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The water–salt solutions of star-shaped six-arm poly-2-alkyl-2-oxazines and poly-2-alkyl-2-oxazolines were studied by light scattering and turbidimetry. The core was hexaaza[26]orthoparacyclophane and the arms were poly-2-ethyl-2-oxazine, poly-2-isopropyl-2-oxazine, poly-2-ethyl-2-oxazoline, and poly-2-isopropyl-2-oxazoline. NaCl and N-methylpyridinium p-toluenesulfonate were used as salts. Their concentration varied from 0–0.154 M. On heating, a phase transition was observed in all studied solutions. It was found that the effect of salt on the thermosensitivity of the investigated stars depends on the structure of the salt and polymer and on the salt content in the solution. The phase separation temperature decreased with an increase in the hydrophobicity of the polymers, which is caused by both a growth of the side radical size and an elongation of the monomer unit. For NaCl solutions, the phase separation temperature monotonically decreased with growth of salt concentration. In solutions with methylpyridinium p-toluenesulfonate, the dependence of the phase separation temperature on the salt concentration was non-monotonic with minimum at salt concentration corresponding to one salt molecule per one arm of a polymer star. Poly-2-alkyl-2-oxazine and poly-2-alkyl-2-oxazoline stars with a hexaaza[26]orthoparacyclophane core are more sensitive to the presence of salt in solution than the similar stars with a calix[n]arene branching center.

Enantiomeric hydroxy-terminated 4-armed star-shaped lactide oligomers (H4LLAO15 and H4DLAO15) with the degree of polymerization per arm, n = 15 and a hydroxy-terminated 4-armed star-shaped e-caprolactone oligomer (H4CLO n ) with n = 7 or 15 were crosslinked with methylenediphenyl 4,4′-diisocyanate at a weight ratio of H4LLAO15/H4DLAO15 = 1/0 or 1/1 produced conetworks (MH-4LLAO15/4CLO n s or MH-4scLAO15/4CLO n s) with the weight ratios of (H4LLAO15 + H4DLAO15)/H4CLO n of 75/25, 50/50 and 25/75 in addition to the homonetworks (MH-4LLAO15, MH-4scLAO15 and MH-4CLO n ). The conetwork with a higher oligolactide (LAO) fraction and longer arm length of the oligocaprolactone segment possessed a better compatibility. Stereocomplex (sc) crystallites of the LAO segments were dominantly formed for MH-4scLAO15 and all MH-4scLAO15/4CLO n s, which were regenerated during cooling and subsequent heating processes after melt. However, LAO homo-crystallites for MH-4LLAO15/4CLO n s were not regenerated at all. MH-4LLAO15/4CLO15s and MH-4scLAO15/4CLO15s exhibited higher tensile toughnesses than MH-4LLAO15/4CLO7s and MH-4scLAO15/4CLO7s, respectively. Especially, the tensile toughness (25.8 MJ m−3) of MH-4scLAO15/4CLO15 75/25 was much higher than that (14.6 MJ m−3) of MH-4LLAO15/4CLO15 75/25.

Star-shaped poly(ethylene glycol) (PEG) chain termini were functionalized with alendronate to create transient networks with reversible crosslinks upon addition of calcium ions. The gelation ability of alendronate-functionalized PEG was greatly dependent on the number of arms and arm molecular weight. After mixing polymer and calcium solutions, the formed hydrogels could be cut and then brought back together without any visible interface. After 2 minutes of contact, their connection was strong enough to allow for stretching without tearing through the previous fracture surface. Oscillatory rheology showed that the hydrogels recovered between 70 and 100% of the original storage and loss modulus after rupture. Frequency sweep measurements revealed a liquid-like behavior at lower frequencies and solid-like at high frequencies. Shifting frequency curves obtained at different calcium and polymer concentrations, all data collapsed in a single common master curve. This time-concentration superposition reveals a common relaxation mechanism intrinsically connected to the calcium-bisphosphonate complexation equilibrium.

The reactions of diglycerol-based 4-armed enantiomeric lactide oligomers (DG4LLAO and DG4DLAO, DGDLAO/DGLLAO = 1/1) and a 1,3-propanediol-based 2-armed rac-lactide oligomer (PD2racLAO) with hexamethylene diisocyanate produced bio-based polyesterurethane networks (PEU-DG4scLAO/PD2racLAOs) with different feed ratios of stereocomplex (sc) lactide oligomer (DG4scLAO = DG4DLAO + DG4LLAO) and PD2racLAO. Crystallization behavior and physical properties of PEU-DG4scLAO/PD2racLAOs were compared with those of the corresponding pentaerythritol- and glycerol-based polyesterurethane networks (PEU-PE4scLAO and PEU-GC4scLAO) with no PD2racLAO fraction. The X-ray diffraction analysis revealed that sc crystallites were formed without any homo-crystallization for PEU-DG4scLAO/PD2racLAOs 100/0-25/75 in a similar manner to PEU-PE4scLAO or PEU-GC3scLAO. Differential scanning calorimetric analysis for PEU-DG4scLAO/PD2racLAOs 100/0-25/75 revealed that the sc crystallites were not regenerated during a cold crystallization process of the quenched samples, but regenerated by isothermal crystallization from the melt. This result was a marked contrast to the previous result that sc crystallites were almost completely regenerated by the cold crystallization for PEU-PE4scLAO and PEU-GC3scLAO. Polarized optical microscopic analysis revealed that the incorporation of 25% of PD2racLAO enhanced the sc-nucleation efficiency, and further addition caused the reduction of overall crystallization. PEU-DG4scLAO/PD2racLAO 100/0 exhibited a higher elongation at break and tensile toughness than PEU-PE4scLAO and PEU-GC3scLAO. Tensile strength and elongation at break for PEU-DG4scLAO/PD2racLAOs decreased with increasing feed of PD2racLAO.

