Application of the degree of swelling to the analytical characterization of styrene-divinylbenzene copolymers and their chloromethyl and phosphinomethyl derivatives

Reactive Polymers, 14 (1991) 75-80

75

Elsevier Science Publishers B.V., Amsterdam

Short Communication

APPLICATION OF THE DEGREE OF S W E L L I N G TO THE ANALYTICAL C H A R A C T E R I Z A T I O N OF S T Y R E N E - D I V I N Y L B E N Z E N E C O P O L Y M E R S A N D THEIR C H L O R O M E T H Y L A N D P H O S P H I N O M E T H Y L DERIVATIVES E. P A E T Z O L D , G. O E H M E * and H. P R A C E J U S

Division of Complex Catalysis, Central Institute of Organic Chemistry, Academy of Sciences of the G. D. R., Buchbinderstr. 5-6, Rostock (Germany) (Received April 15, 1990; accepted in revised form August 13, 1990)

Four lightly-crosslinked styrene-divinylbenzene resins (2 % D VB) and their chloromethylated and phosphinated derivatives have been investigated with respect to the degree of swelling and the degree of substitution. We found a linear correlation between the degree of substitution and the ratio of the degree of swelling of each functionalized polymer to the degree of swelling of each precursor polymer. Consideration of the properties of precursor polymers allowed the adaption of reference data from the literature. Deviations observed in the case of phosphinated resins probably originate in intraresin phosphonium salt formation.

Crosslinked organic polymers are widely used as supports for the heterogenization of transition metal complex catalysts [1-5]. Styrene-divinylbenzene (DVB) copolymers with a different content of DVB as crosslinking reagents are particularly important. The support plays an active role in the function of the catalyst and a series of analytical methods has been developed to characterize the resins. Typical analytical data include the DVB content, the size of particles, surface area and

* To whom correspondence should be addressed. 0923-1137/91/$03.50

pore diameter, and elemental analysis of any functional groups and the active sites of the catalytic species [6]. Depending on the DVB content some authors classify polystyrene resins into four types [7,8]. The Merrifield types with - 2% DVB, which are insoluble but able to swell considerably in most organic solvents, seem to be most the important. Sometimes, however, macroreticular resins are used as supports for transition metal catalysts [9]. Advances in developing the catalytic activity of polymer-attached transition metal complexes depend on the stability of the resin structure during functionalization and com-

© 1991 - Elsevier Science Publishers B.V.

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plex immobilization reactions. Obviously, these reactions occur preferably at the polymer surface; however, in many cases only partially. The purpose of this paper is to show the influence of functionalization on the structure of different crosslinked styreneDVB copolymers through the measurement of the degree of swelling [6].

portant for understanding the relatively high "dry volume" as can be seen in Table 2. The main part of °' parex" was removed after polymerization by steam distillation. These precursor resins were purified according to ref. [10]. Chloromethylation and phosphination are described in ref. [10-12]. The following procedures are representative:

Chloromethylation EXPERIMENTAL The styrene-DVB copolymers D to G were gifts from Chemisches Kombinat Bitterfeld Division of Ion Exchange Resins. The resins have been prepared by a suspension polymerization with 2% of technical grade "divinylbenzene" as crosslinking component, with the following composition: 1.98% of amethylstyrene, 6.67% of m-diethylbenzene, 2.29% of o-diethylbenzene, 0.49% of p-diethylbenzene, 30.67% of m-ethylstyrene, 6..73% of p-ethylstyrene, 39.84% of m-divinylbenzene, 11.36%, 11.36% of p-divinylbenzene, 0.02% of naphthalene. Resins D, F and G were synthesized by polymerization in the presence of 30% "parex" ( n - C 8 - C 1 4 alkanes) as inert component. This can be im-

Starting resins D, E, F or G (100 g) were swollen in dichloromethane (700 ml) for one hour. Chloromethyl methyl ether and SnC14 were added in amounts shown in Table 1 and the whole mixture slowly stirred for 1 h at the temperature shown in Table 1. The resin was filtered by suction and washed with absolute methanol (2 1). Purification was achieved by stepwise extraction in a Soxhlet apparatus with dichloromethane, water, methanol, acetone, always for periods of four to six hours. The resins were dried by freeze drying and were stored in an argon atmosphere.

