Influence Of Molar Mass Research Articles

Rheology and Shear Orientation of a Nematic Liquid Crystalline Side-Group Polymer with Laterally Attached Mesogenic Units

The shear orientation of a nematic side-group liquid crystalline polymer (SG-LCP) with side-on fixed mesogenic units was investigated by means of rheo-birefringence and rheo-small angle light scattering. Rheological properties of the polymer depend on molecular weight. Macroscopically aligned samples were obtained in creep experiments, but the orientation was destroyed by oscillatory shear flow. The shear modulus of a low molar mass sample in the nematic and isotropic phase superposed to a common master curve. The low-frequency modulus of a high molar mass sample, however, decreased at the phase transition, and time−temperature superposition was not possible. Preshearing led to a further decrease of the modulus. Rheo-birefringence measurements revealed a clear influence of molar mass on both the final value and the orientation state after cessation of shear. Rheo-small angle light scattering also showed a strong influence of molecular weight. In polarizing microscopy, a banded texture was observed with a ...

A qualitative study to the influence of molar mass on retention in gradient polymer elution chromatography (GPEC)

AbstractGradient Polymer Elution Chromatography (GPEC) appears to be a powerful method for the determination of chemical composition distributions (CCD) of high molar mass copolymers. In order to perform these experiments, molar mass dependence of the retention time must be minimized. It is shown that variation in solvent and non‐solvent strength is a powerful method for adjusting the molar mass dependence. There appears to be a relation between molar mass dependence of retention behavior in GPEC on one hand and solubility under critical solvent conditions on the other hand. This phenomenon can be explained qualitatively from the important precipitation/redissolution mechanism in GPEC.

Phase behavior of the ternary system water/hydroxyethyl cellulose/nonionic surfactant

The phase behavior of ternary aqueous solutions of two samples of hydroxyethyl cellulose (HEC) and oligoethylene glycol mono(n-alkyl) ethers CxEy (x: 11;y: 28, 40) at 25°C has been studied above the CMC of CxEy. The influence of molar mass of HEC and the number of ethylene glycol units on the phase diagram has been investigated. Both binary systems water/HEC and water/CxEy are completely miscible. The ternary mixture of water/polymer/nonionic surfactant is homogeneous if the weight fraction of water is larger than 0.93, or else it can separate segregatively, i.e., HEC is enriched in one phase, the surfactant in the other. The theoretical description is based on an equation for the Gibbs energy of mixing which takes polar conformations into account. The phase diagrams are calculated by means of a new method which does not require the derivatives of the Gibbs energy of mixing.

A rheological study of shear induced crystallization

The isothermal crystallization of three isotactic polypropylene (iPP) types, with different molar mass (distributions), was studied after a well defined shear treatment of the melt at an elevated temperature and a subsequent quench to the crystallization temperature. For these experiments a standard rheometer of the cone and plate configuration was used. The development of the crystallization was monitored by dynamic oscillatory measurements. Shearing in the melt was shown to enhance subsequent crystallization at lower temperatures. Not only the total shear at constant rate is of importance, but also the chosen combination of rate and shearing time. Moreover, a pronounced influence of molar mass was detected. The exploration of the melting temperatures and times which are necessary for an erasion of the memory effects showed that the effect of shearing could not completely be erased, possibly as a consequence of mechanical degradation.

Influence of the block length on the structure of micelles formed by polystyrene‐block‐poly(ethylene‐co‐propene) in octane and 5‐methyl‐2‐hexanone

AbstractThe influence of molar mass and chemical composition of the copolymer on the structural parameters of copolymer micelles was investigated. Two polystyrene‐block‐poly(ethylene‐co‐propene) copolymers with the same polystyrene block length but different poly(ethylene‐co‐propene) length were used. The micelles were studied in solutions of octane and 5‐methyl‐2‐hexanone, selective solvents for poly(ethylene‐co‐propene) (PEP) and polystyrene (PS) blocks, respectively. Static light scattering and viscosity measurements were carried out in order to determine the weight‐average molar mass, radius of gyration, second virial coefficient and hydrodynamic radius of the micelles. The association number of the micelles depends on the location of the largest copolymer block in the micelle structure. An influence of the copolymer structure on the micelle dimensions was also found.