Following our previous paper on the course of the formation of star-polymers from oligo(oxyethylene)alcoholates as arms precursors and diglycidyl ethers as core building units [1], the nature of polymer alcoholate groups formed in this process has been studied. Primary alcoholate groups reacting with diepoxide or epoxide function in polymer give initially predominantly secondary alcoholate groups in the product. However, a small fraction of primary alcoholate groups of polymer is formed from the very beginning. When consumption of epoxide groups increases the contribution of polymer primary groups increases too, reaching eventually from 5 to 15% of total alcoholate groups, depending on reaction conditions. The increase of this proportion with the reaction progress is explained by intramolecular reaction of alcoholate groups with epoxide ones (cyclization) giving a large proportion of primary alcoholate groups. This explanation was supported by the quantum-mechanical calculations of the possible routes of cyclization.

There is a demand for materials to replace or augment the use of sutures and staples in surgical procedures. Currently available commercial surgical adhesives provide either high bond strength with biological toxicity or polymer and protein-based products that are biologically acceptable (though with potential sensitizing potential) but have much reduced bond strength. It is desirable to provide novel biocompatible and biodegradable surgical adhesives/sealants capable of high strength with minimal immune or inflammatory response. In this work, we report the end group derivatization of 8-arm star PEOs with aldehyde and amine end groups. Gels were prepared employing the Schiff-base chemistry between the aldehydes and the amines. Gel setting times, swelling behavior and rheological characterization were carried out for these gels. The mechanical-viscoelastic properties were found to be directly proportional to the crosslinking density of the gels, the 10K PEO gel was stiffer in comparison to the 20K PEO gel. The adhesive properties of these gels were tested using porcine skin and showed excellent adhesion properties. Cytotoxicity studies were carried out for the individual gel components using two different methods: (a) Crystal Violet Staining assay (CVS assay) and (b) impedance and cell index measurement by the xCELLigence system at concentrations >5%. Gels prepared by mixing 20% w/w solutions were also tested for cytotoxicity. The results revealed that the individual gel components as well as the prepared gels and their leachables were non-cytotoxic at these concentrations. Statement of Significance This work presents a new type of glue that is aimed at surgery applications using a water soluble star shaped polymer. It show excellent adhesion to skin and is tough and easy to use. We show that it is very biocompatible based on tests on live human cells, and could therefore in principle be used for internal surgery. Comparison with other reported and commercial glues shows that it is stronger than most, and does not swell in water to the same degree as many other water based bioadhesives.

We investigated the phase behavior of thin film, thickness h ≈ 100 nm, mixtures of a polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymer with star-shaped polystyrene (SPS) molecules of varying functionalities f, where 4 ≤ f ≤ 64, and molecular weights per arm Marm. The miscibility of the system and the surface composition varied appreciably with Marm and f. For large values of Marm, regardless of f, the miscibility of the system was qualitatively similar to that of linear chain PS/PS-b-P2VP mixtures – the copolymer chains aggregate to form micelles, each composed of an inner P2VP core and PS corona, which preferentially segregate to the free surface. On the other hand, for large f and small Marm, SPS molecules preferentially resided at the free surface. Moreover, blends containing SPS molecules with the highest values of f and lowest values of Marm were phase separated. These observations are rationalized in terms of competing entropic interactions and the dependence of the surface tension of the star-shaped molecules on Marm and f.

The reactions of methylenediphenyl 4,4’-diisocyanate (MDI) with hydroxy-terminated 4-armed star-shaped l -lactide oligomer (H4LAO n ) and 4-armed star-shaped e-caprolactone oligomer (H4CLO n ) with the degree of polymerization per one arm, n = 3, 5 or 10 produced conetworks [MH4(LA/CL)O n s] with the feed H4LAO n /H4CLO n weight ratios of 75/25, 50/50 and 25/75. The formation of conetwork structures with different crosslinking densities was confirmed by the swelling test and FT-IR spectral analysis. Scanning electron microscopic analysis revealed that the oligolactate (LAO) and oligocaprolactone (CLO) segments are compatibilized for all the conetworks except for MH4(LA/CL)O 10 25/75. Differential scanning calorimetry and dynamic mechanical analyses revealed that all the conetworks are substantially amorphous, and that only one glass transition temperature ( T g ) was observed for each of the conetworks except for MH4(LA/CL)O 10 25/75. Tensile properties of MH4(LA/CL)O n s were largely affected by the influence of the T g value which changes according to the LAO/CLO ratio. MH4(LA/CL)O 5 50/50 ( T g : 33.3 °C) exhibited the highest tensile toughness among all the conetworks.

In this work, a star-shaped polymer consisting of a cationic poly[2-(dimethylamino) ethyl methacrylate] (PDMAEMA) shell and a zwitterionic poly[N-(3-(methacryloylamino) propyl)-N,N-dimethyl-N-(3-sulfopropyl) ammonium hydroxide] (PMPD) corona was grafted from a polyhedral oligomeric silsesquioxanes (POSS)-based initiator via atomic transfer radical polymerization (ATRP). The reported star-shaped polymer could form stable micelles in aqueous solutions even in the presence of serum. In addition, anti-cancer drug doxorubicin and tumor-suppressing p53 gene were loaded in the process of micelle formation. The formed polyplex was biocompatible and highly efficient for both drug and gene delivery. Furthermore, the polyplex was able to cause a high apoptotic rate of tumor cells both in vitro and in vivo. This combination delivery strategy offers a promising method for cancer therapy and can be used for further clinical applications.

The combination of living/controlled cationic cyclopolymerization and crosslinking polymerization of bifunctional vinyl ethers (divinyl ethers) was applied to the synthesis of core-crosslinked star-shaped polymers with rigid cyclized arms. Cyclopolymerization of 4,4-bis(vinyloxymethyl)cyclohexene (1), a divinyl ether with a cyclohexene group, was investigated with the hydrogen chloride/zinc chloride (HCl/ZnCl2) initiating system in toluene at 0 °C. The reaction proceeded quantitatively to give soluble poly(1)s in organic solvents. The content of the unreacted vinyl groups in the produced polymers was less than ∼3 mol%, and therefore, the degree of cyclization of the polymers was determined to be ∼97%. The number-average molecular weight (Mn) of the polymers increased in direct proportion to monomer conversion and further increased on addition of a fresh monomer feed to the almost completely polymerized reaction mixture, indicating that living cyclopolymerization of 1 occurred. The chain linking reactions among the formed living cyclopolymers with 1,4-bis(vinyloxy)cyclohexane (3) as a crosslinker in toluene at 0 °C produced core-crosslinked star-shaped cyclopoly(1)s [star-poly(1)s] in high yield (100%). Dihydroxylation of the cyclohexene double bonds of star-poly(1) gave hydrophilic water-soluble star-shaped polymers with rigid arm structure [star-poly(1)-OH] with thermo-responsive function in water. Tgs of star-poly(1) and star-poly(1)-OH were 135 °C and 216 °C, respectively; these values are very high as vinyl ether-based star-shaped polymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1094–1102

