Synthesis and crystal structures of multifunctional tosylates as basis for star-shaped poly(2-ethyl-2-oxazoline)s

The synthesis of well-defined polymer architectures is of major importance for the development of complex functional materials. In this contribution, we discuss the synthesis of a range of multifunctional star-shaped tosylates as potential initiators for the living cationic ring-opening polymerization (CROP) of 2-oxazolines resulting in star-shaped polymers. The synthesis of the tosylates was performed by esterification of the corresponding alcohols with tosyl chloride. Recrystallization of these tosylate compounds afforded single crystals, and the X-ray crystal structures of di-, tetra- and hexa-tosylates are reported. The use of tetra- and hexa-tosylates, based on (di)pentaerythritol as initiators for the CROP of 2-ethyl-2-oxazoline, resulted in very slow initiation and ill-defined polymers, which is most likely caused by steric hindrance in these initiators. As a consequence, a porphyrin-cored tetra-tosylate initiator was prepared, which yielded a well-defined star-shaped poly(2-ethyl-2-oxazoline) by CROP as demonstrated by SEC with RI, UV and diode-array detectors, as well as by 1H NMR spectroscopy

Libraries of statistical hydroxypropyl acrylate containing copolymers with LCST properties prepared by NMP

The nitroxide-mediated copolymerization of 2-hydroxypropyl acrylate (HPA) with N-acryloylmorpholine (Amor) or N,N-dimethylacrylamide (DMA) was investigated using N-tert-butyl-N-(1′-diethylphosphono-2,2′-dimethylpropyl)-O-(2-carboxyl-prop-2-yl) (BlocBuilder) alkoxyamine initiator and additional free nitroxide (SG-1). Different reaction conditions, such as the concentration of additional SG-1, were tested to optimize the homopolymerizations using a Chemspeed ASW2000 automated parallel synthesizer. Best control for the homopolymerizations (polydispersity indices of 1.2−1.3) of all three monomers was achieved using 20% additional SG-1 (relative to the initiator) at a reaction temperature of 110 °C for 2 M solutions in N,N-dimethylformamide and a monomer/initiator ratio of 100/1. Libraries of P(Amor-stat-HPA) and P(DMA-stat-HPA) were synthesized with 0−100 mol % HPA with 10 mol % increments using the optimized conditions obtained for the homopolymerizations. The resulting polymers had narrow molecular weight distributions, and their compositions, determined using 1H NMR spectroscopy and elemental analysis, were close to the theoretical compositions. In addition, all copolymers of both libraries had single glass transition temperatures (Tg), and the transition temperatures decreased from the Tg of P(Amor) (147 °C) and P(DMA) (111 °C) to the Tg of P(HPA) (22 °C) with increasing HPA content. The cloud point of P(HPA) showed concentration dependence as well as a concentration dependent hysteresis. The cloud points of aqueous solutions of the copolymer libraries could be tuned from 21.4 to 88.0 °C and to 82.9 °C for P(Amor-stat-HPA) and P(DMA-stat-HPA), respectively, at a concentration of 1 wt %. LCST behavior was observed for copolymers with >40 wt % HPA in P(Amor-stat-HPA) and >55 wt % HPA in the P(DMA-stat-HPA) library

Libraries of methacrylic acid and oligo(ethylene glycol) methacrylate copolymers with LCST behavior

Homopolymers of methacrylic acid (MAA), monoethyleneglycol methyl ether methacrylate (MEOMA), diethyleneglycol methyl ether methacrylate (MEO2MA), oligo(ethyleneglycol) methyl ether methacrylate (OEGMA475 and OEGMA1100) and oligo(ethyleneglycol) ethyl ether methacrylate (OEGEMA246) were synthesized with various chain lengths via reversible addition fragmentation chain transfer (RAFT) polymerization. The homopolymers of MAA, MEOMA and OEGMA1100 did not show any cloud point (CP) in the range of 0–100 °C, whereas at a pH value of 7, the CPs were found to be 20.6, 93.7, and 20.0 °C for p(MEO2MA), p(OEGMA475) and p(OEGEMA246), respectively, with an initial monomer to initiator ratio of 50. Furthermore, statistical copolymer libraries of MAA with OEGMA475 and OEGMA1100 were prepared. The cloud points of the random copolymers of MAA and OEGMA475 were found to be in the range of 20–90 °C; surprisingly, even though the homopolymers of MAA and OEGMA1100 did not exhibit any LCST behavior, the copolymers of these monomers at certain molar ratios (up to 40% OEGMA1100) revealed a double responsive behavior for both temperature and pH. Finally, the cloud points were found to be in the range of 22–98 °C, measured at pH values of 2, 4, and 7, while no cloud point was detected at pH 10. © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7138–7147, 200