Indian Journal of Textile ResearchVol. 1, December 1976, pp, 120-123

Molecular Weight Distribution of Polyacrylonitrile Poly-mer Grafted onto Cotton and Solubility Behaviour of the

Graft Copolymer in CadoxenV. N. SHARMA

Applied Chemistry Section, The Bombay Textile Research Association, Bombay 400 086&

E. H. DARUWALLADepartment of Chemical Technology, University of Bombay, Bombay 400 019

Received 16 November 1976; accepted 27 November 1976

Graft copolymerization of acrylonitrile with different molecular weights of the grafted chains has been carriedout employing different techniques of initiation, viz. eerie ion, y-irradiation, FeH-H,O. and anionic grafting. Thegrafted chains have been separated from the cellulose backbone and their molecular weight distribution has heendetermined through a fractionation technique employing dimethyl formamide and methanol as solvent and non-solventrespectively. The solubility behaviour in cadoxen of the samples grafted by different initiation techniques has heenexplained in relation to the molecular weight of the grafted chains.

THE physical properties of grafted cotton andits solubility in an appropriate solvent dependto a large extent on the nature of the monomer

used for grafting, graft add-on and length and dis-tribution of the grafted chains. Several investigatorshave reported the effect of different initiation techni-ques on the graft add-on, length of the polymerchains and the degree of substitution of cellulose':".However, no information is available on the relation-ship between the solubility of the grafted chains inan appropriate solvent and the length and distri-bution of the grafted chains.

Tn the present investigation, an attempt has beenmade to separate the grafted polyacrylonitrile polymerobtained from grafted cotton into fractions of morehomogeneous molecular weight. The solubilitybehaviour in cadoxen of the polyacrylonitrile-cottongraft copolymer obtained employing different initia-tion techniques has been expiained in relation to themolecular weight of the grafted polyacrylonitrilepolymer.

Materials and Methods

Grafting was carried out on well scoured andbleached yarn of 80s. The fabric employed wassinged, desized, scoured and bleached medium cottonpoplin of 98 ends/in (32s) and 68 picks/in (26s).

Grafting Techniques

Ceric ion-- Grafting on yarn employing eerieammonium nitrate as the initiator was carried outaccording to the method described elsewhere".

"{-Irradiation - The simultaneous irradiation graft-ing technique was employed for grafting acrylonitrilefrom aqueous solution using a "I-irradiation source(doze rate, 0.24 m radjhr) for different durations.

Fe2+-H2()2 - Yarn samples were soaked in 0.1 ~s120

ferrous ammonium sulphate solution for 2 min andthen rinsed with distilled water. The treatedsamples were immersed in a boiling solution of acry-lonitrile and then hydrogen peroxide (0.03 %) wasadded. The samples were refluxed for 30 mill inthe reaction mixture and subsequently washed withwater.

Anionic grafting - Yarn samples were swollen indry dimethyl sulphoxide (OMSO) for 24 hr at 300eand DMSO was subsequently solvent exachangedwith dry methanol. Methanol was removed bydecantation, 280 ml of sodium methoxide in methanolwas then added and the reaction allowed to proceedfor different durations with mild agitation at 30°C.Unreacted reagent was extracted from the yarn withfour changes of dry ntvTSO. These treated sampleswere allowed to react with acrylonitriie in tetra-hydrofuran (THF). Acrylonitrile concentration inTHF was varied to achieve monomer/initiator concen-tration ratio in the range 22-1 10, keepi ng the totalvolume at 270 ml (THF + acrylonitrile). To removethe homopolymer formed during grafting, all thegrafted samples obtained by the above techniqueswere SUbjected to Soxhlet extraction for about 90 hrusing dimethyl formam ide as solvent.

