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Copolymers based on styrene and divinylbenzene synthesized in the presence of DEHPA—I. Structural characterization
0014-3057(95)ooo78-x
Eur. Polym. J. Vol. 31, No. 12, pp. 1243-1250, 1995 Copynght Q 1995 Elsewer Science Ltd Printed in Great Bntain. All rights reserved 0014-3057/95 69 50 + 0.00
COPOLYMERS BASED ON STYRENE AND DIVINYLBENZENE SYNTHESIZED IN THE PRESENCE DEHPA-I. STRUCTURAL CHARACTERIZATION F. M. B. COUTINHO’*, ‘Institute
C. C. R. BARBOSA2
and
OF
S. M. REZENDE2
de Macromol&das, Universidade Federal do Rio de Janeiro, P.O. Box 68525, Rio de Janeiro, RI 21945-970 and ‘Institute de Engenharia Nuclear, CNEN, Rio de Janeiro, RJ, Brazil (Recehed
I June 1994; accepted in final form 3 October
1994)
Abstract-Styreneedivinylbenzene copolymers were synthesized by suspension polymerization in the presence of bis-2-diethylhexylphosphoric acid (DEHPA) and methyl ethyl ketone (MEK) as diluents for the monomers. The influence of DEHPA/MEK ratio and dilution degree on the formation of porous structure of the copolymers was Investigated by surface area, pore volume, pore size distribution and apparent density. It was found that 50% DEHPA m the diluent mixture always leads to macroporous sorbents whatever the MEK content.
INTRODUCTION
The growing interest for porous styrendivinylbenzene (STY-DVB) copolymer beads in the last 30 yrs is due to their great number of applications as chromatographic packing, polymer-supported catalysts, polymer-immobilized extractants and starting materials for the synthesis of ion exchange resins [l-3]. The specified application of these copolymers are closely related to their porous structure and swelling properties. It has been established that the morphology of these copolymers obtained by suspension polymerization is strongly influenced by the polymerization conditions: monomers, diluent nature, dilution degree of the monomers, crosslinking degree, reaction temperature, etc. [4, 51. The thermodynamic affinity of the monomers diluent for the copolymer determines decisively its morphology. When styrene and divinylbenzene are copolymerized by a suspension process in the presence of a good solvent for the polymer through chains (good diluent), two kinds of porous structures can be obtained: gel or macroporous. At low DVB content the final structure is an expanded gel. When the DVB content and dilution degree are high, a macroporous copolymer is obtained. On the other hand, when the diluent is a poor solvent for the polymer chains (bad diluent), phase separation during the polymerization process takes places and is responsible for the formation of macroporous structures. When mixtures of good and bad diluents are used the copolymers present a porous structure with intermediary characteristics in relation to the copolymers prepared with the pure diluents [6-81. When liquid phosphoric esters, aliphatic amines and oximes both aliphatic and aromatic are employed as diluents the resultant copolymers are designed polymeric sorbents or polymer-immobilized extrac*To whom
all correspondence
should
be addressed.
tants. Having no vinyl groups, these diluents do not participate in the polymerization process directly but may serve as non-solvating diluents which are retained by adsorption in the polymeric structure. In this case the structure of the resultant copolymer and its properties may be strongly influenced by the type of extractant [9]. Kanczor and Meyer [lo] using this method have prepared macroporous STY-DVB copolymer sorbents with bis-2-diethylhexylphosphoric acid (DEHPA) and tributylphosphate (TBP). This type of resin called Levextrel (from Leaerkusen extraction elution) can be technically used as conventional ion exchange resins, that is, by combinmg their well-known simple technology with the selectivity of liquid extractants in the enrichment or in the separation of heavy metal ions present in weakly or strongly acid solutions. Using those materials in chromatographic columns, any separation problem can be solved by offering sufficient theoretical plates obtainable by simple elongation of the column length
v11.
In the present paper we relate our study on the characteristics of polymer sorbents prepared in the presence of a mixture of DEHPA/MEK (methyl ethyl ketone) in different degrees of dilution.
