X-ray fluorescence (XRF) spectra of poly(buty1 cyanoacrylate) initiated, in tetrahydrofuran, by triphenylphospine and terminated by SO,, show the persistent presence of phosphorus and sulfur in the polymer, in near-equivalent proportions, with the sulfur content partially removable by anion-exchange. It is concluded that all chains have initial phosphonium groups, and, in abesence of any hydrolysis-formed HZSO4, are macrozwitterions with terminal -SO;. Acid-terminated chains should have proton-capped ends and initial phosphonium+ -HSO; ion-pairs.The theory that Lewis bases, such as phosphines and amines can initiate anionic polymerization by addition to form an "internal" counter-cation to the anionically propagating chain, has received experimental support in only a few cases. Thus, Jaacks (for triphenylphosphine (Ph3P)/methylene malonic ester')) and Ranagajec (for triethylphosphine (Et3P)/methacrylonitrile2)) detected combined phosphorus in the polymers, and spectra (ultraviolet (UV) and nuclear magnetic resonance (NMR), respectively) of the oligomers characteristic of phosphoniudcarbanion model compounds. With other monomers, information has come, so far, only from the cyanoacrylates. Here the ethyl ester, initiated by various phenazine dyes, has been found to give coloured polymers having absorption intensities inversely proportional to chain-length'). The ethyl and butyl esters, initiated by Ph3P and by pyridine4), gave evidence of phosphonium and pyridinium spectra in oligomer solutions, but lacked the confirmation of presence in the isolated polymers. The evidence presented here, from persistent X-ray fluorescence (XRF) spectra, has hitherto been recorded only in an academic dissertation5).
Experimental partThe purification and drying of solvents, tetrahydrofuran (THF) and N,N-dimethylformamide (DMF), reagents, and butyl cyanoacrylate monomer (BCA) were as already described in several references3"). The SO,-DMF adduct was prepared by distillation of SO3 from 50 wt.-% oleum under vacuum directly into DMF, diluting to stock solutions of SO3 concentration measured by NaOH titration, and storage under dry nitrogen blanket.Polymerizations were performed at room temperature (ca. 20 "C) under dry-Nz blanket, under standard conditions: 50 mL THF, 1-3 mL BCA, to give initial monomer concena) Istituto die Studi Chimico-Fisici di Macromolecule Sintetiche e Naturali, Via de Marini 6, in the range 0.1-0.3 m o m followed by microsyringe additions of SO3-DMF adduct, and finally similar additions of THF solutions of pyridine or triphenylphosphine. The reactions were followed by temperature rise (up to ca. 3 "C). Under the relatively high initiator concentrations used (ca. 5 mmoVL) these were complete in less than 5 min. Polymers were isolated by precipitation from large volumes (ca. 400 mL) of methanol or hexane. After drying, molar masses were determined by size-exclusion chromatography (calibrated as in ref .6)). XRF spectra were observed before and after various solvent-extraction or re-precipitation procedures.XRF int...
