Elastomers diol crosslinkers

If the diol chain extender is used in exact molar proportion to the unreacted isocyanate, then a linear polyurethane elastomer is obtained. The resulting thermoplastic elastomer may be extruded or injection-moulded, and the properties arise from the ability of the hard and soft segments to form semi-crystalline domains that act as virtual crosslinks in the polymer and give it elastomeric properties, as shown in Figure 1.17. 

Polyurethane elastomers derive their elastomeric properties from phase separation of the hard and soft copolymer segments, such that the hard (urethane) segment domains serve as crosslinks between the amorphous soft segment domains, which are usually polyesters or polyethers. We are interested in the systems in which the hard segments are prepared from diphenyl-methane 4,4 -diisocyanate (MDI) with a linear diol as the chain extender ... 

Thus, from high MW diols (MW = 1000-4000 daltons) polyethers (polyalkyleneoxides, polytetrahydrofuran (PTHF)), polyesters, polycarbonates (PC), polybutadienes, etc., by the reaction with diisocyanates [toluene diisocyanate (TDI), or pure diphenyl methane diisocyanate (MDI)], high MW linear polyurethanes are obtained (no crosslinking), with high elasticity (polyurethane elastomers, spandex fibres, some adhesives and sealants, etc). 

Chem. Descrip. Aliphatic urethane diol resin modifier Uses Modifier for amino or isocyanate crosslinked coatings, elastomers, and adhesives, automotive, aerospace, wood/paper, and general industrial coatings, and inks Features Water-sol. reduces VOCs... 

The obtained theoretical predictions have been verified in experiments on real elastomers. The elastomers tested in our experiments were amorphous polybutadiene urethanes (PBU) wifli polymer network of different density 0.3 kmol/m (PBU-1), 0.05 kmol/m (PBU-2), 0.2 kmol/m (PBU-3), 0.1 kmol/m (PBU-4). Oligooxypropylene triol - Laprol 373 was used as a crosslinking agent at the curing of prepolymer of oligobutadiene diol. The elastomer specimens were manufactured in the form of disks, 35 mm in diameter and 2 mm thick. The kinetics of specimen swelling was determined in low-molecular liquids toluene, dibutyl sebacate (DBS), dioctyl sebacate (DOS). 

The index m in Eqs. [10.33] and [10.34] is a measure of ability of a liquid to mpture a physical network of elastomer. Table 10.13 presents the values of the m parameter obtained at 298K for swelling of PBU crosslinked polydiene urethane epoxide, PDUE, crosslinked elastomers of butadiene-nitiile mbbers SCN-40, SCN-26, SCN-18 and also for crosslinked polyether urethane, PEU, synthesized from polytetramethylene oxide diol having M. 1000. Dibutyl phthalate, DBP, and tributyl phosphate, TBP, were used. 

However it is also established that the commonly used diphenylmethane and naphthalene diisocyanate-based elastomers are frequently chain-extended with glycols. Table 3.12 contrasts the effects of diamine and glycol chain extenders with a toluene diisocyanate/polyether-based prepolymer, Adiprene LI00. With the unsymmetrical diisocyanates, such as TDI and MDI, polyol chain extenders give elastomers of poorer properties than diamines, and it is usually desirable to introduce additional crosslinking into diol-extender elastomers by the use of a proportion of a triol such as... 

The blocked isocyanate function of aminimides also allows their use as polyurethane adhesives. Thus bis(aminimides) crosslink with polyester or polyether diols to yield a range of elastomers dependent upon the structure of the bis(aminimide) and the co-reactant chosen. For example, bis(aminimides) mixed with polyhydroxyl components can provide stable, single-package prepolymer compositions which yield polyurethanes on heating without the problem of isocyanate moisture sensitivity which can plague polyurethane applications. 

Elastomeric networks with thermoreversible linkages are receiving growing interest as it is possible to reprocess them several times by simple reheating. In this field, thermoplastic elastomers (ABS) [63] and iono-mers (Surlyn) [64] have been widely developed and applied. Several attempts have been reported to apply the same principles to statistical copolymers of ethylene with maleic anhydride or acrylic and methacrylic acids [65], crosslinked with diols and/or ethoxylamines [66]. The idea which sustained these papers was to take advantage of the thermoreversibility of ester linkage. 

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