Die Angewandte Makromolekulare Chemie 64 ( 1 977) 169-1 77 ( N r . 945)

High Polymer Division of the Shri Ram Institute for Industrial Research, 19, University Road, Delhi-7, India

Effect of y-Irradiation on Bisphenol-A Based Unsaturated Polyesters-Part I1

S. K. Gupta* and R. T. Thampy**

(Received 5 November 1976)

SUMMARY: Unsaturated polyesters made by using bisphenol-A, dimethyl-di-(3,5-dichloro-4-hydro-

xyphenyl) methane, and dimethyl-di-(3,5-dibromo-4-hydroxyphenyl) methane, respective- ly, were exposed to a dose of 18 Mrad from a Co60 source. On irradiation, there is very little change in the halogen content in the polyesters, determined by Parr Bomb method. This indicates their stability to y-irradiation. Study of acid value, intrinsic viscosity and isomerisation of these polyesters before and after irradiation corroborates to some extent that incorporation of aromatic rings in the polyester chain stabilises it against radiation. Minor changes in acid values and intrinsic viscosities are discussed.

ZUSAMMENFASSUNG : Ungesattigte Polyester aus Bisphenol-A bzw. Dimethyl-di-3,5-dichlor-4-hydroxyphe-

nyl-methan und Dimethyldi-3,5dibrom-4-hydroxyphenyl-methan wurden einer 18 Mrad Dosis aus einer Co60-Quelle ausgesetzt. Untersuchungen des Halogengehalts, der Saure- zahl, der Grenzviskositat und des Isomerengehalts vor und nach der Bestrahlung deuten auf eine verhaltnismal3ig hohe Strahlungsbestandigkeit hin.

Introduction

In continuation of our earlier studies' - 4 on chemical resistant polyesters, especially effect of y-irradiation on chlorendic acid based polyesters, it was felt worthwhile to study the stability of polyesters based on bisphenol-A, dimethyl-di-(3,5-dichloro-4-hydroxyphenyl) methane and dimethyl-di-(3,5- dibromo-4-hydroxyphenyl) methane to y-irradiation, and to correlate these

* Materials Group, Vikram Sarabhai Space Centre, Trivandrum - 695022. ** Shri Ram Institute for Industrial Research, Delhi - 11OOO7.

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studies with the structure of the polyesters. In order to do that, these polyesters were irradiated with a Co60 source. Halogen content, amount of carboxyl groups by acid value, intrinsic viscosity, isomerisation of unsaturation of the irradiated and of the original samples were determined and these were correlated with the structure of the polyester.

Experimental

Polyesters Containing Bisphenol-A and i t s Halogenated Deriuatiues

Bisphenol-A,dimethyl-di-(3,5-dichloro-4-hydroxyphenyl)methane, and dimethyl-di-(3,5- dibromo-4-hydroxyphenyl) methane, were condensed with chloromethyl acetate to form diester ether of respective bisphenols. With one mole of these diester ethers of bisphenols, two moles of propylene glycol were condensed by transesterification to give diols. These diols were polycondensed with two moles of maleic anhydride and one mole of propylene glycol for 2 h, resulting in base polyesters. The detailed preparation of these polyesters has been published earlier*).The compositions of these polyesters are given in Tab. 1.

Tab. 1. Composition of Bisphenol-A based Polyesters.

Resin Kind of bisphenol Bisphenol Maleic Prop ylene No. derivative anhydride glycol

(mol) (mol) (mol)

1 Bisphenol-A 1 2 3 2 Dimethyldi-(3,5-dichloro-4- 1 2 3

3 Dimethyldi-(3,5-dibromo-4- 1 2 3 hydroxyphenyl) methane

hydroxyphenyl) methane

Source of Irradiation

Cobalt6" source supplied by the Atomic Energy Commission Canada, Chalk River, Ontario, Canada, and installed in the Indian Agricultural Research Institute, Delhi, was used. It is a 1999 curie source of 220 gamma cells.

