered polymer matrix (Brostow, 1990; Carrher, 1981;

Metal complex structuring is promising in terms of the influence on properties of polyurethanes. The significance of this trend is conditioned by the ability of metal complexes to order the macromolecular chains, as well as affect the electrical properties of

In the early studies (Davletbaeva et al., 1998) devoted to imparting special properties to polyurethanes by their coordination bonding, it was shown that the interaction of aromatic isocyanates with copper chloride (CuCl2) in the acetone medium in the presence of trace amounts of water proceeded as a sequence of chemical transformations including simple addition and decomposition reactions, redox processes, and subsequent complexation (Fig. 1).

The ultimate products are polynuclear complexes of azoaromatic compounds, in which copper ions occurring in two variable oxidation states are connected by chloride bridges (Fig. 1). As it is seen from the structural formulas, some copper ions are stabilized at the initial degree of oxidation due to the formation of heterovalent pairs connected by сhloride bridges. Free isocyanate groups present in these compounds are able to react with oligodiols of different nature. Polyurethanes obtained in such manner form polymer network by coordination bonding of urethane groups and azogroups which are the part of a

It is shown that the chloride bridges are replaced by heteroatoms that are present in polymer chains while metal ions are coordinatively bound to macromolecules to crosslink them and, occurring in two interacting variable oxidation states, to form local centers of exchange interactions. As a result of electron transfer from one local coordinated unit to another, which is mediated by electron-donating groups, such as an ester group, the

**3. Reactions of aromatic isocyanates and urethane prepolymers with** 

the iron ion (III) led to the formation of azoaromatic compounds shown in figure 2.

Further studies established that similar structural units could be formed even in the polyurethane matrix itself as a result of its modification with metal complexes synthesized for this purpose. A characteristic feature of these coordination compounds is the presence of chloride-bridged metal ions in their structure. One of such crosslinking metal complex system was prepared by the reaction of iron chloride (FeCl3) with ethanolamine (EA). It was found that reactions involving aromatic isocyanates and EA in the coordination sphere of

conductivity of polyurethane increases by several orders of magnitude.

**coordination compounds of iron (III)** 

**2. Coordination compounds based on the aromatic isocyanates and** 

**copper (II) chloride for the synthesis of polyurethanes** 

**Figure 1.** Formation of polynuclear complexes of azoaromatic compounds.

The Modification of Polyurethanes by Highly Ordered Coordination Compounds of Transition Metals 37

Fe

Fe

Ar N N Ar

Fe

Ar N N Ar

Fe

Ar N N Ar

Ar N N Ar

Fe

where

CH

Ar =

NH3 Cl

Fe CH

NCO

O C HN O

CH3

**,**

.

O Fe <sup>=</sup>

, ,

CH3

NCO ,

**Figure 3.** Formation of stack coordination compounds.

supramolecular structures chains (Fig. 4).

Mössbauer studies of iron coordinated compounds reveal that the magnetic ordering is observed at relatively high temperature (80 K). Mössbauer spectrum obtained in transmission geometry at the temperature of the sample being equal to 80 K consists of two components, namely, a doublet in the middle of the spectrum corresponding to the residues of the initial FeCl3, dissolved in the matrix (less than 10% of the total area under the spectrum) and the magnetically ordered component with a hyperfine field average value of about 430 kE and the isomer shift, indicating a high-spin state of the Fe (III) ion. The absence of partial component in the middle of the spectrum is caused by the long average size of

NCO

**Figure 2.** Scheme of formation of azoaromatic compounds.

The continuation of this reaction is the formation of stack coordination compounds in which metal ions form coordination bonds with azogroups (Fig. 3).

**Figure 3.** Formation of stack coordination compounds.

2 4

 NH3 H2C

 NH3 H2C

2

O

O

nFeCl3 nNH2 CH2 CH2 OH

Ar N C O

Cl

CH2 CH2

Cl

Cl

CH2 CH2

NH2 (CH2)2 OH

CH2 NH3

Cl

Fe

Cl O

Ar N C O

 NH3 H2C

where Ar - NCO

O

CH2 NH3

Fe

Cl O

2ArNCO

n

CH2 CH2

2

2 n

n

2 NH2 (CH2)2 OH NH3 (CH2)2 O

 NH3 H2C

2

O

n/2

The continuation of this reaction is the formation of stack coordination compounds in which

 NH3 H2C

O C HN O

O

CH2 NH3

Cl

Cl

n

Fe

Cl O

Cl

CH2 CH2

NH2 (CH2)2 OH

CH2 CH2

CH3

n/2 **,**

HO CH2 CH2 NH CH O

NCO , NCO

Cl

CH2 CH2

, ,

CH2 NH3

Cl

CH3

**Figure 2.** Scheme of formation of azoaromatic compounds.

metal ions form coordination bonds with azogroups (Fig. 3).