Liquid Crystalline Comb-Shaped Poly (Vinyl Ether)S with Cyanbiphenyl Mesogenic Groups

Abstract The synthesis of the series of new liquid crystalline comb-shaped poly(vinyl ether)s with cyanbiphenyl mesogenic groups is reported. Methylenic spacer groups of the different lengths (n=2–6,11) were used. Polymers were prepared by cationic polymerization corresponding vinyl ethers. The influence of molar mass and molar mass distribution on the mesomorphic properties and phase transitions has been studied. The effect of chemical structure of the main chain on the mesomorphic properties is discussed.

Separation of stat‐copoly(styrene/2‐methoxyethyl methacrylate) samples according to composition by gradient high‐performance liquid chromatography

AbstractStatistical copolymers of styrene (S) and 2‐methoxyethyl methacrylate (MEMA) (13–87 mass % of the latter monomer) were investigated by gradient HPLC on columns with either silica or CN‐bonded phase packings. The samples were injected in THF solution. The starting eluent was in each case a nonsolvent (isooctane or mixtures of isooctane with THF and methanol). Separation was achieved by increasing the concentration of THF or methanol in the eluent. A calibration mixture of four copolymers (26, 49, 62, and 87% MEMA) was investigated according to the principles of chromatographic cross‐fractionation (CCF) by size exclusion chromatography and subsequent gradient HPLC. The influence of molar mass on HPLC retention was small and, for the samples investigated by CCF, independent of copolymer composition. The composition effect on detector signal was also studied. At 230 nm wavelength and with MEMA content in the range between 20 and 40%, the effect was small and caused the average composition calculated from CCF results to deviate from the directly measured value by not more than 0.2 or 0.8% for the two copolymers investigated.

Saturated polyesters as emulsifiers for emulsion copolymerization of unsaturated polyester resins with styrene

AbstractIntramolecularly crosslinked macromolecules (ICM) from unsaturated polyesters (UP) and styrene, respectively from technical divinylbenzene (t‐DVB), were prepared by emulsion copolymerization (ECP). Saturated polyesters of different compositions and molar masses between 1200 and 2400 were used as emulsifiers (ESP). The influence of molar mass and structure at various concentrations of the ESP on yield, number and diameter of the ICM and their composition was studied. For comparison, also sodium dodecyl sulfate (SDS) was used as emulsifier.

Two-dimensional analysis of copolymers by size-exclusion chromatography and gradient-elution reversed-phase precipitation chromatography

Poly(styrene—co-acrylnitrile) samples were fractionated by size-exclusion chromatography and subsequent high-performance precipitation liquid chromatography (HPPLC) of effluent fractions. HPPLC was performed on a reversed phase column by using a mobile-phase composition gradient with eluting power increasing from 2,2,4-trimethylpentane as a non-solvent to tetrahydrofuran as a solvent. A mixture of two model copolymers of 23 and 30 wt. % acrylonitrile, having molar masses of 825 and 190 kg/mol, respectively, and a commercial SAN copolymer were studied. The correction of retention volumes for the influence of molar mass was determined, and applied in the evaluation of the data for the commercial sample.

The oxidation of poly(vinyl pyrrolidone) with Ce(IV)

AbstractIt was established that commercial poly(vinyl pyrrolidone) (PVP) may contain hydroperoxides, hydroxyl groups, carbonyl groups and double bonds in the main chain, and substances of low molar mass such as hydrogen peroxide and 2‐pyrrolidone, products of PVP oxidation during processing, handling and/or storage. In a scheme PVP reacting sites with Ce(IV) used as an initiator in the reaction of copolymerization of PVP with vinyl monomers were shown. It was concluded that PVP hydroperoxides were responsible for the formation of a respective homopolymer, whereas PVP hydroxyl groups may form radicals capable of the polymerization of a comonomer. The influence of molar mass of mother PVP on the course of the reaction of copolymerization of PVP was also discussed.

Influence of molar mass and catalysts on the kinetics of crystallization and on the orientation of poly(ethylene terephthalate)

Poly(ethylene terephthalate) with different molar masses and different catalysts and additives (calcium acetate, manganese acetate, triphenylphosphate) was synthesized. The influence of the molar mass distribution, and of the additives used, on the rate of crystallization was studied. Also the dependence of the orientation obtained during drawing at elevated temperatures on the drawing conditions, on the average molar mass, and on the additives was investigated. It is shown that, under the same drawing conditions, an increase in molar mass leads to greater orientation. Also, at very small draw rates the orientation in the samples containing calcium acetate is greater than in those containing manganese acetate.

Influence of molar mass and of nucleating agents on the orientation of polyethylene terephthalate

Influence of molar mass and of nucleating agents on the orientation of polyethylene terephthalate