PEO Arms Research Articles

Chain-Folding and Overall Molecular Conformation in a Novel Amphiphilic Starlike Macromolecule

The crystallization and self-assembly behavior of an amphiphilic starlike macromolecule (ASM) with a lipophilic core and four poly(ethylene oxide) (PEO) arms (Mn = 2000 g/mol) were characterized by synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction at different crystallization temperatures (Tc). The overall d-spacing of the alternating amorphous core and crystalline PEO lamellae almost doubled from 11.4 nm for samples quenched into liquid nitrogen to 21.0 nm for Tc = 42 °C, indicating gradual transitions from nearly once-folded to fractionally folded and finally to extended chain crystals with increasing the Tc. On the basis of SAXS, transmission electron microscopy, and computer simulation results, it was suggested that the lamellae contained an interdigitated, single-layered PEO crystal, and an amorphous layer consisted of a double-layered lipophilic core and amorphous PEO. A folded (four PEO arms at one side of the core) rather than an extended (two PEO arms on each side o...

Biological Evaluation of Polyester Dendrimer: Poly(ethylene oxide) “Bow-Tie” Hybrids with Tunable Molecular Weight and Architecture

High molecular weight (MW) polymers have shown promise in terms of improving the properties and the efficacy of low MW therapeutics. However, new systems that are highly biocompatible, are biodegradable, have well-defined MW, and have multiple functional groups for drug attachment are still needed. The biological evaluation of a library of eight polyester dendrimer-poly(ethylene oxide) (PEO) bow-tie hybrids is described here. The group of evaluated polymers was designed to include a range of MWs (from 20000 to 160000) and architectures with the number of PEO arms ranging from two to eight. In vitro experiments revealed that the polymers were nontoxic to cells and were degraded to lower MW species at pH 7.4 and pH 5.0. Biodistribution studies with (125)I-radiolabeled polymers showed that the high MW carriers (>40000) exhibited long circulation half-lives. Comparison of the renal clearances for the four-arm versus eight-arm polymers indicated that the more branched polymers were excreted more slowly into the urine, a result attributed to their decreased flexibility. Due to their essentially linear architecture that does not provide for good isolation of the iodinated phenolic moieties, the polymers with "two arms" were rapidly taken up by the liver. The biodistributions of two long-circulating high MW polymers in mice bearing subcutaneous B16F10 tumors were evaluated, and high levels of tumor accumulation were observed. These new carriers are therefore promising for applications in drug delivery and are also useful for improving our understanding of the effect of polymer architecture on pharmacokinetic properties.

One-Pot Synthesis of Star-Shaped Macromolecules Containing Polyglycidol and Poly(ethylene oxide) Arms

Synthesis of fully hydrophilic star-shaped macromolecules with different kinds of arms (A(x)B(y)C(z)) based on polyglycidol (PGL, A(x)) and poly(ethylene oxide) (PEO, C(z)) arms and diepoxy compounds (diglycidyl ethers of ethylene glycol (DGEG) or neopentyl glycol (DGNG) in the core, B(y)) forming the core is described. Precursors of arms were prepared by polymerization of glycidol with protected -OH groups. The first-generation stars were formed in the series of consecutive-parallel reactions of arms A(x) with diepoxy compounds (B). These first-generation stars (A(x)B(y)), having approximately O-, Mt+ groups on the cores, were used as multianionic initiators for the second generation of arms (C(z)) built by polymerization of ethylene oxide. The products with M(n) up to 10(5) and having up to approximately 40 arms were obtained. The number of arms (f) was determined by direct measurements of M(n) of the first-generation stars (M(n) of arms A(x) is known), compared with f calculated from the branching index g, determined from R(g) measured with size-exclusion chromatography (SEC) triple detection with TriSEC software. The progress of the star formation was monitored by 1H NMR and SEC. These novel water-soluble stars, having a large number of hydroxyl groups, both at the ends of PEO arms as well as within the PGL arms, can be functionalized and further used for attaching compounds of interest. This approach opens, therefore, a new way of "multiPEGylation".

Preparation of poly(ethylene oxide) star polymers and poly(ethylene oxide)–polystyrene heteroarm star polymers by atom transfer radical polymerization

AbstractPoly(ethylene oxide) (PEO) star polymer with a microgel core was prepared by atom transfer radical poylmerization (ATRP) of divinyl benzene (DVB) with mono‐2‐bromoisobutyryl PEO ester as a macroinitiator. Several factors, such as the feed ratio of DVB to the initiator, type of catalysts, and purity of DVB, play important roles during star formation. The crosslinked poly(divinyl benzene) (PDVB) core was further obtained by the hydrolysis of PEO star to remove PEO arms. Size exclusion chromatography (SEC) traces revealed the bare core has a broad molecular weight distribution. PEO–polystyrene (PS) heteroarm star polymer was synthesized through grafting PS from the core of PEO star by another ATRP of styrene (St) because of the presence of initiating groups in the core inherited from PEO star. Characterizations by SEC, 1H NMR, and DSC revealed the successful preparation of the target star copolymers. Scanning electron microscopy images suggested that PEO–PS heteroarm star can form spherical micelles in water/tetrahydrofuran mixture solvents, which further demonstrated the amphiphilic nature of the star polymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2263–2271, 2004