Phosphination of the chloromethylated resins All operations were made with the exclusion of water and air. Triphenylphosphine

TABLE 1 Chloromethylation of styrene-divinylbenzene copolymers a Chloromethylated resin

Reaction temp. ( ° C)

chloromethyl methyl ether (ml)

SnC14 (ml)

% C1

DScl b (retool/ 100 g)

DC EC-1 EC-2 EC-3 EC-4 FC-1 c FC-2 FC-3 FC-4 GC c

25 42 25 25 35 42 25 25 35 42

200 200 50 125 250 200 50 125 250 200

10 20 5 10 20 20 5 10 20 20

11.2 18.2 3.2 10.7 17.9 14.7 5.5 8.4 17.7 12.6

38.8 72.0 9.8 36.8 69.5 54.0 17.9 27.9 68.5 44.7

100 g resin, 700 ml dichloromethane, 1 hr. b DS ° = degree of substitution of chloromethylated polymer. c Chloromethylated twice.

a

(26.2 g, 0.1 mol) was dissolved

in tetrahydrofuran (THF) (400 ml) and reacted with lithium foil (2 g, 0.29 mol) for 8 h. The dark red solution was filtered over glass wool and the lithium phenyl converted into lithium chloride, benzene and isobutene by dropwise addition of tert-butylchloride (10.9 ml, 0.1 mol). A suspension of (150 ml) was added to the solution of lithium diphenylphosphide. After stirring for one day at room temperature the resins were filtered and washed successively with deaerated water (2 x 150 ml), ethanol (2 X 150 ml) or acetone (2 X 150 ml) and dried at 100° C in an Abderhalden drying apparatus. The functionalized resins were characterized by chlorine and phosphorus elemental analyses [ 131. The dry and swollen volumes, V, and V,, were measured in graduated and carefully calibrated tubes using between 2 and 5 g of resin. V, in toluene was stable after an equilibration time of 24 h [7]. Swelling experiments with phosphinated resins were performed in deaerated toluene under argon. IR spectra of the resins were measured on a Beckman IR-12 spectrophotometer in KBr pellets. RESULTS

Four different styrene-DVB copolymers (D, E, F and G) with 2% DVB were functionalized as shown in Scheme 1, where (a) is CH,OCH,Cl; SnCl, cat., room temperature, l-6 h, and (b) is LiPPh,, THF, room temperature, 24 h.

1

Scheme 1.

The precursor polymers were synthesized by suspension polymerization with 2% of technical grade divinylbenzene (for analysis, see Experimental). Polymers D, F and G were formed in the presence of 30% “parex” as inert component, which is almost completely removable after polymerization by steam distillation. All substituted polymers 2 and 3 were characterized by the “degree of substitution”, DS,, or DS,, calculated from the Cl- or P-elemental analysis, and the “degree of swelling”. q = V,/V,, determined in toluene as the ratio between the swollen volume ( V,) and the dry volume (V,). The unusually high dry volume of resin D probably results from a residue of the inert component (“parex”). The data are summarized in Table 2. The last column contains the ratio of the degree of swelling of substituted and precursor polymers. In all phosphinated polymers we found a residue of chlorine, DSc,(,,, probably as a result of reduced accessibility in the reaction with alkali metal phosphides, and a tendency to phosphine quaternization. In some cases the sum DS, + DSc,(,, is significantly smaller than the starting value DSc, (e.g. EC-4 + ECP4; FC-2 -+ FCP-2; FC-4 + FCP-4) and we suggest that partial reduction of chloromethyl groups by lithium phosphide and residual lithium phenyl may be responsible. V, seems to be little altered with functionalization and, as a rule, we used the value of the precursor polymer. Figure 1 reveals a linear correlation between the degree of substitution and the “rel-

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ative degree of swelling" for chloromethylated resins ( r = 0 . 9 8 ) . Whereas swelling remains almost unchanged in the precursor polymer and in the lightly-chloromethylated products we observe a remarkably reduced degree of swelling in the phosphinated polymers. The dry volumes of the precursor resins are similar, the swelling volumes, however,

depend on the method of polymerization [68]. In all cases the degree of swelling decreased with an increasing degree of substitution. Probably the pore size is strongly influenced by the functionalization process, i.e., the penetration of solvent is hindered. In accordance with this suggestion the large diphenylphosphino group has a greater in-

TABLE 2 Swelling data and degree of substitution of chloromethylated and phosphinated styrene-divinylbenzene copolymers derived from four precursor resins Entry

