Properties Of Amphiphilic Block Copolymers Research Articles

The Influence of Hydrophobic Blocks of PEO-Containing Copolymers on Glyceryl Monooleate Lyotropic Liquid Crystalline Nanoparticles for Drug Delivery.

The investigation of properties of amphiphilic block copolymers as stabilizers for non-lamellar lyotropic liquid crystalline nanoparticles represents a fundamental issue for the formation, stability and upgraded functionality of these nanosystems. The aim of this work is to use amphiphilic block copolymers, not studied before, as stabilizers of glyceryl monooleate 1-(cis-9-octadecenoyl)-rac-glycerol (GMO) colloidal dispersions. Nanosystems were prepared with the use of poly(ethylene oxide)-b-poly(lactic acid) (PEO-b-PLA) and poly(ethylene oxide)-b-poly(5-methyl-5-ethyloxycarbonyl-1,3-dioxan-2-one) (PEO-b-PMEC) block copolymers. Different GMO:polymer molar ratios lead to formulation of nanoparticles with different size and internal organization, depending on the type of hydrophobic block. Resveratrol was loaded into the nanosystems as a model hydrophobic drug. The physicochemical and morphological characteristics of the prepared nanosystems were investigated by dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), fast Fourier transform (FFT) analysis and X-ray diffraction (XRD). The studies allowed the description of the lyotropic liquid crystalline nanoparticles and evaluation of impact of copolymer composition on these nanosystems. The structures formed in GMO:block copolymer colloidal dispersions were compared with those discussed previously. The investigations broaden the toolbox of polymeric stabilizers for the development of this type of hybrid polymer/lipid nanostructures.

Multidetector‐ThF3 as a Novel Tool for the Investigation of Solution Properties of Amphiphilic Block Copolymers

In this study, multidetector Thermal FFF (ThF3) is utilized to study amphiphilic block copolymers in different selective and nonselective solvents. Depending on the solvent quality and the polymer concentration, amphiphilic block copolymers can form aggregates or micelles; the blocks can adopt different coil conformations. ThF3 is chosen because of the noninvasive nature of the technique that will not destroy the conformations that amphiphilic block copolymers can adopt in selected solvents. The effect of different polymer–solvent systems on the diffusion and thermal diffusion coefficients, and the resultant separation, is studied. It is found that, depending on the solvent, the macromolecules adopt extended coil or partially collapsed coil conformations. Experimental conditions are identified where the block copolymers behave similar to one of their parent homopolymers. For the first time, it has been shown that ThF3 is a unique tool to study the solution properties and the coil conformations of amphiphilic copolymers and to relate this information to the fractionation behavior of the polymers. image

Synthesis, characterization and properties of amphiphilic block copolymers of 2-hydroxyethyl methacrylate and polydimethylsiloxane prepared by atom transfer radical polymerization

A series of amphiphilic poly(2-hydroxyethyl methacrylate)-b-polydimethylsiloxane-b-poly(2-hydroxyethyl methacrylate) (pHEMA-b-PDMS-b-pHEMA) (A-B-A) triblock copolymers were synthesized with varying block molecular weights. Control over the polymerization, micellar size and size distribution, dynamic mechanical properties, and film morphology of nine triblock copolymers was investigated as a function of block length. The polymerization resulted in copolymers with polydispersity index below 1.5. The self-assembly behavior of the triblock copolymers was studied in selective solvents for A and B blocks. The micellar diameter was determined by dynamic light scattering and transmission electron microscopy. The film morphologies were investigated by small angle X-ray scattering. Phase separation was observed when the blocks had similar molecular weights (symmetry). However, the ordering of the morphology was disrupted when the blocks lengths were asymmetric. Phase separation was observed by atomic force microscopy when the block molecular weights were symmetric. The viscoelastic properties were examined using dynamic mechanical analysis. The modulus and crosslink density increased with increasing pHEMA content. Number of aggregations is very small when THF was used compared with methanol and methanol–water. Aggregation of copolymers was difficult in THF due to back-folding and looping of PDMS block. This was unfavorable as it increases free energy of system. This probably resulted in higher CMC of pHEMA-b-PDMS-b-pHEMA copolymers in THF than in methanol. Micellar size of most of triblock copolymers in THF was smaller than in methanol.

