Strategies toward well‐defined polymer nanoparticles inspired by nature: Chemistry versus versatility

Polymeric nanoparticles are promising delivery platforms for various biomedical applications. One of the main challenges toward the development of therapeutic nanoparticles is the premature disassembly and release of the encapsulated drug. Among the different strategies to enhance the kinetic stability of polymeric nanoparticles, shell‐ and core‐crosslinking have been shown to provide robust character, while creating a suitable environment for encapsulation of a wide range of therapeutics, including hydrophilic, hydrophobic, metallic, and small and large biomolecules, with gating of their release as well. The versatility of shell‐ and core‐crosslinked nanoparticles is driven from the ease by which the structures of the shell‐ and core‐forming polymers and crosslinkers can be modified. In addition, postmodification with cell‐recognition moieties, grafting of antibiofouling polymers, or chemical degradation of the core to yield nanocages allow the use of these robust nanostructures as “smart” nanocarriers. The building principles of these multifunctional nanoparticles borrow analogy from the synthesis, supramolecular assembly, stabilization, and dynamic activity of the naturally driven biological nanoparticles such as proteins, lipoproteins, and viruses. In this review, the chemistry involved during the buildup from small molecules to polymers to covalently stabilized nanoscopic objects is detailed, with contrast of the strategies of the supramolecular assembly of polymer building blocks followed by intramicellar stabilization into shell‐, core‐, or core–shell‐crosslinked knedel‐like nanoparticles versus polymerization of polymers into nanoscopic molecular brushes followed by further intramolecular covalent stabilization events. The rational design of shell‐crosslinked knedel‐like nanoparticles is then elaborated for therapeutic packaging and delivery, with emphasis on the polymer chemistry aspects to accomplish the synthesis of such nanoparticulate systems. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Investigation of segmental reorganization within amphiphilic block polymer nanoparticles derived from shell crosslinked micelle templates: Shell crosslinked knedel-like inversion

The construction of nanoscopic materials by synthetic methodologies that iterate covalent and supramolecular interactions has been developed over the past three decades as a powerful method to afford complex functional materials. Indeed, the present study was nearly lost in the archives of dissertation research completed in 2001, which revealed nanoscale conformational dynamics in the segmental reorganization, and partial inversion, of topologically shell crosslinked knedel-like (SCK) nanoparticles. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 204–214     

Zwitterionic shell‐crosslinked micelles from block‐comb copolymer of PtBA‐b‐P(PEGMEMA‐co‐DMAEMA)

Through reversible addition‐fragmentation chain transfer (RAFT) polymerization of t‐butyl acrylate (tBA) and RAFT copolymerization of 2‐dimethylaminoethyl methacrylate (DMAEMA) with poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), block‐comb copolymer of PtBA‐b‐P(PEGMEMA‐co‐DMAEMA) was prepared. After the self‐assembly of PtBA‐b‐P(PEGMEMA‐co‐DMAEMA) into core‐shell spherical micelles, P(PEGMEMA‐co‐DMAEMA) segments of the shell was crosslinked with 1,2‐bis(2‐iodoethoxy)ethane and the core of PtBA was selectively hydrolysized with trifluoroacetic acid. Thus, zwitterionic shell‐crosslinked micelles with positively charged outer shell and negatively charged inner core were obtained. Dynamic light scattering, transmission electron microscope, Zeta potential measurement, and nuclear magnetic resonance were used to confirm the formation of the zwitterionic shell‐crosslinked micelles. They showed the excellent resistance to the variation of pH value and possessed the positive values throughout the whole range of pH range even if the carboxylic groups of the micelles was much more than ammonium groups. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Novel Structured Composites Formed from Gold Nanoparticles and Diblock Copolymers

We report a simple procedure to prepare a novel Au‐micelle composite with a core‐shell‐corona structure. This composite is prepared by reduction of tetrachloroauric acid (HAuCl₄ · 3H₂O) in dilute aqueous solution containing polystyrene‐block‐poly(4‐vinylpyridine) micelles and poly(ethylene oxide)‐block‐poly(4‐vinylpyridine) copolymers. The micelles with a polystyrene core and a poly(4‐vinylpyridine) shell are transformed into Au‐micelle composites with a polystyrene core, a swollen hybrid Au/poly(4‐vinylpyridine) inner shell, and a poly(ethylene oxide) corona by direct physisorption of gold particles with poly(4‐vinylpyridine) chains.