Fe

Cl O

Ar Ar N N

n

 NH3 H2C

O

CH2 NH3

Cl

Ar N C O

Cl

CH2 NH3

Cl

Fe

Cl O

Cl

Fe

Cl O

Cl

Mössbauer studies of iron coordinated compounds reveal that the magnetic ordering is observed at relatively high temperature (80 K). Mössbauer spectrum obtained in transmission geometry at the temperature of the sample being equal to 80 K consists of two components, namely, a doublet in the middle of the spectrum corresponding to the residues of the initial FeCl3, dissolved in the matrix (less than 10% of the total area under the spectrum) and the magnetically ordered component with a hyperfine field average value of about 430 kE and the isomer shift, indicating a high-spin state of the Fe (III) ion. The absence of partial component in the middle of the spectrum is caused by the long average size of supramolecular structures chains (Fig. 4).

The Mössbauer study confirms the columnar structure of the obtained metal complexes, the possibility of their fixation in a flexible-chain polymer matrix containing electron-donating groups, and the existence of magnetic ordering at temperatures below 70 K. Sizes of very thin magnetic fields correspond to high-spin state of iron(III) ions (S=5/2).

The Modification of Polyurethanes by Highly Ordered Coordination Compounds of Transition Metals 39

matrix. Mössbauer studies of urethane prepolymer confirm these assumptions. The resulting spectra are also of superparamagnetic nature at temperatures below 47K

When polyurethanes are modified by coordination compounds synthesized on the basis of FeCl3 and EA, the minimum values of specific volume electrical resistance (about 108 Ohm∙sm) are recorded in the concentration area of 0,1% in terms of iron chloride. It should be noted that the ions of iron (III) in the above reactions do not change the oxidation level.

**4. Modification of urethane prepolymer by coordination compounds of** 

In one of the worked out highly ordered coordination compounds of transition metals for modification of polyurethanes N,N'-Diethylhydroxylamine (DEHA) is used as a ligand exhibiting the properties of a reducing agent. The most appropriate transition metal compound is copper (II) chloride. Some of the Cu (II) ions interacting with DEHA reduce

2 CuCl2

It was ascertained that the metal complex system showed the ability to interact with aromatic isocyanates to form azoaromatic compounds. The result was the formation of

It was established, that metal-complex modification of polyurethanes results in the change of their physicomechanical properties and spasmodic reduction (by 3-4 orders) of volumetric and superficial electric resistance. The reduction of the specific bulk electrical resistance by 3-4 orders is the most significant effect accompanying the metal-complex binding of polyurethanes. In this case the electrical resistance falls spasmodically depending on the nature of flexible chains of polyurethanes, the range of transition -metal ions concentrations. If the content of metal-complex modifying agent is increased further, the electrical resistance increases to some extent. The main role in the mechanism of charge transmission in metal-coordinated polyurethanes is assigned to electron-donating groups which are included in the structure of flexible chains of polyurethane matrix and the

O Cu 2Cl H

Ar N N Ar Cu 2Cl

O C HN O

 ArNCO HO(CH2)2NH(CH2)2OH

CH3

NCO , NCO

(Davletbaeva et al., 2006).

**copper (I, II)** 

CH3CH2

CH3CH2

NOH

where Ar - NCO

the oxidation level and turn into Cu (I) (see Fig. 5).

CH3

columnar coordination compounds (Fig. 6).

CH3CH2

CH3CH

N

, ,

presence of transition metal ions having two degrees of oxidation in it.

**Figure 5.** The mechanism of interaction of copper (II) chloride with DEHA.

It is known that to achieve the effect of magnetic ordering it is necessary that the chain of interacting ions of iron (III) should be long enough and combine up to a few thousand ions. The criterion for judging the length of the chain of magnetic ordered iron ions is relatively high blocking temperature of supermagnetism and the barrier value of effective anisotropy field. In our view, due to significant anisotropy in the structure of the complex the most likely assumption is the increasing of the potential barrier with the increase of chain length. The longer the chain, the higher its strength and the ability to build columns in a polymer matrix, and the specific properties of the structured polymer matrix are more pronounced as well.

**Figure 4.** The Mössbauer spectrum of metal complex system based on FeCl3 and EA.

The metal complex system is used for structuring urethane prepolymer containing terminal isocyanate groups. Considering the high flexibility of the urethane prepolymer chain, it can be assumed that the urethane groups will be coordinately bound with iron ions. The result of this interaction should be the formation of columnar structures directly in the polymer matrix. Mössbauer studies of urethane prepolymer confirm these assumptions. The resulting spectra are also of superparamagnetic nature at temperatures below 47K (Davletbaeva et al., 2006).

When polyurethanes are modified by coordination compounds synthesized on the basis of FeCl3 and EA, the minimum values of specific volume electrical resistance (about 108 Ohm∙sm) are recorded in the concentration area of 0,1% in terms of iron chloride. It should be noted that the ions of iron (III) in the above reactions do not change the oxidation level.