EXPERIMENTAL
PROCEDURES
Materials Commercial styrene (STY) and divinylbenzene (DVB) were washed with 10% aq. NaOH to remove inhibitor, followed by several washes with water and then vacuum distilled. The solvating diluent methyl ethyl ketone (MEK) and the non-solvating diluent bis-2-diethylhexylphosphoric acid (DEHPA) were used as received. The diluent contents were expressed as percentages of the total volume of the monomers. The DVB content was kept constant (30%) and was expressed as molar percent in relation to 0.3 mol of styrene. The initiator 2,2’-azo-bis-isobutyromtrile (AIBN) was purified by recrystallization from methanol. The poly
1243
1244
F. M. B. Coutinho
merization aqueous phase contained: polyvinyl (89%). hydrolized (0.5%) and NaCl (0.5%).
alcohol
diluent phases. The diluent mixtures may remain in the network phase throughout the copolymerization producing expanded networks (gel-type copolymers), or may separate out of the network phase resulting in the formation of macroporous copolymers. The choice of MEK was due to its solvating power for the copolymers based on STY-DVB and its ability to solubilize DEHPA. Thus, MEK can distribute DEHPA homogeneously in the polymer network. Four series of STY-DVB copolymers with 25. 50, 75 and 100% of DEHPA are shown m Table 1. For each one of these series, the effects of DEHPA/MEK ratio on the apparent density, surface area, pore volume, average pore diameter and pore size distributlon were Investigated. The differences on the texture characteristics produced by the different diluent compositions were larger or smaller depending on the diluent amount and on the DEHPA/MEK ratio. When the copolymers were obtamed in the presence of MEK as the only monomers, diluent copolymers with higher apparent density and transparent appearance were produced. According to Millar and co-workers [16], the non-porous copolymers were formed in an expanded state during the copolymerization and. after removal of the solvatmg diluent from the copolymer. no stable porosity (macroporosity) remained in its network. Copolymers with lower apparent density and higher surface area were produced when DEHPA proportion was increased (Fig. 1). In a general way the surface area of the produced copolymer particles increased by enhancing the solvating power of the diluent mixture (Fig. 2). The pore volume and the average pore diameter of the copolymer particles depended on the diluent mixture concentration. The system with low DEHPA proportion (25%) and low MEK proportion (0 and 25%) produced structures with small pore volumes (Fig. 3) and small average pore diameters (Table 1). indicating the formation of gel-type structures. Increasing MEK in this system, the pore size
Polymerization The suspension polymerization was carned out m a flask fitted with a mechanical stirrer, N, inlet condenser and a Hg seal. The solution containing the monomers, the dduents (MEK and DEHPA) and initiator was poured into the reactor which contained the aqueous phase at room temperature. The temperature was then raised to 7Ok 0.5”C and the speed of stirring was adjusted according to the desired size of drops that were produced by the mixmg of the two phases and kept constant during the polymerization time (24 hrs). After the reaction period, the polymer beads were washed with warm water, filtered and sieved. The fraction in the range of 0.074-O. 149 mm (lOCL200 mesh) was collected. This fraction was extracted with acetone m a Soxhlet apparatus in order to remove the diluents. Four series of copolymers containing 25,50, 75 and 100% of DEHPA were prepared. For each one of those, the percentages of MEK were, respectively, 0, 25, 50, 75 and 100%. Texture characterization The surface area (S) was determmed by nitrogen adsorption measurements follo%ng the B. E. T. method [12]. the average pore diameter (D) and the pore size distrlbutlon were determined by nitrogen desorptlon measurements following the B. J. H. (Barret, Joyner and Halenda) method [ 131 on an Accelerated Surface Aiea and Porosimetry Analyser (ASAP)-Model ZOO&Micromeritics. The total pore volumes (i,) were determined by two methods, by water uptake [14] and by nitrogen desorption measurements following the B. J H. method. In the B. J. H. method the range of average pore diameter evaluated is between 17 and 3000 A. The apparent density was measured by the graduated cylinder method [ 151.
RESULTS
The tained
AND
DISCUSSION
structure characteristics of the sorbents obwith DEHPA and MEK as diluents are con-
trolled by the polymerdiluent which determine the partition the diluent system between
mixture interactions of the constituents of the network and the Table
I Charactensncs
et al.
of
copolymers
STY-DVB
Dllutlon degree
DEHPA/MEK rat10 viv
Surface area
Water
POW
Pore average
uptake
volume
diameter
Opucal
P/.)
W)
(m’:g)
(cm’/&
(cm’&)
6)
appearance
0 13 0 I5 0 29 0.44 0.49 0.41 0.53 0.57 0.61 0 58 0.64 0.76 0.70 I .oo I 00 0.82 0.96 I .20 I .32 I 90
0 080 0 100 0 270 0.400 0.430 0.350 0.470 0.470 0.530 0.650 0.300 0.400 0.360 0410 0 480 0.250 0.260 0.260 0 260 0.390
25 50
75 100 125 50 15 100 125 150 15 100 I25 150 175 100 I25 I50 175 200
0 25
25
50
75
100
50 75 100 0 25 50 75 100 0 25 50 75 100 0 25 50 75 100
T, transparent: 0, opaque.
