Polyesters, hydroxy terminated

Many diols and polyols like 1, 4-butanediol and hydroxy-terminated polyesters or polyethers or polyesteramides are used for reaction with diisocyanates commercially. 

Hydroxy-terminated polyester (HTPS) is made from diethylene glycol and adipic acid, and hydroxy-terminated polyether (HTPE) is made from propylene glycol. Hydroxy-terminated polyacetylene (HTPA) is synthesized from butynediol and paraformaldehyde and is characterized by acetylenic triple bonds. The terminal OH groups of these polymers are cured with isophorone diisocyanate. Table 4.3 shows the chemical properties of typical polymers and prepolymers used in composite propellants and explosives.E4 All of these polymers are inert, but, with the exception of HTPB, contain relatively high oxygen contents in their molecular structures. 

Typical examples of HCP are hydroxy-terminated polybutadiene (HTPB), car-boxy-terminated polybutadiene (CTPB), hydroxy-terminated polyether (HTPE), hydroxy-terminated polyester (HTPS), and hydroxy-terminated polyacetylene (HTPA). The physicochemical properties of various types of HCP are described in Section 4.2.3. 

HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HNS NTO NTO/HMX NTO/HMX NTO/HMX PETN PETN PETN PETN PETN PETN PETN PETN PETN PETN RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX TATB/HMX Cariflex (thermoplastic elastomer) Hydroxy-terminated polybutadiene (polyurethane) Hydroxy-terminated polyester Kraton (block copolymer of styrene and ethylene-butylene) Nylon (polyamide) Polyester resin-styrene Polyethylene Polyurethane Poly(vinyl) alcohol Poly(vinyl) butyral resin Teflon (polytetrafluoroethylene) Viton (fluoroelastomer) Teflon (polytetrafluoroethylene) Cariflex (block copolymer of butadiene-styrene) Cariflex (block copolymer of butadiene-styrene) Estane (polyester polyurethane copolymer) Hytemp (thermoplastic elastomer) Butyl rubber with acetyl tributylcitrate Epoxy resin-diethylenetriamine Kraton (block copolymer of styrene and ethylene-butylene) Latex with bis-(2-ethylhexyl adipate) Nylon (polyamide) Polyester and styrene copolymer Poly(ethyl acrylate) with dibutyl phthalate Silicone rubber Viton (fluoroelastomer) Teflon (polytetrafluoroethylene) Epoxy ether Exon (polychlorotrifluoroethylene/vinylidine chloride) Hydroxy-terminated polybutadiene (polyurethane) Kel-F (polychlorotrifluoroethylene) Nylon (polyamide) Nylon and aluminium Nitro-fluoroalkyl epoxides Polyacrylate and paraffin Polyamide resin Polyisobutylene/Teflon (polytetrafluoroethylene) Polyester Polystyrene Teflon (polytetrafluoroethylene) Kraton (block copolymer of styrene and ethylene-butylene)... 

The acid-catalysed etherification of glycol, between glycol and a hydroxy-ethyl-terminated molecule, or between two hydroxy-terminated polyester molecules cannot be totally discounted, however, for the rate of formation of diethylene glycol during the preparation of polyester by direct esterification of TA is greater than when DMT is used, and the former rate can be markedly lowered using certain buffers [42]. 

Thermoplastic elastomers exhibit physical properties that are similar to those of cast and millable elastomers at ambient temperatures. These materials, however, are not crosslinked and flow at elevated temperatures. They are fabricated like other thermoplastic polymers, are high in molecular weight, and are hydroxy-terminated. Such polymers form from linear hydroxy-terminated polyester or polyethers that are condensed with diisocyanates and glycols. Strict stoichiometry must be maintained to achieve high molecular weights. 

Block copolyesters also form in reactions between hydroxy and acid chloride-terminated prepolymers. This can take place in the melt or in solution in such solvents as chlorobenzene or o-dichlorobenzene. For relatively inactive acid chlorides, like terephthaloyl chloride, high reaction temperatures are required. Phosgene also reacts with hydroxy-terminated polyesters to form block copolymers. The reactions must be carried out in an inert solvent. Block copolyethers also form readily by ester interchange reactions with low molecular weight diesters ... 

