Diisocyanate chain, aromatic

Japan s Showa Highpolymers, part of the Showa Denko group, and Korea s SK Chemicals both have small plants producing aliphatic (polybutylene succinate) and aliphatic-aromatic (polybutyrate adipate terephthalate) polyesters. Both firms also offer their resins in the USA. Showa s Bionelle products are used in commodity bags, agricultural films, traffic cones, and industrial trays. Some Bionolle grades are modified with diisocyanate chain extenders to improve stiffness and thermal properties. 

TPEs associating both rigid and soft polyester blocks have also been described. They cannot be obtained by the melt polyesterification used for polyesterether TPEs, since interchange reactions would yield random—rather than block — copolyesters. The preferred method involves the reaction of OH-terminated aliphatic and aromatic-aliphatic polyesters with chain extenders such as diisocyanates and results in copoly(ester-ester-urethane)s. 

Singer S.M. and Allot M.T., Thermoplastic polyurethane elastomer based on a saturated hydroxyl terminated polyol, difunctional aromatic chain extender and 1,5-naphthalene diisocyanate, US Patent 5 599 874, 1997. 

In Figure 6, the larger values of A b for systems 4 and 5 compared with the other systems illustrate the increased opportunities for intramolecular reaction in tetrafunctional compared with trifunctional systems. Further, the smaller values of b for system 5 compared with those for system 1, with the same value of v, probably indicated that equation(3) relatively undercounts the opportunities for intramolecular reaction for tetrafunctional as compared with trifunctional reactants, so that smaller values of b are required in compensation. System 3, based on aromatic diisocyanate, gives the largest values of b, characteristic of its stiffer chain structure. 

Telechelic polymers rank among the oldest designed precursors. The position of reactive groups at the ends of a sequence of repeating units makes it possible to incorporate various chemical structures into the network (polyether, polyester, polyamide, aliphatic, cycloaliphatic or aromatic hydrocarbon, etc.). The cross-linking density can be controlled by the length of precursor chain and functionality of the crosslinker, by molar ratio of functional groups, or by addition of a monofunctional component. Formation of elastically inactive loops is usually weak. Typical polyurethane systems composed of a macromolecular triol and a diisocyanate are statistically simple and when different theories listed above are... 

PCL-diol and diphenylmethane-i -diisocyanate (MDI), by R. delemar lipase were examined. These polyurethanes have both the hydrogen bonds among polymer chains and aromatic rings in the polymer molecules. R. delemar lipase could hydrolyze the polyurethanes though the rate of hydrolysis toward polyurethanes decreased as compared to that ward PCL-diol. The rate of hydrolysis decreased with decreasing the Mn of PCL-moiety of polyurethanes (Figure T). 

Aromatic diamines are the most commercially used chain extenders with TDI-based polyurethanes. The rate of reaction of a simple aromatic diamine is too great for normal use. Thus the rate of reaction is commonly controlled by having substitutes on the aromatic ring. An example is the simple diisocyanate MDA and MOCA with the chlorine atoms in MOCA slowing the reaction to a useable rate. 

Jahnisch et al. used an IMM falling-film microreactor for photochlorination of toluene-2,4-diisocyanate [38] (see also Chapter 4.4.3.3, page 161). As a result of efficient mass transfer and photon penetration, chlorine radicals were well distributed throughout the entire film volume, improving selectivity (side chain versus aromatic ring chlorination by radical versus electrophilic mechanism) and spacetime-based yields of l-chloromethyl-2,4-diisocyanatobenzene compared to those obtained using a conventional batch reactor. 

The reaction of toluene-2,4-diisocyanate with chlorine to l-chloromethyl-2,4-diisocyanatobenzene was carried out in a falling-film microstructured reactor with a transparent window for irradiation [264]. There are two modes of reaction. The desired radical process proceeds with the photoinduced homolytic cleavage of the chlorine molecules, and the chlorine radical reacts with the side chain of the aromatic compound. At very high chlorine concentrations radical recombination becomes dominant and consecutive processes such as dichlorination of the side chain may occur as well. Another undesired pathway is the electrophilic ring substitution to toluene-5-chloro-2,4-diisocyanate, promoted by Lewis acidic catalysts in polar solvents at low temperature. Even small metallic impurities probably from corrosion of the reactor material can enhance the formation of electrophilic by-products. 

Several types of diisocyanates (aromatic, aliphatic, cyclo aliphatic) and many different glycol-chain extenders (open-chain aliphatic, cyclo aliphatic, aromatic aliphatic) can be used to produce TPU-elastomer hard segments. In the more conventional and practical formulations only a single diisocyanate component is used to make a TPU, so the diisocyanate is common to both the hard and soft segments. The polymer chemist makes his diisocyanate and glycol-chain-extender component selections based on such considerations as desired TPU mechanical properties, upper service temperature, environmental resistance, solubility characteristics, and economics. 

In diisocyanates where the two isocyanate groups are on different aromatic rings or where they are separated by aliphatic chains the effect of one isocyanate or urethane group on a second isocyanate group is less pronounced. The effect becomes still less as the aromatic rings are separated further and further from each other, for example, by progressively longer aliphatic chains. 

Usually, methylene diisocyanate (MDI) is used with m-phenyl diamine (m-PDA) with hard (aromatic amine) or- soft (amine terminated polyether with MW of 500-5400 Daltons) chain extenders. With optimized formulations and extruder-mold conditions, cycle times of 3 to over 5 min can be obtained. With the use of internal mold release agents, the cycle time can be reduced to less than 2 min. Typical RIM operations for the production of automotive parts can run down to 1-min cycle time. These products range from the softer bumper covers to stiffer vertical body panels, such as fenders, doors, and quarter panels. 

In the case of PUR block polymers, for example, the hard segments may consist, of a combination of aromatic diisocyanates and soft chain diols, and... 

A number of different hindered diamines have been investigated as a substitute for MOCA (1). In addition to diamine curing agents, which are used most frequently with elastomers based on polyether polyols and toluene diisocyanate (TDI), prepolymers based on polyether or polyester polyols and 4,4 -diphenylmethane diisocyanate (MDI), can be cured with diols to yield elastomers with similar properties to those of diamine-cured polyester-TDI elastomers. The most common chain extender is butanediol. However, to achieve improved mechanical properties, especially at elevated temperatures, aromatic diols are often used. The most common one is hydroquinone di-(beta-hydroxy-ethyl) ether (HEQ). 

In 2001, an efficient step-growth polycondensation approach, reminiscent of that used to prepare metal-metal-bonded polymers 217 and 218, was successfully developed to yield polyurethanes 225 with Mo2lt2 clusters in the backbone. " Well-characterized polymers with molecular weights of up to 136,000 (PDI = 3.1), which correspond to a number average of around 30 clusters per polymer chain, were obtained by means of this method. It involved treatment of a diol of the Mo2lt2 cluster with the diisocyanate OCN-R-NGO (R = aliphatic or aromatic spacer) in the presence of a tin catalyst. The unusual optical properties of organometallic clusters will drive applications-oriented work on these materials. " ... 

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