Polymer International 44 (1997) 397È401

Preparation of Some Large CyclicOxyethylene Succinate Ether-esters¤

B. R. Wood, S. C. Hamilton & J. A. Semlyen*

Department of Chemistry, University of York, Heslington, York YO1 5DD, UK

(Received 24 February 1997 ; accepted 12 June 1997)

Abstract : Cyclic oligomers of tetraethyleneglycol succinatepentaethyleneglycol succinate[O(CH2CH2O)4 . CO .CH2CH2 . CO]

x,

and hexaethyleneglycol succinate[O(CH2CH2O)5 . CO .CH2CH2 . CO]x were prepared by dilute solution ringÈ[O(CH2CH2O)6 . CO .CH2CH2 . CO]xchain transesteriÐcation reactions. The cyclic products were characterized by

GPC, FAB mass spectrometry and NMR spectroscopy. The molar concentra-tions of the cyclics were determined using GPC and are compared in this paper.The cyclic ether-ester oligomers were fractionated by preparative GPC to give aseries of narrow molar mass fractions with dispersities of c 1É05. The(M1 w/M1 n)cyclic tetraethyleneglycol succinate monomer was crystallized and its structuredetermined by X-ray crystallography.

Polym. Int. 44, 397È401 (1997)No. of Figures : 6. No. of Tables : 0. No. of References : 20

Key words : large cyclic ether-esters, gel permeation chromatography, X-raycrystal structure, tetraethyleneglycol succinate, pentaethyleneglycol succinate,hexaethyleneglycol succinate

INTRODUCTION

As part of a general study of large ring compounds andcyclic polymers1h3 we have developed synthetic routesto large ring esters.4h10 Recently we have reported thatthe synthetic method can be modiÐed for the prep-aration of large ether-ester rings based upon tetra-ethyleneglycol succinate repeat units.11 Bradshaw,12Singh13 and Ogawa14 and their co-workers have shownthat monomer and dimer oxyethylene succinate ringscan be made in reasonable yield by an alternative syn-thetic route. This paper describes how large cyclic ether-esters can be prepared using ringÈchain reactions. The

¤ Dedicated to Professor Bob Stepto on the occasion of his60th birthday.* To whom all correspondence should be addressed.Contract grant sponsor : Engineering and Physical SciencesResearch Council.Contract grant sponsor : Defence Research Agency.Contract grant sponsor : Courtaulds Coatings Ltd, Felling,Tyne and Wear.

cyclic oligomers of such ether-esters should demonstratecomplexing behaviour with metal ions in a similar wayto that of crown ethers15 and calixarenes16 and theycould be of use in ion separation techniques, e.g. inwaste-water decontamination.17

In this paper we outline the preparation and charac-terisation of a series of large ring aliphatic ether-estersbased upon oxyethyleneglycol succinate repeat units,

(where m\ 4, 5,[O(CH2CH2O)m

. CO .CH2CH2 . CO]x

6 and x \ 1È8). The monomers are shown in Fig. 1.

EXPERIMENTAL

Materials

Dimethylsuccinate (98] % pure) and tetra-ethyleneglycol (97%) were supplied by Lancaster Syn-thesis Company Ltd. Pentaethyleneglycol (98%) andhexaethyleneglycol (97%) were supplied by AldrichChemical Company Ltd. The catalysts used in thesereactions were dibutyltin bis(2-ethylhexanoate) and

3971997 SCI. Polymer International 0959-8103/97/$17.50 Printed in Great Britain(

398 B. R. W ood, S. C. Hamilton, J. A. Semlyen

Fig. 1. Monomer structures.

tetraisopropylorthotitanate. The former was supplied byAldrich Chemical Co. Ltd, whilst the latter was suppliedby Fluka Chemical Ltd.

All the above reagents were used as received with nofurther puriÐcation.

Preparations

The cyclic oligomers were produced as a result of a two-stage synthesis. The Ðrst stage involved the preparationof high molar mass chains. This was accomplished by amelt polycondensation reaction between dimethyl suc-cinate and one of the oligo-oxyethyleneglycol mono-mers. The second stage involved the generation of cyclicoligomers from the linear polymer by a dilute solutionringÈchain transesteriÐcation reaction.

