High molecular weight RTPU's are single- or two-phase polymers that can be prepared by the reaction of approximately stoichiometric amounts of a low molecular weight diol chain extender (molecular weight of not more than 300) and optionally a high molecular weight diol (molecular weight generally in the range of from 500 to 8000) with a dusocyanate. These RTPU's have a glass transition temperature (T _g ) of not less than 50°C and typically have a hard segment content of not less than 75 percent. The disclosure and preparation of RTPU's is described, for example, by Goldwasser et al. in U.S. Patent 4,376,834

Because RTPU's tend to have a weight average molecular weight greater than 200,000 and a capacity for intermolecular hydrogen bonding, these polymers require very high thermal and/or mechanical energy input to generate the homogeneous, plasticated melt needed for thermoplastic forming processes such as injection molding or extrusion. The requirement for high energy input in the melting/plasticating stages may stall the screw of an injection molding machine or extruder, or may result in localized overheating of material due to high shear in the transition zone of the screw, which in turn causes polymer degradation and splay defects in the molded part.

One method for overcoming these processing problems is to incorporate a chain stopper such as a monofunctional alcohol into the formulation, as disclosed by Quiring in U.S. Patent 4,371 ,684. Unfortunately, physical properties of the RTPU product, such as T _g and toughness, suffer at the expense of improved processability. Alternatively, urethane molecular weight can be reduced by deliberately polymerizing with a deficiency of isocyanate (that is, an excess of hydroxyl groups). As disclosed by Ulnch in Kirk-Othmer: Encyclopedia of Chemical Technology, Vol. 23, 3rd Ed., p. 598 (1983), such products are preferred for use in extrusion processes. However, in practice, the molecular weight of the polymer may be very difficult to control for some large scale manufacturing processes using this off-ratio approach. It is therefore desirable to find a practical way to improve processability of RTPU's without sacrificing physical properties.

The present invention is a rigid thermoplastic polyurethane having a T _g of at least 50°C and further having a sufficient concentration of units of an aromatic diol to lower the temperature at which the rigid thermoplastic polyurethane can be melt processed. In another aspect, the present invention is a thermoplastic polyurethane having a flex modulus of at least 690,000 kPa (100,000 psi), and further having a sufficient concentration of units of an aromatic diol to lower the temperature at which the thermoplastic polyurethane can be melt processed The compositions of the present invention show improved processability with insubstantial loss of physical properties.

The RTPU of the present invention contains a hard segment of the reaction of a dusocyanate, a diol chain extender having a molecular weight of not more than 300, and an aromatic diol The term aromatic diol is used herein to describe an aromatic or heteroaromatic moiety having two OH groups attached to the aromatic carbon atoms. The hard segment content of the RTPU is sufficiently high to

produce a resin having a T _g of greater than 50°C, and preferably constitutes from 5, more preferably from 90, to 100 weight percent of the RTPU

A thermoplastic polyurethane that is not by definition an RTPU may be used in the present invention provided sufficient amounts of suitable fillers, reinforcing fibers, or other thermoplastic materials are added to achieve a flex modulus of at least 690,000 kPa (100,000 psi). Suitable fillers include talc, silica, mica, or glass beads, or mixtures thereof, suitable reinforcing fibers include glass, carbon, or graphite fibers, or mixtures thereof, and suitable thermoplastics include acrylonitπle- butadiene-styrene, polyacetal, nylon, polybutylene terephthalate, polyethylene terephthalate, and ionomers As used herein, the term 'TPU" refers to a rigid TPU or a TPU having a flex modulus of at least 690,000 kPa (100,000 psi) .

The aromatic diol generally has a molecular weight of not more than 500 Examples of aromatic diols include, but are not restricted to, resorcinol, catechol, hydroquinone, dihydroxynaphthalenes, dihydroxyanthracenes, bιs(hydroxyaryl) fluorenes, dihydroxypheπanthrenes, dihydroxybiphenyls, 4,4'-dιhydroxystιlbenes; and bιs(hydroxyphenyl) propanes Preferred aromatic diols include hydroquinone, 4,4'-dιhydroxybιphenyl, 9,9-bιs(4-hydroxyphenyl) fluorene, 4,4'-dιhydroxy- α-methylstilbene; and bisphenol A

Preferred diisocyanates include aromatic, aliphatic, and cycloaliphatic diisocyanates and combinations thereof Representative examples of these preferred diisocyanates can be found, for example, in U S Patents 4,385,133, 4,522,975; and 5,167,899 More preferred diisocyanates include 4,4'-dιιsocyanatodιphenylmethane, p-phenylene diisocyanate, 1 ,3-bιs(ιsocyanatomethyl)cyclohexane, 1 ,4-dιιsocyanatocyclohexane, hexamethylene dusocyanate, 1 ,5-naphthalene dusocyanate, 3,3'- dιmethyl-4,4'-bιphenyl diisocyanate, 4,4'-dιιsocyanatodιcyclohexylmethane, and 2,4-toluene dusocyanate, or mixtures thereof More preferred are 4,4'-dιιsocyanatodιcyclo-hexylmethane and 4,4'- dnsocyanatodiphenylmethane Most preferred is 4,4'-dιιsocyanato-dιphenylmethane.

