Polymer Branching Research Articles

Sequenced Ethylene−Propylene Copolymers: Effects of Short Ethylene Run Lengths

Two sequenced ethylene−propylene (EP) copolymers possessing methyl groups every fifth (EP5) or seventh (EP7) carbon have been prepared using an olefin metathesis polycondensation/hydrogenation strategy, thus generating methyl branched polyolefins with short ethylene run lengths of 4 or 6 carbons, respectively. Precise spacing of methyl branches along both copolymer backbones imparts pristine microstructure and targeted comonomer ratios in the copolymer. Extensive NMR spectral data are presented detailing polymer microstructure, branching analysis, and end-group identification. Thermal analysis using differential scanning calorimetry revealed multiple low-temperature relaxations for EP7 and glass transition temperature of −63 °C for EP5, and FT-IR analysis suggests no crystallinity under ambient conditions. A new ADMET monomer synthesis is also reported for the development of highly functionalized polyolefins or sequenced ethylene copolymers.

Controlled polymerizations as tools for the design of star‐like and dendrimer‐like polymers

AbstractThis paper highlights our recent efforts to engineer polymer chains in star‐like and dendrimer‐like architectures using atom‐transfer radical polymerization (ATRP) and anionic ring‐opening polymerization (AROP) of ethylene oxide as synthetic tools. The scope and limitations of ATRP are first discussed when this method of controlled radical polymerization is applied to multifunctional initiators for the synthesis of star polymers by the core‐first approach. The switch from ATRP to AROP of ethylene oxide and vice versa allows access to branched amphiphilic block copolymers exhibiting core–shell structures. Stress is also put on the methodologies for the selective branching of polymeric chain‐ends, with a view to introducing ω‐geminal functionalities from which further polymer branches can be grown. When linear polymer precursors are used, such a strategy leads to asymmetric and mikto‐arm stars but the same can be applied to multi‐arm stars so as to generate so‐called ‘dendrimer‐like (co)polymers’ that are dendrimers with true macromolecular generations. Copyright © 2006 Society of Chemical Industry

Pressure and Temperature Dependence of LDPE Viscosity and Free Volume: The Effect of Molecular Structure

Abstract Temperature and pressure dependencies of shear and elongational viscosities were examined using rotational and capillary rheometers. Two different batches of the same polymer grade have shown that the molecular structure diversion significantly influences the magnitudes of pressure coefficients, which vary more than the temperature coefficients. The pressure effect on viscosity notably depends on the amount of long-chain branching in polymer. Further, the paper shows that pVT data analysis via the Simha-Somcynsky equation of state can be employed to reveal differences in temperature and pressure viscosity dependencies through the free volume fraction.

Star polystyrenes by anionic star–star coupling reactions with divinylbenzene

AbstractThe incremental addition of divinylbenzene was used to generate star polystyrenes in a nearly full conversion of a living polystyrenyl anion. The dramatic increase in the molecular weight of the star polystyrenes with a limited supply of the living polystyrene supported the formation of gradient‐star polystyrenes through star–star coupling. The stoichiometric analysis of the star polymers revealed that their connection polymer had a shorter length than their branch polymer. The measured solution viscosity of the gradient‐star polymers greatly deviated from a linear correlation with the molecular weight and was in parallel to a theoretical simulation based on a highly branched structure of the gradient‐star polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2579–2586, 2006

Molecular Simulations for Entangled Polymer Dynamics

A novel method for multi-body molecular simulations for entangled polymers including branch polymers, polymer blends and copolymers is developed in this study. Entangled polymer dynamics is important in industry and still challengeable in polymer science due to complicated rheology caused by a broad variety of controllable polymer architectures such as molecular weight, molecular weight distribution, long chain branching, copolymerization, etc. and freedom of their blends. Conventional molecular simulations are inadequate to the polymer dynamics in long time range because of huge calculation cost. Theoretical approaches based on reptation theories are essentially difficult for multi-component situations due to the self-consistent treatment of entanglement among many chains. In this study a new method of molecular simulations for entangled polymer dynamics is developed based on the primitive chain network model where polymers are considered as primitive chains forming real network in 3D space similarly to the conventional molecular simulations and distinguishably from other entanglement based models. Reasonable consistency on established scaling behaviors for static and dynamic properties and quantitative agreement with experiments for linear and nonlinear rheology have been confirmed for linear and branched polymers. For copolymers and blends reasonable results have been obtained on phase behaviors.

