Anionic synthesis of diblock copolymer brushes and functional polymers.

摘要

A new method to prepare diblock copolymers and homopolymer brushes on oxide surfaces by anionic polymerization has been developed using a surface-bound 1,1-diphenylethylene monolayer. Properties of the brushes were characterized by XPS, AFM, FTIR-ATR, X-ray reflectometry and contact angle measurements. Thicknesses as high as 24 nm (ellipsometry) were obtained for a "grafting from" strategy. Reacting a covalently attached monolayer of 1,1-diphenylethylene units with n-butyllithium created an initiator layer for the "grafting from" strategy. The corresponding 1,1-diphenylhexyllithium derivatives initiated the polymerization of isoprene and the living chain ends were functionalized by ethylene oxide. The functionalization reaction decreased the advancing contact angle from 86 +/- 2° for "grafted from" polyisoprene to 47 +/- 3° for "grafted from" hydroxy-terminated polyisoprene and the XPS carbon (1s) scans at 286.7 eV were consistent with carbon bonded to alcohol groups. The hydroxy-terminated polyisoprene brush was converted to the corresponding potassium alkoxide with diphenylmethylpotassium and used to initiate ethylene oxide polymerization. For comparison, telechelic polyisoprenes were "grafted to" the silicon substrates. AFM results for surface roughness of "grafted from" polyisoprene brushes were 3---5 A (rms). The XPS C(1s) scans for the PI-PEO diblock brush showed carbon bonded to oxygen at 286.7 eV and saturated carbon at 285 eV.;The amount of ethylene oxide oligomerization for functionalization of poly(styryl)lithium in benzene at 25°C was determined using MALDI-TOF MS, 1H and 13C NMR. For reactions times ranging from 12 h to 4 weeks using 10 equivalents of ethylene oxide, the corresponding amounts of dimeric oligomerization varied from 4% to 34%. Chemically insignificant amounts of oligomer were found using 4 equivalents of ethylene oxide ([EO]/[PLi]) up to 12 h. Trimeric oligomerization of ethylene oxide was detected after 1 week (1%) and 4 weeks (4%) by MALDI-TOF MS. The quantitative results from MALDI-TOF MS agreed well with results from both 1H and 13C NMR analyses. The quantitative aspects of MALDI-TOF MS compared to 1H and 13C NMR for the determination of the amount of EO oligomerization have been established through the synthesis and characterization of the model dimeric oligomer product, o-[2-(2-hydroxyethoxy)ethyl]polystyrene.