Chain Stopper Research Articles

Acyclic Triene Metathesis Oligo‐ and Polymerization of High Oleic Sun Flower Oil

AbstractHigh oleic sunflower oil, a renewable raw material consisting of triglycerides with internal CC‐double bonds, was polymerized via acyclic triene metathesis (ATMET) to highly branched and functionalized polyesters. If the Hoveyda–Grubbs second generation catalyst was used and methyl acrylate was introduced as a chain stopper, the molecular weight of the obtained polymers could be tuned by varying the ratio of the triglyceride and methyl acrylate. Using the first generation Grubbs catalyst for the polymerization of high oleic sunflower oil, no cross‐linking was observed, even without the use of a chain stopper. The resulting branched materials were characterized by GPC, 1H and 13C NMR, and ESI‐MS.magnified image

Phosphorus‐containing renewable polyester‐polyols via ADMET polymerization: Synthesis, functionalization, and radical crosslinking

AbstractAn α,ω‐diene containing hydroxyl groups was prepared from plant oil‐derived platform chemicals. The acyclic diene metathesis copolymerization (ADMET) of this monomer with a phosphorus‐containing α,ω‐diene (DOPO II), also plant oil derived, afforded a series of phosphorus containing linear polyesters, which have been fully characterized. The backbone hydroxyls of these polyesters have been acrylated and radically polymerized to produce crosslinked polymers. The thermomechanical and mechanical properties, the thermal stability, and the flame retardancy of these phosphorus‐based thermosets have been studied. Moreover, methyl 10‐undecenoate has been used as chain stopper in selected ADMET polymerizations to study the effect of the prepolymers' molecular weights on the different properties of the final materials. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1649–1660, 2010

Anions as Efficient Chain Stoppers for Hydrogen-Bonded Supramolecular Polymers

The chain length of hydrogen-bonded supramolecular polymers and thus their rheological properties can be controlled by the presence of so-called chain stoppers: these monofunctional monomers are able to interact with the monomers and break the polymer chains. In this letter, we show that the use of anions, strong hydrogen bond competitors, instead of precisely designed complementary units is a very simple approach to tuning the rheology of a bisurea-based hydrogen-bonded supramolecular polymer. All of the anions tested were able to break the supramolecular chains, resulting in a dramatic drop in the viscosity of the solutions and were found to be more efficient than a previously described organic stopper. A careful study of the rheological properties of bisurea solutions in the presence of H2PO4,N(C4H9)4 showed that the presence of this ion does not modify the nature of the bisurea supramolecular assembly. For a molar fraction of stopper of only 10(-5), the viscosity of bisurea solutions decreases by a factor of 10 as a result of the formation of shorter supramolecular assemblies.

Acyclic Triene Metathesis Polymerization with Chain‐Stoppers: Molecular Weight Control in the Synthesis of Branched Polymers

AbstractThe synthesis of branched macromolecules from renewable resources via olefin metathesis is described. We observed that it is possible to control the molecular weight during the acyclic triene metathesis (ATMET) of a triglyceride by the application of methyl acrylate as a chain stopper for this straightforward one step one pot polymerization. The resulting branched materials were characterized by GPC, NMR as well as ESI‐MS and the combination of these techniques provided valuable insights into the polymer structure as well as occurring side reactions during this olefin metathesis polymerization reaction.magnified image

Acyclic Diene Metathesis with a Monomer from Renewable Resources: Control of Molecular Weight and One‐Step Preparation of Block Copolymers

The preparation of a long-chain aliphatic alpha,omega-diene from plant oil derivatives and its subsequent polymerization through acyclic diene metathesis (ADMET) is described. The ADMET bulk polymerization of the thus-obtained monomer, undecyl undecenoate, was investigated and optimized by applying ruthenium-based metathesis catalysts from Grubbs and Hoveyda-Grubbs, leading to high-molecular-weight polyesters. Moreover, by applying different amounts of methyl 10-undecenoate as a chain stopper in this ADMET step growth polymerization, the molecular weight of the resulting polyester could be tuned in a range from approximately 10 to 45 kDa. Finally, the application of a poly(ethylene glycol) methyl ether acrylate as the chain stopper led to the preparation of ABA triblock copolymers in a one-step, one-pot procedure.

