KINETICS OF RADIATION INDUCED GRAFTING OF DIMETHYL­ACRILAMIDE (DMAA) ONTO ETHYLENE TETRAFLUOROETHYLENECOPOLYMER (AFLON COP) FILM

Mirzan T. Razzak*

ABSTRACT

KINETICS OF RADIATION INDUCED GRAFTING OF DlMETHYL-ACRILAMIDE(DMAA) ONTO ETHYLENE TETRAFLUOROETHYLENE COPO-LYMER (AFLON COP)FILM. Attempt has been made for grafting of hydrophilic monomer, dimethylacrylamide, DMAA,onto a film of ethylenetetratluoroethylene (AFLON COP) and its kinetics were studied. The graftingwas carried out by a simultaneous irradiation technique. It was found that the DMAA monomer couldbe grafted easily onto AFLON COP film in the presence of either acetone or ethylacetate as a solvent.The dependence of the rate of grafting on monomer concentration was found to be 2.00 and 2.37 in thepresence of acetone and ethylacetate solvent, respectively. The overall activation energy for the graft­ing process was calculated to be 11.55 kcallmole. The rate of grafting was found to be proportional to0.5 power of dose rate. These activation energy and the rate dependence values indicate that the graft­ing of DMAA onto AFLON COP film was proceeded by a free radical mechanism. Appropriate irradi­ation dose for the grafting was then determined to be 0.75 kGy at room temperature and at DMAAconcentration in the range of 23 to 50 vol %.

AIlSTRAK

KINETIKA RADIASI GRAFTING MONOMER DI-METILAKRILAMII>A (DMAA)KEPADA FILM KOPOLIMER ETILEN TETRAFLUORAETILEN (AFLON COP). Telah di­lakukan upaya menggrafting monomer hidrofilik di-metilakrilamida (DMAA) kepada film kopolimeretilentctratluoroetilen (AFLON COP) dengan teknik rad'iasi secara simultan. Kinetika grafting selanjut­nya diamati secara seksama. Didapatkan bahwa monomer DMAA dapat digrafting dengan mudahkepada film AFLON COP bila aseton atau etilasetat digunakan sebagai salah satu pelarut. Laju graftingdidapatkan berbanding langsung dengan pangkat 2 dan pangkat 2,37 dari konsentrasi monomer bilamasing-masing digunakan pelarut aseton dan etil asetat. Laju grafting juga berbanding langsung denganpangkat 0,5 dari laju dosis radiasi dan energi pangaktifan didapatkan sebesar 11,5 kcal/mol. Hal inimenllnjukkan bahwa proses radiasi grafting monomer DMAA kepada film AFLON COP berlangsllngdengan mekanisme radikal bebas. Dosis radiasi 0,75 kGy dan konsentrasi monomer DMAA dalamdaerah 23-50 vol % yang diiradiasi pada temperatur ruang dapat menghasilkan kadar grafting yangoptimal.

INTRODUCTION

Alternate copolymer of ethylentetratluoroethylen (AFLON COP) is an at­tractive tluoropolymer as well as polytetratluoro ethylene (PTFE).

There are 50 mol % of ethylene units besides 50 mol % of tetratluoroethyl­ene units in the component of AFLON COP. As a consequence of the exitence of

* Center for the Application of Isotopes and Radiation, SATAN

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this ethylene units, it can be expected that AFLON COP may has a relatively higher

graftabil ity.Radiation induced modification of AFLON COP as well as modification of

polytetrafluoroethylene (1) by grafting of hydrophilic monomer has an essentialpractical interest. This is because the grafted fluoropolymers can be used for bloodcompatible materials (4) and reserve osmosis membranes (5) or other specific appli­cation.

It has been reported previously (2) that N,N,Dimethylacrilamide (DMAA)monomer exhibits a good blood compatibility when it is grafted onto PTFE (1) andonto natural rubber tubes (2, 3).

In the present work, attempt has been made to grafting of N,N dimethyla­crylamide (DMAA) onto the AFLON COP film and its kinetics was studied.