20 30 79 84 89 51 66 68 88 88 68 86 80 92 106 57 63 61 61 94
84 75 99 I53 I59 224 233 233 I91 250 133 143 I35 136 143 126 124 I25 129 133
T T T 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1245
Copolymers based on styrene and divinylbenzene-I
0.65; +
0.6-
DEHPA/M
25% DEHPAhl 0.55
i*-
’
50% DEHPAhl
.++-
0.5
75% DEHPA/M
ii&
DEHPA/M
0.4-
\\ ‘-1 ‘k. 0 -.. ......._.._._ 0.35_._ --.- ..__ -. --a... -.... _,._ 1L .-. .__ --..._._.,._ ...+....__._._,_ 0.3~-kh_.__ “--..g_..__ ..__ _, -------S..._..._ 0.250.2
I$ .___ ____-~---.-.‘_-__._--_E, .---.- ......__._‘.~ 1 75
25
0
ME&
s: I 100
V/V (%)
M = STY + DVB in volume Fig, 1. Influence of MEK content on apparent density for various amounts of DEHPA.
-w-
0% DEHPA/M + 25% DEHPA/M + 50% DEHPA/M . ..f+_ 75% DEHPA/M -*._. 100% DEHPA/M
0
I
0
25
75
MEK%
M = STY
l
DVB
in
f
100
V/V (%I
volume
Fig. 2. Influence of MEK content on specific surface area for various amounts of DEHPA.
F. M. B. Coutinho
1246
et al.
-m-
0%
DEHPA/M
2;
DEHPA/M
5; DEHPA/M __.~.. 75% DEHPA/M ..y+. 100%
0
25
75
50
MEKIM
V/V
DEHPA/M
100
(%I
M = STY + DVB in volume Fig. 3. Influence of MEK
content
on pore volume
for various
amounts
of DEHPA.
0% MEK 0.9-
+ 25% MEK
0.0-
s 3 r;E 2 a n $ 5 ‘a g
o.i‘-
+I+50% MEK _.e_..
0.6-
75% MEK x 100% MEK
0.50.40.30.20.1 0, 10
I
!
I
I111111
,
I111111
1000
100
I
Iillr
1
Pore Diameter (A) Fig. 4. Pore size distribution
for copolymer
prepared
with 25% DEHPA.
Copolymers
based on styrene
and divinylbenzene--I
1247
-m0% MEK -+25% MEK _.*... 50% MEK _.~.._ 75% MEK % 100% MEK
0.8-
>
I
I
I
I1
I,,,,,
I
100
I
I
!I,,,
1000
10000
Pore Diameter (A) Fig. 5. Pore size distribution
for copolymer
prepared
with 50% DEHPA.
0% MEK
g S : E S
0.8-
+ 25% MEK ...*.
0.5
50% MEK .__f3_.
0.4-
% 100% MEK
75% MEK
B $
03
5 h g
0.2-
0.1 -
Pore Diameter (A) Fig. 6. Pore size distribution
for copolymer
prepared
with 75% DEHPA.
F. M. B. Coutinho
1248
et al.
-m0% DEHPA 25% DEHPA
0.4-1
* 50% DEHPA _._@._. 75% DEHPA ._3&_.
x Q
0.25-
$ %
0.2-
B u
0.15-
100% DEHPA
0.1 0.05 1 01 10
I
I
I
I111111
100
I
II
1000
I
I11111
10000
Pore Diameter (A) Fig. 7. Pore size distribution
for copolymer prepared with 100% DEHPA.
distribution curves of the copolymers were shifted towards larger pore sizes (Fig. 4) and the pore volume increased, indicating a more pronounced phase separation provoked by the increase of dilution degree. For the copolymers produced with 50% of DEHPA the average pore diameter practically did not change and the pore volumes increased considerably with the dilution degree indicating that a homogeneous distribution of DEHPA among the polymeric domains has occurred, producing a more regular porous structure. The pore size distribution curves of these copolymers were similar (Fig. 5). At higher DEHPA proportions (75 and 100%) the opposite effect occurred, the pore volume and the average pore diameter decreased and the pore size distribution curves were shifted towards smaller pore sizes (Figs 6 and 7). For these systems, with high porosities, the pore volume characterization by the B. J. H. method was not good enough. Thus, water uptakes were employed as a better method to evaluate the copolymers with high pore volumes. The results obtained by water uptake method were compared with those obtained by mercury porosimetry. It was verified that the two methods produced very similar results. They represent the fixed pore volume as defined in the literature [14]. In the system with 25% DEHPA an increase in the solvating power of the diluent mixture increased the average pore diameter and yielded a more regular porous structure with small water uptake values. In this case the water uptake values were very close to pore volume values determined by the B. J. H. method. At DEHPA proportion of 50% the pore volume values determined by B. J. H. method were also close to the water uptakes.
