Core-shell polyacrylate and polystyrene-block-polyacrylate stars

The polymerization of p-(iodomethyl)styrene (PIMS) yields well-defined branched polymers with reactive iodomethyl groups. The branched poly[p-(iodomethyl)styrene] was used as the transfer agent in the iodine mediated radical polymerization of vinyl monomers. The polymerization proceeds in a controlled way and yields polystyrene and poly(t-butyl acrylate) star polymers with reactive groups at the end of their arms. Polymers so obtained were also used to prepare stars with block copolymer arms: polystyrene-block-poly(t-butyl acrylate). The characterization of star structures was performed by NMR and gel permeation chromatography with absolute molar mass detection (MALLS). Preliminary characterization of the thermal properties of these novel materials is reported.     

Linear viscoelastic properties of mixtures of 3- and 4-arm polybutadiene stars

The viscoelastic properties of a three-arm and a four-arm star polybutadiene with the same arm molecular weight (M_a) were studied. The zero-shear recoverable compliance (J⁰_e) and plateau modulus (G⁰_N) for these stars are the same. The zero-shear viscosity (η₀) of the three-arm star is 20% lower than that of the four-arm star. Mixtures of the stars had J⁰_e and G⁰_N unchanged. A $\text{50}\text{50}$ mixture of the three- and four-arm star was diluted with a low molecular weight linear polybutadiene. G⁰_N∝ø²; J⁰_e∝ø^?1 and M_e∝ø^?1, as expected for dilution with a θ-solvent.     

Colloidal gel from amphiphilic heteroarm polyelectrolyte stars in aqueous media

We report on the gelation capability of polystyrene/poly(2-vinyl pyridine) amphiphilic heteroarm polyelectrolyte stars in acidic salt-free aqueous media. The star polymers associate through hydrophobic interactions, by retraction of the stretched arms under no interdigitation conditions, in the dilute regime forming colloidal soft nanoparticles comprising about 6 stars, At concentrations significantly higher than the hydrodynamic overlap concentration (c > 40c^∗), the crowding of the colloidal nanoparticles drives a jamming transition, leading to a colloidal gel. The intermediate overlap regime (c^∗ < c < 40c^∗) is characterized by a significant compaction of the polyelectrolyte entities prior interdigitation and jamming.     

Intermolecular radical addition of alkoxyamines onto olefins: An easy access to advanced macromolecular architectures precursors

Novel “second generation” alkoxyamines, derived from N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl (so-called SG1) as initiators for nitroxide-mediated polymerization (NMP) were synthesized by intermolecular radical 1,2-addition (IRA) of a high dissociation rate constant alkoxyamine (BlocBuilder^®, also called MAMA-SG1) onto various activated olefins, such as n-butyl acrylate, acrylic acid, dimethylacrylamide, 2-hydroxyethylacrylate and styrene. The potential of this radical addition was further applied to the synthesis of multifunctional alkoxyamines as precursors for complex macromolecular architectures, namely 3- and 4-arm star polymers. For this, tri- and tetra-acrylates were synthesized by reaction of acryloyl chloride with the 1,1,1-tris(hydroxymethyl)ethane and pentaerythritol, respectively, in the presence of triethylamine. The addition of MAMA-SG1 onto these olefins led to the tri- and tetra-functional SG1-based alkoxyamines which were further used to prepare polystyrene stars of controlled molecular weights and polydispersity values not exceeding 2. The individual arms were recovered by hydrolysis of the ester groups of the star core originating from the alkoxyamine initiator under basic conditions. The decreasing molecular weight determined by GPC during hydrolysis demonstrated the star architecture of the polymers.     

Synthesis and thermoresponsive properties of four arm, amphiphilic poly(tert-butyl-glycidylether)-block-polyglycidol stars

A series of four arm stars with copolymer arms composed of poly(tert-butyl-glycidylether)-b-polyglycidol were prepared using a multi-step process based on anionic ring-opening polymerization. Control of the length of the arms and the number of functional (hydroxyl) reactive groups was achieved by anionic polymerization. Stars with molar masses up to 12200 g/mol were prepared. The amphiphilic character of the star structure was varied using different polyglycidol block lengths. The star structure and molar mass of the obtained stars were characterized by SEC-MALLS and NMR spectroscopy.The temperature behavior of an aqueous solution of the obtained polymers was also investigated. The phase transition temperature was strongly dependent on the hydrophilic-hydrophobic balance of the star structure and varied in the range of 25-59 °C. As shown by DLS and SEM, the stars formed temperature-sensitive spherical aggregates in aqueous solution. The aggregates may be used for controlled transport and release of active compounds.     

