Polymer Branching Research Articles

Evaluation of Amphiphilic Star/Linear-Dendritic Polymer Reverse Micelles for Transdermal Drug Delivery: Directing Carrier Properties by Tailoring Core versus Peripheral Branching.

The reverse micelle self-assembly of lipophile-functionalized poly(ethylene glycol) (PEG) dendrimer hybrids is probed for applications in carrier-mediated transdermal drug delivery. Under investigation are topologically diverse amphiphiles featuring controlled branching motifs at either the polymer core (one-, two-, and four-arm PEG) and the polar/nonpolar interface (peripheral dendritic generations 0-2). Thus, a systematic investigation of the effect of branching location (core vs peripheral) on carrier properties is described. Dye-encapsulation experiments verify these materials are capable of forming well-defined aggregates and solubilizing polar compounds. Further quantification of reverse micelle critical micelle concentration and dye loading capacity for the branched amphiphile library was obtained through spectroscopy characterization. Both core and peripheral branching are shown to significantly influence dynamic encapsulation behavior, with evidence of location-based contributions extending beyond multiplicity of branching alone. Finally, the in vitro transdermal diffusion of the reverse micelle carriers was investigated through Franz diffusion cell experiments using physiologically relevant juvenile porcine dermis. The permeation results, combined with previously reported aggregate size trends, show the complex relationship between polymer branching and transdermal transport, with the lowest core- and highest peripherally-branched amphiphilic analogs exhibiting optimal transdermal permeation characteristics for this set of branched carriers.

Correlation between Comprehensive 2D Liquid Chromatography and Monte Carlo Simulations for Branched Polymers

Detailed knowledge on structural information is required to derive the rheological properties of branched polymers. Size-exclusion chromatography with triple-detection (TD-SEC), comprising a concentration, a light scattering, and a viscosity detector, is a powerful tool to analyze the degree of branching of polymers as a function of their molar masses. However, TD-SEC alone is incapable of fully deconvoluting complex polymer systems. In this study we discuss a more sophisticated approach that includes coupling of TD to our recently described novel online two-dimensional liquid chromatography method (2D-LC), based on solvent gradient at near-critical conditions in the first dimension. Thus, a contour plot of the branching ratio is presented, and unique detailed information on the degree of branching can be derived for branched polycarbonate (PC) sample. Furthermore, the molar mass distributions of separated linear and branched PC chains as well as their fractions in the polymer are quantified. The correspo...

EXPERIMENTAL STUDY OF THE CRACK BRANCHING SPEED IN POLYMERS

One of the little-studied problems of modern mechanics and the physics of fracture is the branching of the crack, which is observed in materials of a different nature. For his research, an analysis of the criteria and mechanisms for crack branching. The investigations of crack branching in polymers and steel, fractographic investigation of the fracture surface are considered; criteria for crack branching as a dynamic stress intensity factor, crack speed. It is established that the crack at branching in brittle plastics reaches the limiting propagation speed V * = 500 – 800 m/sec. Tensile tests of flat samples from polymethylmethacrylate (PMMA) at temperatures of +20 and –60°C were carried out, with measurement of crack speed by the method of rupture of conducting strips. A measuring device based on a precision converter of signals of resistance thermometers and thermocouples «TERCON», connected to a computer, was created. Measured crack speed for rectilinear crack propagation in the mirror, matte, and feather zones of fracture surface of the PMMA; with single branching of the crack; with multiple branching of cracks with parallel movement of the front of several cracks. A hypothesis is proposed for the physical mechanism of fracture branching.

