ABSTRACT
A modest structural change of a ß-diketiminate-supported aluminium complex leads to dramatic differences in the reactivity towards cyclopentenone. While the bulkier complex efficiently executes Diels Alder transformations the smaller analogue performs unique polymerisation of this substrate. This observation appears to be unprecedented in the chemistry of Lewis acids and cyclic dienophiles as it represents a unique way to polymerise a functionalised olefin.
ABSTRACT
The separation of an oligo(methyl acrylate) distribution, obtained from reversible addition-fragmentation chain transfer (RAFT) polymerization, in a discrete (dispersity=1) oligomeric library (degree of polymerization between 1 and 22) is presented. The properties of this library in terms of diffusivity, glass transition temperature, and viscosity are determined, filling a significant knowledge gap associated with these materials. The obtained oligomer library is used to construct artificial oligomer distributions on demand. These artificial oligomer distributions are used to highlight the potential to tailor physical properties of a material, while concomitantly demonstrating the limitations associated with size-exclusion chromatography analysis of molecular weight and dispersity in particular.
ABSTRACT
Functional precision polymers based on monodisperse oligo(N-substituted acrylamide)s and oligo(2-substituted-α-hydroxy acid)s have been synthesized. The discrete sequences originate from a direct translation of side-chain functionality sequences of a peptide with well-studied properties. The peptide was previously selected to solubilize the photosensitizer meta-tetra(hydroxyphenyl)chlorin. The resulting peptidomimetic formulation additives preserve the drug solubilization and release characteristics of the parent peptide. In some cases, superior properties are obtained, reaching up to 40 % higher payloads and 27-times faster initial drug release.
ABSTRACT
2-cyano-2-propyl dithiobenzoates (CPDB)-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization was monitored by online flow microreactor/mass spectrometry. This enabled the reactions to be followed in a time-resolved manner, closely resolving product patterns in the reaction mixtures at any point in time. RAFT polymerization was investigated for low RAFT to monomer ratios, enabling the monitoring of the early stages of a typical RAFT polymerization. The expected transition from pre- to the RAFT main equilibrium is observed. However, very high abundancies for cross-termination products were also identified, both in the pre- and main equilibrium stage. This is a somewhat surprising result as such products have always been expected, but to date have not been observed in the majority of studies. Product isolation and NMR analysis revealed that cross-termination occurs in the para position of the benzoate ring and becomes fully irreversible via re-aromatization of the ring in a H-shift reaction. The present data suggest a pronounced chain-length dependence of the cross-termination reaction, which would explain why the products are seen here, but not in other studies.
ABSTRACT
Linear monodisperse 18- and 20-mer acrylates are obtained via consecutive synthesis of two sequence-defined acrylate 9- and 10-mers, followed by disulfide coupling utilizing reversible addition-fragmentation chain transfer (RAFT) end group chemistry. The sequence-defined oligoacrylates are accessed via consecutive single (SUMI) and multiple (MUMI) unit monomer insertions through RAFT polymerization, using the extensive acrylate monomer library as functional building blocks. Aminolysis of the trithiocarbonate macroRAFT end group and in situ oxidation of the thiols to form a disulfide bridge lead to the formation of 18- and 20-mer acrylates. In this approach, one or multiple acrylate building blocks can be inserted in each step by chain extension to form a stable carbon-carbon backbone. Isolation of the targeted monodisperse oligomers, from the statistical mixtures obtained at first, is performed by flash column chromatography with high efficiency. It is shown that the SUMI and MUMI strategy, when combined with flash column chromatography separation, is highly efficient and allows to construct monodisperse materials of very considerable length starting from cheap and very versatile building blocks.
ABSTRACT
A technique for the continuous on-line monitoring of polymerization processes by electrospray ionization mass spectrometry (ESI-MS) is presented via coupling with a commercial microreactor system. The potential is demonstrated by monitoring polymerizations in real time under synthesis conditions. Furthermore, a single acrylate monomer insertion into a oligo-RAFT agent, as used in the synthesis of monodisperse sequence controlled materials, was optimized by on-line screening of reaction conditions.
ABSTRACT
A versatile, cost-effective approach to the rapid, fully unattended preparation of systematic quasi-diblock copolymer libraries via sequential RAFT polymerization in an automated synthesizer is reported. The procedure is demonstrated with the synthesis of a 23 member library of low dispersity poly(butyl methacrylate)-quasiblock-poly(methyl methacrylate) covering a wide (fivefold) range of molar mass for the second block in a one-pot, sequential, RAFT polymerization.