Metal complexation of polymeric amino ligands derived from N,N′-methylenebis(acrylamide)-crosslinked polyacrylamides

Macromol. Chem. Phys. 197,2089-2102 (1996) 2089

Metal complexation of polymeric amino ligands derived from NJV-methylenebis(acry1amide)-crosslinked polyacrylamides

Lissy Jose, K N. Rajasekharan PiIlai*

School of Chemical Sciences, Mahatma Gandhi University, Priyadarshini Hills P. O., Kottayam-686 560, Kerala, India

(Received: April 28, 1995; revised manuscript of October 2, 1995)

SUMMARY The N,W-rnethylenebis(acry1amide) (NNMBA)-crosslinked polyacrylamide supported

amino ligands undergo complexation with Cr(III), Mn(II), Fe(III), Pb(I1) and Cd(I1) ions. Complexation is maximum for Cr(II1) ion. The metal intake decreases as the crosslinking increases. The NNMBA resin can be reused after complexation and desorption without appreciable reduction in amino capacity. The IR spectrum of the Cr(II1) complex gives an additional peak for sulfate complexation and the amino peak undergoes a negative shift, which is a clear evidence of metal coordination through the amino nitrogen. EPR, electronic spectra and magnetic moment are indicative of a distorted geometry for Cu(II), Cr(III), Fe(II1) and Mn(I1) complexes. Cd(II), Pb(I1) complexes are diamagnetic. Complexation brings about vivid changes in the surface morphology of polymeric Iigand. The thermal stability of Cr(II1) complex increases as the metal content increases.

Introduction

In recent years there has been a growing awareness in the field of the coordination chemistry of polymer-metal complexes, since they constitute a n important part of the contemporary chemistry of high molecular weight, bioinorganic and coordination compounds. This development was delayed due to the absence of powerful analytical tools. The lack of vigorous theoretical understanding and the instrumentation for studying the physicochemical aspects of metal complexes also affected the development adversely. The complete understanding of the complexation reaction, the coordination structure, the conformation state in solution and the effects of the macromolecular system in polymer-metal complexes are areas which still remain unsolved completely. The correlation between the trends of complexation and the structural factors characteristic of the macromolecular matrix is important in the design and the development of new and selective complexons for metal ions. Significant progress was achieved in the synthesis and utilization of functional polymers The macromolecular structural features of the polymer support material have been proved to contribute significantly to the reactivity of the functional groups 7- ‘O). A systematic investigation of the variables of macromolecular structure on complexation would contribute to the study of polymeric complexing agents which find varied applications in different branches of chemistry ’ - I 3 ) .

The paper describes the preparation of polyacrylamides with 2-20 mol-To of NNMBA crosslinks, transamidation with ethylenediamine to poly(N-2-aminoethylacrylamide)s, complexation with various transition metal ions, influence of time and

0 1996, Huthig & Wepf Verlag, Zug CCC 1022-1 352/96/$10.00

2090 L. Jose, V. N. Rajasekharan Pillai

pH on complexation, swelling studies, recyclability and characterization by IR, UV- visible and electron paramagnetic resonance (EPR) spectroscopies as well as magnetic susceptibility, scanning electron microscopy (SEM) and thermogravimetry (TG).

Experimental part

General

All the reagents were of certified ACS reagent grade. The purest available metal salts were used to prepare metal ion solution. The IR spectra were recorded on a Shimadzu IR 470 IR spectrophotometer, UV spectra on a Shimadzu UV-160A UV-visible spectrophotometer, magnetic measurements with Gouy balance, TG curves on a Delta Series TGA-7 thermal analyser at a heating rate of 10°C. min-' in nitrogen atmosphere and SEM on a Jeol JSM-35 C scanning electron microscope.

