Polymers causes

A plasticizer is a substance the addition of which to another material makes that material softer and more flexible. This broad definition encompasses the use of water to plasticize clay for the production of pottery, and oils to plasticize pitch for caulking boats. A more precise definition of plasticizers is that they are materials which, when added to a polymer, cause an increase in the flexibiUty and workabiUty, brought about by a decrease in the glass-transition temperature, T, of the polymer. The most widely plasticized polymer is poly(vinyl chloride) (PVC) due to its excellent plasticizer compatibility characteristics, and the development of plasticizers closely follows the development of this commodity polymer. However, plasticizers have also been used and remain in use with other polymer types. 

External Plasticizers. There are two distinct groups of external plasticizers. A primary plasticizer, when added to a polymer, causes the properties of elongation and softness of the polymer to be increased. These changes are brought about by mechanisms described below. A secondary plasticizer, when added to the polymer alone, does not bring about these changes and may have limited compatibiUty with the polymer. However, when added to the polymer in combination with a primary plasticizer, secondary plasticizers enhance the plasticizing performance of the primary plasticizer. For this reason secondary plasticizers are also known as extenders. 

Butadiene is also known to form mbbery polymers caused by polymerization initiators like free radicals or oxygen. Addition of antioxidants like TBC and the use of lower storage temperatures can substantially reduce fouling caused by these polymers. Butadiene and other olefins, such as isoprene, styrene, and chloroprene, also form so-called popcorn polymers (250). These popcorn polymers are hard, opaque, and porous. They have been reported to... 

Primary thermal processes where energy from an external source is applied to the polymer, causing a gradual rise in temperature. The rate of temperature rise will depend on the rate of supply of energy and on the thermal and geometrical characteristics of the material being heated. 

The low unsaturation requires powerful curing systems whilst the hydrocarbon nature of the polymer causes bonding problems. To overcome these problems chlorinated and brominated butyl rubbers (CIIR and BUR) have been introduced and have found use in the tyre industry. 

Insertion of styrene units into the macromolecules of AN polymers causing steric hindrances because of the threedimensional phenyl groups, results in an appreciable decrease of the rate of thioamidation in comparison with PAN. 

The conformation of a polymer in solution is the consequence of a competition between solute intra- and intermolecular forces, solvent intramolecular forces, and solute-solvent intermolecular forces. Addition of a good solvent to a dry polymer causes polymer swelling and disaggregation as solvent molecules adsorb to sites which had previously been occupied by polymer intra- and intermolecular interaction. As swelling proceeds, individual chains are brought into bulk solution until an equilibrium solubility is attained. 

Kovacina, T. A. et al., Ind. Eng. Chem., Prod. Res. Dev., 1983, 22, 170-172 The insoluble polymer formed in the liquid phase was pressure- and shock-sensitive and should not be heated above 25°C. Cutting with a razor or breaking the polymer causes detonation and ignition. 

Plasticisers are compatible and miscible with their host polymer causing them to swell and allowing them to be used for coating, moulding, spraying (when used as a suspension in a liquid solvent) or calendering, extrusion and injection moulding (when used as a polymer melt). 

Electrochemiluminescence Emission occurring in solution, from an electronically excited state produced by high-energy electron transfer reactions Electrogenerated chemiluminescence Emission produced at an electrode surface Oxyluminescence Emission from polymers caused by oxidative processes (presence of oxygen is required)... 

However, Ph2SnHCl is also consumed by two other side reactions. The first is precipitation of a polymer caused by basicity of MeO-. 

Electrostatic repulsion between high-energy electrons -produced from an accelerator, or by photon interaction with substrate atoms - and valency electrons in the polymer cause excitation and ionization. The chemical reactions result from these species. 

The use of so-called toners to improve the color has been described above. It should be remarked that all measures to overcome defects of a polymer caused by disregarding the basic principles of chemistry are rarely of durable success, because any additive will complicate or affect the polymeric system in an undesired way. 

The thermal stability and lightfastness of polyesters is particularly necessary for technical and high-performance applications. The modification of the polymer causes disorder and affects the stability as well as some other properties. PET modified by DEG suffers particularly from photo-oxidative reactions due to the presence of the sensitive ether bonds. These copolymers need special stabilization depending on the kind and degree of modification. The UV stability can also be influenced by the technology of the process, whereby slight improvements of DMT-based polymer are observed [29],... 

The heat-insulating properties of polymers cause some problems in the first phase of moulding, the hot temperature of the mould is transmitted slowly within the thermoplastic. If the part is rather thick, the softening and shaping of the core is very long. There is the same drawback for the cooling phase. 

The marked variation in stereostructure of diene polymers caused by changes in the counter-ion and solvent when butadiene or isoprene are polymerized anionically, are as yet not fully explained. Much progress has been made on elucidating the causes of variations in the cis/trans ratio of the l h structures in these systems (], , ), but the causes of the change in the ratio of 1 2 to 1 U structures in butadiene for example has been left largely unresolved. In dioxane, for instance, the amount of 1 2 structure decreased from with Li counter-ion at 15°, to hl% with Cs (I4). Less variation is found in THF because a substantial part of the reaction is carried by the free ion. Changes are also observed in polyisoprene ( ). 

Careful preliminary tests were necessary to demonstrate the suitability of these methods for the present study. In particular, it was necessary to verify that the radioactivity detectable in the polymer may not be caused by contamination or other processes different from the ones taken into consideration. It was then found that it is possible to remove throughly from the polymer the last traces of unreacted ethylaluminum or of its soluble complexes with titanium compounds by washing with anhydrous hydrocarbon. No alkylation of the preformed polymer caused by triethylalu-minum or its derivatives has been observed (4 ). 

Before carrying out such determinations in an attempt to estimate the number of active centers correctly, it has been necessary to define the magnitude of the eventual radioactive contaminations of the polymers, caused by phenomena extraneous to the polymerization process. 

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