Soft segment amorphous

Taking into account that the Tg of the soft-segment amorphous phase lies between -50 and 0 °C, depending on the PCc content (Table 5.3), one can expect that at room temperature such a phase will be a very soft material much closer to a liquid than to a solid. For this reason one may expect that 0 and, as a result, that H will be depressed with increasing values of w according to the simple expression ... 

By means of the microhardness additivity law (eq. (4.3)) one can attempt to evaluate the contribution of the soft-segment amorphous phase to the overall micro-hardness. For a four-phase system as in the present case (Fig. 6.7), (two crystalline modifications and two amorphous phases), eq. (4.3) can be written as ... 

The melt temperature of a polyurethane is important for processibiUty. Melting should occur well below the decomposition temperature. Below the glass-transition temperature the molecular motion is frozen, and the material is only able to undergo small-scale elastic deformations. For amorphous polyurethane elastomers, the T of the soft segment is ca —50 to —60 " C, whereas for the amorphous hard segment, T is in the 20—100°C range. The T and T of the mote common macrodiols used in the manufacture of TPU are Hsted in Table 2. 

In the case of the polycrystalline polyester thermoplastic rubbers the simple domain theory does not seem to apply. With these rubbers it would appear that they contain spherulitic structures consisting of 4GT radial lamellae with inter-radial amorphous regions that are mixtures of PTMEG soft segments and noncrystalline hard segments. 

The soft segments made from asymmetrical (amorphous) polyols are important for two-component structural adhesives and one-component moisture-curing adhesives. These materials are applied and usually cured at room temperature. 

Random block copolymers of polyesters (hard segments) and amorphous glycol soft segments, alloys of ethylene interpolymers, and chlorinated polyolefins are among the evolving thermoplastic elastomers. 

Another criterion for catalyst selection is relative comonomer incorporation. The proposed material design is one in which the soft segment (SS) is amorphous and the hard segment (HS) contains as little comonomer as possible. To achieve this combination, the chain shuttling catalysts must have very different reactivity ratios. 

Crystalline Hard Segment Amorphous Soft Segment... 

The transition behavior from DSC studies, summarized in Table V, is consistent with the two-phase structure expected. The low-temperature glass-transition, T, is associated with the continuous (PTHF) soft segment phase, whereas, the transitions at T and Tm are associated with the amorphous and... 

Taking into account the chemical composition of the copolymers under investigation as well as the fact that the Tg of the hard Segments of PBT is around 50 °C one has to assign the observed glass transition temperatures (T i) to the amorphous phase arising from the soft segments (Table 5.3). 

The data obtained from calorimetric, dynamic mechanical and X-ray analysis (Table 5.3) indicate the existence in the copolymers of three phases - two amorphous and one crystalline. The hard PBT segments give rise to the crystalline phase and to one of the amorphous phases the soft segments contribute to the second amorphous phase. These three phases are characterized by their transition temperatures Tm, Tg2 and Tgi, respectively (Table 5.3). 

Figure 5.13. Schematic model showing the hard PBT particles (crystalline cores and surface amorphous regions) embedded in the amorphous phase of the soft segments. (From Balta Calleja etai, 1998.)...

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