**2. Synthesis**

The reaction was provided in solid. Fig. 1 describes the scheme of PGU synthesis. There occur both deblocking of polyisocyanate groups and urethane bonds formation.

There were obtained powdered PGU, hot-pressed samples and reinforced PGU with calculated degree of polysaccharide hydroxyl group substitution of 20, 40, 60, 80 and 100%. As far as obtained polymer is quite new and unexplored polymer material, not full range of the hydroxyl/urethane ratio was studied by methods presented in this Chapter. The obtained materials are acid-, alkali- and thermo resistant.

The reaction path was controlled using sampling procedure and sample analysis with FTIR spectroscopy.

Characteristic band at 2276 cm-1 which appears after heating the reactive mixture up to 130oC demonstrates the process of isocyanate groups deblocking. On the initial stages of reaction all of PGU samples show increasing intensity of this band due to active isocyanate group formation.

Interaction of N=C=O groups with the nearest primary and secondary hydroxyl groups of polysaccharide leads to decreasing intensity of characteristic band 2276 cm-1 during next 10 min. Diffusion limitations of this reaction are determined by heterogeneity of reactive mixture and results in retarding of urethane bonds formation. Mechanic stirring of reactive mixture allows improve reactive centers contact and leads to total disappearance of isocyanate groups in the system. (Fig 2.а). Consumption of hydroxyl groups is accompanied by disappearance of the band at 3165 cm-1 and decreasing of intensity band at 1209 cm-1 (valence vibrations and deformation vibrations of O-H bond in glucuronic acid residue respectively) and by intensity reduction of the band at 3215 cm-1 (valence vibrations of primary OH-groups in mannopyranose cycles) (Fig 2 c).

**Figure 1.** Scheme of PGU synthesis

432 Polyurethane

with latent isocyanate-containing reagent blocked polyisocyanate is also a prominent advantage of developed technique. PGU were obtained via interaction of xanthan hydroxyl groups and isocyanate groups of deblocked above 125oC PIC (Kozak & Nizelskii, 2002).

Microbial polysaccharide xanthan is produced by xanthomonas campestris pv. Campestris bacteria (Gzozdyak et al., 1989). Xantan is well known and most widely used microbial exopolysaccharide. It is used in light industry (textile), heavy industry (drilling and oil production) and food industry as well as in agriculture, forestry, pharmaceutics, medicine and cosmetics. The water solutions of xantane have unique rheological properties due to metal cation complexing ability and formation of primary, secondary and higher levels of structure. The main chain of the polysaccharide is alike to cellulose and its side-chains

Blocked polyisocyanate is latent reagent which is able to produce reactive isocyanate groups under elevated temperature. It is multifunctional latent reagent that can consist of 40 to 70 % of dimeric compound , 20 to 60 % of tetramer and 1 to 5 % of trimer and hexamer. Melting temperature interval of blocked PIC is from 80 to-95 oС, NCO-group unblocking temperature ranges from 125 to 130 oС. PIC is soluble in most of organic solvents and can be

The reaction was provided in solid. Fig. 1 describes the scheme of PGU synthesis. There

There were obtained powdered PGU, hot-pressed samples and reinforced PGU with calculated degree of polysaccharide hydroxyl group substitution of 20, 40, 60, 80 and 100%. As far as obtained polymer is quite new and unexplored polymer material, not full range of the hydroxyl/urethane ratio was studied by methods presented in this Chapter. The

The reaction path was controlled using sampling procedure and sample analysis with FTIR

Characteristic band at 2276 cm-1 which appears after heating the reactive mixture up to 130oC demonstrates the process of isocyanate groups deblocking. On the initial stages of reaction all of PGU samples show increasing intensity of this band due to active isocyanate

Interaction of N=C=O groups with the nearest primary and secondary hydroxyl groups of polysaccharide leads to decreasing intensity of characteristic band 2276 cm-1 during next 10 min. Diffusion limitations of this reaction are determined by heterogeneity of reactive mixture and results in retarding of urethane bonds formation. Mechanic stirring of reactive mixture allows improve reactive centers contact and leads to total disappearance of isocyanate groups in the system. (Fig 2.а). Consumption of hydroxyl groups is accompanied by disappearance of the band at 3165 cm-1 and decreasing of intensity band at 1209 cm-1 (valence vibrations and deformation vibrations of O-H bond in glucuronic acid residue

occur both deblocking of polyisocyanate groups and urethane bonds formation.

obtained materials are acid-, alkali- and thermo resistant.

(pendants) consist of glucose, mannose and glucuronic acid residues.

used both in powder and liquid form.

**2. Synthesis** 

spectroscopy.

group formation.

Increasing intensity of the band at 3364 cm-1 (in characteristic doublet of N-H valence vibrations), appearance of the 1635 cm-1 band in the region of NH deformation vibrations (amide II) and changes of intensity of 1650 and 1590 cm-1 bands respond to formation of urethane bonds and releasing of blocking agent (Fig 2b).

In the wave numbers range from 3000 to 3500 cm-1redistribution is observed of the intensities of absorption bands corresponding to hydrogen linked OH-groups. That points on redistribution of intermolecular bonds in the system during polysaccharide cross-linkage and PGU formation.

Polyglucanurethanes: Cross-Linked Polyurethanes Based on Microbial Exopolysaccharide Xanthan 435

*H2O H2SO4 NaOH*

**Table 1.** The weight change of PGU20 exposed in deionized water, concentrated sulphuric acid (V=20

Presenting mass of absorbed water in modified and non-modified samples of exopolysaccharide as mass loss at the first stage (temperature interval 45 – 150oC) we can see that amount of absorbed water correlates with balance of hydroxyl and urethane groups in the system (Fig.3). It corresponds with the fact that system hydrophilic properties correlate with amount of hydroxyl groups. Weight loss at this stage is 1,5; 2,5; 8,5 % wt. for PGU80,

**Figure 3.** TGA curves - TG (1), DTG (2), DTA (3) of initial reagents: xanthan (а), blocked PIC (b); curves DTG (c) and TG (d) for initial reagents and PGU of various composition: xanthan (1), 2- PGU20 (2),

(c) (d)

(a) (b)

1 0,081 0,085 0,081 2 0,213 0,205 0,431 3 0,217 0,213 0,489 7 0,250 0,224 0,485 13 0,425 0,241 0,489

ml, 30% wt.) and concentrate alkali solution (V=20 ml, 40% NaOH).

Time, day

Sample weight, g

PGU40, PGU20, respectively.

PGU40, PIC (4)

**Figure 2.** IR spectra of reactive mixture for PGU60 at temperature 130oC(1), 150оС (2), at 150оС after 10 min (3), after 20 min (4) after 30 min(5)

According to FTIR spectra of various PGU (PGU40, PGU80 and PGU100) the number of isocyanate groups released at the initial stage of reaction correlates with the polyisocyanate content in the system. During the first 10 min the process of polyisocyanate deblocking dominates. At the same time the urethane group formation occurs via interactiom of NCO groups and polysaccharide hydroxyl groups in acid residue of glucuronic acid and/or hydroxyl groups of mannose. The time when the urethane group formation begins to dominate depends on balance of the reagents in reaction mixture.
