New unsymmetrical cycloaliphatic epoxypolyesterimides

Die Angewandte Makromolekulare Chemie 199 (1992) 75-85 (Nr. 3457)

Departament de Quimica (Organica), Facultat de Cikncies Quimiques de Tarragona,

Universitat de Barcelona, Plaqa Imperial Tarraco 1, 43005 Tarragona, Spain

New unsymmetrical cycloaliphatic epoxy pol yes terimides

Antoni Roig, Angels Serra*, Virginia Cadiz, Ana Mantecon

(Received 24 October 1991)

SUMMARY: New bisepoxy unsymmetrical cycloaliphatic derivatives have been synthesized. The

different reactivity of both oxirane rings (cycloaliphatic and glycidylic) has been tested against carboxylic acids giving rise to normal and abnormal opening to the glycidyl group. Homopolymerization reaction was also observed. Polymer structures were identified by I3C NMR spectroscopy. Thermal analysis carried out allowed to confirm their good thermal properties.

ZUSAMMENFASSUNG: Es wurden neue unsymmetrische cycloaliphatische Bisepoxyderivative hergestellt.

Die unterschiedliche Reaktionsfahigkeit der zwei Oxiranringe (cycloaliphatisch und glycidylisch) gegeniiber Carbonsaure wurde untersucht, wobei eine normale und ano- male Ringoffnung der Glycidylgruppen beobachtet wurde. Eine Homopolymerisation des Oxirans wurde ebenfalls beobachtet. Mit Hilfe der I3C-NMR-Spektroskopie wurde die Struktur der Polymeren ermittelt. Die neuen Epoxidharze zeigen gute ther- mische Eigenschaften.

Introduction

According to the studies carried out in our laboratory, whose objectives are to prepare new epoxy resins of increased thermal stability, we had reported the improvement in the thermal properties of diglycidyl epoxy resins including aromatic and preformed imide rings on their backbone I s 2 .

The more rigorous demands from increasingly complex technologies have led to other types of epoxy resins being synthesized. Thus, we describe in this paper the synthesis of several resins replacing the aromatic rings in the

* Correspondence author.

0 1992 Huthig & Wepf Verlag, Basel CCC 0003-3146/92/$05.00 75

A. Roig, A. Serra, V. Cadiz, A. Mantecon

backbone by cycloaliphatic structures which can lead to compact molecules with increased crosslink density. The fact that there are no linear aliphatic spacers in the skeleton of the polymers imparts rigidity to the thermoset resins; simultaneously, T, values increase with the corresponding variation of curing temperatures.

These resins have been synthesized from carboxylic diacids and unsymmetrical diepoxy monomers, the oxirane rings of which show different reactivity against a nucleophilic agent. Therefore, it was possible to obtain linear polymers with well defined epoxy cycloaliphatic end groups, capable to crosslinking.

Likewise, the presence of hydroxy groups directly attached to the backbone must enhance this crosslinking with anhydrides.

Experimental

Reagents

Nadic (bicyclo[2.2. I] hept-5-ene-2,3-dicarboxylic) and cis-I ,2,3,6-tetrahydrophthalic anhydride (Fluka), epichlorohydrin (Scharlau) and benzyltrimethylammonium chloride (BTMA) (Merck) were used without further purification.

m-Chloroperbenzoic (MCPB), succinic, adipic and itaconic acid (Probus) were used as supplied.

All solvents were purified by distillation before use.

Synthesis of imide derivatives

Nadimide (Ia) and cis-I ,2,3,6-tetrahydrophthalimide (IIa) were synthesized from the corresponding anhydrides and ammonium carbonate by fusion. Nadimide was purified by solving in benzene and precipitation with n-hexane (m. p. 164- 165 "C); cis-l,2,3,6-tetrahydrophthalimide was purified by recrystallization from CCl, (m. p.

The preparation of N-propylnadimide (Ib) and N-propyltetrahydrophthalimide (IIb) was carried out by condensation of the corresponding anhydrides and N- propylamine in a Dean-Stark separator using benzene as solvent. I b m. p. 53 - 54 "C, IIb m.p. < 30°C.

127- 128 "C).

76

New unsymmetricaI cycloaliphatic epoxypolyesterimides

Synthesis of epoxy derivatives

The syntheses of N-glycidyl derivatives were accomplished by reaction of the corresponding imide (Ia and Ila) with epichlorohydrin in excess (1 : 30) using BTMA as catalyst, as has been previously reported ' .

