Polymer Branching Research Articles

Structure and Dynamics of a Polysaccharide Matrix: Aqueous Solutions of Bacterial Levan

The polysaccharide levan is a homopolymer of fructose and appears in nature as an important structural component of some bacterial biofilms. This paper reports the structural and dynamic properties of aqueous solutions of levan of various origin obtained from dynamic rheological, small-angle X-ray scattering, static and dynamic light scattering, as well as density and sound velocity measurements, determination of polymer branching after per-O-methylation, and microscopy. Besides samples of commercially available levan from Zymomonas mobilis and Erwinia herbicola, we also isolated, purified, and studied a levan sample from the biofilm of Bacillus subtilis. The results of dynamic rheological and light scattering measurements revealed very interesting viscoelastic properties of levan solutions even at very low polymer concentrations. The findings were complemented by small-angle X-ray scattering data that revealed some important differences in the structure of the aqueous levan solutions at the molecular level. Besides presenting detailed dynamic and structural results on the polysaccharide systems of various levans, one of the essential goals of this work was to point out the level of structural information that may be obtained for such polymer systems by combining basic physicochemical, rheological, and various light scattering techniques.

Bioapplications of poly(amidoamine) (PAMAM) dendrimers in nanomedicine

Poly(amidoamine) (PAMAM) dendrimers are a novel class of spherical, well-designed branching polymers with interior cavities and abundant terminal groups on the surface which can form stable complexes with drugs, plasmid DNA, oligonucleotides, and antibodies. Amine‐terminated PAMAM dendrimers are able to solubilize different families of hydrophobic drugs, but the cationic charges on dendrimer surface may disturb the cell membrane. Therefore, surface modification by PEGylation, acetylation, glycosylation, and amino acid functionalization is a convenient strategy to neutralize the peripheral amine groups and improve dendrimer biocompatibility. Anticancer agents can be either encapsulated in or conjugated to dendrimer and be delivered to the tumor via enhanced permeability and retention (EPR) effect of the nanoparticle and/or with the help of a targeting moiety such as antibody, peptides, vitamins, and hormones. Biodegradability, non-toxicity, non-immunogenicity, and multifunctionality of PAMAM dendrimer are the key factors which facilitate steady increase of its application in drug delivery, gene transfection, tumor therapy, and diagnostics applications with precision and selectivity. This review deals with the major topics of PAMAM dendrimers including structure, synthesis, toxicity, surface modification, and also possible new applications of these spherical polymers in biomedical fields as dendrimer-based nanomedicine.

Signal amplification for multianalyte electrochemical immunoassay with bidirectional stripping voltammetry using metal-enriched polymer nanolabels

A novel bidirectional (anodic and cathodic) stripping voltammetric immunoassay (SVI) was designed for the simultaneous determination of multiple model cancer biomarkers (AFP, CEA and CA19-9) in a single run, based on the integration of Envision complex loaded metal nanoparticles as signal tags and immunomagnetic beads as capture probes. The Envision complex, which is a long branching polymer consisting of numerous secondary antibodies and horseradish peroxidase (HRP), was employed for signal amplification by labeling corresponding detection antibodies and further loading metal nanoparticles (CdS, PbS and gold) to prepare distinguishable metal signal tags. Herein, the generation of immunosensing probes involved the co-immobilization of three types of primary anti-AFP, anti-CEA, and anti-CA19-9 antibodies onto a single magnetic Dynabead. After a two-binding step sandwich-type immunoassay, the Envision/CdS, Envision/PbS and Envision/Au signal tags were introduced onto the surface of the Dynabeads. The subsequent bidirectional voltammetric analysis of stripping metal components from immunocomplexes for quantification of tumor biomarkers was performed in a microcell with minimum capacity of 50μL. Experimental results showed the immunoassay enabled the simultaneous determination of multiple biomarkers over a broad range of concentrations (AFP, 1pgmL−1–50ngmL−1; CEA, 1pgmL−1–50ngmL−1; CA19-9, 5pgmL−1–100ngmL−1) with detection limits reaching 0.02pgmL−1 for AFP, 0.05pgmL−1 for CEA, and 0.3pgmL−1 for CA19-9. The results indicated that the proposed bidirectional multiplexed immunoassay can increase the number of analytes by SVI and has high sensitivity, excellent stability, and great promise for applications in clinical cancer diagnosis.