These hydroxy-terminated polyesters may have applications as prepolymers for other high molecular weight polymers. These could condense with diisocyanates to produce polyurethane foams [44], either flexible or rigid. They also may have compatibility with epoxy resins and polyester to give rise to polyester epoxy resins, polyester-polyamide [41], and polyester-polyether copolymers. The further condensation with some unsaturated monomer may result in thermoset film formers. They can be used as a mildness additive in metal-working lubricants. 

Elastanol grade) MW = 420, hydroxyl No. = 322 Hydroxy-terminated polyester of North American Urethanes,... 

As already mentioned, the soft segment is typically a hydroxy-terminated polyester or polyether, although other hydroxy-terminated materials have also been used and studied, including polyols based on polybutadiene... 

Most hydroxy-terminated polyesters are made by coesterifying two polyols (a diol and a triol) and two diacids (an aliphatic dibasic acid and an aromatic dicarboxylic acid or its anhydride). The ratio of moles of dibasic acid to polyol must be less than 1 so as to give terminal hydroxyl groups and avoid gelation. Molecular weight is controlled by this ratio the smaller the ratio, the lower the molecular weight. The molecular weight distribution Mn, and /n are all controlled by the diol-to-triol ratio. The ratio of aromatic to aliphatic dibasic acids controls Tg of the resin. 

Water-thinnable polyester coatings have been formulated with low molecular weight oligomeric hydroxy-terminated polyesters (171). Up to about 20% of water dissolves in a polyester-Class I MF resin binder, reducing the viscosity to about half This permits making solvent-free coatings. 

Typical diisocyanates include 2,4- and 2,6-toluene diisocyanate (TDI), and methylenediphenyl-4,4 -diisocyanate (MDI). Depending on whether a rigid or elastomeric flexible polyurethane is required, the diols can be either simple diols, e.g. butan-l,4-diol, or polymeric poly ether diols (e.g. poly-THF) or hydroxy-terminated polyesters. Cross-linkage is provided by the addition of small amounts of glycerol. Carbon dioxide is liberated by the presence of trace amounts of water and this is often used as the blowing agent for foams. 

The polymers making up this group of polyesters are linear saturated polyesters of molecular weight less than 10 000. Polyesters of this type find commercial application mainly as plasticizers. It may be noted that low molecular weight saturated polyesters of a different kind are also of commercial importance these are hydroxy-terminated polyesters which are used for the preparation of polyurethanes. These intermediate polymers are described in Section 14.3.2.2. 

Polyurethane fibres of a kind different to those described above have become important within the last decade these are elastomeric fibres, which are commonly called spandex fibres. These products are made either by solution spinning or by reaction spinning. In the first process, a hydroxy-terminated polyester (e.g., an adipate) or polyether (e.g., poly(oxytetramethylene) glycol) is treated with an excess of diisocyanate (e.g., tolylene diisocyanate) to give an isocyanate-terminated pre-polymer similar to those used for cast elastomers (Section 14.6.1). The pre-polymer is dissolved in a strongly polar solvent (e.g., dimethylformamide) and treated with an aliphatic diamine or hydrazine to effect chain extension with hydrazine the following reaction occurs ... 

Heat-curing systems are based on a combination of hydroxy-terminated polyesters or polyethers and blocked polyfunctional isocyanates. When the temperature is raised, the blocking agent is removed and the free isocyanate groups react with the hydroxy groups to effect cure. The usual blocking agent is phenol and a typical blocked isocyanate is prepared by reaction of trimethylol-propane (1 mole), tolylene diisocyanate (3 mole) and phenol (3 mole) ... 

The final type of polyurethane available is known as the two-part polyol system. One component contains the isocyanate containing compound such as a prepolymer or adduct and the second component is a hydroxy group terminated resin which may or may not contain a catalyst. The most commonly used hydroxy-terminated components are polyols, castor oil, hydroxy-terminated polyesters and some epoxy resins. By varying the components of such a system a wide range of cured properties can be achieved ranging from high flexibility to very hard or brittle. The curing reactions and properties of the different polyurethanes are summarised in Table 10.9. 

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