N-glycidylnadimide (Ig)

M.p. 167- 169"C, epoxy equiv. 221 g/eq; 'H NMR (CDCl,) 6 (ppm): 6.1 (2H, s), 3.6 (1 H, dd), 3.4 (3H, m), 3.3 (2H, m), 3.0 (1 H, m), 2.7 (1 H, t); 2.5 (1 H, dd), 1.7 (1 H, d), 1.5 (1 H, d); ',C NMR (CDCI,) S (ppm): 177.5 (s), 134.5 (d), 51.8 (t), 48.2 (d), 45.6 (t), 45.5 (d), 44.6 (d), 39.8 (t).

N-glycidyltetrahydrophthalimide (IIg)

M.p. 85-86"C, epoxy equiv. 211 g/eq; 'H NMR (CDCl,) S (ppm): 5.9 (2H, t), 3.7 (IH,dd), 3.6(1H, dd), 3.1 (3H,m),2.7(lH, t), 2.6-2.5(3H,m),2.2(2H,m); I3C NMR (CDCl,) S (ppm): 179.7 (s), 127.8 (d), 127.7 (d), 48.5 (d), 45.8 (t), 40.3 (t), 39.1 (d), 23.5 (t).

The epoxycycloaliphatic rings were obtained by epoxidation of double bonds with m-chloroperbenzoic acid at room temperature and adding bis(3-tert-butyl-4-hydroxy-5-methylpheny1)thioether in order to avoid the degradation of peracid,. In all the cases 1,2-dichIoroethane was used as solvent.

Epoxy derivative of N-propylnadimide (EpIb)

M. p. 143 - 144 "C; 'H NMR (CDCI,) 6 (ppm): 3.4 (2H, t), 3.2 (2H, d), 3.1 (2H, s), 3.0(2H,m),1.6(lH,m),1.5(2H,m),l.l(1H,d),0.9(3H,t);'3CNMR(CDC13) 6 (pprn): 178.2 (s), 47.4 (d), 46.8 (d), 40.1 (t), 38.7 (d), 29.2 (t), 20.7 (t), 11.3 (9).

Epoxy derivative of N-propyltetrahydrophthalimide (EpIIb)

M.p. 80-83 "C; 'H NMR (CDCl,) S (ppm): 3.3 (2H, t), 3.05 (2H, m), 2.7 (2H, m), 2.6 (2H, m), 2.1 (2H, m), 1.5 (2H, m), 0.8 (3H, t); I3C NMR (CDCl,) S (ppm): 180.8 (s), 50.4 (d), 40.4 (t), 34.9 (d), 22.0 (t), 20.6 (t), 10.9 (9).

77


Epoxy derivative of N-glycidylnadimide (EpIg)

M. p. 158- 161 "C; 'H NMR (CDCI,) S (ppm): 3.6 (1 H, dd), 3.5 (1 H, dd), 3.2 (2H, m),3.1(3H,m),3.0(2H,m),2.7(1H,t),2.6(1H,dd), 1.6(1H,m), 1.1(1H,d);I3C NMR (CDCI,) 6 (ppm): 178.0 (s), 48.3 (d), 47.6 (d), 47.2 (d), 46.2 (t), 40.5 (t), 39.0 (d), 29.4 (t).

Epoxy derivative of N-glycidyltetrahydrophthalimide (EpIIg)

M.p. 88-90°C; 'H NMR (CDCI,) S (ppm): 3.6 (1 H, dd), 3.4 (1 H, dd), 3.0 (3H, m), 2.7 (2H, m), 2.6 (1 H, t), 2.5 (3H, m), 2.1 (2H, m); I3C NMR (CDCI,) S (ppm): 180.4 (s), 50.5 (d), 48.8 (d), 45.9 (t), 40.6 (t), 35.1 (d), 22.1 (t).

Synthesis of model compounds

All the reactions were conducted in a thermostated oil bath at 110 "C. A typical run is as follows: 0.2 g (0.1 mmol) of IIg, 0.06 g (0.05 mmol) of succinic

acid, 1 rng (0.005 mrnol) of BTMA, and 1.5 ml of acetone were introduced in a screwed tube under argon atmosphere during 54 h (determined by control TLC using benzene/acetone (8:2, v/v) as eluent) in the oil bath. The mixture was dried and identified by NMR spectroscopy.

Polymer synthesis

5 meq of diepoxy compound, 4.5 mmol of diacid, 0.05 mmol of BTMA as catalyst, and 1 ml of acetone were mixed. Since the condensation reaction can not be controlled by TLC, all the runs were heated at 1 40 "C during 60 h.