A new method for synthesizing hyperbranched polymers with reductive groups using redox/RAFT/SCVP

The novel hyperbranced polymers containing reductive groups were successfully prepared and characterized using redox/reversible addition fragmentation chain transfer (RAFT)/self-condensing vinyl polymerization (SCVP) method. Several redox initiating chemicals such as Cu(III)/-CONH2, Ce(IV)/-CONH2 and Ce(IV)/-OH were chosen to increase the free radical generating rate, and the chain transfer agent (CTA) was used to reduce the molecular chain propagating rate, in order to obtain polymers with high degree of branching. Detailed analyses based on the molecular weight, α value and the degree of branching of polymers (DB) obtained from 1H-NMR spectra and multi detector size exclusion chromatography (MDSEC) suggested the acquiring of hyperbranced polyacrylamides with Cu(III)/-CONH2 and Ce(IV)/-CONH2 as initiator in the presence of the CTA. Meanwhile, the as-prepared poly(N-hydroxymethyl acrylamide) (PNHAM) with higher DB value (0.48) proved that using Ce(IV)/-OH as the initiator could increase the free radical generating rate and diminish the gap between the propagating rate and the initiation rate during the reaction procedure. In addition, the effect of oxidant concentration on the Mark-Houwink index (α) value and the DB was also studied.

Nanodynamics of Dendritic Core–Multishell Nanocarriers

The molecular dynamics of polymeric nanocarriers is an important parameter for controlling the interaction of nanocarrier branches with cargo. Understanding the interplay of dendritic polymer dynamics, temperature, and cargo molecule interactions should provide valuable new insight for tailoring the dendritic architecture to specific needs in nanomedicine, drug, dye, and gene delivery. Here, we have investigated polyglycerol-based core-multishell (CMS) nanotransporters with incorporated Nile Red as a fluorescent drug mimetic and CMS nanotransporters with a covalently bound fluorophore (Indocarbocyanine) using fluorescence spectroscopy methods. From time-resolved fluorescence depolarization we have obtained the rotational diffusion dynamics of the incorporated dye, the nanocarrier, and its branches as a function of temperature. UV/vis and fluorescence lifetime measurements provided additional information on the local dye environment. Our results show a distribution of the cargo Nile Red within the nanotransporter shells that depends on solvent and temperature. In particular, we show that the flexibility of the polymer branches in the unimolecular state of the nanotransporter undergoes a temperature-dependent transition which correlates with a larger space for the mobility of the incorporated hydrophobic drug mimetic Nile Red and a higher probability of cargo-solvent interactions at temperatures above 31 °C. The measurements have further revealed that a loss of the cargo molecule Nile Red occurred neither upon dilution of the CMS nanotransporters nor upon heating. Thus, the unimolecular preloaded CMS nanotransporters retain their cargo and are capable to transport and respond to temperature, thereby fulfilling important requirements for biomedical applications.

Multi-Objective Optimization of Bulk Vinyl Acetate Polymerization with Branching

Inclusion of long chain branching (LCB) in polymers is a challenging and important task in any free radical polymerization as LCB influences polymer product quality. In the present case, batch optimization study for the bulk polymerization of vinyl acetate has been considered to find optimal process conditions for imparting LCB in polymer architecture. A theoretical study has been conducted with a validated model to observe the effect of live radical concentration on LCB as this is an important factor for branching in polymer via chain transfer to polymer route. In order to obtain better polymer product in less time at various temperatures, a need was observed to perform a multi-objective optimization study as the selected objectives were conflicting in nature. Owing to the complex nature of moment-based species balance equations and molecular weight distribution function, elitist non-dominated sorting genetic algorithm II (NSGA II), a well-established multi-objective evolutionary algorithm, has been employed as an evolutionary computation method to find out the Pareto optimal solutions. Minimization of polymerization time, maximization of molecular weight and maximization of number average degree of branching (Bn) can be simultaneously achieved, while the solutions were obtained within the experimental range of polydispersity index and weight average molecular weight (Mw) given in the open literature. Results show a wide range of process choices satisfying process objectives and constraints, both in low as well as high temperature regions.

