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Iranian Polym er Journal / V olume 10 N um ber 4 (2001)

026-1265/2001

Unsaturated Polyesters from Benzofuro[2,3-b]

benzofuran-2,9-dicarboxylic Acid'

Behzad Pourabas

Faculty of Chemical Engineering, Sahand University of Technology, P .O Box: 51335/1996, Tabriz, I

.R

. Iran

R e c e iv e d 1 6 J a n u a r y 2 0 0 1 ; a c c e p t e d 2 5 J u ly 2 0 0 1

ABSTRACT

Unsaturated polyesters because of their valuable applications and versati le

preparation are the most interesting resins among the cross-linkable

polymers and a huge volume of works is completed or currently running on

this type of polymers . This work is of those kinds resembling the incorporation

of new monomers into the ordinary unsaturated polyester resins and

investigating the influence of this monomer on the resin properties By this

way the monom er, which is of interest in this work constitutes benzofuro[2,3-

b]benzofuran-2,9-dicarboxylic acid . This monomer was synthesized by the

authors in 1996 for first time

. For polymerization, this molecule, maleic

anhydride and seve ral diols were reacted in a polycondensation reaction to

yield the unsaturated resins. The produced resins were characterized

subsequently by H NMR and IR spectra, measur ing mo lecu la r weigh t, and

inherent viscosity . On the other hand, thermal and environmental resistance

(resistance to acidic and alkaline moiety) was investigated on the cured

resins with styrene 30 (by weight), as are described in the paper Their

thermal and chem ical stability show an acceptable range o f properties.

Key Words unsa turated polyester benz ofuro-benz ofuran polycondensa tion curing thermal stability

INTRODUCTION

Unsaturated polyester resin is the

reaction product

of

an unsaturated dibasic acid or a mixture

of them

with

a saturated dibasic acid and a polyhydric alcohol

The

product is then thickened with a vinyl monomer,

mostly styrene to go to curing . Curing process takes

place by the help

of

organic peroxide [1] . Because

of

'their valuable applications,

a large

number

of

works

are

carried out by

focusing on

introduction of new

kinds

monomers [25],

curing and

processing

conditions [68] and even their modification to reach

better processing condition and properties [911] The

reader

can find

plenty of

general information about

these unsaturated resins [1216] but among them

reference 17

is a distinguished

cite because of its

(a) Part of this paper w as introduced in the 5th Iran

. Seminar on Polym

. Sci

. & Techn ol, Am ir Kabir Universi ty of Technology, 1214 Sep . 2000, Tehran.

( an ) To w hom cor respondence shou ld be addressed . E-mail : po rabs@yahoo .com

237

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Um for

rad Polyesters from Benzofircot2,3-bI benzofuran-2,9-dicarboxylicAcid

useful information especially given for the production

of these resins.

The aim of the present work is to use a

molecule namely benzofuro[2,3-b)benzofuran-2,9-

dicarboxylic acid (diacid I) into the structure of

unsaturated polyesters resins as a saturated dibasic

acid

. The diacid I, as presented below, is a relatively.

new molecule which was synthesized firstly in 1996

by the author at the University of Shiraz, Iran [18

19 )

. After that time, the diacid 11 or its derivatives

have been used in several interesting works by several

workers

. The diacid I, for example, was introduced

into polyamides by reacting with several diamines

[20] or was converted to its corresponding diamine,

and then reacted with several diacids (also including

diacid I) to produce another series of polyamides [20

21) . Several other works are published or are

currently under investigation.

According to the aim of this research work

diacid I, maleic anhydride and several diols including

ethylene glycol, diethyleneglycol, triethylene glycol,

were reacted in a polyesterification reaction and the

isolated resins were investigated by several means

t h e r e a ft e r .

EXPERIMENTAL

Materials and Instruments

Solvents and reagents were purchased from Merck and

Fluka Co . and were used without further purification.

IR Spectra were recorded by a Unicam Matteson 1000

a n d

' H N M R s p e c t r a b y a B r u k e r 2 00 M H z S p e c t r o s p i n

i n s t r u m e n t s .

