Macroporous polymers derived from vinylamine; synthesis and characterization

Eur. Polym..L Vol. 25, No. 4, pp. 331-340, 1989 Printed in Great Britain. All rights reserved

0014-3057/89 $3.00 + 0.00 Copyright © 1989 Pergamon Press plc

MACROPOROUS POLYMERS DERIVED FROM VINYLAMINE; SYNTHESIS AND CHARACTERIZATION HAMID TBAL, JOELLE MORCELLET, MICHI~LEDELPORTE and MICHEL MORCELLET* Laboratoire de Chimie Macromol6culaire, U.A.351 du CNRS, Universit6 des Sciences et Techniques de Lille Flandres Artois, 59655 Villeneuve d'Ascq Cedex, France (Received 1 September 1988)

Almtract--Macroporous beads containing N-vinyl-tertbutyl carbamate (NVTBC) as the main component and styrene, methyl-methacrylate or methacrylic acid as comonomer have been prepared by suspension polymerization using divinylbenzeneor ethyleneglycoldimethacrylate as cross-linking agent. Heptane was used as the porogenic agent. After solvolysis,parent copolymers containing vinylamine instead of NVTBC were obtained. These beads were characterized by chemical composition and extent of solvolysis. Their textural features (specific area and porous volume) were also determined by nitrogen adsorption~lesorption isotherms and mercury porosimetry. The influences of the following parameters on the chemical and physical features of the beads were studied and discussed: nature and concentration of the cross-linking agent, concentration of the porogenic agent, nature of the comonomer.

INTRODUCTION

Poly(vinylamine) (PVA) is a water soluble polymer of considerable potential application and thus has received increasing attention during recent years. The chemical reactivity of the amino group allows introduction in the polymer of various functional groups such as iminodiacetic, aminophosphonic, dithiocarbamate or thiourea [1]. Due to the complexation properties of these functional groups towards transition metal ions, one of the most important practical applications of vinylamine (VA)-based copolymers is their use as chelating resins, provided that they have been made insoluble by cross-linking. This paper describes the synthesis and characterization of a series of VA-based cross-linked copolymers. As VA monomer cannot be isolated, synthesis of the polymers requires the preparation of a polymeric precursor followed by suitable modification. The less expensive method of preparation of VA is probably the Hofmann degradation of poly(acrylamide) [2]. Nevertheless, the reaction is never complete and gives rise to side reactions such as the formation of carboxylate groups. More recently, a method using the transformation of poly(acrylic acid) into PVA by a Schmidt reaction has been used; it is CH2=

(9

CH I C = O I Ct

NaN3

CH 2 = C H I CON 3

vinylacetamide) [6], poly(N-vinylsuccinimide)[1] and poly(N-vinylphtalimide) [7, 8] have been used as polymeric precursors. It is now accepted that the best method is that first proposed by Hart [9-13] which consists of the synthesis, polymerization and hydrolysis of N-vinyl-tertbutylcarbamate (NVTBC). To obtain insoluble samples, it is possible either to post-reticulate PVA using a bifunctional crosslinking agent reacting with some of the amino groups or to introduce a cross-linking agent such as divinylbenzene (DVB) or ethyleneglycol dimethacrylate (DMG) during the polymerization. We have chosen the second method which allows the synthesis of polymers with better defined physical features. This paper refers to the preparation of macroporous copolymers of VA with another monomer (styrene, methyl methacrylate (MMA), methacrylic acid (MA), cross-linked by DVB or DMG. These samples are prepared by suspension polymerization of NVTBC with another monomer, in the presence of a porogenic agent, followed by hydrolysis. EXPERIMENTAL

Monomers NVTBC (4) was synthesizedby the method of Hart [9-11] adapted by Hughes and St Pierre [13], without further modification (Scheme 1): A

tBuOH •

*To whom all correspondence should be addressed.