     

Diblock copolymers,micelles, and shell‐crosslinked nanoparticles containing poly(4‐fluorostyrene): Tools for detailed analyses of nanostructured materials

Amphiphilic core–shell nanostructures containing ¹⁹F stable isotopic labels located regioselectively within the core domain were prepared by a combination of atom transfer radical polymerization (ATRP), supramolecular assembly, and condensation‐based crosslinking. Homopolymers and diblock copolymers containing 4‐fluorostyrene and methyl acrylate were prepared by ATRP, hydrolyzed, assembled into micelles, and converted into shell‐crosslinked nanoparticles (SCKs) by covalent stabilization of the acrylic acid residues in the shell. The ATRP‐based polymerizations, producing the homopolymers and diblock copolymers, were initiated by (1‐bromoethyl)benzene in the presence of CuBr metal and employed N,N,N′,N″,N″‐pentamethyldiethylenetriamine as the coordinating ligand for controlled polymerizations at 75–90 °C for 1–3 h. Number‐average molecular weights ranged from 2000 to 60,000 Da, and molecular weight distributions, generally less than 1.1 and 1.2, were achieved for the homopolymers and diblock copolymers, respectively. Methyl acrylate conversions as high as 70% were possible, without observable chain–chain coupling reactions or molecular weight distribution broadening, when bromoalkyl‐terminated poly(4‐fluorostyrene) was used as the macroinitiator. Poly(4‐fluorostyrene), incorporated as the second segment in the diblock copolymer synthesis, was initiated from a bromoalkyl‐terminated poly(methyl acrylate) macroinitiator. After hydrolysis of the poly(methyl acrylate) block segments, micelles were formed from the resulting amphiphilic block copolymers in aqueous solutions and were then stabilized by covalent intramicellar crosslinking throughout the poly(acrylic acid) shells to yield SCKs. The SCK nanostructures on solid substrates were visualized by atomic force microscopy and transmission electron microscopy. Dynamic light scattering was used to probe the effects of crosslinking on the resulting hydrodynamic diameters of nanoparticles in aqueous and buffered solutions. The presence of fluorine atoms in the diblock copolymers and resulting SCK nanostructures allowed for characterization by ¹⁹F NMR in addition to ¹H NMR, ¹³C NMR, and IR spectroscopy. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4152–4166, 2001     

The preparation of amphiphilic core‐shell nanospheres by using water‐soluble macrophotoinitiator

The amphiphilic poly(AM‐co‐SA)‐ITXH macrophotoinitiator was synthesized by precipitation photopolymerization under UV irradiation with isopropylthioxanthone (ITX) as free radical photoinitiator. A novel method has been developed to prepare amphiphilic core‐shell polymer nanospheres via photopolymerization of methyl methacrylate (MMA) in aqueous media, with amphiphilic copolymer macrophotoinitiator poly(AM‐co‐SA)‐ITXH. During polymerization, the amphiphilic macroradicals underwent in situ self‐assembly to form polymeric micelles, which promoted the emulsion polymerization of the monomer. Thus, amphiphilic core‐shell nanospheres ranging from 70 to 140 nm in diameter were produced in the absence of surfactant. The conversion of the monomer, number average molecular weights (M_n), and particle size were found to be highly dependent on the macrophotoinitiator and monomer concentration. The macrophotoinitiator and amphiphilic particles were characterized by FTIR, UV‐vis, ¹H NMR, TEM, DSC, and contact angle measurements. The results showed the particles had well‐defined amphiphilic core‐shell structure. This new method is scientifically and technologically significant because it provides a commercially viable route to a wide variety of novel amphiphilic core‐shell nanospheres. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 936–942, 2010     

Novel biobased photo‐crosslinked polymer networks prepared from vegetable oil and 2,5‐furan diacrylate

