O O O O Bu Bu O Bu O m n p HO OH O O Bu m,n or p step 1 i, ozone ii, Amberlyst A27:BH4 form (48 h, room temp.) O RSX O RO2SO OSO2R O O Bu m,n or p step 2 Amberlyst A27 (24 h, room temp.) R = Ts or Tf X = Cl or O(S02CF3) 408 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 408–409† A Clean and High Yield Synthesis of Oligo(butyl methacrylate) with Sulfonate End Groups using Polymer Supported Reagents† John R. Ebdon and Stephen Rimmer* The Polymer Centre, Lancaster University, Lancaster LA1 4YA, UK Oligo(butyl methacrylate) with sulfonate ester end groups is prepared in a two-step process involving ozonolysis of a poly(butyl methacrylate-co-butadiene) with supported reductive work-up followed by sulfonylation with a supported base.Oligomers with functional end-groups (telechelic oligomers) find uses in many important spheres such as in biomaterials, drug delivery, surface coatings and reactive processing. Clean synthesis of these materials is difficult, firstly because conventional liquid–liquid extraction of reaction mixtures of oligomers often results in the formation of stable emulsions and secondly because other purification procedures used in organic chemistry, such as recrystallization, are not generally useful. Thus, reactions on oligomers may often be extremely time consuming and are usually low-yield processes.Oligomers with sulfonate end groups have been prepared previously by several groups,1 but as far as we are aware sulfonate ester functional oligomers with acrylic or methacrylic backbones have not been reported. We have been seeking ways of synthesizing such materials using clean methodologies. One such method is to use supported reagents.Here we report a clean high-yield method of synthesizing sulfonate ester functional oligomers. The main feature of this synthesis is that the steps involve immobilization of all the reagents and by-products on solid supports, so that simple filtration is the only purification step necessary.The use of a supported strategy also has a second advantage, that is that it is possible to compensate for the low concentration of functional groups (end groups) by using a large excess of the supported reagent. The method is outlined below and represented schematically in Scheme 1. Synthesis of Oligo(butyl methacrylate) with Hydroxy End Groups (OBMA+2OH).—In the first step, an unsaturated polymer was ozonized and then worked up with borohydride supported on Amberlyst A27.The details of this step have been reported previously.2 The number average molecular weight, Mn, of the hydroxy ended oligomer was 1700 g molµ1 (measured by GPC, calibrated against polystyrene standards). Synthesis of Sulfonate Ester Functional Oligo(butyl methacrylate) with Sulfonate Ester End Groups (OBMA+2 Tf and OBMA+2Ts).—The results from the second step are recorded in Table 1. Initially, reactions with the non-supported amine, triethylamine, were attempted.This reaction gave close to a quantitative yield of tosylated oligomer when the reaction was carried out in toluene, but very low yields were obtained in dichloromethane. However, while the majority of the amine hydrochloride precipitated from the toluene solution, a significant amount of salt remained in solution. Also, excess toluene-p-sulfonyl chloride remained in solution. In a small molecule reaction these by-products would be removed by aqueous extraction.When this was attempted with this system, stable emulsions resulted. These emulsions did phase-separate but only after settling for approximately 1 week. The amount of material recovered from this reaction was approximately 50% of that charged and it was still contaminated with large amounts of toluenep- sulfonic acid. This then is clearly an impracticable route. The replacement of the triethylamine with a supported amine solved these problems.Thus tosylated and triflated oligomers were prepared by using Amberlyst A21 as the base. All of the hydrochloride by-product was removed by simply filtering off the resin. Similarly, it was possible to drive the reaction to high yield by using a large excess of sulfonyl derivative/amine reagent. Since the excess reagent is also bound to the resin, removal of this is no longer problematic. *To receive any correspondence (e-mail: s.rimmer@ lancaster.ac.uk). †This is a Short Paper as defined in the Instructions for Authors, Section 5.0 [see J.Chem. Research (S), 1997, Issue 1]; there is therefore no corresponding material in J. Chem. Research (M). Table 1 Results of sulfonation ester synthesis Mass yield Yield of sulfonate Solvent R X Amine (mass%) end groups (mol%) Dichloromethane Toluene Toluene Toluene Toluene Toluene Ts Ts Ts Tf Tf Tf Cl Cl Cl OSO2CF3 OSO2CF3 Cl TEA TEA A21 TEA A21 A21 50 50 100 50 100 100 0 99+ 99+ 50 99+ 99+ R and X refer to the structures in Scheme 1, i.e.R=Ts or Tf; X=Cl or O(SO2CF3) Scheme 1 Steps in the synthesis of sulfonate ester functional oligo(butyl methacrylate)J. CHEM. RESEARCH (S), 1997 409 It is noteworthy that the choice of solvent is important in both the supported reaction and the non-supported reaction. At this stage insufficient data are available to determine whether this is an observation of general significance or if it is a feature of oligo(butyl methacrylate) reactions.The FTIR spectrum of a triflated product is shown in Fig. 1. The complete absence of an IR absorption peak associated with hydroxy stretching (at 3200–3000 cmµ1) is clear evidence of the success of these reactions. Also, a new band at 1820 cmµ1, associated with the sulfonate end group, can be seen. The sulfonate end groups could also be observed in the 1H NMR spectrum (CH2 a to the sulfonate group observed at 4.1–4.2 ppm). Fig. 2 shows the 1H NMR spectrum. These spectra also illustrate the high purity of the materials prepared using this methodology, the only impurity being from the remnants of toluene.Thus we have shown that it is possible to prepare, in quantitative yield, oligomers with sulfonyl ester end groups using a supported amine and sulfonyl derivatives. The products are not contaminated with by-products or reagents and are easily recovered. Work is continuing on further nucleophilic substitution reactions on the end groups. Experimental Preparation of Hydroxy Functional Oligo(butyl methacrylate) (OBMA+2OH).—Monomer-starved emulsion polymerization was used to prepare poly(butyl methacrylate-co-butadiene) (PBMAco- BD); the recipe has been previously published.2 The feed contained 17 mol% butadiene while the final polymer contained 12.5 mol% alkene units attributable to butadiene residues (as measured by 1H NMR).The Mn of the polymer was 209 kg molµ1 (GPC calibrated with polystyrene standards). The polymer was isolated from the latex by coagulation in a saturated solution of magnesium sulfate.The polymer was then redissolved in acetone and precipitated into methanol. This was repeated twice. The PBMA-co-BD (20 g) was dissolved in distilled chloroform and ozonized at room temperature for 24 h. Ozone was generated by an electric discharge- type generator and was fed in at a rate of 74 g hµ1. After this time, nitrogen was passed through the vessel for 10 min so that excess ozone could be removed.The solution was then added to a column packed with Amberlyst A27 in the BH4 µ form (10 g). The polymer solution was recirculated through the column, by means of a peristaltic pump, for 48 h. The solvent was then removed to yield a highly viscous colourless oil. Mn=1740 g molµ1 (GPC), dC CH2OH=59.2, 59.7, 60.2. Yield=100%). Preparation of Sulfonate Ester Functional Oligo(butyl methacrylate). ·Reactions with non-supported amine were first attempted as follows: (i) OBMA+2OH (2.5 g) was dissolved in dry dichloromethane (10 ml).Triethylamine (TEA) (1.3 g) was then stirred with tosyl chloride (TsCl) (0.36 g) for 30 min. The dichloromethane solution was then added and the reaction left stirring for 1 week. The solid was filtered off and the product washed with deionized water. This resulted in the production of stable emulsions so that purification took several months to effect. (ii) OBMA+2OH (30 g) was dissolved in toluene (100 ml). TsCl (15.2 g) was mixed with freshly distilled TEA (30 ml) for 30 min. The solution of OBMA+2OH was then added. The reaction was stirred for 5 d at room temperature, after which the precipitate was filtered off and the solution washed with deionized water. Again stable emulsions resulted from this aqueous work-up. Reaction with supported amine Amberlyst A21. OBMA+2OH (2 g) was dissolved in distilled toluene (or chloroform) (80 cm3). Amberlyst A21 that had been thoroughly washed with ethanol and then vacuum dried was added. The sulfonyl derivative was then added (5 g). The beads were agitated by passing dry nitrogen through the vessel for 24 h. Then the beads were filtered off. Received, 3rd June 1997; Accepted, 9th July 1997 Paper E/7/03859C References 1 L. Vandenberge, S. Vandamme, M. J. O. Anteunism and D. Tavernier, Bull. Soc. Chim. Belg., 1991, 100, 115 and references cited therein. 2 S. Rimmer, J. R. Ebdon and M. J. Shepherd, React. Funct. Polym., 1995, 26, 145. Fig. 1 FTIR spectrum of triflated OBMA+2OH Fig. 2 1H NMR spectrum of triflated OBMA+2OH