M olecular weight distribution of the polyacrylonitrilegrafted polymer -- The grafted polyacrylonitrilepolymer was separated from the cellulose backboneby total hydrolysis of the cellulose support using 72 %sulphuric acid, with a liquor to material ratio of20: I. After 4 hr, the hydrolysed solution was dilutedto a concentration of 3 0:' of the acid and the solutionwas boiled in a reflux apparatus for 40 min to completethe hydrolysis. During boiling, the graft polymerseparated in the solution, which was then filtered off.The residue was puri!~cd by dir;:,;olvins in uilll~tJlJlformamidc and precipitating out with methanol.This polymer was subjected to further fractionation

SHARMA & DARUWALLA : MOL. WT DISTRIBUTION & SOLUBILITY BEHAVIOUR OF GRAFf COPOLYMER

to obtain polymer chains of more uniform molecularweight.

Fractionation of the polyacrylonitrile graft polymerwa~ ca~ried out by the proce~ure suggested by Flory7,

which IS based on the fractional precipitation of thepol~~er dissolved in dimethyl formam ide by thea?dltlOn o~ methanol. Polyacrylonitrile (10 g) wasdissolved 111 about 800 ml dimethyl formamide-methanol mixture in a 5 litres round bottomed flaskThis solution was filtered through a G2-sintered glas~fu",~el and centrifuged to remove any suspendedundissolved particles. Methanol was added to thissolution, 250 ml being sufficient to reach the firstcloud point at 30°C. The turbidity was dissolvedby raising the temperature of the flask to 40°C. Theflask was then kept immersed in a thermostat at~0:±0.05°C. The solution was then kept overnightIn the thermostat. The supernatant clear solutionwas siphoned out into another round bottomed flask.The concentrate phase in the first flask was collected.The supernatant solution was then subjected tofurther precipitation following the above procedure.In this manner, 4-5 fractions of the polymer couldbe separated out.

Determination of molecular weight -- The molecularweights of polyacrylonitrile grafts after separationf~om the cellulose backbone and subsequent fractiona-non were determined by viscosity measurements.The viscosities of polyacrylonitrile solutions ofdifferent concentrations in dimethyl formam ide weredetermined using suitable Ostwald viscometers. Themolecular weight of the polymer was determined usingthe equations

["1)J = 4.72 X 10-4 (M)O.733Determination of polydispersity index -- The mole-

cular weight (M,) of each fraction was determinedviscometrically, as described earlier. The numberaverage molecular weight (Mn) and weight averagemolecular weight (MlV) of the whole polymer wereobtained using the following equations":

1Mn l:W,M,Mw = :EW,M,

where Wi is the weight of the ith fraction.The polydispersity index (I) for the polymer is givenby the expression'?

J = MwMn

Solubility in cadoxen -- The cadoxen solvent (cad-mium, 5 :± 0.1 %; et~ylenediamine, 29 :± 1.0 %) usedwas prepared according to the method recommendedby Achwal and Gupta'v. Finely cut samples weredissolved in cad oxen solvent to obtain 0.1 ~~ solutionand the viscosity of the solution was measured at28°C using a suitable Ostwald viscometer. When the~rafted cotton sample did not dissolve completelyIII the cad oxen solvent, the solubility was determinedas follows. The grafted sample, finely cut, was addedto cad oxen solvent in a stoppered Erlenmeyer flaskand stirred for 3 hr. The solution was then filteredthrough a G3-sintered glass crucible and theamount of undissolved sample was determinedgravimetrically.

Results and DiscussionThe results obtained reveal that the average mole-

cular weights of the polymer chains in the differentfractions lie in different ranges, depending on the totalgraft add-on as well as the technique of initiationemployed (Tables 1-4). Over the range of graft add-on e~amil!-ed (2.4-18 %), when the y-irradiationtec~nlque IS employed for initiating the grafting re-action, the average molecular weight of the graftedchains is quite high (2. I x I O~ - 2 x 105) while withanionic grafting, grafted polymer chains of com-paratively low molecular weight (3.5 x 103 - 8.7 X loa)are obtained. Whe~ .. ce~ic ion and Fe2+-H202system are used for imuatmg the grafting reaction,the average molecular weights of the grafted chainsare more or less of similar order of magnitude(J.45 x 104 to 8 x 10.1) and they lie between thoseobtained using the y-irradiation and anionic initiationtechniques.