ETHYLENE POLYMERIZATION WITH NICKEL DIIMINE COMPLEXES CONTAINING PSEUDOHALIDES

Nickel-diimine complexes DADNiX2 (DAD= 2,6-iPr2-C6H3-N=C(Me)-C(Me)=N-2,6-iPr2-C6H3) containing the non-chelating pseudo-halide ligands isothyocyanate and isoseleniumcyanate (X= NCS 1 and NCSe 2) were synthesized and used in ethylene polymerization activated by methyaluminoxane (MAO) at temperatures from 0 to 50°C. Polymerizations with these complexes were compared with the analogous Ni-diimines halide (X= Br 3) as non-chelating ligand. All systems were very active in this polymerization. The increase of reaction temperature favored the increase in catalytic activity. The catalyst system 1/MAO was more stable than the others, showing the best catalytic activity at the molar ratio Al/Ni between 200 and 300. System 2/MAO showed to be the less stable and less active, particularly at 50°C. Polyethylenes obtained with systems 1, 2 and 3 show high molecular weights, are branched polymers, and predominately amorphous, but the majority still present DSC endothermal events related to melting of small crystals. When halide (Br) are compared with these pseudo-halides, different activities, polymerization kinetics and characteristics of the final polymer indicated modification in the active species caused by the non-chelating ligand. Polymer molecular weight and branching content was not significantly influenced by the non-chelating ligand, being much more dependent on the MAO/Ni molar ratio and polymerization temperature.

Characterization and analytical development for amphiphilic poly(γ-glutamic acid) as raw material of nanoparticle adjuvants

Amphiphilic graft copolymer consisting of poly(γ-glutamic acid) (γ-PGA) as the hydrophilic backbone and L-phenylalanine ethyl ester (Phe) as the hydrophobic side chain is an important biodegradable polymer with great potential in medical applications. In this research, we established analytical methods for the characterization and quality control of γ-PGA-graft-Phe (γ-PGA-Phe), which forms nanoparticles in aqueous solution, as a deployment platform in practical applications for vaccine adjuvants. The SEC-RI/MALS system, which uses size exclusion chromatography (SEC) coupled with a multi_angle light scattering (MALS) detector and refractive index (RI) detector, was developed to evaluate the characteristics of various types of polymers. By this method, it was indicated that absolute molecular weight (MW) should be used to measure the branch polymer. A gradient reversed phase HPLC (RP-HPLC) method was developed for the content of γ-PGA-Phe and the impurity levels to control product quality and safety. This quantitative approach could become key elements for identifying and characterizing γ-PGA-Phe. In addition, the degradation mechanism of γ-PGA-Phe was also identified as cleavage of main-chain of γ-PGA-Phe based on the stability study of γ-PGA-Phe in buffer solution with various pH values. The analytical developments described above will be important for use in both characterization and formulation design of biopolymers. Nanoparticles (NPs) composed of well-characterized biodegradable γ-PGA-Phe are expected to have a variety of potential clinical applications such as their use as drug and vaccine carriers.

Orientational cross correlations between entangled branch polymers in primitive chain network simulations.

Although it has not been frequently discussed, contributions of the orientational cross-correlation (OCC) between entangled polymers are not negligible in the relaxation modulus. In the present study, OCC contributions were investigated for 4- and 6-arm star-branched and H-branched polymers by means of multi-chain slip-link simulations. Owing to the molecular-level description of the simulation, the segment orientation was traced separately for each molecule as well as each subchain composing the molecules. Then, the OCC was calculated between different molecules and different subchains. The results revealed that the amount of OCC between different molecules is virtually identical to that of linear polymers regardless of the branching structure. The OCC between constituent subchains of the same molecule is significantly smaller than the OCC between different molecules, although its intensity and time-dependent behavior depend on the branching structure as well as the molecular weight. These results lend support to the single-chain models given that the OCC effects are embedded into the stress-optical coefficient, which is independent of the branching structure.

Assessment of the Branching Quantification in Poly(acrylic acid): Is It as Easy as It Seems?

Branching in polymers is an important feature that plays a role in their applications. The degree of branching (DB) has been quantified in several polymers using NMR spectroscopy. In this work, the DB of poly(acrylic acid), PAA, was quantified. The precision and accuracy of DB quantification in this polymer has been assessed for the first time. Incomplete dissolution lowers the accuracy of DB. Moisture content, chain end, and impurities have to be taken into account to assess the solubility correctly. The incomplete solubility may be partially due to some clustering and it might for example explain the notable inaccuracy of the molecular weights determined by SEC for PAA. The error introduced during data treatment in NMR spectroscopy affects the precision of DB. This study enables the design of the best approach for a precise and accurate DB quantification not only for PAA but also for other branched polymers. An accurate DB increases the knowledge of the polymer structure, enhancing the capacity to tailo...