CH

I N

@

®

also incomplete and gives copolymers of acrylic acid and VA [3-5]. Another route to PVA is the synthesis of a polymeric precursor followed by hydrolysis or some similar cleavage reaction. In this way, poly(N-

CH 2 =

II C

,

o

,"

CH 2 = CH I NH I C=O

®,

OtBu

All manipulations leading to 4 were carried out under an efficient fume hood due to the toxic nature of the chemicals. Special care was taken in the drying of tertbutanol in the last step of the synthesis to ensure a good yield of 4 (60%). 4 is a solid at room temperature (m.p. 64°). Styrene, MMA and MA were commercial products (Janssen) which were used as received. DVB was a commercial product (Merck) containing 35% p-DVB, 15% m-DVB, 331

332

HAMID TeAL et al. pension is well-established, the temperature is increased to 80 ° (if necessary) and the dispersing agent is added. After 15-20 min with D M G or 45-60 min with DVB, the sticking point occurs. The stirring speed is then increased to 450-500 rpm to avoid coalescence. 15 min later, the gel point is attained and the beads are no longer sticky. The stirring speed is then reduced to 220 rpm and the reaction mixture is stirred for 8 hr. During this period, the beads harden and acquire their mechanical properties. The beads are then decanted off and washed with water.

35% m-ethylbenzene, 15% p-ethylbenzene; it was used without purification and appropriate corrections were made in the calculation of the molar ratios in the reacting mixture. D M G was used without further purification (Merck; 99% purity). Heptane was used as a diluent (or porogenic agent) in the suspension polymerization. Its content is expressed as weight percent of the total organic phase. Azo-bisisobutyronitrile was used as initiator at a concentration of 1% of the monomer mixture. An ammoniacal salt of a copolymer of styrene and maleic anhydride was the dispersing agent at a concentration of 1.25% in water. The protective agent was gum arabic (1% in water).

Post-treatment After polymerization, the diluent (heptane) is extracted with methanol in a soxhlet for 24 hr and the beads are dried for 24 hr at 60 ° under vacuum.

Polymerization Compound 4 was copolymerized with styrene, M M A or M A as comonomer, with DVB or D M G as cross-linking agent, according to Scheme 2: R1 I • x CH2=CH

+

R3 I

y CH2=C

I NH I

+

AIBN

z CH2=C

I

A

I ~4

R2

C=O

CH2~C

I

I R3

OtBu

4

[ NH I

RI I

R3 I

R2

R4 I

C~-~O

~CH2--

I OtBu

HCI C2HsOH o~-

dioxane

C'~'~

I R3

~1

c.2-

+--NH;CI"

c..-

R2

R3 I

z

+

t BuOH

+ CO 2

R4

*'"~" CH 2 - - C

I

I R3 RI=

RI

H

and R 2 = ~ ( ~ Styrene

=

CH 3

R3

=

CH 3

. k and

R 2 -- - - C - - O C H 3 It

and

R 4 -- [ ' ~

0

Methyl

methacrylate

or R 2 = - - C - - O H II 0

Methacrylic

The process of suspension polymerization was essentially that described by Guyot et al. [14] with some modifications related with the nature of the monomers and cross-linking reagents. A typical copolymerization was as follows. The whole experiment was carried out under N 2. A volume of water corresponding to a 4-fold excess compared to the total volume of the organic phase [4 plus DVB (or DMG) plus the comonomer plus heptane] is heated in the reactor at 70 ° in the case of D M G and 80 ° for DVB. At low stirring speed (220 rpm), gum arabic is then added as a protecting agent, then 4 is added to the mixture and allowed to melt. After complete melting, a solution prepared separately and containing the other components (initiator, comonomer, cross-linking agent and diluent) is added. This addition is the zero time of the reaction. When the sus-

acid

Divinylbenzene

(DVB)

or R 4 = - C - O - ( C H 2 } ^ - O - C II 0

"

Glycol dimethacrylate

II 0 (DMG)