Phase transition behaviours of a single dendritic polymer.

Dendritic polymers with highly branching structures exhibit many unique properties. In this paper, a computational study using the Wang-Landau sampling technique is carried out to reveal the phase transition behaviours of dendritic homopolymers with various branching structures. Two types of dendritic homopolymers, dendrimers/dendrigrafts (D/D) and hyperbranched (HB) polymers are studied. It is found that with increasing degree of branching in the dendritic polymer, the liquid-solid (LS) transition temperature increases and the coil-globule (CG) transition becomes weak. Additionally, under similar degrees of branching and polymerization, D/D polymers have a higher LS transition temperature than HB polymers. The reason is that the D/D polymers have greater regularity in the radial distribution of the branching units, which facilitates monomer packing during the LS transition. The distinctive internal unit distribution at various temperatures is quantitatively analysed. Our results show the importance of dendritic polymer structure regularity in phase transition behaviours and are valuable in guiding the structural design of dendritic macromolecules for functionalization applications.

Kinetics and Mechanisms of Radical-Based Branching/Cross-Linking Reactions in Preformed Polymers Induced by Benzophenone and Bis-Benzophenone Photoinitiators

The general mechanism for photo-cross-linking of preformed polymers is studied by comparing the efficacy of monofunctional benzophenone (BP) and bifunctional bis-benzophenone (BP-BP) photoinitiators for inducing radical chain branching reactions in glassy polystyrene (PS) and rubbery poly(n-butyl acrylate) (PnBA). Upon UV irradiation, macroradicals form and initiate a variety of cross-linking and scission reactions. The kinetics and mechanisms of these macroradical reactions were monitored by gel permeation chromatography (GPC) measurements of changes in the polymer molecular weight distributions. Molecular weight increases are associated with chain branching while decreases in molecular weight are indicative of chain scission. We study the early stages of radical recombination where branching is manifest as the formation of three- and four-arm star polymers that are soluble and can be detected/differentiated by GPC. Branching is observed even in glassy PS; however, the reactions are much faster in rubbery PnBA, consistent with the expected influence of main chain mobility. At equal chromophore equivalents, BP-BP was found to be more efficient than BP for producing macroradicals, primarily due to a lower degree of self-quenching in BP-BP. When added to glassy PS, the higher efficiency of BP-BP did not translate into more chain branching, except at high additive concentration where the probability of BP-BP chain bridging reactions becomes significant, but instead led to a higher degree of main chain scission. The latter result was attributed to the larger distance between chromophores for BP-BP than for BP at equal benzophenone equivalents. In marked contrast, almost no main chain scission was found for either additive in PnBA, and BP-BP proved more effective for promoting chain branching. The susceptibility to main chain scission is found to be dependent upon the location of radical formation by hydrogen abstraction from the polymer. In PS, radicals can form on the chain backbone, and radical scission reactions lead to fragmentation of the polymer chain. In PnBA, radicals form preferentially on the pendant side chains, and radical scission reactions do not lead to main chain breakage. A simple probability-based model was found to capture the salient features of radiation-induced branching in preformed polymers.

Covalent functionalization of multi-walled carbon nanotubes with quaternary ammonium groups and its application in ion chromatography

An approach for fabrication of core–shell composite beads was described, with polystyrene–divinylbenzene (PS–DVB) as the core and multi-walled carbon nanotubes (MWCNTs) as the shell through electrostatic attraction-induced self-assembly. MWCNTs were easily quaternized with a defined number of bonded layers and desirable positive charge by a multi-step synthesis, using methylamine and 1,4-butanediol diglycidyl ether as monomers to build a branching polymer that has quaternary ammonium groups. PS–DVB beads were sulfonated by sulfuric acid to provide opposite charge, which had electrostatic interaction with quaternized MWCNTs. Functionalization of MWCNTs was characterized by techniques that include Fourier transform infrared spectroscopy, thermogravimetry and scanning electron microscopy. The dispersion of MWCNTs in deionized water was enhanced after the grafting of cationic polyelectrolytes on them, which was in agreement with the positive charge at any pH value. With the PS–DVB/MWCNT composite beads as anion exchange phase and potassium hydroxide solutions as eluent, the common inorganic anions were well separated with high stability.

