Starch, urea, ethanol MERCK (Mumbai), and sodium hydroxide were used without further purification. Solvents such as acetone, DMF, DMSO, and (s.d fine chemicals) methanol were purified by standard procedure before use. Manganese (II) acetate tetrahydrate [Mn(CH₃COO)₂ · 4H₂O], copper (II) acetate monohydrate [Cu(CH₃COO)₂ · H₂O], nickel (II) acetate tetrahydrate [Ni(CH₃COO)₂ · 4H₂O], cobalt (II) acetate tetrahydrate [Co(CH₃COO)₂ · 4H₂O], and zinc (II) acetate dihydrate [Zn(CH₃COO)₂ · 2H₂O] were used without further purification. All the microorganisms were provided by C.S.A. Agricultural University, Kanpur.

The infrared (IR) spectra were recorded on a Perkin-Elmer infrared spectrometer model 621 by using KBr pellets. The ¹H-NMR spectra were recorded on a JOEL-FX-100 FT NMR instrument in dimethylsulfoxide (DMSO) solution and tetramethylsilane (TMS) as an internal standard. The elemental analysis of carbon, hydrogen, and nitrogen was carried out on a Perkin-Elmer model-2400 elemental analyzer (CDRI Lucknow). The percentage of metals was determined by complexometric titration against EDTA after decomposing with concentrated nitric acid (HNO₃). The solubility of polymeric ligand and its metal polychelates were checked at room temperature in different solvents. The thermal stability of polymer and its metal polychelates have been evaluated for recording thermograms by TA analyzer 2000 at a heating rate of 20°C per minute under Nitrogen atmosphere. The Tg and Tm of the synthesized polymeric resin (SUr) and its metal complex have been evaluated by PYRES DIAMOND DSC instrument. The electronic spectra of the metal complexes were recorded on a Perkin-Elmer Lambda-EZ 201, and magnetic susceptibility measurements were done with vibrating sample magnetometer. The biodegradable testing was carried out through CO₂ evolution method in the laboratory itself.

The important IR bands and their assignments of polymeric resin (poly-SUr) and its metal complexes are listed in Table 2. In the IR spectra of poly-SUr, bands that appeared in the region 3402 cm⁻¹ for νOH. The vibrational bands appeared at 1250 cm⁻¹ and 1080 cm⁻¹ are assigned to the νC-N and νC-O, respectively. The bands were observed at 2936-2850 cm⁻¹ for CH₂ asymmetric and symmetric stretching vibrations. For νO=C-NH (amide carbonyl linkage), vibrational bands appeared at 1778 cm⁻¹ and N-H bending appeared at 1654 cm⁻¹. In the case of metal complexes, vibrational bands appeared for O=C-NH (amide carbonyl linkage) shifted to the lower frequencies and indicating the coordination of amide nitrogen to metal ion, and this can be explained by the donation of electrons from nitrogen to metal atom. The νC-O also registered a significant shift to lower frequency indicating the participation of metal through the phenolic oxygen. The νO-H also registered lowering in frequency [15]. In all the polymer metal complexes, some additional bands also appeared in the regions of 610–603 cm⁻¹ and 552–548 cm⁻¹, which support the coordination of metal through oxygen and nitrogen [16, 17].

The ¹H-NMR bands ranges of polymeric resin and its metal complex with Zn (II) are given in Table 3. The resin showed a signal at 8.394 ppm for O=C-NH protons of amide carbonyl group. The bands appeared at 5.079–5.003, 4.718, 3.699, and 5.557 ppm due to pyranose ring of starch. Bands appeared at 3.45–3.32 ppm due to OH protons [18]. In the spectrum of poly-SUr-Zn (II) complex, the bands for O=C-NH shifted from their original position at 7.940 ppm, which suggested the involvement of metal ions in coordination [18].

The ¹³C-NMR band ranges of polymeric resin (poly-SUr) and its metal complex with Zn(II) are given in Table 4. The ¹³C-NMR bands of poly-SUr showed resonance band at 159.42 ppm due to the carbonyl carbon of amide. The pyranose carbons of starch molecules in the polymeric resin showed bands in the region 98.14, 69.89, 77.20 and 55.67 ppm, respectively [19, 20]. In case of metal complex bands showed shifting in comparison with the corresponding bands of polymeric resin as 155.76, 78.88, 64.53, 71.63, and 54.12 ppm, which also support the participation of metal ions.