Strain-promoted azide-alkyne cycloaddition “click” as a conjugation tool for building topological polymers

Strain-promoted azide-alkyne cycloaddition “click” reaction (SPAAC) was successfully used as a tool in synthesis of star polymers by grafting onto approach. The application of SPAAC method in star polymer synthesis was investigated for coupling reaction of the dibenzocyclooctyne (DIBO) end group of polystyrene (PS) and poly(ethylene glycol) (PEG) with coupling agents bearing 2, 3, or 4 azido groups. Firstly, well-defined linear DIBO-terminated PS was obtained by atom transfer radical polymerization (ATRP) of styrene using a DIBO containing ATRP initiator and linear DIBO-terminated PEG was obtained by terminal functionalization of PEG monomethyl ether (PEG-OH). Then a series of star PS and PEG bearing two, three and four arms were prepared respectively by subjecting SPAAC coupling reaction between the linear polymer-DIBO and the azido tethered core molecules at 30 °C without catalyst. The obtained star PS showed a well-defined structure after fractional precipitation to remove slightly excess linear polymers, and all the star polymers were characterized via Fourier transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance spectroscopy (¹H NMR), size exclusion chromatography (SEC) and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS).     

Synthesis and characterization of a novel liquid crystalline star‐shaped polymer based on α‐CD core via ATRP

Well‐defined side‐chain liquid crystalline star‐shaped polymers were synthesized with a combination of the “core‐first” method and atom transfer radical polymerization (ATRP). Firstly, the functionalized macroinitiator based on the α‐Cyclodextrins (α‐CD) bearing functional bromide groups was synthesized, confirmed by ¹H‐NMR, MALDI‐TOF, and FTIR analysis. Secondly, the side‐chain liquid crystalline arms poly[6‐(4‐methoxy‐4‐oxy‐azobenzene) hexyl methacrylate] (PMMAzo) were prepared by ATRP. The characterization of the star polymers were performed with ¹H‐NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermal polarized optical microscopy (POM). It was found that the liquid crystalline behavior of the star polymer α‐CD‐PMMAzo_n was similar to that of the linear homopolymer. The phase‐transition temperatures from the smectic to nematic phase and from the nematic to isotropic phase increased as the molecular weight increased for most of these samples. All star‐shaped polymers show photoresponsive isomerization under the irradiation with Ultraviolet light. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of well-defined hydrophilic block copolymer brushes by aqueous ATRP

Homopolymer brushes of poly(N,N-dimethylacrylamide) (PDMA), poly(methoxyethylacrylamide) (PMEA) and poly(N-isopropylacrylamide)(PNIPAM) grown on atom transfer radical polymerization (ATRP) initiator functionalized latex particles were used as macroinitiators for the synthesis of PDMA-b-PNIPAM/PMEA, PMEA-b-PDMA/PNIPAM and PNIPAM-b-PDMA block copolymer brushes by surface initiated aqueous ATRP. The grafted homopolymer and block copolymer brushes were analyzed for molecular weight, molecular weight distribution, chain grafting density, composition and hydrodynamic thickness (HT) using gel permeation chromatography-multi-angle laser light scattering, ¹H NMR, particle size analysis and atomic force microscopy (AFM) techniques. The measured graft molecular weight increased following the second ATRP reaction in all cases, indicating the second block had been added. Chain growth depended on the nature of the monomer used for block copolymerization and its concentration. Unimodal distribution of polymer chains in GPC with non-overlap of molar mass-elution volume curves implied an efficient block copolymerization. This was supported by the increase in HT measured by particle size analysis, equilibrium thickness observed by AFM and the composition of the block copolymer layer by ¹H NMR analysis, both in situ and on cleaved chains in solution. ¹H NMR analysis of the grafted latex and cleaved polymers from the surface demonstrated that accurate determination of the copolymer composition by this method is possible without detaching polymer chains from surface. Block copolymer brushes obey the same power law dependence of HT on molecular weight as homopolymer brushes in good solvent conditions. The NIPAM-containing block copolymer brushes were sensitive to changes in the environment as shown by a decrease in HT with increase in the temperature of the medium.     