Host–Guest Driven Self‐Assembly of Linear and Star Supramolecular Polymers

Supramolecular plasticity: The remarkable host–guest properties of phosphonate cavitands have been exploited in the self-assembly of supramolecular polymers (see picture) that feature guest-triggered reversibility and template-driven conversion from linear into star-branched forms. The structurally similar but complexation-inefficient thiophosphonate cavitand acts as chain stopper to control the degree of polymerization. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z801002_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Rheological characterisation of bis-urea based viscoelastic solutions in an apolar solvent

The rheological properties of hydrogen bonded reversible aggregates in apolar solvent have been investigated. The zero shear viscosity, the plateau modulus and the terminal viscoelastic relaxation time exhibit power laws dependencies with the concentration that have been compared with the behaviours expected for reversible polymers. It appears that the dynamics originate from scission/recombination mechanisms. Moreover, the growth of the aggregates with concentration follows the laws observed and predicted for worm-like micelles at low concentrations allowing the length of the aggregates to be estimated 500 nm at 3 g L −1. However, at the highest concentrations investigated, deviations from the power laws suggest the presence of some intrinsic chain stopper poisons in the solutions.

Rheology of a reversible supramolecular polymer studied by comparison of the effects of temperature and chain stoppers

The rheology of a reversible supramolecular polymer is studied by comparing the effects of an increase in temperature and the addition of chain stoppers. The dependence of the zero-shear viscosity and the terminal relaxation time on temperature is exponential, and the activation energy for viscous flow can be calculated. Above a critical stopper fraction, power laws describe the stopper dependence of the viscosity and relaxation time. A simple model for the effect of the addition of chain stoppers on the average degree of polymerization adequately describes the results. A comparison of flow curves at several temperatures and stopper fractions reveals considerable differences between solutions with the same zero-shear viscosity. These are mainly associated with differences in the terminal relaxation time. A mechanism of shear-induced alignment and subsequent elongation of chains is proposed, with which the experimental results are consistent.

Chain Stoppers in Reversible Supramolecular Polymer Solutions Studied by Static and Dynamic Light Scattering and Osmometry

The effect of the addition of chain stoppers to solutions of hydrogen-bonded reversible supramolecular polymers was studied by vapor pressure osmometry and static and dynamic light scattering. Vapor pressure osmometry showed that within the range of concentrations studied the average degree of polymerization is independent of the overall monomer concentration and roughly inversely proportional to the mole fraction of chain stoppers, in agreement with theoretical predictions. The correlation length as measured by static light scattering has a maximum at the overlap concentration in solutions without chain stoppers. In the presence of a fixed fraction of chain stoppers, the results coincide with those without chain stoppers at low and high concentrations, but there is a plateau in the correlation length at intermediate concentrations. From the data, information about the association constant and the persistence length of the chains is obtained. The effectiveness of the chain stopper is discussed, and the results from osmometry and static light scattering are compared. Dynamic light scattering was used to measure the time autocorrelation function. From the characteristic decay time, the hydrodynamic correlation length was calculated. For solutions above the overlap concentration, the distribution of decay times showed a second peak at longer times. It is not yet fully understood what the mechanism behind this slow mode is.

Supramolecular ABA Triblock Copolymers via a Polycondensation Approach: Synthesis, Characterization, and Micelle Formation

The combinatorial optimization of the reaction conditions of 1,16-bis(2,2‘:6‘,2‘ ‘-terpyridin-4‘-yloxy)hexadecane 1 with RuCl3 under reductive conditions to form supramolecular polymers with a bis-tpy-Ru(II) type connectivity, utilizing gel permeation chromatography as well as UV/vis spectroscopy as screening tools, led to an improved understanding of important polymerization parameters. Moreover, the obtained knowledge could be applied to the designed synthesis of an A-b-B-b-A type supramolecular triblock copolymer utilizing a α-terpyridine-ω-methyl-poly(ethylene glycol) polymer as a chain stopper during the polycondensation-like reaction. The resulting triblock copolymer revealed a composition of approximately 33 repeat units of 1, outlining the value of the applied optimized conditions for its synthesis. Furthermore, it was observed that the synthesized triblock copolymer was able to form micelles in water. Finally, these micelles were investigated by dynamic light scattering, atomic force microscopy, as well as transmission electron microscopy.