Two amphiphilic block copolymers using hydrophobic poly(e-caprolactone) (PCL) and hydrophilic poly(ethylene glycol) (PEG) were successfully synthesized. One of them is an (A-b-B)(4) type star polymer [(PCL-b-PEG)(4)] and the other one is a Y-shaped PEG-(PCL)(2). A star-shaped polymer (PCL-b-PEG)(4) was prepared by ring-opening polymerization (ROP) of epsilon-caprolactone continued by click reaction of (PCL-azide)(4) and PEG-alkyne. The synthesis of Y-shaped PEG-(PCL)(2) block copolymer was carried out via Diels-Alder click reaction of a furan protected maleimide end-functionalized PEG (PEG-MI) with an anthracene end-functionalized PCL following the ROP of epsilon-caprolactone. The characterization of micelles is carried out using both materials in aqueous media as drug delivery vehicles, which showed satisfying results and enhanced the cytotoxic effect of the anti-cancer drug vinorelbine (VLB). However, micelles consisted of Y-shaped unimers were found to be more convenient for delivery of hydrophobic drugs such as VLB because they formed in lower concentration, carrying a higher amount of drugs and owing a monomodal distribution. We concluded that the free tails of hydrophobic chains in Y-shaped block copolymer facilitate the assembly of amphiphilic material in water to form micelles.

Poly[2-(Dimethylamino) ethyl acrylate] (PDMAEA) based polymers have been studied as potential gene delivery system. However, few reports emerging in literature suggesting that star-shaped PDMAEA based polymers are performing better in polyplexation with DNA, cytotoxicity and transfection, as compared to linear counterparts. Nonetheless, little evidences exist on direct comparison between the linear and star-shaped polymer structures. To address this, a series of new star-shaped PDMAEA polymers with linear counterparts were synthesised and directly compared their polyplexation with DNA and cytotoxicity in culture cell lines. The star-shaped PDMAEA polymers were synthesised using pentaerythritol tetrakis [2-(dodecylthiocarbonothioylthio)-2-methylpropionate] (4-arm DDMAT) RAFT agent in a “core-first” approach, whereas 2-(dodecylthiocarbonothioylthio)-2-methylpropionate was used to synthesise linear PDMAEA polymers. In order to investigate the effect of molar mass, both star-shaped and linear PDMAEA were synthesised in low (10 kDa) and high (20 kDa) molar mass. It must be noted here that the overall molar mass of the star-shaped polymer was equal to that of the linear counterparts. Interestingly, we found that the star-shaped polymer has slightly smaller hydrodynamic diameter (more compact) relative to linear counterparts, and importantly, star-shaped PDMAEA binds to DNA at much lower nitrogen to phosphate ratio (N/P ratio). However, the cytotoxicity studies in cultured 3T3 murine cell lines demonstrated that both star-shaped and linear counterparts have no toxicity at low 10 kDa, but significantly toxic at higher 20 kDa molar mass, this finding confirmed that the molar mass of PDMAEA play a key role in cytotoxicity effect, not variable polymer structures. Taken together, star-shaped PDMAEA binds more effectively to DNA than linear counterparts and showed no toxicity at 10 kDa molar mass at variable polymer concentrations.

A star-shaped amphiphilic polymer with arms of polystyrene and sodium salt of polymethacrylic acid on the common fullerene (C60) branching center was prepared by hydrolysis of polar chains in a heteroarm star-shaped fullerene (C60)-containing polymer. The micelle-forming properties of the amphiphilic polymer were examined by small-angle neutron scattering. Structure of solutions of the polymer in D2O is discussed.

To reduce the complexity to monitor the bio-absorbable polymer in the implants, a new hyper branched star shaped polymer was developed with the synergetic combination of bio-absorbability and fluorescent characteristics. These hyper branched polymers were synthesized using arm fist method (AFM). This kind of advanced fluorescent specific bioabsorbable polymer (FBAP’s) is in high demand due to several advantages in replacing traditional materials for implants. Here, we have reported the molecular arrangement of the hyper branched polymer with respect to the fluorescent behavior.

Amphiphilic heteroarm star-shaped polymers have important theoretical and practical significance. In this work, amphiphilic heteroarm star-shaped polymer was synthesized by the use of polyfunctional chain transfer agent via sequential free radical polymerization in two steps. First, conventional free radical polymerization of methyl methacrylate (MMA) initiated by 2,2′-azobis (isobutyronitrile) (AIBN) was carried out in the presence of polyfunctional chain transfer agent, pentaerythritol-tertrakis (3-mercaptopropinate) (PETMP). At appropriate monomer conversion, about two-arm s-PMMA having two residual thiol groups at the chain center was obtained. Second, the s-PMMA obtained above was used as macro-chain-transfer agent for free radical polymerization of acrylic acid (AA). The heteroarm star-shaped polymer with the hydrophobic PMMA segment and the hydrophilic PAA segment was obtained. The successful synthesis of heteroarm star-shaped polymers, (PMMA)2(AA)2, was confirmed by 1H-NMR and its self-assembly behavior in different solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Three-arm (A(2)B) and four-arm (A(2)B(2)) star-shaped copolymers based on biocompatible and biodegradable hydrophobic poly(epsilon-caprolactone) (PCL) (A arms) and biocompatible and bioeliminable hydrophilic poly(ethylene oxide) (PEO) (B arms) were synthesized by the coupling of an omega-azide terminated PEO chains with PCL chain bearing one (A(2)B) or two (A(2)B(2)) alkyne functions at the middle of the chain by the copper mediated azide-alkyne cycloaddition (CuAAC). The amphiphilic behavior of these different stars was confirmed by micellization experiments in water followed by dynamic light scattering and transmission electron microscopy analyses. The efficiency to stabilize PLA nanoparticles was investigated in function of the stars structure.

