The assembly behavior of diblock copolymers in solution can be modulated by block length, block ratio, solvent properties, and preparation route. Different assembly morphologies such as spherical micelles, cylindrical micelles, vesicles, and large compound vesicles have been obtained for diblock copolymers with shorter solvated block, such as poly(acrylic acid)-b-polystyrene (PAA-b-PSt). In the present work, we reported an easy-going route to prepare PAA-b-PSt assemblies with different morphologies through reversible addition−fragmentation-transfer (RAFT) dispersion polymerization of styrene in methanol with trithiocarbonated PAA as macromolecular chain transfer agent. Because this RAFT dispersion polymerization exhibited controlled features, the consecutive growth of PSt block led to the successive transition of the obtained PAA-b-PSt assemblies from spherical micelles, cylindrical micelles, vesicles, to large compound vesicles, confirmed by the combination of electron microscopy, laser light scattering, and chemical structural analysis. PAA-b-PSt assembly morphologies and their transition have been adjusted by polymerization conversion, St/PAA feed ratio, and methanol amount, which were elucidated in view of thermodynamic consideration. The mechanisms for the formation of vesicle and the reorganization of vesicles were suggested. This polymerization-induced self-assembly and self-organization provides an efficient way to prepare different nano/microsized polymeric structures.

Using a facile approach, we successfully made large “defect-free” hyperbranched polystyrene (PSt) chains with uniform subchains between two branching points from the interchain “clicking” of a seesaw-type linear macromonomer [azide∼∼∼alkyne∼∼∼azide] prepared by ATRP with a following conversion of two bromine-ends into two azide-ends, where ∼∼∼ denotes a PSt chain (1.65–31.0 kg/mol). The “click” reaction kinetics monitored by a combination of size exclusion chromatography (SEC) and laser light scattering (LLS) reveals that the degree of self-polycondensation (DP) is related to the reaction time (t) as ln(DP+ 1)/2 = ([A]0 k AB,0)/β arctan(βt), where [A]0 and k AB,0 are the initial alkyne concentration and the initial reaction rate between the azide and alkyne groups, respectively; β is a constant and its reciprocal (1/β) represents the time at which k AB = k AB,0/2. The results reveal that 1/β is scaled to the macromonomer’s molar concentration ([C]) and molar mass (M) as 1/β ∼ [C]−0.35 M 0.55, indicating that 1/β is governed by the interchain distance and diffusion, respectively. Each hyperbranched sample can be further fractionated into a set of narrowly distributed “defect-free” hyperbranched chains with different molar masses by precipitation. The LLS results show, for the first time, that the root-mean-square radius of gyration (⟨R g⟩) and hydrodynamic radius (⟨R h⟩) of “defect-free” hyperbranched polystyrenes in toluene at 25 °C are scaled to the weight-average molar mass (M w) as ⟨R g⟩ = 5.53 × 10–2 M w 0.464 and ⟨R h⟩ = 2.95 × 10–2 M w 0.489, respectively, where the exponents are smaller than the predicted 1/2.

A nanoreactor with temperature-responsive poly(N-isopopylacrylamide) (PNIPAM) coated on the external pore mouth of mesoporous silica hollow spheres and Au nanoparticles at the internal pore mouth were fabricated. Such spatial separation allows both Au nanoparticles and PNIPAM to function without interfering with each other. Transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectra, and temperature-dependent optical transmittance curves demonstrate successful grafting of PNIPAM. This nanoreactor shows repeated on/off catalytic activity switched by temperature control. It shows excellent catalytic activity toward 4-nitrophenol (4-NP) reduction at 30 °C [below lower critical solution temperature (LCST) of PNIPAM] with a turnover frequency (TOF) of 14.8 h(-1). However, when the temperature was 50 °C (above LCST), the TOF dropped to 2.4 h(-1). Kinetic studies indicated that diffusion into the mesopores of the catalyst was the key factor, and the temperature-responsive behavior of PNIPAM was able to control this diffusion.

b S Supporting InformationH yperbranched polymers have attracted much interest because of their useful chemical and physical properties, resulting from their branching topology and a high number of end groups. 1À4 For a given weight concentration, their smaller hydrodynamic volume and functional periphery lead to a variety of current and potential applications, including their usages as coatings and resins additives, 5,6 viscosity modifiers, 7,8 and novel carriers. 4,9À11 Commonly, hyperbranched polymers are synthesized through the step-growth approach, such as polycondensation, addition step-growth reactions and cycloaddition, or the chain-growth approach, including the self-condensing vinyl copolymerization and the ring-opening multibranching polymerization. The detailed methodologies have been extensively reviewed. 1À4,12 Hyperbranched polymers with short subchains behave like small rigid and hard "balls" so that their properties are mainly related to their size. On the other hand, for hyperbranched polymers with longer subchains, proper microscopic conformation variation and entanglement can greatly affect their macroscopic properties. For example, the swollen and collapse of long subchains of a hyperbranched polymer additive in a solution or dispersion can alternate its macroscopic viscosity by a factor of hundreds. This is why the research and development of various hyperbranched polymers made of subchains longer than the entanglement length has attracted much attention in the past two decades. People coined different terms to describe them as Hyper-Macs, 13 arborescent graft polymers, 14 and dendrigrafts. 15 Using the chain-growth approach, Gnanou et al. 16 and Dworak et al. 17 tried to develop different techniques for the preparation of hyperbranched chains with a desired architecture. However, their methods involved a multistage and time-consuming process, inevitably resulting in broadly distributed subchains. While in the step-growth approach, AB 2 type of macromonomers can be interconnected into hyperbranched chains with a "controllable" architecture through polyesterification 18À20 and poly-Williamson coupling reaction 13 between two reactive A and B functional groups. Note that for a given weight concentration a solution of long initial macromonomer chains contains a very limited number of reactive A and B groups. In order to effectively couple them together, Pan et al. 21 utilized alkynylÀazide polycycloaddition to make hyperbranched polystyrene (PSt) chains with claimed short uniform subchains. On the other hand, Hutchings et al. 22 described an iterative convergent strategy to make dendritically branched chains using a multistaged Williamson coupling process.In reality, there exist two types of AB 2 macromonomers-Y-type: two reactive B groups are at one end and A is at the other end; seesaw-type: each chain end is attached with one reactive B group and A is in the middle. They lead to different topologies of hyperbranched polymers. Using Y-type macromonomers, some of B groups inevitably remain...

Poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) in aqueous solutions shows one fast and one slow relaxation mode in dynamic light scattering (DLS), but the mixture of PAA and PEO (PAA/PEO) in aqueous solution only has a single fast mode. The effects of pH, polymer concentration, and salt concentration on these two modes have been investigated using laser light scattering (LLS), viscometry, and rheological measurements. Our results showed that the hydrogen bonding between carboxylic group and ether oxygen led to the formation of large complexes among PAA-g-PEO chains, which were absent between PAA and PEO chains in PAA/PEO aqueous solutions. The addition of formamide can break these interchain complexes because the hydrogen bonding between formamide and PAA segment is stronger than that between PEO and PAA segment. Thermodynamically speaking, the formation of hydrogen bonds among PAA-g-PEO chains leads to a less entropy loss than that between PAA and PEO chains in PAA/PEO aqueous solution, because in the former case PEO is already chemically connected to PAA backbone. Therefore, the same enthalpy gain is sufficient to compensate the entropy loss in PAA-g-PEO aqueous solution relative to that in PAA/PEO aqueous solution, resulting in large interchain PAA-g-PEO complexes.