Preparation of multifunctional and well-defined macromolecules requires a smart selection of the most suitable controlled polymerization technique in combination with appropriate click reactions. In this review, we provide an overview on the use of various ''clickable'' initiators and monomers as well as on the postpolymerization modifications that have been widely used to construct clickable macromolecules. As such, this contribution will aid polymer chemists to select a suitable combination of CRP and click methodologies to design the target structures.

This feature article provides, for the first time, an overview of the research that guided the way from fundamental studies of the thermo-responsive phase separation of aqueous polymer solutions to polymeric sensor systems. The incorporation of solvatochromic dyes into thermoresponsive polymers as well as the concepts of polymeric sensors are presented and discussed in detail.

The interest in "smart" functional materials that respond to changes in the environment strongly increased in the last years owing to the desire to control complexity and to create systems that adapt or respond to the environment. Moreover, such "smart" materials are used to design and develop new responsive materials for a wide range of applications in various fields, such as biotechnology, [1][2][3] drug delivery, [4][5][6] particle transport, [7] and optical sensing. [8][9][10][11] Recently, a thermoresponsive fluorescent nanogel was applied as an intracellular thermometer, that is, to monitor the temperature in living cells. [12] A current trend in the field of optical sensing is the development of dual sensors that respond simultaneously and independently to different stimuli. [13] In recent years, dual optical sensors have been reported for pressure and temperature, [14] oxygen and temperature, [15][16][17][18] oxygen and carbon dioxide, [19][20][21] as well as oxygen and pH value. [22][23][24] Surprisingly, no dual sensor has been reported for temperature and pH value, which would be beneficial, for example to monitor chemical reactions and for biological diagnostics.We have aimed to develop a soluble dual sensor that responds to both temperature and pH value. The solubility of the sensor material allows monitoring in situ while at the same time providing information about homogeneity and local conditions. In contrast to reported dual sensors, which are generally based on two different sensing chromophores, we have combined a pH-responsive solvatochromic dye with a thermoresponsive polymer. Solvatochromic dyes change color in response to changes in solvent polarity. [25][26][27] Recently, it was reported that combining a solvatochromic dye with a temperature-responsive polymer leads to a color change upon changing the temperature, as in the dissolved state the dye is in contact with water while in the collapsed state the dye is dissolved in the less polar precipitated polymer. [8][9][10]12] Herein, we report our efforts to develop a dual sensor that senses temperature by the solubility transition of a thermoresponsive polymer and senses the pH value by a pHresponsive solvatochromic dye, namely disperse red 1 (DR1, 1; Scheme 1). [28,29] Poly(oligoethyleneglycol methacrylate) (POEGMA) was chosen as temperature sensing polymer on the basis of its biocompatibility and the possibility of tuning the lower critical solution temperature (LCST) by copolymerizing different OEGMA monomers. [30][31][32] Since the polymer solubility transition can depend on the molar mass distribution of the copolymer, a well-defined polymer is required to ensure homogeneous solubility of the sensing polymer. Therefore, a controlled radical polymerization process, namely reversible addition fragmentation chain transfer (RAFT), [33][34][35] was applied to prepare welldefined copolymers of OEGMA and a methacrylate monomer functionalized with disperse red 1 (DR1-MA, 3; Scheme 1).For this purpose monomer 3 was prepared by esterification of...

A series of thermoresponsive diblock copolymers of poly [2-(dimethylamino)ethyl methacrylate-block-di(ethyleneglycol) methyl ether methacrylate], poly(DMAEMA-b-DEGMA), were synthesized by reversible addition−fragmentation chain transfer (RAFT) polymerizations. The series consist of diblock and quasi diblock copolymers. Sequential monomer addition was used for the quasi diblock copolymer synthesis and the macro-chain transfer approach was utilized for the block copolymer synthesis. The focus of this contribution is the controlled variation of the ratios of DMAEMA to DEGMA in the copolymer composition, resulting in a systematic polymer library. One of the investigated block copolymer systems showed double lower critical solution temperature (LCST) behavior in water and was further investigated. The phase transitions of this block copolymer were studied in aqueous solutions by turbidimetry, dynamic light scattering (DLS), variable temperature proton nuclear magnetic resonance ( 1 H NMR) spectroscopy, zeta potential, and cryo transmission electron microscopy (cryo-TEM). The block copolymer undergoes a two-step thermo-induced self-assembly, which results in the formation of multilamellar vesicles after the first LCST temperature and to unilamellar vesicles above the second LCST transition. An interplay of ionic interactions as well as the change of the corresponding volume fraction during the LCST transitions were identified as the driving force for the double responsive behavior.

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Efficient delivery of short interfering RNAs reflects a prerequisite for the development of RNA interference therapeutics. Here, we describe highly specific nanoparticles, based on near infrared fluorescent polymethine dye-derived targeting moieties coupled to biodegradable polymers. The fluorescent dye, even when coupled to a nanoparticle, mimics a ligand for hepatic parenchymal uptake transporters resulting in hepatobiliary clearance of approximately 95% of the dye within 45 min. Body distribution, hepatocyte uptake and excretion into bile of the dye itself, or dye-coupled nanoparticles can be tracked by intravital microscopy or even non-invasively by multispectral optoacoustic tomography. Efficacy of delivery is demonstrated in vivo using 3-hydroxy-3-methyl-glutaryl-CoA reductase siRNA as an active payload resulting in a reduction of plasma cholesterol levels if siRNA was formulated into dye-functionalised nanoparticles. This suggests that organ-selective uptake of a near infrared dye can be efficiently transferred to theranostic nanoparticles allowing novel possibilities for personalised silencing of disease-associated genes.

Here a method is presented for the temperature‐switchable assembly of viral particles into large hierarchical complexes. Dual‐functional diblock copolymers consisting of poly(diethyleneglycol methyl ether methacry­late) (poly(DEGMA)) and poly((2‐dimethylamino)ethyl methacrylate) (poly(DMAEMA)) blocks self‐assemble electrostatically with cowpea chlorotic mottle virus (CCMV) particles into micrometer‐sized objects as a function of temperature. The poly(DMAEMA) block carries a positive charge, which can interact electrostatically with the negatively charged outer surface of the CCMV capsid. When the solution temperature is increased above 40 °C, to cross the cloud point temperature (Tcp) of the DEGMA block, the polymer chains collapse on the surface of the virus particle, which makes them partially hydrophobic, and consequently causes the formation of large hierarchical assemblies. Disassembly of the virus–polymer complexes can be induced by reducing the solution temperature below the Tcp, which allows the poly(DEGMA) blocks to rehydrate and free virus particles to be released. The assembly process is fully reversible and can sustain several heating–cooling cycles. Importantly, this method relies on reversible supramolecular interactions and therefore avoids the irreversible covalent modification of the particle surface. This study illustrates the potential of temperature‐responsive polymers for controlled binding and releasing of virus particles.