One new three-arm star-shaped polymer was synthesized by the core-first way using atom transfer radical polymerization (ATRP) method. This polymer contained charged iridium (Ir) complex as the luminescent core and 2-(carbazol-9-yl) ethyl methacrylate as the arm repeat unit. Its structure was confirmed by elemental analysis, nuclear magnet resonance (NMR) and photoluminescence (PL). The polymer has a relatively low polydispersity index (PDI) of 1.30 with excellent thermal stability. It also possesses significant redox behavior with a HOMO level of −5.21 eV, which will be of benefit to hole-injection. The PL spectrum of the polymer in film state has a stable peak at 565 nm, however, its PL in dichloromethane solution varied with its concentration. It demonstrated effective energy transfer from the arm unit to the core in the host–guest system. This indicated that when the length of the arm is properly designed, highly luminescent materials can be achieved with emission at 565 nm.

This article reports on the synthesis of a new pH-sensitive amphiphilic A2B mikto-arm star-shaped aliphatic copolyester [with A = poly(e-caprolactone) and B = tertiary amine-bearing poly(e-caprolactone)] with two hydrophobic arms and one hydrophilic arm when protonated at pH = 5.5. First, the ring-opening polymerization of e-caprolactone (eCL) was initiated by an aliphatic diol substituted by an alkyne. The copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) was use to convert the alkyne into a hydroxyl group prone to initiate the ring-opening copolymerization of γ-bromo-e-caprolactone (γBreCL) and eCL. After the substitution of the bromide atoms into azide functions, the N,N-dimethylprop-2-yn-1-amine was grafted onto the azide bearing PCL arm by CuAAC, with the purpose to make the B arm hydrophilic at low pH. The precursors of the A2B copolymers were characterized by 1H NMR, SEC, and MALDI-TOF. As expected, the A2B copolyester was soluble into water at pH = 5. The formation of polymersomes in water at pH 5 was assessed by DLS and TEM analyses. The effects of the architecture and the molecular weight of the A2B copolymers on the formation of polymersomes were investigated. Moreover, the versatility of our approach was demonstrated by the synthesis of an AB2 star-shaped copolyester. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

In this feature article, we present a short review on the recent development in the construction of structurally perfect red and blue light-emitting materials and highlight such research in our group. We focus mainly on the three-dimensional conjugated structures such as dendrimers, hyperbranched polymers, star polymers, spirobifluorene-based polymers, and spiro-bridged ladder-type oligomers and polymers. Results indicated three-dimensional conjugated structures can efficiently decrease the aggregation of materials, resulting in the improving of the light-emitting efficiency.

This paper describes the synthesis of a novel amphiphilic AB 2 triarm star-shaped copolymer with A = non-toxic and biocompatible hydrophilic poly(ethylene oxide) (PEO) and B = biodegradable and hydrophobic poly(e-caprolactone) (PCL). A series of AB 2 triarm star-shaped copolymers with different molecular-weights for the PCL block were successfully synthesized by a three-step procedure. α-Methoxy-ω-epoxy-poly(ethylene oxide) (PEO-epoxide) was first synthesized by the nucleophilic substitution of α-methoxy-ω-hydroxy-poly(ethylene oxide) (MPEO) on epichlorohydrin. In a second step, the α-methoxy-ω,ω′-dihydroxy-poly(ethylene oxide) (PEO(OH) 2 ) macroinitiator was prepared by the selective hydrolysis of the ω-epoxy end-group of the PEO-epoxide chain. Finally, PEO(OH) 2 was used as a macroinitiator for the ring-opening polymerization (ROP) of e-caprolactone (eCL) catalyzed by tin octoaote (Sn(Oct) 2 ). PEO-epoxide, PEO(OH) 2 and the AB 2 triarm star-shaped copolymers were assessed by 1 H NMR spectroscopy, size exclusion chromatography (SEC) and MALDI-TOF. The behavior of the AB 2 triarm star-shaped copolymer in aqueous solution was studied by dynamic light scattering (DLS) and transmission electron microscopy (TEM).

Novel star-shaped copolymers consisting of multiarm polyethylene glycol and low molecular weight linear polyethylenimines (MAPEG-LPEIs) with a high transfection efficiency and low cytotoxicity were designed and synthesized as nonviral gene delivery carriers. The cationic polymers were prepared by conjugating low molecular weight linear PEI (2.5 kDa) to six-arm PEG-NHS (10 kDa) in two different compositions. Two copolymers, MAPEG-LPEI(3) and MAPEG-LPEI(6) with molecular weights of 17.5 kDa and 25 kDa respectively, were synthesized. The MAPEG-LPEI(3)/pDNA and MAPEG-LPEI(6)/pDNA polyplexes are stably dispersed in aqueous media with a narrowly distributed size range of200 nm as determined by dynamic light scattering. Furthermore, these polyplexes showed different surface charges depending upon the relative proportion of MAPEG and LPEI. Moreover, these polyplexes can protect pDNA from enzymatic degradation in serum containing media up to 24 h. These polyplexes were able to efficiently transfect luciferase-coded reporter gene into HeLa cancer cells and showed considerable gene transfection efficacy even in 50% serum-conditioned media in vitro. MAPEG-LPEI(6) exhibited higher transfection activity than that of MAPEG-LPEI(3) at the same weight ratios. Furthermore, MAPEG-LPEI/pDNA polyplexes were less toxic than LPEI/pDNA complexes as determined by MTT assay. These favorable results could be attributed to the combined effect of low molecular weight LPEI and multiarm PEG. The special structural features of the multiarm star-shaped central PEG core play an important role in achieving higher transfection efficiency as it imparts higher charge density to polyplexes and prevents the unwanted aggregation of the smaller polyplex particles. These two important factors contributed toward enhanced gene transfection. On the other hand, LPEI provides low cytotoxicity and effective complexation with pDNA in the designed architecture. Therefore it is possible to achieve enhanced gene transfection by using these two components, namely, pivotal multiarm PEG core and LPEI, in optimal ratio as observed in the case of MAPEG-LPEI(6).