The systems with higher DEHPA proportions (75 and 100%) produced structures with higher water uptake values. These results can be attributed to the occurrence of a more pronounced phase separation provoked by the increase of the content of the non-solvating diluent. Hence the formation of structures with larger pores [5]. In these series the pore volume values determined by B. J. H. method were smaller than the pore volume values determined by water uptakes. This can be attributed to partial characterization when pore volume is determined by B. J. H. method for copolymer with high porosity. The difference between water uptake values and pore volume tend to increase as the copolymer porosity increases (Table 1). Figure 8(aHf) shows the optical appearance of the resins obtained in absence and in presence of DEHPA. The copolymers prepared using only MEK as diluent presented a homogeneous structure with a transparent appearance unlike the copolymers obtained at determined MEK/DEHPA ratios which present a heterogeneous structure with an opaque appearance because of the light scattering caused by their heterogeneous structures 1171. CONCLUSION
We have verified in this work that the most critical experimental condition to obtain macroporous copolymers was the concentration of DEHPA. Copolymers synthesized with 50% DEHPA presented macroporous characteristics in terms of optical appearance, total pore volume and pore size distribution, whatever the MEK content employed.
Copolymers
based
on styrene
and divinylbenzene-I
1249
Fig. 8. Optical appearance of resins based on STYDVB synthesized with 30% DVB, DEHPA/MEK ratios = O/100 (a) 100% dil.; 25/O (b) 25% dil.; 50/O (c) 50% dil.; 75/O (d) 75% dil.; 75/75 (e) 150% dil. and 100/25 (f) 125% dil. Magnification: 63 x
Acknowledgements-The authors thank the Instituto de Engenharia Nuclear (IEN/CNEN), Nitriflex S. A., Industria e Comercio, Conselho National de Desenvolvimento Cientifico e Tecnoldgico (CNPq) and Conselho de Ensino para Graduados e Pesquisa (CEPG/UFRJ). REFERENCES 1. R. Kunin. Ion Exchange Resins, 2nd edn. Krieger, Melbourne (1972). 2. G. Gliickner. Polymer Characterization by Liquid Chromatography, Vol. 34, Elsevier, Berlin (1987). 3. F. M. B. Coutinho and D. Rabelo. Eur. Polym. J. 28, 1553 (1992).
4. J. Seidl, J. Malinsky, K. Dusek and W. Heit Z. Adv. Polym. Sci. 5, 113 (1967). 5. W. L. Sederel and G. J. De Jong. J. appl. Pal) Jrn Sci. 17, 2835 (1973). 6. I. C. Poinescu and G. Beldie. Angew. Makromol .c yhem. 164. 45 (1988). 7. F. M. B.‘Coutinho and D. Rabelo. Polym. Bull. 311, 585 11993). 8. F. MI B. Coutinho, M. I. N. Siqueira and C 2. R. Barbosa. Eur. Polym. J. 26, 1189 (1990). 9. S. Belfer, Y. Egozy and E. Korngold. J. appl. PNolym. Sci. 29, 3825 (1984). IO. M. W. Kanczor and A. Meyer. Hydrometallur$ !Y 3, 65 (1978).
1250
F. M. B. Coutinho et al.
10. M. W. Kanczor and A. Meyer. Hydrometallurgy 3, 65 (1978).
11. R. Krijebel and A. Meyer. Proc. ht. Solv. Extract. Conf. (Lyon) 3, 2095 (1974). 12. S. Brunauer. P. H. Emmet and E. Teller. .I. Am. them. Sot. 60, 309 (1938). 13. E. P. Barrett. L. G. Jovner and P. 0. Halenda. .I. Am. them. Sot. 73, 373 (1951). 14. D. Rabelo and F. M. B. Coutinho. Polym. Bull. 30, 725 (1993).
15. ASTM-D1895, and Pourability
Apparenl Density, Bulk of Plastic Materials-1979.
Factor
Annual Plastics ASTM,
Book of ASTM Standarts, Part 35, General Test Methods, Nomenclature. (1979). 16. J. R. Millar, D. G. Smith, W. E. Marr and T. R. E. Kresman. J. Polvm. Sci: Part A 3. 265 (1965). 17. K. A. Kun and R. Kunin. J. Polym. Sci., Part A- I 6, 2689 (1968).