Sieving is used to separate the beads into four fractions: 0.315-1ram; 1-2mm; 2-3.15mm; > 3 . 1 5 m m dia. In the following, only the second fraction (1-2 mm) will be used as the white and opaque beads are more homogeneous and more spherical for this fraction. Solvolysis The tertbutylcarbamate protecting groups in the prepolymers are removed by HC1 in ethanol or dioxane depending of the nature of the cross-linking agent, D M G or DVB respectively (Scheme 2). 5 g of beads are mixed with 25 ml of solvent with stirring and a 20-fold excess of cone. HC1 is added at room temperature. The mixture is stirred

Synthesis and characterization of polymers derived from VA for 24 hr. The beads are then filtered off and washed with distilled water until neutral pH. Finally, the beads are extracted with methanol in a soxhlet for 24 hr and dried under vacuum at 60 ° for 24 hr. The solvolysis is much more difficult with the beads than with linear soluble poly(Nvinyl-tertbutylcarbamate) (PNVTBC) for which the reaction is completed within 30mn [10-11]. With the beads, the extent of the solvolysis never exceeds 80%.

333

lOO

/// 50 --

//

///./////1

Elemental analysis

./

The pre-polymers containing the NVTBC residue and the polymers resulting from solvolysis and containing both the NVTBC and the VA residue were analysed for both nitrogen and chloride. From these results, the extent of the solyvolysis was determined for each sample. Texture determination

The surface area was obtained from nitrogen adsorption~tesorption measurements following the BET method [15] (apparatus Quantasorb Jr). Mercury porosimetry was used to determine the porous volume and the pore size distribution; pore radii >94A. (apparatus Carlo Erba 800).

0

50

100 fa

RESULTS AND DISCUSSION

Fig. 1. Weight fraction F a of NVTBC in the beads vs the weight fraction f~ of NVTBC in the monomer mixture: O--styrene as comonomer, DVB as cross-linking agent; *--styrene as comonomer, DMG as cross-linking agent; and © - - M M A as comonomer, DMG as cross-linking agent.

The influence of four main parameters has been studied, viz. the n a t u r e of the cross-linking agent, its c o n c e n t r a t i o n , the nature o f the c o m o n o m e r and, in a few cases, the c o n c e n t r a t i o n o f the porogenic agent. Table i gives the chemical features of the beads prepared from N V T B C a n d styrene as c o m o n o m e r with DVB, D M G or D V B / D M G mixtures as crosslinking agent. In these experiments, the c o n c e n t r a t i o n of h e p t a n e was kept constant. In Fig. 1 is plotted the weight fraction F~ of the N V T B C residue in the beads vs the weight fraction )ca of N V T B C in the m o n o m e r mixture. These results show that i n c o r p o r a t i o n of N V T B C in the beads is easier w h e n the cross-linking agent is D M G . This is confirmed by c o m p a r i s o n of G D 70205 and G D 701010. The effect may be explained by considering the synthesis of linear copolymers of N V T B C [16]: the study of the copolymerization parameters for NVTBC-styrene and NVTBC-MMA mixtures shows that, in the second case, a m u c h higher a m o u n t o f N V T B C is incorporated. The two series of results m a y be c o m p a r e d if it is assumed that styrene and M M A are analogues of D V B a n d D M G respectively.

In addition, the use of M M A as c o m o n o m e r in place of styrene increases the a m o u n t of N V T B C in the beads (Table 2 a n d Fig. 1). Several solvents were tried as a m e d i u m for the solvolysis. F o r the D V B beads, the best results were obtained with dioxane as solvent. As an example, the extent of solvolysis was only 10% in ethanol and 6 3 % in dioxane for the D 80 beads. This is not surprising since dioxane is a good solvent and ethanol a precipitant for poly(styrene). The extent of solvolysis is directly related with the affinity between the beads and the solvent a n d with the swelling ratio. F o r the D M G beads, on the contrary, the best results were o b t a i n e d with ethanol as solvent. According to previous work, ethanol is the best solvent for the solvolysis of linear PVA [13]. The solvolysis of the beads was carried out for 24 hr. U n d e r these conditions, it is never complete (the highest value was 81% for samples G D 70205 and D 40); whereas the solvolysis of linear P N V T B C is complete within 30rain [3]. In some cases, an

Table 1. Chemical characterization of the beads containing styrene as comonomer Starting mixture Beads

Ref.

