Rubbery polyurethanes

Curing of the acetylenic polyacetals to rubbery polyurethanes could be achieved with any of a number of commercially available diisocyanates, including 2,4-toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), dianisidine diisocyanate (DADI), and 4,4 -diisocyanatodiphenyl-methane (MDI). The first two diisocyanates were studied most extensively. The reactions were carried out in solution in benzene, toluene, and ethylene bromide, and in bulk. The bulk reaction, which is the only... 

The usual methods of synthesis of polypropylene oxide) lead to low molecular weight compounds which can be hydroxyl-ended [111]. Poly(-oxypropylene) polyols are used in the synthesis of rubbery polyurethanes [112,113]. 

The IPNs prepared were composed of a rubbery polyurethane and a glassy epoxy component. For the polyurethane portion, a carbodiimide-modified diphenyl-methane diisocyanate (Isonate 143L) was used with a polycaprolactone glycol (TONE polyol 0230) and a dibutyltin dilaurate catalyst (T-12). For the epoxy, a bisphenol-A epichlorohydrin (DER 330) was used with a Lewis acid catalyst system (BF -etherate). The catalysts crosslink via a ring-opening mechanism and were intentionally selected to provide minimum grafting with any of the polyurethane components. The urethane/epoxy ratio was maintained constant at 50/50. A number of fillers were included in the IPN formulations. The materials used are shown in Table I. 

This section is subdivided into two parts based on the two types of LLNL Halthane adhesives. The basic distinction between these adhesives is the modulus of the rubbery plateau. Halthane 73-series adhesives are tough, rubbery polyurethanes with a modulus of about 10 Pa at room temperature. On the other hand, Halthanes 87-1, 87-2, and 88-2 are stiff, almost glassy adhesives with a modulus of about 10 Pa at room temperature. 

Heterogeneity of polyols derived from hydroformylation/reduction has a negative effect on the mechanical properties of rubbery polyurethanes [9]. For... 

Over the years there has been some interest in vulcanized maleated polyisoprenes because of their superior solvent resistance, flex cracking resistance and ageing resistance compared with conventional natural rubber vulcanizates. However where these properties are of importance there are other readily available polymers such as plasticized PVC, ethylene-vinyl acetate copolymers and the rubbery polyurethanes which may be more suitable. For this reason the maleated rubbers have not become of any commercial significance. 

Figure 1.1 A caravan sandwich panel being sprayed with a moisture-hardening rubbery polyurethane adhesive, in a solvent, prior to bonding on the inner skin. The absence of mechanical fasteners greatly increases the production rate and results in a more pleasing appearance.

To overcome brittleness these materials are sometimes blended with rubbery materials and with polyurethanes. These polymers may contain unsaturated groups, particularly at the chain ends, so that graft structures may be produced rather than simple mixtures. 

If polypropylene is too hard for the purpose envisaged, then the user should consider, progressively, polyethylene, ethylene-vinyl acetate and plasticised PVC. If more rubberiness is required, then a vulcanising rubber such as natural rubber or SBR or a thermoplastic polyolefin elastomer may be considered. If the material requires to be rubbery and oil and/or heat resistant, vulcanising rubbers such as the polychloroprenes, nitrile rubbers, acrylic rubbers or hydrin rubbers or a thermoplastic elastomer such as a thermoplastic polyester elastomer, thermoplastic polyurethane elastomer or thermoplastic polyamide elastomer may be considered. Where it is important that the elastomer remain rubbery at very low temperatures, then NR, SBR, BR or TPO rubbers may be considered where oil resistance is not a consideration. If, however, oil resistance is important, a polypropylene oxide or hydrin rubber may be preferred. Where a wide temperature service range is paramount, a silicone rubber may be indicated. The selection of rubbery materials has been dealt with by the author elsewhere. ... 

