Radical ring-opening polymerization of a thionolactone gives degradable thioester-functional polymers.

Telechelic thermo- and light-responsive polymers based on poly(oligo(ethylene glycol) methyl ether methacrylate) P(OEGMA) with azobenzene functionalities at the end groups were synthesized. In a reversible addition-fragmentation chain transfer (RAFT) polymerization using a functionalized chain transfer agent (CTA) containing a pentafluorophenyl (PFP) activated ester, oligo(ethylene glycol) methyl ether methacrylate (OEGMA, Mn ∼ 300 g mol-1 ) could successfully be polymerized with good control over molecular weight, very high conversions, and narrow molecular weight distributions. Polymers derived from this CTA possessed an activated ester at the R-end of the polymer chain as well as a dithioester ω-terminus. The ω-dithioester group of each polymer chain could quantitatively be either removed with AIBN treatment or substituted with a PFP ester by using a modified diazo compound. As a consequence, a postmodifiaction of the telechelic reactive end groups was possible through a polymer analogous reaction with aminofunctionalized azobenzene. P(OEGMA) polymers containing azobenzene end groups showed a reversible light- and temperature-controlled phase transition in water. Higher values for the lower critical solution temperature (LCST) were measured after irradiation of the aqueous polymer solutions due to the higher polarity of cis-azobenzene. The LCST differences between irradiated and nonirradiated solutions increased linearly upon the ratio of azobenzene units up to 4.3

Reversible addition fragmentation chain transfer (RAFT) polymerization is one of the most extensively studied reversible deactivation radical polymerization methods for the production of well-defined polymers. After polymerization, the RAFT agent end-group can easily be converted into a thiol, opening manifold opportunities for thiol modification reactions. This review is focused both on the introduction of functional end-groups using well-established methods, such as thiol-ene chemistry, as well as on creating bio-cleavable disulfide linkages via disulfide exchange reactions. We demonstrate that thiol modification is a highly attractive and efficient chemistry for modifying RAFT polymers.

Poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) is shown to possess insoluble– soluble transitions (UCST-type phase behavior) in a large variety of aliphatic alcohols. Samples of different molecular weights ranging from 5 kg mol1 to 23 kg mol1 prepared by the RAFT process and featuring different end groups at each end were analyzed by cloud point measurements. Transitions occurred sharply and were fully reversible. The UCST was found to increase with an increasing molecular weight. Hydrophobic (alkyl chain) end groups were found to lower the critical temperature in isopropanol, while rigid aromatic end groups raised the transition temperature. In ternary mixtures of isopropanol/chloroform/POEGMA, the UCST decreased with an increasing chloroform concentration, with 10 vol% of chloroform accounting for a 30 C drop. In mixtures of isopropanol/ hexane/POEGMA, the cloud point increased significantly only with hexane concentrations above 30 vol%, at which level a 2 C transition temperature increase was found. Addition of water to isopropanol solutions had a strong effect, with 1 vol% of water causing a decrease of the transition temperature of 12.5 C. With an increasing chain length of the solvent, the cloud point increased, while a branching of the hydrocarbon chains lowered the cloud point. Samples of 23 kg mol1 POEGMA were for instance found to have cloud points of 22.0 C in ethanol, 35.7 C in isopentanol, and 75.4 C in dodecanol

The influence of the chemical structure of both end groups onto the lower critical solution temperature (LCST) of poly[oligo(ethylene glycol) monomethyl ether methacrylate] (POEGMA) in water was systematically investigated. POEGMA of Mn = 3550 g/mol and Mw/Mn = 1.14 prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization was equipped with two different functional end groups in a one-step postpolymerization reaction combining activated esters, functional amines, and functional methane thiosulfonates. As end groups, n-propyl, n-hexadecyl, di(n-octadecyl), poly(ethylene glycol)-550 (PEG), 1H,1H-perfluorononyl, azobenzene, and trimethylethylammonium groups were systematically combined with methyl, n-hexadecyl, and 1H,1H,2H,2H-perfluorooctyl groups. Polymers were characterized by gel permeation chromatography, dynamic light scattering, and turbidimetry. Hydrophobic end groups at either end of the polymer chain decreased the LCST. For hydrophobic groups at both ends of the chain their influence was additive. Two large hydrophobic end groups allowed micelle formation below the LCST and an LCST higher than to be expected from nonaggregated polymers. The strongest hydrophobic effect was found for rigid aromatic end groups, which was attributed to their incompatibility with the flexible polymer chain. Charged end groups increased the LCST and could compensate for the effect of hydrophobic end groups at the opposite end group. PEG end groups could mask a hydrophobic influence of the opposite end group and stabilized the LCST