EXPERIMENTAL

Materials. Ethylenetetrafluoroethylene copolymer (AFLON COP) film of 50um thick (sp.grav. 1.73 gr/cm3) was supplied by Asahi Glass Co-Ltd. The AFLONCOP film was cut into sample size of 3.50 x 3.50 em, washed thoroughly with tapwater and detergent and distilled water. It was then dried in vacuum for at least 2hours at room temperature and weighed.

N,N dimethylacrylamide (DMAA) monomer CH2-CH-CO - N (CH3)2' waspurchased from Kohjin Co-Ltd. (Japan) and used as received.

Other reagent grade chemicals were used directly without further purifica-tion.

Grafting Procedure. The procedure of grafting was carried out by a simul­taneous (direct) irradiation method as follows:A weighed AFLON COP sample film was placed in a specially designed glassampoule and then a given volume of DMAA monomer solution was introduced intothe glass ampoule.

The ampoule was connected to a vacuum line apparatus and it was degassedby an alternate freezing and thawing cycles to obtain a degree of vacuum to be 10.4torr.

The ampoule was warmed-up to room temperature and irradiated withgamma rays from a Cobalt-60 source at a given dose and dose rate. Dosimetry wasconducted by ferroussulfate (Fricke) dosemeter.

The irradiated AFLON COP sample was then taken out from the glassampoule, washed and soaked avernight in distilled water. It was then boiled in dis­tilled water for 6 hours to extract completely the residual monomer and the homo­polymer involved in the sample.

The sample was dried under vacuum for 24 hours at room temperature, andweighed.

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The percent of grafting was calculated by the following equation,

Degree of grafting (wt%) Wg - Wo x 100Wo

where Wo and Wg represent the weights of the initial and grafted film, respectively.Infra Red Measurement. Infra red spectra was recorded by an attenuated

total reflection (ATR-IR) technique using a JASCO IRA-2 grafting infra red spec­trophotometer.

RESULTS AND DISCUSSION

Effect of Solvent. Effect of solvent on the yield of grafting is indeed verycomplex. However, it has been known that appropriate solvent should be selected toobtain a high grafting yield.

Accordingly, the different in capability of solvent to swell the trunk polymerwill affects significantly the yield or grafting.

Table I shows the degree of grafting that can be achieved, when differentsolvents are used for radiation-induced grafting of DMAA onto AFLON COP films.

As can be seen in Table 1, acetone and ethyl acetate are two kinds of sol­vents that capahle to produce a relatively high degree of grafting i.e. 101 % and 68wt%, respectively. From these results, the kinetic study of radiation-induced graft­ing of DMAA onto AFLON COP film is carried out in the present of acetone orethyl acetate as a solvent. Fig. 1 shows the degree of grafting which can be obtainedin the presence of acetone as it was compared with the presence of ethyl acetate as asolvent. It can be seen in Fig. 1, the degree of grafting increases as the irradiationtime increases, hut the initial rate of grafting in acetone was found to be higher thanthat in ethyl acetate. From the slope of the curve of Fig. I, it can be calculated butthe initial rate of grafting is 2.63% /h and 1.08% /h in the presence of acetone andethyl acetate, respectively. These values demonstrate that acetone is a better solventfor grafting of DMAA onto AFLON COP as far as the degree of grafting in con­cerned .

Effect of Monomer Concentration. Effect of monomer concentration ongrafting of DMAA onto AFLON COP film is shown in Fig. 2. It can be seen thatthe degree of grafting, for any cases of monomer concentration, increases withirradiation time (dose). Moreover, the higher the monomer concentration the higherthe rate and the degree of grafting at a given irradiation time.

Fig. 3, shows the logarithmic relationship between the rate of grafting andDMAA concentration. The dependence of the rate of grafting on monomer concen-

tration was found to he 2.00 and 2.37 in the present of acetone and ethyl acetate,

175

respectilvely. Such dependence is lowered in case of acetone as a solvent, it may be

attributed a better diffusion of monomer Into the Interior region of the APLON COPfilm.

Effect of Temperature. Effect of temperature on grafting yield is shown inFig. 4. As can be seen in Fig. 4, the degree of grafting increases with irradiationtime and the higher temperature resulting the higher rate of grafting. These suggestthat the diffusion of viscous is hindered at a lower irradiation temperature (for

example at O°C). Consequently, the rate and the degree of grafting become lower asat it is compared to those obtained at elevated temperature.

