Graft Copolymerization of Methacrylic Acid, Acrylic Acid and Methyl Acrylate onto Styrene–Butadiene Block Copolymer

Methyl acrylate, methacrylic acid, and acrylic acid have been graft copolymerized onto styrene–butadiene block copolymer. All three monomers react through the macroradical interacting with the double bond of butadiene. The site of reaction has been established by infrared spectroscopy. For methyl acrylate every unit of the styrene–butadiene block copolymer is grafted but only a small fraction is grafted when the acids are used. The difference apparently lies in the fact that the reaction with the ester is homogeneous while with the acids the reactions are heterogeneous

Polyethylene and Polypropylene Nanocomposites based upon an Oligomerically-Modified Clay

Montmorillonite clay was modified with an oligomeric surfactant, which was then melt blended with polyethylene and polypropylene in a Brabender mixer. The morphology was characterized by X-ray diffraction and transmission electron microscopy, while thermal stability was evaluated from thermogravimetric analysis and the fire properties by cone calorimetry. The nanocomposites are best described as mixed immiscible/intercalated/delaminated systems and the reduction in peak heat release rate is about 40% at 5% inorganic clay loading

Poly(Methyl Methacrylate), Polypropylene and Polyethylene Nanocomposite Formation by Melt Blending using Novel Polymerically-Modified Clays

Two new organically-modified clays that contain an oligomeric styrene or methacrylate have been prepared and used to produce nanocomposites of poly(methyl methacryate), polypropylene and polyethylene. Intercalated nanocomposites and, in some cases, exfoliated or mixed intercalated/exfoliated nanocomposites of all of these polymers have been produced by melt blending in a Brabender mixer. The use of the styrene-containing clay permits the direct blending of the clay with polypropylene, without the usual need for maleation, to produce the nanocomposites. The systems have all been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, cone calorimetry and the measurement of mechanical properties. These novel new clays open new opportunities for melt blending of polymers with clays to obtain nanocomposites with important propertie

Polystyrene Nanocomposites based on Carbazole-Containing Surfactants

New organically-modified clays containing a carbazole unit were prepared and the number of long alkyl chains on the surfactant was varied. The clay was used to prepare polystyrene nanocomposites by both bulk polymerization and melt blending. The dispersion of these clays in the polymer matrix was evaluated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal stability of the clays and the nanocomposites were analyzed by thermogravimetric analysis (TGA) while the fire properties were evaluated by cone calorimetry. If more than two alkyl chains were present, the gallery spacing is apparently overcrowded, leading to poor dispersion. Bulk polymerization gave nanocomposites with better dispersion and reduced flammability when compared to the melt blending process

Thermal and Flame Properties of Polyethylene and Polypropylene Nanocomposites Based on an Oligomerically–Modified Clay

An oligomerically-modified clay was made using a surfactant which is the ammonium salt of an oligomer. The newly modified clay contains 37.5% inorganic clay and 62.5% oligomer. Polyethylene and polypropylene nanocomposites were made by melt blending the polymer with the oligomerically-modified clay in a Brabender mixer at various clay loadings. The structure of the nanocomposites was characterized by X-ray diffraction and transmission electron microscopy. Mechanical testing showed that the polyethylene nanocomposites had an enhanced Young\u27s modulus and slightly decreased elongation, while the changes for polypropylene nanocomposites are small compared with the virgin polymers. The thermal stability and flame properties were evaluated using thermogravimetric analysis and cone calorimetry, respectively. The plasticising effect of the oligomer was suppressed because of the increased inorganic content. The maximum reduction in peak heat release rate is about 40%