Synthesis and Energy-Transfer Properties of Hydrogen-Bonded Oligofluorenes

A set of fluorene oligomers has been synthesized by stepwise palladium-catalyzed (Suzuki) couplings of fluorene monomers. Ureidopyrimidinones (UPy), functional groups that can dimerize via quadruple hydrogen bonds, were attached to both ends of the oligofluorenes. The resulting bis-UPy-terminated oligomers self-assemble into supramolecular chain polymers. For comparison, oligofluorenes of the same oligomer lengths but without terminal hydrogen-bonding groups were synthesized. Chains of hydrogen-bonded fluorenes can be simply endcapped by a variety of chain stoppers, molecules that have one UPy group. In this manner, we have endcapped the hydrogen-bonded fluorene chains with either oligo(p-phenylenevinylene) or perylene bisimide. Energy-transfer experiments in solution and the solid state demonstrate that oligofluorenes can donate energy to a variety of energy acceptors, but that this energy transfer occurs most effectively when the donor fluorene is hydrogen-bonded to the acceptor.

Chain Stopper-Assisted Characterization of Supramolecular Polymers

Supramolecular polymers are dynamic materials; consequently, their molar mass is concentration dependent. However, the present experimental results show that an efficient chain stopper (i.e., a monofunctional monomer) can be used to block the concentration dependence of the molar mass of a hydrogen-bonded supramolecular polymer, over a realistic concentration range. This fact was used to derive the molecular weight and radius of gyration of the stopped supramolecular chains (by light scattering) as well as the intrinsic viscosity. In a second step, the molecular weight of the bis-urea-based supramolecular polymer (EHUT) was determined in the absence of a chain stopper.

Dynamics of reversible supramolecular polymers: Independent determination of the dependence of linear viscoelasticity on concentration and chain length by using chain stoppers

The linear viscoelasticity of solutions of a hydrogen bonded reversible supramolecular polymer in the presence of a chain stopper was studied by rheometry and by dynamic light scattering using probe particles. The use of chain stoppers enabled the independent variation of the degree of polymerisation and the monomer concentration, and the effect of both parameters on rheology was investigated. Scaling exponents were obtained for the chain length and concentration dependence of the zero-shear viscosity and the terminal relaxation time, and these were compared to theoretical values. The results indicate that the reversible supramolecular polymer is semiflexible, and that both breaking and reptation of chains contribute to the stress relaxation. The parameters from macroscopic rheometry were compared to microscopic values obtained from probe particle diffusion. The particles probe the macroscopic viscoelastic parameters if their size is large compared to the correlation length in the system and to the (persistence) length of the polymer chains.

Control of Molecular Weight for Auto-Catalyzed Poly(ortho ester) Obtained by Polycondensation Reaction

Polycondensation of auto-catalyzed poly(ortho ester)s (POE x LA y ) containing lactic acid units in the polymer backbone is described. The use of n-decanol during the polymerization as a chain stopper allows good control of polymer molecular weight. POE 70 LA 30 based on 3,9-diet-hylidene-2,4,8,10-tetraoxaspiro[5.5]undecane (DETOSU), 1,10-decanediol-lactate and 1,10-decanediol and synthesized by using 5, 10 and 15 mol % of n-decanol were characterized by 13 C NMR, 1 H NMR and FT-IR. The thermal and viscoelastic properties of such polymers as well as their molecular weight distribution are also reported.

Identification of Derivatives of Bisphenol A Diglycidyl Ether and Novolac Glycidyl Ether in Can Coatings by Liquid Chromatography/Ion Trap Mass Spectrometry

A reversed-phase liquid chromatographic method combined with fluorescence and multiple mass spectrometric detection in series is presented for the separation and structure elucidation of bisphenol A diglycidyl ether (BADGE) and novolac glycidyl ether (NOGE) derivatives. Atmospheric pressure chemical ionization in the positive ion mode and collision induced fragmentation in the ion trap allowed identification of BADGE- and NOGE-related compounds originating from reactions of the glycidyl ethers with bisphenols, solvents, and chain stoppers. Two extracts from food-can coatings were investigated in detail. It was possible to elucidate the structures of many substances and consequently to draw conclusions about the production of the lacquers.

Fully soluble poly( p-phenylenevinylene)s via propagation control of the polymer chain conjugated lengths

PPV and its alkoxy-substituted derivatives are a well-established class of materials for polymeric light emitting diode application. MEH-PPV (poly[2–methoxy–5–(2′–ethylhexyloxy)– p–phenylenevinylene]s), as a typical example of the solution processable conjugated polymer for PLED device fabrication, possesses good solubility in common organic solvents. However, gelation or micro-gelation always occurs during the polymerization process, especially when the polymer is prepared from the bis-bromomethyl monomer through the Gilch route. Herein, we present the synthesis of fully soluble MEH-PPV by the addition of molecular weight modifiers (chain stoppers or free radical scavengers) in the polymerization system. The polymers synthesized in this work were characterized by FTIR, NMR, UV–vis spectroscopy and GPC. The results indicate that the molecular weights of the polymers can be effectively controlled by the addition of chain stopper (benzyl bromide) or chain blocking antioxidant (2,6-di -tert-butyl-4-methylphenol). The mechanism of polymerization in the presence of these additives is also discussed.