Synthesis and characterization of four‐arm star‐shaped polymers and copolymers

Four‐arm star‐shaped polymers and copolymers were obtained by transition metal‐catalyzed atom‐transfer radical polymerization (ATRP). The polymers were characterized by FTIR and ¹H‐NMR spectroscopy. Gel permeation chromatography results indicated the formation of polystyrene and polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) arms with controlled molecular weights. In dilute solution, the linear polymers had higher inherent viscosities than star‐shaped ones. Thermogravimetric analysis showed a similar degradation mechanism for linear and star‐shaped polymers. Differential scanning calorimetry indicated the successful formation of diblock star‐shaped copolymers. Copyright © 2006 Society of Chemical Industry     

Temperature-sensitive and highly water-soluble titanate nanotubes

Water-soluble titanate nanotubes (TNTs) with temperature-responsive shells were synthesized by grafting poly(N-isopropylacrylamide) (PNIPAAm) from TNTs via surface atom transfer radical polymerization (ATRP) using ATRP agent functionalized TNTs as macroinitiator. Proton Nuclear magnetic resonance spectroscopy (¹H NMR), Fourier-transform infrared (FT-IR) and thermogravimetric analyses (TGA) results prove the successful graft of PNIPAAm chains from TNTs. TGA shows that the amount of PNIPAAm grown from the TNTs increased with the increase of monomer/initiator ratio. Transmission electron microscope (TEM) measurements displays the obtained TNTs-g-PNIPAAm nanohybrids have a core-shell structure of TNT cores and PNIPAAm shells. In addition, the functional nanotubes demonstrate a reversible low critical solution temperature (LCST) transition with the increase of solution temperature. The synthetic method presented here can also be extended to graft other stimuli responsive polymers from TNTs.     

Atom transfer radical polymerization of methylmethacrylate and styrene initiated by 3,5‐bis(perfluorobenzyloxy)benzyl 2‐bromopropanoate

The synthesis of polymethylmethacrylate (pMMA) and polystyrene (pSt) were realized with newly synthesized initiator, 3,5‐bis(perfluorobenzyloxy)benzyl 2‐bromopropanoate (FBr) in the presence of copper bromide (CuBr) and N,N,N′,N″,N″‐pentamethyl‐diethylenetriamine (PMDETA) by using atom transfer radical polymerization (ATRP). The perfluorinated aromatic group containing initiator was prepared by esterification of the (3,5‐bis[(perfluorobenzyl)oxy]‐phenyl alcohol. Both initiator and polymers were characterized by ¹H‐NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. The ATRP was supported by an increase in the molecular weight of the forming polymers and also by their monomodal molecular weight distribution. Contact angle measurements of water and ethylene glycol on films of synthesized polymers indicated higher degree of hydrophobicity than that of pure pMMA and pure pSt. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Scale-up precision synthesis of octa-arm polyisobutylene stars

Summary This paper concerns the scale-up precision synthesis of octa-arm polyisobutylene (PIB) stars. Specifically, we have optimized to the 100–200 g scale the preparation of star polymers consisting of eight PIB arms radiating from a calix[8]arene core. The synthesis strategy involved the use of a calix[8]arene fitted with eight p-C(CH₃)₂OCH₃ groups as the initiator in conjunction with mixed BCl₃/TiCl₄ coinitiators in hexanes/methyl chloride solvent systems at − 80 °C. Various possible side-reactions have been identified and means for their suppression/elimination were developed. Received: 29 December 1999/Revised version: 22 May 2000/Accepted: 22 May 2000     

Electrochemically mediated atom transfer radical polymerization (eATRP)

This review covers both fundamental aspects and applications of electrochemically mediated atom transfer radical polymerization (eATRP). eATRP setup is discussed in detail, together with the advantages and limitations of this technique. All relevant parameters that can influence eATRP outcome are evaluated (e.g. applied current and potential, stirring and diffusion, solvents and supporting electrolytes). Various materials prepared by eATRP are described, including homopolymers, block copolymers, star polymers, and surface grafted polymer brushes. In addition, other electrochemical techniques conceptually similar to eATRP are discussed, including copper-catalyzed azide-alkyne cycloaddition, electrochemical micropatterning, reversible addition-fragmentation chain transfer polymerization using redox-sensitive initiators, and catalyst removal by electrochemical reduction. The increasing research activity in the last decade indicates that electrochemically regulated methods are becoming valuable tools in the design and synthesis of advanced polymer materials.     