The general method is outlined in detail for the prep-aration of the tetraethyleneglycol succinate (TGS)polymer. The preparations of both the pentaethyle-neglycol succinate (PGS) and the hexaethyleneglycolsuccinate (HGS) chains were carried out under similarconditions.

Preparation of poly(tetraethyleneglycol succinate) chains.The polymer was prepared by a polycondensation reac-tion between dimethylsuccinate and tetraethyleneglycol.The two reagents were added in equimolar proportions(0É35 mol) to a multinecked round-bottomed Ñaskequipped with an overhead stirrer, a nitrogen inlet, athermometer and a distillation head. The contents ofthe Ñask were raised to a temperature of approximately80¡C with continuous stirring to ensure thoroughmixing. The transesteriÐcation catalyst tetra-isopropylorthotitanate (0É5 wt%) was added and thetemperature raised to 120¡C for a period of 18 h, duringwhich time methanol was evolved and distilled o†. TheÑask contents were then raised to 150¡C for 24 h undervacuum (15 mmHg) to further remove methanol fromthe reaction in order to produce mainly linear polymer.

Preparation of tetraethyleneglycol succinate rings. Tofavour the formation of poly(tetraethyleneglycolsuccinate) rings, the chain polymer (15É0 g), preparedusing the above procedure, was reÑuxed in chloroben-zene (800 ml, 130¡C) under dilute solution conditionswith dibutyltin bis(2-ethylhexanoate) as the tran-

sesteriÐcation catalyst for 96 h. The progress of the reac-tion was monitored by removal of 5É0 ml samples atregular daily intervals. Each sample was rotary evapo-rated to dryness and then analysed by gel permeationchromatography (GPC). The total product after 96 hwas collected and rotary evaporated to dryness andthen analysed by GPC, nuclear magnetic resonancespectroscopy (NMR) and fast atom bombardment(FAB) mass spectroscopy.

Pentaethyleneglycol succinate and hexaethyleneglycolsuccinate rings were obtained by dilute solution ringÈchain transesteriÐcation reactions carried out undersimilar conditions to the above and then analysed byGPC, NMR and FAB mass spectroscopy.

Characterization

Gel permeation chromatography (GPC). The productsfrom the polymerization and cyclization reactions wereanalysed using a GPC instrument. The instrument usedwas a Knauer GPC equipped with four PLgel 3kmmixed-E columns connected in series. The instrumentwas supplied by Polymer Laboratories Ltd and wasÐtted with a Shimadzu RID-6A refractive index detec-tor. Samples were analysed in chloroform at ambienttemperature at a Ñow rate of 0É3 mlmin~1. The instru-ment was calibrated using narrow molar mass poly-styrene standards.

The cyclic oligomers were fractionated on a pre-parative GPC instrument to give a series of sharp molarmass fractions. The instrument used two 5 km ultrastry-ragel columns (70 mm] 300 mm) connected in seriesand was supplied by Waters (Millipore) Ltd. Toluenewas used as eluant.

NMR spectroscopy. 1H NMR spectra were obtainedusing a Joel 270 MHz spectrometer. The samples weredissolved and analysed in deuterated chloroform.

Mass spectroscopy. FAB mass spectra of the cyclic pro-ducts were obtained using an Autospec spectrometerwith dichloromethane as solvent.