Relation between the concentration of adrenaline and its action

It is a remarkable fact upon which several authors have commented that, despite the great mass of research which has been undertaken into the manner in which drugs produce their effects upon the animal body, very few attempts have been made to determine the influence of the dosage of the drug upon its effects. This is the more surprising when it is borne in mind that an accurate understanding of the relation between the dosage and the effect of a drug is essential for the scientific administration of remedies. It is true that spasmodic attempts were made from time to time to repair this gap in the structure of pharmacological science, but these attempts lacked the accurate observation of simple reactions between the drug and the tissues which is the fundamental requisite in this branch of study, and were based too largely on speculative assumptions to constitute any advance. It is only within the last three or four years that the subject has been investigated along strictly scientific lines. Studies in the relation between the concentration and the action of a drug fall into two large groups. In the one group, the action is an irreversible one: the cells are destroyed by the action of the drug. The disinfectants are the chief members of this group. The haemolysins also belong to this group and have been very thoroughly studied by several workers. When the action of such substances is examined it is found that the concentration- action curves have a characteristic S-shaped form. ( By "concentration -action "curve is meant the curve which is obtained when the action expressed as the percentage of the maximum possible action is plotted against the corresponding concentration). The shape of these curves is explained as follows. It is assumed that the cells offer a definite resistance to the action of any agent which is liable to destroy them. But the resistances offered by individual cells vary considerably in degree and the sigmoid form of the curves is in fact due to these resistances being distributed among the cells in accordance with the law of probability. In the other group are placed all those drugs whose action is reversible: that is the drug produces a stimulation or a depression of the special function of the tissue and from this stimulation or depression the tissue recovers completely when the drug is removed. Most of the drugs used in therapeutics belong to this group and among them is adrenaline. It might be anticipated that the concentration-action curves in this would have a different form from the frequency curves of the previous group, since the question of resistance to destruction by a toxic agent does not arise. This anticipation is realised by the work of Clark and by the experiments which will be described later in this paper. Two independent investigators, however, claim to have obtained S- shaped concentration- action curves from adrenaline, a drug whose action is clearly reversible. These claims fall to be discussed in detail in a later section, when reasons will be brought forward for rejecting them as mistaken. Meantime it may be taken that the two groups of drugs exist and have a fundamentally different mode of action. As adrenaline is a member of the second group, the remainder of the discussion in this section will be confined to this group. The next question to be considered is how drugs with reversible actions do produce their effects upon the cells of a tissue. The work of Straub was the first attempt to throw light upon this matter. Straub examined the actions of a number of drugs on the hearts of the frog and of Aplysia. He found that in the cases of veratrin, morphine, and strychnine, the maximum action coincided with the maximum content of the drug in the heart muscle cells themselves;: whereas in the cases of muscarine and atropine a maximum action was produced although the heart muscle cells themselves contained little or no drug; the surrounding fluid, however, had a high percentage of the drug. Thus he subdivided this group of drugs with reversible reactions into two sub-groups: (a) Concentration poisons, of the veratrin type, in which the action depends on the concentration of the drug attained in the cells; (b) Potential poisons, of the muscarine type. Straub applied the term "potential poison" to muscarine since the action appeared to depend on the difference in concentration of the poison within the cell and in the fluid surrounding the cell. He considered that pilocarpine and adrenaline also belonged to this group. The potential poisons have attracted much more attention from investigators than the concentration poisons and as adrenaline is believed to be a member of the group, it is necessary to discuss them further. Straub's theory of their action was that as the drug entered the cell it produced a change at the surface which was responsible for the effect produced: this surface change was dependent on the actual transit of molecules through the cell membrane Straub thought that the entry of the drug into the cell actually antagonised the action of the drug, the concentrations outside and within the cell becoming the same. This view has been challenged. It implies that when a solution of one of these potential poisons is brought into contact with a tissue, the tissue undergoes a change of state from which it later recovers even although it is still bathed in the solution which produced the original change. But while such effects have been observed they are not invariable. Thus Clark points out that no recovery occurs when the frog's heart is exposed for long periods to atropine solutions, and the same is true of the action of nicotine on the rectus abdominis of the frog; moreover,even in the case of those drugs which do show the recovery effect, it is found to be inconstant. The action of these drugs therefore cannot be ascribed merely to the difference in concentration of the poisons outside and inside the cell; it is not due to a surface change which is dependent on the entry of the drug into the cell. Recent work has, however, confirmed Straub's belief that these drugs act upon the surface of the cell. Thus Clark found that the action produced by acetyl choline on the frog's heart and the amount of acetyl choline taken up by the heart cells bore no relation to one another. Cook in a study of the antagonism of acetyl choline by methylene blue found that heart cells adsorb methylene blue slowly, this adsorptive action being irreversible, but that the action of methylene blue in antagonising acetyl choline was rapidly produced and as rapidly removed by washing out the dye. He adds that a heart can regain its full sensitivity to acetyl choline although it is deeply stained by methylene blue. These experiments show very clearly that these drugs produce their effects by causing some change at the surface of the cell, and that this process is quite independent of the entry of the drug into the cell. What is, then, the nature of this change which occurs at the surface of the cell? One possibility is that it may consist in the formation of a continuous layer of molecules of the drug over the surface of the cell. This is negatived, however, in the case of acetyl choline at any rate, by Clark's finding that the area of the cell surface is about two hundred times greater than the area occupied by the number of molecules required to produce an action on the cell. Another possibility is that the drug may undergo some sort of reversible combination with specialised receptors in the cell. This idea has been adopted by many workers and in particular unimolecular formulae have been applied to explain the relation between the concentration and the action of drugs. Arrhenius attempted to explain even some irreversible reactions,; viz. haemolyses, in this way, but this suggestion is now discredited. In the case of reversible reaction however the case is different. For, turning again to Clark's work upon acetyl choline we find that acetyl choline acts upon the heart over a ten - thousand fold range of concentration in accordance with the formula: Kx=y/(100-y) where x = molar concentration of the drug; y = action expressed as percent. of maximal action; K = constant This at once suggests that the drug acts by combining with some receptor in the cell according to a unimolecular reaction. The number of receptors in the tissue must be assumed to be limited while the molecules of drug are in great excess. The success which attended the application of the formula mentioned to the actual observations suggested the need for an investigation to determine how far the actions of other members of the potential poison group could be explained in the same manner. The present paper describes a study of the action of adrenaline on the pain muscle coats of the arteries, from this point of view. The action of adrenaline on the blood pressure is afterwards discussed, after the fundamental relation between the concentration and the action has been established. The later discussion is concerned mainly with the various modifications introduced into the fundamental relation by the conditions of the circulation, physical or, physiological

