Number Of End Groups Research Articles

Modulating Ion Transport and Self-Assembly of Polymer Electrolytes via End-Group Chemistry

We report a rational design of solid-state dry polymer electrolytes with high conductivity, high mechanical strength, and improved cation transference number. Thiol–ene click chemistry provided orthogonal control over the type and number of end groups in poly(styrene-b-ethylene oxide) (PS-b-PEO) block copolymers. This approach permitted the synthesis of PEO chains with reduced crystallinity, reminiscent of PEO oligomers, thereby playing a key role in improving the room temperature conductivity. Intriguingly, the incorporation of diol or dicarboxylic acid end groups in PS-b-PEO produced a well-defined gyroid structure, leading to order of magnitude improvements in the storage modulus. Out of the various samples examined, the electrolytes bearing terminal diol displayed the highest ionic conductivity and a 2-fold increase in lithium transference number. The improvements in performance are attributed to the reduced interchain aggregation and the anion stabilization mediated by the terminal diol group. The fa...

Supramolecular system based on cylindrical micelles of anionic surfactant and silica nanoparticles

The influence of silica nanoparticles (22nm) on viscoelasticity in micellar solutions of anionic surfactant sodium oleoyl methyl taurate was investigated. It was shown that viscosity and relaxation time extremely change with increasing nanoparticle concentration in surfactant solution, and elastic modulus reaches a constant value after rising to a concentration up to 0.9wt.%. The temperature rise leads to a significant increase in the viscosity of surfactant solutions by adding nanoparticles. This fact is caused by an increase in the number of end groups in cylindrical micelles, which are able to attach to nanoparticles.

One-Step Synthesis of Thermally Curable Hyperbranched Polymers by Addition–Fragmentation Chain Transfer Using Divinyl Monomers

Free radical bulk and solution polymerizations of a divinyl monomer, ethylene glycol dimethacrylate (EGDMA), in the presence of methyl 2-(bromomethyl)acrylate as an addition–fragmentation chain transfer agent were investigated to synthesize thermally curable hyperbranched polymers by a one-step reaction. Soluble polymers were obtained up to high conversion of EGDMA, and the molecular weight and molecular weight distribution of the polymers increased with increasing EGDMA conversion. 1H NMR and MALDI-MS analyses revealed that the soluble polymers were obtained after the consumption of a considerable amount of the pendant methacryloyl groups, and one polymer chain contained a number of end groups indicating the formation of hyperbranched polymers. The isolated hyperbranched polymers underwent thermal curing above 110 °C without curing agents, and the polymers having a large number of pendant methacryloyl groups resulted in a significant increase in glass transition temperature, i.e., from around room temperature to above 210 °C.

Theoretical study of the surface properties of poly(dimethylsiloxane) and poly(tetrafluoroethylene)

Molecular dynamics (MD) simulations of poly(dimethylsiloxane) (PDMS) and poly(tetrafluoroethylene) (PTFE) were carried out to determine their surface properties and energies. This study helps to gain better insight into the molecular modeling of PDMS and PTFE, in particular how different approaches affect calculations of surface energy. Current experimental and theoretical data were used to further understand the surface properties of PDMS and PTFE as well as to validate and verify results obtained from the combination of density functional theory (DFT) calculations (including periodic boundary conditions) and MD simulations. Detailed analysis of the structure and electronic properties (by calculation of the projected density of states) of the bulk and surface models of PDMS and PTFE was performed. The sensitivity of the surface energy calculation of these two polymers to the chemistry and model preparation was indicated. The balance between the molecular density, weight (which also reflects bond orientation in the surface region), bond flexibility, and intramolecular interactions including bond stretching was revealed to govern the results obtained. In modeling, the structural organization of polymer near a given surface (types and number of end groups and broken bonds due to application of different cut offs of the periodic structure) also significantly affects the final results. Besides the structural differences, certain simulation parameters, such the DFT functionals and simulation boxes utilized, play an important role in determining surface energy. The models used here were shown to be sufficient due to their good agreement with experimental and other theoretical data related to surface properties and surface energies.