Enhanced removal of trace antibiotics from turbid water in the coexistence of natural organic matters using phenylalanine-modified-chitosan flocculants: Effect of flocculants’ molecular architectures

Removal of two typical antibiotics (norfloxacin and tylosin) at trace level in turbid water simultaneously containing natural organic matters (NOMs) was conducted using two phenylalanine (Phe)-modified-chitosan flocculants (CHS-Phe and CHS-PPhe) with different molecular architectures. Response surface methodology (RSM) was applied for interactive effects evaluation and optimization of various parameters. CHS-Phe with linear molecular architecture displays higher removal efficiencies of antibiotics than commercial flocculants. By contrast, CHS-PPhe, owning the same Phe functional groups but comb-like architecture (polyPhe polymer branches grafted on chitosan backbone), shows poor performance. Deep mechanism investigations indicated that, for hydrophilic and flexible CHS-Phe linear molecules, bridging and sweeping flocculation for antibiotics were enhanced by electrostatic attraction, π-electron-containing interaction, and H-bond between introduced Phe groups and antibiotic molecules. However, for comb-like CHS-PPhe, excessively hydrophobic polyPhe branches aggregated to coils. This phenomenon caused fewer exposed flocculation sites outwards, although the interactions of Phe-antibiotic still existed. 3D response surfaces of CHS-Phe generated by RSM exhibited that, concentrations of coexisting kaolin and HA, as well as pH and flocculant dosage, can be controlled to obtain desired performance. This work enriches the knowledge of effect of molecular architecture of flocculants on contaminant removal, and provides guidance for flocculation parameter control.

Hydrophilic Phage-Mimicking Membrane Active Antimicrobials Reveal Nanostructure-Dependent Activity and Selectivity.

The prevalent wisdom on developing membrane active antimicrobials (MAAs) is to seek a delicate, yet unquantified, cationic-hydrophobic balance. Inspired by phages that use nanostructured protein devices to invade bacteria efficiently and selectively, we study here the antibiotic role of nanostructures by designing spherical and rod-like polymer molecular brushes (PMBs) that mimic the two basic structural motifs of bacteriophages. Three model PMBs with different well-defined geometries consisting of multiple, identical copies of densely packed poly(4-vinyl-N-methylpyridine iodide) branches are synthesized by controlled/"living" polymerization, reminiscent of the viral structural motifs comprised of multiple copies of protein subunits. We show that, while the individual linear-chain polymer branch that makes up the PMBs is hydrophilic and a weak antimicrobial, amphiphilicity is not a required antibiotic trait once nanostructures come into play. The nanostructured PMBs induce an unusual topological transition of bacterial but not mammalian membranes to form pores. The sizes and shapes of the nanostructures further help define the antibiotic activity and selectivity of the PMBs against different families of bacteria. This study highlights the importance of nanostructures in the design of MAAs with high activity, low toxicity, and target specificity.

A Second-Coordination-Sphere Strategy to Modulate Nickel- and Palladium-Catalyzed Olefin Polymerization and Copolymerization.

Transition-metal-catalyzed copolymerization reactions of olefins with polar-functionalized comonomers are highly important and also highly challenging. A second-coordination-sphere strategy was developed to address some of the difficulties encountered in these copolymerization reactions. A series of α-diimine ligands bearing nitrogen-containing second coordination spheres were prepared and characterized. The properties of the corresponding nickel and palladium catalysts in ethylene polymerizations and copolymerizations were investigated. In the nickel system, significant reduction in polymer branching density was observed, while lower polymer branching densities, as well as a wider range of polar monomer substrates, were achieved in the palladium system. Control experiments and computational results reveal the critical role of the metal-nitrogen interaction in these polymerization and copolymerization reactions.

A Second‐Coordination‐Sphere Strategy to Modulate Nickel‐ and Palladium‐Catalyzed Olefin Polymerization and Copolymerization

AbstractTransition‐metal‐catalyzed copolymerization reactions of olefins with polar‐functionalized comonomers are highly important and also highly challenging. A second‐coordination‐sphere strategy was developed to address some of the difficulties encountered in these copolymerization reactions. A series of α‐diimine ligands bearing nitrogen‐containing second coordination spheres were prepared and characterized. The properties of the corresponding nickel and palladium catalysts in ethylene polymerizations and copolymerizations were investigated. In the nickel system, significant reduction in polymer branching density was observed, while lower polymer branching densities, as well as a wider range of polar monomer substrates, were achieved in the palladium system. Control experiments and computational results reveal the critical role of the metal−nitrogen interaction in these polymerization and copolymerization reactions.