Eur. Polym. J. Vol. 31, No. 12, pp. 1243-1250, 1995 Copynght Q 1995 Elsewer Science Ltd Printed in Great Bntain. All rights reserved 0014-3057/95 69 50 + 0.00
COPOLYMERS BASED ON STYRENE AND DIVINYLBENZENE SYNTHESIZED IN THE PRESENCE DEHPA-I. STRUCTURAL CHARACTERIZATION F. M. B. COUTINHO’*, ‘Institute
C. C. R. BARBOSA2
and
OF
S. M. REZENDE2
de Macromol&das, Universidade Federal do Rio de Janeiro, P.O. Box 68525, Rio de Janeiro, RI 21945-970 and ‘Institute de Engenharia Nuclear, CNEN, Rio de Janeiro, RJ, Brazil (Recehed
I June 1994; accepted in final form 3 October
1994)
Abstract-Styreneedivinylbenzene copolymers were synthesized by suspension polymerization in the presence of bis-2-diethylhexylphosphoric acid (DEHPA) and methyl ethyl ketone (MEK) as diluents for the monomers. The influence of DEHPA/MEK ratio and dilution degree on the formation of porous structure of the copolymers was Investigated by surface area, pore volume, pore size distribution and apparent density. It was found that 50% DEHPA m the diluent mixture always leads to macroporous sorbents whatever the MEK content.
INTRODUCTION
The growing interest for porous styrendivinylbenzene (STY-DVB) copolymer beads in the last 30 yrs is due to their great number of applications as chromatographic packing, polymer-supported catalysts, polymer-immobilized extractants and starting materials for the synthesis of ion exchange resins [l-3]. The specified application of these copolymers are closely related to their porous structure and swelling properties. It has been established that the morphology of these copolymers obtained by suspension polymerization is strongly influenced by the polymerization conditions: monomers, diluent nature, dilution degree of the monomers, crosslinking degree, reaction temperature, etc. [4, 51. The thermodynamic affinity of the monomers diluent for the copolymer determines decisively its morphology. When styrene and divinylbenzene are copolymerized by a suspension process in the presence of a good solvent for the polymer through chains (good diluent), two kinds of porous structures can be obtained: gel or macroporous. At low DVB content the final structure is an expanded gel. When the DVB content and dilution degree are high, a macroporous copolymer is obtained. On the other hand, when the diluent is a poor solvent for the polymer chains (bad diluent), phase separation during the polymerization process takes places and is responsible for the formation of macroporous structures. When mixtures of good and bad diluents are used the copolymers present a porous structure with intermediary characteristics in relation to the copolymers prepared with the pure diluents [6-81. When liquid phosphoric esters, aliphatic amines and oximes both aliphatic and aromatic are employed as diluents the resultant copolymers are designed polymeric sorbents or polymer-immobilized extrac*To whom
all correspondence
should
be addressed.
tants. Having no vinyl groups, these diluents do not participate in the polymerization process directly but may serve as non-solvating diluents which are retained by adsorption in the polymeric structure. In this case the structure of the resultant copolymer and its properties may be strongly influenced by the type of extractant [9]. Kanczor and Meyer [lo] using this method have prepared macroporous STY-DVB copolymer sorbents with bis-2-diethylhexylphosphoric acid (DEHPA) and tributylphosphate (TBP). This type of resin called Levextrel (from Leaerkusen extraction elution) can be technically used as conventional ion exchange resins, that is, by combinmg their well-known simple technology with the selectivity of liquid extractants in the enrichment or in the separation of heavy metal ions present in weakly or strongly acid solutions. Using those materials in chromatographic columns, any separation problem can be solved by offering sufficient theoretical plates obtainable by simple elongation of the column length
v11.
In the present paper we relate our study on the characteristics of polymer sorbents prepared in the presence of a mixture of DEHPA/MEK (methyl ethyl ketone) in different degrees of dilution.