The syntheses, properties and some applications of star-shaped polymers with arms constituted of homo- or copolymers of poly(ethylene oxide) (PEO) is reviewed. The general description of the methods of syntheses, including “arm first” and “core first” procedures, of various types of star-shaped polymers is given as an introduction, without a detailed analysis of the involved chemical procedures. Then, the synthesis of star polymers (including miktoarm stars) with strictly defined as well as with varying number of arms and having cores formed from small and/or large molecules: branched, cross-linked, dendritic, etc., is described. Examples of the large number of various structures of star-shaped PEO polymers described in the literature are presented in a series of tables. Recently elaborated procedure for the synthesis of the star-shaped PEO polymers using hydroxyl terminated precursors of arms and diepoxides as core forming molecules is described in more detail because the method has a general significance and may be applied for the synthesis of a variety of star polymers. Interest in star-shaped and branched systems based on poly(ethylene oxide) (PEO) is mainly motivated by their potential applications in the biomedical and pharmaceutical areas. Therefore, the properties and applications of PEO stars are also reported, as, e.g., drug carriers, surface modifiers, and components of membranes, and/or hydrogels.

BACKGROUND: Star-shaped polymers are very attractive because of their interesting properties such as reduced viscosity, good solubility, low glass transition temperature and fast response to external stimuli. The incorporation of azobenzene moieties in star-shaped polymers could significantly widen their potential applications in various optical devices. One of the most important properties of the azobenzene chromophore is its reversible trans–cis photoisomerization induced by UV or visible light. Photoisomerization induces conformational changes in azopolymer chains, which in turn lead to macroscopic variations in chemical and physical properties of the surroundings and media. RESULTS: This study reports the synthesis of azobenzene-functionalized two-, three- and four-arm telomers via free radical telomerization using the di-, tri- and tetrafunctional chain transfer agents 1,2- and 1,4-benzenedimethanethiol, trimethylolpropane-tris(2-mercaptoacetate) and pentaerythritol-tetrakis(3-mercaptopropionate), respectively, in the presence of azobisisobutyronitrile. Azotelomers were characterized using gel permeation chromatography and 1H NMR and Fourier transform infrared spectroscopy. Thermal phase transition behaviors were investigated using differential scanning calorimetry and polarized optical microscopy. Azotelomers synthesized in this study showed reversible photoisomerization and a fast generation of birefringence. CONCLUSION: Considering the photoisomerization behavior and birefringence of the two-, three- and four-arm azotelomers, it can be concluded that they could be potential candidates for use in various optical devices. Copyright © 2009 Society of Chemical Industry

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-PMMAzon 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

A new star-shaped polymer comprising of full fluorene units was synthesized by Suzuki polycondensation between an A3 type monomer and an AB type monomer. For comparison, a fluorene-based linear polymer was also prepared. The star-shaped polymer was soluble in common organic solvents and gave the number-average molecular weight, Mn, of more than 12,000 and the weight-average molecular weight, Mw, of exceeded 22,000. The polymer showed similar optical behavior both in solution and in the solid state. After an annealing process, the linear fluorene-based polymer showed an additional bathochromic emission at about 550 nm, whereas such red-shifted emission was fully eliminated for the fluorene-based star-shaped polymer. Cyclic voltammetry (CV) measurement of the polymer indicated that the polymer was reversible under p-doping.

Well defined azobenzene containing (co)polymers have been synthesized by atom transfer radical polymerization and subsequent polymeranalogeous reaction for introduction of the chromophores. Four different series were prepared varying only one of the following material parameters at a time, while keeping the others constant. Varied were the molecular weight, the azobenzene content, the glass transition temperature and the molecular architecture of the copolymers. With these four series of (co)polymers the influence of the molecular parameters on the photoinduced formation of surface relief gratings was investigated.

Novel synthetic transfection vectors with linear triblock and star-shaped diblock copolymer architectures have been synthesized by atom transfer radical polymerization (ATRP). Based on 2-(dimethylamino)ethyl methacrylate (DMAEMA) and copolymerization with poly(ethyleneglycol) α-methoxy, ω-methacrylate (MAPEG), the synthesis was realized using CuBr ligated with 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA) as catalytic complex and either ethyl 2-bromoisobutyrate (EB i B) or bis(α-bromoisobutyryl) N -methyl diethanolamine (DEA) or tris(α-bromoisobutyryl) triethanolamine (TEA) as (multifunctional)initiator. The polymers were characterized by GPC and NMR. The solution properties of these homopolymers and palm-tree-like copolymers were investigated by viscometry either in pure water or in buffered aqueous solutions. Interestingly, all the synthesized polymers show polyelectrolyte effect in Millipore water (25 °C) and in Hepes (20 mM) buffer solution (pH 7.4, NaCl 155 mM, 25 °C). Fitting of these viscometric data according to either Fuoss or Fedors equation allows for calculating the intrinsic viscosity of the polymers. These results are compared with dynamic light scattering (DLS) experiments to determine absolute masses. Finally, DEA based palm-tree-like copolymer is investigated to AFM measurement and micelles were observed at pH 8.

BACKGROUND: Generation of stars around in situ formed cores provides a facile approach to star-shaped polymers. Therefore the self-condensing atom transfer radical copolymerization (SCATRCP) of N-[4-(α-bromoisobutyryloxy)phenyl]maleimide (BiBPM) and a large excess of styrene (St) was investigated. RESULTS: BiBPM and St formed a charge transfer complex (CTC), which underwent the SCATRCP, leading to the branched core initiating the atom transfer radical polymerization of St, finally giving star-shaped polystyrene (PS). Kinetic and structural study showed that a higher dosage of BiBPM resulted in an enhanced polymerization rate, a higher degree of branching and a larger number of short PS arms. Differential scanning calorimetry suggested that the glass transition temperature of the star-shaped PS decreased with molecular weight. Melt rheometry showed that even a slightly branched architecture of the PS led to a significantly lower viscosity; both the melt flow index and the activation energy increased with the degree of branching. CONCLUSION: Due to the preferential consumption of BiBPM and formation of a CTC, even a very low dosage of BiBPM could lead to star-shaped PS, which, in comparison with linear analogues, could possess much better melt fluidity. Copyright © 2008 Society of Chemical Industry

