Transition maps, polymers

In all the above three polymers only a single process is apparently observed in the time window for PCS (10-6 to 100 s). The shape of the relaxation function is independent of temperature. The temperature dependence of (r) follows the characteristic parameters observed for mechanical or dielectric studies of the primary (a) glass-rubber relaxation. Relaxation data obtained by many techniques is collected together in the classic monograph of McCrum, Read and Williams41. The data is presented in the form of transition maps where the frequencies of maximum loss are plotted logarithmically... 

To observe the rubber-glass transition directly it is necessary to go to higher temperatures and in principle the transition can be followed upwards in temperature and frequency using a transition map. Such maps are available for many polymers, and such high-frequency information as is available indicates that the hypersonic loss peaks fall in the region of the merged a and line (15). 

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... 

One of the most common methods utilized to characterize the phase behavior of polymer blends employs low amplitude cyclic deformation studies to obtain the elastic and viscoelastic properties. This method, termed dynamic mechanical characterization, yields high resolution of polymer transitions including secondary relaxation processes, crystalline melting transitions and of primary importance, the glass transition. This method maps the data over a broad temperature range to ascertain the phase behavior. 

Solid amorphous polymers normally exhibit two relaxation processes which coalesce to form one process at high temperatures. The a process is observed above the glass transition temperature and is due to the microbrownian motions of the chains. The jS process, which is normally observed below Tg but can also be observed in a limited range above Tg, is due to limited motions of the main chain or, where present, the motions of dipolar side chains. The frequency-temperature location of these processes is indicated schematically in Figure 8 and the coalescence of a and j processes to form the ajS process is seen to occur above Tg. The loci of these processes vary greatly with chemical structure, tacticity, plasticizer content and sample orientation. Transition maps have been given for many amorphous polymers, based on dielectric, NMR and mechanical relaxation results. The loci obtained from the different methods are found to be similar for a given polymer. 

The important conclusion drawn from the above studies on PS(OH)/PMMA in solution and bulk is that complexes formed in dilute solutions can be preserved during the process of film casting. In particular, when we use an inert solvent whose Ejp is close to zero, the critical hydroxyl contents in proton-donating polymers for complexation estimated by viscosity or LLS are comparable to that for the miscibility-to-complex transition in bulk, which can be easily detected by DSC or TEM. Therefore, by combining the results from both solution and bulk, it should be possible to construct a map for a given blend system visualizing how the immiscibihty, miscibihty and complexation of the blend depend on the content of interacting sites. 

In order to represent the temperature dependence of the process frequencies corresponding to the various transitions, it is usual to consider a relaxation map, as it is called, in which the logarithm of the frequency is plotted as a function of 1/T, where T is the absolute temperature. A typical example is shown in Fig. 2 for a polymer exhibiting two solid state transitions (/I and y), in addition to the a transition. It is worth pointing out that the lower the transition temperature, the smaller the activation energy. 

Figure 10.1 Time-temperature map. Shape of main boundaries for linear or network polymers. (I) Glassy brittle domain B, ductile-brittle transition. (II) Glassy ductile domain G, glass transition. (Ill) Rubbery domain. The location of the boundaries depends on the polymer structure but their shape is always the same. Typical limits for coordinates are 0-700 K for temperature and 10-3 s. (fast impact) to 1010 s e.g., 30 years static loading in civil engineering or building structures. Fpr dynamic loading, t would be the reciprocal of frequency. For monotone loading, it could be the reciprocal of strain rate s = dl/ Idt.

Figure 11.2 Shape of relaxation maps (coordinates of transitions a, p, and y in a graph In (frequency) - reciprocal temperature). Left polymers having their a and p transitions well separated (example polycarbonate, amine-crosslinked epoxy). Right polymers with close a and p transitions (example polystyrene, unsaturated polyester).

Miyashita et al. carried out miscibility characterization of CA blends with poly(N-vinyl pyrrolidone) (PVP), poly(vinyl acetate) (PVAc), and poly(N-vinyl pyrrolidone-co-vinyl acetate) random copolymers [P(VP-co-VAc)s] [ 104]. On the basis of thermal transition data obtained by differential scanning calorimetry (DSC), a miscibility map (Fig. 8) was completed as a function of the degree of substitution (DS) of CA and the VP fraction in P(VP-co-VAc). Figure 9 compares results of the DSC measurements between two blending pairs of CA/P(VP-co-VAc) corresponding to the polymer combinations marked as A and B in Fig. 8. In the data (Fig. 9b) for the blends of CA (DS = 2.95) with P( VP-co-VAc) of VP = 51 mol %, we can readily see a sign of poor miscibility, as is evidenced from the lack of an appreciable shift in the... 

The nonplant synchrotron IR microspectroscopic analysis at the NSLS beamline included drug metabolites in hair [31], depth profiling of photodecomposition of polymer layers [19], and numerous mammalian tissue probings, including the brain tissue of rats that had consumed D2O in their drinking water [10]. A summary of the plant material experience from BNL over a continuous 15-month period was reported in 1998 [17], and included the spectra of individual cells within a wheat primary root and the mapping of transitions between the botanical parts of wheat, safflower, oats, corn and barley. 

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