Poly loss maxima

A typical loss maximum of this type was observed for poly(methyl methacrylate) containing caprolactam or derivatives of cyclohexane12,13. It is noteworthy70 that in the latter case the relaxation induced by the cyclohexyl group present in the incorporated plasticizer and the secondary relaxation of poly(cyclohexyl methacrylate) or poly(cyclohexyl acrylate) are characterized by an identical temperature position, 190 K (1 Hz), and activation energy, 47.9 kJ/mol (AU = 47.7 kJ/mol is reported for the chair-chair transition of cydohexanol). Hence, it can be seen that the cyclohexyl ring inversion, which represents a specific molecular motion, is remarkably insensitive to the surrounding molecules. 

The effect of the side chain bulkiness has been further studied on a series of chloro derivatives of poly(ethyl methacrylate)(PEMA). Though poly(2-chloroethyl methacrylate) exhibits69 a pronounced peak at Ty = 117 K, poly(2,2,2-trichloroethyl methacrylate), poly(2,2,2-trichloro-l-methoxyethyl methacrylate), and poly(2,2,2-trichloro-l-ethoxyethyl methacrylate) do not show (Fig. 6) any low-temperature loss maximum above the liquid nitrogen temperature157. However, these three polymers probably display a relaxation process below 77 K as indicated by the decrease in the loss modulus with rising temperature up to 100 K. Their relaxation behavior seems to be similar to that of PEMA rather than of poly(2-chloroethyl methacrylate) which is difficult to explain. 

Under viscoelastic measurements poly(cycloalkyl methacrylates) show a loss maximum (designated y), located in the very low temperature range (T <-60 °C), as illustrated in Fig. 6 in the case of poly(cyclohexyl methacrylate). Such a series of polymers has been extensively studied by Heijboer in his Ph.D. thesis [5], by performing viscoelastic studies at 1 Hz (sometimes 180 kHz) as a function of temperature and exploring quite a large number of cycloalkyls, either substituted or not. In cyclopentyl, cyclohexyl, cyclohep-tyl derivatives, the y transition was shown to occur at ca. - 185 °C (180 Hz), - 80 °C (1 Hz), - 180 °C (1 Hz), respectively. The associated activation energies, a> are 13, 47, 26kJmol 1 for the cyclopentyl, cyclohexyl, cycloheptyl derivatives, respectively. 

Polyethylene samples were also exposed to conditions which created 0.4% clustered water and dielectric data taken at low temperatures on the samples. The same loss maximum noted In polycarbonate and polysulfone near -100 C at 1 kHz was also noted In polyethylene. A special polyethylene sample was molded around a PTFE sheet. The PTFE was removed and replaced with distilled water. This sample was equivalent to a thin water layer between polyethylene sheets. The dielectric behavior of this sample was quantitatively equivalent to that of the polyethylene containing spherical clusters of water if the difference in geometry of the water phase is taken into account. Figure 7 shows the logarithm of the frequency of loss maxima due to water clusters versus reciprocal temperature for polyethylene, polycarbonate, poly(vlnyl acetate and polysulfone. The polysulfone data from Allen are shown for comparison and It Is seen that the data can be Interpreted as a single mechanism with an activation energy of 7 kcal/ mole. 

Water absorbed in a polymer can exist in an unassociated state or as a separate phase (cluster). In this investigation the DSC technique of water cluster analysis was used in conjunction with coulometric water content measurements to characterize the water sorption behavior of polysulfone and poly(vinyl acetate) The polysulfone had to be saturated above its Tg (190°C) and quenched to 23°C for cluster formation to occur while cluster formation occurred isothermally at 23°C in the poly(vinyl acetate) Both polymers showed an enchancement of their low temperature 3-loss transitions in proportion to the amount of unclustered water present. Frozen clustered water produced an additional low-temperature dielectric loss maximum in PVAc and polysulfone common to polyethylene and polycarbonate as well. Dielectric data obtained on a thin film of water between polyethylene sheets was in quantitative agreement with the clustered water data. 

For the poly a-olefins the methyl reorientation process does not appear to lead to a noticeable mechanical loss maximum. On the other hand a low-loss process is found (9) for PcMPO around 90°K. (104 c.p.s.) which may include such reorientation. 

Dynamic mechanical results for polypropylene crystal aggregates (40) grown at 60°C. from 0.1% xylene and for poly(1-butene) crystals (95) from a 2% Decalin solution have been obtained at temperatures from 210°K. For these specimens the peak caused by the principal amorphous transformation at 300°K. (103 c.p.s.) (64, 91) is greatly reduced while a loss maximum closer to the melting point is found at 390°K. (102 c.p.s.) for polypropylene and 340°-360°K. (102 c.p.s.) for poly(-l butene) these maxima are attributed to motion in the crystalline regions. 

The influence of water on the poly(amide-iimde) was also determined with dielectric thermal analysis. Two samples were run one was as-received and the other was dried for 7 hours at 190 C. They are shown in Figures 4a and 4b. Figure 4a illustrates the effects of water on the low temperature loss between -100 and 0 C. There were also ionic conductivity losses between 0 and 70 C. The ionic conductive losses were determined from the slope (-1) of the loss maximum peak height versus log frequency plots. These were attributed to mobile ions. This ionic mobility was dependent on water. 

