Acta Polymerica 39 (1988) Nr. 9

492 BOGOEVA-GATSEVA, GABRIELYAN and GALBRAIKH: Graft copolymerization of acrylamide onto polycaproamide

Graft copolymerization of acrylamide onto polycaproamide with the redox system K,S,O,/Na,S,O~ G. BOGOEVA-GATSEVA*, G. A. GABRIELYAN** and L. S. GALBRAIKH**

*) Technical University, Skopie/Yugoslavia **) Moscow Textile Institute, Moscow/USSR

Kinetics and mechanism of the graft copolymerization process of acrylamide onto polycaproamide, initiated by the redox system K,S,O,/Na,S,O, in the presence of the heptaazocyclohexadecine complex of Cu( I) fixed on the polyamide matrix, were studied. The process of graft copolymerization takes place with maximum rate and efficiency a t a molar ratio of [Na,S,O,] :[K,S,O,] = 4.3. The kinetical parameters of the graft copolymerization as well as of the homopoly- merization during the process of grafting have been determined.

Pfropfcopolymerisation uon Acrylamid auf Polycaproamid mit dem Redoxsystem K,S,O,/Na,S,O, Kinetik und Mechanismus der Pfropfcopolymerisation von Acrylamid auf Polycaproamid bei Initiierung mit dem Redoxsystem K,S,O,/Na,S,O, in Gegenwart des an der Polyamidmatrix fixierten Heptaazocyclohexadecin-Komplexes von &(I) wurden untersucht. Die Pfropfcopolymerisation erfolgt mit maximaler Geschwindigkeit und Effektivitat beim molaren Verhaltnis [Na,S,O,] :[K,S,O,] = 4,3. Die kinetischen Parameter der Pfropfcopolymerisation sowie der wahrend des Pfropfprozesses ablaufenden Homopolynierisation wurden bestimmt.

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qmposaHHoii K2S,08/Na,S,0, B ~PHCYTCTBHH r e n ~ a a 3 o u ~ ~ ~ r o r e ~ c a ~ e q ~ l ~ o ~ o r o KoMnneKca Cu( I ) , npeAsapnTenbrro klCCJfeAOBaHa KIIHeTHKa II MeXaHkI3M PeaKuHII nPHBIIBOqHOB IIOJIIIMepH3aqHII aKpIIJIaMkIRa K nOJIHKanpOaMH~y, IIHII-

$HKCHpOBaHHOrO B IIOJIHaMHHHOfi MaTpHqe. MaKCIIMaJIbHaH CKOpOCTb Pi 3@$eKTHBHOCTb IIPHBHBKH ~ a 6 n 1 o ~ a e ~ c ~ IIpH MOJIbHOM COOTHOIUeHIIH Na,S,O, -k K,S,Oa = 4,3. OIIpeAeJIeHbI KHHeTH’IeCKHe IIapaMeTpbI lIpHBHBOqHOP IIOJIII- ~ e p m a q ~ ~ II r o ~ o n o n ~ ~ e p 1 1 3 a q a n B npouecce IIPHBHBKII.

1. Introduction

Recently considerable attention is paid to the problem of synthesizing modified chemical fibres with properties similar t o those of natural fibres. The problem has grown especially acute for polycaproamide (PA-6) fibres, the demand for which is slipping down mainly due to poor hygienic properties and wax- like handle. A number of works has been published on modifi- cation o f PA-6 fibres by graft polymerization methods t o the effect of creating cotton-like properties [ l ] , enhancing their hydrophilic capacity, dyeability and antistatic characteristics [2-41. Recently a method of “Hydramide” fibre production on the basis of graft copolymer of PA-6 with poly(acry1amide) (PAA) was developed by Hungarian researchers [5 ] .

