Polyurethane Amorphous thermoplastics

During the last two decades, many special fluoropolymers have been developed, such as fluorosilicones fluorinated polyurethanes fluorinated thermoplastic elastomers new, second-generation polymers and copolymers based on PTEE amorphous... 

The following examples show thermally induced shape-memory. The first three examples are exclusively physically cross-linked. These examples are two polyurethanes representing thermoplastic shape-memory polymers with Ttrans = Tm or Tg, and a high molecular weight, amorphous polynorbornene. Examples of covalently cross-linked shape-memory networks are so-called heat-shrinkable materials and a shape-memory network with a crystallizable switching segment (Ttrans = Tm) that has been developed for biomedical application. 

Polyurethane. This rubber is mainly thermoset, but thermoplastic processability can be achieved by block copolymers of amorphous polyurethane rubber with strongly hydrogen-bonded crystalline polyurethane blocks. 

Melt processing is a common alternative that is particularly useful for dealing with thermoplastic polymers and holds great interest because of the ease with which the process could be scaled up to industrial standards. Thermoplastic polyurethane nanocomposites can be fabricated by melt compounding of CNTs with polymer resin. Melt processing makes use of the fact that thermoplastic polymers soften when heated. Amorphous polymers like elastomer... 

Isoplast. [Dow] Thermoplastic polyurethane, some glass-reinforced amorphous engineering resin with crystalline properties for extruskm and inj. mold g applies. 

Bayhydrol D 155-BOE/IB/W] Bayhydrol D 270. See Polyester resin, thermoplastic Bayhydrol PR 135] Bayhydrol PR 340, Bayhydut BL 5140. See Polyurethane resin Baykisol 30. See Silica, amorphous hydrated Bay laurel extract. See Laurel (Laurus nobilis) extract... 

Linear Elastic and Rubber Elastic Behavior. Although stiffening is quite noticeable in the glassy regime of the amorphous phase, the most spectacular effect is seen in the rubber elastic regime phase, as already evoked in the case of reinforcement by cellulose whiskers (2). The PA6-clay hybrids example presented in Table 3 is quite representative of the situation encoimtered with semi crystalline thermoplastics, but elastomeric networks benefit as well of clay layer dispersion with a two- to threefold increase in modulus for polyurethane or epoxy networks... 

The mobility of the soft phase in a two-segment thermoplastic elastomer polyurethane, as derived from H NMR, correlates well with mechanical properties [224,225]. The soft poly(tetramethylene oxide) segments consist of both crystalline and amorphous phases. The observed 100-fold decrease in storage modulus, G, between 200 and 280 K corresponds to the transition of the amorphous part of the soft blocks from a glassy to a rubbery... 

Crystallizable Block Copolymer Morphologies While the largest part of the block copolymer literature describes totally amorphous materials, one or more of the blocks may form semicrystalline regions. Examples include polyester-polyether block copolymers (39), where the poly(tetramethylene terephthalate) polyester blocks crystallize, and the thermoplastic polyurethane elastomers, where the polyurethane hard blocks crystallize (40). 

Domain structures similar in external form to the S—B—S polymers have been observed in the thermoplastic polyurethane rubbers with their development being very dependent on the precise composition and on their thermal history (Allport et al. quoted by Allport and Mohajer, 1973). In their excellent review on these rubbers Allport and Mohajer point out that on the evidence available it cannot be assumed that all of the hard segments are present in the spherical domains, nor that these domains consist only of hard segments. It does however appear a reasonable supposition that the spherical domains are rich in hard segments whilst the amorphous matrix in which the domains are embedded are rich in soft segments. 

Method D appears to be possibly the most important type of isocyanate-based adhesive system. It is similar to Method B in that a preformed, fully reacted, high molecular weight polymer is employed as a vehicle in the adhesive formulation. The strength of the vehicle holds adherend members in exact position after assembly until the full bond has formed. Method D differs from Method B in that its vehicle polymer is a polyurethane. A further difference is that the inherent adhesive character and strength of the polyurethane vehicle frequently enables its use without added di- or poiyisocyanate. This strength may be realized in essentially amorphous compositions such as the thermoplastic polyurethane elastomers or millable gums. Or it may be achieved with crystallizing urethane adhesive polymers. 

Control of enantiomorphic selectivity in polymerization of the substituted oxiranes can lead to controlled-structure polymers, the properties of which will range from crystalline thermoplastics to amorphous elastomer precursors such as are used as soft segments in polyurethanes. Crystallizable sequence distributions in highly controlled-structure polymers can lead to thermoplastic elastomers and/or to elastomers that will stress-crystallize that is, crystallize on stretching as does natural rubber (79). 

Polyurethane thermoplastic elastomers (PTE) are characterized by microphase separation into an SS microphase and HS microdomains. In fact, the versatile physical and thermomechanical properties of TPE, which make them attractive for several technological applications, are based on their microphase-separated structure. The glass transition temperature, Tg, of the amorphous SS microphase is typically below 0°C, so that at room temperature the material behaves as an elastomer. At high temperatures (typically above 100°C), dissociation of the physical bonds occurs, the HS microdomains are destroyed and the material flows as a linear polymer. In addition to microphase separation, intermolecular hydrogen bonding and partial crystallization of the SS microphase often contribute to the thermoplastic elastomeric behavior of PTE. 

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