Dosimetry

Dose rates were determined with a Fricke dosimeter6 using G(Fe3')= 15.5, c(Fe3+)=2225 I/mol cm at 304 mp. The dose was 2400 rad/min for Fricke dosimeter.

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Irradiation of the Samples

The powdered polyester resins were filled in pyrex tubes. These tubes were sealed under vacuum. These tubes containing polyester samples number 1 , 2, and 3 were irradiated in the gamma cell mentioned above for 125 h.

Thus total energy received by the polyester is 2400x 125 x 60= 18OOOOOO= 18 Mrad.

Determination of Halogen Content by Alkoxide Method

About 0.2g of the polyester was weighed accurately and transferred into a 250ml conical flask and dissolved in 20ml of isopropyl alcohol. About 2.5 g of metallic sodium was introduced into the flask and the content was refluxed for 2 h. The excess sodium was dissolved in 50% isopropyl alcohol. The content was boiled for another lOmin, diluted and neutralised with dil. nitric acid. Standard silver nitrate was added in slight excess and coagulated the silver chloride and silver bromide. The excess silver nitrate was estimated by titrating against potassium thiocyanate solution using ferric ammonium sulphate as indicator. The end point is the appearance of red ferric thiocyanate colour. Side by side, blank determination was carried out. The halogen content is given by the following formulas:

% of chlorine 35.46(B - A) N W

80(B -A) N w % of bromine =

B =Volume in ml of standard potassium/thiocyanat solution required for the blank

A = Volume in ml of standard potassium/thiocyanate solution required for the test

N =Normality of standard potassium/thiocyanate solution. W = Weight of polyester taken for estimation. Results are given in Tab. 2.

determination.

with polyester.

Tab. 2. Halogen content in polyester before and after irradiation by alkoxide hydrolysis method.

Resin No. Halogen before irradiation Halogen after (%) irradiation (%)

2 3

0 Chlorine 14.6 Bromine

16.4 Chlorine 18.9 Bromine

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Determination of Chlorine and Bromine Contents by Parr Bomb Method 0.200 to 0.225 g of finely powdered sample of the polyester was added to a clean, dry,

22ml Parr bomb cup. 0.5g of dry powdered sugar and a standard measure (15g) of NalOa was added. The bomb was closed tightly with the lid and the retaining rings, and shaked vigorously to mix the contents. Then 2ml of water was added to the depression in the bomb cover. A very low Bunsen flame was applied to the bomb. The air was adjusted to the burner to give a cone about 1 '/2" in height. The apex of which was just short of contact with the bottom of the bomb. It was allowed to heat until the water in the lid started to boil.

When the bomb was cooled, it was removed from the quenching bath. It was rinsed off with water and opened. The bomb cup was placed on its side in a clean 600ml beaker and water was added until about half covered. The bomb cover was rinsed off thoroughly with water, catching the rinsings in the same beaker. The beaker was covered with a watch glass and it was heated slightly until the content of the bomb was dissolved. The bomb cup was removed and rinsed thoroughly with water, catching the rinsings in the same beaker. After adding 2 to 3 drops of indicator, the solution was neutralised with H N 0 3 and an excess of 5 ml of HN03 was added. 2 ml of nitrobenzene and 50 ml of 0.1 N AgN03 solution were added. The solution was stirred until AgCl or AgBr became a spongy mass. The solution was filtered through a weighed gauch funnel quantitatively. The residue was dried at 100°C for one h. Then the gauch funnel was weighed along with the residue. The percentage of chlorine and bromine was calculated as follows:

Wt. of the residue 35.5 ,00 "/, of chlorine in the sample = x -

Wt. of sample taken 143.5

Wt. of the residue % of bromine in the sample = Wt. of sample taken 188

Results are given in Tab. 3.

Tab. 3. Halogen content in polyesters before and after irradiation by Parr bomb method.

Resin No. Halogen before Halogen after irradiation irradiation (%) ( %)

2 3

20 34

19.5 32.5

Determination of Acid Value

About 2.5 g of polyester resin was dissolved in 50ml of benzyl alcohol. This solution was titrated against standard alcoholic KOH, using methyl red as indicator'. Results are given in Tab. 4.