NVTBC (wt %)

ST (wt %)

D10 10 60 D30 30 40 D40 40 30 D60 60 20 D 80 80 10 G20 20 50 G40 40 30 G60 60 10 G70 70 0 GD70205 70 5 GD701010 70 10 'From elemental analysis for nitrogen. bFrom elemental analysis for chloride.

DVB (wt %)

DMG (wt %)

30 30 30 20 10

5 10

30 30 30 30 20 10

Heptane (wt %) 40 40 40 40 40 40 40 40 40 40 40

NVTBC"

(wt %) 2.7 9.9 13.6 16.5 36.9 10.5 27.9 33.0 53.6 56.6 46.2

(meq/g) 0.19 0.69 0.95 1.15 2.58 0.74 1.95 2.31 3.75 3.96 3.23

(wt %) 1.1 3.3 6.5 4.9 15.5 4.8 6.8 9.0 28.5 34.1 18.7

VAb

(meq/g) 0.14 0.41 0.82 0.61 1.95 0.60 0.85 1.13 3.58 4.29 2.35

Extent of solvolysis (%) 70 57 81 49 63 77 38 42 72 81 58

HAMID TBAL et al.

334

Table 2. Chemical characterization of the beads containing M M A or MA as cononomer

Ref.

NVTBC (wt %)

Comonomer (wt %)

DMG (wt %)

Heptane (wt %)

40 60 40 60

30 MMA 10 M M A 30 MA I 0 MA

30 30 30 30

40 40 40 40

GM 40 GM 60 G A 40 G A 60

NVTBC a (wt %) (meq/g) 30.2 47.8 6.7 15.9

(wt %)

(meq/g)

Extent of solvolysis (%)

12.2 16.0 0.95 1.0

1.53 2.01 0.12 0.13

63 48 25 10

VA b

2.11 3.34 0.47 1. I 1

~From elemental analysis for nitrogen. bFrom elemental analysis for chloride.

additional solvolysis reaction was carried out on the same beads in order to enhance the transformation of the NVTBC groups into VA groups but the results were generally poor (the best was an increase from 38 to 50% for sample G 40). The values given i n Table 1 refer to one period of 24 hr solvolysis. Figure 2 shows that the extent of solvolysis increases with the content of NVTBC residues. The shape of the curve suggests that the reaction is catalysed by the presence of the VA functions already formed (the solvolysis of PNVTBC is easily complete) [3]. Table 2 gives the results obtained with M M A or M A as comonomer. As stated above, the use of M M A promotes the copolymerization of NVTBC. On the contrary, the amount of NVTBC incorporated into the beads is low when M A is used as comonomer although the actual concentration of MA in the polymerization medium is probably lower % NH~ CI -

100

/ • GD 70205

/

e/G 70

50 ~•"~G 40

% NVTBC I

I

I

i

0

I

I

I

=

i

50

I

100

Fig. 2. Extent of solvolysis (fraction of NVTBC groups converted into NH~- C1-) vs the weight fraction of NVTBC in the beads.

