Floor temperature

The ceihng temperature phenomenon is observed because Aff is highly exothermic, while AS is mildly exoentropic. The opposite type of phenomenon occurs in rare instances where AS is endoentropic (AS = +) and AH is very small (either + or —) or zero. Under these conditions, there will be a floor temperature Tf below which polymerization is not possible. This behavior has been observed in only three cases—the polymerizations of cyclic sulfur and selenium octamers and octamethylcyclotetrasiloxane to the corresponding linear polymers (Secs. 7-lla). AH is 9.5, 13.5, and 6.4 kJ moU respectively, and AS is 27, 31, and 190 J moU respectively [Brandrup et al., 1999 Lee and Johannson, 1966, 1976]. 

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If the floor is too warm or too cool, occupants may feel uncomfortable due to warm or cool feet. For people wearing light indoor shoes, it is the temperature of the floor rather than the material of the floor covering that is important to comfort. Figure 6.4 shows the percentage of dissatisfied for seated or standing people as a function of floor temperature. 

TABLE 6.5 Range of Floor Temperature for Three Categories of Thermal Environment ... 

FIGURE 8.61 Heat transfer from a heated floor versus room and floor temperatures. 

Floor temperature dissatisfaction risk The degree of dissatisfaction experienced by occupants in a space due to the floor surface temperature. 

The effect of temperature is similar in these systems. Thus, yield was little affected or was reduced with decrease in temperature. At a certain temperature level, depending on the nature and concentration of initiator and solvent, yields dropped to zero. This floor temperature is -60 °C for f-BuCl/MeCl and f-BuBr/MeCl and -40 °C for f-BuCl/MeBr and t-BuBr/MeBr. 

Combining all these findings, i.e. initiator efficiencies, polymerization rates and yields, and floor temperatures, a relative order of initiator reactivities can be obtained. For the t-BuX/Me 3 Al/MeX systems, the initiator reactivity is f- BuCl > f-BuBr > r-BuI = 0. The nature of solvent also affects initiator reactivity as follows MeCl > MeBr > Mel = 0. 

Yields were higher using Med than MeBr. Also, the floor temperature was higher using MeBr than MeCl for both t-BuCl and f-BuBr initiators. 

The effect of temperature on yields was insignificant in the range from -25 °C to -55 °C. At and below —60 °C, yields dropped slightly while polymerization did not occur at -75 °C. The floor temperature for these systems is about —65 °C. 

The rate of polymerization was higher in the presence than in the absence of r-BuX. Decreasing temperatures strongly reduced conversion and rates in the absence of f-BuX, particularly at or below—50 °C. In contrast, conversions and rates remained fairly constant when r-BuX was added in the range from —30 °C to —65 °C. The floor temperature was -75 °C for r-BuX/Et2 AlI/MeCl system. 

Initiator efficiencies (Table 8) calculated for yields obtained at —60 °C decreased in the order f-BuI > t-BuBr > f-BuCl. Initiator reactivity based on initiator efficiency, rates of polymerization and floor temperature decreased as f-BuI > t-BuBr > f-BuCl and depending on solvents as MeCl > MeBr, Mel = 0. 

The effect of f-BuX, Et2 A1X and MeX on PIB yield and polymerization rate was studied (Sections V, VI, VII). Relative initiator reactivities were determined based on yields, initiator efficiencies at —60 °C, polymerization rates and floor temperatures. Initiator reactivity orders can be summarized as follows ... 

The effect of temperature on PIB yield shows the existence of a floor temperature, i.e., a temperature below which initiation does not take place. 

Using the f-BuX/Me3Al/MeX system, a preferred reagent addition sequence has been found to be /-C4Hg/MeX/Me3 Al/t-BuX. This sequence has been used in these investigations. Based on polymerization rates at —40 °C, overall polymer yields, floor temperature and initiator efficiencies at —40 °C, overall initiator reactivity is found to decrease as f-BuCl > f-BuBr > t-BuI = 0 and initiator reactivity is dependent on solvent as MeCl > MeBr > Mel = 0. Similarity of reactivity sequences in isobutylene polymerization and in cationic model initiation and termination studies13) suggest that initiator reactivities are determined by the rate of initiation, Rj. 