Attempts have also been made in the present studyto determine the polydispersity of grafted polymerchains obtained using different initiation techniques

TABLE 1 - MOLECULAR WEIGHT DISTRIBUTION OF POLYACRY-LONITRILE POLYMER OBTAINED FROM COTTON GRAFTED ATDIFFERENT GRAFT ADD-ONS (CERIC ION INITIATION TECHNIQUE)

Graftadd-on

%

2.4

Fraction Weight Weight MolecularNo. g fraction weight

(Wi) (Mi)

\ 0.142 0.1002 21,0002 0.326 0.2301 42,0003 0.694 0.4898 64.5004 4.255 0.1799 89,000

1 0.\21 0.0601 11,0002 0.\8\ 0.0899 32,0003 0.363 0.1802 49.0004 1.067 0.5298 79.0005 0.282 0.1400 93,500

\ 0.399 0.1801 39,5002 0.310 0.1399 60,0003 0.507 0.6801 80,500

6.2

15.8

TABLE 2 - MOLECULAR WEIGHT DISTRIBUTION 'OF POLYACRY-LONITRILE POLYMER OBTAINED FROM CoTTON FABRICS GRAFTEDAT DIFFERENT GRAFf ADD-ONS (y-IRRADIATION INITIATION

TECHNIQUE)

Graftadd-on

%

Fraction Weight Weight MolecularNo. g fraction weight

(Wi) (Mi)

1 0.139 0.0700 21,0002 0.575 0.2898 96,0003 1.151 0.5801 120,0004 0.119 0.0599 179,000

1 0.430 0.2060 123,0002 0.207 0.5783 151,0003 0.246 0.1179 180,0004 0.204 0.0977 200,000

1 0.132 0.0500 60,0002 0.211 0.0799 93,0003 0.527 0.1998 140,0004 1.583 0.6001 167,0005 0.185 0.0701 194,000

121

3.1

6.0

8.8

INDIAN J. TEXT. RES., VOL. I, DECEMBER 1976

TABLE 3 - MOLECULAR WEIGHT DISTRIBUTION OF POLYACRY-LONITRILE POLYMER OBTAINED FROM COTTON FABRICS GRAFTEDAT DIFFERENT GRAFT ADD-ONS (FERROUS-PEROXIDE INITIATION

TECHNIQUE)

Graftadd-on

0/'0

FractionNo.

Weightg

Weightfraction

(Wi)

0.09000.09990.23990.51010.0699

Molecularweight

(!vIi)

14,50032,00041,50063,50071,000

2.9 0.1920.2130.4901.0870.l49

I2345

6.5 12345

12345

0.1660.1660.4060.7570.322

15,00030,00045,00060,00080,000

8,00021,00041,00060,00080000

0.09140.09140.22340.41660.1772

18.0 0.1350.2530.6410.4890.152

0.08080.15150.38380.29280.0910

TABLE 4 - MOLECULAR WEIGHT DISTRIBUTION OF POLYACRY-LONITRILE POLYMER OBTAINED FROM Co'rrox FABRICS GRAFTED.n DIFFERENT GRAFT ADD-ONS (ANIONIC TECHNIQUE OF

INITIATION)

Graft Fraction Weight Weight Molecularadd-on No. g fraction weight

% (Wi) (Mi)

2.4 I 00407 0.3160 40002 0723 0.5613 60003 0.158 0.1227 7000

5.9 1 0.108 0.0700 35002 0.463 0.3003 45003 0.971 0.6297 5500

8.8 I 0.286 0.1997 55002 0.316 0.2207 65003 0.758 0.5293 74004 0.072 0.0503 8700

through the calculation of the polydispersity index,as interpreted by Schulz'", Values of polydispersityindex are of the order of 1.01-1.37, dependingon the method of initiation and the extent of grafting(Table 5).