Novel biobased crosslinked polymer networks were prepared from vegetable oil with 2,5‐furan diacrylate as a difunctional stiffener through UV photopolymerization, and the mechanical properties of the resulting films were evaluated. The vegetable oil raw materials used were acrylated epoxidized soybean oil (AESO), acrylated castor oil (ACO), and acrylated 7,10‐dihydroxy‐8(E)‐octadecenoic acid (ADOD). 2,5‐Furan dicarboxylic acid (FDCA), which can be synthesized through the oxidative dehydration of C6 sugars, was identified by the US Department of Energy as one of 12 priority chemicals for establishing the green chemistry industry of the future. 2,5‐Furan dimethanol (bis‐hydroxymethylfuran), which can be derived from FDCA, was used as a starting material to synthesize 2,5‐furan diacrylate, which was used as a biobased comonomer along with AESO, ACO, or ADOD to form photo‐crosslinked polymer networks. The synthesis of acrylate derivatives was confirmed using FT‐IR and ¹H‐NMR spectroscopic techniques. The composition of the reaction mixture was changed to obtain crosslinked polymer networks with various mechanical properties. The addition of 2,5‐furan diacrylate increased the tensile strengths of the polymer films by up to 1.4–4.2 times relative to those obtained without the addition. These fully biobased polymers derived from vegetable oil and sugar can be used as environmentally friendly renewable materials for various applications to replace the existing petroleum‐based polymers currently used. Copyright © 2013 John Wiley & Sons, Ltd.     

Perfluorocarbon‐loaded shell crosslinked knedel‐like nanoparticles: Lessons regarding polymer mobility and self‐assembly

Reversible addition‐fragmentation chain transfer polymerization was employed to synthesize a set of copolymers of styrene (PS) and 2,3,4,5,6‐pentafluorostyrene (PPFS), as well as block copolymers with tert‐butyl acrylate (PtBA)‐b‐PS‐co‐PPFS, with control over molecular weight and polydispersity. It was found that the copolymerization of styrene and PFS allowed for the preparation of gradient copolymers with opposite levels of monomer consumption, depending on the feed ratio. Conversion to amphiphilic block copolymers, PAA‐b‐(PS‐co‐PPFS), by removing the protecting groups was followed by fitting with monomethoxy poly(ethylene glycol) chains. Solution‐state assembly and intramicellar crosslinking afforded shell crosslinked knedel‐like (SCK) block copolymer nanoparticles. These fluorinated nanoparticles (ca. 20 nm diameters) were studied as potential magnetic resonance imaging (MRI) contrast agents based on the ¹⁹F‐nuclei; however, it was found that packaging of the hydrophobic fluorinated polymers into the core domain restricted the mobility of the chains and prohibited ¹⁹F NMR spectroscopy when the particles were dispersed in water without an organic cosolvent. Packing of perflouro‐15‐crown‐5‐ether (PFCE) into the polymer micelle was demonstrated with good uptake efficiency; however, it was necessary to swell the core with a good solvent (DMSO) to increase the mobility and observe the ¹⁹F NMR signal of the PFCE. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1023–1037, 2009     

Modeling the effect of compatibilizers in the coarsening of ternary polymer blends with core‐shell morphology

Numerical simulations of the phase separation and coarsening of particulate, ternary polymer blends have been performed using a ternary form of the modified Cahn–Hilliard equation. The third component was chosen to be a compatibilizer, typically being a random copolymer of the major components. The results show that compatibilized blends follow the same Lifshitz–Slyozov coarsening law as binary systems. Slower coarsening rates, indicating system stabilization, were observed for blends containing ∼10% compatibilizer and exhibiting a core‐shell morphology. Larger amounts of compatibilizer resulted in significantly higher coarsening rates. This appears to be a result of the greater affinity of the compatibilizer for the major component and warrants further experimental investigation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1301–1306, 2000     

Construction of temperature responsive hybrid crosslinked self‐assemblies based on PEG‐b‐P(MMA‐co‐MPMA)‐b‐PNIPAAm triblock copolymer: ATRP synthesis and thermoinduced association behavior