Synthesis, Assembled Structures, and Optoelectronic Properties of Amphiphilic Block Copolymers Containing Anthracene Units in the Main Chain

AbstractNovel amphiphilic block copolymers containing the anthracene unit in the main chain are synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization of a cyclic monomer, 10‐methylene‐9,10‐dihydroanthryl‐9‐spirophenylcyclopropane (MDS). A hydrophilic macro‐chain transfer agent is prepared by RAFT polymerization of 2‐hydroxyethyl acrylate (HEA). The polymerizations of MDS using the poly(HEA) afford amphiphilic block copolymers, in which the hydrophobic poly(MDS) segment has a perfectly alternating structure composed of an anthracene unit and a styrene unit, owing to the ring‐opening polymerization system. Characteristic assembled structures and optoelectronic properties of the amphiphilic block copolymers are investigated in various selective solvents.

Effect of the lithium cation on the sorption and electrical properties of amphiphilic block copolymers and their composites

AbstractThe use of lithium cation in composites of block copolymers [polyethylene‐b‐polyethylene oxide (PE‐b‐50%PEO and PE‐b‐80%PEO)] and their derivatives was tested as a modifier of the vapor sorption and impedance of these complexes. The block copolymer PE‐b‐80%PEO was modified by oxidation of its hydroxyl end group to both a carboxylic acid group (PE‐b‐80%PEO)CH2COOH and its sodium salt (PE‐b‐80%PEO)CH2COO− Na+ for the purpose of improving its compatibility and performance as a matrix for composites. These modified copolymers were characterized by FTIR, DSC, and mass spectrometry. The sorption of water of these copolymers and their composites with lithium nitrate was also compared, as well as the electrical properties of their composites were measured by electrical impedance spectroscopy. For the composites obtained with PE‐b‐80%PEO and lithium nitrate, it was found that lithium cation plays an important role increasing the sorption rate, which is maximized for the PE‐b‐80%PEO + (21% lithium nitrate) composite. For the copolymers (PE‐b‐80%PEO)CH2COOH and (PE‐b‐80%PEO)CH2COO− Na+ and their composites, the highest sorption rate was observed for salt in the following order: COO− Na+ > COOH > OH. The PE‐b‐80%PEO + (21% lithium nitrate) composite behaves as a solid polymeric ionic conductor fitting the Williams–Landel–Ferry equation. However, both (PE‐b‐80% PEO)CH2COOH and (PE‐b‐80%PEO)CH2COO− Na+ + (21% lithium nitrate) composites fitted the Variable Range Hopping equation, indicating a conductance trend with temperature governed by a thermally activated with energy of 0.482 and 0.524 eV and not by a relaxation process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1809–1817, 2010

Amphiphilic star block copolymers: Influence of branching on lyotropic/interfacial properties

How can the degree of branching influence the lyotropic properties of amphiphilic block copolymers? In order to provide a qualitative answer to this question, we have prepared a library of poly(propylene sulfide)- bl-poly(ethylene glycol) (PPS–PEG) block copolymers, varying the hydrophobic block (PPS) length and its branching degree and thus producing diblock, triblock (that can be seen as two-armed star), tri-armed star and tetra-armed star structures. The PEG block, on the contrary, was kept constant (linear PEG2000). Although all the polymers exhibited a qualitatively similar lyotropic behaviour, an increased degree of branching of the hydrophobic block caused clear differences in the rheology of lyotropic phases, with an increasingly softer character, and in the organisation of the PEG chains, which appeared to adopt possibly more extended and dehydrated conformations.