Polysulfobutylbetaine (SBB) (co)polymers, zwitterionic species bearing ammonium and sulfonate groups\ud separated by a butyl spacer in every repeat unit, were prepared through three different synthetic routes\ud and their aqueous solution behaviour was studied. Postpolymerization quaternization of poly[2-(dimethylamino)ethyl\ud methacrylate] with 1,4-butanesultone resulted in incomplete modification due to the low\ud reactivity of this alkylating agent. RAFT radical polymerization of SBB-functional (meth)acrylate monomers\ud and their copolymerization with a sulfopropylbetaine (SPB) methacrylate yielded well-defined (co)polymers\ud with low dispersities 1.13 ≤ ĐM ≤ 1.23 at monomer conversions of 75–92%. For a series of SBB\ud methacrylate homopolymers with increasing degrees of polymerization from 66–186 measured upper\ud critical solution temperature (UCST) cloud points increased from 27–77 °C. Cloud points of statistical\ud SPB-SBB copolymers with similar degrees of polymerization, but varying molar compositions, increased\ud linearly with SBB content offering a simple means of UCST tuning. Additionally, novel SBB acrylamide\ud homo- and copolymers were prepared by postpolymerization modification of poly(pentafluorophenyl\ud acrylate) with an SBB-functional amine and in mixtures with benzylamine as a hydrophobic modifier. In all\ud cases, the SBB (co)polymers had significantly higher UCSTs than their more common SPB counterparts,\ud greatly extending the temperature range of tuneable UCST transitions and making the investigated SBB\ud (co)polymers advantageous for exploiting their ‘smart’ behaviour. In this respect, combining SBB functionality\ud with hydrophobic benzylacrylamide comonomers is presented as a simple means of increasing the\ud maximum salt concentration at which UCST behaviour (which shows an antipolyelectrolyte effect) can be\ud observed, enabling UCST transitions in aqueous solutions containing a physiological concentration (9 g\ud L−1\ud ) of NaCl

"smart" materials rely on very distinct material responses on a macroscopic and/or microscopic level. This can be achieved by crafting stimulus-responsive polymers into nanostructured materials, including smart nanoparticles, which are receiving increasing attention specifically in the biomedical field. [2,3] Amphiphilic block copolymers are well-known to undergo self-directed assembly in selective solvents providing access to a range of soft matter nanoparticles [4][5][6][7] with applications in coatings, [8] electronics, [9] drug delivery, [10] and cancer therapy, [11,12] among others. Traditionally, the preparation of such nanoparticles has been accomplished by initial synthesis and molecular dissolution of well-defined parent copolymers which are subsequently "processed", often via time-consuming step-wise dialysis, to give the targeted nano-object. Another drawback of this well-established approach is the generally low concentration of the final copolymer nanoparticles (≤1.0 wt% is common) which limits industrial application and study of such nanoparticles in areas where high Polymerization-induced self-assembly (PISA) is an extremely versatile method for the in situ preparation of soft-matter nanoparticles of defined size and morphologies at high concentrations, suitable for large-scale production. Recently, certain PISA-prepared nanoparticles have been shown to exhibit reversible polymorphism ("shape-shifting"), typically between micellar, worm-like, and vesicular phases (order-order transitions), in response to external stimuli including temperature, pH, electrolytes, and chemical modification. This review summarises the literature to date and describes molecular requirements for the design of stimulus-responsive nano-objects. Reversible pH-responsive behavior is rationalised in terms of increased solvation of reversibly ionized groups. Temperature-triggered order-order transitions, conversely, do not rely on inherently thermo-responsive polymers, but are explained based on interfacial LCST or UCST behavior that affects the volume fractions of the core and stabilizer blocks. Irreversible morphology transitions, on the other hand, can result from chemical post-modification of reactive PISA-made particles. Emerging applications and future research directions of this "smart" nanoparticle behavior are reviewed.

The direct synthesis of methacrylic-based soft polymeric nanoparticles via reversible addition-fragmentation chain transfer dispersion polymerization (RAFTDP) is described. The use of poly[2-(dimethylamino)ethyl methacrylate]s, of varying average degree of polymerization (X¯n), as the stabilizing blocks for the RAFTDP of 3-phenylpropyl methacrylate (PPMA) in ethanol at 70 °C, at various total solids contents, yielded the full spectrum of self-assembled nanoparticles (spherical and worm aggregates and polymersomes). We also demonstrate that nanoparticle morphology can be tuned simply by controlling temperature. This is especially evident in the case of worm aggregates undergoing a thermoreversible transition to spherical species - a process that is accompanied by a macroscopic degelation-gelation process.