The electronic spectra of metal complexes were recorded in DMSO. The electronic spectral bands and their magnetic moments are depicted in Table 5. The magnetic moment of the Mn (II) complex was 5.69 B.M., Which suggested the presence of five unpaired electrons. The electronic spectrum of polymer complex of Mn(II) exhibited three bands at 18870 cm⁻¹, 22980 cm⁻¹, and 25330 cm⁻¹, which may reasonably correspond to ⁴T_1g(G) ← ⁶A_1g(F), ⁴T_2g(G) ← ⁶A_2g(F), and ⁴A_1g(G) ← ⁶A_1g(F) transitions, respectively, which indicates an octahedral environment around the Mn(II) ion [21], and its ligand field parameters 10Dq, B, β and β ⁰ values are 7960, 625, 0.68 and 32%. The polymer complex of Co(II) has a magnetic moment of 4.10 B.M. corresponding to four unpaired electrons and showed three bands at 9800 cm⁻¹, 14080 cm⁻¹ and 20400 cm⁻¹ which were assigned to ⁴T_2g(F) ← ⁴T_1g(F), ⁴A_2g(F) ← ⁴T_1g(F), and ⁴T_1g(P) ← ⁴T_1g(F) transitions, respectively, which indicates an octahedral environment around the Co(II) ion [22, 23], and its ligand field parameters 10Dq, B, β and β ⁰ values are 6193 cm⁻¹, 729 cm⁻¹, 0.75 and 25%, respectively. The octahedral polymer complex of Ni(II) was expected to be paramagnetic owing to two unpaired d-electrons, and the experimental magnetic moment was found to be 2.77 B.M. The electronic spectra showed three bands at 8355 cm⁻¹, 12155 cm⁻¹, and 23809 cm⁻¹which were assigned to ³T_2g(F) ← ³A_2g(F), ³T_1g(F) ← ³A_2g(F), and ³T_1g(P) ← ³A_2g(F) transition, respectively, which is in the favor of octahedral geometry for polymer complex of Ni(II) [24], and its ligand field parameters 10Dq, B, β and β ⁰ values are 5952 cm⁻¹, 744 cm⁻¹, 0.69, and 31%, respectively. The above discussion very strongly indicates an octahedral geometry around the central metal ion in all metal complexes. It accounts for the occupation of two coordinating sites by H₂O out of six in making the octahedral environment.

In another study the electronic spectra of the SUr-Cu(II) exhibited two bands, at 15380 cm⁻¹ and 25000 cm⁻¹ due to ²A_1g ← ²B_1g(F) and charge transfer spectra, respectively, which indicate square planar geometry [25]. In the present study the magnetic moment value of SUr-Cu(II) was found to be 1.9 B.M., which is in accordance with square planar geometry. The SUr-Zn(II) is diamagnetic and showed tetrahedral geometry.

The thermal decomposition of polymeric resin and its polymer metal complex [SUr-Mn(II)] were studied by the thermogravimetric method. The thermogravimetric curves of polymeric resin and its polymer metal complex are depicted in Figure 1 and the thermal analytical data are listed in Table 6. The polymeric resin started to decompose with weight loss from 7%–8% at 150°C because the boiling point of the plasticizer outclassed 150°C was mainly ascribed to water loss, and the mass loss from 150°C to the onset temperature was related to the volatilization of both water and plasticizer. The decomposition of polymeric resin was slow in the initial stage, but above 200°C, weight loss became fast. The thermal data indicate that the thermal stability of the poly-SUrs upto 250°C; however, its metal complexes decrease the decomposition and reduced mass loss at the onset temperature. The volatility of the polymer metal complex was reduced because of the formation of coordination bond with the polymeric resin. Polymer metal complex started to decompose with weight loss 4%-5% at 150°C and the decomposition rate of metal complexes was very slow upto 275°C, but above 275°C, weight loss became fast. This result revealed that metal complex [SUr-Mn(II)] show better heat resistant characteristics than these of the polymeric resin due to the coordination of metal ions.

The DSC measurement served to determine the glass transition temperature Tg and decomposition behavior, and for this, the calorimetric curves of the polymeric resin and its polymer metal complexes are reported in Figure 2. The decomposition temperature scattered typical range is of 242°C for polymeric resin and the Tg scattered is in the range of 127°C for polymeric resin; this evolution could be ascribed due to the interaction between the starch and urea. The strong hydrogen bond formed between starch and urea, which decreased starch chain mobility and consequently increased the matrix glass transition temperature, but in the case of polymer metal complexes, the decomposition temperature and Tg increased. The decomposition temperature scattered typical range for polymer complex of Co(II) is 282°C and the Tg scattered is in the range of 141°C. This is the evidence that the thermal stability is enhanced by the incorporation of metal into the organic backbone. The glass transition temperature of these polymers increased by metal incorporation, and lower Tg and Tm are related to amount of starch and urea in the initial composition. This is the first evidence that starch participates in the chemical reaction and is becoming part of macromolecular structure. In addition, the Tg variation of metal incorporated polymer depends on the amount of metal ions and also the cross-linking effect of polymer between two chains of starch and strong hydrogen bonding which affects on chain mobility of starch modified in different ways.

It is a laboratory respirometric method that uses compost pile inocula given in Table 7(a) as a biotic function, [26] but the user may use other microbial environmental interest, with certain typical polymers that are readily biodegradable (such as aliphatic polyester or polyamides) and with biopolymer materials (paper, cotton cloth, cellulose, cellophane); it is convenient to use especially designed flask for this purpose (Anthony L. Andrady (1998) by Chapman and Hall London).

The test method might be carried out in water or soil but latter one is discussed here. Although in both cases a suitable volume of activated sludge to obtain complete mineralization of the sample in about a month is used as inoculums, about 10 cm³ per liter is recommended for aqueous system and we have used 5 cm³ per 50 g with cold medium successfully. The inoculums must be used the same day as collected and kept aerated until used. Also sufficient urea and potassium hydrogen phosphate (0.1 and 0.05 % of weight of polymer substrate) are added to the medium to fortify it and to promote further microbial growth.

The biodegradation rates of starch, polymeric resin, and polymer metal complexes for a comparative study are shown in Figure 3 and predicted in Table 7(b) and 7(c), respectively. From these figure and Table, it can be seen that the biodegradation rates of polymer metal complexes were lower than those of starch polymer after 187 hrs, and that the biodegradation rates of polymeric resin and starch polymer were in good coherence after 187 hrs and 200 hrs, respectively, that would be because the starch and urea support to the microorganism growth and degradation behavior.