It should be remarked that dilution of the monomer decreases the entropy of polymerization and, hence, even if its value were positive for pure monomer it eventually becomes negative at a sufficiently high dilution. Therefore, for any system showing the phenomenon of floor temperature, polymerization becomes impossible at any temperature below a certain critical monomer concentration. 

Finally, the data published by Gee (30) permit one to evaluate the sharpness of a transition involving floor temperature. Gee studied the temperature dependence of the viscosity of liquid sulfur and observed its sudden, steep increase at a critical temperature followed by its decrease at still higher temperatures. He developed the first, relatively complete theory of equilibrium polymerization of liquid sulfur (30) from which he estimated the chain length of the polymeric sulfur at various temperatures. His results have been recently confirmed by experimental measurements of magnetic susceptibility of the liquid sulphur (50) and its electron spin resonance (57). 

Gee s theory was unified by Toboesky and Eisenberg (31) and further improved by Tobolsky et al. (52) who removed the original restriction demanding an multiple numbers of 8 S atoms in each chain. This theory demands the existence of a transition (floor) temperature and excellently accounts for its sharpness as determined from Gee s results. A similar situation is observed in liquid selenium (32). 

In Figure 8.1, by mile 30 the gas in the pipeline has cooled to within a few degrees of the ocean floor temperature, so that approximately 23 wt% methanol in the free water phase is required to prevent hydrate formation and subsequent... 

In the field of processing, the glass transition is rather a floor temperature because the polymerization (cure) exhibits a very slow or even negligible rate in the glassy state (see Chapter 5). Many important properties, such as the yield stress or the fracture toughness at a temperature T are sharply linked to (Tg — T). Some qualitative and important quantitative differences between the glassy and rubbery states are listed in Table 4.1. 

Snyder, R.L. and J.H. Connell (1993). Ground cover height affects pre-dawn orchard floor temperatures. Calif. Agri., 47 9-12. 

In very special cases the entropy of the polymer is larger than the entropy of the monomer. If, moreover, the reaction is endothermic, so that both AH and AS are negative, then there is a minimum temperature, where above polymerisation will proceed below this temperature the monomer is stable. In such a special case the critical temperature is called the floor temperature. An example is the polymerisation of crystalline sulphur. 

Fiber-reinforced polymer systems, 38 Fickian diffusion, 665 Fick s law, 663,684 Field flow fractionation, 20 Filled polymers, 38 First normal stress coefficient, 545 difference, 640 First-order transition, 27,152 Flame-retardant additives, 861 Flammability, 847 Flashing, 804 Flash line region, 807 Flexibility of a chain molecule, 246 Flexible polymer molecules, 706 Flexural deformation under constant load, 825 Flexural formulas, 826 Flexural rigidity, 877 Floor temperature, 751 Flory-Huggins... 

Part V Properties determining the chemical stability and breakdown of polymers. In Chapter 20, on thermomechanical properties, some thermodynamics of the reaction from monomer to polymer are added, included the ceiling and floor temperatures of polymerization. Chapters 21 and 22, on thermal decomposition and chemical degradation, respectively, needed only slight extensions. 

In exoenthalpic and exoentropic polymerizations, AGP° eventually becomes positive above a temperature known as the ceiling temperature (AGP° = AHP°/TCASP° > 0). For example, the ceiling temperature of bulk styrene is =400° C, whereas that of methyl methacrylate is =200° C. In contrast, AGP° becomes positive below a floor temperature when the polymerization is endoenthalpic and endoentropic (AGP° = AHp°/TfASp° > 0), such as in the polymerization of Sg (T/ = 160° C). 

The ceiling (or floor) temperature varies with the equilibrium monomer concentration, with the highest (or lowest) temperature corresponding to that of a bulk polymerization [Eq. (18)]. 

The terms ceiling and floor temperatures usually refer to bulk conditions unless stated otherwise. Because polymerization does not occur when the initial monomer concentration is at or below the equilibrium monomer concentration, [ML in the above equations can be replaced with [M]0. This demonstrates that AGP will be negative even if AGP° is positive if [M]0 is high enough, and that polymerization will occur. For example, although tetrahydrofuran (THF) does not polymerize at 25° C when [M]0 = 1 mol/L (4 Gp° > 0), it does polymerize at concentrations [M]0 > 5 mol/L (AGP < 0) because at 25° C [ML 5 mol/L [29]. 

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