Synthesis of NNMBA-crosslinked pobacrylamides

Polyacrylamides with 2- 20 mol-Yo of N,W-methylenebis(acry1amide) (NNMBA) crosslinks were prepared by solution polymerization of the monomers in water at 70 "C using potassium persulfate as the initiator. For the preparation of 2 mol-% NNMBA- crosslinked polymer, acrylamide (20.87 g), NNMBA (0.924 g) and K,S,O, (100 mg) were separately dissolved in water. They were mixed together, diluted with 100 mL water, and heated on a water bath with stirring at 70°C till the polymer got precipitated. The polymer formed was collected by filtration, washed with water, ethanol, benzene and methanol and dried at 70°C. Polyacrylamides with 4, 8, 12 and 20 mol-Yo of NNMBA crosslinks were prepared by varying the mole fractions of the monomers in the feed.

Preparation of poly(N-2-aminoethylacrylamide)

The dried sample of polyacrylamide (10 g) was added to well stirred ethylenediamine (100 mL). The mixture was refluxed at 100-110°C for 9 h. The reaction mixture after transamidation was poured into water containing crushed ice. The resin was filtered off, washed with NaCl solution (0.1 M) until the filtrate was free from ethylenediamine as indicated by the absence of blue colouration with ninhydrin reagent. The gel was again washed with distilled water to remove the chloride ions. The resin was finally washed with methanol and dried at 70 "C.

Estimation of the resin amine content

The NNMBA-crosslinked amino resin (100 mg) was neutralised by equilibration with HCI (0.2 N, 10 mL). The resin sample was filtered and washed. The filtrate, together with washings, was titrated against NaOH (0.2 N) to a phenolphthalein end point.

Complexation of amino resin with metal ions

The metal ion intakes of the resin with varying extents of NNMBA crosslinks were carried out with Cr(III), Mn(II), Fe(III), Cd(I1) and Pb(I1) ions by batch equilibration method. 100 mg each of the resin samples was stirred with a definite concentration of excess metal salt solution (0.05 M, 80 mL) for 9 h. The concentration of the metal ion before and after

Metal complexation of polymeric amino ligands . . . 209 1

complexation was estimated, Pb(I1) and Cd(I1) by complexometry using xylenol orange ind i~a tor '~) , Cr(III), Mn(I1) and Fe(1II) by spectrophotometry at 575, 544 and 299 nm, respectively '9.

p H studies

The metal ion intake of the resin was studied at different pH to get the optimum pH for maximum complexation. pH of the metal solution was adjusted by adding 1 M acid or 1 M NaOH as shown by a pH meter. The amino resin (100 mg) was added to the metal solution (80 mL) of definite pH and kept for complexation by stirring for 9 h. The metal ion concentration before and after complexation was estimated.

Distribution coefficients

Fro the pH data the distribution coefficients were calculated using the equation:

Amount of the metal ion complexed (mg) x Vol. of the solution (mL) Amount of the metal ion uncomplexed (mg) x Wt. of the resin (g)

K , =

Time-course of complexation

Batch studies were carried out with 4% NNMBA-crosslinked amino resin to find out the time required for maximum complexation. 160 mL each of Cr(III), Pb(II), Cd(II), Mn(I1) and Fe(II1) solution (0.2 mg/mL solution) were mixed with amino resin (100 mg) and stirred. At regular intervals aliquots were withdrawn from the test solution and estimated.

Swelling studies

The NNMBA-crosslinked amino resin (500 mg) was equilibrated with distilled water (30 mL) for 48 h. It was filtered and the adhering water was removed by pressing with filter paper. Weight of the swollen resin was determined. It was kept to dry in vacuum for 24 h, and finally the weight of dry resin was also detected. From these two weights, equilibrium water content (EWC) can be calculated

Wt. of swollen resin - Wt. of dried resin Wt. of swollen resin

EWC (070) = x 100

For the swelling study of the complexed resins, 500 mg each of the resin was equilibrated with Cr(II1) salt solution containing 26 mg Cr(II1) ions and swelling studies were similarly carried out after filtering and washing.

