Search

Here, we report on the evaluation of critical packing parameters, PC, of l-tyrosine and ethylene glycol (PEG) amphiphilic block copolymers. The copolymers were synthesized via l-tyrosine-N-carboxyanhydride ring-opening polymerization using different amino-terminated PEGs as macroinitiators. The size and shape of their associates formed in water were investigated by transmission electron microscopy and dynamic and static light scatterings. The copolymers containing 20–30 wt. % of Tyr formed rod-like micelles. The copolymers with 30–50 wt. % of Tyr formed spherical vesicles, while those with 50–80 wt. % Tyr formed irregularly shaped polymeric nanoparticles. PC of the copolymers was estimated as the ratio of the van der Waals volume of the hydrophobic block (V) to its length (L) and the cross-sectional area of the polar block (SH). The values of SH for each copolymer were calculated according to the equation obtained from the correlation analysis of the published data. The hydrophobic block length L was calculated in three ways, i.e., assuming that polytyrosine adopts (1) stretched, (2) amyloid hairpin, or (3) Gaussian coil conformation. In the latter case, the best match of the calculated PC values with the morphology of the copolymer assemblies was observed. [ABSTRACT FROM AUTHOR]

Amphiphilic copolymers with poly (alkyl acrylate) as hydrophobic and poly (acrylic acid) (AA) as hydrophilic block have been synthesised. The alkyl chain was varied from butyl to dodecyl, thereby varying systematically the polarity of the hydrophobic block whose length was between 35 and 70, while the PAA block had ~ 100 units. Such relatively short amphiphiles should equilibrate quickly in aqueous solution, and their corresponding self-assembly properties were characterised by means of critical micelle concentration (cmc) determination. Detailed information regarding the aggregate structures was obtained by static light scattering (SLS) and small angle neutron scattering (SANS). This could be correlated with the molecular architecture of the copolymers and the degree of ionisation of the PAA block. Generally, it is found that the aggregation numbers become smaller upon fully charging the PAA head group and only for dodecyl acrylate really well-defined micellar aggregates are formed. This means that the extent of hydrophobicity of the alkyl acrylate block and its length determine in a clear fashion the propensity for micelle formation and the mass and aggregation number of the formed micelles. [ABSTRACT FROM AUTHOR]

A series of amphiphilic graft copolymers with hydrophilic polyethylene glycol (PEG) backbone and different densities of hydrophobic poly(butyl methacrylate) (PBMA) side chains were synthesized via a strategy combining polycondensation and through activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) technology. The hydrophilic macro-ATRP initiators having different amounts of active side bromo atoms were first synthesized by reacting the small ATRP initiator which contains two hydroxyl groups with hexamethylene diisocyanate (HDI) and polyethylene glycol (PEG1000). By graft from technology, the amphiphilic graft copolymers were then synthesized via ARGET ATRP of butyl methacrylate (BMA) using the hydrophilic macro-ATRP initiators. The steric shield effects of the macro-initiator lowered the polymerization rate and final conversion of BMA. The amphiphilic graft copolymers in aqueous media had critical micelle concentration (CMC) in the range of 10−6 to 10−7 g/mL, which were determined by fluorescence method using pyrene as a probe. The aggregate sizes of the amphiphilic graft copolymers in different solvents changed greatly, which were due to different interactions between the amphiphilic graft copolymers and the solvents and the incompatibility between PEG and PBMA segments. [ABSTRACT FROM AUTHOR]

Copolymers of poly(ε-caprolactone) containing zwitterionic sulfobetaine may be used as biomedical materials. The interaction of these materials with proteins is rarely reported. In this study, amphiphilic copolymers PCL-PDEAS, PCL-PEG200-PDEAS, and PCL-PEG400-PDEAS, which contained poly{N-[2-(methacryloyloxy)ethyl]-N,N-diethyl-N-(3-sulfopropyl)-ammonium} (PDEAS), were designed and synthesized in order to explore interaction of these materials and their micelles with proteins. The structure of the copolymers was confirmed by H-NMR, Fourier transform infrared spectroscopy (FTIR), and element analysis (EA). The copolymers could form either films or micelles. The adsorption of bovine serum albumin (BSA) and fibrinogen (Fg) on the copolymer films and their micelles was studied. The results showed that BSA adsorbed on the films presented different tendencies from their micelle formulation. The protein adsorption may be related to the hydration in the shell of the micelles and the electrostatic interaction between the charges of zwitterion and the protein. The reason for the different amounts of protein adsorption between film and micelle formulation is the difference of molecular chain arrangement and charge distribution of PCLDEAS copolymer. [ABSTRACT FROM AUTHOR]