EXPERIMENTAL
PROCEDURES
Materials Commercial styrene (STY) and divinylbenzene (DVB) were washed with 10% aq. NaOH to remove inhibitor, followed by several washes with water and then vacuum distilled. The solvating diluent methyl ethyl ketone (MEK) and the non-solvating diluent bis-2-diethylhexylphosphoric acid (DEHPA) were used as received. The diluent contents were expressed as percentages of the total volume of the monomers. The DVB content was kept constant (30%) and was expressed as molar percent in relation to 0.3 mol of styrene. The initiator 2,2’-azo-bis-isobutyromtrile (AIBN) was purified by recrystallization from methanol. The poly
1243
1244
F. M. B. Coutinho
merization aqueous phase contained: polyvinyl (89%). hydrolized (0.5%) and NaCl (0.5%).
alcohol
diluent phases. The diluent mixtures may remain in the network phase throughout the copolymerization producing expanded networks (gel-type copolymers), or may separate out of the network phase resulting in the formation of macroporous copolymers. The choice of MEK was due to its solvating power for the copolymers based on STY-DVB and its ability to solubilize DEHPA. Thus, MEK can distribute DEHPA homogeneously in the polymer network. Four series of STY-DVB copolymers with 25. 50, 75 and 100% of DEHPA are shown m Table 1. For each one of these series, the effects of DEHPA/MEK ratio on the apparent density, surface area, pore volume, average pore diameter and pore size distributlon were Investigated. The differences on the texture characteristics produced by the different diluent compositions were larger or smaller depending on the diluent amount and on the DEHPA/MEK ratio. When the copolymers were obtamed in the presence of MEK as the only monomers, diluent copolymers with higher apparent density and transparent appearance were produced. According to Millar and co-workers [16], the non-porous copolymers were formed in an expanded state during the copolymerization and. after removal of the solvatmg diluent from the copolymer. no stable porosity (macroporosity) remained in its network. Copolymers with lower apparent density and higher surface area were produced when DEHPA proportion was increased (Fig. 1). In a general way the surface area of the produced copolymer particles increased by enhancing the solvating power of the diluent mixture (Fig. 2). The pore volume and the average pore diameter of the copolymer particles depended on the diluent mixture concentration. The system with low DEHPA proportion (25%) and low MEK proportion (0 and 25%) produced structures with small pore volumes (Fig. 3) and small average pore diameters (Table 1). indicating the formation of gel-type structures. Increasing MEK in this system, the pore size
Polymerization The suspension polymerization was carned out m a flask fitted with a mechanical stirrer, N, inlet condenser and a Hg seal. The solution containing the monomers, the dduents (MEK and DEHPA) and initiator was poured into the reactor which contained the aqueous phase at room temperature. The temperature was then raised to 7Ok 0.5”C and the speed of stirring was adjusted according to the desired size of drops that were produced by the mixmg of the two phases and kept constant during the polymerization time (24 hrs). After the reaction period, the polymer beads were washed with warm water, filtered and sieved. The fraction in the range of 0.074-O. 149 mm (lOCL200 mesh) was collected. This fraction was extracted with acetone m a Soxhlet apparatus in order to remove the diluents. Four series of copolymers containing 25,50, 75 and 100% of DEHPA were prepared. For each one of those, the percentages of MEK were, respectively, 0, 25, 50, 75 and 100%. Texture characterization The surface area (S) was determmed by nitrogen adsorption measurements follo%ng the B. E. T. method [12]. the average pore diameter (D) and the pore size distrlbutlon were determined by nitrogen desorptlon measurements following the B. J. H. (Barret, Joyner and Halenda) method [ 131 on an Accelerated Surface Aiea and Porosimetry Analyser (ASAP)-Model ZOO&Micromeritics. The total pore volumes (i,) were determined by two methods, by water uptake [14] and by nitrogen desorption measurements following the B. J H. method. In the B. J. H. method the range of average pore diameter evaluated is between 17 and 3000 A. The apparent density was measured by the graduated cylinder method [ 151.
RESULTS
The tained
AND
DISCUSSION
structure characteristics of the sorbents obwith DEHPA and MEK as diluents are con-
trolled by the polymerdiluent which determine the partition the diluent system between
mixture interactions of the constituents of the network and the Table
I Charactensncs
et al.
of
copolymers
STY-DVB
Dllutlon degree
DEHPA/MEK rat10 viv
Surface area
Water
POW
Pore average
uptake
volume
diameter
Opucal
P/.)
W)
(m’:g)
(cm’/&
(cm’&)
6)
appearance
0 13 0 I5 0 29 0.44 0.49 0.41 0.53 0.57 0.61 0 58 0.64 0.76 0.70 I .oo I 00 0.82 0.96 I .20 I .32 I 90
0 080 0 100 0 270 0.400 0.430 0.350 0.470 0.470 0.530 0.650 0.300 0.400 0.360 0410 0 480 0.250 0.260 0.260 0 260 0.390
25 50
75 100 125 50 15 100 125 150 15 100 I25 150 175 100 I25 I50 175 200
0 25
25
50
75
100
50 75 100 0 25 50 75 100 0 25 50 75 100 0 25 50 75 100
T, transparent: 0, opaque.
