Multiarm Star Research Articles

Novel multiarm star block copolymer ionomers as proton conductive membranes

Novel multiarm star block copolymer ionomers containing hydrophobic fluorinated block at the periphery and partially sulfonated polystyrene block at the core with varying ion exchange capacities (IECs) were synthesized.

Drug-loaded pseudo-block copolymer micelles with a multi-armed star polymer as the micellar exterior.

Supramolecular constructed pseudo block copolymer micelles based on β-cyclodextrin terminated 4 and 7 armed star poly(N-vinylpyrrolidone) and adamantane terminated linear poly(ε-caprolactone) were prepared. The size, morphology, stability and protein adsorption were experimentally examined. The micelles with 7 armed PVP chains as the micellar exterior showed the lowest amount of protein adsorption and the best stability in media. When cabazitaxel, a new taxane, was loaded into the micelles, 14.4% drug loading content and 85% encapsulation efficacy were achieved. In vitro cytotoxicity studies demonstrated that the cabazitaxel-loaded micelles show significant cytotoxicity against drug-resistant A2780/T cell lines. Biodistribution studies showed that the micelles can almost double the content of cargo in tumor sites compared with the free cargo. In vivo antitumor activity examinations indicated that cabazitaxel-loaded micelles show superior antitumor activity over free paclitaxel and free cabazitaxel.

Highly efficient synthesis and characterization of multiarm and miktoarm star-long-branched polymers via click chemistry

Two series of 3–12 multiarm star polymers and 4-miktoarm star copolymer of butadiene and styrene, in which the Mn of arm was higher than 20 kg mol−1, were synthesized with high efficiency (from 85.0% to 96.1%) via click chemistry.

Synthesis of multiarm star copolymers based on polyglycerol cores with polylactide arms and their application as nanocarriers

Hyperbranched polyglycerol (hPG) with two different molecular weights (hPG2400and hPG8000) was used as a macroinitiator for the polymerization of lactide.

Successful synthesis of distinct dendritic unimolecular initiators suitable for topologically attractive star polymers

Synthesis of two types of dendritic unimolecular initiators containing an initiator number functionality of up to 48 has been described and their efficiency in the synthesis of multiarm star polymers has been confirmed.

UV-absorbent lignin-based multi-arm star thermoplastic elastomers.

Lignin-grafted copolymers, namely lignin-graft-poly(methyl methacrylate-co-butyl acrylate) (lignin-g-P(MMA-co-BA)), are synthesized via "grafting from" atom transfer radical polymerization (ATRP) with the aid of lignin-based macroinitiators. By manipulating the monomer feed ratios of MMA/BA, grafted copolymers with tunable glass transition temperatures (-10-40 °C) are obtained. These copolymers are evaluated as sustainable thermoplastic elastomers (TPEs). The results suggest that the mechanical properties of these TPEs lignin-g-P(MMA-co-BA) copolymers are improved significantly by comparing with those of linear P(MMA-co-BA) copolymer counterparts, and the elastic strain recovery is nearly 70%. Lignin-g-P(MMA-co-BA) copolymers exhibit high absorption in the range of the UV spectrum, which might allow for applications in UV-blocking coatings.

New epoxy thermosets modified with amphiphilic multiarm star polymers as toughness enhancer

The synthesis and characterization of two novel amphiphilic multiarm star polymers with linear polyethylene glycol (PEG) and poly(ε-caprolactone) (PCL) arms and their use as toughening modifiers of epoxy anhydride thermosets are reported. The new star polymers were obtained by partial pegylation of a hyperbranched polyester and subsequent growth of PCL arms. The curing process was studied by calorimetry and thermomechanical analysis, demonstrating the accelerating effect and the influence on gelation of the hydroxyl terminal groups. The curing kinetics was analyzed by model-free and model-fitting methods. The final properties of the resulting materials were determined by thermal and mechanical tests. The addition of the star-like modifiers led only to notable improvement on impact strength in the material containing a 10% of the star with PCL and PEG arms, without compromising glass transition temperature and thermal stability. The morphology of the resulting materials depended on the structure of the toughness modifier used, as demonstrated by electron microscopy, but all modified thermosets obtained showed phase-separated morphologies with nanosized particles.