Three-dimensional resist development simulation with discrete models

Control and minimization of line-edge roughness (LER) is a crucial problem for further advancements in lithography. To simulate LER, a switch from continuous to discrete, molecular level resist models is required. This article presents a new algorithm for the discrete resist structure generation with nonoverlapping polymer distributions and a novel development simulation approach. The presented concept allows simultaneously the simulation of macroscopic profile dimensions as well as of microscopic roughness properties of the resist. Required microscopic dissolution times of the polymers are derived from the corresponding simulated local macroscopic development rates. By retaining all other resist parameters unchanged in the simulation, the isolated influence of varying the assumed polymer size, branching geometry, and dissolution time variations on LER is examined with this new method. Small, strongly tangled polymers lead to considerably lower LER values than bigger or less bended polymers. Compared to the investigated polymer size and geometry, the examined range of variances in the dissolution times has only a weak influence on LER.

Effect of branching of cyclo-olefin copolymers and polycarbonate polymers on mechanical and optical properties: Ab initio and molecular simulation study

Mechanical and optical properties of branched cyclo-olefin copolymers (COC) and polycarbonate polymers (PC) were studied by molecular dynamics simulations and ab initio calculations. In addition, the effect of structural modifications of the polycarbonate on the optical properties was investigated by ab initio calculations. The branching of PC and COC chains was found to increase flexibility and processability of the polymers without significantly weakening the optical properties. The calculated bulk and Young's moduli were clearly lower for the branched polymers. Ab initio calculations of isotropic polarizabilities and refractive indexes were sensitive to the applied basis set and level of theory. The branching of PC and COC had a modest effect on the refractive indexes as compared with the effect of modifications of the polycarbonate backbone. The highest refractive index of the series was obtained when the backbone carbon atom of polycarbonate was replaced with sulphur atom. This observation is in agreement with experimental data.

Distribution of degrees of polymerization in statistically branched polymers with tetrafunctional branch points: model calculations

AbstractStockmayer's classical theory of statistical branching of polymers, as modified by Thurmond and Zimm, and subsequently by Kilb, has been used to describe the evolution of the distribution of the degrees of polymerization with conversion up to the gel point in the copolymerization of a vinyl monomer with a small amount of a divinyl monomer. The weight fractions of molecules with a particular number of branch points per molecule, the averages of the degrees of polymerization of these molecules, and some other characteristics were calculated as functions of a complex variable—the branching parameter γ, including the composition of the monomer mixture, relative reactivities of the individual types of double bonds, and conversion. From these calculations, a few general conclusions on the behaviour of the model system can be drawn. The conclusions are likely to be qualitatively valid also for systems not strictly conforming to the model. Copyright © 2005 Society of Chemical Industry

Impact of Branching on the Phase Behavior of Polymers

We have studied the effect of branching on the solution phase behavior of branched homopolymers using grand canonical Monte Carlo (GCMC) simulations in conjunction with multihistogram reweighting and finite-size scaling analysis. The critical temperature (Tc) and the £ temperature (£) decrease as polymer branching is increased, but the drop in £ is less pronounced than that of Tc. The critical volume fraction (c) rises with the degree of branching. Branched polymers are found to obey the Shultz-Flory relationship and exhibit a power-law behavior in c vs chain length, with similar scaling exponents as those for their linear counterparts. Comparisons of the GCMC results are made to results of the lattice cluster theory (LCT). It is observed that the LCT significantly underestimates the impact of polymer branching on the critical behavior of polymers. We speculate this discrepancy between the two formulations to be due to an inadequate representation of the variation of polymer conformations with branching and neglect of fluctuations in the LCT theory. Branched and hyperbranched polymers (dendrimers) have received a lot of attention recently due to their emerging applications in catalysis, 1 nanomaterial syn- thesis 2 and biomedicine. 3,4 Understanding the role that branching plays in determining the rheological and thermodynamical properties of a polymer melt or its so- lution is currently an active area of research. Although significant advancements have been made in elucidating the conformational properties of branched polymers, 5 comparatively little progress has been made in under- standing the impact of branching on the miscibility and critical behavior of polymers in solution. In this study, we investigate the effect of branching on the liquid- liquid phase separation and critical parameters of

Electrostatic Self-Assembly and Covalent Fixation with Cationic and Anionic Telechelic Precursors for New Loop and Branch Polymer Topologies

An electrostatic self-assembly of cationic and anionic polymer precursors and subsequent covalent fixation has been performed to construct a series of loop and branch polymer topologies. The process employed the two cationic polymer precursors (1a and 1b) having two pyrrolidinium salt groups either at both chain ends (1a) or at the designated interior positions (1b), and the two anionic counterparts (2a and 2b) having two carboxylate groups either at both chain ends (2a) or at a single chain end (2b). A series of electrostatic polymer−polymer self-assemblies have been prepared by the combination of cationic and anionic precursors, i.e., 1a/2a, 1a/2b, and 1b/2a, respectively, through simple coprecipitation of the precursor polymer mixture into an aqueous medium. The subsequent covalent conversion of the electrostatically self-assembled products by heating under dilution could produce a ring polymer from 1a/2a, a tadpole polymer from 1a/2b, and a two-tail tadpole, having a loop and two branches, polymer from 1b/2a, respectively.