A novel amphiphilic thermosensitive poly(ethylene glycol)₄₅‐b‐poly(methyl methacrylate₄₆‐co‐3‐(trimethoxysilyl)propyl methacrylate)₂‐b‐poly(N‐isopropylacrylamide)₄₂₉ (PEG₄₅‐b‐P(MMA₄₆‐co‐MPMA₂)‐b‐PNIPAAm₄₂₉) triblock copolymer was synthesized via consecutive atom transfer radical polymerization techniques. The thermoinduced association behavior of the resulting triblock copolymers in aqueous medium was further investigated in detail by ¹H NMR, transmission electron microscopy, and dynamic light scattering. The results showed that at the temperature (25 °C) below the LCST, PEG₄₅‐b‐P(MMA₄₆‐co‐MPMA₂)‐b‐PNIPAAm₄₂₉ triblock copolymers self‐assembled into the core crosslinked micelles with the hydrophobic P(MMA‐co‐MPMA) block constructing a dense core, protected by the mixed soluble PEG and PNIPAAm chains acting as a hydrophilic shell simultaneously. With an increase in temperature, the resulting core‐shell micelles converted into a new type of micelles with the hydrophilic PEG chains stretching out from the hydrophobic core through the collapsed PNIPAAm shell. On the other hand, at the temperature (40 °C) above the LCST, such triblock copolymers formed the crosslinked vesicles with the hydrophobic PNIPAAm and P(MMA‐co‐MPMA) blocks constructing a membrane core and the soluble PEG chains building the hydrophilic lumen and the shell. On further decreasing the temperature, the resulting vesicles underwent transformation from the shrunken to the expanded status, leading to the formation of swollen vesicles with enlarged size. This study is believed to present the first formation of two types of hybrid crosslinked self‐assemblies by thermoinduced regulation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Bioinspired core‐crosslinked micelles from thymine‐functionalized amphiphilic block copolymers: Hydrogen bonding and photo‐crosslinking study

Bioinspired core‐bound polymeric micelles, based on hydrogen bonding and photo‐crosslinking, of thymine have been prepared from poly(vinylbenzylthymine)‐b‐poly(vinylbenzyltriethylammonium chloride). The amphiphilic block copolymer was synthesized by 2,2‐tetramethylpiperidin‐1‐oxyl‐mediated living radical polymerization in water/ethylene glycol solution. Micelle characterization and critical micelle concentration measurements demonstrated that the hydrogen bonding of the attached thymine units stabilizes the micelles. Further, core‐crosslinked polymeric micelles were formed by ultraviolet (UV) radiation showing that the stability of the micelle could be controlled by the UV crosslinking of the attached thymines. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Well‐Defined SiO2@P(EtOx‐stat‐EI) Core–Shell Hybrid Nanoparticles via Sol‐Gel Processes

Positively charged nanoparticles (NPs) are very interesting for biomedical and pharmaceutical applications, such as nonviral gene delivery. Here, the synthesis of SiO₂ nanoparticles with a covalently grafted poly(2‐ethyl‐2‐oxazoline) (PEtOx) shell (SiO₂@PEtOx) is presented. PEtOx with a degree of polymerization of 20 and 38 is synthesized via microwave supported cationic ring‐opening polymerization and subsequently end‐functionalized with a triethoxysilyl linker for subsequent grafting to silica particles with hydrodynamic radii of 7, 31, and 152 nm. The resulting SiO₂@PEtOx particles are characterized by using dynamic light scattering (DLS), transmission electron microscopy (TEM, cryoTEM), and scanning electron microscopy (SEM) to determine changes in particle size. Thermal gravimetrical analysis is used to quantify the amount of polymer on the silica surface. Subsequent in situ transformation of SiO₂@PEtOx particles into SiO₂@P(EtOx‐stat‐EI) (poly(2‐ethyl‐2‐oxazoline‐stat‐ethylene imine) grafted silica particles) under acidic conditions inverts the surface charge from negative to positive according to ζ‐potential measurements. The P(EtOx‐stat‐EI) shell could be used for the deposition of Au NP afterward.

     

Cagelike polymer microspheres with hollow core/porous shell structures

Submicron‐scaled cagelike polymer microspheres with hollow core/porous shell were synthesized by self‐assembling of sulfonated polystyrene (PS) latex particles at monomer droplets interface. The swelling of the PS latex particles by the oil phase provided a driving force to develop the hollow core. The latex particles also served as porogen that would disengage automatically during polymerization. Influential factors that control the morphology of the microspheres, including the reserving time of emulsions, polymerization rate, and the Hildebrand solubility parameter and polarity of the oil phase, were studied. A variety of monomers were polymerized into microspheres with hollow core/porous shell structure and microspheres with different diameters and pore sizes were obtained. The polymer microspheres were characterized by scanning electron microscopy, transmission electron microscopy, optical microscopy, and Fourier transform infrared spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 933–941, 2007     

Synthesis of a thermoresponsive shell‐crosslinked 3‐layer onion‐like polymer particle with a hyperbranched polyglycerol core