Guanidinated multi-arm star polyornithines with a polyethylenimine core for gene delivery

Multi-arm star polyornithines PEI-P(Orn)n are prepared by grafting polyornithine arms onto branched polyethylenimine (PEI) with an Mw of 600 via the ring-opening polymerization of N-carboxyanhydride of benzyloxycarbonyl ornithine. To enhance gene delivery efficiency and reduce cytotoxicity, the amino side groups on the polyornithine arms are partially guanidinated that transforms the ornithine units to arginine units. Thus, the guanidinated products G-PEI-P(Orn)n contain multiple poly(ornithine-co-arginine) arms. PEI-P(Orn)n and G-PEI-P(Orn)71 mediate the transfection of pGL3 plasmid to 293T cells almost as efficient as 25 kDa PEI in serum-free medium. Notably, in contrast to the dramatically lowered efficiency of 25 kDa PEI in the presence of serum, the efficiency of G-PEI-P(Orn)71 can be retained or even enhanced in the medium containing 10% serum. The improved serum-compatibility and high efficiency of the guanidinium-modified star polyornithines make them promising for gene delivery.

Effect of hydroxyl ended and end-capped multiarm star polymers on the curing process and mechanical characteristics of epoxy/anhydride thermosets

Multiarm star polymers have been synthesized by cationic ring-opening polymerization of ɛ-caprolactone from a hyperbranched poly(ethyleneimine) core and end-capped with acetic anhydride. These star polymers have been used as modifiers in diglycidylether of bisphenol A/methyl tetrahydrophthalic anhydride/benzyl dimethylamine formulations. The curing process is studied by dynamic scanning calorimetry and rheometry and the resulting thermosets are characterized by dynamic mechanical thermal analysis and thermogravimetry. Internal stresses generated during curing are measured and interpreted in terms of the thermal-mechanical properties of the cured materials. The influence of the modifier in the toughness improvement of the cured thermosets is determined by standardized impact tests and the microstructure of the material observed by scanning electron microscopy.

New Epoxy-Anhydride Thermosets Modified with Multiarm Stars with Hyperbranched Polyester Cores and Poly(ϵ-caprolactone) Arms

Multiarm star polymers with hyperbranched aromatic or aromatic-aliphatic cores and poly(ϵ-caprolactone) arms have been used as toughness modifiers in epoxy-anhydride formulations catalyzed by benzyldimethylamine. The curing process has been studied by dynamic scanning calorimetry, demonstrating little influence of the mobility of the reactive species and the hydroxyl content on the kinetics of this process. The obtained materials were characterized by thermal and mechanical tests and the microstructure by electron microscopy. Homogeneous thermosets have been obtained with a remarkable increase in impact strength without compromising glass transition temperature, thermal stability or hardness.

Small angle X-ray scattering investigation of multiarm star sulfonated polystyrene based ionomer membranes

A series of multiarm star sulfonated polystyrene (SPS) and SPS-block-poly(2,2,3,3,3-pentafluoropropyl methacrylate) block copolymer (SPS-b-PFPMA) based ionomer membranes have been prepared and characterized by Small Angle X-ray Scattering (SAXS). SPS membranes showed well-defined ionomer peaks corresponding to an average distance of ∼7nm between the ionic clusters. The effects of different ion exchange capacities (IEC) and different number of arms on the ionomer peak were investigated. Larger IEC values increased the number of ionic clusters and decreased the average distance between the ionic clusters. At constant IEC, the average distance between the clusters increased with the number of arms of the star polymers. Upon hydration, the ionic clusters got swollen and the distance between the ionic clusters increased by ∼1–2nm. Power law decay of intensity at high-q region with a slope of −4 indicated well-separation of hydrophilic SPS clusters in the matrix of hydrophobic PS domains with sharp interfaces. In the case of SPS-b-PFPMA membranes, in addition to ionomer peak, a second more intense peak at lower q corresponding to a spacing of ∼25nm was observed. This larger length scale structuring was attributed to the phase separation of SPS block at the core and PFPMA block at corona. Both the distance between the ionic clusters and the length of larger scale structuring decreased with increasing IEC indicating attractive interactions between ionic clusters. The results are important in understanding the effect of IEC, number of arms and the composition of the block copolymer arms on the morphology of multiarm star sulfonated polystyrene membranes which have potential for higher proton conductivity polyelectrolyte membranes.

Glassy States in Asymmetric Mixtures of Soft and Hard Colloids

By employing rheological experiments, mode coupling theory, and computer simulations based on realistic coarse-grained models, we investigate the effects of small, hard colloids on the glassy states formed by large, soft colloids. Multiarm star polymers mimic hard and soft colloids by appropriately varying the number and size of their arms. The addition of hard colloids leads, depending on their concentration, to either melting of the soft glass or the emergence of two distinct glassy states. We explain our findings by depletion of the colloids adjacent to the stars, which leads to an arrested phase separation when the repulsive glass line meets the demixing binodal. The parameter-free agreement between experiment, theory, and simulations suggests the generic nature of our results and opens the route for designing soft-hard colloidal composites with tunable rheology.