Well-defined star shaped polymers with α-Cyclodextrin (α-CD) core linking PMMA-block arms were synthesized by atom transfer radical polymerization (ATRP). Gel polymer electrolytes (GPEs) were prepared by encapsulating electrolyte solution of 1 mol L−1 of LiClO4/EC-PC (volume 1:1) into the obtained star shaped polymer host. The ionic conductivity of the GPEs and the cycling characteristics of LiCoO2/GPEs/Graphite cell were studied by electrochemical impedance spectroscopy and charge-discharge testing, respectively. The results indicate that the GPEs have a high ionic conductivity up to 1.63 × 10−3 S cm−1 at room temperature and exhibit a high electrochemical stability potential of 4.5 V (vs. Li/Li+). The discharge capacity of LiCoO2/GPEs/Graphite cell is about 98% of its initial discharge capacity after 20 cycles at 0.1 C rate. Discharge capacity of the model cell with GPEs is stable with charge-discharge cycling.

A small molecule core (TMP-SK3) with three terminal carboxyl groups was synthesized successfully by the reaction of 1,1,1-trihydroxymethylpropane with the excessive sebacic acid diacetic anhydride (SK). Then, the core molecule was used as a coupling agent to condensate with polyethylene glycols (PEG) of different molecular weights or polyethylene glycol monomethyl ether (PEGm) in the presence of stannous octoate as catalyst and diphenyl ether as an azeotropic agent to remove water. Thus, the three-arm star-shaped PEGs was obtained successfully and characterized by 1H-NMR, DSC, GPC and XRD etc.. DSC measurements indicate that the crystallizing and the melting temperatures of the three-arm star-shaped PEGs were different from those of the corresponding linear PEG because the existence of TMP-SK3 altered its crystallizing velocity and perfect degree of crystallization.

A small molecule (GMS-SA2) with one alkyl chain and two terminal carboxyl groups was synthesized successfully by the reaction of glyceryl monostearate (GMS) with excess succinic anhydride (SA). Then, GMS-SA2 was used as a coupling agent to condensate with polyethylene glycols (PEG) of different molecular weight or polyethylene glycol monomethyl ether (PEGm) in the presence of stannous octoate as catalyst and diphenyl ether as azeotropic agent. The AB2 star-shaped miktoarm copolymers were obtained successfully and were characterized by 1H-NMR, DSC, GPC, XRD, FTIR and polarizing microscopy. The results of DSC and XRD measurements indicate that the crystallization temperature and the melting temperature of the AB2 star-shaped miktoarm copolymers are different from those of the corresponding linear PEGs, because the existing of GMS-SA2 alters their crystalline growth velocity and the perfect degree of crystals. It is very important to control the crystal morphology of star-shaped copolymers by introducing the miktoarm into the starshaped polymers and adjusting its content in star-shaped polymers.

Novel amphiphilic ABC miktoarm star terpolymers were synthesized that consist of hydrophilic poly(ethylene oxide) (PEO), hydrophobic poly(e-caprolactone) (PCL), and pH-sensitive poly(2-vinylpyridine) (P2VP), thus a water-soluble block upon protonation. In the first step, poly(ethylene oxide monomethyl ether) (MPEO) was capped by one ω-epoxy end group by reaction of the original hydroxy end group with epichlorohydrin. MPEO-b-P2VP diblock copolymers were prepared by nucleophilic addition of living P2VP-Li+ chains onto the epoxy group of MPEO's. Finally, the hydroxy group formed at the junction of the MPEO and P2VP blocks was used to initiate the ring-opening polymerization of e-caprolactone in the presence of tin octoate. The ABC star-shaped triblocks were characterized by 1H NMR spectroscopy and size exclusion chromatography.

The comparative studies on the miscibility and phase behavior between the blends of linear and star-shaped poly(2-methyl-2-oxazoline) with poly(vinylidene fluoride) (PVDF) were carried out in this work. The linear poly(2-methyl-2-oxazoline) was synthesized by the ring opening polymerization of 2-methyl-2-oxazoline in the presence of methyl p-toluenesulfonate (MeOTs) whereas the star-shaped poly(2-methyl-2-oxazoline) was synthesized with octa(3-iodopropyl) polyhedral oligomeric silsesquioxane [(IC 3 H 6 ) 8 Si 8 O 12 , OipPOSS] as an octafunctional initiator. The polymers with different topological structures were characterized by means of Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy. It is found that the star-shaped poly(2-methyl-2-oxazoline) was miscible with poly(vinylidene fluoride) (PVDF), which was evidenced by single glass-transition temperature behavior and the equilibrium melting-point depression. Nonetheless, the blends of linear poly(2-methyl-2-oxazoline) with PVDF were phase-separated. The difference in miscibility was ascribed to the topological effect of PMOx macromolecules on the miscibility.

In this paper, two types of three-arm star mesogen-jacketed crystal polymers (MJLCPs) with different core (that is hard core and soft core) were synthesized by 2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene (MPCS), which was initiated by two different trifunctional initiators 1,3,5-(2′-bromo-2′-methylpropionato)benzene (Ia) and 1,1,1-tris(2-bromoisobutyryloxymethyl)propane (Ib), respectively. Characterization of these polymers by 1H NMR and GPC clearly supported the formation of a three-arm star-shaped PMPCS. The resulting three-arm star PMPCS possessed narrow molecular weight distribution, and its molecular weight (Mn,NMR) agreed well with the theoretical value, which reveals the quantitative initiation efficiency. The liquid-crystalline behaviors of the two types of three-arm star polymer with different structure were also investigated by differential scanning calorimeter (DSC) and polarized optical microscope (POM). We found that the liquid-crystalline behavior was incorrelated with structure of core but correlated with the length of three-arm star polymer arm. Only each arm of the three-arm star-shaped polymers with a Mn,GPC beyond 0.90 × 104 g/mol could form a liquid crystalline phase,which was found to be stable up to the decomposition temperature of these tri-arm MJLCPs.