Polymerization behaviors and polymer branching structures in ATRP of monovinyl and divinyl monomers

Polymerization behaviors and polymer branching structures in atom transfer radical polymerizations of styrene with 1,6-bismaleimidohexane (BMIH), tri-ethylene glycol dimethacrylate (tri-EGDMA) and divinylbenzene (DVB) as the branching agents have been studied, the mole ratio of monomer to branching agent is 30/1.0. Their polymerization behaviors are quite different because of the different levels of interaction between styrene and the branching agents. The charge transfer complex effect between BMIH and styrene causes core-formation. The DVB system exhibits the slowest evolution of branching because there is no interaction between styrene and DVB. The branching structure indicator b(g′ = gb) from the Zimm branching factor at the same molecular weight proves that polymers formed in the tri-EGDMA and DVB systems are randomly branched molecules because tri-EGDMA and DVB were randomly distributed in their primary chains, while the BMIH system contained randomly branched molecules besides the star-like molecules due to the subsequent coupling reactions between the branched molecules after core-formation.

An H‐shaped polymer bonding β‐cyclodextrin at branch points: Synthesis and influences of attached β‐cyclodextrins on physical properties

AbstractWe report on the synthesis of an H‐shaped polymer bonding β‐cyclodextrin (β‐CD) at branch points and influences of attached β‐CD on physical properties. First, a poly(ethylene glycol)(PEG)‐based functional macroinitiator bearing two azidos and four chlorines at chain‐ends (PEG‐2N3(‐4Cl)) was prepared via terminal modification reactions. Then, PEG‐2N3(‐4Cl) was applied to initiate the atom transfer radical polymerization of N‐isopropylacrylamide, leading to the synthesis of an H‐shaped block polymer with PEG as the central chain and poly(N‐isopropylacrylamide) (PNIPAM) as side‐arms (PEG‐2N3(‐4PNIPAM)). Azido groups were at the branch points of the polymer. Finally, the click reaction between PEG‐2N3(‐4PNIPAM) and alkynyl monosubstituted β‐cyclodextrin (β‐CD) afforded another H‐shaped polymer with two β‐CDs bonding at the polymer branch points (PEG‐2CD(‐4PNIPAM)). The glass transition temperature (Tg) and lower critical solution temperature (LCST) of the H‐shaped polymer increased after the attachment of β‐CD. The self‐assembly and thermal responsive behaviors, as well as the encapsulation behaviors of PEG‐2CD(‐4PNIPAM) were also altered. When temperature was below the LCSTs, PEG‐2N3(‐2PNIPAM) dissolved in water molecularly, whereas PEG‐2CD(‐4PNIPAM) could self‐assemble into nano‐sized micelles. After the LCST transitions, PEG‐2N3(‐4PNIPAM) aggregated into micron‐sized unstable particles, whereas PEG‐2CD(‐4PNIPAM) transformed into PNIPAM‐cored nanomicelles. Besides, PEG‐2CD(‐4PNIPAM) can encapsulate doxorubicin below its LCST due to the formation of micelles. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Polymer Hydrophobicity Has a Positive Effect on the Oral Absorption of Cyclosporine A from Poly(ethylenimine) Based Nanomedicines

Hydrophobic drugs are problematic to deliver. We have previously shown that poly(ethylenimine) (PEI) amphiphile nanoparticles facilitate the oral absorption of the model drug cyclosporine A (CsA). We hypothesised that polymer molecular features (molecular weight, a branched or linear polymer architecture, polymer hydrophobicity) would drive this oral absorption enhancement. To test this hypothesis, we synthesised five linear PEI amphiphiles (Mn ~ 1.3 kDa or 13 kDa) and two branched PEI amphiphiles (Mn ~ 4 kDa or 10 kDa) by cetylation of PEI, followed by methylation to give N-cetyl, N-methyl, N,N-dimethyl, N,N,N-trimethyl poly(ethylenimines). Polymer aggregation, CsAencapsulation, polymer in vitro cytotoxicity and polymer enabled oral drug absorption were all studied. The polymers aggregated in aqueous media, with critical micellar concentrations (CMCs) ranging from 0.2 – 0.9 mg mL-1. The polymer CMCs, CsA encapsulation (up to 0.36 g CsA per g of PEI amphiphile) within the 60 – 200 nm nanoparticles and rat oral drug absorption after a 7.5 mg kg-1 dose of CsA, polymer nanoparticles (polymer, drug weight ratio – 5: 1) all increased with polymer hydrophobicity, although these parameters were not affected by polymer molecular weight or polymer branching. Release of CsA from a tablet dosage form was enhanced in the presence of the more hydrophilic branched polymer, however, as the more hydrophobic polymers endowed the tablets with longer disintegration times. Cell cytotoxicity (A431 cells and rat erythrocytes) was similar for all polymers (A431 IC50 = 10 – 50 μg mL-1 and 50% haemolysis = 30 – 55 μg mL-1).We conclude that the most important parameter controlling amphiphilic polymer nanoparticle enabled oral drug absorption is the hydrophobicity of the polymer amphiphile.

