Core‐shell nanoparticles with hyperbranched poly(arylene‐oxindole) interiors

Core‐shell type star polymers composed of poly(tert‐butyl acrylate) (poly(t‐BuA)) arms and 100% hyperbranched poly(arylene‐oxindole) interiors were synthesized via the “core‐first” method. Atom transfer radical polymerization of t‐BuA initiated by 2‐bromopropionyl terminal groups of the hyperbranched core was applied for the synthesis of the stars. The resultant star structures were characterized by gel permeation chromatography with triple detection. Polymers of molar masses M_n up to 1.68 × 10⁵ g/mol were obtained. The obtained star polymers compared with the linear counterparts of the same molar mass have a much more compact structure in solution. The intrinsic viscosities of the stars are also significantly lower than their linear counterparts. Light scattering experiments were performed to provide information about the size of these macromolecules in solution. Preliminary characterization of the thermal properties of these novel materials is also reported. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1120–1135, 2009     

Synthesis and micellization of star‐like hyperbranched polymer with poly(ethylene oxide) and poly(ε‐caprolactone) arms

Novel star‐like hyperbranched polymers with amphiphilic arms were synthesized via three steps. Hyperbranched poly(amido amine)s containing secondary amine and hydroxyl groups were successfully synthesized via Michael addition polymerization of triacrylamide (TT) and 3‐amino‐1,2‐propanediol (APD) with feed molar ratio of 1:2. ¹H, ¹³C, and HSQC NMR techniques were used to clarify polymerization mechanism and the structures of the resultant hyperbranched polymers. Methoxyl poly(ethylene oxide) acrylate (A‐MPEO) and carboxylic acid‐terminated poly(ε‐caprolactone) (PCL) were sequentially reacted with secondary amine and hydroxyl group, and the core–shell structures with poly(1TT‐2APD) as core and two distinguishing polymer chains, PEO and PCL, as shell were constructed. The star‐like hyperbranched polymers have different sizes in dimethyl sulfonate, chloroform, and deionized water, which were characterized by DLS and ¹H NMR. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1388–1401, 2008     

Synthesis and characterization of two classes of hyperstar polymers bearing hyperbranched cores grafted with linear arms

New hyperstar polymers (HSP) consisting of two different hyperbranched (hb) aromatic/aliphatic cores grafted with linear polymer arms were successfully synthesized. The hb cores were based on either hb poly(vinylbenzylchloride) synthesized by SCVP‐ATRP or hb polyester from a polycondensation reaction. For the core‐first approach, the hb cores have been modified to hb macroinitiators initiating either the cationic ring‐opening polymerization of oxazolines (Oxa) or the atom transfer radical polymerization of alkylmethacrylates. For potential use as reactive binders in epoxy coatings the HSPs were equipped with a defined amount of OH‐groups during arm growth via controlled block‐copolymerization with nonfunctionalized and OH‐functionalized monomers, either an oxazoline (OH)Oxa (2‐[1‐(hydroxymethyl)ethyl]‐oxazoline) or a methacrylate HEMA (2‐hydroxyethyl methacrylate). The amount of OH‐groups could be well adjusted in this way. The hyperstars were comprehensively characterized with respect to chemical structure and molecule dimension. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000–000, 2012     

Investigation of the conformation of hyperbranched poly(arylene oxindole)s using hyper‐Rayleigh scattering

A hyperbranched poly(arylene oxindole), a poly(methacrylate), and a dendrimer, to which the same nonlinear optical chromophore was attached via a small, rigid spacer, were prepared. The difference in hyper‐Rayleigh scattering intensities was measured and compared. From this study, it was concluded that the chromophores, and hence the functional groups in the macromolecule before functionalization, are orientationally correlated in the dendrimer, whereas they are not in the linear and hyperbranched polymer. More in particular, the chromophores in the dendrimer are fixed in a centrosymmetric way because of the globular structure, whereas there is no orientational correlation between the chromophores in linear and hyperbranched polymer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3740–3747, 2009     

Fluoride‐terminated hyperbranched poly(arylene ether phosphine oxide)s via nucleophilic aromatic substitution