Polymers were dried in vacuo at 40°C for 24 h and were obtained in practically quantitative yields.

Characterization and measurements

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

IR spectra were recorded on a Nicolet 5ZDX FT-IR spectrometer (KBr pellets). 'H and I3C NMR spectra were obtained using Varian XL-200 and EM 360 A spectro- meters with DMSO-d, and CDCI, as solvents and TMS as internal standard.

78

New unsymmetrical cycloaliphatic epoxypolyesterimides

The epoxy equivalent (E.E.) was determined by the Jay-Dijkstra-Dahmen method, variation Ciba4. This method is only used for glycidylic compounds, since it fails for cycloaliphatic oxiranes.

Viscosity measurements (qinh in dl/g) were run with 0.5% (w/v) solutions in DMF at 30 5 0.1 "C with an Ubbelohde type viscosimeter in an AVS 310 Schott automatic apparatus.

Thermogravimetric studies were carried out with a Perkin-Elmer TGA 7 system in N, atmosphere at a heating rate of 20 K/min. Calorimetric studies were carried out on a Mettler DSC-30 thermal analyzer.

Results and discussion

Diepoxy derivatives

At first, the syntheses of diepoxy monomers were accomplished as shown in Scheme 1.

0 0 II I1 lrc> N - C H 2 - CH- \ / CH,

L C 0 route 1 r L C' 11 I1 O [a Ila

0 -.-

0 0

0 Ic Ilc -,-

It was necessary to follow the synthetic route 1 which implies three steps (from anhydride) instead of the simplest way 2, since both double bonds of N- allylimide derivatives do not suffer simultaneous epoxidation by reaction with m-chloroperbenzoic acid as had previously been reported by ShokalS in a similar case.

Ig and IIg were obtained in high purity (98 -99vo) at the expense of their yields (about 50vo from imide precursors).

These compounds were identified by IR and NMR spectroscopy. Absorptions due to the glycidyl groups appear at 850 cm-'. Likewise, signals

79


in 'H and 13C NMR spectra are attributable to the glycidylic moiety, and those which have been widely described by us for related compounds' are observed too.

The epoxidation reaction with MCPB occurs with better yields at room temperature. The shortest reaction time was found for tetrahydrophthalimide derivatives. This fact can be explained on the basis of the steric hindrance due to the methylene bridge of the nadic derivatives. In the case of the latter compound, only the ex0 isomer can be observed by NMR spectroscopy. Conversely, the epoxidation of tetrahydrophthalimide derivative leads to a mixture of endo and ex0 isomers in a very different ratio. The conformational equilibrium of the cyclohexane ring does not allow us to assign unmistakably both isomers and to know which is the predominant one.

The epoxidation of the cycloaliphatic double bond in nadimide produces a shielding of 3 ppm in the initial olefinic proton signal. Moreover, the chemical shift difference between the two methylene bridge protons increases in the epoxidized derivative according to the observation reported by Christo16.

In the same way the epoxidation of the double bond in tetrahydrophthalimide derivatives shows a shielding of 3 - 4 ppm of the initial olefinic proton.

A similar effect is observed in the 13C NMR spectra of nadimides, where a shielding of the methylene bridge carbon is also observed'. All these observa- tions can be explained with the loss of the double bond anisotropic effect.

Model compounds

In order to make a preliminary study of the process of polymerization with carboxylic diacids, the monofunctional compounds epoxidized N-propylnadimide (EpIb) and epoxidized N-propyltetrahydrophthalimide (EpIIb) were tested with succinic acid. On the other hand, N-glycidylnadimide (Ig) and N- glycidyltetrahydrophthalimide (IIg) were tested, too. In this way, the reaction ability of both epoxy rings, cycloaliphatic and glycidylic, against nucleophilic agent (carboxylic acid) was verified.

The lower melting points of starting materials in comparison to aromatic glycidylimides reported by us*,2 allow to carry out the reaction in the melt instead of solution. This is an advantageous method in order to facilitate the separation of the final products and to increase their yields.

The reaction of EpIb with succinic acid leads to a complex mixture of several products. This result can be explained by a typical rearrangement of norbornylic carbocations, possible intermediates of this reaction*. Therefore,

80


this fact prevents the obtention of stereoregular polymers from bisepoxyna- dimides in acid medium.