In general, the elevating of temperature may facilitates the diffusion ofmonomer as well as the mobility of chain segment. In other words, the increasing oftemperature may causes the enhancement of monomer diffusion and therefore causesthe increase in initial rate of grafting.

However, the increase in chain segment mobility favors the bimoleculartermination of primary and growing chain radicals. The later obviously decreasesthe rate and the degree of grafting.

Arrhenius plots for this grafting system is shown in Fig. 5. The overallactivation energy for the grafting process was calculated to be 11. 15 kcal/mol.

This value suggests that the grafting of DMAA onto AFLON COP wasproceeded by a free radical mechanism and it is also markedly influenced by theirradiation temperature.

Effect of Dose Rate. Effect of dose rate on radiation-induced grafting ofDMAA onto AFLON COP film in the present of ethyl acetate as a solvent is repre­sented in Fig. 6. It can be seen that the degree of grafting increases with irradiationtime (dose). At a higher dose rate, the degree of grafting was found to be leveled offfaster than that at lower one. This demonstrates that the recombination of free radi­

cal should be faster at a higher dose rate and it was followed by termination of graft­ing reactions.

Fig. 7, shows the logarithmic relationship between the rate of grafting anddose rate. From the slope of those above logarithmic plots, the rate of grafting wascalculated to be proportional to 0.5 power of dose rate.

This value indicates that the grafting of DMAA onto AFLON COP was

proceeded by a free radical mechanism and it is proceeded only with bimoleculartermination of growing chain radicals.

Infra Red Spectra. In order to prove spectroscopically whether the DMAAmonomer is grafted onto AFLON COP film, infra red spectra of grafted AFLONCOP film (AFLON-g-DMAA) was compared to that virgin AFLON COP film.

As can be seen in Fig. 8, the grafted film gives the absorption peak near1620 cm-I which is ascribed to -C=O stretching vibration comes from DMAA.

On the other hand, the peak near 1160 cm-I is ascribed to -CF stretchingvibration and it comes from AFLON COP.

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This IR spectra proves clearly that the existence of grafted chain of DMAAin the grafted AFLON COP.

CONSCLUSION

Dimethylacrylamide (DMAA) monomer can be grafted easily onto copoly­mer of ethylenetetratluoroethylene (AFLON COP) film in the presence of acetone orethylacetate as a solvent. The grafting process was found to be markedly affected bymonomer concentration, irradiation, irradiation temperature, dose and dose rates.

The overall activation energy was calculated to be 11.15 kcl/mol and therate dependence can be summarized as the following equation: Rp = k .10.5. M2,

where Rp is the initial rate of radiation-indu'ced grafting of DMAA onto AFLONCOP, k is a coefficient, I is the dose rate (kGy/ha) and M is DMAA concentrationin acetone (vol %).

It was also can be concluded that total dose of 0.75 kGy and DMAA concen­tration in the range of 23 to 50 vol % are appropiate conditions to obtain a reasona­hie degree of grafting.

ACKNOWLEDGEMENT

Author gratitutes to Prof. Yoneho Tahata and Dr. K. Otshuhata for valuahlediscussion.

REFFERENCES

1. MIRZAN, T.R., OTSUHATA, K., and TABATA, Y, Radiation-induced graft­

ing of N,N-dimethylacrylamide onto polytetratluoroethylene, J. of AppliedPolymer Science 33 (1987) 2345.

2. MIRZAN, T.R., OTSUHATA, K., TABATA, Y., OHASHI, F., andTAKAUCHI, A.T., Modification of natural rubber for biomaterials. (1) Radia­

tion induced grafting of N,N dimethylacrylamide onto natural rubber tubes, J.of Applied Polymer Science 36 (1988) 645.

3. OTSUHATA, K., MIRZAN, T.R., TABATA, Y., OHASHI, F., andTAKAUCHI, AT, Improvement of antithrombogenicity of a tluoropolymer byradiation-induced grafting of hydrophilic monomer, J. of the Chemical Societyof Japan, Chemistry and Industrial Chemistry lQ (1985) 1935.