A series of AB_x‐type triarylphosphine oxide monomers, bis‐(4‐fluorophenyl)‐(4‐hydroxyphenyl)phosphine oxide ( 4a ), bis‐(3,4‐difluorophenyl)‐(4‐hydroxyphenyl)phosphine oxide ( 4b ), and 4‐hydroxyphenyl‐bis‐(3,4,5‐trifluorophenyl)phosphine oxide ( 4c ) were prepared, characterized, and polymerized under nucleophilic aromatic substitution conditions [N‐methylpyrrolidone (NMP), K₂CO₃] to provide the corresponding hyperbranched poly(arylene ether phosphine oxide)s with number‐average molecular weights ranging from 9200 to 14,600 Da. NMR spectroscopic analysis indicated the presence of highly branched products with an approximate degree of branching of 0.57. The polymers were soluble in a variety of typical organic solvents and displayed excellent thermal stability. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1456–1467, 2002     

Synthesis and characterization of new poly(ethyleneimine)‐g‐poly(methyl methacrylate) star‐block copolymers with hyperbranched cationic core

Hyperbranched polyethyleneimine (hb‐PEI) is used as polymeric scaffold to synthesize new PEI‐g‐polymethylmethacrylate (PEI‐g‐PMMA) block copolymers, consisting of a hyperbranched, partially quarternized cationic core, and PMMA‐arms. The arms are grafted to the PEI scaffold by means of the “grafting to” method. Ammonium groups, covalently bond to the hyperbranched core, provide good adhesion to negatively charged surfaces, even in case of low‐surface charges. The PMMA strands provide compatibility of the macromolecules to PMMA matrices, hence generating potential dispersants, and compatibilizers for PMMA. A peculiar association behavior in organic solution is observed as supported by dynamic light scattering and DOSY measurements. First evidences of the applicability of the macromolecules as dispersants to prepare PMMA‐nanocomposites are given. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3700–3715     

Star polystyrene‐b‐hyperbranched polyglycidol: Synthesis and ionic conductivity

In this work, novel star‐hyperbranched block copolymers containing four polystyrene arms and hyperbranched polyglycidol at the end of each arm (sPS‐b‐HPG) have been synthesized. The polystyrene arms were prepared through atom transfer radical polymerization of styrene starting from a four‐arm initiator. The hydroxyl‐terminated PS star polymers served as precursors for the cationic ring‐opening polymerization of glycidol using BF₃·OEt₂ as the catalyst. The chemical structures of these block copolymers were characterized by using ¹H and ¹³C NMR. DSC analysis indicated that the star‐hyperbranched block copolymers exhibited two distinct glass transition temperatures corresponding to the linear PS and the HPG segments, respectively. The addition of LiClO₄ increased the T_g of HPG segments at low concentrations, however, decreased the T_g at high concentrations. The T_g of PS segments was not affected by the addition of salts at all. Furthermore, the interaction of sPS‐b‐HPG with LiBr was studied by using viscosity analysis based on the Jones–Dole equation. The star‐like PS core strengthened the interaction of sPS‐b‐HPG with Li ions that could facile the inhomogeneous distribution of Li cations and anions in different phases, which is important in polymeric electrolytes for lithium chemical power sources. The ionic conductivity of one sPS‐b‐HPG/LiClO₄ electrolyte was measured to be higher than that of HPG/LiClO₄ electrolyte. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 949–958, 2009     

Synthesis of unimolecular reversed micelle consisting of a poly(L‐lactide) shell and hyperbranched D‐mannan core

A novel biodegradable unimolecular reversed micelle consisting of a poly(L ‐lactide) (PLA) shell and a hyperbranched D ‐mannan (HBM) core, that is, a chestnut‐shaped polymer (PLA–HBM), was synthesized by the polymerization of L ‐lactide on HBM with 4‐(dimethylamino)pyridine (DMAP) as the catalyst. The obtained polymers were soluble in dimethyl sulfoxide, tetrahydrofuran, and chloroform but insoluble in H₂O. The molecular weights of the PLA chain on PLA–HBM tended to increase with increasing polymerization time. The number of PLA chains on PLA–HBM could be controlled by the ratio of DMAP to the sugar unit in HBM. The obtained copolymer, PLA–HBM, acted as a unimolecular reversed micelle with an encapsulation ability toward the hydrophilic molecule. In addition, the entrapped hydrophilic molecules were slowly released from the core of PLA–HBM, and the release rate was accelerated by the breaking of the PLA chains of the shell when proteinase K as a hydrolase of PLA was used. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 406–413, 2006     

