ABA triblock copolymers: from controlled synthesis to controlled function

The ABA amphiphilic block copolymers, poly(hydroxyethyl methacrylate-hlock-methylphenylsilane-block-hydroxyethyl methacrylate) (PHEMA-PMPS-PHEMA) and poly[oligo(ethylene glycol) methyl ether methacrylate-block-methylphenylsilane-block-oligo(ethylene glycol). methyl ether methacrylate] (POEGMA-PMPS-POEGMA) were successfully synthesised via atom transfer radical polymerisation (ATRP). Macroinitiators suitable for the ATRP of oligo(ethylene glycol) methyl ether methacrylate and 2-hydroxyethyl methacrylate were synthesised from the condensation reaction of alpha,omega-dihalopolymethylphenylsilane and 2'-hydroxyethyl 2-bromo-2-methylpropanoate. The copolymers were characterised using H-1 NMR and C-13 NMR spectroscopy and molecular weight characteristics were determined using size exclusion chromatography and H-1 NMR. The aggregation behaviour of some of the copolymers in water was studied using transmission and scanning electron microscopy and dynamic light scattering. These revealed the prevalent aggregate species to be micelles. Larger aggregates of 300-1000 nm diameter were also observed. The UV induced degradation of the aggregates was studied by UV-Vis spectroscopy. The thermal behaviour of selected copolymers was studied by differential scanning calorimetry and microphase separation of the two components was demonstrated

How Do Spherical Diblock Copolymer Nanoparticles Grow during RAFT Alcoholic Dispersion Polymerization?

A poly(2-(dimethylamino)ethyl methacrylate) (PDMA) chain transfer agent (CTA) is used for the reversible addition–fragmentation chain transfer (RAFT) alcoholic dispersion polymerization of benzyl methacrylate (BzMA) in ethanol at 70 °C. THF GPC analysis indicated a well-controlled polymerization with molecular weight increasing linearly with conversion. GPC traces also showed high blocking efficiency with no homopolymer contamination apparent and Mw/Mn values below 1.35 in all cases. 1H NMR studies confirmed greater than 98% BzMA conversion for a target PBzMA degree of polymerization (DP) of up to 600. The PBzMA block becomes insoluble as it grows, leading to the in situ formation of sterically stabilized diblock copolymer nanoparticles via polymerization-induced self-assembly (PISA). Fixing the mean DP of the PDMA stabilizer block at 94 units and systematically varying the DP of the PBzMA block enabled a series of spherical nanoparticles of tunable diameter to be obtained. These nanoparticles were characterized by TEM, DLS, MALLS, and SAXS, with mean diameters ranging from 35 to 100 nm. The latter technique was particularly informative: data fits to a spherical micelle model enabled calculation of the core diameter, surface area occupied per copolymer chain, and the mean aggregation number (Nagg). The scaling exponent derived from a double-logarithmic plot of core diameter vs PBzMA DP suggests that the conformation of the PBzMA chains is intermediate between the collapsed and fully extended state. This is in good agreement with 1H NMR studies, which suggest that only 5−13% of the BzMA residues of the core-forming chains are solvated. The Nagg values calculated from SAXS and MALLS are in good agreement and scale approximately linearly with PBzMA DP. This suggests that spherical micelles grow in size not only as a result of the increase in copolymer molecular weight during the PISA synthesis but also by exchange of individual copolymer chains between micelles and/or by sphere–sphere fusion events

Plastic- and liquid-crystalline architectures from dendritic receptor molecules

Host molecules with U-shaped receptor cavities have been derivatized at their convex side with two n-hydrocarbon tails (1), two first-generation (2), and two second-generation (3) monodendritic hydrocarbon tails. Although hosts 1 and 2 display plastic-crystalline behavior, evidence suggests that host 3 forms a cubic liquid-crystalline phase. In this phase, molecules of 3 are arranged in spherical supramacromolecular assemblies, in which the receptor cavities are situated in the core and the hydrocarbon tails at the periphery. The 1:1 host-guest complex of 3 with methyl 3,5-dihydroxybenzoate forms a similar liquid-crystalline phase, with the guest included in the core of the assemblies

Self-assembled nanoreactors

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Monitoring Protein−Polymer Conjugation by a Fluorogenic Cu(I)-Catalyzed Azide−Alkyne 1,3-Dipolar Cycloaddition\ud

The Cu(I)-catalyzed azide−alkyne cycloaddition (CuAAC) has recently proven to be a powerful synthetic tool in various fields of chemistry, including protein−polymer conjugation. In this article, we describe a fluorogenic CuAAC, which allows for efficient monitoring of protein−polymer conjugation. We show that profluorescent 3-azido coumarin-terminated polymers can be reacted with an alkyne-functionalized protein to produce a strongly fluorescent triazole-linked conjugate. Upon formation of the product, the evolution of fluorescence can accurately be determined, providing information about the course of the CuAAC. As a proof of concept, we synthesized several 3-azido coumarin terminated poly(ethylene glycol) (PEG) chains and investigated their conjugation with alkyne-functionalized bovine serum albumin (BSA) as a model protein. CuAAC conjugation was shown to be very efficient and proceeded rapidly. Conversion plots were constructed from measuring the fluorescence as function of reaction time. An additional benefit of the fluorogenic CuAAC is the in situ labeling of bioconjugates. We envision that the fluorogenic protein−polymer conjugation is not restricted to the reaction system reported in this work, but may also be ideal to screen for optimal reaction conditions of various other system

Synthesis of Polymer-Biohybrids: From Small to Giant Surfactants

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