Novel superhydrophobic silica/poly(siloxane‐fluoroacrylate) hybrid nanoparticles prepared via surface‐initiated ATRP and their surface properties: The effects of polymerization conditions

A series of superhydrophobic poly(methacryloxypropyltrimethoxysilane, MPTS‐b‐2,‐2,3,3,4,4,4‐heptafluorobutyl methacrylate, HFBMA)‐grafted silica hybrid nanoparticles (SiO₂/PMPTS‐b‐PHFBMA) were prepared by two‐step surface‐initiated atom transfer radical polymerization (SI‐ATRP). Under the adopted polymerization conditions in our previous work, the superhydrophobic property was found to depend on the SI‐ATRP conditions of HFBMA. As a series of work, in this present study, the effects of polymerization conditions, such as the initiator concentration, the molar ratio of monomer and initiator, and the polymerization temperature on the SI‐ATRP kinetics and the interrelation between the kinetics and the surface properties of the nanoparticles were investigated. The results showed that the SI‐ATRP of HFBMA was well controlled. The results also showed that both the surface microphase separation and roughness of the hybrid nanoparticles could be strengthened with the increase of the molecular weight of polymer‐grafted silica hybrid nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Air‐tolerantly surface‐initiated AGET ATRP mediated by iron catalyst from silica nanoparticles

Well‐defined polymer‐nanoparticle hybrids were prepared by a newly reported method: atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) mediated by iron catalyst. The kinetics of the surface‐initiated AGET ATRP of methyl methacrylate from the silica nanoparticles, which was mediated by FeCl₃/triphenylphosphine as a catalyst complex, ascorbic acid as a reducing agent, N,N‐dimethylformamide as the solvent in the presence of a “sacrificial” (free) initiator, was studied. Both the free and grafted polymers were grown in a control manner. The chemical composition of the nanocomposites was characterized by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. Thermogravimetric analysis was used to estimate the content of the grafted organic compound, and transmission electron micrographs was used to observe the core‐shell structure of the hybrid nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2006–2015, 2010     

Synthesis of well‐defined amphiphilic graft copolymer bearing poly(2‐acryloyloxyethyl ferrocenecarboxylate) side chains via successive SET‐LRP and ATRP

A series of well‐defined ferrocene‐based amphiphilic graft copolymers, consisting of poly(N‐isopropylacrylamide)‐b‐poly(ethyl acrylate) (PNIPAM‐b‐PEA) backbone and poly(2‐acryloyloxyethyl ferrocenecarboxylate) (PAEFC) side chains, were synthesized by the combination of single‐electron‐transfer living radical polymerization (SET‐LRP) and atom transfer radical polymerization (ATRP). A new ferrocene‐based monomer, 2‐(acryloyloxy)ethyl ferrocenecarboxylate (AEFC), was prepared first and it can be polymerized via ATRP in a controlled way using methyl 2‐bromopropionate as initiator and CuBr/PMDETA as catalytic system in DMF at 40 °C. PNIPAM‐b‐PEA backbone was synthesized by sequential SET‐LRP of NIPAM and HEA at 25 °C using CuCl/Me₆TREN as catalytic system followed by the transformation into the macroinitiator by treating the pendant hydroxyls with α‐bromoisobutyryl bromide. The targeted well‐defined graft copolymers with narrow molecular weight distributions (M_w/M_n < 1.20) were synthesized via ATRP of AEFC initiated by the macroinitiator. The electro‐chemical behaviors of PAEFC homopolymer and PNIPAM‐b‐(PEA‐g‐PAEFC) graft copolymer were studied by cyclic voltammetry. Micellar properties of PNIPAM‐b‐(PEA‐g‐PAEFC) were investigated by transmission electron microscopy and dynamic light scattering. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4346–4357, 2009     

Tailor‐made hybrid nanostructure of poly(ethyl acrylate)/clay by surface‐initiated atom transfer radical polymerization