However, the reaction of EpIIb with succinic acid in a molar ratio of 2: 1 gives the expected opening of the oxirane ring, stereospecific in antig. Therefore, epoxidized tetrahydrophthalimide glycidyl derivative (EpIIg) allows to obtain linear polymers by opening of both oxirane rings.

The use of 13C NMR spectroscopy was proved to be clear and conclusive in order to determine the new structures. Between 60 and 80 ppm five different signals appear, as can be seen in Fig. 1. DEFT experiments indicate that they are tertiary carbons.

6 (ppml

I

I 20

Fig. 1 . l3C NMR spectrum of the reaction product of the cycloaliphatic epoxide of N-propyltetrahydrophthalimide (EpIIb) with succinic acid in DMSO-d,.

The identification of these signals is made by means of empirical calcula- tions and adding trifluoroacetic acid (TFA) lo. This reagent (fourfold excess was added directly to the NMR tube) esterifies the hydroxy groups formed by the ring opening and causes a deshielding of 50 ppm in signal 1, corresponding to the CH group directly attached to the OH. The direction and the magnitude of this shift are in agreement with those expected for replacement of the

81


hydroxy group with the trifluoroacetate group in a-position to the analyzed carbon atom". Moreover, a small deshielding (3 ppm) is observed in the signal corresponding to the CH group (1') with the trifluoroacetate group in the b-position.

As we have mentioned above, our starting model compound was a mixture of two isomers (ex0 and endo). For this reason we can observe splitting of these signals due to different stereoplacements.

The presence of a fifth signal (h) indicates that a parallel reaction takes place. This reaction could be the homopolymerization of oxirane ring that leads to a polyether. A similar reaction was reported previously by us l 2 for glycidylic compounds.

The assignment of this signal (h) to the CH produced by homopolymerization reaction was made on the basis of the following facts:

1. No shift is observed after esterification with TFA; this implies that there are no neighbouring hydroxy groups.

2. No splitting is observed, hence this signal must correspond to a carbon in a symmetrical unit, such as a polyether.

3. This homopolymerization was confirmed by heating the model compound with an inorganic acid (perchloric acid) in absence of nucleophilic reagents. The 13C NMR spectrum of the crude reaction product showed the same signal.

By heating this model compound with BTMA catalyst, the starting product was recovered inaltered. It seems to support the need of protic medium so that cycloaliphatic homopolymerization of oxirane takes place, conversely to the homopolymerization reaction of glycidylic compounds that takes place even in a neutral medium 1 2 .

The opening of the oxirane ring leads to splittings in the imide carbonyl signals and cycloaliphatic carbons (2,2' and 3,3'). On the other hand, the ester carbonyl signal splits because of the presence of stereoisomers mentioned above.

The study of the reaction of glycidyl model compounds (Ig and IIg) with succinic acid in a molar ratio of 2: 1 by means of 13C NMR spectroscopy allows to detect the normal and abnormal ring opening of the oxirane ring and the mentioned homopolymerization reaction.

In Fig. 2 the signals attributable to the three different compounds originating from the processes mentioned above can be seen. All the carbon assignments are labelled on the same spectrum. It is remarkable that an unsymmetrical oxirane ring, such as a glycidyl compound, leads to a greater number of signals of homopolymerization.

82


0 0 II

N- CH2-CH - CHz- OOC-CH,-CH,- COO<H,-CH- 3 9 5 6 7 8 9

I OH

I OH I!

0

61 , 3 I1 I

~ * ' ' I ' , ' ' l ' ' ' ' , ' I ' ' " ' ' I I ' , ' I " ' ' I 1 " ' I ' I " I ' 7 , ~ ~ " " l " ~ ' " ' " , ~ " ' l ~ 180 160 140 120 100 8 0 6 0 4 0 20

Fig. 2. I3C NMR spectrum of the reaction product of the N-glycidyltetrahydrophthalimide (IIg) with succinic acid in CDCl, .

Linear polymerization

Polymers were prepared in a similar way as above using a molar ratio diepoxide/diacid 1.1 : 1 in order to ensure epoxy end groups that could be crosslinked in a further step to three-dimensional networks. Three different carboxylic diacids were tested: succinic, adipic, and itaconic acid.

The fact that two different oxirane rings are present in the same monomer led to a selectivity, since the glycidylic oxirane ring is more reactive than the cycloaliphatic one. This renders well defined oxirane cycloaliphatic end groups on the polymer backbone. Thus, the further crosslinking of these resins will be accomplished only by anhydrides as curing agents since these groups do not react with amines ' 3.

