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Maude Le Hellaye Catherine Lefay Thomas P. Davis Martina H. Stenzel Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2008,46(9):3058-3067
The simultaneous ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) and 2‐hydroxyethyl methacrylate (HEMA) polymerization via reversible addition fragmentation chain transfer (RAFT) chemistry and the possible access to graft copolymers with degradable and nondegradable segments is investigated. HEMA and ε‐CL are reacted in the presence of cyanoisopropyl dithiobenzoate (CPDB) and tin(II) 2‐ethylhexanoate (Sn(Oct)2) under typical ROP conditions (T > 100 °C) using toluene as the solvent in order to lead to the graft copolymer PHEMA‐g‐PCL. Graft copolymer formation is evidenced by a combination of size‐exclusion chromatography (SEC) and NMR analyses as well as confirmed by the hydrolysis of the PCL segments of the copolymer. With targeted copolymers containing at least 10% weight of PHEMA and relatively small PHEMA backbones (ca. 5,000–10,000 g mol?1) the copolymer grafting density is higher than 90%. The ratio of free HEMA‐PCL homopolymer produced during the “one‐step” process was found to depend on the HEMA concentration, as well as the half‐life time of the radical initiator used. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3058–3067, 2008 相似文献
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Paul Kosma Martina Strobl Andreas Hofinger Jens Ø. Duus Bent O. Petersen Klaus Bock Helmut Brade 《Monatshefte für Chemie / Chemical Monthly》2002,133(4):561-570
Summary. Methyl glycosides of Kdo and a (2→8)-linked Kdo disaccharide were prepared which contain a deuterium label at C-8 of the reducing unit. The label was introduced in fair
diastereoselectivity upon reduction of an aldehyde group using a chiral borane complex derived from N-benzyloxycarbonyl-(S)-proline which produced the 8-(S)-deuterated derivative as the major isomer. Further coupling with a Kdo bromide gave the α-(2→8)-linked disaccharide in good yield. The deprotected disaccharide serves as a model for NMR spectroscopic
studies on the side chain conformation of a carbohydrate epitope from the bacterial pathogen Chlamydia.
Received September 17, 2001. Accepted October 17, 2001 相似文献
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Edgar H. H. Wong Martina H. Stenzel Thomas Junkers Christopher Barner‐Kowollik 《Journal of polymer science. Part A, Polymer chemistry》2009,47(4):1098-1107
Several nitrones and one nitroso compound have been evaluated for their ability to control the molecular weight of polystyrene via the recently introduced radical polymerization method of enhanced spin capturing polymerization (ESCP). In this technique, molecular weight control is achieved (at ambient or slightly elevated temperatures) via the reaction of a growing radical chain with a nitrone forming a macronitroxide. These nitroxides subsequently react rapidly and irreversibly with propagating macroradicals forming polymer of a certain chain length, which depends on the nitrone concentration in the system. Via evaluation of the resulting number‐average molecular weight, Mn, at low conversions, the addition rate coefficient of the growing radicals onto the different nitrones is determined and activation energies are obtained. For the nitrones N‐tert‐butyl‐α‐phenylnitrone (PBN), N‐methyl‐α‐phenylnitrone (PMN), and N‐methyl‐α‐(4‐bromo‐phenyl) nitrone (pB‐PMN), addition rate coefficients, kad,macro, in a similar magnitude to the styrene propagation rate coefficient, kp, are found with spin capturing constants CSC (with CSC = kad,macro/kp) ranging from 1 to 13 depending on the nitrone and on temperature. Activation energies between 23.6 and 27.7 kJ mol−1 were deduced for kad,macro, congruent with a decreasing CSC with increasing temperature. Almost constant Mn over up to high monomer to polymer conversions is found when CSC is close to unity, while increasing molecular weights can be observed when the CSC is large. From temperatures of 100 °C onward, reversible cleavage of the alkoxyamine group can occur, superimposing a reversible activation/deactivation mechanism onto the ESCP system. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1098–1107, 2009 相似文献