Showing papers on "Polystyrene published in 1975"

Diffusion and partitioning of macromolecules within finely porous glass

Abstract: Measurements of diffusion and partitioning of nearly monodisperse polystyrene, having molecular weights of from 600 to 670,000, in chloro-form and dichloroethane and of two proteins in aqueous solution were made with leached borosilicate glass cubes having a narrow pore size distribution and pore radi of from 2.5 to 47.6 nm. With increasing ratio of molecular to pore size, the partition coefficient for all solutes decreased; the ratio of effective to bulk diffusivity decreased for the proteins but remained constant for polystyrene. This suggests that polystyrene behaved like a free-draining macromolecule under the conditions of this study.

New useful reagents for peptide synthesis. Insoluble active esters of polystyrene-bound 1-hydroxybenzotriazole.

Abstract: Insoluble 1-hydroxbenzotriazole-bound polystyrene was prepared through a series of chemical modifications of commercially available polystyrene. Reaction of 3-nitro-4-chlorobenzyl alcohol or of 3-nitro-4-chlorobenzyl bromide with polystyrene in the presence of aluminium trichloride yielded (3-nitro-4-chloro)benzylated polystyrene. Upon reaction with hydrazine it was converted to (3-nitro-4-hydrazine) benzylated polystyrene which was cyclized, by acidolysis, to yield 1-hydroxybenzotriazole-bound polystyrene. This was coupled, using N, N' -dicyclohexylcarbodiimide as the coupling agent, to many N-blocked amino acid derivatives, yielding polymeric polystyrene-bound active esters. Such derivatives are highly reactive and their efficacy in the synthesis of several peptides, including that of the tetrapeptide Boc-L-Leu-L-leu-L-Val-0bzl-L-Tyr-0Bzl and of thyrotropin-releasing hormone was demonstrated.

The mechanism of crazing in polystyrene

Abstract: Under tensile strain the inhomogeneous surface microstructure of thin polystyrene films gave rise to the formation of ∼300 A nuclei in which large strains were localized even at the glass transition. At lower temperatures these nuclei coalesced into disk-shaped microneck zones. Fibril formation within these zones and a stable craze structure was possible only with molecular weights higher than 10,000 to 37,500.

Polyurethane—polystyrene interpenetrating polymer networks

Abstract: Two component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks), composed of a polystyrene network (crosslinked with divinyl benzene) and a polyester-polyurethane network (crosslinked with trimethylolpropane), were made. Electron microscopy and glass-transition measurements showed that phase separation had resulted with some interpenetration, presumably occurring at the boundaries. At a composition of about 75 percent polyurethane, a phase inversion occurred, the continuous phase being polystyrene at polyurethane compositions of less than 75 percent. The stress-strain properties and hardness measurements agreed with these results. Enhanced tensile strength was observed in the IPN's in a concentration range where modulus reinforcement was not evident. A small enhancement in tear strength and thermal stability was also noted.

Diluent effects on molecular motions and glass transition in polymers. I. Polystyrene–toluene

Abstract: The effects of diluent on molecular motions and glass transition in the polystyrene–toluene system was studied by means of dielectric, thermal, and NMR measurements. Three dielectric relaxations were observed between 80 and 400°K. On the basis of NMR measurements on solutions in toluene and in deuterated toluene, relaxation processes were assigned to segmental motions of polystyrene, rotations of toluene, and the local motions of polystyrene and toluene in order of appearance from the high-temperature side. The concentration dependence of the relaxation strength and of the activation energy for the primary relaxation (that at the highest temperature) show a step increment at about 50% by weight. The activation plots for the primary process were expressed by the Vogel–Tamman equation. With this equation, the temperatures at which the mean dielectric relaxation time becomes 100 sec is determined. This agrees well with the glass-transition temperature Tg and hence Tg in concentrated solution is expressed by in terms of the parameters A, B, and T0 of the Vogel–Tamman equation. The values of A and B are, respectively, about 12 and 0.65 and independent of the concentration. The physical meaning of these parameters is discussed.

Experiments with soap‐free polymerization of styrene in the presence of alcohols

Abstract: Polystyrene latexes have been synthesized by a method based on that Kotera et al.4 The polymerization rates and yields have been improved by the addition of an alcohol (methanol) to the reactants. The effects of varying the methanol content and other process variables on the polymerization and on the properties of the latex are reported.

