Die Angewandte Makromolekulare Chemie 155 (1987) 93 - 99 (Nr. 2543)

Departamento de Quimica (Quimica Orghnica), Facultad de Ciencias Quimicas de Tarragona, Universidad de Barcelona, Plaza Imperial Tarraco n0 1,

Tarragona, Spain

A Modification of Diglycidylether of Bisphenol A with Diimide-Diacids

Angels Serra, Virginia Chdiz*, and Ana Mantech

(Received 25 February 1987)

SUMMARY: A conventional epoxy resin derived from Bisphenol A has been modified with aro-

matic diacids containing a preformed imide ring in order to achieve an improvement in their thermal properties. These new resins were characterized by IR and i3C-NMR spectroscopy, and it was possible to verify two types of oxirane ring openings by di- imide-diacid.

ZUS AMMENFASSUNG: Ein herk6mmliches Epoxyharz aus Bisphenol A wurde mit einer Dicarbonsiiure,

die aromatische Imidgruppen enthat, modifiziert, um das thermische Verhalten zu verbessern.

Mit der IR- und i 3 C-NMR-Spektroskopie wurden die neuen Epoxyharze charakte- risiert; es war auch moglich, zwei Arten der offnung der Oxirangruppe zu bestiitigen.

Introduction

The aim of the present work was to obtain epoxy resins with increased thermal stability.

In the last years some Japanese patents have been describing the thermal stability increase of epoxy resins of diglycidylether of bisphenol A (DGEBA) derivatives when imide rings are introduced into their back- bones.

In the recent papers we described the synthesis of new epoxy resins derived from dicarboxylic acids with preformed imide rings and their corresponding

* Correspondence author.

0 1987 Hllthig& Wepf Verlag, Basel O003-3146/87/$03.00 93

A. Serra, V. Ckdiz, and A. Mantecon

diglycidyl ester^^.^. Polyesterimides with good thermal resistance were obtained.

The formation of diglycidyl esters has been reported to be difficult. There- fore we have replaced them by DGEBA in order to compare their thermal stabilities.

On the other hand this change leads to an improvement in their solubility and therefore in their processability.

The polymerization is considered to proceed as follows:

HOOC-R-Ar-R-COOH + C H 2 - C H - C H 2 - O Q ~ ~ O - C H 2 - C ~ - $ H 2 0

\ /

CH3 0

-0 C - R - A r - R - C - O - C H 2 - $ H - C H 2 - 0 ~ ~ & - C H 2 - C H - C H f 0 ? f" OH CH3 L

A r

Experimental

Materials

Diglycidylether of bisphenol A (DGEBA) was obtained by a normal reaction with

Diimide-diacids were obtained as described previou~ly~.~. N-methyl pyrrolidone (NMP) (Merck) was purified by distilling in vac. N,N-dimethylformamide (DMF) (Merck) was dried with phosphorous pentoxide

epichlorohydrin (EPC), bisphenol A, and NaOH.

and distilled under reduced pressure.

94

Modification of DGEBA with Diimide-Diacids

Polymer Synthesis

The reactions were conducted in NMP at 1 1O"C, using a reaction flask fitted with a stirrer, thermometer, and under N, atmosphere.

A typical run is as follows: 0.05 mol of diimide-diacid and 0.1 equivalent of DGEBA (on the basis of calculated E.E.) were mixed in NMP (50 ml). The mixture was heated at 110 "C and then benzyltrimethylammonium chloride (BTMA) (0.005 mol) was added to one batch. Disappearance of initial diimide-diacid was controlled by acid index measurements. When the acid index values remained constant the mixture was cooled and poured into ice water. The filtered product was washed with water and dried at room temperature in vac. for 48 h. The polymer yields were practi- cally quantitative.

Characterization and Measurements

The melting points are uncorrected and were determined on a Tottoli capillary

IR spectra were recorded on a Beckmann IR 4260 spectrometer (KBr pellets). 13C-NMR spectra were obtained with a Varian XL 200 spectrometer working at

Viscosity measurements were taken in 0.5% (w/v) solution in DMF at 30 k 0.1 "C

Thermogravimetric analyses were carried out using a Perkin-Elmer TGS-2 thermo-

The epoxy content was expressed in g/equivalent and determinated by the Jay and

The determination of the acid index was carried out as reported4.

melting point apparatus.

50.3 MHz. Samples were run in DMSO-4 with TMS as internal standard.

with an Ostwald type viscosimeter.

balance in N, atmosphere and at a heating rate of 10"C/min.

Dijkstra and Dahmen method, variation by Ciba') .

Results and Discussion

All polymerizations were carried out in N-methyl pyrrolidone using BTMA as catalyst.

The reaction course and the disappearance of initial diimide-diacid could be followed by acid index measurements.

The need of BTMA as catalyst can be seen in Fig. 1 where plots show the decrease of the acid index with increasing time.

In Tab. 1 the acid index values at the beginning and at the end of the reac- tion are collected. When these values remained unchanged, this was con- sidered as final reaction point.

95

A. Serra, V. Ciidiz, and A. Mantecon

12 ik,

j 8. , , , , , , I

0 100 200 300 Loo 500 t(min)

Fig. 1. Variation of the acid index values vs. reaction time. Diimide-diacid was 3 a; (- V -) with catalyst, ( - V -) without catalyst.

