A convenient 4-step (2-pot) approach for the synthesis of biocompatible, double hydrophilic linear-hyperbranched block copolymers based on poly(ethylene oxide) (PEO) and poly(glycerol) (PG) is ...described. The polymers consisting exclusively of an aliphatic polyether structure were prepared from linear PEO-b-(l-PG) precursor block copolymers, obtained via anionic polymerization of ethylene oxide and subsequently ethoxyethyl glycidyl ether (EEGE). In order to generate initiating functionalities for glycidol, the protected hydroxyl groups of the P(EEGE) block were recovered by hydrolysis with hydrochloric acid. Partial deprotonation of the linear poly(glycerol) block with cesium hydroxide permitted hypergrafting of glycidol onto the alkoxide initiating sites, using the slow monomer addition technique. Detailed studies showed that narrow polydispersity was only obtained with Cs counterions, while use of potassium resulted in larger polydispersities. The resulting linear-hyperbranched PEO-b-(hb-PG) block copolymers exhibited low polydispersities M w/M n in the range of 1.09−1.25, depending on the molecular weight of the hyperbranched block. Molecular weights of the block copolymers ranged from 3 700 to 15 700 g/mol, varying both the length of the linear PEO segments as well as the hyperbranched block.
Hyperbranched polyglycerol (PG) is established as one of the few hyperbranched polymers that offer the possibility to control molecular weight up to M n = 6000 g/mol. This work introduces a facile ...2-step strategy that relies on the use of a low molecular weight PG (M n = 500 and 1000 g/mol) as a macroinitiator for the slow addition of glycidol, permitting to overcome previous limitations concerning molecular weights and molecular weight control. A systematic investigation of the effect of the degree of deprotonation on the control of the polymerization reaction has been carried out. A series of hyperbranched PGs with molecular weights up to M n = 24000 g/mol has been obtained under fully controlled conditions. The polydispersities of the samples prepared were in the range of 1.3 to 1.8. In summary, we present the first example of a synthetic strategy for a hyperbranched polymer that is now accessible over a broad range of molecular weights (300−24000 g/mol) without the ubiquitous problem of large polydispersities or the necessity for solid supports. In addition, the samples permitted a systematic study of the degree of branching DB of the hyperbranched PGs of elevated molecular weight. Values of DB = 0.60 to 0.63 were obtained, approximating the theoretical limit of 0.66 for slow monomer addition.
All polymeric chemosensitizers proposed thus far have a linear poly(ethylene glycol) (PEG) hydrophilic block. To testify whether precisely this chemical structure and architecture of the hydrophilic ...block is a prerequisite for chemosensitization, we tested a series of novel block copolymers containing a hyperbranched polyglycerol segment as a hydrophilic block (PPO-NG copolymers) on multi-drug-resistant (MDR) tumor cells in culture. PPO-NG copolymers inhibited MDR of three cell lines, indicating that the linear PEG can be substituted for a hyperbranched polyglycerol block without loss of the polymers’ chemosensitizing activity. The extent of MDR reversal increased with the polymers affinity toward the cells and the expression level of P-glycoprotein. In contrast with Pluronic L61, which increases viability of tumor cells in the absence of drugs, PPO-NG chemosensitizers are completely devoid of this property undesired in cancer therapy, making them promising candidates for application as novel MDR reversal agents.
Interactions between styrene-acrylate latexes and cement are investigated with emphasis of the charge properties of the polymer particles by means of calorimetry, adsorption measurement, and confocal ...laser scanning microscope. Three latexes with varied surface charges of polymer particles were prepared by respectively using methacrylic acid (MAA), sodium styrene sulfonate (SSS) and methyl poly(ethylene glycol) methacrylate (MPEGMA) as water soluble monomers during synthesis. It is found that the polymer latexes retard cement hydration in two manners, namely the delaying effect represented by a delayed hydration peak and the slowing down effect characterized by a reduced main hydration peak during the acceleration period. The delaying effect is closely related to the concentration of carboxylic groups existing in the latex, while the depression effect of hydration rate is majorly caused by the adsorption of polymer particles on surface of cement grains and proportional to the total charge density of polymer particles.
Controlled phase changes: Thermosensitive Au nanoparticles with tunable lower critical solution temperature have been prepared by coating the nanoparticles with a thermo‐ and pH‐responsive ...hyperbranched polyelectrolyte. The globular, polyfunctional structure of the hyperbranched polymers offer new options to control phase‐transition temperatures of the nanoparticles (see aggregation equilibrium in diagram).