Synthesis and surface properties of amphiphilic block copolymers polyvinylpyrrolidone-block-polystyrene

Amphiphilic block copolymers of N-pyrrolidone and styrene were prepared by chain transfer to organogermanium compounds bis(pentafluorophenyl)germane and tris(pentafluorophenyl)germane. The relative chain-transfer constants were determined. The surface properties of the isolated block copolymers with various numbers of units in the hydrophilic block were studied. The polar and dispersive components of the surface tension of films of the amphiphilic block copolymers were calculated by the Zisman method.

Recent Research Progress in the Synthesis and Properties of Amphiphilic Block Co-polymers and Their Applications in Emulsion Polymerization

Amphiphilic block co-polymers are an interesting class of polymeric surfactants. They have been used as rheology modifiers, stabilizing agents of latexes, emulsifiers, de-emulsifiers, flocculants, etc. In this paper the recent advances made in the synthesis of amphiphilic block co-polymer via controlled free-radical copolymerization are reviewed and surfactant properties of amphiphilic block co-polymers are described, such as critical micelle concentrations, surface activity, solubilization capacity of hydrophobic substances in micelles and foaming property. The effect of some parameters on the emulsion polymerization is presented, such as the composition and structure of amphiphilic block co-polymers, block length and the weight ratio of the hydrophilic and hydrophobic segments, and block co-polymer concentration.

Assembled Structures and Chiroptical Properties of Amphiphilic Block Copolymers Synthesized by RAFT Polymerization of N -Acryloyl-L -alanine

Amino acid-based amphiphilic block copolymers involving poly(N-acryloyl-L-alanine), poly(A-Ala-OH), which exhibits a characteristic chiroptical property and pH-dependent solubility, have been synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The direct polymerization of A-Ala-OH without any protecting chemistry using the dithiocarbamate-terminated polystyrene or poly(N-acryloyl-L-phenylalanine methyl ester) as a macrochain transfer agent produced well-defined amphiphilic block copolymers. The self-assembly behaviors and chiroptical properties of these amphiphilic block copolymers in selective solvents were investigated by dynamic light scattering, circular dichroism, and UV–Vis spectroscopic methods.

Polyelectrolyte Complexes in Solution and in Bulk

AbstractFor Abstract see ChemInform Abstract in Full Text.

Effect of Architecture on the Micellar Properties of Amphiphilic Block Copolymers: Comparison of AB Linear Diblock, A2B2, A3B3, and (AB)3 Star Block Copolymers

The influence of architecture on aqueous micellar properties of amphiphilic block copolymers AB‐1, A2B2, A3B3, and (AB)3 (A = polyisobutylene (PIB), B = poly(methyl vinyl ether) (PMeVE)), with approximately constant A and B segment lengths, was investigated. A comparison of AB‐1 with AB‐2 and AB‐3 diblock copolymers having similar composition but higher total molecular weight suggested spherical core‐shell morphology for AB‐3 and vesicles for AB‐1 and AB‐2. Similarly to AB‐1, star block copolymers A2B2, A3B3, and (AB)3 also formed vesicles with unusually high aggregation number (N agg) and hydrodynamic radius (R h). The critical micelle concentration (CMC) measured by fluorescence spectroscopy at 20°C increased in the order (AB)3 = AB‐1 < A2B2 ∼ A3B3. The temperature dependence of R h and N agg has been determined in the temperature range of 20–30°C. R h and N agg remained approximately constant in the whole temperature range for A2B2, A3B3, and (AB)3. A substantial increase in both R h and N agg occurred at 25°C for AB‐1. The particle size distribution for all block copolymers remained narrow in the whole temperature range. Below 25°C, R h increased in the order (AB)3 < AB‐1 < A2B2 < A3B3 and N agg increased in the (AB)3 < A3B3 < A2B2 < AB order. The numbers of AB units in the micelles, however, were similar. Micelles of A2B2 and A3B3 consisted of 5600 and 5700 AB units respectively, while these numbers were slightly lower for AB‐1 (4500) and (AB)3 (4800).