Controlled Synthesis of Multi‐Arm Star Polyether–Polycarbonate Polyols Based on Propylene Oxide and CO2

Multi-arm star copolymers based on a hyperbranched poly(propylene oxide) polyether-polyol (hbPPO) as a core and poly(propylene carbonate) (PPC) arms are synthesized in two steps from propylene oxide (PO), a small amount of glycidol and CO2 . The PPC arms are prepared via carbon dioxide (CO2 )/PO copolymerization, using hbPPO as a multifunctional macroinitiator and the (R,R)-(salcy)CoOBzF5 catalyst. Star copolymers with 14 and 28 PPC arms, respectively, and controlled molecular weights in the range of 2700-8800 g mol(-1) are prepared (Mw /Mn = 1.23-1.61). Thermal analysis reveals lowered glass transition temperatures in the range of -8 to 10 °C for the PPC star polymers compared with linear PPC, which is due to the influence of the flexible polyether core. Successful conversion of the terminal hydroxyl groups with phenylisocyanate demonstrates the potential of the polycarbonate polyols for polyurethane synthesis.

Photocuring of cycloaliphatic epoxy formulations using polyesters with multiarm star topology as additives

ABSTRACTMultiam star polyesters were synthesized by growing poly(ε‐caprolactone) (PCL) arms from hyperbranched polyesters cores of different molecular weight and used as polymeric modifiers in UV‐curable cationic formulations based on a biscycloaliphatic epoxy resin. The effect of the multiarm stars on the curing kinetics has been investigated by real‐time FTIR. The thermal‐mechanical properties of the photocured thermosets have been studied with calorimetry and dynamomechanical and thermogravimetric analysis. Impact strength tests have been performed to assess their effect on the toughness of the cured materials. An accelerative effect of these modifiers has been observed as a consequence of the participation of the hydroxyl groups of the modifiers in the cationic curing of the epoxy resin. A modest increase in toughness accompanied by a decrease in the glass transition are observed, as a consequence of the incorporation of the modifiers into the network structure, leading to homogeneous, in situ reinforced materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40005.

Star graft copolymer via grafting-onto strategy using a comb!ination of reversible addition-fragmentation chain transfer arm-first technique and aldehyde-aminooxy click reaction

A facile synthetic pathway to a multi-arm star graft polymer has been developed via a grafting-onto strategy using a combination of a reversible addition–fragmentation chain transfer (RAFT) arm-first technique and aldehyde–aminooxy click reaction. A star backbone bearing aldehyde groups was prepared by the RAFT copolymerization of acrolein (Ac), an existing commercial aldehyde-bearing monomer, with styrene (St), followed by crosslinking of the resultant poly(St-co-Ac) macro-RAFT agent using divinylbenzene. The aldehyde groups on the star backbone were then used as clickable sites to attach poly(ethylene glycol) (PEG) side chains via the click reaction between the aldehyde groups and aminooxy-terminated PEG, leading to a structurally well-defined star graft copolymer with arms consisting of poly(St-co-Ac) as backbone and PEG as side chains. Crystalline morphology and self-assembly in water of the obtained star graft copolymer were also investigated. Opportunities are open for the star graft copolymer to form either multimolecular micelles or unimolecular micelles via control of the number of grafted PEG side chains. © 2013 Society of Chemical Industry

Enhanced chemical reworkability of DGEBA thermosets cured with rare earth triflates using aromatic hyperbranched polyesters (HBP) and multiarm star HBP‐b‐poly(ε‐caprolactone) as modifiers

A hyperbranched aromatic polyester (HBPOH) has been synthesized, and poly(ε‐caprolactone) arms have been grown on some of its end hydroxyl groups (HBPCL). These modifiers have been used in cationic diglycidyl ether of bisphenol A formulations cured with ytterbium triflate as cationic initiator. The effect of HBPOH and HBPCL on the curing kinetics has been studied using differential scanning calorimetry (DSC). The obtained materials have been characterized by dynamomechanical analysis, DSC, thermogravimetric analysis and mechanical tests. The modifiers are incorporated into the thermosetting network because of the participation of the end hydroxyl groups in the cationic curing of epoxides by the activated monomer mechanism. Homogeneous thermosets have been obtained with a remarkable increase in impact strength without sacrificing elastic modulus or hardness. A compromise between the rigid structure of the aromatic hyperbranched core and the flexibilizing effect of the poly(ε‐caprolactone) arms is believed to be responsible for the overall thermal and mechanical properties of the materials. The use of these polymeric modifiers increases the thermal stability of the resulting materials because of the low degradability of the aromatic ester groups in the hyperbranched core and the incorporation of the modifier into the network structure. However, the presence of such ester groups makes them reworkable by hydrolysis or alcoholysis in an alkaline medium, thus opening a way for recovery of valuable substrates. Copyright © 2013 John Wiley & Sons, Ltd.