Atomic force microscopy based quantitative mapping of elastic moduli in phase separated polyurethanes and silica reinforced rubbers across the length scales

ABSTRACTIn the work presented here atomic force microscopy (AFM) based mechanical mapping techniques - HarmoniX imaging and Peak Force Tapping - were applied to determine the surface elastic modulus of phase separated polyurethanes and silica reinforced rubbers across the length scales. Segmented polyether polyurethanes (PUs) were prepared with varying stoichiometric ratio of the isocyanate and hydroxyl groups. The effect of molar mass, as well as the type and number of end-groups on their morphology was investigated. Smooth PU samples for AFM imaging were prepared by ultramicrotonomy. The micro phase separated morphology of the phase separated PUs showed characteristic “fingerprint” AFM phase images. Surface modulus values obtained by AFM were compared to bulk modulus values obtained by tensile testing. The moduli were mapped quantitatively with nanoscale resolution and were in excellent agreement for both AFM modes. Surface mean moduli values do not coincide with bulk values obtained via tensile testing which is attributed to fundamentally different averaging procedures and effects that lead to the respective modulus values obtained via surface and volume averaging. EPDM and SBR rubbers and rubber blends thereof were prepared with varying concentrations of silica nanoparticles and studied in order to investigate the effect of different composition on the resulting morphology (filler distribution) and elastic moduli on a specific rubber or rubber blend sample. Elastic moduli of the rubber and rubber blend samples were first measured by bulk tensile testing. The morphology of the rubber samples was visualized by height and phase imaging. Surface elastic moduli of silica reinforced rubbers and rubber blends were mapped quantitatively and compared with bulk tensile test results. AFM allowed the determination of modulus distributions at the sections imaged. As potential reasons for the observed differences between bulk and surface modulus different averaging procedures like surface and bulk averaging of AFM vs. tensile testing, different filler distributions in SBR and EPDM and the AFM modulus calibration procedures can be named.

ChemInform Abstract: Tailoring Dendronized Polymers

AbstractReview: 85 refs.

Quantitative mapping of elastic moduli at the nanoscale in phase separated polyurethanes by AFM

The micro phase separated nanoscale morphology of phase separated polyurethanes (PUs) was visualized by atomic force microscopy (AFM) height and phase imaging of smooth surfaces obtained by ultramicrotonomy. PUs were obtained from 4,4′-methylenbis (phenyl isocyanate) (MDI), 1,4-butanediol (BD) and poly(tetrahydrofurane) polyether polyol (PTHF). The segmented polyether PUs with varying stoichiometric ratio of the isocyanate and hydroxyl groups were prepared to investigate the effect of molar mass, as well as the type and number of end-groups on their morphology and mechanical performance.The PU samples studied show characteristic “fingerprint” AFM phase images. Novel dynamic imaging modes of AFM, including HarmoniX material mapping and Peak Force Tapping were used to assess the mechanical performance of phase separated polyurethanes quantitatively as a function of their molecular structure. The values of surface elastic moduli were determined with nanoscale resolution and were in excellent agreement for both AFM modes. While tensile testing provides a bulk average value for the elastic modulus of the elastomers, the novel AFM based elastic moduli mappings introduced enable the study of surface stiffness with nanoscale resolution in a quantitative way.

Tailoring dendronized polymers

Dendrimers are branched or hyperbranched synthetic oligomers or macromolecules with their size, molar masses, number of end groups and delicate compositions being precisely controlled. These characteristics have made dendrimers very good candidates as scaffolds of spherical molecules whose size ranges from several to tens of nanometres. When the dendritic segments are densely grafted along a linear polymer, so-called dendronized polymers or denpols are obtained. Owing to the steric hindrance between neighboring dendrons, especially in high generation, the dendronized polymers show a wormlike morphology whose flexibility and diameter are mainly dependent upon the generation of grafted dendrons. Therefore, denpols may be regarded as one-dimensional molecular nanoobjects. In this article, the recent development of a remarkable synthesis, control of composition and morphologies are featured.