Recyclability of complexed resin

The crosslinked polyacrylamide amino complexes (500 mg) were subjected to desorption by diluted acids. Mn(II), Pb(I1) and Cd(I1) ions were desorbed by stirring with HCI (15 mL, 2 N) and Cr(II1) and Fe(II1) by H,SO, (15 mL, 2 N). The desorbed metal ions were collected and estimated. The resin after the acid treatment was washed with dilute NaOH followed by distilled water. The resin was again subjected to complexation.


Results and discussion

Synthesis of NNMBA-crosslinked amino-functional polyacrylarnides

Polyacrylamides with 2 - 20 mol-Yo of NNMBA crosslinks were prepared by solution polymerization of the monomers in water at 70 "C using potassium persulfate as the initiator (Eq. (I)). Amino functions were incorporated into these crosslinked systems by transamidation with excess ethylenediamine at 100 "C (Eq. (2)).

-cn2-cn-cn2-cn-cn -cn- I I 2 1 CONH2 CO CONH2

CH2- $" cn = cn + co

NH

y2 7OoC, water

NH NH I

co 1 co I I cn-cn2 -cn -cn-cn -cn-cn -cn-

2 1 CONH2

I I

I I NH K2S200 ,

2 1 CONH2

2 1 NNMBA CONH2

l0O0C (2) t

Presence of excess ethylenediamine prevented multitransamidation reaction and further crosslinking. Since the ethylenediamine itself was used as the solvent for the reaction medium there was no possibility of hydrolysis and breaking of NNMBA crosslinking. The amino functions were detected by semi-quantitative ninhydrin reaction 16). The transamidated polymer developed a deep blue colour with ninhydrin reagent. The ligand functions were estimated by equilibrating a definite amount of the resin with excess HCl (0.2 N, 20 mL). The unreacted acid was estimated by titration against standard NaOH (0.2 N).

As expected for a crosslinked system, the ligand capacity decreases with increasing crosslinking (Fig. 1). This arises from the reduced availability of the amide groups buried within the crosslinks for transamidation with ethylenediamine. With increasing crosslinking the diffusion of the low molecular weight reagents into the interior of the networks is limited by the increased rigidity of the support 17) .

The increased reactivity and complexation of NNMBA-crosslinked polyacrylamide based systems with moderate amount of crosslinks (5 - 10 mol-Yo) have been reported I * ) . This arises from the heterogeneity developed in the polymerization

Metal complexation of polymeric amino ligands . . . 2093

I I I I I

0 1 8 12 16 20 Crosslink density in rnol-%

Fig. 1

1.0

.c 0.8 ; m Y 0 c

0.6 C 0 ._ - 2 0.L a, I

0.2

0 I I I I I I I I I I

0 L 8 12 16 20 Crosslink density in rnol-%

Fig. 2.

Fig. 1. Dependence of transamidation on the extent of NNMBA crosslinking

Fig. 2. Trend in complexation of metal ions with extent of NNMBA crosslinking

process 19). Microdomains of increased crosslinking were developed in these particular crosslinked polyacrylamides. But the decrease in ligand concentration with increase in crosslinking in this case arises from the uniform distribution of crosslinking points during polymerization.

Effect of extent of NNMBA crosslinking on complexation

The complexations of amino ligands supported on polyacrylamides in different structural evironments were investigated towards Cr(III), Fe(III), Mn(II), Cd(I1) and Pb(I1) by batch equilibration technique at their natural pH. The metal intakes of the various resins are given in Tab. 1 .

