Chemical structure, Influence

Learning to recognize the properties of a substance by examining a chemical formula is an important part of mastering chemistry. Fortunately, common acids and bases fall into a small number of structural categories. In this section we describe how to recognize acids and bases, hi Section 17-1 we explain how chemical structure influences acidity. 

The emulsifying properties of these polymeric surfactants demonstrate that the chemical structure influences the kinetic behaviour of interfacial tension reduction. An increase of sulfopropyl moieties reduces the interfacial tension slower while an increase in 2-hydroxy-3-phenoxy propyl moieties reduces the interfacial tension faster. The ionic strength of the emulsion appears to increase the rate of tension reduction. The average droplet size of oil-in-water emulsions in presence of previously dissolved 2-hydroxy-3-phenoxy propyl sulfopropyl dextran is around 180 nm immediately after preparation and increases with time. The presence of ionic moieties appeared to facilitate emulsification at low polymer concentrations due to electrostatic repulsions between the oil droplets [229]. 

The simple test system with wheat coleoptiles made it possible to extensively study how chemical structure influences activity. It was found that an auxin (or antiauxin) had to have ... 

The chemical and physical characteristics of plastics are derived from the four factors of chemical structure, form, arrangement, and size of the polymer. As an example, the chemical structure influences density. Chemical structure refers to the types of atoms and the way they are joined to one another. The form of the molecules, their size and disposition within the material, influences mechanical behavior. It is possible to deliberately vary the crystal state in order to vary hardness or softness, toughness or brittleness, resistance to temperature, and so on. The chemical structure and nature of plastics have a significant relationship both to properties and the ways they can be processed, designed, or otherwise translated into a finished product (Figures 3.8 and 3.9). 

The effect of the urea linkage (in the HS), on the extent of phase separation and other polymer properties can be revealed by the study of polymers thermal behaviour (TGA and DSC). As seen in Table 4.18, the chemical structure influenced the PUUs thermal stability. The materials PUUi had 5% weight loss temperatures (T5) ranging between 285 - 315 C, while those of materials PUDB and PUMD were of 191 -265°C. Polymers PUU1-4 showed DTG maxima between 375 -440°C, the highest value belonging to PUU obtained with DBDI and PTMO. 

So in this volume we shall start by examining the chemical molecular structure of plastics and rubbers, and then the shapes of the molecules and how these change under the constraints of temperature, time and available space. At this point we shall consider how the chemical structure influences the bulk morphology, and how this in turn affects the molecular motion.With an understanding of the dynamics of molecular movement and the morphology, we go on to examine the ways that these influence the bulk mechanical properties. 

Paul J. Flory addressed the problem of predicting the shape of a polymer molecule and so provided an understanding of the way in which chemical structure influences conformational changes in polymers. His approach was essentially an extension of that presented above for pentane and the substituted hexanes. He considered that the range of the important interactions was very short. This approximation is surprisingly accurate and has allowed theoretical prediction of the equilibrium structures of many polymers, at least when the molecules are present as separate entities in dilute solution. 

Physical aging processes are influenced by chemical structure insofar as it is partly responsible for molecular chain length, tacticity, branching, and the arrangement of substituents. Thus, chemical structure influences the formation of physical structure and morphology of plastics. 

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