Polymer Hydrophobicity Has a Positive Effect on the Oral Absorption of Cyclosporine A from Poly(ethylenimine) Based Nanomedicines

Hydrophobic drugs are problematic to deliver. We have previously shown that poly(ethylenimine) (PEI) amphiphile nanoparticles facilitate the oral absorption of the model drug cyclosporine A (CsA). We hypothesised that polymer molecular features (molecular weight, a branched or linear polymer architecture, polymer hydrophobicity) would drive this oral absorption enhancement. To test this hypothesis, we synthesised five linear PEI amphiphiles (Mn ~ 1.3 kDa or 13 kDa) and two branched PEI amphiphiles (Mn ~ 4 kDa or 10 kDa) by cetylation of PEI, followed by methylation to give N-cetyl, N-methyl, N,N-dimethyl, N,N,N-trimethyl poly(ethylenimines). Polymer aggregation, CsAencapsulation, polymer in vitro cytotoxicity and polymer enabled oral drug absorption were all studied. The polymers aggregated in aqueous media, with critical micellar concentrations (CMCs) ranging from 0.2 – 0.9 mg mL-1. The polymer CMCs, CsA encapsulation (up to 0.36 g CsA per g of PEI amphiphile) within the 60 – 200 nm nanoparticles and rat oral drug absorption after a 7.5 mg kg-1 dose of CsA, polymer nanoparticles (polymer, drug weight ratio – 5: 1) all increased with polymer hydrophobicity, although these parameters were not affected by polymer molecular weight or polymer branching. Release of CsA from a tablet dosage form was enhanced in the presence of the more hydrophilic branched polymer, however, as the more hydrophobic polymers endowed the tablets with longer disintegration times. Cell cytotoxicity (A431 cells and rat erythrocytes) was similar for all polymers (A431 IC50 = 10 – 50 μg mL-1 and 50% haemolysis = 30 – 55 μg mL-1).We conclude that the most important parameter controlling amphiphilic polymer nanoparticle enabled oral drug absorption is the hydrophobicity of the polymer amphiphile. Keywords: Bioavailability, cyclosporine A, nanomedicines, nanoparticles, oral absorption, poly(ethylenimine).

Synthesis and characterization of ethylene-propylene copolymer and polyethylene using α-diimine nickel catalysts

Nickel-based catalysts of dibromo[N,N′-bis(2,6-diisopropylphenyl)-2,3-butanediimine]nickel(II) (A) and dibromo[N,N′-(phenanthrene-9,10-diylidene)bis(2,6-diisopropylaniline)]nickel(II) (B) were synthesized under controlled conditions. The catalysts A, B and mixed of 1:1 weight ratio of them were used for ethylene-propylene (EP) copolymerization and ethylene polymerization. Methylaluminoxane (MAO) was used as a cocatalyst. The polymers were characterized by means of FT-IR, 1H NMR and DSC (Differential scanning calorimetry). In ethylene polymerization using mixed of 1:1 w/w of the catalysts A and B degree of branching polymer chain decreased with increasing monomer pressure while increased with enhancing polymerization temperature. In ethylene-propylene copolymerization using mixed of 1:1 w/w of A and B, the catalytic system showed the maximum activity at about [Al]/[Ni] = 2000:1 ratio and further addition of MAO did not affect the activity of the catalyst. Increasing the copolymerization temperature from 20 to 80 °C decreased the productivity of the catalytic system while increased the ethylene content of the copolymer. Decreasing relative pressure of P Pr /P Et from 9:1 to 1:1 increased the ethylene contents of the copolymers from 51 % to 72 % while decreased the viscosity average molecular weight (M v ) and glass transition temperature (T g ) of the products. A copolymer with more rubber-like behavior was obtained in relative pressure of P Pr /P Et (5:1) and total pressure of 5 bars.