20 30 79 84 89 51 66 68 88 88 68 86 80 92 106 57 63 61 61 94
84 75 99 I53 I59 224 233 233 I91 250 133 143 I35 136 143 126 124 I25 129 133
T T T 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1245
Copolymers based on styrene and divinylbenzene-I
0.65; +
0.6-
DEHPA/M
25% DEHPAhl 0.55
i*-
’
50% DEHPAhl
.++-
0.5
75% DEHPA/M
ii&
DEHPA/M
0.4-
\\ ‘-1 ‘k. 0 -.. ......._.._._ 0.35_._ --.- ..__ -. --a... -.... _,._ 1L .-. .__ --..._._.,._ ...+....__._._,_ 0.3~-kh_.__ “--..g_..__ ..__ _, -------S..._..._ 0.250.2
I$ .___ ____-~---.-.‘_-__._--_E, .---.- ......__._‘.~ 1 75
25
0
ME&
s: I 100
V/V (%)
M = STY + DVB in volume Fig, 1. Influence of MEK content on apparent density for various amounts of DEHPA.
-w-
0% DEHPA/M + 25% DEHPA/M + 50% DEHPA/M . ..f+_ 75% DEHPA/M -*._. 100% DEHPA/M
0
I
0
25
75
MEK%
M = STY
l
DVB
in
f
100
V/V (%I
volume
Fig. 2. Influence of MEK content on specific surface area for various amounts of DEHPA.
F. M. B. Coutinho
1246
et al.
-m-
0%
DEHPA/M
2;
DEHPA/M
5; DEHPA/M __.~.. 75% DEHPA/M ..y+. 100%
0
25
75
50
MEKIM
V/V
DEHPA/M
100
(%I
M = STY + DVB in volume Fig. 3. Influence of MEK
content
on pore volume
for various
amounts
of DEHPA.
0% MEK 0.9-
+ 25% MEK
0.0-
s 3 r;E 2 a n $ 5 ‘a g
o.i‘-
+I+50% MEK _.e_..
0.6-
75% MEK x 100% MEK
0.50.40.30.20.1 0, 10
I
!
I
I111111
,
I111111
1000
100
I
Iillr
1
Pore Diameter (A) Fig. 4. Pore size distribution
for copolymer
prepared
with 25% DEHPA.
Copolymers
based on styrene
and divinylbenzene--I
1247
-m0% MEK -+25% MEK _.*... 50% MEK _.~.._ 75% MEK % 100% MEK
0.8-
>
I
I
I
I1
I,,,,,
I
100
I
I
!I,,,
1000
10000
Pore Diameter (A) Fig. 5. Pore size distribution
for copolymer
prepared
with 50% DEHPA.
0% MEK
g S : E S
0.8-
+ 25% MEK ...*.
0.5
50% MEK .__f3_.
0.4-
% 100% MEK
75% MEK
B $
03
5 h g
0.2-
0.1 -
Pore Diameter (A) Fig. 6. Pore size distribution
for copolymer
prepared
with 75% DEHPA.
F. M. B. Coutinho
1248
et al.
-m0% DEHPA 25% DEHPA
0.4-1
* 50% DEHPA _._@._. 75% DEHPA ._3&_.
x Q
0.25-
$ %
0.2-
B u
0.15-
100% DEHPA
0.1 0.05 1 01 10
I
I
I
I111111
100
I
II
1000
I
I11111
10000
Pore Diameter (A) Fig. 7. Pore size distribution
for copolymer prepared with 100% DEHPA.
distribution curves of the copolymers were shifted towards larger pore sizes (Fig. 4) and the pore volume increased, indicating a more pronounced phase separation provoked by the increase of dilution degree. For the copolymers produced with 50% of DEHPA the average pore diameter practically did not change and the pore volumes increased considerably with the dilution degree indicating that a homogeneous distribution of DEHPA among the polymeric domains has occurred, producing a more regular porous structure. The pore size distribution curves of these copolymers were similar (Fig. 5). At higher DEHPA proportions (75 and 100%) the opposite effect occurred, the pore volume and the average pore diameter decreased and the pore size distribution curves were shifted towards smaller pore sizes (Figs 6 and 7). For these systems, with high porosities, the pore volume characterization by the B. J. H. method was not good enough. Thus, water uptakes were employed as a better method to evaluate the copolymers with high pore volumes. The results obtained by water uptake method were compared with those obtained by mercury porosimetry. It was verified that the two methods produced very similar results. They represent the fixed pore volume as defined in the literature [14]. In the system with 25% DEHPA an increase in the solvating power of the diluent mixture increased the average pore diameter and yielded a more regular porous structure with small water uptake values. In this case the water uptake values were very close to pore volume values determined by the B. J. H. method. At DEHPA proportion of 50% the pore volume values determined by B. J. H. method were also close to the water uptakes.