The polymers were soluble only in high polar solvents such as DMF, NMP, and DMSO. This fact is in accordance with the possible slight crosslinking due to the homopolymerization mentioned above.

Nuclear magnetic resonance allowed us to characterize the repeating units of these polymers. Fig. 3 shows the 13C NMR spectrum of the polymer derived from succinic acid and EpIIg. All carbon assignments are labelled. As

83


6 (pprn)

Fig. 3. 13C NMR spectrum of the polymer from epoxidized N-glycidyltetrahydrophthalimide (EpIIg) and succinic acid in DMSO-d, .

can be observed, the spectrum shows a great number of signals, but almost all of them could be assigned according to the study accomplished with both model compounds. We must point out that both types of ring opening, normal and abnormal, of the glycidylic oxirane ring are observed besides the cycloaliphatic ring opening. The signals labelled 8 + 8', assignable to carbonyl ester carbons, and 9 + 9, attributable to methylene carbon directly attached to carbonyl ester groups undergo a splitting, making clear that processes mentioned above have taken place.

Likewise, as can be expected, several signals attributable to homopolymerization (marked h) appear. Also the signals e l , e2, and e3, corresponding to cycloaliphatic oxirane end groups, can be observed and allow us to confirm the different reactivity of both oxirane rings and the short-length chain. This observation is in agreement with the low inherent viscosities measured that are collected in Tab. 1.

The thermal stability of polymers was evaluated by TGA measurements. These cycloaliphatic epoxy polyesterimides have good thermal stability as it is evident from the parameters listed in Tab. 1.

As can be seen, the maximum degradation temperatures are higher than 400 "C, comparable to previously reported L 2 aromatic resins. However, the weight residue at 500°C is lower due to the less unsaturated structure. These

84

New unsymmetrical cycioaiiphatic epoxypolyesterimides

Tab. 1.

Polymer from qinh Tg TmUa Weight residue Temperature at

Characteristics of the polymers from EpIIg and different carboxylic diacids.

(dl/g) ("C) ("C) at 500°C 10% weight loss ("C)

Succinic acid 0.145 90.8 428.6 2.0 372.5 Adipic acid 0.196 56.1 420.0 10.8 365.0 Itaconic acid 0.069 89.8 416.2 6.4 264.8

a Maximum decomposition temperature.

results allow us to confirm that substitution of aromatic rings by cycloaliphatic moieties leaves the good thermal stability unchanged.

T, values are collected in the same table. The lowest value corresponds to adipic acid derivative and it can be rationalized on the basis of the longer aliphatic chain which supplies a higher flexibility to the molecule. The fact that these T, values are above 50°C implies that these epoxy resins will be crosslinkable above room temperature with carboxylic anhydrides.

A. Mantecon, V. Cadiz, A. Serra, P. A. Martinez, Angew. Makromol. Chem. 148 (1987) 149 A. Serra, V. Cadiz, P. A. Martinez, A. Mantecon, Angew. Makromol. Chem. 138 (1986) 185 Y. Kishi, M. Aratoni, H. Tanino, T. Fukuyama, T. Goto, S. Inoue, S. Sugire, H. J. Kakoi, Chem. SOC., Chem. Commun. 1972, 64 B. Dobinson, W. Hofman, B. P. Stark, The Determination of Epoxide Groups, Pergamon Press Ltd., London 1970, p. 40 US 2925403 (1960), Shell Oil Co., Inv.: E. C. Shokal, C. A. 54 (1960) 15273b H. Christol, J. Coste, F. Plenat, Ann. Chim. (Paris) 4 (1969) 93 H. Christol, J. Coste, F. Plenat, Ann. Chim. (Paris) 4 (1969) 105

* J. Meinwald, S. S. Labana, L. L. Labana, G. H. Wahl Jr., Tetrahedron Lett. 6 (1965) 1789 S. Patai, The Chemistry of the Ether Linkage, Interscience Publishers, London 1967, p. 395 T. Biedron, P. Kubisa, S. Penczek, J. Polym. Sci., Part A: Polym. Chem. 29 (1991) 619 F. W. Wehrli, A. P. Marchand, S. Wehrli, Interpretation of Carbon-13 NMR Spectra, Wiley, New York 1988, p. 52 M. Galia, A. Mantech, V. Cadiz, A. Serra, Makromol. Chem. 191 (1990) 11 11 H. Batzer, E. Nikles, Chimia 16 (1962) 57

*

lo

I '

l 3

85

Documents

New unsymmetrical cycloaliphatic epoxypolyesterimides