Hybrid nanoarchitecture of tailor‐made Poly(ethyl acrylate)/clay was prepared by surface‐initiated atom transfer radical polymerization (SI‐ATRP), by tethering ATRP initiator on active hydroxyl group, present in surface as well as in the organic modifier of the clay used. Extensive exfoliation was facilitated by using these initiator modified clay platelets. Poly(ethyl acrylate) chains with controlled polymerization and narrow polydispersities were forced to be grown from within the clay gallery (intergallery) as well as from the outer surface (extragallery) of the clay platelets. The polymer chains attached onto clay surfaces might have the potential to provide the composites with enhanced compatibility in blends with common polymers. Attachment of the initiator on clay platelets was confirmed by Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), elemental analysis, Wide‐angle X‐ray diffraction (WAXD), and microscopic analysis. Finally, end group analysis (by Matrix‐Assisted Laser Desorption Ionization Mass Spectrometry, and chain extension experiment) of the cleaved polymer and morphological study (by WAXD, Transmission Electron Microscopy), performed on the polymer grafted clays examined the effect of grafting on the efficiency of polymerization and the degree of dispersion of clay tactoids in polymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5014–5027, 2008     

Preparation of well-defined polystyrene/silica hybrid nanoparticles by ATRP

Immobilization of the atom transfer radical polymerization (ATRP) macroinitiators at the silica nanoparticle surfaces was achieved through surface modification with excess toluene-2,4-diisocynate (TDI), after which the residual isocyanate groups were converted into ATRP macroinitiators. Structurally well-defined polystyrene chains were grown from the nanoparticle surfaces to yield individual particles composed of a silica core and a well-defined, densely grafted outer polystyrene by ATRP, which was initiated by the as-synthesized silica-based macroinitiator. FTIR, NMR and gel permeation chro-matography (GPC) were used to characterize the polystyrene/silica hybrid particles.     

Synthesis of poly(tert‐butyl acrylate‐block‐vinyl acetate) copolymers by combining ATRP and RAFT polymerizations

The synthesis of poly(tert‐butyl acrylate‐block‐vinyl acetate) copolymers using a combination of two living radical polymerization techniques, atom transfer radical polymerization (ATRP) and reversible addition‐fragmentation chain transfer (RAFT) polymerization, is reported. The use of two methods is due to the disparity in reactivity of the two monomers, viz. vinyl acetate is difficult to polymerize via ATRP, and a suitable RAFT agent that can control the polymerization of vinyl acetate is typically unable to control the polymerization of tert‐butyl acrylate. Thus, ATRP was performed to make poly(tert‐butyl acrylate) containing a bromine end group. This end group was subsequently substituted with a xanthate moiety. Various spectroscopic methods were used to confirm the substitution. The poly(tert‐butyl acrylate) macro‐RAFT agent was then used to produce (tert‐butyl acrylate‐block‐vinyl acetate). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7200–7206, 2008     

Synthesis,surface properties,and morphologies of poly[methyl(3,3,3‐trifluoropropyl)siloxane]‐b‐polystyrene‐b‐poly(tert‐butyl acrylate) triblock copolymers by a combination of anionic ROP and ATRP

A series of well‐defined poly[methyl(3,3,3‐trifluoropropyl)siloxane]‐b‐polystyrene‐b‐poly(tert‐butyl acrylate) (PMTFPS‐b‐PS‐b‐PtBA) triblock copolymers were prepared by a combination of anionic ring‐opening polymerization of 1,3,5‐trimethyl‐1,3,5‐tris(3′,3′,3′‐trifluoropropyl)cyclotrisiloxane (F₃), and atom transfer radical polymerization (ATRP) of styrene (St) and tert‐butyl acrylate (tBA), using the obtained α‐bromoisobutyryl‐terminal PMTFPS (PMTFPS‐Br) as the macroinitiators. The ATRP of St from PMTFPS‐Br, as well as the ATRP of tBA from the obtained PMTFPS‐b‐PS‐Br macroinitiators, has typical characteristic of controlled/living polymerization. The results of contact angle measurements for the films of PMTFPS‐b‐PS‐b‐PtBA triblock copolymers demonstrate that the compositions have an effect on the wetting behavior of the copolymer films. For the copolymer films with different compositions, there may be different macroscale or nanoscale structures on the outmost layer of the copolymer surfaces. The films with high content of PtBA blocks exhibit almost no ordered microstructures on the outmost layer of the copolymer surfaces, even though they have microphase‐separated structures in bulk. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Kinetic analysis of surface‐initiated SET‐LRP of poly(N‐isopropylacrylamide)