Synthesis of functionalized multiarm poly(ethylene oxide) stars

Six arm poly(ethylene oxide) (PEO) stars carrying either 6 pyridyl or 12 hydroxyl groups at their periphery were synthesized using an arm-first approach. To this end, two novel α,ω-heterodifunctional PEO's, namely α-ketal,ω-hydroxy and α-pyridyl,ω-hydroxy PEO's were synthesized and, after the deprotonation of their hydroxyls, deactivated onto hexachlorocyclophosphazene which served to build the core. Quaternization of the stars containing six outer pyridyl groups created positive charges at their periphery while the acidic treatment of stars carrying terminal ketal rings afforded six arm PEO stars with 12 peripheral hydroxyls. The latter compound was subsequently deprotonated and used to polymerize ethylene oxide by a classical core-first approach. This resulted in the formation of highly branched PEO's also referred to as dendrimer-like PEO stars which consisted of a first generation of six PEO arms and a second generation of 12 hydroxy-ended PEO branches.

A Spramolecular Star-Like Polymer

This study reports the creation of star-like chain architecture through complexation of a mono-amino terminated poly(ethylene oxide) (PEO-NH2) with a macrocyclic compound, 4-sulfonic calix[n]arene (n=4 and 8) (SCA-n). The complexes were prepared in aqueous solution to render proton transfer from the sulfonic acid groups in SCA-n to the amino groups in PEO-NH2, and thereby generated 4- and 8-arm star-like complexes with the PEO arms attached to the SCA-n cores via ionic bonding. Formation of the complexes was verified by titration, solubility test, and dilute solution viscometry. The intrinsic viscosities ([η]) of the complexes in toluene were 60% higher than that of neat PEO-NH2, showing that the star-like structure retained in nonpolar solvents. On the other hand, PEO arms dissociated from the cores in water, so that the complexes and neat PEO-NH2 displayed similar [η]. The star-like supramolecules showed a SAXS peak associated with the core-core correlation in the melt with the inter-core distance of 7.3 nm. The concentration fluctuation in the melt was completely destroyed upon the crystallization of PEO arms. In the semicrystalline state, the SCA-n cores were excluded from the crystal lattice and resided in the interlamellar amorphous regions. Measurements of the crystal thickness by SAXS indicated that the PEO chains in the crystals were once- and twice-folded in neat PEO-NH2 and the complexes crystallized at 40 °C, respectively.

Segmental dynamics in stars of poly(ethylene oxide) chains grafted to fullerene

We have studied the structure and dynamics of star-shaped poly(ethylene-oxide) (PEO), grafted to fullerene, in D 2O-solutions as compared to linear polymer. The neutron scattering gives the radius of stars having a value close to the end-to-end distance of their PEO arms. The spin-echo measurements revealed a strong damping of segmental diffusion in stars showing stretched relaxation behavior.

Star Poly(ethylene oxide)s from Carbosilane Dendrimers

A series of 4-arm, 8-arm, and 16-arm poly(ethylene oxide)s (PEO) have been synthesized from hydroxy functionalized carbosilane dendrimers of generation zero, one, and two, respectively. The PEO arms are grown anionically from the multifunctional cores. The polymers have narrow molecular weight distributions. Analysis of the molecular weight, intrinsic viscosity, and translational diffusion coefficient in methanol confirms the star structure of the polymers. The aqueous solutions of the star PEOs appear normal. Low molecular weight star polymers, however, show abnormally low intrinsic viscosities and are adsorbed on the size exclusion column hydrogel material.

Amphiphilic heteroarm star copolymers of polystyrene and poly(ethylene oxide)

Amphiphilic heteroarm star copolymers bearing polystyrene (PS) and poly(ethylene oxide) (PEO) branches have been synthesized by sequential anionic ‘living’ copolymerization. These samples have been characterized adequately and shown to exhibit rather well-defined structures. The functionality of the stars is influenced mainly by the molar ratio of divinylbenzene per living ends and the molecular weight of the linear PS precursor. These star copolymers exhibit association phenomena not only in water but also in tetrahydrofuran, which is not a selective solvent for the different arms. Finally, it has been shown that the PEO arms can be crystallized, forming well-defined spherulites. This ability is strongly affected by the PEO content and the thermal history of the samples.