A novel thermoresponsive shell crosslinked three‐layer onion‐like polymer particles were prepared using hyperbranched polyglycerol (PG) as parents compound, the periphery hydroxyl groups of PG were transformed into trithiocarbonates (? SC(S)S? ) first; then, it was used as chain transfer agent to prepare star‐like block copolymer of N‐isopropyl acrylamide (NIPA) and N,N‐dimethylaminoethyl acrylate (DMA) in sequence via reversible addition fragmentation chain transfer (RAFT) process. Thus, a three‐layer polymer, PG? [SC(S)S? (DMA)? b? (NIPA)]_n, was obtained. The middle layer of poly(DMA) was then crosslinked with 1,8‐diiodoctane, and the resulting onion‐like three‐layer polymer showed a lower critical solution temperature (LCST) in water because of the outer layer of poly(NIPA). The LCST value only slightly depended on the crosslinking degree. Finally, the ? SC(S)S? were transformed into thiols by sequential treating with sodium borohydride and formic acid; thus, the core molecule was chemically detached from the crosslinked shell and a novel shell crosslinked polymer particle was obtained. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5652–5660, 2005     

Core–shell and gradient morphology polymer particles analyzed by X‐ray photoelectron spectroscopy: Effect of monomer feed order

The synthesis of composite latex particles possessing core–shell and gradient morphologies, respectively, using seeded starve‐fed semibatch emulsion polymerization of styrene (St) and methyl methacrylate (MMA) is presented. The focus is on the effect of the monomer feed order on the particle morphology development. The particle morphology is assessed using a novel approach which entails comparing the experimental surface composition as a function of polymerization time (particle growth) obtained by X‐ray photoelectron spectroscopy with the predicted surface composition using a mass balance mathematical model. Both types of composite latexes (core–shell and gradient) feature changes with polymerization time in the oxygen/carbon surface composition which enables one to track the morphology development. Differential scanning calorimetry is also implemented to analyze the extent of phase separation. The monomer feed order is shown to play a crucial role—under the present conditions, gradient and core–shell particles are obtained if the feed order is St/MMA (St fed first), but not if the feed order is reversed. These findings illustrate that thermodynamic factors are important, given that thermodynamically it is more favorable for MMA‐rich chains to occupy the oil–water interface to reduce the interfacial tension. Systems where St is the second stage monomer lead to mixed structures rather than the targeted core–shell or gradient morphology with St‐rich chains at the particle surface. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2513–2526     

Structured Hybrid Nanoparticles via Surface‐Initiated ATRP of Methyl Methacrylate from Ordered Mesoporous Silica

Structured hybrid nanoparticles were synthesized via surface‐initiated atom transfer radical polymerization of MMA from ordered mesoporous silica (OMS) nanoparticles with various morphologies. The design of the OMS particles was adjusted to target either spherical core‐shell or cylindrical morphologies with a mean diameter below 400 nm. The polymer growth via ATRP from the silica surface was well‐controlled as demonstrated by the macromolecular characteristics of the grafted chains. Original hybrid multilayered nanoparticles composed of either a dense silica core or hollow core; an inner OMS shell showing radial orientation of the mesopores and an outer PMMA shell with controlled thickness were successfully prepared.

     

Preparation of Core–Shell Nanofibers with Selectively Localized CNTs from Shish Kebab‐like Hierarchical Composite Micelles

A novel and facile bottom‐up strategy for preparing core‐shell nanofibers with selectively localized carbon nanotubes is developed using hierarchical composite micelles of crystalline‐coil copolymer and carbon nanotubes as the building blocks. An amphiphilic di‐block copolymer of poly (p‐dioxanone) (PPDO) and PEG (polyethylene glycol) functionalized with pyrene moieties at the chain ends of PPDO blocks (Py‐PPDO‐b‐PEG) is designed for constructing composite micelles with multiwalled carbon nanotubes (MWCNTs). The self‐assembly of Py‐PPDO‐b‐PEG and MWCNTs is co‐induced by the crystallization of PPDO blocks and the π–π stacking interactions between pyrene moieties and MWCNTs, resulting in composite micelles with “shish kebab”‐like nanostructure. A mixture of composite micelles and polyvinyl alcohol (PVA) water solution is then used as the spinning solution for preparing electrospun nanofibers. The morphologies of the nanofibers with different composition are investigated by SEM and TEM. The results suggest that the MWCNTs selectively localized in the core of the nanofibers of MWCNTs/Py‐PPDO‐b‐PEG/PVA. The alignment and interfusion of composite micelles during the formation of nanofibers may confine the carbon nanotubes in the hydrophobic core region. In contrast, the copolymer without pyrene moieties cannot form composite micelles, thus these nanofibers show selective localization of MWCNTs in the PVA shell region.