High Strength of Physical Hydrogels Based on Poly(acrylic acid)-g-poly(ethylene glycol) Methyl Ether: Role of Chain Architecture on Hydrogel Properties

This investigation was to study the connections between polymer branch architecture of physical hydrogels and their properties. The bottle-brush-like polymer chains of poly(acrylic acid)-g-poly(ethylene glycol) methyl ether (PAA-g-mPEG) with PAA as backbones and mPEG as branch architecture were synthesized and in situ grafted from silica nanoparticles (SNs) to construct hydrogels cross-linked networks in aqueous solutions. The structural variables to be discussed included molecular weight and molar ratio of branch chains, and new aspects of the formation mechanism of physical hydrogels with branch structure in the absence of organic cross-links were present. The results indicated that the differences of polymer chain architecture could be distinguished via their different interactions that are present by gelation process and mature gel properties, such as gel strength and swelling ratio. The gelation occurred at the critical polymer concentration and molecular weight, respectively, and the inorganic/organic (SNs/PAA-g-mPEG) nanoparticles began to entangle and construct the cross-linking networks afterward. The gel-to-sol transition temperature (T(g-s)) and radii of SNs that were encapsulated by polymer chains as a function of time for chains' disentanglement were monitored according to the observation of the dissolution process, and the molecular weight between two consecutive entanglements (M(e)) was calculated thereafter. This study showed that the introduction of branch chain onto the linear backbone significantly promoted the chain interactions and increased entanglement density, which contributed to the hydrogels' network integrity and rigidity, thus illustrating greater elongation at break and tensile strength than the hydrogels formulated with linear polymer chains.

An experimental design methodology to evaluate the importance of different parameters on flocculation by polyelectrolytes

Aggregation of particles is fundamental for improving the performance of many solid/liquid processes. Aggregation can be induced by different means, and one of the most common is based on the addition of polymeric additives, namely polyelectrolytes. In this work we have studied the flocculation of precipitated calcium carbonate (PCC), which is used as a filler in papermaking, and is induced by a range of cationic polyacrylamides with different structures, varying in molar mass and degree of branching. The flocculation process was monitored continuously using the LDS technique (laser diffraction scattering), which provides information about the size distribution and structure (fractal dimension) of the aggregates, for each sampling instant and, thus, about the kinetic curve for the flocculation process. This information has then been used to produce a model, based on an experimental design strategy, which allows us to relate flocculation efficiency with the PEL characteristics and concentration. The Partial Least Squares (PLS) regression method was selected to perform the regression, given the significant co linearity among the input variables. The results obtained lead us to conclude that the polymer intrinsic viscosity (related with the PEL molar mass and charge density, and supplying information about the volume of the polymer molecule in the solution) and the degree of branching are the parameters with a stronger influence on flocculation efficiency. The PLS models developed were also successfully validated using an independent data set, which provides confidence on their consistency and prediction accuracy. Surface plot of flocculation efficiency (y) against intrinsic viscosity‐IV (X 3 ) and degree of branching of the polyelectrolyte chain (X 1 ). IV and degree of branching are the polymer characteristics with stronger influence on flocculation efficiency. ► Flocculation of calcium carbonate induced by cationic polyacrylamides was studied. ► LDS allowed the construction of the kinetic curves for the flocculation process. ► An experimental design strategy was used to obtain a flocculation efficiency model. ► The model response is mostly dependent on polymer intrinsic viscosity and branching.