These values are of a lower order of magnitudethan those obtained by Simionescu et af.12 for poly-methyl methacrylate grafted on to viscose rayonthrough the ozonization technique of grafting. Theseinvestigators employed column chromatography forfractionation, and the values of polydispersity indexare of the order of 3.5-6, depending on the condi-tions of grafting. On the other hand, Gulina et al.13obtained a very narrow range of distribution of mole-cular weight in the case of grafting of polyacrylonit-rile and polymethyl methacrylate through the Fe2-!--H202 initiation technique. The sedimentation methodfor fractionation was used by these investigators andthe values for polydispersity index obtained are of theorder of 1.5. The lower values of polydispersity indexobtained in the present study can be attributed to thefact that very sharp fractions of the polymers could

122

not be obtained through the fractional precipitation •technique and only 4-5 fractions could be separatedout satisfactorily. Polyacrylonitrile polymer ofvery low molecular weight could not be separatedinto sharp fractions even on the addition of largequantities of the non-solvent, methanol.

The solubility behaviour of grafted cottons insuitable solvents depends on the extent of graft add-on,the degree of substitution of the hydroxyl groups inthe cellulose chains during grafting and the length ofthe grafted polymer chains, all being influenced by theinitiation technique employed. For instance, when'Y-irradiation, Fe2+-H202 and eerie ion techniquesare employed, up to a graft add-on of about 3%,the grafted samples have been found to be soluble incadoxen to a considerable extent (86-98%), whilein the same range of graft add-on, samples obtainedby the anionic initiation technique are soluble onlyup to about 13~Io(Table 6). This may be due to thefact that in the case of y-irradiation, eerie ion and Fe2+-H202 techniques, the molecular weight of the polymerchains grafted on to cellulose is high, but the numberof points at which the grafts are attached to the cellu-

TABLE 5 - POLYDISPERSITY INDEX OF POLYACRYLONITRILIiPOLYMER OBTAINED FROM COTTON FABRICS GRAFTED ATDIFFERENT GRAFT ADD-ONS (DIFFERENT INITIATION TECHNIQUES)

Grafting Graft Mn Mw Mw1 = --,--

technique add-on Mn%

Cerie ion 2.4 5.00xlOe 5.90x 10e 1.186.2 4.90x lOe 6.70 x io- 1.37

15.8 6.50x lOe 7.03 x lOe 1.08

y-irradiation 3.1 8.70x lOe 1.09 x 10" 1.266.0 1.51 x 10' 1.53 x 10' 1.018.8 1.40xI0· 1.50x 10' 1.07

FeH-HsO. 2.9 4.14 x loe 5.18 x io- 1.256.5 4.75x io- 5.30 x 1()4 1.12

18.0 4.23 x 10' 4.44x lOe 1.05

Anionic 2.4 5.00x 10' 5.49 x 10' 1.105.9 4.97xI0· 5.09 x 10' 1.028.8 6.79x 10' 6.90x 10' 1.02

TABLE 6 - SOLUBILITY BEHAVIOUR IN CADOXEN OF CaTIONGRAFTED WITH POLYACRYLONITRILE AT DIFFERENT GRAFT ADD-

ONS

Grafting Graft add-on Solubility in cad oxentechnique % %Untreated cotton 100

Ceric ion 2.4 986.2 40

15.8 13

y-irradia tion 3.1 896.0 188.8 7

Fes+-HsO. 2.9 866.5 48

18.0 10

Anionic 2.4 135.9 118.8 5

SHARMA & DARUWALLA : MOL. WT DISTRIBUTION & SOLUBILITY BEHAVIOUR OF GRAFT COPOLYMER

lose backbone are less as compared to anionicgrafting, where the molecular weight of the graftedchains is low and the degree of substitution ishigh. Under these conditions, in the case of y-irradia-tion, eerie ion and Fe2+-H202 techniques, sufficientnumber of hydroxyl groups in the cellulose chains willbe available for complex formation with cadoxensolvent, resulting in higher solubility, while in anionicgrafting, a large number of hydroxyl groups areblocked during the grafting reaction and the tendencyof the grafted cellulose for complex formation withthe solvent is lower, resulting in a marked decreasein the solubility of the grafted sample.

AcknowledgementThis work forms part of the research carried out

under grant number [FG-In-466 UR-A 7-(20)-226]issued by the Agricultural Research Service, UnitedStates Department of Agriculture and the authors aregrateful for the grant received. Their thanks are alsodue to Shri T. V. Ananthan, Director, The BombayTextile Research Association, Bombay, for providingfacilities to carry out this work.

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