Suppression of Crystallization in Polydimethylsiloxanes and Chain Branching in Their Phenyl-Containing Copolymers

While incorporation of only a few mol % of diphenylsiloxy-, DiPhS, repeat units into polydimethylsiloxane, PDMS, chains is enough to completely suppress their crystallization, it also leads, in polymers obtained by silanolate-initiated ring-opening polymerization, to a puzzling and yet unexplained chain branching which significantly distorts polymer molecular weight distributions and affects their chain conformation. In contrast to this, we found that introduction of comparable amounts (ca. 5 mol %) of diethylsiloxy-, DiEtS, units into the same type of polymers also suppresses polymer crystallization but does not lead to any detectable branching, yielding polymers with the most probable molecular weight distribution and typical random coil conformation in a thermodynamically good solvent, such as toluene. On the basis of the results of a 29Si NMR and SEC-MALS study, we propose that branching in DiPhS-containing polymers is caused by a nucleophilic attack of initiating silanolate anions on their Si–CAr sid...

Physicochemical characterization of water-soluble chitosan derivatives with singlet oxygen quenching and antibacterial capabilities

New water-soluble chitosan derivatives (WSCh) were obtained by Maillard reaction (MR) between glucosamine (GA) with both low and medium molecular weight chitosans (Ch). The WSCh showed larger solubility than the respective Ch, while their deacetylation degree (DD) decreased by approximately 12%. Infrared spectroscopy experiments of WSCh confirmed the formation of imine bonds after MR with intensified pyranose structure, and sugar molecules as polymer branches. However, a 6-times reduction of the molecular weight of WSCh was measured, indicating the breakdown of the polysaccharide chain during the MR. The polysaccharides quenched singlet molecular oxygen (1O2), with rate quenching constants correlating with the DD value of the samples, suggesting the important role of amino groups (−NH2) in the deactivation of 1O2. Additionally, all polysaccharides presented antimicrobial activity against pathogenic bacteria, e.g. Staphylococcus aureus, Escherichia coli, Salmonella sp., Enterococcus faecalis and Listeria ivanovii, as tested by their minimum inhibitory concentration (MIC). This way we obtained new water-soluble polysaccharides, with similar functional properties to those presented by native Ch, enhancing its potential application as carrier material for bioactive compounds.

New method of investigation of polysulfone thermal destruction

The regularities of branching and thermal destruction processes of polysulfones of different chemical structure at 150–500°С are studied depending on the nature of the reactive medium and blocking method of the terminal groups with the use of a special device for a gas chromatograph allowing one to investigate the branching and thermal destruction of polymers. It is found that the nature of the solvent and deactivator of the terminal hydroxyl groups substantially affects the crosslinking and destruction processes of polysulfones.

Manipulation of polymer branching density in phosphine-sulfonate palladium and nickel catalyzed ethylene polymerization

A series of palladium and nickel catalysts bearing heteroaryl-aryl moieties were prepared and applied to ethylene polymerization and copolymerization reactions.

Influence of Block versus Random Monomer Distribution on the Cellular Uptake of Hydrophilic Copolymers.

The use of polymers has revolutionized the field of drug delivery in the past two decades. Properties such as polymer size, charge, hydrophilicity, or branching have all been shown to play an important role in the cellular internalization of polymeric systems. In contrast, the fundamental impact of monomer distribution on the resulting biological properties of copolymers remains poorly studied and is always only investigated for biologically active self-assembling polymeric systems. Here, we explore the fundamental influence of monomer distribution on the cellular uptake of nonaggregating and biologically passive copolymers. Reversible addition-fragmentation chain-transfer (RAFT) polymerization was used to prepare precisely defined copolymers of three hydrophilic acrylamide monomers. The cellular internalization of block copolymers was compared with the uptake of a random copolymer where monomers are statistically distributed along the chain. The results demonstrate that monomer distribution in itself has a negligible impact on copolymer uptake.