Synthesis of Hyperbranched Multiarm Star Block Copolymers and Their Application as a Drug‐Delivery System

ABSTRACTA novel hyperbranched multiarm star block copolymers was synthesized. The atom transfer radical polymerization initiators were anchored on the surfaces by the reaction of amino‐functionalized silica modified by 3‐aminopropyltriethoxysilane with α‐bromoisobutyryl bromide. The composites (SNs‐g‐HPCMS‐b‐PHEMA‐b‐PNIPAAm) with silica nano particles as core and hyperbranched star block copolymers as arms was prepared by iron(III)‐mediated surface‐initiated polymerization with FeCl3·6H2O as catalyst, triphenylphosphine as ligand, ascorbic acid as reducing agent, N,N‐dimethylformamide as solvent, and 4‐chloromethylstyrene, 2‐hydroxyethylmethacrylate, and N‐isopropylacrylaminde as monomers, respectively. The resultant products were characterized by Fourier‐transform infrared spectroscopy, N2 adsorption/desorption measurements, thermogravimetric analysis, differential scanning calorimeter, and transmission electron micrographs. With aspirin as the model drug, the drug‐release behavior of the hybrid materials was studied. The release behavior could be controlled by the temperature, which will have potential applications in biomedicine and biotechnology. © 2013 Wiley Periodicals, Inc. Adv Polym Technol 2013, 32, 21375; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21375

New chemically reworkable epoxy coatings obtained by the addition of polyesters with star topologies to diglycidyl ether of bisphenol A resins

A new multiarm star with hyperbranched aromatic–aliphatic polyester core and poly(ɛ-caprolactone) arms (HBPCL) was synthesized and characterized. Mixtures of diglycidyl ether of bisphenol A (DGEBA) resin and different proportions of this star type modifier were cured using a thermal cationic curing agent, Yb(OTf)3. The HBPCL prepared has hydroxyl groups as chain ends, which are capable of chemically incorporating to the epoxy matrix by means of the monomer activated mechanism. This, together with the chemical structure of the modifier, allowed the preparation of new homogeneous thermosets for coating applications. The curing mixtures were investigated by differential scanning calorimetry (DSC) to study the curing process and evaluate the kinetic parameters of the formulations. These studies demonstrated that HBPCL decreased the curing rate and affected the gelation process. The thermosets obtained showed an improvement in impact strength with a discrete reduction of the Tg. The modified coatings showed an increased reworkability in alkaline solution with the maintenance of thermal stability.

Stereocomplex Formation in Polylactide Multiarm Stars and Comb Copolymers with Linear and Hyperbranched Multifunctional PEG

AbstractA systematic comparison between graft poly(l‐lactide) copolymers with different topologies and their ability to form stereocomplexes with poly(D‐lactide) (PDLA) is performed. Comb and hyperbranched copolymers based on functional poly(ethylene glycol) and poly(l‐lactide) with molecular weights in the range of 2000–90 000 g mol−1 and moderate molecular weight distributions (Mw/Mn = 1.08–1.37) are prepared via the combination of anionic and ring‐opening polymerization. Two “topological isomers,” a linear poly(ethylene oxide)/poly(glycerol) (PEG/PG) copolymer and a branched PEG/PG copolymer are used as backbone polymers. Furthermore, the stereocomplex formation between PDLA and the hyperbranched and comb copolymers containing poly(l‐lactide) arms is studied. Stereocomplex formation is confirmed by DSC as well as by Fourier transform IR (FTIR) and Raman spectroscopy.magnified image

New epoxy thermosets modified with multiarm star poly(lactide) with poly(ethyleneimine) as core of different molecular weight

Multiarm stars containing a hyperbranched poly(ethyleneimine) core of different molecular weight and poly(lactide) arms were synthesized by cationic ring-opening polymerization of lactide from a hyperbranched poly(ethyleneimine) core. After characterization by rheometry, calorimetry, thermogravimetry and nuclear magnetic resonance, these polymers were used as chemically modifiers in the anionic curing of diglycidylether of bisphenol A epoxy resin. The curing process was studied by dynamic scanning calorimetry, demonstrating the influence of the mobility of the reactive species and the hydroxyl content on the curing kinetics. The resulting materials were characterized by thermal and mechanical tests. The addition of the multiarm stars led to homogeneous materials with a slight improvement on the impact strength in comparison with the neat material, without compromising the glass transition temperature. The reworkable nature of the materials was demonstrated by monitoring the changes in their glass transition under thermal rework conditions.