Elastomers from polyester polyols

Polyester polyols are based on saturated aHphatic or aromatic carboxyHc acids and diols or mixtures of diols. The carboxyHc acid of choice is adipic acid (qv) because of its favorable cost/performance ratio. For elastomers, linear polyester polyols of ca 2000 mol wt are preferred. Branched polyester polyols, formulated from higher functional glycols, are used for foam and coatings appHcations. Phthalates and terephthalates are also used. 

In addition, polyester polyols are made by the reaction of caprolactone with diols. Poly(caprolactone diols) are used in the manufacture of thermoplastic polyurethane elastomers with improved hydrolytic stabiHty (22). The hydrolytic stabiHty of the poly(caprolactone diol)-derived TPUs is comparable to TPUs based on the more expensive long-chain diol adipates (23). Polyether/polyester polyol hybrids are synthesized from low molecular weight polyester diols, which are extended with propylene oxide. 

Molded urethanes are used in items such as bumpers, steering wheels, instrument panels, and body panels. Elastomers from polyurethanes are characterized by toughness and resistance to oils, oxidation, and abrasion. They are produced using short-chain polyols such as polytetram-ethylene glycol from 1,4-butanediol. Polyurethanes are also used to produce fibers. Spandex (trade name) is a copolymer of polyurethane (85%) and polyesters. 

Much work has been done on the incorporation of castor oil into polyurethane formulations, including flexible foams [64], rigid foams [65], and elastomers [66]. Castor oil derivatives have also been investigated, by the isolation of methyl ricinoleate from castor oil, in a fashion similar to that used for the preparation of biodiesel. The methyl ricinoleate is then transesterified to a synthetic triol, and the chain simultaneously extended by homo-polymerization to provide polyols of 1,000, 000 molecular weight. Polyurethane elastomers were then prepared by reaction with MDl. It was determined that lower hardness and tensile/elongation properties could be related to the formation of cyclization products that are common to polyester polyols, or could be due to monomer dehydration, which is a known side reaction of ricinoleic acid [67]. Both side reactions limit the growth of polyol molecular weight. 

The largest-volume polyether used is obtained from propylene oxide polymerized under basic conditions. Polyester polyols are produced from a number of different materials involving diacids and diols to give the ester linkage. Aliphatic polyesters generally are used for elastomers to impart chain flexibility. 

Preparation of Cast Elastomers. The cast elastomers were prepared in a two-step procedure. First prepolymers were made from one polyether polyol (poly(oxy-tetramethylene) glycol of 1000 M.W., (POTMG)) and two polyester polyols (adipate polyester of 2000 M.W. (PAG) and polycaprolactone of 1250 M.W. (PCL)) by reaction with the corresponding diisocyanates (MDI, PPDI, CHDI or NDI) at an NCO/OH ratio of 2/1. The temperature was maintained at 80°C and periodic samples were withdrawn to determined the isocyanate content. When the isocyanate content of the mixture reached within 0.3% of the calculated value, the reaction was stopped by cooling. The prepolymer could be kept for a period of six months in the absence of moisture. The isocyanate-terminated prepolymers were then chain-extended with... 

TABLE II - Properties of Elastomers Prepared from Polyester-MDI Prepolymer (Vibrathane 6020) Cured with B.D, EG, HQEE Polacure No. 740M, Polyol 50-1180 and Vibracure 3095. 

The hydroxyl terminated polybutadienes lead to PU with physico-mechanical properties significantly lower than those of PU based on polyether or polyester polyols. The nonpolar polymeric chain and the extraordinary hydrophobicity mean that hydroxy terminated polybutadienes are used for special applications, due to their excellent electrical insulation properties which are equal or superior to epoxies or silicone elastomer systems. The hydrolytic stability of PU elastomers derived from hydroxyl terminated polybutadiene is superior to the majority of other types of PU. Thus, some specific applications of... 

This relative order explains that numerous physico-mechanical properties of the polyurethanes based on polyester polyols are superior to the polyurethanes derived from polyether polyols or from polyhydrocarbon polyols (this relative order is valuable for PU elastomers, flexible and rigid PU foams). 

Polyurethane elastomers from both polyester and polyether polyols have been made from the diisocyanates CHDI and PPDI and found to possess high strength and low compression set. A feature of all... 

Polyester polyols are an important class of urethane raw materials, with applications in elastomers, adhesives, etc. They are usually made from adipic acid and ethylene glycols (polyethylene adipate) ... 

One of the more advanced technical offerings from castor oil is a line of polyester diols, triols, and higher functional polyols derived from 100% castor oil as products for the preparation of polyurethane prepolymers and elastomers [68]. The Polycin line of polyols are prepared by transesterification of ricinoleic acid and derivatives. The producers (Vertellus) offer diol and triol products, as well as a recently developed series of diol and triol glyceryl ricinoleate esters that are stated to be prepared from 100% castor oil, making them fully renewable in content. The products are recommended for coatings, sealants, and adhesive applications. 

The polyols used for solid urethane elastomers must contain very low water contents, otherwise porosity would result in a reaction with the diisocyanate as a result of CO2 generation. Many polyesters are supplied in flake form but the flaking process and the flake form are both susceptible to absorption of atmospheric moisture. By filling the containers with the liquid polyester taken directly from the still and cooling under dried air, the uptake of atmospheric moisture is minimized. When required the polyester can then be melted using electric drum heaters and passed through a heat exchanger to obtain the required temperature. 

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