Benzofuro[2,3-b[benzofuran-2,9-dicarboxylic Acid

Diacid I).

The diacid I was synthesized by the previously

published method [1920].

Polyesterification

In a 100 mL three-necked flask, equipped with stirrer,

N

2 inlet and Dean-Stark reflux condenser, diacid I

(7

.4 g, 25 mmol), diol (55 mmol) and maleic anhyd-

ride (2

.65 g, 27 mmol,) were placed . Xylene (4 mL)

and p-toluene sulphonic acid (1 g as catalyst) were

added and stirring was started . The stream of N

2

was

installed and temperature was raised and controlled at

I70180

'

C . Xylene-water mixture was distilled off as

azeotropic mixture and collected in Dean-Stark

receiver as a two-phase liquid. Xylene (upper phase)

was recycled to the reaction mixture . Due to the lower

amount of used xylene it is necessary to use a small

scale Dean-stark condenser

. The type, which was used

had a receiver of size 10 cm height with a diameter of

+ II n + HO

R

O H

HOOC

COOH

HO O C

C O O H

P I R= --CH 2 CH

P II R=CH2

C H

2 -0CH

CH - -

PIll

R= CHz--CH

2 0CH2

--CH

2

--OCH

2

C H

2

Scheme I

. Po lyes t e r i f i ca t ion and s t ruc tu re o f p repared unsa tu ra t ed po lyes t e rs .

0 0 O

C O R O C

C=C

C O R

O

+ H O

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Pourabas B.

T a b l e 1

. P a ly es t e r i f ca t io n r ea c t io n co n d i t io n s an d p h y s i ca l p ro p e r t i e s o f t h e p o ly es t e r s .

P o ly es t e r R e a c

. tim e (h ) A cid n um ber

P h y s i ca l

state

M o l

. weight

IM

.rt

b

P I

2

.5 9.5

solid 5x10 3 .035

PI I

3 6 .9 viscous

mate r ia l

4.4x10 0 .148

Pill

.5

1 5

.6 viscous

material

1 .1x104

0 .066

a)

Determined by end group analysis method (acid numbers after purification).

b) at

30

'

C for solutions of polyesters

in DMF(dLlg).

Table 2

. IR Cha racter i s t ic

peaks

for the po lyes ter res ins .

Polyester

-OH, -COO H C=C-H

C=O Peaks assigned to diacid I

(e n d gro u p s) (stre tc h in g )

( e s t e r s )

_

P I

3446 3142 3089 1726

1618 1495 777 55 3 661

P 1 1 3500 3107 3071

1725

1618 1495 777 551 861

PI I I

3589

3116

3071

1725

1618 1495 55 3 669

.5 cm

. In order to reach better efficiency and easier

placed in the receiver part of Dean-stark. Acid

numbers were checked on small sample of reaction

mixture over period of 0 .5 h

. The polyesterification

reaction stopped when the subsequent acid values had

remained unchanged.

The polyesters prepared were purified twice

from chloroform solution by precipitation with light

petroleum ether (bp 60-70

'

C).

Curing Conditions

A mixture of polyester/styrene (70/30, w/w) and

benzoyl peroxide (1 % by weight) was prepared . T h e

prepared mixtures then were applied on small glasses

Lams) as thin films

and

cured at 70 'C for 24 h.

RESULTS AND DISCUSSION

In the present work, the unsaturated polyesters were

synthesized by reaction of diacid I, maleic anhydride

and several dials (Scheme I).

In the early part of the experiments polyester-

ification reactions ran without p-toluene sulphonic

acid, (i

.e

., without catalyst). All were unsuccessful

and we had to use catalyst

. A solventless system has

preference in the polyesterification reactions, in order

to reach higher molecular weight and a product easier

for purification. In this way the reaction was difficult

to proceed at the initial stage because all the

4000 3000

2000

Wavenumber cm

f

Figure 1

FTIR Spec t ra for P I

0 2 4 6 8

ppm

Figure 2 N NMR Sp ectra for PII .