Thus, investigation of new effective methods of modification of PA-6 fibres, particularly by graft polymerization of various vinyl monomers onto ready-made fibres, as well as the study of the kinetics and the grafting mechanism, are both of scientific and significant practical value. Most promising are the grafting methods which provide the synthesis of graft copolymers with- out homopolymer formation. From this aspect it may be of interest to refer to our previous publication [6], where the results of research in the field of graft polymerization of methacrylic acid onto PA-6 fibre in the presence of the K,S,O,/Na,S,O, system confirmed the principal feasibility of graft copolymers of PA-6 being synthesized without homopolymer formation. In the present article we present the results of an investigation of graft polymerization reaction of acrylamide (AA) onto PA-6, initiated by the redox system K,S,O,/Na,S,O, in the presence of copper ions.

2. Experimental

I t is known [7] that the effectiveness of redox systems in graft polymerization processes can be considerably enhanced by fixing one of its components on the fibre. Therefore, modifi- cation was effected with PA-6 fibres into which copper ions were introduced by pretreatment in an aqueous solution of salts. Grafting was carried out in the aqueous solution of the monomer (recrystallized from benzene) a t p H = 7 and tempzrature 323 to 343 K. The components of the initiating system, K,S,O, (2.0% of AA mass) and Na,S,O, were introduced to the reaction

medium simultaneously. After completion of the reaction, the fibre was extracted by hot water to remove unreacted AA and the produced homopolymer. PAA was isolated from the reac- tion medium and water after the extraction of samples by pre- cipitating in acetone. The amount of the obtained graft copo- lymer was determined from the increase of fibre mass after t h e extraction of liomopolymer and drying. Monomer convcrsion in the process of I t omopolymerization was investigated spec- trophotometrically. As the third componcnt o f the redos system some aqua- and complex copper compounds were used including acetate, copper sulphate, complex of copper with ethylene diamine tetraformic acid (EDTF) as well as the hepta- azocyclohexadecine (HHD) complex of nnivalcnl copper (CU(I)).

3. Results and discussion

According t o the results of previous investigations, t h e most effective component of t h e given redox system is the HHD-complex of Cu(1) (Figure 1). Therefore further ana-

I

0 5 10 15 min 20 Time

Fig. 1. Dependence of the amount of grafted PAA on PA-6 on time in the presence of various copper compounds (0 .002~0 of fibre mass). T = 323 K ; [AA] = 1.13 mole 1-l; [NazSa03] : [K,S,O,] = 4 : 1. I - Cu(I1) sulphate; 2 - Cu(I1) acetate;

3 - Cu(I1) EDTF; 4 - Cu(1) HHD

BOGOEVA-GATSEVA, GABRIELYAN and GALBRAIKH: Graft copolymerization of acrylamide onto polycaproamicle

Acta Polymerica 39 (1988) Nr. 9

493

0 10 20 30 min Time

80 % ~

60 $ t e

40 Q

0

PO

% C ': 60 c C

40 B

20

0 10 20 30 min Time

Fig. 2. Dependence of the amount of grafted PAA and AA conversion in homopolymerization reaction on time for differ- ent molar ratios [Na,S,O,] : [K2S20,] = R. Reaction condi- tions: [AA] = 1.13 mole 1-l; T = 333 K [Cu+] = 0 . 0 0 2 ~ 0 of fibremass. (a) [Na,S,O,] = 0.003 mole 1-l; curvesl, 6 - R= 1.0; 2, 5 - R = 1.7; 3, 4 - R = 2.7. (b) [K,S,O,] = O.OO1lmol~l-l; curves 1, 5 - R = 2.7; 2, 4 - R = 4.3; 3, 6 - R = 5.7;

7, 8 - R = 1.0

lysis of the reaction regularities of the graft polymerization of AA onto PA-6 was carried out with application of the redox system consisting of K2S20s, Na2S203 and the HHD- complex of Cu(1) (0.002~0 of fibre mass).