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y-Irradiation on Unsaturated Polyesters

Tab. 4. Acid values of polyester before and after irradiation.

Resin No. Before irradiation After irradiation

1 26 29 2 25 27 3 22 16

Determination of Intrinsic Viscosity

Specific viscosities of the polyester solutions of 2 %, 1.75 %, 1 .5 %, 1.25 %, 1 %, 0.75 %, 0.5%, and 0.25% concentration in benzyl alcohol were determined with the help of Ostwald viscometer in a thermostat at 30°C. The extrapolation of a,& to zero concentra- tion gave the intrinsic viscosity [ a ] . The intrinsic viscosities of these polyesters were determined before and after irradiation, the results are shown in Fig. 1.

o s o ~ f '

::: 0,o 1 1,5 20

OO 0,5 100 Concentration (%) -

Fig. 1. Intrinsic viscosities of polyesters (resin No. 1, 2, 3 ) before and after (l', 2', 3') irradiation.

Quantitative Estimation of Isomers by IR-Spectroscopy

For quantitative estimation of maleate and fumarate in unsaturated polyesters, techni- ques developed in our laboratory were used'. The results of maleate/fumarate estimation before and after gamma irradiation are given in Tab. 5 .

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Tab. 5. Estimation of isomers by IR-spectroscopy.

Resin No. Before irradiation After irradiation

Maleate Fumarate Maleate Fumarate ( %) ( %) (%I ( %)

1 2 3

16.7 83.3 17.1 82.9 14.7 85.5 15.0 85.0 13.5 86.5 13.8 86.2

Discussion

The aim of our studies as reported earlier is to develop polyesters having combination of properties like chemical resistance, heat and flame resistance, low dielectric constant along with low dielectric losses and stability to radiation. In this connection polyesters based on chlorendic acid and isophthalic acid were evaluated earlier'.2,4. It revealed that incorporation of isophthalic acid helped to attain the combination of properties up to limited extent, and com- position number 3 containing chlorendic acid and isophthalic acid in the ratio of 3/2 mol seems to be the best compromise to obtain the above mentioned properties in the chlorendic acid based polyesters. But still the radiation damages are appreciable in this composition. This may be because of the distance between the aromatic rings in the .chain and other groups like chlorendate, fumarate etc. in the chain. Therefore, as described earlier5 polyester No. 1, 2, and 3 were synthesized by incorporating bisphenol-A, di- methyl-di-(3,5-dichloro-4-hydroxyphenyl) methane and dimethyl-di-(3,5-di- bromo-4-hydroxyphenyl) methane in the chain, respectively.

In order to find the effect of irradiation on these polyesters, a dose of 18 Mrad was given to them and they were studied for structural changes.

These polyesters were analysed for chlorine and bromine contents before gamma-irradiation and after gamma-irradiation by mild method like alkoxide hydrolysis of halogens' and by drastic method i.e. Parr bomb method. In case of polyester No. 1, there is no halogen, whereas polyester No. 2 contains chlorine and polyester No. 3 contains bromine. Values of chlorine content before and after irradiation in polyester No. 2 by Parr bomb method are 20 and 19.5% (Tab. 3). From this it may be inferred that there is almost no change in the chlorine content after irradiation, and the polyester No. 2

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is stable to irradiation. But the chlorine content results by alkoxide hydrolysis, i.e. 0% before irradiation and 16.4% after irradiation in polyester No. 2 (Tab. 2) are somewhat strange. This may be ascribed to the fact that C-Cl bond in dimethyl-di-(3,5-dichloro-4-hydroxyphenyl) methane is stronger" than C-Cl bond in cyclic and acyclic compounds and alkoxide method, being mild one, hardly imparts sufficient energy to break C-Cl bond in polyester No. 2 before irradiation. Alkoxide method becomes effective after irradiation. This may be attributed to photoionisation of chlorine from the benzene nuclei of dimethyl-di-(3,5-dichloro-4-hydroxyphenyl) methane".