The observed trend in complexation is Cr(II1) > Mn(I1) > Pb(I1) > Fe(II1) > Cd(I1). The metal ion intake decreases with increasing crosslinking, as in the case of amino capacity. Thus the 2% crosslinked system has maximum complexation, decreases with increasing crosslinking (Fig. 2). Thus the major factor deciding the trend in complexation is the nature and extent of crosslinking, which in turn affect the extent of functionalization, flexibility and compatibility of the polymer matrix with the aqueous medium.

p H dependence of complexation

The pH dependence of complexation was followed using 2% crosslinked resin at the pH range above and below the natural pH of the metal salt solution in water (Tab. 2). In all cases the upper limit of pH range was just below the precipitation. The optimum


Tab. 1. Metal ion intake of NNMBA-crosslinked polyacrylamide amino resin

Crosslink density in mol-Yo Cr(II1) Mn(I1) Fe(1 I I) Pb(I1) Cd(I1)

Metal ion intake in meq/g

2 0.95 0.91 0.45 0.64 0.45 4 0.87 0.76 0.40 0.58 0.27 8 0.78 0.46 0.36 0.38 0.17

12 0.71 0.35 0.29 0.3 1 0.15 20 0.35 0.16 0.26 0.22 0.08

Tab. 2. polyacrylamide supported amine

pH dependence and distribution coefficient (Kd) of 2% NNMBA-crosslinked

Metal PH Metal ion intake K,/(mL/g) in mg/g

Cr(II1)

Mn(I1)

Fe(II1)

Cd(I1)

Pb(I1)

1.75 2.00 2.25 2.50

5.00 5.40 5.75 6.00

2.00 2.20 2.50 2.75

4.50 4.75 5 .oo 5.25 5.75

4.50 4.75 5.00 5.25 5.75

51.68 53.74 57.03 67.84

39.10 50.48 5 1.28 32.72

42.5 49.1 47.1 46.9

36 48 .54 36 27

140 1 44 159 151 144

227 238 240 327

333 492 504 262

243 295 279 278

169 244 284 169 150

3 634 4219

10341 5 950 4219

p H for Cr(II1) is 2.5, Mn(I1) 5.75, Fe(II1) 2.2, Pb(I1) and Cd(I1) 5. For Cr(II1) complexation, the metal ion intake increases with increase of pH, for Fe(III), Mn(II), Pb(I1) and Cd(I1) the metal ion intakes reaches a maximum at the optimum pH and thereafter decreases.


Distribution coefficient

The dependence of distribution coefficient on pH was calculated (Tab. 2). The Kd values at pH of maximum complexation are in the order Pb(I1) S- Mn(I1) > Cr(II1) > Fe(I1I) > Cd(I1). The Kd value (in mL/g) at optimum pH for Pb(I1) is 10341, for Mn(I1) 504, for Cr(II1) 327, for Fe(II1) 295 and for Cd(I1) 284. The distribution coefficient of Pb(I1) is very much greater than that of the other metals. Hence Pb(I1) is preferentially sorbed by the resin in presence of other metal ions. Suzuki et al. separated In(II1) and Zn(I1) as well as Sm(II1) and Co(I1) from a mixture of the two metal ions using DVB-crosslinked polystyrene containing diethylenetriamine- N,N-bis(methy1enephosphonate) group, based on the large difference in the Kd values between the two metals'').

Time-course of complexation

The time-course of complexation of 4% NNMBA-crosslinked amino resin towards the different metal ions was followed by monitoring the change in concentration of the metal solution at regular intervals of time. The maximum Cr(II1) complexation was achieved in 4 h; Pb(I1) required 5 h for complete complexation, while Cd(I1) and Mn(I1) required 3 h and 2.5 h, respectively (Fig. 3). The rapid complexation is due to the hydrophilic nature of the polymer support, which enables the solvation of the matrix in aqueous environments, and this enhances the complexation with metal ion.

Kinetics of comp Iexation

Complexation of 2% NNMBA-crosslinked polyacrylamide towards Cr(II1) ion was carried out in kinetic terms by studying the metal ion intake of the ligand at regular intervals of time at 301 K and 31 1 K in order to calculate Arrhenius parameters and activation energy of the reaction. The rate of the reaction fits in to the first-order kinetics. The plot of lg (a-x) against time t is a straight line. The kinetic parameters of complexation were calculated from the Arrhenius equation which is used in the form

and the entropy of activation was calculated using the equation

eAS*'R = A h/(kT)

where A is the Arrhenius parameter, T the absolute temperature, R the gas constant, h the Planck constant, AS* the entropy of activation and k the Boltzmann constant.