To initiate grafting of AA onto PA-6 it is possible to use the bicomponent system K&Os/COpper ions (in complex form) as well as K2S20s alone (Table 1). However, the analysis revealed that the advantage of the system K2S208/Na2S203/HHD-copper complex over the bicom- ponent system K2S20a/HHD-Cu(1) is the possibility of a considerable increase in the yield ratio of the graft copoly- mer to the amount of homopolymer produced in the course of the reaction by regulating the molar ratio reducer/ oxidator (Figure 2). From Figure 2 it may be seen that with increase of the thiosulphate concentration in the system the effectiveness of grafting increases due to decrease of monomer conversion in homopolymerization reaction. At the molar ratios Na,S203: K2S2Os = 1: 1 to 2.7 : 1, the AA polymerization rate considerably exceeds the graft polymerization rate (the initial homopolymeri- zation rate is 5 . 10-4 mol . 1-1 . s-l and the graft poly- merizatiori rate is Ci - I W 5 mole 1-l. s-l for [AA] = 0.84 mol . 1-l). At the molar ratio Na2Sp03:K2Sz08 = 4.3 the

initial rates of graft and homopolynierization reactions are levelled out and the further increase in this ratio does not lead to an increase of grafting effectiveness.

High degree of AA conversion in the homopolymerization reaction during graft polymerization initiated by the given redox system, which is quite efficient for grafting other acrylic monomers without homopolymer formation, is obviously connected with high affinity of AA to the chain transfer reaction [8].

Figure 3 gives the data on the effect of A h concentration in aqueous solution on the yield of graft copolymer. With the increase of monomer concentration the initial reaction rate is increased, the AA homopolymerization rate varying in the similar way. Attention should be paid to the fact that the amount of both graft polymer and homopolymer comes to maximum a t a period of 20min and remains stable further on. This occurs due to A h polymerization being practically completed by the time.

The study of the kinetics of AA graft polymerization onto PA-6 reveals notable differences in graft polymerization and homopolymerization reaction regularities. Calculated from kinetic data the order of the grafting reaction in monomer concentration is 0.5, which indicates AA in side reactions. Reaction orders in respect of K,SzOs and Na2S,0, (Figure 2) are 0.7 and 0.15, respectively. Besides, the order of the homopolymerization reaction in respect of monomer concentration, which occurs in the course of grafting, is 1.2, and in respect of K2S20s and Na2Sz03 it is 0.61 and 0.53, respectively. Elevated orders in initiator concentration both for graft and homopolymerization show the involvement of peroxodisulphate in the reactions of chain break and its transfer onto the monomer. The observed enhanced order of homopolymerization reaction in thiosulphate concentration as compared with graft polymerization seems to be caused by the involvement of thiosulphate in the inactivation reaction of primary sul- phate radicals. This is confirmed by the increase of grafting efficiency a t the increase of the molar ratio [Na2SIO3]: [K2S20s] (Figure 4). The observed considerable difference of reaction orders in monomer concentration may be accounted for by involvement of AA in the chain transfer reaction thus initiating homopolymerization.

c 4 - -

15

10

5

0 5 1s 25 min 35 Tim c

Fig. 3. Dependence of the amount of grafted PAA on time in t h e course of the reaction in AA solutions with concentrations 0.84 mol. I-1 (I), 1.13 mol. 1-1 ( 2 ) , 1.41 mole 1-1 (3). T = 333 K;

[Na2S,0,] : [K,S,O,] = 2.7; [Cu+] = 0.002%

Acta Polymerica 39 (1988) Nr. 9

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K2S208 K2S208/HHD-Cu(I) K2S208/Na2S20, (1 : 4)/ HHD-Cu(I)

BOGOEVA-GATSEVA, GABRIELYAX and GALBRAIKH : Graft copolymerization of acrylamide onto polycaproamide

4.3 62 70 35.4

39.2 42

Table 1. Dependence of the yield of PA-6 graft copolymer with A A and A A conversion in the homopolymerization reaction on the

type of the initiating system

I Yield of 1 AA conversion in graft homopolymeri-

copolymer zation Initiator system I % / %

I

! O t / Table 2. Dependence of graft yield, A A homopolymerization

and grafting efficiency on the type of initiation (T = 333 K; [AA] = 0.84 mol - 1-l)