Branching Features of a Polymer

Two parameters characterizing the branching features of polymers, branching density (BD), and branching completeness (BC), are proposed. Both have values of zero (0) for linear polymers. Branching density has the values of 1/2, 2/3, and (f – 2)/(f – 1) for the fully and densest branched polymers formed from tri-, tetra-, and f-functional monomers typed AB f –1. Branching completeness will reach the value of one (1) for a completely branched polymer, where all possible branching monomeric units have reacted at least tri-functionally and all units are either terminal or dendritic. Branching density is close to the mole fraction of terminal units, and BC is close to the mole fraction of dendritic and terminal units in the branching polymers. The major advantage of these parameters is their independence of the degree of polymerization (dp). Branching density depends on the functionalities (f) of monomer units; BC does not. The higher the fraction of the dendritic unit monomerically bonded to a higher number of other units (the higher the terminal units fraction), the denser branched the polymer and the higher the BD. The BC and BD can be used in a simple way for describing multicharacter branching systems and for comparing the branching characters among them without any theoretical limitations. Physical quantities (namely, the number of dendritic and terminal units and the degree of polymerization) used for BD and BC evaluation can be determined directly from practical analyses, where NMR is most useful. The BC and BD, however, do not concisely describe branching characteristics for a polymer with cyclization or crosslinking in its structure.

Preparation of AB2 Monomers and the Corresponding Hyperbranched Polyureas in a One‐Pot Procedure

AbstractNovel AB2 monomers and corresponding hyperbranched polyureas are prepared in a one‐pot process. AB2 monomers are synthesized by a highly selective reaction of carbonyl biscaprolactam (CBC) with triamines comprising one secondary and two primary amino groups. Only the primary amines react with CBC, yielding blocked isocyanates. On heating, self‐condensation of the obtained monomer solution takes place, yielding polymers with Mn up to 11 000 Da. Mark‐Houwink exponents of 0.3 and branching frequencies of 0.3 demonstrate the hyperbranched topology. Each polymer molecule comprises one secondary amino group in the focal point and numerous active blocked isocyanates located at the end of the polymer branches. The polymers are fully characterized by means of 1H NMR, 13C NMR, MALDI‐TOF, SEC, and DSC.

Structure Dependence of Charged States in “Linear” Polyaniline as Studied by In Situ ATR-FTIR Spectroelectrochemistry

The electrochemical doping of emeraldine salt and emeraldine bases with different weight average molecular weights was studied by in situ Fourier transform infrared (FTIR) spectroelectrochemistry using attenuated total reflection (ATR) technique. The formation and stabilization of charge carriers in polyaniline during p-doping was followed in dependence of the chain branching. The potential dependence of the IR bands during the oxidation of the polymer clearly demonstrates the formation of the different charged polymer structures (π-dimers, polarons, and bipolarons). It is shown that IR bands usually attributed to a semiquinoid polaron lattice correspond in fact to doubly charged species, π-dimers, which are face-to-face complexes of two polarons. Bands corresponding exclusively to polarons have been identified at 1266, 1033, and 1010 cm(-1), suggesting that polarons are predominantly stabilized on the linear segments near the polymer branches by phenazine.

Effect of Molecular Architecture on the Polyelectrolyte Structuring under Confinement

The paper addresses the structuring and rheology of semidilute polyelectrolyte solutions with varied concentration and degree of polymer branching. The used polymer is constituted of the units of sodium 2-acrylamido-2-methylpropanesulfonate (NaPAMPS) with the branching inserts of 2-(2-bromopropionyloxy)ethyl acrylate (BPEA). The content of the branching units of BPEA in the polyelectrolytes was 6, 17, and 24%. Comparison of data obtained by small-angle X-ray scattering (SAXS) and colloidal probe atomic force microscope (CP-AFM) was used to study the effects of a solid–solid confinement on the structuring. Scattering peaks from SAXS and oscillatory force curves from CP-AFM indicate a transient network of polyelectrolyte chains with structural parameters such as interchain distance, correlation length, and interaction strength. The interchain distance and the correlation length obtained by SAXS (bulk) and CP-AFM (confinement) are in the same range, suggesting no compression of the network in the confined geometry. The interchain distance is not affected by the degree of branching at a fixed monomeric unit concentration. The correlation length (the range of ordering), the strength of the interchain interactions, and the solution viscosity, on the other hand, depend slightly on the degree of branching. The electrostatic correlation length and the interaction strength are smaller for 17% and 24% branched chains, reflecting a more disordered network.