Atactic polypropylene segmental relaxation

FIGURE 6.7 Atactic polypropylene segmental relaxation times (solid symbols) from mechanical spectroscopy, dynamic light scattering, dielectric relaxation, and NMR, along with the global time-temperature shift factors (open symbols) from dynamic mechanical spectroscopy, creep compliance, and viscosity. Vertical shifts were applied to superpose the data (Roland et al., 2001). 

Figure 21 Segmental relaxation times and shift factors for global chain dynamics of atactic polypropylene. Segmental relaxation i>, NMR v, dielectric spectroscopy , light scattering o, mechanical dynamic spectroscopy 0, creep compliance measurements. Shift factors for global chain dynamics

A TSC study of isotactic and atactic polypropylene, high density polyethylene, ethylene-propylene block copol)uners, ethylene-propylene rubbers and blends thereof [8] in the y and p relaxation range helped to identify the molecular origin of the relaxation peaks. Two 3 processes were observed in the copolymer samples, one (p,) around —5°C, the other one (Pj) at about -50°C. The former is attributed to the PP chains, while the latter is ascribed to microscopically random ethylene-propylene rubber segments. 

Thermorheologically complex behavior is shown in Figure 21 where the temperature dependencies for segmental (relaxation times) and chain (shift factors) dynamics are compared for atactic polypropylene. For both processes, different methods are combined. 

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