The systems with higher DEHPA proportions (75 and 100%) produced structures with higher water uptake values. These results can be attributed to the occurrence of a more pronounced phase separation provoked by the increase of the content of the non-solvating diluent. Hence the formation of structures with larger pores [5]. In these series the pore volume values determined by B. J. H. method were smaller than the pore volume values determined by water uptakes. This can be attributed to partial characterization when pore volume is determined by B. J. H. method for copolymer with high porosity. The difference between water uptake values and pore volume tend to increase as the copolymer porosity increases (Table 1). Figure 8(aHf) shows the optical appearance of the resins obtained in absence and in presence of DEHPA. The copolymers prepared using only MEK as diluent presented a homogeneous structure with a transparent appearance unlike the copolymers obtained at determined MEK/DEHPA ratios which present a heterogeneous structure with an opaque appearance because of the light scattering caused by their heterogeneous structures 1171. CONCLUSION
We have verified in this work that the most critical experimental condition to obtain macroporous copolymers was the concentration of DEHPA. Copolymers synthesized with 50% DEHPA presented macroporous characteristics in terms of optical appearance, total pore volume and pore size distribution, whatever the MEK content employed.
Copolymers
based
on styrene
and divinylbenzene-I
1249
Fig. 8. Optical appearance of resins based on STYDVB synthesized with 30% DVB, DEHPA/MEK ratios = O/100 (a) 100% dil.; 25/O (b) 25% dil.; 50/O (c) 50% dil.; 75/O (d) 75% dil.; 75/75 (e) 150% dil. and 100/25 (f) 125% dil. Magnification: 63 x
Acknowledgements-The authors thank the Instituto de Engenharia Nuclear (IEN/CNEN), Nitriflex S. A., Industria e Comercio, Conselho National de Desenvolvimento Cientifico e Tecnoldgico (CNPq) and Conselho de Ensino para Graduados e Pesquisa (CEPG/UFRJ). REFERENCES 1. R. Kunin. Ion Exchange Resins, 2nd edn. Krieger, Melbourne (1972). 2. G. Gliickner. Polymer Characterization by Liquid Chromatography, Vol. 34, Elsevier, Berlin (1987). 3. F. M. B. Coutinho and D. Rabelo. Eur. Polym. J. 28, 1553 (1992).
4. J. Seidl, J. Malinsky, K. Dusek and W. Heit Z. Adv. Polym. Sci. 5, 113 (1967). 5. W. L. Sederel and G. J. De Jong. J. appl. Pal) Jrn Sci. 17, 2835 (1973). 6. I. C. Poinescu and G. Beldie. Angew. Makromol .c yhem. 164. 45 (1988). 7. F. M. B.‘Coutinho and D. Rabelo. Polym. Bull. 311, 585 11993). 8. F. MI B. Coutinho, M. I. N. Siqueira and C 2. R. Barbosa. Eur. Polym. J. 26, 1189 (1990). 9. S. Belfer, Y. Egozy and E. Korngold. J. appl. PNolym. Sci. 29, 3825 (1984). IO. M. W. Kanczor and A. Meyer. Hydrometallur$ !Y 3, 65 (1978).
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10. M. W. Kanczor and A. Meyer. Hydrometallurgy 3, 65 (1978).
11. R. Krijebel and A. Meyer. Proc. ht. Solv. Extract. Conf. (Lyon) 3, 2095 (1974). 12. S. Brunauer. P. H. Emmet and E. Teller. .I. Am. them. Sot. 60, 309 (1938). 13. E. P. Barrett. L. G. Jovner and P. 0. Halenda. .I. Am. them. Sot. 73, 373 (1951). 14. D. Rabelo and F. M. B. Coutinho. Polym. Bull. 30, 725 (1993).
15. ASTM-D1895, and Pourability
Apparenl Density, Bulk of Plastic Materials-1979.
Factor
Annual Plastics ASTM,
Book of ASTM Standarts, Part 35, General Test Methods, Nomenclature. (1979). 16. J. R. Millar, D. G. Smith, W. E. Marr and T. R. E. Kresman. J. Polvm. Sci: Part A 3. 265 (1965). 17. K. A. Kun and R. Kunin. J. Polym. Sci., Part A- I 6, 2689 (1968).