Enzymatic degradation of hyperbranched polyesters

AbstractIn this work, the enzyme‐catalyzed degradation of hyperbranched polyesters (HBPEs) was investigated. Enzymatic degradation experiments were performed in a phosphate buffer in the presence of the lipases Candida cylindracea, Pseudomonas cepacia, Novozym 388, Amano CE, Lipomod 34P, and Cal‐B, whereas control experiments were performed in the same system without lipases. The extent of polymer degradation was determined by quantification of the released free fatty acids by gas chromatography. The influence of the alkane chain length and the number of alkane chain end groups on the lipase‐catalyzed hydrolysis of esterified HBPEs was investigated systematically. It was found that the increase in the alkane chain length of the end groups diminished the enzymatic degradation of the polymer, whereas the number of end groups had no influence on the degradation rate. The effect of temperature on the rate of degradation was also described. Surface morphological changes that occurred during the degradation were assessed with reflected electron microscopy. The changes in the crystallinity of the polymers after they were subjected to degradation were qualitatively determined with differential scanning calorimetry through the quantification of the enthalpy of melting. The enthalpy of melting of one HBPE sample increased from 79 to 90 and 94 J/g with and without the action of Lipomod 34P, respectively, in 7 days, showing the changes in the crystallinity of the polymer. The results prove that modified HBPEs are an important new class of biodegradable materials with a predictable degradation mechanism, and the degradation can be adjusted on the basis of the molecular engineering. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Synthesis of Dendrimers Terminated by Bis(diphenylphosphinomethyl)amino Ligands and Use of Their Palladium Complexes for Catalyzing C−C Cross-Coupling Reactions

The synthesis of two new series of phosphorus-containing dendrimers capped by bis(diphenylphosphinomethyl)amino groups linked to either tyramine or l-tyrosine methyl ester is reported up to the third generation (48 end groups). The corresponding complexes obtained in situ by reaction with Pd(OAc)2 are used as catalysts in three types of C−C cross-coupling reactions, namely, Suzuki, Sonogashira, and Heck reactions, in the presence of water. A slightly positive dendritic effect is observed in the case of the Sonogashira reaction: the conversion increases when the generation (size and number of end groups) of the dendritic catalyst increases. In all cases, the series built from tyramine is more efficient than the series built from l-tyrosine, showing the influence of the local hindrance, and the dendrimers are generally more efficient than the corresponding monomers.

Glass transition temperature and architecture of branched poly(methyl methacrylates)

It has been shown that, for a number of MMA-based copolymers prepared through the copolymerization of MMA with a bifunctional comonomer in the presence of a chain-transfer agent, an increase in the concentration of the comonomer (the branching agent) is accompanied by a rise in the molecular mass of the copolymers and a reduction in their glass transition temperature T g by 30–40°C. This phenomenon provides evidence for the presence of branches in the copolymers and the incorporation of the chain-transfer agent into the branches. The value of T g linearly declines with an increase in the between the concentration of the branching agent and the molecular mass of the copolymer, that is, with an increase in the number of branches (and end groups) in a macromolecule. A correlation between the glass transition temperature and the rheological and diffusion-sorption characteristics of the branched copolymers has been established. The number of end groups in the copolymers under study has been calculated in accordance with the previously advanced model for the formation of branched macromolecules. The experimental dependences of T g on the content of the branching agent, the number of end groups, and the molecular mass of the copolymers confirm this model.

Hyperbranched polymers: unique design tool for coatings

Hyperbranched polymers are a new class of polymeric material belonging to the group of macromolecules with highly branched structures and a large number of end groups. The structure of these polymers has a great impact on their physical and chemical properties. Many commercially-available chemicals can be used as the monomers in these systems, which should extend the availability and accessibility of hyperbranched polymers with various new end groups, architectures and properties. Because of their unique behaviour, hyperbranched polymers are suitable for a wide range of applications, especially for coatings.

Grafting Polymerization of Acrylonitrile onto LDPE Film: Study on Grafting Chain Length and Density with UV-vis Spectroscopy

Grafting polymerization of acrylonitrile onto low density polyethylene film was studied further following the earlier work [1]. A novel and effective method was developed to directly determine the number of end-groups, i.e. phenyls at the end of grafted chains with UV-vis spectroscopy; according to the number of phenyl end-groups and the weight of grafted polymers, grafting chain length and density were estimated; investigations indicated both of these two parameters could be practically controlled.