A series of novel multi-armed (di-, tri- and tetra-armed) mesogen-jacketed liquid crystal polymers (MJLCPs) were synthesized by atom transfer radical polymerization (ATRP) of {2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene}(MPCS) using di-, tri- and tetrafunctional initiator, respectively. The results show that the number average molecular weight (M n,GPC ) was increased versus monomer conversion, and the polydispersities were quite narrow ( 1.87 x 10 4 g/mol, 1.84 × 10 4 g/mol, 2.69 × 10 4 and 3.68 x 10 4 g/mol, which were initiated by coil difunctional initiator, hard difunctional initiator, trifunctional initiator and tetrafunctional initiator, respectively. All the liquid crystalline phase was found to be stable up to the decomposition temperature of these multi-armed MJLCPs.

A unimolecular templating star-shaped polymer with a compatibilizing outer corona, prepared by tandem ROP/ATRP procedures, was dispersed into a thermosetting organosilicate. The organic polymer was thermalized to leave behind its latent image in the matrix with a pore size that reflected the size of the polymer molecule, and provided the expected reduction in dielectric constant.

The synthesis of four-armed star mesogen-jacketed liquid crystal polymer was achieved by atom transfer radical polymerization in chlorobenzene solution using pentaerythritol terakis(2-bromoisobutyrate) (PT-Br) as an initiator and CuBr/sparteine complex as a catalyst. The results show that the number average molecular weigh is creased linearly vs. monomer conversion, and that the polydispersities were quite narrow ( 1 H NMR. The liquid-crystalline behavior of the four-armed star polymer was studied using DSC and POM. Only the polymer with a M n,GPC beyond 3.68×10 4 g/mol formed a liquid crystalline phase which was quite stable with a high clearing point.

Isotactic (it-) PMMA anions prepared with t-C4H9MgBr in toluene were reacted with ethylene glycol dimethacrylate (EGDMA) in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to obtain a star shaped polymer. 1H NMR, SEC-LALLS and SEC-differential viscometric analyses of the polymer clearly indicated that the polymer is a highly branched star polymer with crosslinked dimethacrylate core; the number of arms was estimated to be 20–30. A similar reaction of syndiotactic (st-) PMMA anions formed with t-C4H9Li-(n-C4H9)3Al in toluene with EGDMA was unsuccessful. However, the use of butane-1,4-diol dimethacrylate instead of EGDMA resulted in the effective formation of star polymers having st-PMMA arms; the number of arms was estimated to be 139. As a result, two types of star -shaped polymethacrylates with it- and st-PMMA arms were obtained.

The two-region Okada–Numasawa model for solutions of star-shaped polymers has been improved by means of a change in the integration order and introduction of a concentration-dependent and molar-mass-dependent Flory–Huggins interaction parameter (the second and third approximations of the Flory–Huggins theory). To overcome calculation difficulties, a special algorithm for computing coexistence curves of polymeric systems with an UCST has been used. The agreement between the experimental and calculated coexistence curves for the star-shaped polystyrene (PS)–cyclohexane system has been improved: the difference between T c s is ∼0.33 K against ∼12 K as given by the original model.

It is important to develop tailor-made biodegradable/biocompatible polymer networks usable for biomaterials whose thermal and mechanical properties are easily controlled by changing the composition. We synthesized sugar-alcohol-based polymer networks (SPN-mscLAO/3CLO, m = 4, 5 or 6) by the crosslinking reactions of erythritol, xylitol or sorbitol-based m-armed star-shaped l-lactide and d-lactide oligomers (HmSLLAO and HmSDLAO), a glycerol-based 3-armed star-shaped ε-caprolactone oligomer (H3SCLO) and hexamethylene diisocyanate (HDI) at the weight ratios of HmSLLAO/HmSDLAO = 1/1 and (HmSLLAO + HmSDLAO)/H3CLO = 100/0, 75/25, 50/50, 25/75 or 0/100). The influence of the arm number on the crystallization behavior, thermal and mechanical properties of SPN-mscLAO/3CLOs were systematically investigated by comparing with those of sugar-alcohol-based homochiral polymer network (SPN-mLLAO, m = 4, 5 or 6) prepared by the reaction of HmSLLAO and HDI. Stereocomplex (sc) crystallites are dominantly formed for SPN-mscLAO/3CLOs 100/0–25/75, whereas SPN-mLLAOs were amorphous. The higher order of melting temperature of sc-crystals for SPN-mscLAO/3CLOs 100/0–25/75 was m = 5 > m = 6 > m = 4. The sc-crystallinities of SPN-4scLAO/3CLOs 100/0–50/50 were significantly lower than those of SPN-mscLAO/3CLOs 100/0–50/50 (m = 5 and 6). The larger order of the sc-spherulite size at crystallization temperature of 110 °C was m = 5 > m = 6 > m = 4 for SPN-mscLAO/3CLO 100/0. The size and number of sc-spherulites decreased with increasing crystallization temperature over the range of 110–140 °C and with increasing CLO fraction. Among all the networks, SPN-5scLAO/3CLOs 75/25 and 50/50 exhibited the highest and second highest tensile toughnesses (21.4 and 20.3 MJ·m−3), respectively.

We demonstrate utilization of star-shaped polymers as high-density polymer brush coatings and their effectiveness to inhibit the adhesion of platelets and bacteria. Star polymers consisting of poly(2-hydroxyethyl methacrylate) (PHEMA) and/or poly(methyl methacrylate) (PMMA) were synthesized using living radical polymerization with a ruthenium catalyst. The polymer coatings were prepared by simple drop casting of the polymer solution onto poly(ethylene terephthalate) (PET) surfaces and then dried. Among the star polymers prepared in this study, the PHEMA star polymer (star-PHEMA) and the PHEMA/PMMA (mol. ratio of 71/29) heteroarm star polymer (star-H71M29) coatings showed the highest percentage of inhibition against platelet adhesion (78–88% relative to the non-coated PET surface) and Escherichia coli (94–97%). These coatings also showed anti-adhesion activity against platelets after incubation in Dulbecco's phosphate buffered saline or surfactant solution for 7 days. In addition, the PMMA component of the star polymers increased the scratch resistance of the coating. These results indicate that the star-polymer architecture provides high polymer chain density on PET surfaces to prevent adhesion of platelets and bacteria, as well as coating stability and physical durability to prevent exposure of bare PET surfaces. The star polymers provide a simple and effective approach to preparing anti-adhesion polymer coatings on biomedical materials against the adhesion of platelets and bacteria.