The single‐electron transfer living radical polymerization (SET‐LRP) of N‐isopropylacrylamide (NIPAM) from silicon wafer modified with an initiator layer composed of 2‐bromopropionyl bromide (2‐BPB) fragments is described. The amount of Cu(0) generated in situ by the disproportination of Cu(I) to Cu(0) and Cu(II) in the presence of 2,2′‐bipyridine (2,2′‐bpy) ligand and N,N‐dimethylformamide (DMF) solvent at 90 °C is dependent on the ratio of [CuBr]/[CuBr₂]. By proper selection of the [CuBr]/[CuBr₂] ratio, well‐controlled SET‐LRP polymerization of NIPAM was observed such that the thickness of the layer consisting of chains grown from the surface increased linearly with the molecular weight of chains polymerized in solution in identical. In addition, the calculation of grafting parameters, including surface coverage, σ (mg/m²); grafting density, Σ (chain/nm²); and average distance between grafting sites, D (nm), from the number‐average molecular weight, M _n (g/mol), and ellipsometric thickness, h (nm), values indicated the synthesis of densely grafted poly(NIPAM) films and allowed us to predict a “brush‐like” conformation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Preparation and characterization of poly(2‐methacryloyloxyethyl phosphorylcholine)‐block‐poly(D,L‐lactide) polymer nanoparticles

A poly(D,L ‐lactide)–bromine macroinitiator was synthesized for use in the preparation of a novel biocompatible polymer. This amphiphilic diblock copolymer consisted of biodegradable poly(D,L ‐lactide) and 2‐methacryloyloxyethyl phosphorylcholine and was formed by atom transfer radical polymerization. Polymeric nanoparticles were prepared by a dialysis process in a select solvent. The shape and structure of the polymeric nanoparticles were determined by ¹H NMR, atomic force microscopy, and ζ‐potential measurements. The results of cytotoxicity tests showed the good cytocompatibility of the lipid‐like diblock copolymer poly(2‐methacryloyloxyethyl phosphorylcholine)‐block‐poly(D,L ‐lactide). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 688–698, 2007     

Synthesis of gold–poly(methyl methacrylate) core–shell nanoparticles by surface‐confined atom transfer radical polymerization at elevated temperature

Surface‐confined atom transfer radical polymerization was used to prepare gold nanoparticle–poly(methyl methacrylate) core–shell particles at elevated temperature. First, gold nanoparticles were prepared by the one‐pot borohydride reduction of tetrachloroaurate in the presence of 11‐mercapto‐1‐undecanol (MUD). MUD‐capped gold nanoparticles were then exchanged with 3‐mercaptopropyltrimethoxysilane (MPS) to prepare a self‐assembled monolayer (SAM) of MPS on the gold nanoparticle surfaces and subsequently hydrolyzed with hydrochloric acid. The extent of exchange of MUD with MPS was determined by NMR. The resulting crosslinked silica‐primer layer stabilized the SAM of MPS and was allowed to react with the initiator [(chloromethyl)phenylethyl] trimethoxysilane. Atom transfer radical polymerization was conducted on the Cl‐terminated gold nanoparticles with the CuCl/2,2′‐bipyridyl catalyst system at elevated temperature. The rates of polymerization with the initiator‐modified gold nanoparticles exhibited first‐order kinetics with respect to the monomer, and the number‐average molecular weight of the cleaved graft polymer increased linearly with the monomer conversion. The presence of the polymer on the gold nanoparticle surface was identified by Fourier transform infrared spectroscopy and transmission electron microscopy. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3631–3642, 2005     

Synthesis and characterization of poly(methyl methacrylate)‐block‐poly(methylphenylsilane)‐ block‐poly(methyl methacrylate) by atom transfer radical polymerization

