Chain conformation and viscometric behaviour of high molecular weight polystyrene in solvent/nonsolvent mixtures

Summary Viscometric studies on high molecular weight polystyrene in solvent/nonsolvent binary mixtures are reported. Polymer behaviour is affected by the preferential adsorption phenomena determining the appearance of two theta temperatures, one intramolecular (B=0, -1) and the other intermolecular (A₂=0). For very high molecular weight polystyrene, theta intramolecular strongly approaches theta intermolecular due to a decrease in selective adsorption and in the vicinity of the theta condition the conformation transitions disappear.     

The reinforcement of polystyrene and poly(methyl methacrylate) interfaces using alternating copolymers

Asymmetric double cantilever beam studies are presented that document the ability of alternating copolymers to strengthen a polymer/polymer interface. For polystyrene/poly(methyl methacrylate) interfaces, these results show that the alternating copolymer is the least effective sequence distribution of a linear copolymer at strengthening the polystyrene/poly(methyl methacrylate) interface, where the copolymers that are compared all have similar molecular weight and composition. The results also demonstrate that the effect of copolymer molecular weight on the ability of the copolymer to strengthen an interface is controlled by the balance between the increased entanglements and decreased miscibility of the copolymer with the homopolymers with increasing molecular weight.     

Preferential adsorption coefficient of polymers

The recent formulation of the preferential adsorption coefficient, λ, which takes into account differences in molecular contact surface and in free volume, is tested by comparing theoretical with experimental values of λ from the literature. Seven different systems containing polystyrene and poly(methyl methacrylate) are considered. Agreement between theory and experiment is reached by treating the contact surface of the polymer as a fitting parameters, s. The adjusted values of s are: (a) systematically higher than the ones calculated from chain geometry; (b) largest in systems containing specific interactions (methanol). The connection between this enhanced apparent contact surface of the polymer and the ternary interaction parameter of the classical theory of λ, is analysed.     

The Strength of an Adhesive Weak Boundary Layer

The strength of model adhesive joints composed of different thicknesses of low (10,300 narrow distribution) molecular weight polystyrene sandwiched between high molecular weight poly(methyl methacrylate) has been studied. The joints model a polymer-to-polymer adhesive bond across a low-strength boundary layer. As an appraisal of strength, the fracture toughness was measured by driving a cleavage wedge into the specimens along the polystyrene layer and analyzing the results with Kanninen's equation. The fracture toughness for both crack growth initiation K_Ic and arrest K_Ia was essentially that for bulk poly(methyl methacrylate) until the polystyrene layer exceeded 1 μm, at which K_Ic and K_Ia fell by approximately 85%. Examination of the fracture surfaces of specimens with polystyrene layers less than 1 μm thick revealed that the fracture path was predominantly in the poly(methyl methacrylate). Possible reasons for this are discussed.     

An experimental study of adsorption of polymers on activated carbon: Butadiene—styrene polymers and poly(methyl methacrylate)

An experimental study of the extents and rates of adsorption of several polymers from various solvents onto activated carbon has been carried out. The polymers studied included polystyrene, polybutadiene, butadiene–styrene copolymers and poly(methyl methacrylate). The solvents included toluene, cumene, decalin, 2-pentanone, and methyl ethyl ketone (MEK). Polystyrene is adsorbed from the different solvents in the order MEK, 2-pentanone, cumene, toluene, decalin. The adsorption from toluene, decalin, and cumene is in the order polystyrene, polybutadiene butadiene—styrene copolymer. The fact that the copolymer is adsorbed less than either homopolymer is striking. The variation of molecular weight distribution with extent of adsorption has been studied. It was found that low molecular weight polymer was preferentially adsorbed in the early stages of the experiment, but high molecular weight polymer was adsorbed at longer times. The apparent adsorption rate constants have been evaluated for the various systems and resolved into external mass transfer, internal (intraparticle) mass transfer, and adsorption rate constants. The experimental data have been applied to the prediction of the elution of the polymers from chromatographic columns packed with activated carbon.     

Further evidence for the effects of critical concentration fluctuations on the diffusion-controlled reaction kinetics in binary polymer mixtures

Summary Kinetics of the intramolecular photodimerization reaction of a molecular probe, 9-(hydroxymethyl)-10-[(Naphthylmethoxy)-methyl] anthracene (HNMA) was studied in the miscible region of binary polymer mixtures. Poly(ethylene oxide)/poly(methyl methacrylate)(PEO/PMMA), polystyrene/poly(vinyl methyl ether) (PSH/PVME) and deuterated polystyrene/poly(vinyl methyl ether) (PSD/PVME) mixtures were used as binary polymer blends. It was found that the reaction kinetics is strongly affected by the concentration fluctuations in the vicinity of the coexistence curve. These behavior are consistent with the magnitude of the binary interaction parameters X estimated from the small-angle neutron-scattering and the melting point depression data. These experimental results confirm the fact that the reaction kinetics of HNMA reflects the concentration fluctuations with the wavelength comparable to the dimension of the probe.     