Synthesis and self‐assembly of hyperbranched polymers with benzoyl terminal arms

Hyperbranched polyesters (HPs) with a variable content of benzoyl terminal groups were synthesized through the chemical modification of the HPs' cores by substituting a controlled fraction of the terminal hydroxyl groups with benzoyl chloride. The resulting hyperbranched polymers that were modified by benzoyl groups (HPs‐B) were characterized by ¹H NMR, FTIR, differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Research results revealed that self‐assembled structures could be formed in selected solvents (acetone/n‐hexane). It was found that the morphologies of self‐assembled structures could be adjusted by controlling the content of outside benzoyl terminal groups in the hyperbranched polymers, the volume ratio of acetone with n‐hexane, and the concentration of the hyperbranched polymers with benzoyl terminal arms. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5554–5561, 2005     

Synthesis of a new multiarm star polymer based on hyperbranched poly(styrene) core and poly(ε‐caprolactone) arms and its use as reactive modifier of epoxy thermosets

A well‐defined multiarm star copolymer poly(styrene)‐b‐poly(ε‐caprolactone) (PSOH‐b‐PCL) with an average number of PCL arms per molecule of 60 has been prepared. 4‐Chloromethyl styrene (4‐CMS) was polymerized by means of atom transfer radical polymerization (ATRP) to obtain a hyperbranched poly(styrene) with chlorines as terminal groups. Subsequently, chlorines were substituted by reaction with diisopropanolamine (DIPA) to give the hydroxyl‐ended derivative. Finally, the hydroxyl‐ended hyperbranched poly(styrene) has been used as a macroinitiator core to polymerize ε‐caprolactone by means of cationic ring‐opening polymerization so as to obtain the star copolymer. In a second step, PSOH‐b‐PCL was used as reactive modifier of diglycidylether of bisphenol A formulations cured by 1‐methyl imidazole (1‐MI) obtaining nanostructured thermosets. The curing process was studied by dynamic scanning calorimetry and Fourier transform infrared spectroscopy (FTIR). By rheometry, the effect of this new polymer topology on the complex viscosity (η*) of the reactive mixture and on the gelation process was also analyzed. The thermomechanical characteristics of the modified materials were determined. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Poly(dimethylsiloxane) Star Polymers Having Nanosized Silica Cores

Summary: Poly(dimethylsiloxane) (PDMS) star polymers having a nanosized silica particle as a core were prepared by reacting silica nanoparticles with monoglycidylether‐terminated poly(dimethylsiloxane). This star polymer was a hybrid material having an extremely high content of silica. The PDMS arms formed an organic domain to separate the silica particles and to prevent particle aggregation. The star polymers exhibited good thermal stability and high activation energy of their degradation reaction, in comparison to the linear PDMS polymer and the PDMS/silica blending materials. This star polymer can be used as a flame retardant for polymeric materials and this preparation technique can be applied to prepare other star polymers.

An SEM image of poly(dimethylsiloxane) star polymers having nanosized silica particles as a core.     

Synthesis,characterization, and rheological properties of multiarm stars with poly(glycidol) core and poly(methyl methacrylate) arms by AGET ATRP