ABA block copolymers of methyl methacrylate and methylphenylsilane were synthesized with a methodology based on atom transfer radical polymerization (ATRP). The reaction of samples of α,ω‐dihalopoly(methylphenylsilane) with 2‐hydroxyethyl‐2‐methyl‐2‐bromoproprionate gave suitable macroinitiators for the ATRP of methyl methacrylate. The latter procedure was carried out at 95 °C in a xylene solution with CuBr and 2,2‐bipyridine as the initiating system. The rate of the polymerization was first‐order with respect to monomer conversion. The block copolymers were characterized with ¹H NMR and ¹³C NMR spectroscopy and size exclusion chromatography, and differential scanning calorimetry was used to obtain preliminary evidence of phase separation in the copolymer products. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 30–40, 2003     

Preparation of polymer‐grafted carbon black nanoparticles by surface‐initiated atom transfer radical polymerization

Pristine carbon black was oxidized with nitric acid to produce carboxyl group, and then the carboxyl group was consecutively treated with thionyl chloride and glycol to introduce hydroxyl group. The hydroxyl group on the carbon black surface was reacted with 2‐bromo‐2‐methylpropionyl bromide to anchor atom transfer radical polymerization (ATRP) initiator. The ATRP initiator on carbon black surface was verified by TGA, FTIR, EDS, and elemental analysis. Then, poly (methyl methacrylate) and polystyrene chains were respectively, grown from carbon black surface by surface‐initiated atom transfer radical polymerization (SI‐ATRP) using CuCl/2,2‐dipyridyl (bpy) as the catalyst/ligand combination at 110 °C in anisole. ¹H NMR, TGA, TEM, AFM, DSC, and DLS were used to systemically characterize the polymer‐grafted carbon black nanoparticles. Dispersion experiments showed that the grafted carbon black nanoparticles had good solubilities in organic solvents such as THF, chloroform, dichloromethane, DMF, etc. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3451–3459, 2007     

Synthesis of amphiphilic copolymer brushes possessing alternating poly(methyl methacrylate) and poly(N‐isopropylacrylamide) grafts via a combination of ATRP and click chemistry

We report on the synthesis of well‐defined amphiphilic copolymer brushes possessing alternating poly(methyl methacrylate) and poly(N‐isopropylacrylamide) grafts, poly(PMMA‐alt‐PNIPAM), via a combination of atom transfer radical polymerization (ATRP) and click reaction (Scheme 1 ). Firstly, the alternating copolymerization of N‐[2‐(2‐bromoisobutyryloxy)ethyl]maleimide (BIBEMI) with 4‐vinylbenzyl azide (VBA) affords poly(BIBEMI‐alt‐VBA). Bearing bromine and azide moieties arranged in an alternating manner, multifunctional poly(BIBEMI‐alt‐VBA) is capable of initiating ATRP and participating in click reaction. The subsequent ATRP of methyl methacrylate (MMA) using poly(BIBEMI‐alt‐VBA) as the macroinitiator leads to poly(PMMA‐alt‐VBA) copolymer brush. Finally, amphiphilic poly(PMMA‐alt‐PNIPAM) copolymer brush bearing alternating PMMA and PNIPAM grafts is synthesized via the click reaction of poly(PMMA‐alt‐VBA) with an excess of alkynyl‐terminated PNIPAM (alkynyl‐PNIPAM). The click coupling efficiency of PNIPAM grafts is determined to be ～80%. Differential scanning calorimetry (DSC) analysis of poly(PMMA‐alt‐PNIPAM) reveals two glass transition temperatures (T_g). In aqueous solution, poly(PMMA‐alt‐PNIPAM) supramolecularly self‐assembles into spherical micelles consisting of PMMA cores and thermoresponsive PNIPAM coronas, which were characterized via a combination of temperature‐dependent optical transmittance, micro‐differential scanning calorimetry (micro‐DSC), dynamic and static laser light scattering (LLS), and transmission electron microscopy (TEM). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2608–2619, 2009     

Synthesis and self‐assembly of poly(styrene)‐b‐poly(N‐vinylpyrrolidone) amphiphilic diblock copolymers made via a combined ATRP and MADIX approach