Crazing and acoustic emission in poly(methyl methacrylate)/acetone and polystyrene/methanol systems

Craze initiation and growth in the poly(methyl methacrylate)/acetone and polystyrene/methanol systems was studied using photographic and acoustic emission techniques. The poly(methyl methacrylate) system was the only one that produced detectable acoustic emission; however, it was found that craze initiation occurs predominantly in the first half of a sample's lifetime while acoustic emission is detected predominantly in the second half. The detected acoustic emission in the poly(methyl methacrylate) system is believed to be due to the rupture of craze fibrils. Craze initiation in both polymer systems was found to be dependent on stress and time with higher stresses initiating more crazes at earlier times. Although the craze growth rate in both systems exhibited extreme variability, the average growth rate tended to increase with craze size and applied stress. In the poly(methyl methacrylate) system, craze velocity was independent of time but in the polystyrene system it decreased with time. None of the existing craze growth theories were capable of explaining these results.     

Preparation and Characterization of Poly(Methyl Methacrylate) Microbeads by Dispersion Polymerization: Effects of the Medium Composition,Monomer Concentration,Thermal, and Optical Properties

This study investigated the relationship between particle size, particle distribution, thermal, and optical properties of poly(methyl methacrylate) microbeads using dispersion polymerization under various methanol/water (MeOH/H₂O) dispersion medium ratios and methyl methacrylate acid concentrations. The particle size of the poly(methyl methacrylate) microbeads increased when the medium solubility and monomer concentration increased simultaneously. In addition, the molecular weight and polydispersity of the poly(methyl methacrylate) microbeads were increased as the methanol ratio increased. The refractive index increased as the content of the poly(methyl methacrylate) microbeads increased with wavelengths of 546 and 589 nm.     

Graft polymerization of methyl methacrylate onto wool initiated by a hydrogen peroxide-sodium thiosulphate redox system. Part II kinetics and mechanism of the grafting reaction

Methyl methacrylate was grafted onto wool in the presence of an aqueous dioxane solution with a hydrogen peroxide-sodium thiosulphate initiator system, using the optimum conditions found in our previous paper¹⁹. It was stated that up to 90% conversion for the rate of reaction the following equation holds: \documentclass{article}\pagestyle{empty}\begin{document}${\rm R}_{\rm p} = - \frac{{{\rm d}\left[ {\rm M} \right]}} {{{\rm dt}}} = {\rm K} \cdot \left[ {\rm M} \right]^{1.5}$\end{document} where R_p is the overall rate of the graft polymerization, and [M] is the monomer concentration at the time t. The degree of polymerization of the isolated poly(methyl methacrylate) was found to be linearly proportional with the monomer concentration [M]. Investigations of the effect of the ratio of solvent to monomer concentration [S]/[M] on the reciprocal of the degree of polymerization showed that there was no chain transfer caused by the solvent dioxane. The number average molecular weight M?_n of the polymer separated from the grafted wool was found to be within the range of 3–15.9 × 10⁶ as determined by viscosimetry. The molecular weight distribution of the isolated poly(methyl methacrylate) samples was determined by turbidimetric titration. The following relationship was established between the volume fraction of the non-solvent, γ and the number average molecular weight M?ⁿ. of poly(methyl methacrylate): \documentclass{article}\pagestyle{empty}\begin{document}$\gamma = - 0.0285 + \frac{{50.54}}{{\sqrt[3]{{\overline M _n }}}}. $\end{document} The molecular weight distribution curves were found to be rather homogeneous indicating approximately the same chain length of the grafted poly(methy1 methacrylate) on the wool backbone. It was stated before³³ that the number average molecular weight could be determined from the inflection point of the turbidimetric curves. This method can be used for determining the molecular weight of all kinds of poly(methy1 methacrylate) occurring in practice.     