Well‐defined multiarm star block copolymers poly(glycidol)‐b‐poly(methyl methacrylate) (PGOHBr‐b‐PMMA_x) with an average number of PMMA arms of 85, 55, and 45 have been prepared. The core‐first approach has been selected as the methodology using atom transfer radical polymerization (ATRP) of MMA from an activated hyperbranched poly(glycidol) as the core. These activated hyperbranched macroinitiators were prepared by esterification of hyperbranched poly(glycidol) (PGOH) with 2‐bromoisobutyryl bromide. The effect of monomer/initiator ratio, catalyst concentration, time, temperature, and solvent on the growing of the arms has been studied in detail in order to optimize the process and to diminish the radical‐radical coupling. The final products and intermediates were characterized by means of size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) and Fourier transform‐infrared (FTIR) spectroscopy. The length of PMMA arms was determined by SEC after cleavage of ester bond linked to PGOH core. Glass transition temperature (T_g), thermal stability and rheological properties of the multiarm star copolymers were also studied. Finally, tapping mode atomic force microscopy (TMAFM) allowed the clear visualization of nano‐sized particles (80–200 nm) corresponding to individual star molecules. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Star polymer with crosslinked core and water‐soluble poly(N‐hydroxyethylacrylamide)‐arms: Synthesis by arm‐first method using ATRP and characterizations by SEC‐MALS and SAXS measurement in water

Core crosslinked star (CCS)‐polymers with water‐soluble arms composed of poly(N‐hydroxyethylacrylamide) (PHEAA) are described. N‐Hydroxyethylacrylamide was polymerized by the atom transfer radical polymerization consisting of ethyl 2‐chloropropionate, copper(I) chloride (CuCl), and tris[2‐(dimethylamino)ethyl]amine in an ethanol/water mixed solvent at 20 °C. The obtained PHEAA‐arms were subsequently coupled using N,N′‐methylenebisacrylamide as the crosslinking agent and sodium L ‐ascorbic acid (AscNa) as the reaction activator. A total of 17 representative coupling reactions with diverse conditions are discussed together with the characterizations of the products mainly by size exclusion chromatograph equipped with the multiangle laser light scattering detector (SEC‐MALS). Consequently, the coupling reactions provided CCS‐polymers with PHEAA‐arms (CCS‐PHEAAs) having weight averaged‐molecular weights determined by SEC‐MALS (M_w,MALS) ranging from 63.8 kg mol^?1 to 832 kg mol^?1, which corresponded to the average arm‐number (N_arm) ranging from 4.1 to 42, respectively. CCS‐PHEAA with the M_w,MALS of 250 kg mol^?1 was isolated and characterized by small angle X‐ray scattering measurements in 0.05 M NaNO₃ aq. at 25 °C, which was shown to possess a star‐shaped structure and exist as single molecules with a radius of gyration at the infinite dilution condition (<R_g²>_z,0^1/2) of 74 ± 4 Å. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Development of an efficient route to hyperbranched poly(arylene ether sulfone)s

A two‐step route to an AB₂ monomer that underwent polymerization via nucleophilic aromatic substitution to afford hyperbranched poly(arylene ether sulfone)s (HB PAES) was developed. The synthesis of 3,5‐difluoro‐4′‐hydroxydiphenyl sulfone ( 4 ) was accomplished by the reaction of 3,5‐difluorophenylmagnesium bromide with 4‐methoxyphenylsulfonyl chloride, followed by deprotection of the phenol group with HBr in acetic acid. The polymerization of 4 in the presence of 3,4,5‐trifluorophenylsulfonyl benzene or tris(3,4,5‐trifluorophenyl)phosphine oxide as a core molecule afforded HB PAES with number‐average molecular weights ranging from 3400 to 8400 Da and polydispersity index values ranging from 1.5 to 4.8. The presence of cyclic oligomeric species, formed by an intramolecular cyclization process, was a contributing factor to the relatively low molecular weights. The degree of branching (DB) of the HB PAES samples was estimated by a comparison of the ¹⁹F NMR spectra of the polymer samples with those of a series of model compounds, and DB values ranging from 0.51 to 0.70 were determined. The glass‐transition temperatures for the HB PAES samples were in the range of 205–222 °C, as determined by differential scanning calorimetry. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43:3178–3187, 2005     

Manipulation of the molecular weight and branching structure of hyperbranched poly(arylene ether phosphine oxide)s prepared via an A2 + B3 approach