The kinetic parameters are:

Activation energy ( E ) = 122.63 J/mol

Arrhenius parameter ( A ) = 8.67 x lo4 s-'

Entropy of activation (AS*) = - 1.068 J

2096

[5) 100

E \ (5,

C

al Y

C

0 al 5

._

ao c ._ - c

60

LO

20

0

L. Jose, V. N. Rajasekharan Pillai

+ Resin * Complex

as

7s

65 I I I I L

Crosslink density in mol-% o L a 12 16 20

Fig. 4.

0 1 2 3 4 5 6 Time in h

Fig. 3.

Fig. 3. resin

Time-course of complexation of 4% NNMBA-crosslinked polyacrylamide amino

Fig. 4. Trend in equilibrium water content (EWC) of uncomplexed and Cr(II1)-complexed resins with extent of crosslinking

Swelling characteristics

The complexation of a metal ion with a polymer-supported ligand which occurs in a n aqueous environment is decided by the extent of swelling of the crosslinked polymer in water2’). The EWCs of the uncomplexed and Cr(II1)-complexed amino resins (Fig. 4) are in the range 88 to 76% and decrease with increasing crosslinking. The higher water intake of the low-crosslinked system and the lower decrease in EWC with increased crosslinking is because of the polar nature of the polymer chain as well as the crosslinking agent. With increasing crosslinking, the diffusion of the solvent molecules into interior of the rigid gel is difficult because of the presence of consecutive crosslinking points. Complexation with metal ions would lower the swelling characteristics by the introduction of additional crosslinking by complexation 22).

Thus in this case the EWCs of the complexed resins are in the range 82 to 72%. The reduction in swelling with complexation is higher in the low-crosslinked system and decreases with the extent of crosslinking. In low-crosslinked system (2Vo) the polymer


matrix is gel-like and, on complexation, intermolecular chain complexation leads to a higher decrease in volume of the swollen material, resulting in lower uptake of water. With increase in crosslinking the rigidity of the matrix increases, hence the reduction in the water uptake.

Recyclability of the complexed resins

The recyclability of the complexed resins was investigated for the various complexes O f 4% crosslinked resin. Mn(II), Pb(II), Cd(I1) ions were desorbed using 2 N HCl, while Cr(II1) and Fe(II1) required 2N H,SO,. The acid-treated resins, on recycling after neutralization, complexed the same amount of metal ions initially present and were recycled several times without reduction in capacity (Tab. 3).

Tab. 3. Recyclability of 4% NNMBA-crosslinked polyacrylamide amino complexes

Metal Metal ion intake in mg/g

Cr(II1) 49 47.00 46.00 45.00 Fe(II1) 25 24.00 23.00 23.50 Mn(I1) 50 49.50 49.25 49.10 Cd(1I) 51 50.75 50.25 50.00 Pd(I1) 134 133.00 133.50 133.00

a) Number of cycles.

IR spectra

The characteristic absorption peak of polyacrylamide in IR spectra are those of the NH group of amide at 3400-3500 cm-' and C=O at 1680 cm-I. Transamidation developed a secondary amide group at 1445 cm-', and the amino group absorption at 3 500 cm-' appeared much broader by extensive hydrogen bonding. On analysis of the IR spectra of Cr(II1) complex of NNMBA-crosslinked polyacrylamide supported amino ligand, it was found that the absorption at 3 500 cm-l appeared sharp and it was lowered to 3400 cm-I, with shoulders at 3200 cm-' and 3090 cm-' (Fig. 5). The peak at 1110 cm-I became very intense after complexation. This is because of the presence of coordinated SO:- in the Cr(II1) complexz3).