Evolution of chemical structure of polydichlorophosphazene in various solvents and ways to prolong its stability

Polyphosphazenes are an important class of polymers due to their structural flexibility, synthetic versatility and their wide range of properties. Among them, poly(dichlorophosphazene) (PDCP) is an essential intermediate from which most of the polyphosphazenes can be synthesized through nucleophilic substitution reaction. One of the main challenges in its synthetic procedure is to control the side reactions such as undesirable processes of polymer degradation, branching and cross-linking owing to instability of PDCP. In this paper, we have investigated the stability of PDCP and its structural behaviors by the influence of various solvents such as DMSO, DMF, DMAc. THF, DCM, PX, and etc. The polarity of the solvents affected the P+ ions of PDCP, water absorption capacity and its intermolecular interactions which are responsible for degradation and cross-linking of PDCP. The polymeric species and their mechanistic chemistry are characterized by multinuclear NMR, FT-IR and mass spectrometry to confirm their detail structures by changing the solvents.

Systematic Investigations of Ligand Steric Effects on α-Diimine Palladium Catalyzed Olefin Polymerization and Copolymerization

In the Brookhart type α-diimine palladium catalyst system, it is highly challenging to tune the polymer branching densities through ligand modifications or polymerization conditions. In this contribution, we describe the synthesis and characterization of a series of α-diimine ligands and the corresponding palladium catalysts bearing both the dibenzhydryl moiety and with systematically varied ligand sterics. In ethylene polymerization, it is possible to tune the catalytic activities ((0.77–8.85) × 105 g/(mol Pd·h)), polymer molecular weights (Mn: (0.2–164.7) × 104), branching densities (25–116/1000C), and polymer melting temperatures (amorphous to 98 °C) over a very wide range. In ethylene–methyl acrylate (E–MA) copolymerization, it is possible to tune the catalytic activities ((0.3–8.8) × 103 g/(mol Pd·h)), copolymer molecular weights (1.1 × 103–79.8 × 103), branching densities (30–119/1000C), and MA incorporation ratio (0.4–13.8%) over a very wide range. The molecular weights and branching densities could also be tuned in α-olefin polymerization. The tuning in polymer microstructures leads to significant tuning in polyethylene mechanical properties and the surface properties of the E–MA copolymer.

Non-toxic polyester urethanes based on poly(lactic acid), poly(ethylene glycol) and lysine diisocyanate

Poly(lactic acid)-based polymers are highly suitable for temporary biomedical applications, such as tissue support or drug delivery systems. Copolymers of different molecular weight based on poly(lactic acid) and poly(ethylene glycol) were prepared by polycondensation, catalysed by hydrochloric acid. A chain-extension reaction with l-lysine ethyl ester diisocyanate was employed afterwards to obtain polyester urethanes with enhanced properties. The GPC results showed that the molecular weights of the products reached about 50,000 g·mol−1 and the hydrolytic progress was rapid in the first 2 weeks; the drop in Mn equalled approximately 70%. Additionally, elemental analysis of the buffer medium proved that hydrolytic degradation was more rapid in the first stage. Tensile-strength testing revealed that ductility increased alongside reduced molecular weight of poly(ethylene glycol), also suggesting that polymer branching occurred due to side reactions of isocyanate. Based on the envisaged biomedical applications for these polymers, cytotoxicity tests were carried out and the cytotoxic effect was only moderate in the case of 100% polymer extract prepared according to ISO standard 10993-12. In their research, the authors focused on preparing metal-free, catalysed synthesis of polyester urethanes, which could prove useful to numerous biomedical applications.

Investigation of penetration into woven fabric specimens impregnated with shear thickening fluid

Abstract In this paper, the effect of weight fraction of nano silica (hydrophilic fumed silica particles) and molecular mass of polyethylene glycol (PEG) on the rheological properties such as the critical shear rate of fluids has been studied. Dynamic moduli based on strain and the effects of increasing the molecular weight are presented. Constructed samples with high-molecular-weight PEG have higher initial, final and critical viscosities. Also, higher molecular chains in the polymer and preventing the movement of most of these chains against the relative motion of liquid (viscosity) will cause higher viscosity in samples. Critical shear rate is lower in the provided samples with high-molecular-weight PEG. Polymer branches in these suspensions are absorbed by the surface of the particles. Due to OH bonds in the silica particles and also due to the presence of this bond in PEG, creating a hydrogen bond is likely. Such a hydrogen bond between the polymer yarn and the particle surface causes surface absorption of the particles. To show the effect of molecular weight on fibers, woven fabric specimens impregnated with shear thickening fluid (STF) have been examined by penetration and pressure test diagrams have been investigated. In a sample with higher molecular weight, displacement to yield point is higher and residence to penetration does not show much difference.