A series of hyperbranched poly(arylene ether phosphine oxide)s (HB PAEPOs) were prepared via an A₂ + B₃ polymerization scheme with tris(4‐fluorophenyl)phosphine oxide as B₃, and a variety of bisphenols as A₂. The effects of the reactivity of the A₂ monomer, the A:B ratio, the addition mode, the solvent, and the concentration on the final molecular weight, polydispersity index (PDI), and degree of branching (DB) were studied. Soluble HB PAEPOs with weight‐average molecular weights of up to 299,000 Da were achieved. Reactions in which the A₂ component was added slowly resulted in lower DBs (0.2–0.5), whereas the slow addition of the B₃ component provided samples with DBs of approximately 0.75. Reactions performed under high‐dilution conditions afforded completely soluble materials with weight‐average molecular weights of 9000–12,100 Da and PDI values as low as 2.20. The molecular weights achieved under high‐dilution conditions were independent of the mode of monomer addition. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3871–3881, 2003     

Multiarm star nanocarriers containing a poly(ethylene imine) core and polylactide arms

Star polymers (SPs) containing a hyperbranched poly(ethylene imine) (PEI; number‐average molecular weight = 10,000) core and polylactide arms were synthesized via the ring‐opening polymerization of lactide. PEI was used as a multifunctional macroinitiator for the ring‐opening polymerization of lactide. Different lactide monomer/amino‐functional group (LA/NH_n; n = 1 or 2) ratios were used for preparing SPs with different molecular weights. SPs were able to encapsulate small guest molecules such as Rose Bengal; they also transported small, hydrophilic molecules from water to the organic phase. The transport capacity of all the nanocarriers depended on the LA/NH_n ratio used for synthesizing the SPs. Nanocarriers with a higher LA/NH_n ratio had higher transport capacities. The size of all the nanocarriers depended on the type of solvent. In chloroform, these nanoparticles had several sizes that were related to the self‐assembly of these nanocarriers, but in acetone, they were monodisperse, and their size was smaller than that in chloroform. Also, the transport of polar dyes from water to the chloroform phase was possible. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5740–5749, 2006     

Investigation of thermodynamic properties of hyperbranched poly(ester amide) by inverse gas chromatography

Thermodynamic properties of the hyperbranched poly (ester amide) (Hybrane® 1200) were investigated by inverse gas chromatography (IGC) using 19 different solvents as the probes at infinite dilution. Retention data of probes were used for an extensive characterization of the polymer, which includes the determination of the Flory‐Huggins interaction parameter, the weight fraction activity coefficient, the total, partial, and additive solubility parameters. The analysis of the results indicated that the additive value of the solubility parameter is lower than the value obtained from a standard procedure. Furthermore, the solubility parameter decreases with increase of temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2166–2172, 2008     

Unimolecular micelles and reverse micelles based on hyperbranched polyethers—Comparative study of AB2 + A‐R and A2 + B3 + A‐R type strategies

Core‐shell type hyperbranched polymers that are capable of forming unimolecular micelles and reverse micelles in aqueous and hydrocarbon medium, respectively, were synthesized via two approaches, namely AB₂ + A‐R and A₂ + B₃ + A‐R type copolymerizations. In case of micelle‐forming polymers, an AB₂ monomer carrying a decamethylene spacer was used along with heptaethylene glycol monomethyl ether (HPEG) as the A‐R type comonomer. One the other hand, for the preparation of reverse micelle‐forming polymers, an AB₂ monomer containing an oligo(oxyethylene) spacer was used along with cetyl alcohol as the A‐R type comonomer. The former was readily soluble in water while the latter was soluble in hydrocarbon solvents like hexane. NMR spectral studies confirmed that both the approaches generated highly branched structures wherein about 65–70% of the terminal B groups were capped by the A‐R comonomer. Dye‐uptake measurements revealed that the polymers prepared via the AB₂ + A‐R approach exhibited a significantly larger uptake compared with those prepared via the A₂ + B₃ + A‐R approach. This suggests that the AB₂ + A‐R approach generates hyperbranched polymers with better defined core‐shell topology when compared with polymers prepared via the A₂ + B₃ + A‐R approach, which is in accordance with previous studies that suggest that A₂ + B₃ approach yields polymers with significantly lower branching levels and consequently less compact structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 80–91, 2009     

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