An all ATRP route to PMMA-PEO-PS and PMAA-PEO-PS miktoarm ABC star terpolymer

An all Atom Transfer Radical Polymerization (ATRP) route to synthesize miktoarm ABC star terpolymer, μ-(poly(methyl methacrylate)-poly(ethylene oxide)-polystyrene) (μ-(PMMA-PEO-PS)), was demonstrated. Poly(methyl methacrylate) (PMMA) with a halide end group was first prepared by ATRP of MMA. It was then activated under ATRP conditions at 30 °C to add a styrenic-terminated PEO macromonomer, resulting in the formation of PMMA-b-PEO. Finally, the active halide at the junction point of the diblock copolymer was used to initiate the ATRP of St at higher temperature. By a similar approach, μ-(poly(phenyl methacrylate)-poly(ethylene oxide)-polystyrene) (μ-(PhMA-PEO-PS)) was synthesized, hydrolysis of which in basic medium gave μ-(PMAA-PEO-PS). The polymers were characterized by ¹H NMR spectroscopy and gel permeation chromatography.     

Star polymers via atom transfer radical polymerization from adamantane-based cores

A series of novel multifunctional initiators derived from adamantane-based derivatives have been used in the syntheses of various styrenic and (meth)acrylic star polymers by atom transfer radical polymerization (ATRP). Conditions were identified in each system to produce star polymers with nearly monomodal molecular distributions. These synthesized star polymers have glass transition temperatures similar to those known for high-molecular-weight linear polymers. We obtained a series of adamantane-contained star polymers covering a wide range of molecular weights by adjusting the monomer-to-initiator ratio and the solvent polarity. Because of reaction heterogeneity and inevitable termination processes, the occurrence of star-star coupling led to a lower than predicted molecular weight polydispersity. When hydrolyzed from their cores by NaOH, the values of M_w of the arms of the PMMA star polymer did not change with reaction time, at least for the first 48 h of the reaction, which implies that no significant PMMA hydrolysis occurs within this interval of time.     

Synthesis of 4-, 8-, 12-arm star-branched polybutadienes with three different chain-end functionalities using a functionalized initiator

An array of well-defined 4-, 8-, and 12-arm, chain-end functionalized, star polymers and their deuterated analogs has been synthesized using a t-butyldimethylsiloxy-functionalized alkyllithium initiator and anionic polymerization. The design of the synthesis provides for unusually well-defined comparisons of the behavior of the polymers with different chain-end functionality. For each star architecture three polybutadiene polymers were synthesized with the same labeling, the same well-defined degree of branching and molecular weight, but different chain end functionality. Deprotection of the t-butyldimethylsiloxypropyl chain ends of the stars as first synthesized provided stars with hydroxypropyl chain ends. The hydroxypropyl chain ends were further converted to trifluoroethanesulfonyloxypropyl chain ends by tresylation with 2,2,2-trifluoroethanesulfonyl chloride. Measurements of intrinsic viscosities for the hydrogenous and deuterated linear PBs made in the course of characterizing the star functionalities confirm that the dimensions of the linear chains are not affected by isotopic substitution.     

Synthesis of multi‐arm star polystyrene with hyperbranched polyester initiators by atom transfer radical polymerization

Multi‐arm star polystyrenes with hyperbranched polyester (HP3) core were prepared by atom transfer radical polymerization (ATRP). The structures of the polymers were investigated with FTIR and ¹H NMR. GPC results showed that the resultant polymers had relatively broad polydispersity indices that arouse from the macromolecular initiator (HP3‐Br). The thermal properties were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC analysis indicated that polystyrene star polymers had only the glass transition temperatures (T_g), which changes with the weight ratio of multi‐functional macroinitiator‐to‐monomer. In addition, these star polymers could form the spherical micelles in the selected solvent (THF/n‐hexane). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 728–733, 2006     

A novel amphiphilic AB2 star copolymer synthesized by the combination of ring-opening metathesis polymerization and atom transfer radical polymerization