Tab. 1. Preparation and properties of polymers.

Polymer t Acid index Epoxyb) (min) begin end (dl/g) equivalent

l a 210 9.34 0.80 0.08 64800 2a 120 13.38 3.11 0.07 7 100 3a 195 15.60 0.48 0.1 1 18400 l b 300 9.54 1.23 0.06 50700 2b 190 12.14 1.73 0.05 19300 3b 120 17.12 4.19 0.10 58 400

a 0.5% solution in DMF at 3OOC. Epoxy equivalent in g/equivalent.

In the same table, epoxy equivalent values are also collected; it can be seen that they are in general high indicating the disappearance of the oxirane groups.

There are also listed the reaction times and the viscosities, whose values remained unchanged during several weeks of storage.

Solubility measurements are listed in Tab. 2. These compounds are found to be soluble in highly and medium polar solvents.

96

Modification of DGEBA with Diimide-Diacids

Tab. 2. Solubility of the polymers. ~~

Solvent

Polymer n-hexane toluene acetone CHCI, DMF DMSO NMP

l a - + + + + 2a + + 3a + + I b - + + 2b + + 3b +

- -

- -

-

- -

- -

+ + + + + + + + + + + +

+ + + + + + + + + + + +

+ + + + + + + + + + + +

+ + + + + + + + + + + +

- Insoluble; + soluble at room temperature; + soluble by heating. +

Tab. 3. Chemical shifts of the new formed unit C3C-NMR spectra in DMSO-4).

f g h

B -0-C-R-Ar-R-C-O-

H-CH2-

CH2OH

6 @Pm)

l a 69.2 67.0 65.2 61.6 72.8 59.6 2a 69.1 66.7 65.2 62.6 72.4 59.2 I b 68.8 66.7 65.0 62.4 72.2 59.2 2b 69.1 66.8 65.2 63.5 73.6 59.9 3b 68.7 66.5 68.7 63.0 74.5 59.6

Spectral Characteristics

The identification of the repeating unit was fundamentally determined from their spectral data.

97

A. Serra, V. Cbdiz, and A. Mantech

IR spectra of the resins showed strong absorptions around 3500cm-' (vOPH) and 11 10 - 1120 cm-' ( v ~ - ~ ) . We also observed the disappearance of the epoxy band at 910 cm-' and the carboxylic bands.

By I3C-NMR spectroscopy it was possible to verify two attack types to the oxirane ring. Six lines were observed in the zone between 59- 75 ppm. The more inten-

sive ones, f, g, and h, correspond to the attack on the less substituted carbon (normal opening) and the other three less intensive ones (i, j, and k) corre- spond to the attack on the more substituted carbon (abnormal opening). This fact was already reported for similar c o m p o ~ n d s ~ , ~ . In Tab. 3 spectral data of this zone are summarized. All signals of the carbons of the new formed unit appears there. It was impossible to assign unmistakably the signals in the spectrum of the polymer 3a.

Thermal Behaviour

The thermal stability of the polymers was evaluated by TGA measure- ments. The good thermal behaviour of the polymers can be made evident looking at the parameters collected in Tab. 4.

Tab. 4. Decomposition temperatures of the polymers.

Polymer T- Weight loss at temp. ("C) Weight residue (070)

("(2 10% 20% 30% 50% at 500°C ~

l a 434 352 388 41 6 440 27 2a 405 290 348 380 414 38 3a 405 290 344 374 412 36 I b 432 344 380 400 428 23 2b 41 5 290 350 376 414 26 3b 395 338 365 381 405 35

These values are comparable to previously synthesized polyester-imides. An explanation for this fact could be found if we consider the degradation mechanism. As polymer degradation takes place according to the bond energysp9 this similar loss of weight seems to indicate that in the initial step of

98

Modification of DGEBA with Diimide-Diacids

the reaction analogous bonds are broken. Notice that the residual weight percentage at 500 "C is generally smaller than that of polymers which contain a greater number of imide rings per repeating unit. However, these values are much higher than for conventional epoxy resins.

' A. Fukami, S. Eto, H. Nakajima, Jpn. Kokai 76, 131, 529 (1976) Jpn. Kokai Tokkyo Koho 82, 07,028 (1982); C.A. 97 (1983) 40008t Jpn. Kokai Tokkyo Koho 57, 145, 218 (1982); C.A. 98 (1983) 73541k A. Serra, V. Ctidiz, P. A. Martinez, A. Mantech, Angew. Makromol. Chem. 138 (1986) 185 A. Serra, V. Ctidiz, P. A. Martinez, A. Mantech, Angew. Makromol. Chem. 140 (1986) 113 J. I. Gonzhlez, J. de Abajo, S. Gonzhlez-Babe, J. Fonttin, Angew. Makromol. Chem. 55 (1976) 85

' B. Dobinson, W. Hofman, B. P. Stark, The Determination of Epoxide Groups, 1st ed., Pergamon, London 1970, p. 40 C. S. Chen, B. J. Bulkin, E. M. Pearce, J. Appl. Polym. Sci. 28 (1983) 1077 J. Sickfeld, W. Mielke, Prog. Org. Coat. 12 (1984) 27

99