Thermal degradation of aliphatic hyperbranched polyesters and their derivatives

In this study results of thermal degradation of aliphatic hyperbranched polyesters, AHBP, and their derivatives, determined by non-isothermal thermogravimetric analysis in inert atmosphere (N 2) are presented. The thermal stability of linear polyester PHPA (polyhydroxypivalic acid), additionally synthesized from hydroxypivalic acid, was also studied. AHBP samples, from second to tenth pseudo-generation, were synthesized starting from 2,2-bis(hydroxymethyl)propionic acid and di-trimethylolpropane. Modification of some selected AHBP samples was accomplished with the propionyl and benzoyl chloride, as well as with stearic acid. Thermal degradation of AHBP samples starts in the region between 250 °C and 275 °C and it ends around 430 °C. The thermal stability of AHBP samples increases with the number of end groups in the macromolecule, as well as with the modification of end groups with stearic acid and propionyl chloride. An AHBP sample of the fourth pseudo-generation, where all –OH end groups are modified with benzoyl chloride, shows lower thermal stability than the corresponding unmodified sample. The thermal stability of the linear polyester PHPA is lower than the thermal stability of the AHBP samples of the similar molar mass. The activation energies of thermal degradation for all synthesized AHBP samples were also calculated.

Separation and characterization of functional poly( n-butyl acrylate) by critical liquid chromatography

The separation of functional poly( n-butyl acrylate) (PnBA) polymers based on the number of end-groups under critical liquid chromatography (LC) conditions has been studied using a bare-silica column. The (near-) critical solvent compositions for non-, mono-, and difunctional (telechelic) carboxyl-PnBAs were determined in normal-phase LC, using mixtures of acetonitrile, acetic (or formic) acid, and dichloromethane of varying composition. Some formic or acetic acid had to be added to the mobile phase to elute PnBA polymers with carboxyl end-groups. The critical solvent compositions obtained were not exactly the same for non-, mono-, and difunctional PnBA polymers. These were unusual experimental observation, but they were in agreement with theoretic predictions. Nevertheless, low-molecular-mass PnBA samples were successfully separated according to the carboxyl functionality at (near-) critical conditions. With the aid of mass spectrometry (MS), the (near-) critical separation of low-molecular-mass PnBA polymers was confirmed to be mainly based on the carboxyl functionality. Calibration curves for evaporative light-scattering detection (ELSD) were used for quantitative analysis of carboxyl-functional PnBA polymers. The results proved that nearly ideal functionalities (average number of carboxyl end-groups per molecule up to 1.99) were achieved for telechelic PnBAs prepared by one-step reversible addition–fragmentation chain-transfer (RAFT) polymerization of PnBA.

Characterization of glycerin-based polyols by capillary electrophoresis

Methods based on capillary electrophoresis (CE) have been developed to obtain the molar mass distribution (MMD) of glycerin-based polyols and details on the presence of mono- and difunctional byproducts in technical samples. Prior to the analyses the hydroxy end-groups of the trifunctional polyols were converted to chargeable and UV-active moieties with phthalic anhydride (PhAH) as the derivatization reagent. With a method of capillary zone electrophoresis (CZE) samples of glycerin-based polyols with average molar masses up to 6000 were separated according to their charge-to-size ratio. The separations were carried out with a buffer solution containing 50% (v/v) acetonitrile and 10 mM sodium tetraborate, and for detection UV absorption at 220 nm was measured. An approximately linear relation between the reciprocal of the effective mobilities and the degree of polymerisation of the glycerin-based polyols was found. Therefore, the proposed CZE system could be used to determine the degree of polymerisation and polydispersity of technical glycerin-based polyol samples. The effect of the presence of sodium dodecyl sulfate (SDS) in the buffer solution on the CE separation of linear polyethylene glycols (PEGs), polypropylene glycols (PPGs) and ethylene oxide–propylene oxide (EO–PO) copolymers with different molar masses was investigated. The interaction between the charged polymer derivatives and SDS ions in solution increased strongly with the degree of polymerisation and the amount PO in the chain of the polymeric compounds. This behaviour made it possible to invert the migration order of EO–PO containing polymers of different size. With a background electrolyte (BGE) composition of 10 mM SDS and 25% (v/v) acetonitrile in borate buffer mono- and difunctional byproducts were separated from the main glycerin-based polyols based on their number of end-groups. Accurate quantities for the mono- and difunctional impurities in technical glycerin-based polyol products were determined.