Amphiphilic diblock copolymers of polystyrene (PS) and poly(N‐vinylpyrrolidone) (PNVP) were prepared by a combination of ATRP and MADIX. Well‐defined PS with bromine end group was synthesized by ATRP in bulk at 110 °C using (1‐bromoethyl) benzene as an initiator. The Br‐ end group was then converted to xanthate as verified by ¹H NMR spectroscopy, elemental analysis, and UV‐spectroscopy. PS‐b‐PNVP copolymers were produced by MADIX of NVP in bulk at 60 °C using PS‐xanthate as a macro‐chain transfer agent and the kinetics of polymerization were investigated. The structures of PS‐b‐PNVP were characterized using GPC and ¹H NMR. Amphiphilic PS‐b‐PNVP could form spherical micelles with PS cores and PNVP shells in aqueous solution as confirmed by ¹H NMR and laser light scattering (LLS). The values of critical micelle concentration of PS‐b‐PNVP and the average aggregation number of PS‐b‐PNVP in the micelles were measured using pyrene as a probe and static LLS, respectively. The aggregation number increases concomitantly with temperature (10–50 °C), but the hydrodynamic radius of the micelles remains almost constant over the same temperature range, which may indicate shell dehydration at a higher temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5604–5615, 2008     

Iron(III)‐mediated AGET ATRP of styrene using tris(3,6‐dioxaheptyl)amine as a ligand

A commercially available tris(3,6‐dioxaheptyl)amine (TDA‐1) was used as a novel ligand for activator generated by electron transfer atom transfer radical polymerization (AGET ATRP) of styrene in bulk or solution mediated by iron(III) catalyst in the presence of a limited amount of air. FeCl₃ · 6H₂O and (1‐bromoethyl)benzene (PEBr) were used as the catalyst and initiator, respectively; and environmentally benign ascorbic acid (VC) was used as the reducing agent. The polymerizations show the features of “living”/controlled free‐radical polymerizations and well‐defined polystyrenes with molecular weight M_n = 2400–36,500 g/mol and narrow polydispersity (M_w/M_n = 1.11–1.29) were obtained. The “living” feature of the obtained polymer was further confirmed by a chain‐extension experiment. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2002–2008, 2009     

Utilization of poly(vinylchloride) and poly(vinylidenefluoride) as macroinitiators for ATRP polymerization of hydroxyethyl methacrylate: Electroanalytical and graft‐copolymerization studies

The utilization of poly(vinylchloride) (PVC) and poly(vinylidenefluoride) (PVDF) as macroinitiators for atom transfer radical polymerization (ATRP) of hydroxyethyl methacrylate (HEMA) was studied performing electroanalytical investigations and “grafting from” experiments to evaluate the potential modification of such commercial polymers by ATRP. The study was performed changing various operating parameters such as the nature of the copper salt, the ligand, the solvent, the temperature, and the reaction time. Electroanalytical data suggest that PVC can be easily activated by both CuCl/Tris(2‐pyridylmethyl)amine (TPMA) and CuCl/Tris[2‐(dimethylamino)ethyl]amine (Me₆TREN), two catalytic systems widely adopted for ATRP reactions, in a wide range of operating conditions. PVDF is more difficult to be activated, due to the higher strength of the C? F bond. In particular, the utilization of high temperature and of a more reductant redox couple such as Cu(I)Me₆TREN/Cu(II)Me₆TREN was needed to achieve a significant degree of grafting. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2524–2536     

Synthesis and thermoresponsive property of end‐functionalized poly(N‐isopropylacrylamide) with pyrenyl group

N–Isopropylacrylamide (NIPAM) was polymerized using 1‐pyrenyl 2‐chloropropionate (PyCP) as the initiator and CuCl/tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) as the catalyst system. The polymerizations were performed using the feed ratio of [NIPAM]₀/[PyCP]₀/[CuCl]₀/[Me₆TREN]₀ = 50/1/1/1 in DMF/water of 13/2 at 20 °C to afford an end‐functionalized poly(N‐isopropylacrylamide) with the pyrenyl group (Py–PNIPAM). The characterization of the Py–PNIPAM using matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry provided the number–average molecular weight (M_n,MS). The lower critical solution temperature (LCST) for the liquid–solid phase transition was 21.7, 24.8, 26.5, and 29.3 °C for the Py–PNIPAMs with the M_n,MS's of 3000, 3400, 4200, and 5000, respectively; hence, the LCST was dramatically lowered with the decreasing M_n,MS. The aqueous Py–PNIPAM solution below the LCST was characterized using a static laser light scattering (SLS) measurement to determine its molar mass, M_w,SLS. The aqueous solutions of the Py–PNIPAMs with the M_n,MS's of 3000, 3400, 4200, and 5000 showed the M_w,SLS of 586,000, 386,000, 223,000, and 170,000, respectively. Thus, lowering the LCST for Py–PNIPAM should be attributable to the formation of the PNIPAM aggregates. The LCST of 21.7 °C for Py–PNIPAM with the M_n,MS of 3000 was effectively raised by adding β‐cyclodextrin (β‐CD) and reached the constant value of ～26 °C above the molar ratio of [β‐CD]/[Py–PNIPAM] = 2/1, suggesting that β‐CD formed an inclusion complex with pyrene in the chain‐end to disturb the formation of PNIPAM aggregates, thus raising the LCST. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1117–1124, 2006     