than the values given in Table 2 (MA is slightly soluble in water). Table 3 gives the results obtained for NVTBC/ styrene/DMG mixtures varying the amount of heptane or DMG. Changing the concentration of heptane from 20 to 50% has no definite effect on the amount of NVTBC into the beads. The increase of the D M G concentration and the related decrease of the styrene concentration seem to enhance the incorporation of NVTBC as expected from the above discussion. Table 4 presents the values of overall porous volume, specific area and average pore radius for three series of beads before and after the solvolysis. For the G series, the overall porous volume Vp ranges from 0.3 to 1.6 cm3/g and the specific area S never exceeds 55 m2/g. For the D series, the overall porous volume and especially the specific area are higher (up to Vp = 2.0 cm3/g and S = 370 m2/g). As expected, the values for the G D 70205 and GD 701010 samples are intermediate. The solvolysis has no definite effect on the textural features of the three series of beads. The specific area seems to decrease slightly for the G beads and to increase slightly for the two other series. In the following, the distribution curves will refer to samples before solvolysis. Figures 3 and 4 give the pore size distribution in the differential and integral mode for the beads cross-linked with DVB (D series). In all cases, the distribution is multimodal, typical of macroporous polymers and centered around pores with a radius of ca 500 ,~. The integral curve is different for samples D 60 and D 80 but, in these cases, the amounts of DVB are 20 and 10% respectively, instead of 30%. Figures 5 and 6 show the results for the samples cross-linked with D M G (G series): in that case, the distribution is centred around pores of radius 500/~, for low concentrations of NVTBC and is shifted

Table 3. Influence of the concentration of D M G and beptane on the chemical characterization of the beads ST (wt %)

DMG (wt %)

Heptane (wt %)

6001 60 6002 6003

60 60 60 60

10 10 10 l0

30 30 30 30

50 40 30 20

37.3 33.0 52.3 41.6

2.61 2.31 3.66 2.91

21.9 9.0 31.4 22.0

2.75 1.13 3.95 2.77

88c 42 82c 78¢

G 6004 G 60 G 6005

60 60 60

20 10 0

20 30 40

40 40 40

37.7 33.0 49.6

2.64 2.31 3.47

18.5 9.0 23.2

2.33 1.13 2.92

75¢ 42 65¢

Ref. G G G G

~From elemental analysis for nitrogen. bFrom elemental analysis for chloride. ¢After two periods of solvolysis for 24 hr in ethanol.

NVTBC ~ (wt %) (meq/g)

VA b (wt %) (meq/g)

Extent of solvolysis (%)

NVTBC (wt %)

335

Synthesis and c h a r a c t e r i z a t i o n of p o l y m e r s derived from V A Table 4. Physical features of the beads containing styrene Before solvolysis

After solvolysis

Specific area, S (m2/g)

Average pore radius a, ~ (/~)

Overall porous volume, V (cm3/g)

Specific area, S (mS/g)

pore radius, a

Ref.

Overall porous volume, V (cm3/g)

G20 G40 G60 G70

1 0.29 1.60 1.49

39 55 23 28

513 106 1391 1064

0.43 1.38 1.32

42 22 16

205 1254 1650

GD70205 GD701010

1.22 1.86

55 128

444 290

1.27 1.67

48 163

529 205

239 359 330 370 173

67 44 48 101 294

2.09 2.14

401 216

104 198

D10 D30 D 40 D60 D80

0.80 0.80 0.79 1.95 2.00 2V_ aCalculated from f = 1 0 4 . ~ . S

toward higher values (about 10,000A) when the amount of NVTBC increases. Figures 7 and 8 present the effect of the nature of the cross-linking agent on the pore size distribution in the differential and integral modes (beads crosslinked with DVB (D 80), D M G (G 70) or mixtures of DVB and D M G (GD 70205 and GD 701010)). For the G 70 sample, the distribution is centred around pores of large size (about 10,000/~) but seems to be bimodal with another small maximum near 500 .~. When changing D M G for DVB, this family disappears and other families with lower pore size appear. For GD 70205, the distribution is centred around 500/~ and for the beads with high DVB content, two families with intermediate pore sizes are predominant around 500 and 150/L Table 5 gives the results of overall porous volume and specific area measurements for the beads de-

Average

scribed in Table 3. As expected the porous volume increases when the heptane concentration increases whereas the specific area first increases and seems to be maximum for 30% heptane [14, 17]. Figure 9 illustrates the change in the differential pore size Table 5. Influence of the heptane and DMG concentration on the textural features Overall porous volume, Vp (cm3/g)

Ref.

