Hard segments amorphous

Crystalline Hard Segment Amorphous Soft Segment... 

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. 

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. 

The work reported here is concerned with the syntheses and properties of polyether-ester block copolymers containing poly (tetramethylene ether) units of molecular weight of approximately 1000 as the amorphous polyether blocks and a variety of esters as the crystallizable hard segments. The purpose of this study is to correlate changes in synthesis and properties of these thermoplastic and elastomeric copolymers with changes in the concentration and nature of the ester segments, particularly the types of diol and diacid. 

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). 

Since the linear relationship between H and Tg (see Chapter 3) seems to be valid over a rather wide temperamre range (in the present case it is proven for Tg values between —50 and 250 °C at least), eq. (5.16) can be rewritten in such a way that it also accounts for the amorphous hard-segment phase ... 

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 use of monomers that produce amorphous hard segments produces highly compatible systems with poorly defined rubbery plateau and elastomeric behavior. Because no heterogenous conditions develop during the reaction, molecular weight in amorphous polyurethane systems tends to be less affected by reaction rates or polymerization conditions. 

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