Polymer networks and semi-interpenetrating polymer networks (semi-IPNs) based on poly(L-lactide) (PLA) were prepared by reactions of 2,4-tolylene diisocyanate (TDI) and hydroxy-terminated 4-arm star-shaped L-lactide oligomers (H4LAO n ’s) with the degrees of polymerization of lactate unit per one arm, n =3, 5 and 10 in the absence and presence of PLA, respectively. Thermal, mechanical properties and morphologies of the TDI-bridged H4LAO n ’s (TH4LAO n ’s) and TH4LAO n /PLA semi-IPNs were evaluated by comparing with those of PLA. Scanning electron microscopic observation revealed that compatibility between the two components of TH4LAO n /PLA semi-IPNs becomes better with increasing PLA content and n value. Especially, no clear phase-separation was observed for TH4LAO10/PLA 25/75. All the TH4LAO n networks were substantially amorphous and their tan δ peak or glass transition temperatures increased with decreasing n value. The tan δ peak temperatures of TH4LAO3 (86.2 °C) and TH4LAO5 (79.8 °C) were much higher than that of PLA (55.1 °C). All the semi-IPNs except for TH4LAO10/PLA 25/75 displayed two tan δ peaks related to TH4LAO n and PLA. TH4LAO3/PLA 75/25 exhibited a much higher E’ at around 50–90 °C than PLA. TH4LAO5 had the highest tensile strength (90 MPa), modulus (2.5 GPa) and tensile toughness (2.1 MJ m−3) among the TH4LAO n ’s, which were higher than those of PLA (51 MPa, 2.0 GPa and 0.5 MJ m−3), while the semi-IPNs did not exhibit much better tensile properties than PLA did.

Novel metal-containing hydrogels or metal-centered star shaped polymers were prepared by coordination of 2,2′-bipyridyl-modified organic polymers with ruthenium ion. The resulting polymer complexes...

結晶性などの特徴を有し, なおかつ有機溶媒への溶解性に優れた芳香族ポリアミドを得ることを目的としてスター型ポリアミドの合成を検討した. まず, 末端アミノ基とカルボキシル基をそれぞれ8個もつシクロシロキサン骨格からなる2種類のコア分子を合成した. 次に, それらの末端官能基を重合開始点として直接重縮合法によるp-アミノ安息香酸の重合を行い, アミノ末端とカルボキシル末端をそれぞれ有する2種のスター型芳香族ポリアミドを合成した. また, これらのスターポリマーの末端官能基を4-メチル安息香酸塩化物およびp-トルイジンとそれぞれ反応させ, エンドキャッピングを行った. 物性測定の結果, 得られたポリマーは良好な耐熱性と, 同様な繰返し構造からなる線状ポリマーに近い結晶性を示し, しかも有機溶媒に可溶であることが明らかとなった.

Synthetic approaches to metal complexes with polymeric ligands are described. The development of efficient methods for preparing simple bipyridine (bpy) derivatives and their corresponding metal complexes has facilitated their use as initiators and coupling agents in polymer syntheses. Ligand reagents were utilized as initiators in controlled polymerization reactions to form poly(2-R-2-oxazolines) (R = methyl, ethyl, phenyl, undecyl), polystyrenes, poly(methyl methacrylates) (PMMA)s, poly(e-caprolactone)s, and poly(lactic acid)s with bipyridine chelates at the end or centers of the chains. Poly(ethylene glycol) macroligands were formed by a chain-coupling method. Detailed studies of reaction kinetics were performed to determine the scope and limitations of each reaction type with different catalysts and reaction conditions. These results are illustrated for bpyPMMA n (n = 1 or 2), which was prepared by atom transfer radical polymerization with a CuBr/1,4,4,7,7,10-hexamethyltriethylenetetraamine catalyst system. Results of the kinetics investigations performed with other ligands and metalloinitiators are summarized. Macroligands thus prepared were coordinated to a labile metal ion, Fe(II), with standard protocols. Ultraviolet-visible spectral data for selected Fe-centered polymers are provided that confirm the production of the targeted polymeric iron complex products. An inert metal, Ru(II), was used as a template for generating architectural diversity; polymeric complexes with one to six chains emanating from the central core, as well as different heteroarm star products, were prepared.

Os(II)-Centered star-shaped polymer was prepared by the coordination of 2,2’-bipyridyl-terminated poly(oxyethylene) (bpy-POE) with osmium ion. The complexation of polymer ligand with metal ion proceeded as efficiently as that of the low molecular weight ligand. This methodology can easily be extended to various combinations of transition metal ion and polymer ligand. For example, we plan to design a starshaped polymer with a polynuclear Ru(II)-Os(II) bimetallic complex10 at the center core, thus creating a new class of photofunctional materials.

A simple theoretical model was proposed to explain the solubility difference between star-shaped and linear polymers in a solvent. The basic assumption of the model was that probability of intermolecular contacts was low near the centre of a star-shaped polymer because of the higher local segment density. The mixing free energy was obtained by modifying the enthalpy term of the Flory–Huggins free energy. Coexistence curves of star-shaped and linear polymer solutions were calculated, and the results were compared with available experimental data. The present model could predict that star-shaped polymer had a better solubility, but quantitatively it slightly overestimated the difference between the critical temperatures of star-shaped and linear polymer solutions.

Three- and four-arm star shaped polymers, as well as diblock copolymers, are synthesized via acyclic diene metathesis (ADMET) polymerization. This is accomplished by using an asymmetric α,ω-diene containing a terminal double bond and an acrylate, which is polymerized in the presence of multifunctional acrylates as selective and irreversible chain transfer agents using Hoveyda-Grubbs second generation catalyst. High cross-metathesis selectivities are achieved at low temperatures enabling good control over molecular weights. Furthermore, additional polyethyleneglycol (PEG) blocks are attached to these polymers via Heck coupling of the acrylate end-groups of these polymers with aryl iodide functionalized PEG, obtaining three- and four-arm star shaped di- and triblock copolymers with molecular weights up to 31 kDa.