Specific area, S (m2/g)

Average pore radius, f (~)

G6001 G60 G6002 G6003

1.56 1.6 0.53 0.22

8.5 23 46 43

3671 1391 230 102

G6004 G60 G6005

1.53 1.60 1.57

69 23 25

443 1391 1250

%VP 20'

lo

0 .9

I

I

2.4

2.9

3.4

--

~

_ 3.9

4.4 log

a

Fig. 3. Influence of the N V T B C c o n c e n t r a t i o n on the differential pore size d i s t r i b u t i o n in the D series: r-q--D 10; ~ - - D 3 0 ; I--D40; O--D60; and O--D80.

336

HAMID TBAL et al.

VP t (cm3/g) / O '~ 0/0

i/

/ 0

~5

/

o_O--O~____-0 e /

e/ /e

/

o/ /• °

oO,,/ ° / /e

/,.."

/O // /I /0/ //~

~U ~- ~3~.~-* -- ~-*--*--*--* .........~ ~ _ M .El- r l - fl - - 0-[:1 - t 3 - - r~ - . ~ " n - I~'-

0 ~

* ~~

-

0

I 1.9

2.4

I

I

2.9

3.4

3.9

4.4

log

a

Fig. 4. Influence of the NVTBC concentration on the integral pore size distribution in the D series: r-I--D 10; ~ - - D 30; I - - D 4 0 ; O - - D 60; and © - - D 8 0 .

%VP 3o

25

20

-

lO

1.9

2.4

2.9

3.4

3.9

4.4 l~a

Fig. 5. Influence of the NVTBC concentration on the differential pore size distribution in the O series: O---G 20; × - - G 40; ~ - - - G 60; and ~ - - - G 70.

Synthesis and characterization of polymers derived from VA

337

vPt - (cm 3 g)

1.5

./

.5

1.9

2.4

,._.-.~J.//:,~ /-'~ 7

• ~"

2.9

•

3.4

3.9

.

4.4 log a

Fig. 6. Influence of the NVTBC concentration on the integral pore size distribution in the G series: Q~ 20; x - - G 40; ~ - - - G 60; and ~ - - G 70.

%vp

j 25

20

Q

15

10

0 1.9

2.4

2.9

3.4

3.9

4.4 log a

Fig. 7. Influence of the nature of the cross-linking agent on the differential pore size distribution: O---G 70: 30% DMG; O----GD 70205, 20% D M G - 5 % DVB; V - - G D 701010, 10% DMG-10% DVB; and ~ - - D 80, 10% DVB.

338

HAMID TBALet al. VPt (cmS/g)

2

"" ~ ._.._. ..__.__--

. .l 7

2°.° // /

1

1.9

2.4

. °"°-'--°-°"-°"°~

2.9

/

3.4

~'

3.9

4.4

log a

Fig. 8. Influence of the nature of the cross-linking agent on the integral pore size distribution: ~ - 4 3 70: 30% DMG; O ~ D 7 0 2 0 5 , 20% DMG-5% DVB; A--GD701010, 10% DMG-10% DVB; and F-]--D 80, 10% DVB.

distribution when varying the concentration of diluent. At high heptane concentration (50%), only very large pores are present. Sample G 6001 which has a low S value and is made only of very large pores, is at the borderline of the macroporous domain. At intermediate concentration (40%), the distribution is

very fiat and at low heptane concentration (20 or 30%), only rather small pores are present (radius less <300A). Such an effect of the concentration of porogenic agent was previously reported for styrene-DVB copolymers [14]. Figure 10 shows the differential pore size distribu-

%VP 5O

e

40

30

20

•

,o 1.9

,_, 9.4

/"\°__,/ 9.9

3.4

3.g

4.4

log a

Fig. 9. Influence of the concentration of heptane on the differential pore size distribution (DMG concentration 30%): Q--20; A--30; I-7-----40;and , - - 5 0 .

Synthesis and characterization of polymers derived from VA

339

i %VP 2,5

20

1,5

0

~0

r~

4IX,,, ~-"

~.