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 i

Resin a

D DC DCP E EC-1 EC-2 EC-3 EC-4 ECP-1 ECP-2 ECP-3 ECP-4 F FC-1 FC-2 FC-3 FC-4 FCP-1 FCP-2 FCP-3 FCP-4 G GC GCP

DScl b or DSp c (mmole/ (100 g) 38.8 38.1

DScl(n ) d (mmole/ 100 g)

Vd ¢ (ml/g)

V~ f (ml/g)

q g

1.85

7.40 6.80 5.4 5.2 3.6 5.5 4.8 3.7 3.0 5.1 4.25 2.40 5.0 4.10 5.10 4.70 3.36 3.40 4.65 2.90 2.60 8.30 7.00 5.80 3.45

4.0 3.67 2.91 3.16 2.18 3.33 2.91 2.24 1.82 3.10 2.58 1.46 3.13 2.66 3.18 2.93 2.06 2.13 2.74 1.71 1.53 4.87 4.12 3.41

3.1 1.65

72.0 9.8 36.8 69.5 65.3 9.2 24.3 53.4

9.0 2.1 7.2 5.8

1.62

1.70 54.0 17.9 27.9 68.5 45.7 9.0 21.0 46.3

7.3 1.4 5.9 10.1 1.70

44.7 42.4 20.0

2.6

(qR/qo)lO0

h

(%)

91.8 72.8 69.0 105.4 92.1 70.9 57.7 98.1 81.6 46.2 85.0 101.6 93.6 65.8 68.1 87.5 54.6 48.9 84.6 70.0

a First letter arbitrary; C means chloromethylated; CP means phosphinated via chloromethylated resin. Particle sizes (mm diameter): 0.05-0.01 (D, E), 0.1-0.3 (F, G) (all 2% DVB). b DS ° = degree of substitution of chloromethylated polymers. c DSp = degree of substitution of phosphinated polymers. d DS ° = DSp + DSo~rO (nonsubstituted chlorine). ¢ Vd = volume of the dry resin (always derived from the precursor resin). f V~= swelling volume in toluene after 24 h. g

q = V J Vd.

h q0 = degree of swelling of the precursor polymers D, E, F, G; q a = q o or qp. i F r o m ref. [16].

79

cH cl

cHL

/

Ph CL

ii ~'v~>-CH 2PP h 2

CH 2

Ph

Scheme 2.

fluence than the smaller chloromethyl group. Some irregularities have been found in the series of phosphinated polymers (ECP-4, FCP-3 and FCP-4). IR-spectrometric investigation gave some indication of phosphonium chloride formation (absorption band at 1125 c m - 2 [14]) owing to an intraresin reaction [15], as shown in Scheme 2. Such additional crosslinking between the polymer chains would be expected to contribute significantly to a loss of ability to swell. In all cases where anomalies were observed phosphonium salt structures were detected by IR analysis.

(see point 25 in Fig. 1 taken from Ref. [16]). In principle, substitution (functionalization) decreased the penetration of toluene into the resins and lowered the degree of swelling. In a series of chloromethylated and phosphinated polymers the dependence of the degree of substitution on the degree of swelling was almost linear. Irregularities have been found due to intraresin reactions (phosphonium salt formation) in phosphinated polymers. This can be an additional valuable aspect in the analysis of readily accessible swelling data, because a large level of quaternization decreases the level of immobilization of transition metal complexes. In our experience, swelling data are only relevant when referenced to the data for the starting material, and we recommend the ratio qsubstituted/ qunsubstituted to be used as a relative measure of swelling of polymers in toluene.

CONCLUSIONS The systematic examination of the degree of swelling of non-functionalized and functionalized s t y r e n e - D V B copolymers in toluene shows that only by including the swelling behaviour of the starting material (precursor resin) could satisfactory correlations been found. This is important in the discussion of swelling data from the literature DSct or DSp

ACKNOWLEDGEMENT We are very much indebted to Prof. G. Schwachula and his coworkers in Chemisches Kombinat Bitterfeld for the gift of basis polymers. We also want to thank Mrs. R. Kross, Mrs. A Modler and Mrs. B. Aim for technical assistance.

70 60 50 40 30

,e\

20 10

40

60

80

100 qR/qO .100

Fig. 1. Relationship between degree of substitution and "normalized" degree of swelling of chloromethylated (©) and phosphinated (o) resins (abbreviations see Table 2).

80

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