At present there are five types of thermoplastic rubber (TPR). Three of these, the polyurethane, the styrenic and the polyester are termed segmented block copolymers in that they consist of thermoplastic molecules grafted to the rubbery molecules. At room temperature it is the thermoplastic molecules which clump together to anchor the rubbery molecules. When heat is applied the thermoplastic molecules are capable of movement so that the material may be shaped using conventional thermoplastic moulding equipment. 

Polyurethane networks based on triisocyante and diisocyanate connected by segments consisting of polyisobutylene are rubbery and exhibit high temperature properties, hydrolyic stability, and barrier characteristics. ... 

Two-pack polyurethanes Also called urethanes, these materials are similar to two-pack epoxies in that they can be formulated to provide different properties. They can be made into foams or soft, rubbery materials, as well as very hard, tough, abrasion-resistant coatings. 

Atomic force microscopy and attenuated total reflection infrared spectroscopy were used to study the changes occurring in the micromorphology of a single strut of flexible polyurethane foam. A mathematical model of the deformation and orientation in the rubbery phase, but which takes account of the harder domains, is presented which may be successfully used to predict the shapes of the stress-strain curves for solid polyurethane elastomers with different hard phase contents. It may also be used for low density polyethylene at different temperatures. Yield and rubber crosslink density are given as explanations of departure from ideal elastic behaviour. 17 refs. 

Polyurethane propellants derive their name from a rubbery matrix which is formed through the reaction of organic, hydroxyl-carrying... 

Wilkes and coworkers studied polyrotaxanes derived from self-assembly of a polyurethane bearing paraquat moieties and BPP34C10 [130b]. The polyurethanes contained soft (poly(tetramethylene oxide)) and hard (paraquat ionene) segments. Interestingly, dynamic mechanical analysis indicated that polyrotaxanes had higher rubbery plateau moduli than the corresponding backbones. Thermal analysis revealed that the stability was enhanced by the formation of the polyrotaxanes. 

Aminoethylpolyurethane(AEPU). A white, rubbery solid contg ca 30.6% N was obtained by treating 1 g of polyurethane(dis solved in 25 ml of toluene) with 10 ml ethyleneimine and 0.1 mi benzyl chloride in a sealed tube at 100° for 43 hours. Material remaining in-sol in ° reac ion ynivt cuacViA/1... 

Isocyanates (RNCO) are industrially relevant compounds which find application in several fields [9, 106]. Many isocyanates serve as the starting materials for the manufacture of plant protection agents, pesticides, dyes, resins and plastics, textile waterproofing agents, detergents, bleaches, and adhesives. They are also widely used in surface coatings such as paints, sealants and finishes, and in the manufacture of rubbery plastics such as those used to coat wires. Traditionally, diisocyanates are the primary feedstock for the production of polyurethanes. The global market for diisocyanates in the year 2000 was 4.4 million tonnes, of which 61.3% was methylene diphenyl diisocyanate (MDI), 34.1% was toluene diisocyanate... 

The concept of a polyfunctional hard cluster, in which a crosslinks-rich region constitutes a rigid phase, distinct from the rubbery one, has been developed by Nabeth et al. (1996), to explain the properties of certain polyurethane networks but it could be eventually applicable to the networks studied by Rietsch et al. (1976). 

Thermoplastic elastomers (TPE s) are characterized by the exceptional property that, without vulcanization, they behave as cross-linked rubbers. They are block-copolymers, in which blocks of the same nature assemble in hard domains, acting as cross-links between the rubbery parts of the chain. These hard domains lose their function when they reach their softening temperature, so that the material can then be processed as a thermoplast. One of the oldest member of the family of TPE s is SBS (styrene-butadiene-styrene block copolymer), but several other TPE s have been developed, i.a. on the basis of polyesters, polyurethanes and polyolefins. In their properties these polymers cover a broad range between conventional rubbers and soft thermoplastics. 

Chemically, spandex is a thermoplastic elastomer. It is a polyurethane block copolymer consisting of long, soft, rubbery segments alternating with rigid, high-Tg segments (see structure below). 

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