Effects of Chemical Structure

Although these factors have been intensively studied because of their importance in selecting polymers for commercial exploitation, much of our knowledge is empirical in nature, due primarily to the difficulty in distinguishing between intra- and intermolecular effects. Some general features are, however, evident. 

Flexible groups such as an ether link will enhance main-chain flexibility and reduce the glass transition temperature, with the opposite effect being shown by the introduction of an inflexible group, such as a terephthalate residue. 

inflexible side groups increase the temperature of the glass transition, as is illustrated in Table 10.1 for a series of substituted poly-a-olefins  

Source Reproduced with permission from Vincent, P.l. (1965) The Physics of Plastics (ed. P.D. Ritchie), iliffe, London. 

A difference between the effect of rigid and flexible side groups is shown in Table 9.2 for a series of polyvinyl butyl ethers  

The equation, Tm = AHJAS/t is all very well, but like any other thermodynamic equation only gives us a relationship between macroscopic properties. We need to relate the enthalpy and entropy to molecular properties in order to gain insight Fortunately, for this problem we only need to do this qualitatively to gain understanding. 

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TABLE 5.1 Effect of Chemical Structure on Solubility and Glass Transition... 

A striking illustration of the effect of chemical structure on insecticidal properties is provided by the data given in this paper on compounds related to piperonyl butoxide. According to the above theory, the methylenedioxyphenyl nucleus present in this substance is the toxophore. The materials selected for comparison show the reduction in toxicity produced, first, by modifying the toxophore, and, second, by substituting different groups for the auxotox radical. 

Santos V, Morao A, Pacheco Ml, Cirfaco L, Lopes A (2008) Electrochemical degradation of azo dyes on BDD effect of chemical structure and operating conditions on the combustion efficiency. J Environ Eng Manage 18(3) 193-204... 

Luangdilok W, Paswad T (2000) Effect of chemical structures of reactive dyes on color removal by an anaerobic-aerobic process. Water Sci Technol 42(34) 377-382... 

Alexander, M. and Lustigman, B.K. Effects of chemical structure on microbial degradation of substituted benzenes, /. Agric. Food Chem., 14(4) 410-413, 1966. 

The effects of chemical structure of diisocyanate component on the hydrolysis of polyurethanes by R. delemar lipase were examined (Figure 8). The rates of hydrolysis of the polyurethanes containing MDI or tolylene-2,U-diisocyanate (TDI) were smaller than that of the polyurethane containing 1,6-hexamethylene-diisocyanate (HDI). 

Figure 8. Effects of chemical structure of diisocyanate component on the hydrolysis of polyurethanes by R. delemar lipase.

Effect of Chemical Structure of Pectins on Their Interactions with Calcium... 

Chain copolymerization is important from several considerations. Much of our knowledge of the reactivities of monomers, free radicals, carbocations, and carbanions in chain polymerization comes from copolymerization studies. The behavior of monomers in copolymerization reactions is especially useful for studying the effect of chemical structure on reactivity. Copolymerization is also very important from the technological viewpoint. It greatly increases the ability of the polymer scientist to tailor-make a polymer product with specifically desired properties. Polymerization of a single monomer is relatively limited as to the number of different products that are possible. The term homopolymerization is often used to distinguish the polymerization of a single monomer from the copolymerization process. 

The conditions for synergism in surface tension reduction efficiency, mixed micelle formation, and Surface tension reduction effectiveness in aqueous solution have been derived mathematically together with the properties of the surfactant mixture at the point of maximum synergism. This treatment has been extended to liquid-liquid (aqueous solution/hydrocarbon) systems at low surfactant concentrations.) The effect of chemical structure and molecular environment on the value of B is demonstrated and discussed. 

Heitkamp, M. A. Cerniglia, C. E. (1987). The effects of chemical structure and exposure on the microbial degradation of polycyclic aromatic hydrocarbons in freshwater and estuarine ecosystems. Environmental Toxicology and Chemistry, 6, 535—46. 

Effect of Chemical Structure of GibbereUins and Derivatives on Plant Growth... 

The purpose of this paper is to investigate the mechanical properties (plastic deformation, micromechanisms of deformation, fracture) of several amorphous polymers considered in [1], i.e. poly(methyl methacrylate) and its maleimide and glutarimide copolymers, bisphenol A polycarbonate, aryl-aliphatic copolyamides. Then to analyse, in each polymer series, the effect of chemical structure on mechanical properties and, finally, to relate the latter to the motions involved in the secondary transitions identified in [ 1] (in most cases, the p transition). 

Owing to the different mechanisms of deformation involved, it is more appropriate to examine separately the effect of chemical structure in the low temperature range (to about - 40 °C) and at higher temperatures. 

As regards the temperature range above - 40 °C, the effect of chemical structure is limited to the results of toughness of MI and MT0.5I0.5 copolyamides, due to the meaningless data obtained for MT0.7I0.3 copolyamide (as explained above). Furthermore, the temperature dependence is expressed in terms of (T - Ta), since the chain mobility plays an important role in fibril stability in this temperature range. The corresponding data for K c and Gic are plotted as a function of (T - Ta) in Fig. 110. Furthermore, the yield stress, cry, for the two copolyamides is shown as a function of (T- Ta) in Fig. 111. 

Digeronimo, M.J., Boethling, R.S., Alexander, M. (1979) Effect of chemical structure and concentration on microbial degradation in model ecosystems. In Microbial Degradation of Pollutants in Marine Environments. EPA-600/9-79-012. U.S. Environmental Protection Agency, Gulf Breeze, FL. 

Alexander, M., Aleem, M.I.H. (1961) Effect of chemical structure on microbial decomposition of aromatic herbicides. J. Agric. Food Chem. 9, 44-47. 

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