Relaxation gamma

In accordance to the data reported in the literature for bulk hyperbranched polyesters [34,35], three relaxation processes are also observed in thin POHOAc films, (Fig. 23) the alpha relaxation process, representing the dynamic glass transition, the beta process, attributed to the relaxation of the ester groups, and the gamma relaxation process, originating from fluctuations of the —OH end groups. The latter two, which are broad and not well-separated from one another, are only distinguishable in the temperature representation of the dielectric spectra (inset, Fig. 23). 

The assignment of the alpha relaxation was additionally confirmed by AC-calorimetric measurements on thin films of POHOAc [31], The effect of confinement on the overall dynamics of POHOAc is given in Fig. 24, showing the dielectric spectra for different film thicknesses, ranging from 310 nm down to 17 nm. While the beta and the gamma relaxations, as local processes, are not affected with decreasing film thickness (except a decrease of the dielectric... 

Figure 23. Dielectric loss e" versus frequency at different temperatures, as indicated, showing the alpha relaxation process for a thin film of hyperbranched polyesters of 17 nm. Inset. Dielectric loss e" versus temperature at 49 kHz, showing the beta and the gamma relaxation processes for the same sample. Dotted lines serve as a guide for the reader.

It is semicrystalline (50-60%) and melts at 240°C (commercial grade). " It has an alpha relaxation at 140°C, a beta at 90°C, and gamma relaxation at -65°C. Conformation of ECTFE is an extended zigzag in which ethylene and CTFE alternate. The unit cell of ECTFE s crystal is hexagonal. 

The effect of a sample drying procedure (by heating to 150 C) on the low-temperature gamma relaxation of a PK terpolymer... 

Frequency/temperature relation of the beta and gamma relaxations... 

Figure 8.5 Distribution of light-scattering relaxation times for poly(hexyl methacrylate) near its glass-transition range. At the lowest temperature, the primary and secondary relaxations are separating. The long-time part of the gamma relaxation is visible in the short time window of the technique. (From Savin, D.A., Patterson, G.D., and Stevens, J.R., Evidence for the y-relaxation in the light scattering spectra of poly(n-hexyl methacrylate) near the glass transition, /. Polym. Sci. B Polym. Phys., 43, 1504, 2005. With permission.)...

A. K. Rizos, L. Petihakis, K. L. Nagi, J. H. Wu, and A. F. Yee, A Dielectric-Relaxation Study of the Gamma-Relaxation in Tetramethylbisphenol-A Polyearbonate Plasticized by Tris(2-Ethylhexyl) Phosphate Macromolecules 32, 7921—7924 (1999). 

A DMTA study of polyolefin-clay nanocomposites has shown that alpha, beta and gamma relaxations of the polymer were affected by polymer chain branching and clay exfoliation level [50]. Salmeron Sanchez and co-workers [51] studied the structure of the system obtained after free radical copolymerisation of ethyl acrylate and hydroxyethyl methacrylate comonomers using dynamic-mechanical and calorimetric techniques. Copolymerisation theory states that the free radical copolymerisation reaction of two monomers may give rise to a copolymer with a different chain composition from that of the random mixture corresponding to the original solution. In this system, the dynamic-mechanical spectra suggested there were two main alpha relaxation processes in the copolymers. 

Hoffman, J.D., Williams, G. and Passaglia, E. (1966) Analysis of alpha beta and gamma relaxations in polychlorotrifluoroethylene and polyethylene - dielectric and mechanical properties. /. Polym. Sci., C, 14, 173. 

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