Thermoplastic polyurethanes structure

Surprisingly little information is available on simple furanic urethanes and only one investigation on thermoplastic polyurethanes containing the heterocycle (34). The latter made use of difurylic diisocyanates with aliphatic diols to amve at structures like ... 

Soft blocks are composed of linear, dihydroxy poly ethers or polyesters with molecular weights between 600 and 3000. In a typical polymerization of a thermoplastic polyurethane elastomer, the macroglycol is end capped with the full amount of aromatic diisocyanate required in the final composition. Subsequently, the end-capped prepolymer and excess diisocyanate mixture reacts further with the required stoichiometric amount of monomeric diol to complete the reaction. The diol links the prepolymer segments together while excess diol and diisocyanate form short hard-block sements, leading to the (AB)n structure illustrated in Figure 1. Block lengths in (AB)n polymers are frequently much shorter than those in anionically synthesized ABA block copolymers. 

Thermoplastic Polyurethane Elastomer Structure—Thermal Response Relations... 

Polyurethanes. Thermoplastic polyurethanes (TPUs) contain urethane groups, —O—CO—NH— in their structure obtained from the reaction of a diisocyanate (OCN—R—CNO) with a polyol. These polyurethanes are block copol3miers in which hard blocks formed by reaction of a diisocyanate with a short-chain diol alternate with soft blocks formed by reaction of a diisocyanate with a long-chain diol. 

In the current study, samples of impact polystyrene that contained a combination of light stabilizers LS I and LS II and samples that contained no light stabilizers were weathered outdoors in Florida and were monitored for changes in physical appearance and for changes in the chemical structure of the surface by use of a multiple internal reflectance IR spectrophotometer. Also, samples of a thermoplastic polyurethane that was stabilized with just LS I and samples that contained no light stabilizers were weathered and monitored in the same way as the impact polystyrene. We hope to establish at what point... 

Ho et al (1996) examined polyol or polysiloxane thermoplastic polyurethanes (TPUs) as modifiers in cresol-formaldehye novolac epoxy resins cured with phenolic novolac resin for computer-chip encapsulation. A stable sea-island dispersion of TPU particles was achieved by the epoxy ring-opening with isocyanate groups of the urethane prepolymer to form an oxazolidone. The flexural modulus was reduced by addition of TPU and also the Tg was increased due to the rigid oxazolidone structure. Mayadunne et al (1999) extended this work to a series of phenol- and naphthol-based aralkyl epoxy resins. 

In the absence of a blowing agent and with conditions favoring the formation of linear chains, thermoplastic polyurethane elastomers can be formed. Materials with different properties can be obtained by altering the ratio of hard to soft blocks, and it is also observed that, in many cases, the hard segments can crystallize. This can give rise to phase-separated structures, shown schematieally in Figure 2.6, which behave as thermoplastic elastomers (see also Section 15.6). 

One of the most complex types of step-growth reaction is that between a di-glycol, HOROH, and a di-isocyanate, 0=C=NR N=C=0, to produce a polyurethane, which contains the structural unit —O—R O—(C=0)—(NH)—R (NH)—(C=0)—. Several subsidiary reactions can also take place and, although all of the possible reaction products are unlikely to be present simultaneously, polyurethanes usually have complex structures. Thermoplastic polyurethanes are copolymers that usually incorporate sequences of polyester or polyether segments. 

Thermoplastic Polyurethanes (TPUs). The first commercial TPEs were the TPUs, which have the same block copolymer morphology as do the COPs. Their general structure is -A-B-A-B-, where A represents a hard crystalline block derived by chain extension of a diisocyanate with a glycol. The soft block, represented by B, can be derived from either a polyester or a polyether. Typical TPU structures, both polyester and polyether types, are represented here ... 

Fig. 5 The stress-strain response is shown for a glass fiher-SMP composite with a thermoplastic polyurethane matrix. At 10 wt% glass fiber loading, permanent strain evolves in the material, whereas 20 and 30 wt% loadings help stabilize the network structure and lead to less permanent deformation over successive cyclic loading. Reprinted from Ohki et al. [66], Copyright 2004, with permission fi-om Elsevier...

Elastolit SR, Structural RIM polyurethanes, BASF Corp., Urethanes Specialties Elastollan, Thermoplastic polyurethane elastomers, BASF Corp., Urethanes Specialties Elastomag, Magnesium oxide, Morton International Inc., Morton Performance Chemicals... 

It is known that the potential monomers or pol5uner building blocks should have at least one (in the case of addition polymerization) or two double bonds in their structure (in the case of condensation pol5nnerization) to get thermoplastic materials. Therefore, triglycerides should be modified of fimctionalized before pol5nnerization. Nevertheless, there are some examples of thermoplastic biomaterials obtained from naturally functionalized castor oil with homogeneous composition and acceptable polymerization yields. The main thermoplastic materials already synthesized from vegetable oils are thermoplastic polyurethanes (TPUs), polyamides (PA), thermoplastic polyesters, polyesteramides and polyanhydrides. 

Yamasaki, S. Nishiguchi, D. Kojio, K. Fumkawa, M. Effects of Polymerization Method on Structure and Properties of Thermoplastic Polyurethanes. Journal of Polymer Science B, Polymer Physics, 2007, 45, 800-814. 

Bueno-Feirer, C. Hablot, E. Peirin-Sarazin, R Gairigos, M. C. Jimenez, A. Ave-rous, L. Structure and morphology of new bio-based thermoplastic polyurethanes obtained from dimer fatty acids. Macmmolecular Materials and Engineering, 2012, 297(8), 111-19A. 

Thermally induced property loss in polyurethanes occurs by two mechanisms physical, or reversible, breakdown of the polymer network and degradation due to chemical, or irreversible, processes. Physical breakdown is more of a problem with linear, thermoplastic polyurethanes and is related to such problems as softening and creep at elevated temperatures. This can be overcome by incorporating chemical crosslinks into the polymer matrix. Irreversible thermal degradation is a much more serious problem. The thermal stability of these materials is dependent upon their method of preparation and, more importantly, upon the structure of the resulting polymer. Thermolysis usually occurs within the isocyanate-derived portions of the polymer. The order of stability of the various isocyanate-derived linkages most commonly found in polyurethanes is ... 

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