Nonaqueous poly(methyl methacrylate) dispersions: radical dispersion polymerization in the presence of AB block copolymers of polystyrene and poly(dimethyl siloxane)

Well defined AB block copolymers of polystyrene (PS) and poly(dimethyl siloxane) (PDMS) have been prepared with PS molecular weights in the range 8 800 to 43 600 and PDMS molecular weights in the range 2 400 to 48 000. Provided the PS and PDMS molecular weights have a ratio within the range 0.5 to 4.0, these block copolymers stabilize particles of poly(methyl methacrylate) in n-alkanes. The particle size over the range 0.1 to 0.5 μm may be varied by performing dispersion polymerizations of methyl methacrylate as a function of monomer content of the seed stage and as a function of the concentration, molecular weight and composition of the block copolymer. From silicon analyses of the poly(methyl methacrylate) particles, values of the surface area stabilized per PDMS chain were established. The results indicate complete surface coverage of the particles.     

A contribution to the fractionation of polystyrene — poly-(alpha-methylstyrene) mixture using the methyl ethyl ketone — benzene/methanol system

Summary The fractionation of polystyrene, poly(alpha-methylstyrene) and physical mixture of these homopolymers in methyl ethyl ketone — benzene/methanol system was investigated. The solubility of poly(alpha-methylstyrene) increases with the decreasing of molecular weight and becomes similar to polystyrene at ¯M_w 29,000. Polystyrene and poly(alpha-methylstyrene) which precipitate simultaneously have different molecular weight and can be further separated by another method.     

The melt elasticity of polymer blends: Polystyrene/poly(methyl methacrylate)

Samples of general-purpose polystyrene and poly(methyl methacrylate) were melt blended in a special mixer–extruder over the complete range of compositions from 100% polystyrene to 100% poly(methyl methacrylate). The blends were characterized for their melt rheological characteristics in a melt elasticity tester which measured their stress–strain behavior and strain recovery characteristics as a function of time. In addition, the blends were processed through a laboratory fiber spinning apparatus wherein the spinline tension was measured. Large maxima in the amount of recoverable strain, in the time for the strain recovery to finish, and in the melt tension were observed at a weight percent composition of 40% polystyrene and 60% poly(methyl methacrylate). The melt stress-strain curves showed double yield points at certain compositions. The results are discussed in terms of a model consisting of two interpenetrating continuous phases.     

Effects of solvent and concentration on scission of polymers with high-speed stirring

The effects of solvent and concentration on scission of polymers such as poly(methyl methacrylate) (PMMA) and polystyrene (PSt) in solution by high-speed stirring were investigated. Solvents were chloroform (good), benzene (intermediate), and ethyl acetate (poor) for PMMA and methyl ethyl ketone (good), toluene (intermediate) and dioxane (poor) for PSt, respectively. Concentration was varied from 0.04 to 2% w/v. The rate of scission of polymer chains was higher and the final molecular weight was lower in a good solvent than in a poor solvent at a low concentration for both polymers, but vice versa at a high concentration except for PSt in methyl ethyl ketone. Concentration dependence of the scission was large in a good solvent but small in a poor one. Polymer chains were ruptured to lower molecular weights with decreasing concentration, regardless of kind of polymer and solvent, showing that they were more easily broken in the isolated state.     

Method for gel permeation chromatography calibration and the evaluation of Mark–Houwink constants

A novel and simple method is described for evaluation of the Mark–Houwink constants and developing of GPC calibration curve for a polymer where only broad molecular weight distribution samples are available. The method demands the GPC calibration curve for polystyrene and measurement of the intrinsic viscosity and GPC chromatogram of several samples. Results of applying the procedure to polystyrene and poly(methyl methacrylate) are presented.     

Microindentation studies at the near surface of glassy polymers: Influence of molecular weight

The viscoelastic‐plastic properties of various amorphous, glassy polymers [polystyrene (PS), poly(styrene‐acrylonitrile) copolymer (SAN), poly(methyl methacrylate) (PMMA), poly(vinyl chloride) (PVC), polycarbonate (PC)] in the micron and submicron range were investigated by means of load‐displacement analysis from depth‐sensing experiments. Hardness and Young's modulus values decrease rapidly with increasing depth up to a few microns. New data on the glass transition temperature correlation with microhardness are presented. The influence of annealing below the glass transition temperature upon the microhardness for various glassy polymers is pointed out. For PS, the influence of the molecular weight variation and molecular weight distribution on the microhardness is reported. Results are discussed on the basis of an entanglement network model, recently developed to explain the fine structure of crazes in amorphous polymers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1951–1956, 2004     