1000

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Journal Volume

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'Unsaturated Polyesters from Be000fivo[2,1-b1 benmfwan-2,9-dicarboxylic Acid

Table 3

H NM R Characteristic peaks of the polyesters.

Polyester

Heoe ; e OCH2--CH2O-

Ha

l e

P I 6 . 7 8

3

. 3 4

.0 6

.8

P

6 . 6 8 4

. 0 4 .5

6 .0

6

.4

Pil l 6 .4 -8

3 .5 -4

.8

6

.1 -6

.3

Table 4

Film properties of the

cured pol yesters

i n t e rm s o f res i s tance to a lka l i and ac id so lu t ions and a l so

elevated temperatures.

Test

P I

(% )

P I I

( )

P l t t (% )

P I V

(% )

Ac id solut ion (HCI 0

.1 N) 7 (A) 88 B)

(D )

5 (A)

A lkal i solution (NaO H 0

.1 N) 20 (A)

20 (B)

6 5 B )

3 8

(A )

E l e v a t e d te m p

. 180 (C)

35 A) 10 (C)

4 B )

24 A)

Elevated temp

. 250 (C )

40

( A ) 15 (C) 10 (B)

30 (A)

( a ) P e r c e n t

of

w e i g h t l o s t a f te r 24

h .

A )

T h e f i lm r e m a i n e d u n c h a n g e d a n d s a v e d e x c e l le n t m e c h a n i c a l p ro p e r t ie s

( B )

T h e f i lm h a d

p o o r

m e c h a n i c a l p r o p e r t i e s , b ro k e a n d

s e p a r a t e d f r o m a r e g l a s s s u b s t r a t e

(C ) T h e f i lm

u n d e r g o e s b r e a k i n g b u t

d i d n o t s e p a r a t e

f r o m t h e g l a s s s u b s t r a t e

(D ) T h e f i lm w a s

r e m o v e d c o m p l e te l y a l t e r 2 h .

i n g r e d i e n t s w e r e s o l i d ( e xc e p t d i o l ) a n d n o l a r g e r v o l u m e

of xylene would be necessary to be used

. H o w e v e r , th e

contents of the reaction vessel had became sluggish as

r e a c t i o n p r o c e e d e d . On the other hand lower amount of

xylene led us to use a Dean-Stark with small receiver

part (10 cm height and 0 .5 cm diameter) and also an

effective condenser

. Table 1, summarizes the reaction

conditions acid numbers and post-purification physical

state, molecular weight (determined by the end group

analysis, acid numbers) and intrinsic viscosity for the

p r e p a r e d u n s a t u r a te d p o l y e s t e r s .

1R Spectrum for polyester PI (Scheme I) is

shown in Figure 1 and IR characteristic peaks for all

polyesters are summarized in Table 2

. Peaks due to

the diacid I which were observed in IR spectrum of

the polyesters confirm the insertion of the diacid I in

the polyester's structures.

' H NMR Spectrum for polyester PII is shown in

Figure 2. Table 3 summarizes the characteristic

H

NMR peaks for the all prepared polyesters.

Resistance to chemical environment and thermal

properties of the cured polyesters as thin films were

investigated . Acidic (HCI 0

.1 N) and alkaline (NaOH

0

.1 N) solutions and IGA (isothermal gravimetric

analysis) were selected for this purpose

. Table 4

presents the results

CONCLUSION

It can be concluded that diacid I may be replaced for

phthalic acid in the conventional unsaturated

polyester resins and the resins could have enhanced

thermal and chemical properties as the results

showed

. However, many works, which are published

in concern with the diacid I show that it has a

potential to become a commercial molecule, but it is

necessary to find a procedure to produce it more

conveniently and by a higher yield.

ACKNOWLEDGEMENTS

Finally the author wishes to thank Sahand University

of Technology for financial supports and Fellows of

Chemical Engineering Faculty for their advice during

the present work

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