Linear Rheology of Architecturally Complex Macromolecules: Comb Polymers with Linear Backbones

We present a detailed, systematic study of the linear rheological response of model comb homopolymers consisting of linear backbone chains on which branches of the same polymer are grafted. By using polymers of different molecular weights of backbone and branches, different number of branches, and different chemistries, we explore the relaxation mechanisms of these polymers and find their universal features. We apply a tube model theoretical analysis, originally developed by McLeish and co-workers, which has been appropriately modified in order to account for the effects of the fluctuations of the free ends of the backbone (due to the grafting procedure during synthesis) and the polydispersity on the rheology. The satisfactory fitting of the data with the model indicates that the latter is capable of providing a quantitative understanding of the rheology of branched polymers. More specifically, comb polymers exhibit two distinct relaxation processes, assigned to the branches and the backbone. Relaxation p...

Population balance modeling of polymer branching and hyperbranching

Branched polymers have rheological and morphological properties that make them important subjects for investigation. We propose a chain polymerization model for branching kinetics that is not restricted to primary branching on the chain backbone, but incorporates branches on branches (hyperbranching). The proposed method involves multivariate distributions, a subject of considerable interest and activity in population balance modeling. For unsteady-state continuous-flow stirred reactors, the mathematical description is based on population balance equations for branch formation and growth by addition of chains of distributed molecular weight (MW). Computer algebra software facilitates the complex mathematical manipulations for the continuous MW and the discrete branch number. Key properties of branched macromolecules are presented, such as MW moments for various levels of branching, number of branches, and average MW of branches. A major conclusion is that hyperbranching presents distinctly different properties for unsteady batch and steady-state stirred flow reactors, whereas for primary branching, the results are similar.

Synthesis and characterization of branched polymers by a free radical approach using a novel ‘macroiniferter’

Free radical bulk polymerization of styrene and methyl methacrylate (MMA) was carried out using a novel ‘macroiniferter’ which resulted in branched polymers with relatively narrow molecular weight distribution. This approach involving the novel macroiniferter; poly[3-( t-butylperoxy)propyl disulfide] (PBPPDS) that has side chain peroxide groups and main chain disulfide linkages was developed to prepare soluble branched polymers as well as to control the extent of branching in vinyl polymers synthesized via a free radical route. The synthesis, characterization and thermal degradation studies of PBPPDS are reported here for the first time. The resulting polystyrene (PS) and poly(methyl methacrylate) (PMMA) polymers were characterized using gel permeation chromatography (GPC), intrinsic viscosity [ η] measurements and the degree of branching was studied by the determination of g′ factor.

Grafting of branched polymers onto nano-sized silica surface: Postgrafting of polymers with pendant isocyanate groups of polymer chain grafted onto nano-sized silica surface

To control the surface wettability of nano-sized silica surface, the postgrafting of hydrophilic and hydrophobic polymers to grafted polymer chains on the surface was investigated. Polymers having blocked isocyanate groups were successfully grafted onto nano-sized silica surface by the graft copolymerization of methyl methacrylate (MMA) with 2-( O-[1′-methylpropylideneamino]caboxyamino)ethyl methacrylate (MOIB) initiated by azo groups previously introduced onto the surface. The blocked isocyanate groups of poly(MMA-co-MOIB)-grafted silica were stable in a desiccator, but isocyanate groups were readily regenerated by heating at 150 °C. The hydrophilic polymers, such as poly(ethylene glycol) (PEG) and poly(ethyleneimine) (PEI), were postgrafted onto the poly(MMA-co-MOIB)-grafted silica by the reaction of functional groups of PEG and PEI with pendant isocyanate groups of poly(MMA-co-MOI)-grafted silica to give branched polymer-grafted silica. The percentage of grafting increased with increasing molecular weight of PEG, but the number of postgrafted chain decreased, because of steric hindrance. The hydrophobic polymers, such as poly(dimethylsiloxane) were also postgrafted onto poly(MMA-co-MOI)-grafted silica. It was found that the grafting of hydrophobic polymer and the postgrafting of hydrophilic polymer branches readily controls the wettability of silica surface to water.