We present small angle scattering and dielectric spectroscopy results on the influence of an amphiphilic diblock copolymer on the structure and dynamics of a microemulsion. We use a water-in-oil ...(w/o) droplet microemulsion based on the anionic surfactant AOT (sodium bis(2-ethylhexyl) sulfosuccinate), that forms spherical water droplets coated by a monolayer of AOT dispersed in the continuous oil matrix. The studied polymer consists of a hydrophobic poly(propylene oxide) (PPO) block and a hydrophilic hyperbranched polyglycerol with 74 glycerol units (NG
74
). Combining small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) we find that the droplet structure is preserved upon addition of PPO-NG
74
while the interaction distance between droplets increases with increasing polymer content. From SANS we deduce that the NG
74
block is located inside the droplets while the PPO extends into the oil matrix. By measuring the dc-conductivity as a function of temperature we study the dynamic percolation of the microemulsion. While the static structure of the droplet phase remains unchanged, both percolation temperature and phase separation temperature increase linearly with increasing polymer concentration. We explain this finding by a stiffening of the AOT layer induced by the polymer. By means of dielectric spectroscopy we observe two relaxations. The slower one can be related to a polarization at the interface of the water core and the AOT shell (core relaxation) and the faster one is due to the ions in the AOT-shell (cluster relaxation). Polymer addition is found to have a significant influence only on the core relaxation. We apply the cluster relaxation model to estimate the cluster size evolution with increasing polymer concentration.
Incorporation of linear-dendritic amphiphilic diblock copolymer leads to a stiffening of the surfactant layer and stabilization of the droplet phase of a water/AOT/decane microemulsion. This is found by a combination of data from Small Angle Scattering (SAS) and Dielectric Spectroscopy (DS).
Hyperbranched polymers have been synthesized in a microreactor for the first time, employing the known ring‐opening multibranching polymerization of glycidol. Microreactors are well‐known to be ...beneficial for highly exothermic reactions because of their capability to enhance mass and heat transfer due to short diffusion pathways and large interfacial areas per volume. The characteristics of the microstructured reaction system were utilized to engineer a continuous flow process for the preparation of well‐defined hyperbranched polyglycerols with molecular weights up to 1,000 g/mol. Increased flow rates, as well as the use of highly polar solvents, led to the partial formation of very narrowly distributed (Mw/Mn = 1.05–1.15) high molecular weight fractions (Mn up to 150,000 g/mol). NMR‐ and MALDI‐ToF spectra confirmed incorporation of the multifunctional initiator core into the hyperbranched polymer structure.
Well defined hyper‐branched polyglycerols represent a highly versatile and biocompatible class of polymers that are typically prepared by polymerization of glycidol in a tedious batch method. A con‐tinuous flow synthesis protocol has been developed by transferring the reaction to a microstructured device with superior heat and mass transfer, permitting control over the highly exothermal ring‐opening polymerization reaction.
We have prepared a series of amphiphilic dendrimers with hydrophilic aliphatic polyether-type dendritic core and hydrophobic docosyl peripheries. All dendrimers from first up to fourth generation 1−4 ...were synthesized in good yield and high purity by a stepwise convergent approach consisting of a combination of Williamson etherification and hydroboration/oxidation steps. Differential scanning calorimetry (DSC) measurements show that the docosyl peripheries melting temperatures and corresponding heats of fusion decrease only slightly with each generation, indicative of a strong segregation between hydrophilic dendritic core and hydrophobic docosyl periphery. The DSC derived docosyl periphery crystallinity shows a gradual reduction with each generation and is corroborated by wide-angle X-ray scattering (WAXS) experiments. Amphiphilic dendrimer self-assembly in the solid state is investigated by small-angle X-ray scattering. Data from 1, 2, and 3 suggest a bilayer lamellar structure with interdigitated dendritic core packing. In contrast, data from 4 are consistent with a 2-dimensional oblique columnar assembly with hydrophilic core structure. The observed thermal and morphological behaviors are rationalized in terms of high incompatibility and intrinsic interfacial curvature between hydrophilic dendritic core and hydrophobic docosyl periphery arising from the unique dendritic molecular architecture.
