Glass transition broadening

Mixed donor-acceptor monomers. The glass transition temperature of FAIR polymerized with 1 wt-% of TPO as photo-initiator gradually increases with irradiation time (Fig. 7) and conversion (Fig. 8). Furthermore, the glass transition broadens as the crosslinking proceeds due to increasing heterogeneity within the material. For a final conversion of... 

Figure 534. (a) Storage modulus of PET yarn from fibers drawn to various draw ratios. The storage modulus increases with increasing draw ratio (note that 1 dyn/cm = 0.1 Pa) the draw ratio is indicated at each curve (b) Loss tangents for PET yams from fibers drawn to various draw ratios. As the orientation (i.e., draw ratio) and crystalUnity increase, the glass transition broadens and becomes more shallow the draw ratio is indicated at each curve. [Plots (a) and (b) both from Miller and Murayama (1984) reprinted with permission of John Wiley and Sons, Inc.]... 

If highest resolution is required, then the strategy is to use thermal activation to stir away the conformatonal anisotropy operate as close to the glass transition temperature as possible, up to the point at which Ti lifetime broadening predominates. On the other hand, at lower temperatures the lineshape and its temperature dependence may provide useful information (34). 

B. Characteristic Temperatures of Polymerization and Glass Formation, Transition Broadening, and Fragility... 

Another study that focussed on the glass transition temperature of such composites revealed that the a-relaxation in the acrylonitrile/ styrene phase is broadened towards higher glass transition temperatures. It is believed that the shift arises due to the interaction located at the boundary layer between polymer and CNTs (51). 

DSC and DTA. They can be used to confirm suspicious glass transitions revealed by DSC and most important, they can further quantify molecular mobility associated with sub-glass transitions. For example, DSC analysis of poly (ethylene 2,6-naphthalene dicarboxylate) (PEN) only revealed the presence of a glass transition around 112 °C (Hardy et al., 2001). DMA analysis of the same sample, however, revealed two secondary relaxations below this glass transition (Hardy et al., 2001). In the case of humic materials, it is not uncommon for DSC to fail to detect clear thermal transitions due to their heterogeneous nature, which contributes to overlap/ broadening or washout of thermal transitions. As such,TMA and DMA represent powerful, complementary tools to DSC. 

Dynamic Mechanical Properties. Figure 15 shows the temperature dispersion of isochronal complex, dynamic tensile modulus functions at a fixed frequency of 10 Hz for the SBS-PS specimen in unstretched and stretched (330% elongation) states. The two temperature dispersions around — 100° and 90°C in the unstretched state can be assigned to the primary glass-transitions of the polybutadiene and polystyrene domains. In the stretched state, however, these loss peaks are broadened and shifted to around — 80° and 80°C, respectively. In addition, new dispersion, as emphasized by a rapid decrease in E (c 0), appears at around 40°C. The shift of the primary dispersion of polybutadiene matrix toward higher temperature can be explained in terms of decrease of the free volume because of internal stress arisen within the matrix. On the other... 

Struik also (1987-1989) showed that his concept of physical ageing and its affects on the mechanical behaviour can be extended to semi-crystalline polymers the only additional assumption needed is that in semi-crystalline polymers the glass transition is broadened and extended towards the high temperature side. Fig. 13.55 illustrates this. 

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