RESULTS AND DISCUSSION

The melt polymerization of dimethylsuccinate withtetra-, penta- and hexaethyleneglycol proceeded with

POLYMER INTERNATIONAL VOL. 44, NO. 3, 1997

L arge cyclic oxyethylene succinate ether-esters 399

the evolution of methanol and gave broad molar masspolymer chains with weight-average molar masses M1 wof c. 4000 and dispersities of 2 (Fig. 2). Cyclic oligomerswere produced via ringÈchain transesteriÐcation reac-tions using dilute solution conditions with solvent-to-polymer ratios of 50 : 1 by weight. The reactions werefollowed by GPC analysis by the removal of smallsamples at regular intervals from the reaction mixture.For each polymer system it was found that after 96 hreÑux time most of the higher molar mass chains hadbeen transformed into lower molar mass oligomers (Fig.2). GPC analysis showed that cyclic oligomers with upto eight repeat units had been formed from the HGSpolymer and that cyclic oligomers with up to six repeatunits had been produced for both the TGS and PGSpolymers. Mass spectroscopy gave direct evidence forthe cyclic nature of the oligomers, i.e. spectral lines cor-responding to molecular ions comprising up to eightrepeat units for the HGS oligomers (Fig. 3(a)). The lowmolar mass oligomers are shown for the PGS and TGS

Fig. 2. GP chromatograms of cyclic ether-ester oligomers : (a)hexaethyleneglycol succinate (HGS) ; (b) pentaethyleneglycolsuccinate (PGS) ; (c) tetraethyleneglycol succinate (TGS). Thenumbers of observable repeat units (x) are indicated, Broken

lines, chain polymer ; full lines, cyclic oligomers.

Fig. 3. FAB mass spectra for cyclic ether-ester oligomers : (a)hexaethyleneglycol succinate (HGS) ; (b) pentaethyleneglycolsuccinate (PGS) ; (c) tetraethyleneglycol succinate (TGS). Thenumbers of observable repeat units comprising the individual

rings are indicated.

cyclic oligomers (Figs 3(b) and 3(c)). NMR spectroscopyshowed that cyclic oligomers had been formed withonly small amounts of high molar mass chain oligo-mers, i.e. only small chemical shifts corresponding tohigh molar mass methyl-ester-terminated chains wereobserved for all the products from the ringÈchain tran-sesteriÐcation reactions. Similar work involving thepreparation of cyclic aliphatic esters has shown thatthese high molar mass oligomers can be removed fromthe product by solvent extraction or by adsorption onto silica or alumina using column chromatography.Figure 4 shows the NMR spectrum for a narrow molarmass TGS fraction comprising mainly monomeric,dimeric and trimeric molecules. Chemical shifts due to

POLYMER INTERNATIONAL VOL. 44, NO. 3, 1997

400 B. R. W ood, S. C. Hamilton, J. A. Semlyen

Fig. 4. NMR spectrum for narrow molar mass TGS fraction.

protons of oxyethylene and ester groups are clearlyobserved, but not chemical shifts due to chain oligo-mers.

The cyclic oligomers were fractionated using pre-parative GPC to give a series of sharp molar mass frac-tions with dispersities of c. 1É05. Figure 5(M1 w/M1 n)shows the analytical gel permeation chromatograms forsome of the cyclic TGS fractions. The fractionated PGSand HGS cyclic oligomers gave similar chromatograms.The high resolution of the preparative GPC instrumentwas sufficient to enable the cyclic monomer and dimerrings to be isolated as pure compounds. The monomericrings were found to crystallize readily from the melt andthe cyclic TGS monomer yielded crystals suitable forX-ray crystallographic investigations. The structure isshown in Fig. 6.18

The determination of cyclic concentrations in poly-meric systems gives a sensitive measure of the statisticalconformations of the corresponding open chain mol-ecules in a variety of di†erent environments (see Chap. 1of Ref. 1). For cyclics formed in ringÈchain equili-bration, the JacobsonÈStockmayer19 expression can beused to relate the molar cyclization equilibrium con-stants to the mean square end-to-end distancesK

xSr

x2T

for the corresponding open chain molecules as follows :

Kx\A 32nSr

x2TB3@2 1

pRx NAwhere is a symmetry number and is the Avo-pRx NAgadro constant.20

This study has demonstrated that large cyclic ether-esters can be prepared and characterized. They shouldprove to be good candidates for detailed conforma-tional investigations as well as having the potential foruseful applications.