4. OTSUHATA, K., RAZZAK, M.T., COSTANARES, R.L., TA BATA, Y.,OHASHI, F., and TAKAUCHI, A.T., Effect of surface texture grafted film onantithromhogenicity, Radiat. Phys. Chem. 25 3-6 (1985) 537.

5. DESSAUKI, M., HEGASHI, A., and AHMED, M.D., Preparation and selectedproperties of ioncontainig reverse osmosis membranes, RadiaL Phys. Chern. 283 (1986) 273.

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Tabel 1. Effect of solvent on grafting of DMAA onto AFLON COP

film by simultaneous irradiation method*

Sample

GP 3 - 1GP 3 - 2GP 3 - 3GP 3 - 4GP 3 - 5GP 3 - 6GP 3 - 7GP 3 - 5

Solvent

WaterMethanolEthanol

MethylethylketoneEthylacetateCarbontetrachlorideChloroformAcetone

Degree of grafting( wt% )

0.110.950.9512.0068.002.043.80

101.00

* Grafting conditions :Irradiation dose rateTotal irradiation dose

Irradiation temperatureDMAA concentration

178

1.SO kGy /h3.00 kGy300C23.10 Vol %

3:J

• Acetone

• Ethyl acetate

o

o IJ. 2 4 5

Irradiation time (hr)

Figure 1. Degree of grafting vs. irradiation time curves for grafting DMAA ontoAFLON COP in the presence of ethylacetater and acetone .

Dose rate 0.10 kGy, DMAA conc. 23 Vol % and irradiation temperature25°C

179

200

1&0

b.Oc::

;E 120'"•...b.O

,....oQ)

~ 80~o

40

D MAA concentration

•. = 23 Vol % in Etac.6. = 60 Vol% in Etac.Ii = 80 Vol% in Etac.o = 23 Vol% in Acetone• = 60 Vol% in Acetone

I) 1 2 3

Irradiation time (hr)

Figure 2. Degree of grafting vs. irradiation time curves for grafting of DMAA ontoAFLON COP at various monomer concentrations

Dose rate O. JO kGy, DMAA cone. 23 Vol % and irradiation temperature25°C

180

10

• : DMAA in acetone

A : DMAA in ethyl acetate

0,11 2 l~

DMAA (Vol %)

Figure 3. Log-log plots of grafting rate VS. DMAA concentration in acetone andethyl acetate

Dose rate 3.30 kGy/h and irradiation temperature 27°C

181

!)lJ

• = 0 °C

-' ~, 25°C

• = 45 °C

I•-e..

lJ 1 2 3 q

Irradiation time (hr)5 6 7

Figure 4. Effect of temperature on radiation induced grafting of DMAA ontoAFLON COP

DMAA concentration 23 Vol % in ethyl acetate and Dose rate O. 10kGy/h

182

10

---­•....

..s::--o-­o'--'

Ea = 11.15 Kcal/mole

0.1

5.0 3.2 3.4

liT X 1000

3.5

Figure 5. Arrhenius plots of radiation induced-grafting of DMAA onto AFLONCOP

The grafting conditions are the same as in Figure 4

183

20 r /".......•'""""

•~

D,.~'-'" CD 15 . ~c: ;E

~~

'"

•...CD

~?6'0 10 (1)

~~(1)•...

~I/6 • ~3.30kGy/h

CD (1)Q JIi. 0 =- 1.00 kGylh

A = 0.60 kGy/h

r/::, = 0.10 kGy/h

•

•.•..0

246

Irradiation time (hI')

Figure 6. Effect of dose rate on radiation-induced grafting of DMAA onto AFLONCOP

DMAA cone. 23 Vol% in ethylacetate. Irrad. temp. 25"C

184

10

.~ ••..........

R = C 10.5p

0,1(1,1 1

Dose rate (kGy/hr)

j(1

Figure 7. Logarithmic relationship between the rate of grafting and dose rate onradiation-induced grafting of DMAA onto AFLON COP

DMAA concentration 23 Vol % and irradiation temperature 27°C

185

+

-cia1620 cm-1

116p crn-1

+

MnJ 2800 1900 1600 1300 1000 700

186

Wavenumber (em-I)

Figure 8. IR spectra of AFLON-g-DMAA and virgin AFLON COP