Polyelectrolytes on block copolymer surfaces

AbstractSoft lithography and properties of amphiphilic block copolymers are combined in a new technique for the generation of patterned substrates, which can be used in different ways as templates for further processing. In these processing steps the deposition of polyelectrolytes, metals and grafting from polymerizations are used for the construction of different structures.

Effect of Architecture on the Micellar Properties of Amphiphilic Block Copolymers: Comparison of AB Linear Diblock, AAB, and A2B Heteroarm Star Block Copolymers

Amphiphilic AB, A1A2B, and A2B block copolymers, where A = polyisobutylene, B = poly(methyl vinyl ether), and the superscripts denote molecular weight asymmetry, with constant molecular weight and composition have been synthesized by living cationic polymerization. The influence of architecture on aqueous micellar properties of these block copolymers were investigated in the temperature range 20−30 °C by fluorescence spectroscopy and static and dynamic light scattering (SLS and DLS). The critical micelle concentration (cmc) measured at 23 °C increased in the order A2B < A1A2B < AB. The partition equilibrium constants, Kv of pyrene, characteristic of hydrophobicity, increased in the opposite order of cmc. The hydrodynamic radii (Rh) and aggregation numbers (Nagg) of micelles remained approximately constant in the whole temperature range for A1A2B and A2B and below 25 °C for AB. At ∼25 °C, however, there was a sudden increase in both Rh and Nagg for AB. Below 25 °C both Rh and Nagg increased in the order AB...

Soluble Complexes from Poly(ethylene oxide)-block-polymethacrylate Anions and N-Alkylpyridinium Cations

Complexes from poly(ethylene oxide)-b-poly(sodium methacrylate) (PEO-b-PMANa) and N-alkylpyridinium bromides are water soluble, in marked contrast to those from poly(sodium methacrylate). These systems are studied using potentiometric titration, microcalorimetry, ζ-potential measurement, light scattering and electron microscopy. Three regions (A−C) are observed with a complex from PEO-b-PMANa and cetylpyridinuim bromide (C16PyBr) when the composition of the mixture (Z = [C16PyBr]/[COO-]) is varied. (A) At Z < 1 C16PyBr binds electrostatically to the polyion to form soluble complex with a negative ζ-potential. (B) The size of the complex decreases and reaches minimum (o.d. 67 nm) at Z = 1 when ζ = 0. Those stoichiometric complexes are soluble and stable. They appear to be micelles with a core formed by C16PyBr neutralized polyion chains and a shell of PEO chains. (C) With a further increase in Z, the surfactant cations incorporate in the particles (ζ > 0). The particles formed at saturating concentrations of C16PyBr are spherical and remarkably monodisperse. Overall, these systems represent a new class of lyophilic colloids that exhibit combined properties of amphiphilic block copolymers and polyelectrolyte−surfactant complexes.

Synthesis, surface accumulation, and micellar properties of amphiphilic block copolymers

AbstractAmphiphilic block copolymers, i.e., poly(methyl methacrylate)‐b‐poly(2‐dimethylethylammoniumethyl methacrylate), were synthesized by the reaction between two prepolymers. Carboxyl‐terminated poly(methyl methacrylate) and hydroxyl‐terminated poly(2‐dimethylaminoethyl methacrylate) were prepared by radical polymerization of the corresponding monomers in the presence of thioglycolic acid and 2‐mercaptoethanol as a chain transfer agent, respectively. Two condensation methods, i.e., DCC and the acid chloride method, were used for the reactions of these prepolymers. The subsequent quarternization produced the amphiphilic block copolymers. Surface property of poly(methyl methacrylate) films containing this amphiphilic block copolymer was examined by measuring contact angles for water. The addition of only 0.5 wt% of the block copolymer was sufficient to make poly(methyl methacrylate) surfaces hydrophilic. The block copolymer formed a polymeric micelle in acetone–water mixed solvent.