A new amphiphilic AB₂ star copolymer was synthesized by the combination of ring-opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). Two different routes (methods A and B) were employed firstly to prepare the poly(oxanorbornene)-based monotelechelic polymers as the hydrophobic arm bearing dibromo-ended group via ROMP in the presence of two different terminating agents catalyzed by first generation Grubbs catalyst. The values of capping efficiency (CE) of the polymers were determined by NMR, which were 94% and 67% for methods A and B, respectively. Then, the dibromo-ended ROMP polymers were used as the macroinitiators for ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA) to produce two hydrophilic arms. The prepared amphiphilic AB₂ star copolymers poly(7-oxanorborn-5-ene-exo,exo-2,3-dicarboxylic acid dimethyl ester)-block-bis[poly(2-(dimethylamino)ethyl methacrylate)] (PONBDM_n-b-(PDMAEMA_m)₂) with a fixed chain length of hydrophobic PONBDM and various hydrophilic PDMAEMA chain lengths can self-assemble spontaneously in water to form polymeric micelles, which were characterized by dynamic light scattering, atom force microscopy, and transmission electron microscopy measurements.     

Clickable poly(ionic liquid)s for modification of glass and silicon surfaces

Covalent attachment of poly(ionic liquid)s (PILs) by click chemistry on glass or silicon (Si) surfaces was performed. Poly[1-(4-vinylbenzyl)-3-butylimidazolium bis(trifluoromethylsulfonyl)imide] (polyVBBI⁺Tf₂N⁻), and copolymers of polyVBBI⁺Tf₂N⁻ with fluorescein O-methacrylate were synthesized by conducting an atom transfer radical polymerization (ATRP) from initiators containing azide or thioacetate groups. The azide- and thiol-terminated PILs were then successfully grafted onto alkyne and alkene modified glass/Si wafers by thermal azide–alkyne cycloaddition and photoinitiated thiol-ene click reactions, respectively. The modified surfaces were characterized by contact angle measurements and ellipsometry. The fluorescent PIL functionalized surfaces showed strong fluorescence under UV irradiation. This procedure of tethering PILs to substrates also provides an easy way to change the surface hydrophilicity by replacing the anions in the grafted PILs. The present approach could be readily applied for surface modifications with other types of PILs or their copolymers to achieve different functionalities on various surfaces.     

Synthesis of terminal Si-H irregular tetra-branched star polysiloxanes. Pt-catalyzed hydrosilylation with unsaturated epoxides. Polysiloxane films by photo-acid catalyzed crosslinking

Acid catalyzed insertion of octamethylcyclotetrasiloxane (D₄) into the Si-O bonds of tetrakis(dimethylsiloxy)silane leads to irregular tetra-branched star polymers—tetrakis(ω-dimethylsiloxy)poly(dimethylsiloxy)silane (I). The terminal Si-H bonds of I have been modified by Pt-catalyzed hydrosilylation with 4-vinylcyclohexane-1,2-epoxide to yield a tetra-branched star polydimethylsiloxanes (PDMS) with terminal 2′-ethyl-4-cyclohexanyl-1,2-epoxide groups (II). Solutions of this material and a catalytic amounts of diaryl iodonium hexafluoroantimonate, a photo-acid catalyst, were cast onto glass slides and subsequently irradiated. This results in formation of crosslinked PDMS films (V). The soluble tetra-branched PDMS stars have been characterized by ¹H, ¹³C, and ²⁹Si NMR as well as by IR spectroscopy. Their molecular weight distributions have been determined by gel permeation chromatography (GPC), multi-angle laser light scattering (MALLS), and end groups analysis. Their viscosities were measured with a Brookfield viscometer. The thermal stability of the polymers and the crosslinked films were determined by TGA. The glass transition temperatures (T_g)s of the polymers were determined by DSC. The loss (G″) and storage (G′) shear moduli of the films were determined by DMTA. Surface properties of the films were determined by measurement of static contact angles.Similar star polymers, tetrakis(dimethylsiloxy)poly[3′,3′,3′-trifluoropropylmethylsiloxyl]silanes (III) were prepared by acid catalyzed equilibration of tetrakis(dimethylsiloxy)silane with 1,3,5-trimethyl-1,3,5-tris(3′,3′,3′-trifluoropropyl)cyclotrisiloxanes (D₃^F). These were, likewise, modified by Pt-catalyzed hydrosilylation with 4-vinylcyclohexane-1,2-epoxide. Films (VI) of this material were similarly prepared by photo-acid catalyzed crosslinking.