Exclusion chromatography using porous glass. II. Application to hydrophilic polymers

Abstract: A chromatograph employing five columns packed with porous glass of pore size 1250 A to 75 A provided peak retention volumes (VR) that were reproducible and essentially independent of sample size and flow rate when aqueous eluents were used. Calibration was carried out with a series of dextran fractions and polystyrene sulfonate samples, both of moderately narrow molecular weight distribution. The universal calibration method, based on hydrodynamic volume, was tested for four different polymer types. All four types produced a common curve within experimental error, which indicates that absolute molecular weight distributions may be derived from aqueous exclusion chromatography data for at least these polymer types. Additional study using a higher salt concentration produced hydrodynamic-volume plots that superposed with those above. The use of the same set of porous glass columns with polystyrene standards in three different organic solvents produced calibration curves that agreed well with the aqueous curves after corrections were made for differences in available pore volumes.

Slow-release air freshener polymer-blend composition

Abstract: Slow-release air freshener compositions having favorable depletion characteristics comprise an odorant (perfume) intimately dispersed in a polymeric mixture comprising 10-50% by weight of a certain block copolymer, 2-10% by weight polystyrene and 30-50% by weight of ethylene vinyl acetate copolymer.

The distribution of stereochemical configurations in polystyrene as observed with 13C NMR

Abstract: 13C NMR configurational assignments are made for an amorphous polystyrene sample examined at 25.2 MHz and 120°C. The assignments are based strictly on a one-parameter Bernoullian fit that was in satisfactory agreement with the nine observed methylene relative intensities. The methylene regions of the 13C NMR spectra of a polystyrene were examined before and after hydrogenation of the side-chain phenyl substituents. It was concluded that ring current effects have influenced the 13C methylene chemical shifts substantially and are limited largely to contributions from adjacent phenyl substituents. In addition, aromatic substituent parameters are reported that can be used in conjunction with the Grant and Paul parameters for calculating chemical shifts in aromatic hydrocarbons and polymers. Finally, it is concluded that free-radical and n-butyllithium-prepared polystyrenes have essentially atactic structures with meso additions favored over racemic additions by approximately 55/45.

Viscoelastic behavior of polystyrene‐tricresyl phosphate solutions

Abstract: The viscoelastic behavior of solutions of a narrow molecular weight distribution polystyrene in tri-m-toly 1 phosphate has been determined from the glassy to the terminal zones of response. The polymer concentration was varied from one to 100% thereby providing for the first time a complete picture of the influence of a solvent on the time-dependent response of a polymer. A computer analysis, governed by human judgment, has been used to extract retardation spectra which can be used to regenerate the reduced recoverable creep compliance curves within the scatter bands of the data. With the resulting retardation spectra, dynamic compliance and moduli curves have been calculated.

Glass Transition Behaviors of Random and Block Copolymers and Polymer Blends of Styrene and Cyclododecyl Acrylate. I. Glass Transition Temperatures

Abstract: Glass transition temperatures have been studied for the random and block copolymers of styrene and cyclododecyl acrylate.The random copolymers showed a single glass transition temperature, which provided a concave glass transition temperature—composition curve. This concave relationship was fairly well represented by the modified Gibbs—Dimarzio equation of Uematsu and Honda, which includes the influence of the specific character of cyclododecyl acrylate as a monomeric unit.Each of the block copolymers as well as the blends of their component homopolymers showed two separated glass transition temperatures corresponding to the respective ones of poly(cyclododecyl acrylate) and polystyrene; these were independent of the total composition, owing to the incompatibility of the components.

Thickness variation in the thermoforming of poly(methyl methacrylate) and high‐impact polystyrene sheets

Abstract: The influence of material flow properties on the variation of wall thickness in a thermoformed part was investigated by measuring the thickness reduction at the pole of free-formed axisymmetric domes of poly(methyl methacrylate) and high-impact polystyrene. It was found that at a given pole height, the thickness reduction in poly(methyl methacrylate) was less than in high-impact polystyrene, i.e., the wall thickness in a part formed from poly(methyl methacrylate) will be more uniform than in a part formed from high-impact polystyrene by the same technique. This difference in formability was ascribed to a difference in the dependence of the flow stress σ at the thermoforming temperatures on time. The flow stress of both materials was given by σ = Ktm′ϵn, but whereas n was approximately 1 for both materials, m′ was −0.052 and −0.33 for poly(methyl methacrylate) and high-impact polystyrene, respectively. A physical argument and simple analysis led to the conclusion that a large (negative) value of the “stress relaxation index” in a material reduces the degree of uniformity of sheet thickness in a formed part.