Electronic spectra

The electronic spectra of Cu(II), Cr(III), Mn(I1) and Fe(II1) complexes of 2% NNMBA-crosslinked polyacrylamide amine were recorded in Nujol mull. The transitions were assigned (Tab. 4). The Cu(I1) complex exhibits a broad band corresponding to the d-d transition 'B,, --t ,E, with A,, at 14367 cm-' and intense charge transfer bands at 22988 cm-' and 25 641 cm-'. This is suggestive of a distorted


I I

LOO0 3000 2000 1500 1000 500 -Wavenumber in cm-'---

Fig. 5 . IR spectra of: (1) NNMBA-crosslinked polyacrylamide, (2) NNMBA-crosslinked polyacrylamido amino resin and (3) Cr(II1) complex of the resin

Tab. 4. Electronic spectral data of 2% NNMBA-crosslinked polyacrylamide supported amino complexes

Complex Absorption maxima Tentative assignments in cm-'

Cu(I1) complex

Cr(II1) complex

Fe(1 I I) complex

Mn(I1) complex

a) CT Charge transfer.

14367 22988 25 641

17211 23 265 49 400 47 398

'B,, -+ 'E, CT a)

CT

octahedral geometryz4). The electronic spectra of Cr(II1) complex has A,,,= at 17211 cm-I (4A2g -, 'TZ, (F)) and 23265 cm-I (4A0 -+ 2T,g (F)) in addition to the charge transfer transition at 47 398 cm -*. These transitions lead to an octahedral geometry for Cr(II1) complex also. For Fe(II1) and Mn(I1) complexes, the forbidden d-d


transitions of the octahedral system are very weak and merged by the charge transfer transition of the ligand. For Fe(II1) complex there were two weak transitions at 15 220 cm-' (6A,, --t 4T,, (G) and 18484 cm-' (6A,, -+ 4T2g (G))25), Mn(I1) complex has a broad band in the region 20000 cm-' -25000 cm-' which is supported to be the combination of the two transitions 6A,, -+ 4T2, (G), and 6A,, -+ 4E, (G) in high spin octahedral geometry 25).

As the crosslinking increases, A,,, of Cu(I1) complexes undergoes red shift which shows decrease in field strength (Tab. 5).

Tab. 5 . Cu(I1) complex

Electronic spectral data of NNMBA-crosslinked polyacrylamide amino resin/

Metal content in mol-To

Absorption maxima in cm-'

2B,, --t 2E, CT a) CT CT a)

2 14367 22985 25 641 29 069 4 14288 22985 25 641 29 069 8 14 388 22986 25 641 29 069

12 14 306 22988 25641 29 069 20 14471 - 25 515 29 239

a) CT Charge transfer.

EPR spectra

The study of the coordination structure of Cu(I1) complexes of amino function supported on NNMBA-crosslinked polyacrylamide by electron paramagnetic resonance spectroscopy has already been reported 26). The EPR parameters indicate the presence of unpaired electrons in the d x2-y2 orbital. The value of gI1 < 2.3 suggests a covalent nature of the Cu-N bond.

Magnetic moment

The magnetic moments of 2% NNMBA-crosslinked polyacrylamide supported amino complexes were determined by the Gouy method using Hg[Co(NCS),] as the standard. The diamagnetic corrections were computed using Pascal's constant 27). The Cu(I1) complex exhibits a magnetic moment of 1.81 BMa), which is in agreement with the spin only value of one unpaired electron irrespective of the geometry2*). For Cr(II1) complex, the observed magnetic moment 3.82 BM is also within the range of the theoretical value (3.7-3.9 BM) for octahedral complexes29). For Fe(II1) and Mn(I1) complexes the effective magnetic moment values are 5.80 BM and 5.45 BM, which are slightly less than the spin only magnetic moment of d5 high-spin octahedral

a) Bohr magneton = 9.27 X lo-% J .T - ' .


geometry. The theoretical value is 5.9 to 6 BM25329). The magnetic susceptibility and magnetic moment values of polymer metal complexes should be thought of as averaged characteristics, since coordination centres of various geometries and of various magnetic properties may be found within the same macromolecule 30).

