Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry characterization of primary amine end-functionalized polystyrene and poly(methyl methacrylate) synthesized by living anionic polymerization techniques

摘要

The reaction of living anionic polymers with 2,2,5,5-tetramethyl-1-(3-bromopropyl)-1-aza-2,5-disilacyclopentane (1) was investigated using coupled thin layer chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Structures of byproducts as well as the major product were determined. The anionic initiator having a protected primary amine functional group, 2,2,5,5-tetramethyl-1-(3-lithiopropyl)-1-aza-2,5-disilacyclopentane (2), was synthesized using all-glass high-vacuum techniques, which allows the long-term stability of this initiator to be maintained. The use of 2 in the preparation of well-defined aliphatic primary amine alpha-end-functionalized polystyrene and poly(methyl methacrylate) was investigated. Primary amino alpha-end-functionalized poly(methyl methacrylate) can be obtained near-quantitatively by reacting 2 with 1,1-diphenylethylene in tetrahydrofuran at room temperature prior to polymerizing methyl methacrylate at -78 degrees C. When 2 is used to initiate styrene at room temperature in benzene, an additive such as N,N,N',N'-tetramethylethylenediamine is necessary to activate the polymerization. However, although the resulting polymers have narrow molecular weight distributions and well-controlled molecular weights, our mass spectra data suggest that the yield of primary amine alpha-end-functionalized polystyrene from these syntheses is very low. The majority of the products are methyl alpha-end-functionalized polystyrene.