0 1 1 3 b Smol/mol 7 R

Fig. 4. Dependence of the efficiency E of grafting of AA onto PA-6 on the molar ratio R = [Na2S20,] : [K,S,O,]. [AA] = 1.13 mol 1-l; T = 333 K; t = 10 min; [Cu+] = 0.002~0

Initiator system

N a 2 s 2 0 3 K2S20, (in solution) K2S20, (adsorbed on fibre) K2S,08 (chemically bound

with PA-6) K2S,08/Na2S20, (1 : 1) K2S208/Na2S20,/HHD-Cu( I)

(1 : 1; 0.002y0)

Graft yield %

0 4.3 5.0 7.4

4.0 19.2

AA homo-

polymer %

0 62 63 GO

53 70

Grafting efficiency

%

- 2.6 2.8 4.6

3.0 12.0

The increase of the reaction temperature above 333 K has a negligible effect on the graft polymer yield. The determined activation energy of the graft polymerization reaction in the temperature range 323 to 343 K is 53.2 kJ. mol-l, which is nearly the activation energy (67 kJ . mol-1) for grafting of AA onto PA-6 with the initiating system ammonium metavanadate/Cu( 11) [9].

The above results show tha t the initiating system K2S,0,/ Na2S203/HHD Cu( I), which is very effective a t grafting of methacrylic acid onto PA-6, appears ineffective in the graft polymerization of AA. Apparently this is caused b y differences in the initiating mechanisms. In this respect it was of interest to determine the contribution and the effect of the separate components of the redox system both on the grafting process and on AA homopolymeri- zation. According to the obtained data (Table 2) under assumed reaction conditions the presence of Na2S203 alone in the system initiates neither homo- nor graft polymerization of AA. If the grafting process is effected in the presence of K*S,Os alone, no matter if K,S20s is introduced into the fibre (by preimpregnation in aqueous solution) or if the initiator is in the solution, the amount of the graft copolymer produced is extremely low (AA conversion in homopolymerization reaction is about 60%).

I t may be assumed tha t low grafting efficiency in this case is partially connected with the easy involvement of K2S20s in the initiation of homopolymerization as the initiator is either in the solution or easily transferred from the fibre to the solution. Therefore consideration was given to graft- ing onto the fibre which contains chemically fixed K,S20s with the method described elsewhere [lo]. This method provides grafting of acrylonitrile onto PA-6 without homopolymer formation. With application of chemically

bound S2Os2--groups both with or without Na,S203 in the reaction solution, the process is accompanied by the formation of considerable amounts of homopolymer a t low grafting efficiency. It leads to the conclusion tha t the grafting efficiency is mainly influenced b y the presence of copper ions in the redox system. In fact the graft copoly- mer yield under similar conditions with application of fibres containing the HHD complex of univalent copper amounts t o 35%, whereas in the absence of copper i t is only 4%. These data permit to assume tha t the initiating process of AA graft polymerization onto PA-6 is preceded by the formation of the complex between the components of the initiating system and the monomer with possible involvement of polar groups of PA-6 macromolecules [Ill. The homopoly- mer yield is approximately the same also in the absence of copper. This is determined, as was shown in [12], by t.he easier complex formation with charge transfer by means of AA homopolymerization in the presence of peroxodi- sulphate.

References

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BYKOV, A. N., and KOLYSOV, A. E.: Avt. svid. 1032051 (1983).

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[S] MARUTHAMUTHU, P.: Makromol. Chemie, Rap. Comm. 1 (1980) 23.

[9] MUSHRA, M., LENKA, S., and TRIPATHY, A. K.: J. Appl. Polymer Sci. 26 (1981) 2593.

[ lo ] GABRIELYAN, G. A., AFANASEVA, I. S., SHALABI, S. E., DRUZHININA, T. V., and ROGOVIN, Z. A.: Avt. svid. 891 821

[ll] KHALIL, M. I., ABDEL-FATTAH, S. H., and KAXTOUCH,

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Received July 1, 1987 Accepted September 17, 1987