Thermogravimetric studies

The thermal stabilities of 2% NNMBA-crosslinked polyacrylamide supported amino resin and its Cr(II1) complex with varying amounts of complexed metal ion were studied by comparing the corresponding TG curves (Fig. 6). The curves showed three stages of decomposition. The first stage decomposition is due to the removal of adsorbed/coordinated solvent molecules. The second stage is the decomposition of amides and uncoordinated amino groups in the polymer matrix. The third stage is the major decomposition and is used for the kinetic analysis of the TG curves. The phenomenological data of this stage are given in Tab. 6 . The differential3') and approximation methods 32) were used for the kinetic analysis of the TG curves by the least squares method (Tab. 7).

100 360 620 800 Temp. in O C

Fig. 6. NNMBA-crosslinked polyacrylamide amino resin and its Cr(II1) complexes for various metal contents: (1) 0, (2) 19.50, (3) 35.69, (4) 53.26, ( 5 ) 57.00 mg/g

TG curves of 2%

The thermal stability of the Cr(II1) complexes is greater than that of the uncomplexed system. This is due to formation of stable ring structures by complexation. The change in thermal stabilities of metal complexes with the variables of the polymer-support have been reported 33). With increasing complexation the thermal stability gradually increases. Thus the fully complexed system has the highest activation energy for decomposition.

Scanning electron microscopy

Surface morphology of polymer is investigated by making use of scanning electron microscopy. In the present study the change in morphology of polymeric ligands with


Tab. 6. Phenomenological data of the 3rd stage of thermal decomposition of 2% NNMBA-crosslinked polyacrylamide amino resin and its complexes with varying extents of Cr(II1)

Cr(II1) content Decomposition temperature of complex in mg/g

in TG curves a)

Ti/K Tf/K

Peak tempera- Mass loss ture in in 070

DTGb), T,/K

0 (Amine) 578 763 29.5 61 1 74 1 35.69 60 1 833 53.26 61 1 823 57.0 668 858

648 35 65 5 34 61 1 39 646 30 678 31

a) Ti, T,: initial and final decomposition temperature. b, DTG: differential thermogravimetry.

Tab. 7. polyacrylamide amino resin with varying extents of complexed Cr(II1) ions

Kinetic data of the 3rd step of thermal decomposition of 2% NNMBA-crosslinked

Cr(II1) Kinetic dataa) content in mg/g E A E A AS Y AS Y -- - -- -

kJ/mol s-' J kJ/mol s-' J

0 (amine) 110.01 1.34 x lo3 -208.54 0.9951 110.47 2.43 x lo3 -203.58 0.9951 29.5 122.17 1.48 X lo4 -188.69 0.9909 122.62 2.67 X lo4 -183.74 0.9910 35.69 128.17 4.54 x lo4 -178.78 0.9953 128.60 8.17 x lo4 -173.88 0.9953 53.26 153.39 6.13 x lo6 -138.44 0.9914 154.34 1.11 x lo7 -133.50 0.9914 57 177.56 3.10 x 10' - 105.88 0.9957 178.02 5.78 x 10' -100.92 0.9957

a) E activation energy, A: Arrhenius parameter, AS: entropy change, y : correlation coefficient. The first set of values corresponds to differential method, the recond to approximation method.

Fig. 7. its Cr(II1) complex (0.95 meq/g) (magnification 4 0 0 0 ~ )

SEM patterns of: (a) 2% NNMBA-crosslinked polyacrylamide amino resin and (b)


complexation is followed. The SEMs of 2% NNMBA-crosslinked amino resin and the corresponding Cr(II1) complex are given in Fig. 7. The uncomplexed resins have smooth surface with few voids and channels. By complexation with Cr(II1) ion, the surface becomes rough and rigid.

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