ACKNOWLEDGEMENTS

We thank the Engineering and Physical SciencesResearch Council, the Defence Research Agency andCourtaulds Coatings Ltd, Felling, Tyne and Wear forÐnancial support for this work.

A PERSONAL TRIBUTE FROM J. ANTHONY

SEMLYEN

Professor Robert Stepto has a wide range of researchinterests in polymer science and it has been a pleasure

POLYMER INTERNATIONAL VOL. 44, NO. 3, 1997

L arge cyclic oxyethylene succinate ether-esters 401

Fig. 5. GP chromatograms of cyclic tetraethyleneglycol suc-cinate oligomers fractionated using preparative GPC. Thenumbers of observable repeat units for the cyclic oligomers

are indicated.

to have had the opportunity of working with him onaspects of cyclization reactions and the conformationalproperties of cyclic polymers. His enthusiasm andexpertise have been greatly appreciated. Our associationhas extended over many years, there have been closecollaborations between his group in Manchester andours at York and he has contributed to all three bookslisted in Refs 1È3. Professor Stepto has made importantcontributions to both experimental and theoreticalstudies of polymer networks and polymer chain sta-tistics. All of us from the York group extend our bestwishes to him at this time and wish him every success inthe future.

Fig. 6. X-ray crystallographic representation of the structureof the crystalline tetraethyleneglycol succinate ring.

REFERENCES

1 Semlyen, J. A. (ed.), Cyclic Polymers. Elsevier Applied Science,London, 1986.

2 Clarson, S. J. & Semlyen, J. A. (eds), Siloxane Polymers. Prentice-Hall, Englewood Cli†s, NJ, 1993.

3 Semlyen, J. A. (ed.), L arge Ring Molecules. Wiley, Chichester, 1996.4 Wood, B. R., Hodge, P. & Semlyen, J. A., Polymer, 34 (1993) 3052.5 Wood, B. R., Joyce, S. J., Scrivens, G., Semlyen, J. A., Hodge, P. &

OÏDell, R., Polymer, 34 (1993) 3059.6 Wood, B. R., Semlyen, J. A. & Hodge, P., Polymer, 35 (1994) 1542.7 Semlyen, J. A., Wood, B. R. & Hodge, P., Polym. Adv. T echnol. 5

(1994) 473.8 Wood, B. R., Semlyen, J. A. & Hodge, P., Polymer, 38 (1997) 191.9 Hamilton, S. C. & Semlyen, J. A., Polymer, 38 (1997) 1685.

10 Bryant, J. J. L. & Semlyen, J. A., Polymer, 38 (1997) 2475.11 Wood, B. R., Semlyen, J. A. & Hodge, P., Polymer. 38 (1997) 2287.12 Bradshaw, J. S., Bishop, C. T., Nielson, S. F., Asay, R. E.,

Masihdas, D. R. K., Flanders, E. D., Hansen, L. D., Izatt, R. M. &Christensen, J. J., J. Chem. Soc., Perkin T rans. 1, 00 (1976) 2505.

13 Singh, P., Kumar, M. & Singh, H., Indian J. Chem. (B), 26 (1987)64.

14 Ogawa, T., Yoshikawa, A., Wada, H., Ogawa, C., Ono, N. &Suzuki, H., J. Chem. Soc., Chem. Commun., (1995) 1407.

15 Gokel, G., Crown Ethers and Cryptands. Royal Society of Chem-istry, Cambridge, 1991.

16 Gutshe, D., Calixarenes. Royal Society of Chemistry, Cambridge,1989.

17 Asfari, Z., Bressot, C., Vicens, J., Hill, C., Dozol, J. F., Rouquette,H., Eymard, S., Lamare, V. & Tournois, B., ACS Symp. Ser., 642(1996) 376.

18 Cronin, L., Moore, M., Wood, B. R. & Semlyen, J. A., Acta Crys-tallogr., C53 (1997) 940.

19 Jacobson, H. & Stockmayer, W. H., J. Chem. Phys., 18 (1950) 1600.20 Semlyen, J. A., Adv. Polym. Sci., 21 (1976) 43.

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