New polymer syntheses, 88. Thermosetting cholesterin oligocarbonates with propargyl endgroups

AbstractThermosetting cholesteric oligocarbonates were prepared by polycondensation of mesogenic diphenols such as 4,4′‐dihydroxybiphenyl (DHB) or hydroquinone 4‐hydroxy‐benzoate (HQHB; system. name: 4‐hydroxyphenyl 4‐hydroxybenzoate) with methylhy‐droquinone and isosorbide. Trichloromethyl chloroformate served as condensing agent and propargyl alcohol (system. name of propargyl: 2‐propynyl), 4‐propargyloxybenzoyl chloride or 6‐propargyloxy‐2‐napthoyl chloride served as chain stoppers. Most oligocar‐bonates form a cholesteric phase over a broad temperature range. Depending on the mole fraction of isosorbide these oligocarbonates form Grandjean textures when sheared in the molten state.

New Polymer Syntheses. 89. Thermosetting Cholesteric Oligoesters Having Propargyl Endgroups

Three series of cholesteric oligoesters containing propargyl endgroups were prepared by polycondensations of three different dicarboxylic acid dichlorides with mixtures of diols and monofunctional propargyl derivatives in pyridine. These three series are based on terephthaloylchloride, naphthalene-2,6-dicarbonylchloride, and biphenyl-4,4′-dicarbonylchloride. tert-Butylhydroquinone, phenylhydroquinone, and isosorbide were the diols, and propargyl alcohol, 4-propargylthiophenol, and 6-propargyloxynaphthaloyl chloride served as chain stoppers. All isolated oligoesters were thermotropic, but only a few of them were capable of forming a Grandjean texture upon shearing of the cholesteric melt. The thermal crosslinking of the propargyl endgroups was monitored by an exothermic process in the DSC measurements. The lowest cure temperatures (200–240°C) were observed for the 6-propargyloxy-2-naphthoic acid endgroups. Thermal crosslinking in the cholesteric phase was observed for four samples.

Synthesis, characterization, and mechanical properties of an injection moldable polyimide based on 1,4‐diaminobutane

AbstractA partially aliphatic polyimide was synthesized in a two‐step process in N‐methylpyrrolidone (NMP) from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and 1,4‐diaminobutane (DAB). Weight average molecular weights ranging from 35,000 to over 160,000 were obtained by adding different amounts of the chain stopper phthalic anhydride, or by using a slight excess of BTDA. Rheological measurements, supported by a size exclusion chromatography (SEC) analysis before and after injection molding, point to branching or even partial crosslinking during molding of poly(BTDA‐DAB) if reactive amine endgroups are present. By reacting these amine endgroups with benzoyl chloride, branching is limited and a more Newtonian flow is observed. Both non‐endcapped and endcapped reactor powders are ∼60% crystalline (Tg = 170 to 175°C, Tm = 290 to 300°C), but according to wide and small angle X‐ray scattering (WAXS and SAXS) studies on test bars, both the more linear polyimides and their branched counterparts are fully amorphous after injection molding. Nevertheless, poly(BTDA‐DAB) shows interesting mechanical properties like a bending modulus of ∼3.9 GPa, a tensile strength of ∼130 MPa, a tensile elongation at break of ∼13%, and a notched Izod impact of ∼4 kJ/m2.

Model polydiethylsiloxane networks: 1. Synthesis and phase behaviour

The preparation and hydrosilylation crosslinking of well-defined vinyl and ally polydiethylsiloxane (PDES) telechelics are described. End functionalization has been achieved by using divinyltetramethylsiloxane as a chain stopper during the cationic polymerization of hexaethylcyclotrisiloxane or by anionic polymerization of hexaethylcyclotrisiloxane with allyllithium followed by end capping with allyldimethylchlorosilane. Hydrosilylation crosslinking yielded model PDES networks which have been characterized by equilibrium swelling, determination of the sol fraction, differential scanning calorimetry and wide angle X-ray diffraction.