Flexible Dendrimer Synthesis

CHEMISTRY The formation of dendrimers, in which branching polymer chains extend from a central core, normally involves the covalent attachment of the dendrons to a central core. Leung et al. report a dynamic covalent chemistry strategy for the mechanical attachment of dendrons to a core; this pathway, unlike earlier forays, proceeds in high yield. The core bears −CH2NH2+CH2-centers on each arm that act as binding sites for crown ether groups terminated with two primary amines. These amines are then bridged by a dialdehyde-bearing dendron, producing two imine linkages and forming the ring that locks the macrocycle-dendrimer onto the core. These kinetically stable dendrimers form in >90% yields and can be fixed in place by reduction of the C=N bonds with BH3 in tetrahydrofuran and subsequent deprotonation with aqueous NaOH. The formation of each generation (0, 1, and 2) of dendrimer products, which reach molecular weights of up to ∼5000, was verified by mass spectrometry. — PDS J. Am. Chem. Soc. 10.1021/ja0501363.

Exact multileg correlation functions for the dense phase of branching polymers in two dimensions

We consider branching polymers on the planar square lattice with open boundary conditions and exactly calculate correlation functions of k polymer chains that connect two lattice sites with a large distance r apart for odd number of polymer chains k. We find that besides the standard power-law factor the leading term also has a logarithmic multiplier.

High Performance Gene Delivery Polymeric Vector: Nano-Structured Cationic Star Polymers (Star Vectors)

Nano-structured hyperbranched cationic star polymers, called star vectors, were molecularly designed for a novel gene delivery non-viral vector. The linear and 3, 4 or 6 branched water-soluble cationic polymers, which had same molecular weight of ca. 18,000, were synthesized by iniferter (initiator-transfer agent-terminator)-based photo-living-radical polymerization of 3-(N,N-dimethylamino)propyl acrylamide, initiated from respective multi-dithiocarbamate-derivatized benzenes as an iniferter. All polymers produced polyion complexes 'polyplexes' by mixing with pDNA (pGL3-control plasmid), in which the particle size was ca. 250 nm in diameter [the charge ratio < 2/1 (vevtor/pDNA)] and ca. 150 nm (the charge ratio > 2.5/1), and the zeta-potential was ca. +10 mV (the charge ratio > 1/1). When COS-1 cells were incubated with the polyplexes 12 h after preparation under the charge ratio of 5/1, higher gene expression was obtained as an increase in branching, with a little cytotoxicity. The relative gene expression to the linear polymer was about 2, 5, and 10 times in 3-, 4-, and 6-branched polymers, respectively. The precise change in branching of polymers enabled the control of the gene transfer activity.

Observation of wall wettability under imposed flow by fluorescence depolarization: dependence on surface oxygen content and degree of polymer branching

This work was concerned with the dependence of the interfacial tension (Gamma(SL)) on surface degree of oxygen content and on polymer branching degree. The static Gamma(SL) was evaluated by contact angle (theta;(c)) and the dynamic Gamma(SL) by fluorescence depolarization of molecular probes seeded in induced flows of monoethylene glycol. The latter results were interpreted using statistical covariant analysis. Two different systems of flowing films were studied: free films flowing on the surfaces on which they impinge and films flowing inside 1-mm-thick microflow cells. The solid surfaces were polyethylene of low density, medium density, high density, and linear with low density, polypropylene, vinyl acetate co-polymer with oxygen content of 15% and 28%, borosilicate, and tin dioxide. Increase in oxygen content of the surface decreased both the static and the dynamic Gamma(SL), which demonstrated that the presence of oxygen atoms hindered wetting. Only the dynamical Gamma(SL) was sensitive to polymer branching, and it increased as branching degree decreased. This was attributed to the higher hydrogen-atom density at the surface, which favored temporary intermolecular bonds between the surface and the flowing liquid.

Diffusion coefficients in trimethyleneoxide containing comb branch polymer electrolytes

This paper reports on a new comb branch polymer based on trimethylene oxide (TMO) side chains as a polymer electrolyte for potential application in lithium metal rechargeable batteries. The trimethylene oxide (TMO) units are attached to the side chains of a polyepoxide ether to maximize the segmental motion. Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) salt was used to formulate the polymer electrolyte with the new TMO containing polymers. The new polymer electrolytes show improved salt diffusion coefficients ( D s) and conductivity at ambient and subambient temperature compare to the ethylene oxide (EO) counterpart, whereas performance at high temperature (85 °C) remains the same or is actually worse for salt diffusivity.

Biomedicine: Branching polymer could heal cataract wounds

Science NewsVolume 166, Issue 17 p. 269-269 Of Note Biomedicine: Branching polymer could heal cataract wounds First published: 02 July 2009 https://doi.org/10.1002/scin.5591661713AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume166, Issue1723 October 2004Pages 269-269 RelatedInformation