Local mode relaxation

Ct break point at 54°C. This temperature may correspond to the transition temperature (Tg) attributable to the local mode relaxation of polymer main chains. A long alkyl substituent at the nitrogen atom of the indoline moiety enhances the effect of local mobility of polymer chains on the thermal reversion. 

Figure 8.36. The B-relaxation hardly shifts as a function of the measuring frequency due to the presence of a large crystalline phase. The y-relaxation is deary much stronger frequency dependent. An activation energy value of 63 kJ/mole was calculated for the y-relaxation from the slope of this curve. Some typical y-relaxation activation energy values for linear polymers are 63, 54 and 54 kJ/mole for respectively PVC [14], PC and PET [15]. The mechanisms of these y-relaxations are often described as local mode relaxation effects [15]. The same mechanism might also be responsible for the y-relaxation effect in polyketone polymers.

Dynamic mechanical analysis (DMA) is a sensitive method for glass transition temperature measurement, for detection of side-chain and main-chain motions, and for local mode relaxation measurements. Loeal mode relaxation can not be measured by DSC. DMA can give information about the crosslinking process of modified phenolic prepolymer [218] and about the erosslinked material [132]. During DMA measurements, sinusoidally varying stress of frequency is applied to the sample. Frequency and the stress are connected by equation 57, where is the maximum stress amplitude and is the phase angle at which the stress proceeds the strain. 

Transition map of poly(vmyl alcohol) compiled using the DMA data presented in Figure 6.12. An activation energy for the a (motion in crystalline regions), (glass transition) and y (local mode relaxation) transitions can be calculated using the Arrhenius relation... 

Figure 2.22 Transition map of poly(vinyl alcohol). , Motion in crystalline region (i, glass transition y, local mode relaxation...

As is well known, molecular motions such as local mode relaxation of the main chain and rotational mode relaxation of the side chain are not frozra-in at T. The typical temperature dependence of viscoelastic properties is shown schranatkally in Fig. 3 for both crystalline and amoridious polymers. Sub ass transitions (Tp, T, Tg, etc.) corresponding to the freezing of these local motions appear as peaks in a tan temperature curve. 

Figure 7 illustrates this method applied to PMMA and polystyrene. The breaks are observed at and other subglass transition temperatures. The breaks at T, (PMMA) and Tp (PS) indicate the changes in local mode relaxation of the main chain, and those at Tp (PMMA) and T (PS) the onset of rotation of the side-chain ester or phenyl group. 

The quantum yield of the Norrish type II process in the ethylene-carlxMi monoxide (1 %) copolymer at room temperature = 0.025) and the lifetime of the triplet excited state are comparable to those in hydrcwarbon solution under the same conditions This finding can be explained by the fact that at room temperature the copolymer is above its glass transition temperature and hence a large scale nujvement of chain segments is possible even thou the center of ntass of the polymer r nains fixed. When the polymer is cooted, the quantum yfeld begins to drop below —40 °C and reaches zero at—120 °C. Since T of polyethylene is reported to be —80 to —90 °C no occurrence of the Norri II reaction in the polyethylene chain should be associated with the fre ing-in of local mode relaxation of the main drain. 

Local mode relaxation of isolated lignin and its model compounds have been detected by dynamic mechanical measurement, and broad-line nuclear magnetic resonance spectroscopy (b-NMR) [49,53], although this molecular motion has scarcely received attention in recent papers. Transition map of local mode relaxation of various kinds of polymers is found elsewhere [56]. Figure shows second moment of absorption line of b-NMR of DL in powder form. When the relaxation is from the... 

For crystalline polymers as microbial poly[(R)-3-hydroxybutyrate], the loss modulus can exhibit three relaxation phenomena (a, (3, and y in order of decreasing temperature). The a-peak is the main glass transition and reflects the motions in relation to the chains in the amorphous regions. The (3-peak is caused by the local mode relaxation or motions associated with methyl or ester groups. The y-peak corresponds to the chain mobility between the crystalline melting and amorphous processes and depends on the thickness of the lamellae [57,89]. 

P process. This occurs as a small high frequency shoulder to the process and as a small ( mp l moL — 0.1) and broad process. It has an apparent activation energy of about 8 kJ mol" and the process is assigned to be a local mode relaxation in the amorphous regions. 

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