Polyester resin as a compatibilizing agent for some polymeric blends

Dielectric and viscosity techniques were used to determine the degree of the compatibility of poly(methyl methacrylate)/polycarbonate, poly(methyl methacrylate)/ polystyrene, and polycarbonate/polystyrene blends in different ratios (25/75, 50/50, and 75/25 w/w). The effect of the addition of 5, 10, and 20% concentrations of the prepared polyester resin [poly(butylene terephthalate adipate)] on the compatibility of these blends was studied. The dielectric properties were measured over a frequency range (from 100 Hz to 100 kHz) at various temperatures covering the glass‐transition temperatures of the polymers used (from 30 to 170°C). It was found from the dielectric and viscosity measurements that the addition of 10% polyester to poly(methyl methacrylate)/polycarbonate, 20% polyester to poly(methyl methacrylate)/polystyrene, and 5% polyester to polycarbonate/polystyrene blends enhanced the degree of compatibility of such blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preferential and absolute adsorption on poly(l-glutamic acid) in water — dioxane mixtures

The preferential adsorption exhibited by poly(l-glutamic acid) (PLGA) in water-dioxane mixtures has been determined by measuring the specific refractive index increments at constant concentration and at constant chemical potential. These measurements have been carried out at two values of pH (12 and 4.5) and in the presence or in absence of a strong electrolyte (NaCl). At pH 12, in the absence of dioxane, the conformation of the PLGA macromolecule is an ionized chain. When adding low concentrations of dioxane (whether NaCl is present or not) a preferential adsorption of dioxane takes place. While increasing the dioxane concentration the preferential adsorption of dioxane increases and then after passing through a maximum, it decreases and an inversion of the preferential adsorption is observed at higher concentrations of dioxane, water being now preferentially adsorbed. The conformation of PLGA is α-helical, showing that a transition takes place from a disordered ionized state to an ordered one by the addition of dioxane. At pH 4.5, in the absence of dioxane, the conformation of PLGA is α-helical. When adding dioxane in the presence of NaCl, a preferential adsorption of dioxane occurs. While increasing the dioxane concentration no change of the preferential adsorption is observed.     

Inhibition of thin polystyrene film dewetting via phase separation

By addition of a small amount of poly(methyl methacrylate) (PMMA) into polystyrene (PS), we present a novel approach to inhibit the dewetting process of thin PS film through phase separation of the off-critical polymer mixture (PS/PMMA). Owing to the preferential segregation of PMMA to the solid SiO_x substrate, a nanometer thick layer, rich in PMMA phase, is formed. It is this diffusive PMMA-rich phase layer near the substrate that alters the dewetting behavior of the PS film. The degree of inhibition of dewetting depends on the concentration and molecular weight of PMMA component. PMMA with low (15.9k) and intermediate (102.7k) molecular weight stabilizes the films more effectively than that with a higher molecular weight (387k).     

Effects of drawing conditions on the properties of optical fibers made from polystyrene and poly(methyl methacrylate)

Monofilaments possessing various degrees of birefringence were obtained by changing the drawing rate, the molten polymer temperature, and the molecular weight of polystyrene (PS) and poly(methyl methacrylate) (PMMA). The “brittle-toductile” transition point of optically pure PS was found in the range of birefringences of ?0.6 · 10^?3 to ?2.6 · 10^?3. Both the height and position of this point are influenced by M?_w, molecular weight distribution, and polymer melt temperature. The birefringence of PS is higher by two orders of magnitude than that of PMMA in which this transition point has not been observed. The mechanical and optical properties depend not only on the average amount of orientation characterized by the birefringence but on what portion of the relaxation spectrum of the polymer is preferentially oriented. During the drawing of PS and PMMA monofilaments crazes are formed in the centre of the fibers and do not reach the surface.     

Preferential adsorption in polymer/solvent-1 /solvent-2 solutions by infrared spectroscopy

IR spectroscopy is shown to be a suitable technique for preferential adsorption studies in the following solvent-1/solvent-2/polymer systems: poly(N-vinylcarbazole) and polyacenaphthene in nitrobenzene/dioxane, nitrobenzene/ tetrahydrofuran, and nitrobenzene/cyclohexanone. Values of the preferential adsorption parameters derived from the Schultz-Flory theory agree with those from IR when both solvents in the ternary system are considered to be good solvents for the polymer. In the systems studied, the relative adsorptions of solvent-1 and solvent-2 by the polymer depend on the solvent mixture composition. The number of adsorbed molecules and their performance are correlated with the ternary interaction parameters, X_m3, and the Mark-Houwink-Sakurada exponent, a′. The adsorption changes observed are greater in those systems in which tetrahydrofuran was present.