     

β‐Cyclodextrin polymer brushes based on hyperbranched polycarbosilane: Synthesis and characterization

In this article, our main goal is to combine hyperbranched polymer with β‐cyclodextrin (β‐CD) to establish a novel functional polymer species with core‐shell structure and supramolecular system for further application in inclusion technologies and the complex drugs delivery system. Therefore, two β‐CD polymer brushes based on hyperbranched polycarbosilane (HBP) as a hydrophobic core and poly(N,N‐dimethylaminoethyl methacrylate) (PDMA) carrying β‐CD units as a hydrophilic shell were synthesized. Hyperbranched polycarbosilane macroinitiator carrying ? Cl groups (HBP‐Cl) was also prepared by using 1,1,3,3‐tetrmethyldisiloxane, allyl alcohol, and chloroacetyl chloride as reagents. The molecular structures of HBP‐Cl macroinitiator and β‐CD polymer brushes were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance (¹H NMR), ¹³C nuclear magnetic resonance (¹³C NMR) spectroscopies, size exclusion chromatography/multi‐angle laser light scattering (SEC/MALLS) and laser particle size analyzer. The results indicate that the grafted chain length of two β‐CD polymer brushes can be controlled by changing the feed ratio. Differential scanning calorimetry (DSC) results show that two β‐CD polymer brushes have two glass transition temperatures (T_gs) from a hydrophobic core part and a hydrophilic shell part, respectively, and the T_g from PDMA is higher than that of HBP‐g‐PDMA. Thermalgravimetric analyzer (TGA) analysis indicates that the thermostability of two β‐CD polymer brushes is higher than that of HBP, but is lower than that of HBP‐g‐PDMA. Using phenolphthalein (PP) as a guest molecule, molecular inclusion behaviors for two β‐CD polymer brushes were studied. It reveals that two β‐CD polymer brushes possess molecular inclusion capability in PP buffer solution with a fixed concentration. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5036–5052, 2008     

Solvent replacement to thermo‐responsive nanoparticles from long‐subchain hyperbranched PSt grafted with PNIPAM for encapsulation

Long‐subchain hyperbranched polystyrene (lsc‐hp PSt) with uniform subchain length was obtained through copper‐catalyzed azide‐alkyne cycloaddition click chemistry from seesaw macromonomer of PSt having one alkynyl group anchored at the chain centre and two azido group attached to both chain ends [alkynyl‐(PSt‐N₃)₂]. After precipitation fraction, different portions of lsc‐hp PSt having narrow overall molecular weight distribution were obtained for further grafting with alkynyl‐capped poly(N‐isopropylacrylamide) (alkynyl‐PNIPAM), which was obtained via single‐electron transfer living radical polymerization of NIPAM with propargyl 2‐bromoisobutyrate as the initiator and grafted onto the peripheral azido groups of lsc‐hp PSt via click chemistry. Thus, amphiphilic lsc‐hp PSt grafted with PNIPAM chains (lsc‐hp PSt‐g‐PNIPAM) was obtained and would have star‐like conformation in tetrahydrofuran (THF). By replacing THF with water, lsc‐hp PSt‐g‐PNIPAM was dissolved at molecular level in aqueous solution due to the hydrophilicity of PNIPAM and exhibited thermal induced shrinkage of PNIPAM arms. The water‐insoluble lsc‐hp PSt would collapse densely and could be served as a reservoir to absorb hydrophobic chemicals in aqueous solution. The influence of overall molecular weight of lsc‐hp PSt on the absorption of pyrene was studied. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Three‐dimensional thermal annealing: An unconventional method to fabricate monodisperse polymer nanoparticles from polymer films

We develop a simple and feasible method to fabricate polymer nanoparticles by annealing polymer films in a uniform environment. Different from the conventional methods, no extra additive or emulsifier is needed in the preparation processes. Poly(methyl methacrylate) (PMMA) films are used as a model system and annealed at elevated temperatures in ethylene glycol, which provides a uniform three‐dimensional annealing environment and acts as stabilizers once the nanoparticles are formed. After the annealing process, PMMA nanoparticles with monodisperse diameters are formed. By examining the remaining films after the annealing process, the formation mechanism, which involves surface undulation and detachment of polymer nanoparticles, is proposed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2471–2475