Fire properties of styrenic polymer–clay nanocomposites based on an oligomerically-modified clay

An oligomerically-modified clay has been used to fabricate nanocomposites with styrenic polymers, such as polystyrene, high-impacted polystyrene, poly(styrene-co-acrylonitrile) and acrylonitrile–butadiene–styrene by melt blending. The clay dispersion was evaluated by X-ray diffraction and bright field transmission electron microscopy. All of the nanocomposites have a mixed delaminated/intercalated structure. The fire properties of nanocomposites were evaluated by cone calorimetry and the mechanical properties were also evaluated

Methyl Methacrylate Oligomerically-Modified Clay and its Poly (Methyl Methacrylate) Nanocomposites

A methyl methacrylate oligomerically-modified clay was used to prepare poly(methyl methacrylate) clay nanocomposites by melt blending and the effect of the clay loading level on the modified clay and corresponding nanocomposite was studied. These nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry. The results show a mixed intercalated/delaminated morphology with good nanodispersion. The compatibility between the methylacrylate-subsituted clay and poly(methyl methacrylate) (PMMA) are greatly improved compared to other oligomerically-modified clays

Novel Polymerically-Modified Clays Permit the Preparation of Intercalated and Exfoliated Nanocomposites of Styrene and its Copolymers by Melt Blending

Two new organically-modified clays have been made and used to produce nanocomposites of polystyrene, high impact polystyrene and acrylonitrile–butadiene–styrene terploymer. At a minimum, intercalated nanocomposites of all of these polymers have been produced by melt blending in a Brabender mixer and, in some cases, exfoliated nanocomposites have been obtained. The systems have all been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, cone calorimetry and the measurement of mechanical properties. These novel new clays open new opportunities for melt blending of polymers with clays to obtain nanocomposites with important properties

Study on the thermal stability of Polystyryl surfactants and its modified clay nanocomposites

Five oligomeric styrene surfactants, N,N,N-trimethylpolystyrylammonium, N,N-dimethyl-N-benzylpolystyrylammonium, N,N-dimethyl-N-hexadecylpolystyrylammonium, 1,2-dimethyl-3-polystyrylimidazolium, and triphenylpolystyrylphosphonium chlorides were synthesized and used to prepare organically modified clays. Both styrene and methyl methacrylate nanocomposites were prepared by melt blending and the type of nanocomposite was evaluated by X-ray diffraction and transmission electron microscopy. The thermal stability of the organically modified clays and the nanocomposites were studied by thermogravimetric analysis; these systems do give clays which have good thermal stability and may be useful for melt blending with polymers that must be processed at higher temperatures