1.9

2.4

2.9

.

3.4

3,9

4.4

log a

Fig. 10. Influence of the concentration of DMG on the differential pore size distribution (heptane concentration 40"/.): ~--20; & I 3 0 ; and D ~ 4 0 . tion for various D M G concentrations at a constant 40% heptane concentration. As already reported for this range of porogenic agent concentration [14], the pore size distribution is displaced towards large pores when the cross-linking agent concentration increases. Figure 11 gives the integral porous volume distribution corresponding to the two last series of beads.

CONCLUSION

It has been shown that the choice of the crosslinking agent and the comonomer control to a large extent the chemical composition of the beads containing VA groups. In addition, changing the nature and the concentration of the cross-linking agent and the

VP

/

.,'"

/ i

.-""

//

....""

/

/

,.,""

/

,e

/

¢"

/ ] //

!

/

!

,,"

S

/ I

,,,"""

/ 1

illIII /

, ---.-" '

//./ . , /

¢, r

u

,~---~

2

~

I

I

3

I

I

4

~._

log a

Fig. I 1. Influence of the concentration of heptane and DMG on the integral pore size distribution: . . . . . 20% heptane-30% DMG; - - . - - 30% heptane-30% DMG; - - ~ - - 40% heptane-30% DMG; - 50% heptane-30% DMG; . . . . 20% DMG-40% heptane; and ...... 40% DMG-40% heptane.

HAMID TBAL et al.

340

concentration of the porogenic agent causes marked modifications of the textural feature of the beads. By using a mixture of DVB and D M G for cross-linking, it is possible to obtain beads with a high VA content, high porous volume and good specific area. These parameters should be of importance when considering the coordinating properties of the beads for use as chelating resins. In addition, as the solvolysis is not complete, the question arises whether this reaction occurs everywhere in the beads, i.e. the resulting VA functions are evenly distributed inside the beads. This point will be discussed in a subsequent paper, together with a report of the coordinating properties of our beads in relation with their textural features. REFERENCES

1. E. Bayer, K. Geckeler and K. Weing~rtner, Makromolek. Chem. 181, 585 (1980). 2. H. Tanaka and R. Senju. Bull. chem. Soc. Japan. 49, 2821 (1976). 3. C. Chang, D. D. Muccio and T. St Pierre. J. Polym. Sci: Polym. Symp. 74, 17 (1986).

4. T. St. Pierre, G. Vigee and A. R. Hughes. In Reactions on Polymers (Edited by J. A. Moore), pp. 61-72. Reidel, Boston, Mass. (1973). 5. H. Rath and E. Hilscher. German Pat. 1,153,528 (1963). 6. D. J. Dawson, R. D. Gless and R. E. Wingard Jr. J. Am. chem. Soc. 98, 5996 (1976). 7. D. D. Reynolds and W. O. Kenyon. J. Am. chem. Soc. 69, 911 (1947). 8. A. Katchalsky, J. Masur and P. Spitnik. J. Polym. Sci. 23, 513 (1957). 9. R. Hart. Bull. Soc. chim. Belg. 66, 229 (1957). 10. R. Hart. J. Polym. Sci. 29, 629 (1958). I1. R. Hart. Makromolek. Chem. 32, 51 (1959). 12. J. Bloys van Treslong and C. F. H. Morra. R e d Tray. chim. Pays-Bas Belg. 94, 101 (1975). 13. A. R. Hughes and T. St Pierre. Macromolec. Synth. 6, 31 (1977). 14. H. Jacobelli, M. Barthollin and A. Guyot. J. appl. Polym. Sci. 23, 927 (1979). 15. S. Brunauer, P. Emmett and E. Teller. J. Am. chem. Soc. 60, 309 (1938). 16. L. Janus, H. Tbal, J. Morcellet, M. Delporte and M. Morcellet. Unpublished results. 17. M. C. Maillard-Terrier and C. Caze. Eur. Polym. J. 20, 113 (1984).