The dispersion of carbon nanoparticles in water was investigated using dispersants based on block copolymers of poly(acrylic acid) (PAA) and poly(amideimide) (PAI) or a homopolymer of PAA. A diblock copolymer (PAA- block-PAI), triblock copolymer (PAA- block-PAI- block-PAA), and hetero-arm star block copolymer (PAAPAI) with similar molecular weights and PAA contents were used as dispersants. The dispersion of solutions with these polymers was investigated by ζ-potential measurements and transmission electron microscopy. The adsorption of PAI onto carbon nanoparticles was observed. The dispersion of carbon nanoparticles was measured using dynamic light scattering and UV-vis spectroscopy. The dispersibility of carbon nanoparticles increased through the series of copolymers (from most to least dispersed): PAAPAI, PAA- block-PAI, PAA- block-PAI- block-PAA, and homo-PAA. PAA-PAI copolymers behaved as effective dispersants for carbon nanoparticles in water. The presence of a hydrophobic block was essential for dispersion. The architecture of the block copolymers also influenced the dispersion of nanoparticles. Locally concentrated regions of PAA exhibited repulsive interactions, causing dispersion of nanoparticles. PAAPAI demonstrated the greatest potential as an anode binder in lithium-ion batteries because it functioned as a dispersant for the conductive additive. [ABSTRACT FROM AUTHOR]

This work introduces a new polymeric emulsifier, polyglycerol- block-poly(ε-caprolactone), to prepare and stabilize oil-in-water nanoemulsions through the formation of a semi-solid interphase between oil and water. Nanoemulsions are prepared using representative silicone and ester oils, which are widely used for commercial consumer products. The block copolymer is homogeneously solubilized in a mixture of oil and ethanol at 70 °C, and the organic solution is dispersed in water using a conventional homogenizer. Stable nanoemulsions of 220-280 nm in mean diameter are spontaneously generated. The block copolymer is reorganized at the interface to form a robust semi-solid polymeric barrier that can prevent the entrapped oil from diffusing out to the aqueous phase. The barrier exhibits excellent stability against mechanical stresses, allowing nanoemulsions to be very stable during repeated freeze/thaw cycles. This work suggests that polyglycerol-based block copolymers can be a new promising polymeric emulsifier for stabilization of nanoemulsions of various oils. [ABSTRACT FROM AUTHOR]

An effective liver-targeted delivery system was successfully developed by designing ligand-mediated nanoparticles composed of glycyrrhetinic acid (GA)-conjugated block copolymers (glycyrrhetinic acid-modified poly(ethylene glycol)-poly(β-benzyl- l-asparate, GA-PEG-PBLA) synthesized via ring-opening polymerization of the β-benzyl- l-asparate N-carboxyanhydride (BLA-NCA) monomer initiated by GA-modified polyethylene glycol (PEG). Chemical structures of the synthesized polymers were confirmed by H nuclear magnetic resonance (H NMR) and Fourier transform infrared assay (FTIR) and molecular weight determined by gel permeation chromatography (GPC). The copolymers were processed into nanoparticles for delivery of paclitaxel (PTX). In this work, the PTX-loaded nanoparticles were prepared by the emulsion-solvent evaporation method, and the physicochemical properties and cytotoxicity were investigated. The particle sizes of nanoparticles determined by dynamic light scattering measurements were around 70 nm. Transmission electron microscopy showed that the nanoparticles were spherical in shape. The results of in vitro release tests showed that the release profiles of PTX-loaded nanoparticles had a sustained drug release pattern, and PTX release from nanoparticles at pH 5.8 was much faster than that at pH 7.4. The drug release profiles were also fitted for mathematical models to analyze the release mechanism, and the Korsmeyer-Peppas model was found to be the best fit model, indicating a combined effect of diffusion and erosion mechanisms for drug release. The cytotoxicity based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay against human hepatic carcinoma HepG2 cells indicated that the GA-PEG-PBLA nanoparticles had low cytotoxicity and good biocompatibility. These results indicated that the GA-PEG-PBLA nanoparticles could be a novel candidate for liver-targeted delivery of poorly water-soluble anticancer drugs. [ABSTRACT FROM AUTHOR]