Synthesis of polynorbornene‐poly(tert‐butyl acrylate) nanoparticles with original morphologies by tandem ROMP and ATRP in microemulsion

Composite latex particles based on homopolymers and graft‐copolymers composed of polynorbornene (PNB) and poly(tert‐butyl acrylate) (PtBA) were synthesized in microemulsion conditions by simultaneous combination of two distinct methods of polymerization: Ring‐opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). Only one commercial compound (first generation Grubbs catalyst) was used to initiate the ROMP of norbornene (NB) and activate the ATRP of tert‐butyl acrylate (tBA). Well‐defined nanoparticles with hydrodynamic diameters smaller than 50 nm were prepared with original morphologies depending on the monomer compositions, the type of combination (polymer blend or graft‐copolymer), and the conditions of microemulsion polymerizations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

AB2‐type amphiphilic block copolymers composed of poly(ethylene glycol) and poly(N‐isopropylacrylamide) via single‐electron transfer living radical polymerization: Synthesis and characterization

Novel AB₂‐type amphiphilic block copolymers of poly(ethylene glycol) and poly(N‐isopropylacrylamide), PEG‐b‐(PNIPAM)₂, were successfully synthesized through single‐electron transfer living radical polymerization (SET‐LRP). A difunctional macroinitiator was prepared by esterification of 2,2‐dichloroacetyl chloride with poly(ethylene glycol) monomethyl ether (PEG). The copolymers were obtained via the SET‐LRP of N‐isopropylacrylamide (NIPAM) with CuCl/tris(2‐(dimethylamino)ethyl)amine (Me₆TREN) as catalytic system and DMF/H₂O (v/v = 3:1) mixture as solvent. The resulting copolymers were characterized by gel permeation chromatography and ¹H NMR. These block copolymers show controllable molecular weights and narrow molecular weight distributions (PDI < 1.15). Their phase transition temperatures and the corresponding enthalpy changes in aqueous solution were measured by differential scanning calorimetry. As a result, the phase transition temperature of PEG₄₄‐b‐(PNIPAM₅₅)₂ is similar to that in the case of PEG₄₄‐b‐PNIPAM₁₁₀; however, the corresponding enthalpy change is much lower, indicating the significant influence of the macromolecular architecture on the phase transition. This is the first study into the effect of macromolecular architecture on the phase transition using AB₂‐type amphiphilic block copolymer composed of PEG and PNIPAM. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4420–4427, 2009     

Study on the preparation and the self‐assembly of poly(propyleneimine)–poly(styrene) nanoparticles

Using 2‐chloropropionamide derivative of poly(propyleneimine) dendrimer DAB‐dendr‐(NH₂)₃₂ (DAB‐32‐Cl) as the macroinitiator, atom transfer radical polymerization of styrene was successfully carried out in DMF medium. The monodisperse poly(propyleneimine)–polystyrene (dendrimer–PSt) particles with diameters smaller than 100 nm could be prepared. The morphology, size, and size distribution of the dendrimer–PSt particles were characterized by transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS). The effects of reaction temperature, the ratio of St/macroinitiator, and reaction time on the size, and size distribution of the dendrimer–PSt nanoparticles were investigated. In a selective solvent (DMF/H₂O), polymers can self‐assemble into different aggregate configurations such as regular microsphere and wire‐like thread. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2658–2666, 2008