A typical example of these measurements is the mechanical loss factor (for definition, see Section 11). Here a loss maximum for poly (cyclohexyl methacrylate) is observed at — 125°C when the frequency is 10 Hz (Figure 10-26). The maximum is shifted to higher temperatures when the frequency is increased. In addition, the reciprocal loss temperature depends linearly on the logarithm of the frequency (Figure 10-27). Studies on different chemical compounds show that this loss maximum is specific to the cyclohexyl group. The values for both poly(cyclohexyl methacrylate) and poly(cyclohexyl... 

Figure 9.15. X -(GVGIP)32o frequency dependence of loss shear modulus, G" (0.02 to 200 Hz), and of loss permittivity (20 Hz to 10 Hz) as a function of temperature. When the frequency of the loss maximum is sufficiently low, for example, near 1 kHz, loss shear modulus and loss permittivity can both be determined and have been demonstrated to superimpose for the case of the loss maximum for poly(propylene diol). In the case of X -(GVGIP)32o, the maximum occurs at a frequency that is too high to be reached by shear modulus measurements. Nonetheless, the two measurements are... 

Even without an analytical expression to describe the shape of H, it is clear that increasing steepness of H in the transition zone as portrayed in Fig. 12-11 will be accompanied by a compression of the transition from rubberlike to glasslike consistency into a narrower region of logarithmic time scale. Plots of both transient and dynamic moduli and compliances, as exemplified in Chapter 2, rise and fall with steeper slopes. Perhaps the most sensitive index of the sharpness of the transition is the loss tangent, which is plotted in Fig. 12-12 for several prototypes the polyurethane rubber, poly( -octyl methacrylate), poly(vinyl acetate), and Hevea rubber. Here the frequency scale has been arbitrarily selected to make the maxima coincide. The sharpness in the loss maximum correlates with the slope of H in the transition zone. The shape emphasizes the failure of the modified Rouse theory to provide a detailed description of the properties in the transition zone, since it predicts tan 5 = 1 independent of frequency in this region. The drop in tan 5 at high... 

Figure 5.7 shows the results of a dynamic shear experiment carried out on poly(cyclohexyl methacrylate) (PCHMA) in the glassy state. One observes a relaxation process which produces a loss maximum just in the frequency range of the mechanical spectrometer. With increasing temperature the position of the loss maximum shifts to higher values. 

The time-temperature superpositioning principle was applied f to the maximum in dielectric loss factors measured on poly(vinyl acetate). Data collected at different temperatures were shifted to match at Tg = 28 C. The shift factors for the frequency (in hertz) at the maximum were found to obey the WLF equation in the following form log co + 6.9 = [ 19.6(T -28)]/[42 (T - 28)]. Estimate the fractional free volume at Tg and a. for the free volume from these data. Recalling from Chap. 3 that the loss factor for the mechanical properties occurs at cor = 1, estimate the relaxation time for poly(vinyl acetate) at 40 and 28.5 C. 

Jamieson and McNeill [142] studied the degradation of poIy(vinyI acetate) and poly(vinyI chloride) and compared it with the degradation of PVC/PVAc blend. For the unmixed situation, hydrogen chloride evolution from PVC started at a lower temperature and a faster rate than acetic acid from PVAc. For the blend, acetic acid production began concurrently with dehydrochlorination. But the dehydrochlorination rate maximum occurred earlier than in the previous case indicating that both polymers were destabilized. This is a direct proof of the intermolecular nature of the destabilizing effect of acetate groups on chlorine atoms in PVC. The effects observed by Jamieson and McNeill were explained in terms of acid catalysis. Hydrochloric acid produced in the PVC phase diffused into the PVAc phase to catalyze the loss of acetic acid and vice-versa. 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

Similarly to the behavior of isotropic poly(ether ester)s the amplitude and position of the relaxation peaks in the loss curve of the extnidates were influenced by the composition of the amorphous phase. This is determined by the concentration and the degree of polymerization of the ester segments. For the extnidates the observed effect was pronounced only in the case of material C. Here, the glass transition temperature, as determined from the maximum of the so-called a-relaxation peak, increased linearly with decreeing extrusion temperature from - 4 C to 17 For the materials A and B the glass transition temperatures were found to be — 59 and - 50 °C, respectively, independently of the extrusion conditions. 

Here we consider a series of new poly(ester ether carbonate) (PEEC) multiblock terpolymers with varying amount of ether and carbonate soft-segment content. Dielectric relaxation experiments on the same PEECs revealed the existence of two relaxation processes (Roslaniec et al, 1995). The dielectric loss values show the existence of a relaxation maximum appearing at about 0 °C for 10 kHz relaxation) accompanied by a lower temperature relaxation (y relaxation) which appears at about —50 °C. 

Figure 13. Dielectric loss data at various combinations of temperature and pressure as indicated to demonstrate the invariance of the dispersion of the a-relaxation at constant a-loss peak frequency va or equivalently at constant a-relaxation time for (a) poly(vinylacetate) (PVAc), (b) poly(methyltolylsiloxane) (PMTS), and (c) polyfphenyl glycidyl ether)-co-formaldehyde (PPGE) d)poly(oxy butylene) (POB). In all cases, spectra obtained at higher P are normalized to the value of the maximum of the loss peak obtained at the same frequency at atmospheric pressure.

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