Hydrolysis of chlorine by alkoxide method in polyester No. 2 after irradiation may also be assigned to non-adiabatic skips of electrons, involved in chlorine and carbon of dimethyl-di-(3$-dichloro-4-hydroxyphenyl) methane from one energy curve to another energy curve without dissociation. This unusual behav- iour may be understood by recalling that the concept of potential energy curves is meaningful only within the frame work of the Born-Oppenheimer approximation, itself valid only if the nuclei move with infinitesimal velocity. In rigid molecules like benzene it is never the case. Therefore, dissociation of chlorine from polyester No. 2 may be an improbable and more leisurely process on irradiation. But it facilitates the hydrolysis.

In polyester No. 3, values of bromine content before and after irradiation by Parr bomb method are 34 and 32.5% (Tab. 3). From this, it appears that polyester No. 3 is stable to irradiation as there is very little change in bromine content. The results of bromine content by alkoxide hydro- lysis method, i.e. 14.6% before and 18.9% after irradiation are similar to dimethyl-di-(3,5-dichloro-4-hydroxyphenyl) methane based polyesters, to some extent. But in this case, there is some hydrolysis of bromine from tetrabromo bisphenol-A by alkoxide hydrolysis method. This may be attributed to the lower bond strength of C-Br linkage in polyester No. 3 than the bond strength of C-Cl linkage in polyester No. 2. In this case, also there may be photoionization of bromine radical from polyester No. 3. From the results it seems that even after irradiation, hydrolysis of bromine from polyester No. 3 alkoxide method is not effective. This may be due to the much higher atomic weight of bromine than that of chlorine. There may be deposition of energy in the electrons involved in the C-Br linkage of polyester No. 3 by non-adiabatic skips from one energy curve to another energy curve as in case of polyester No. 2.

These three compositions were also studied for carboxylic groups which are indicated by the acid value (Tab. 4). The acid values of polyesters No.

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1, 2, and 3 were 26, 25, and 22 respectively before irradiation. The s k h t increase in acid values on irradiation of bisphenol-A based polyesters may be attributed to the fission of glycol groups to give carbon dioxide and free carboxylic acid groups as it happened in isophthalic acid based polyesters and terephthalate polyesters. In case of polyester No. 3, there is little decrease in acid value. This is not understood properly. Tt may be assigned to the probable initiation of decarboxylation by bromine radicals.

If we look at Fig. 1 which gives the intrinsic viscosities determined in benzyl alcohol solution before and after irradiation, the results corro- borate the inference derived from acid value data. The intrinsic viscosities of polyester No. 1, 2, and 3 before irradiation were 0.057, 0.053, and 0.050, respectively. After irradiation these values got changed to 0.050, 0.040, and 0.035, respectively. From this, it is clear that there is very little change in intrinsic viscosity of bisphenol-A based polyesters (polyester No. 1). It may be due to very little degradation and crosslinking taking place in bisphenol-A based polyesters. This may possibly be attributable to the sponge type protec- tion by which an aromatic system can delocalize radiation energy and subse- quently degrade it. However, little decrease in intrinsic viscosity of halogenated bisphenol-A based polyesters (polyester No. 2 and 3) indicates slight degrada- tion. It may be ascribed to the low energy required for formation of chlorine and bromine radicals which may help in fission of the chain by abstracting hydrogen atoms.

Almost no change in stereomutation data before and after irradiation of these polyesters is noticed and this further corroborates the sponge type protection of aromatic systems and also shows the absence of sensitizer activity of the carboxyl group associated with halogenated acids.

The authors are thankful to the authorities of the Indian Agricultural Research Institute, Delhi, for providing radiation facilities, and Dr. Gupta is grateful to the authorities of VSSC, Trivandrum, for permitting to publish this work.

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S. K. Gupta, R. T. Thampy, Angew. Makromol. Chem. 6 (1969) 161

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