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...

Through atom transfer radical polymerization of styrene with 1,3‐dibromomethyl‐5‐propargyloxy‐benzene as initiator followed by the conversion of bromine end‐groups into azide end‐groups, well‐defined seesaw‐type polystyrene (PSt) macromonomers with two molecular weights (Mn = 8.0 and 28.0 k) were obtained. Thus, a series of long‐subchain hyperbranched (lsc‐hp) PSt with high overall molar masses and regular subchain lengths were obtained via copper‐catalyzed azide–alkyne cycloaddition click chemistry performed in THF and DMF, respectively. The polycondensation of seesaw‐type macromonomers was monitored by gel permeation chromatography. Because DMF is the reaction medium with higher polarity, click reaction proceeds more easily in DMF. Therefore, the growth of lsc‐hp PSt in DMF has faster rate than that in THF for the shorter seesaw‐type macromonomer (Seesaw‐8k). However, THF is the solvent with better solubility to PSt and leads to looser conformation of PSt chains. Thus, for the longer seesaw macromonomer (Seesaw‐28k), lsc‐hp PSt in THF has higher overall molar mass. As well, the self‐cyclization of seesaw‐type macromonomers also depends on both solvent and molar mass of macromonomer. The self‐cyclization degrees of Seesaw‐8k in DMF and THF are almost the same while that of Seesaw‐28k macromonomer is obviously lower in THF. The experimental results suggest a physical consideration to control the growth of hyperbranched polymers. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Herein, we report the synthesis of novel heat-resistant microspheres by self-stabilized precipitation copolymerization of styrene (St) and 2,2′-bis[4-(4maleimidophenoxy)phenyl]propane (BMIP) in an mN-methyl pyrrolidone (NMP)/ isopentyl acetate (IPA) mixed solvent. The effects of the solvent composition, monomer feed ratio, monomer, and initiator concentration on the size and morphology of the resultant poly(BMIP-co-St) microspheres were investigated in detail. Monodisperse, highly cross-linked poly(BMIP-co-St) microspheres with numberaverage diameters ranging from 2.23 to 1.28 μm were successfully obtained at a 1/2 molar ratio of [BMIP]/[St] in NMP/IPA (2/13, v/v). Due to the presence of a rigid imide ring and a highly cross-linked structure, the poly(BMIP-co-St) microspheres exhibited excellent thermal stability with an initial decomposition temperature up to 440 °C and a 30% char residue rate at 750 °C. Additionally, there were some unreacted maleimide groups on the surface of poly(BMIP-co-St) microspheres for further chemical modification, making the poly(BMIP-co-St) microspheres highly interesting as advanced functional materials.

Herein, monodisperse and nanoporous poly­(bismaleimide-co-divinylbenzene) microspheres (PBMs) are fabricated via one-pot self-stabilized precipitation polymerization of 2,2′-bis­[4-(4-maleimidophenoxy)­phenyl]­propane and divinylbenzene in the absence of any dispersants and templates. The particle size, specific surface area, and pore structure of the PBMs could be effectively tailored by tuning the monomer feed ratio and solvent composition. Under optimum reaction conditions, uniform PBMs with a particle size of 1.37 μm were obtained, which exhibit a maximum Brunauer–Emmett–Teller (BET) surface area (556.25 m2/g) and pore volume (0.48 cm3/g). This novel fabrication method for PBMs has significant merits including a simple process free of additives and high efficiency. Furthermore, PBMs loaded with Pd nanoparticles (PBMs@Pd) were easily synthesized via in situ chemical reduction and used as a catalytic microreactor due to their abundant pore structure. As an efficient heterogeneous catalyst for the reduction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH4), the as-prepared PBMs@Pd exhibited excellent catalytic activity with a high turnover frequency value (967.92 h–1) and excellent recyclability. This facile strategy opens up new horizons for the synthesis of porous microspheres with a well-controlled morphology and tunable pore structure, which have great application prospects in the fields of catalysis, adsorption, and energy storage.

Dual thermo-and pH-sensitive network-grafted hydrogels made of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) network and poly(N-isopropylacrylamide) (PNI-PAM) grafting chains were successfully synthesized by the combination of atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and click chemistry. PNIPAM having two azide groups at one chain end [PNIPAM-(N 3 ) 2 ] was prepared with an azidecapped ATRP initiator of N,N-di(b-azidoethyl) 2-chloropropionylamide. Alkyne-pending poly(N,N-dimethylaminoethyl methacrylate-co-propargyl acrylate) [P(DMAEMA-co-ProA)] was obtained through RAFT copolymerization using dibenzyltrithiocarbonate as chain transfer agent. The subsequent click reaction led to the formation of the network-grafted hydrogels. The influences of the chemical composition of P(DMAEMA-co-ProA) on the properties of the hydrogels were investigated in terms of morphology and swelling/deswelling kinetics. The dual stimulus-sensitive hydrogels exhibited fast response, high swelling ratio, and reproducible swelling/deswelling cycles under different temperatures and pH values. The uptake and release of ceftriaxone sodium by these hydrogels showed both thermal and pH dependence, suggesting the feasibility of these hydrogels as thermo-and pH-dependent drug release devices.