Soft segment structure

Figure 3. Typical TFU-elastomer soft-segment structure...

The 75°C transition in Fig. 6 is due to the glassy polymethyl methacrylate becoming rubbery. This rather low transition (PMMA is usually reported to have a Tg of 105°C) is due to the molecular weight of this segment (6). The.-45°C transition is consistent with the soft segment structure. These results indicate that there is very little phase mixing in this block copolymer. 

As observed by us, all the PUs obtained by using mixtures of diisocyanates (PUci PEA and PUci pthf) did not display significant DSC maxima in the region between 20°-150°C characteristic mainly to the ordered soft segment structure as observed in the case of stretched PUd pthf model when the small maximum at 50°C reveals the PTHF moiety crystallization tendency which maintains also after removing the stress. Fig. 3.10 (e), curve 2. Such a tendency was observed also in many other PUs. 

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. 

Urethane structural adhesives have a morphology that is inverse to the toughened epoxy just described. The urethanes have a rubber continuous phase, with glass transition temperatures of approximately —50°C. This phase is referred to as the .soft segment . Often, a discontinuous plastic phase forms within the soft segment, and that plastic phase may even be partially crystalline. This is referred to as the hard segment . A representation of the morphology is shown in Fig. 3 [34]. 

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. 

These materials have two-phase structures based on hard segments of polystyrene and soft segments of butadiene for SBS, or isoprene for SIS, etc. 

SEBS is obtained by hydrogenation of certain TPS block copolymers. The saturated structure of the soft segments enhances oxidation, chemical and thermal resistances. 

SBS block copolymers differ structurally from the random copolymer of styrene and butadiene (SBR). Because styrene and butadiene blocks are incompatible, they form separate phases joined at the junctions where the various blocks are connected. This gives an elastomeric material where the butadiene blocks form the soft segments and the styrene blocks form hard blocks. 

Recent systematic studies on the relation between network structure and substituents in kraft lignin, steam exploded, have shown that the lignin containing networks can be modified in new ways, cf. e.g. (80). Also the toughening of glassy, structural thermosets can be achieved by incorporating a variety of polyether and rubber-type soft segment components in the polymer network structure. 

The properties of PU depend on the proportions of hard and soft segments in the polymer structure. Paul and co-workers synthesised segmented block copolymers of NR and 1,3 butanediol - toluene diisocyanate oligomers [137], NR and bisphenolA-toluene diisocyanate oligomers [138] and characterised them by IR spectroscopy. The... 

One effective approach in increasing the fire resistance of polyurethane (PU) is to incorporate PDMS into its structure.28 Microphase-segregated PU block copolymers containing hydroxyl-terminated silicone as the soft segment have been synthesized. The enhanced siliconated surface of the block copolymer has been confirmed by ESCA and x-ray analyses. 

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