Robust isocratic liquid chromatographic separation of functional poly(methyl methacrylate)

The separation of telechelic poly(methyl methacrylate) (PMMA) prepolymers based on the number of end-groups under critical liquid chromatography (LC) conditions has been studied using a bare-silica column, which can interact with polar functional groups. The critical solvent compositions for non-functional, mono-functional and bi-functional PMMAs were determined in normal-phase LC using mixtures of acetonitrile and dichloromethane (DCM) of varying composition as the mobile phase. The telechelic prepolymers were successfully separated according to hydroxyl (OH) functionality (with zero, one, or two OH groups, respectively) under the critical conditions, in which fast (5 min), base-line separations were obtained independent of molecular weight. Changing the column temperature, flow rate, and mobile-phase composition within a certain range did not affect the functionality separation. Therefore this isocratic LC separation method is quite robust. Evaporative light-scattering detector (ELSD) calibration curves were used for the quantitative analysis of functional PMMA prepolymers.

Phosphorus dendrimers: from synthesis to applications

Various methods of synthesis of phosphorus dendrimers are presented, in particular a fast method which allows creating each generation in only one step, while multiplying by 5 the number of end-groups. These methods of synthesis can easily be modified to place selectively on the surface, inside, within the branches or at the core, functional groups chosen according to the properties or the applications which they can bring. In many cases, the size of the dendrimer (its generation) has an influence on these properties. Various applications in the fields of catalysis, materials, and biology are presented. To cite this article: Anne-Marie Caminade et al., C. R. Chimie 6 (2003).

Synthesis of Poly(propylene oxide) with Strict Control of End Functionality, 1. Initiation with (4‐Methoxy)phenoxy Tetraphenylporphynatoaluminum

AbstractThe polymerization of propylene oxide (PO) initiated by (4‐methoxy)phenoxy tetraphenylporphynatoaluminum (TPPAl‐O‐PMP) was studied with the aim of strictly controlling the end‐group functionality of the resulting poly(propylene oxide) (PPO), together with the molecular weight, in terms of average values and of narrow chain‐length distribution. The influence of the relative amount of reactants used for the preparation of the initiator on the nature and number of end groups was studied by various analytic methods including 1H NMR and UV spectroscopies and matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF) spectrometry. In spite of apparent living behavior observed from size exclusion chromatograpy (SEC) measurements, large variations in the yield of polymerization, determined after several hours of reaction, indicated a strong dependence of the propagation rate on slight variations around the 1:1 stoichiometry of triethylaluminum to the unmetallated porphyrin and to the phenolic ligand. Associated with the anomalous kinetic behavior, differences in the nature of the end groups were unambiguously evidenced by MALDI‐TOF spectrometry for narrow molecular weight (MW) distributed PPOs obtained with a slight excess of triethylaluminum and a slight deficit in added phenol with regard to porphyrin. A mechanism involving side reactions is proposed to account for the observed kinetic and structural features. Immortal polymerization of PO with strict control of MW distribution and functionality is obtained under appropriate conditions and consistently supported by various methods of MW determination.Principle of end‐group functionalization in porphyrin catalyzed PO polymerization.magnified imagePrinciple of end‐group functionalization in porphyrin catalyzed PO polymerization.

Interchromophoric Coupling in Oligo(p-phenylenevinylene)-Substituted Poly(propyleneimine) Dendrimers

Poly(propyleneimine) dendrimers functionalized with oligo(p-phenylenevinylene) (OPV) end groups based on distyrylbenzene show fluorescence properties that depend on dendrimer generation and thereby on the number of end groups. The compounds are investigated using site-selective and time-resolved fluorescence methods. A red shift of the low-temperature emission spectrum is observed with increasing dendrimer generation. This is accompanied by changes in the shape of the lowest absorption band of the dendrimers. Results are interpreted in terms of rapid migration of electronic excitation energy among the OPV units. We find that coupling between the electronic motion on the OPV groups has to be taken into account to explain the magnitude of the red shift in emission. This implies that interchromophoric interactions are sufficiently strong to induce delocalization of the excitation over more than one chromophoric group. Experimental data indicate that off-diagonal disorder is large; i.e., excited-state interchromophoric interaction energies are given by a broad statistical distribution. The off-diagonal disorder is interpreted in terms of the flexible nature of the dendrimer, leading to a broad distribution of distances between the chromophoric end groups. A delayed emission component is observed for the dendrimers, but this component is absent for the isolated OPV unit. The delayed emission is attributed to excimer and/or exciplex formation within the dendrimer.