Preferred diol chain extenders are ethylene glycol, 1 ,3-propanedιol, 1 ,4-butanedιol, 1 ,5- pentanediol, 1 ,6-hexanedιol, diethylene glycol, tπethylene glycol, tripropylene glycol, tetraethylene glycol, neopental glycol, 1,4-cyclohexanedιol, 1 ,4-cyclohexanedιmethanol, 1 ,4- bishydroxyethylhydroquinone, 2,2-bιs(β-hydroxy-4-ethoxyphenyl)propane (that is, ethoxylated bisphenol A), and mixtures thereof. More preferred chain extenders are 1 ,4-butanedιol, 1 ,6- hexanediol, 1 ,4-cyclohexanedιmethanol, diethylene glycol, triethylene glycol, tripropylene glycol, and mixtures thereof

The RTPU may optionally contain blocks of a high molecular weight glycol having a molecular weight in the range from 750, preferably from 1000, and more preferably from 1500, to 8000, preferably to 6000, and more preferably to 5000 These high molecular weight glycol blocks constitute a sufficiently low fraction of the RTPU such that the T _g of the RTPU is above 50°C Preferably, the high molecular weight glycol blocks constitute from 25, and more preferably from 10, to 0 weight percent of the RTPU

The high molecular weight glycol is preferably a polyester glycol or a polyether glycol or a combination thereof. Examples of preferred polyester glycols and polyether glycols include polycaprolactone glycol, polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol, polyethylene adipate, polybutylene adipate, polyethylene-butylene adipate, and poly(hexamethylene carbonate glycol), or combinations thereof

The isocyanate to OH ratio of the reactants varies from 0.95:1 , preferably from 0.975- 1 , and more preferably from 0.985:1 , to 1.05:1 , preferably to 1.025:1 , and more preferably to 1.015:1.

The amount of the aromatic diol used to prepare the TPU is sufficient to lower the temperature at which the TPU can be melt processed In general, the concentration of the aromatic diol will not exceed that amount which causes the tensile elongation at break of the TPU to be less than 5 percent, as determined by ASTM D-638. Preferably, the concentration of the aromatic diol is in the range of from 0 1 , more preferably from 0.5, and most preferably from 2 mole percent, to preferably 15, more preferably 10, and most preferably 5 mole percent, based on the total moles of diol used to prepare the TPU Preferably, the temperature at which the TPU is processed is lowered by at least 5°C, more preferably by at least 10°C, and most preferably by at least 20°C by the presence of the aromatic diol

The polymerization process is usually carried out in the presence of a catalyst that promotes the reaction between isocyanate groups and hydroxy groups Examples of suitable catalysts can be found in Saunders et al., Polyurethanes, Chemistry and Technology, Part I, pp. 228-232 (1963) Such catalysts include organic and inorganic acid salts and organometallic derivatives of bismuth, lead, tin, iron, antimony, uranium, cadmium, cobalt, thorium, aluminum, mercury, zinc, nickel, cerium, molybdenum, vanadium, copper, manganese, and zirconium, as well as phosphines and tertiary organic amines. Representative tertiary organic amines include triethylamine, tπethylenediamine, N,N,N',N'-tetramethylethylenedιamιne, N,N,N',N'-tetraethylethylenedιamιne, N-methylmorpholine, N,N- dimethanolamine, and N,N-dιethanolamιne. Preferred catalysts are tetravalent or divalent organotm compounds such as di-n-butyltin diacetate, dimethyltin dimercaptide, dibutyltin dilaurate, stannous oleate, and stannous octoate. The amount of catalyst used is generally in the range of 0.02 to 2 weight percent, based on the weight of the total polymer The compositions of the present invention can also incorporate various additives, such as antioxidants, fire retardants, impact modifiers (as disclosed, for example, in U.S. Patent 4,567,236), and plasticizers, commonly used in the art in such compositions.

The following example is for illustrative purposes only and is not meant to limit the scope of the invention

Example 1 - Preparation of RTPU's Containing Units Of Bisphenol A

An RTPU was prepared by weighing the appropriate amounts of the diols plus 0.2 percent by weight IRGANOX™ 1010 stabilizer (Trademark of Ciba-Geigy), based on the weight of the diols and the diisocyanate, into a 1000 mL kettle These ingredients were heated to between 80°C and 100°C,

and stripped under vacuum to remove water. After approximately 1 hour of stripping, the hydroxy terminated ingredients were mixed vigorously with diphenyl methane diisocyanate and the hot polymer was poured into pans for cooling. Each cast consisted of a total of 375 g of polymer, catalyzed by 1 drop of FOMREZ™ UL-28 catalyst (Trademark of Witco Corp.). In all cases, the NCO/OH ratio was constant at 1.005.

As shown in Table I, the polymer based on a combination of 98 mole percent 1 ,4-cyclohexanedimethanol (CHDM) and 2 mole percent bisphenol A (BPA) exhibited a processing temperature that was 10C° to 20C° lower than the processing temperatures required for a 100 percent CHDM based polymer. The polymer based on a combination of 96 mole percent 1 ,6-hexanediol (HDO) and 4 mole percent BPA exhibits a similar effect, as shown in Table II. A further benefit of the addition of the BPA in each case was that the holding pressure required to fully pack the mold was reduced by over 1380 kPa (200 psi). Also, the percent tensile elongation of the polymers containing BPA was maintained at acceptable levels.

Table I -The Effect of 2 Percent (%) Bisphenol A on RTPU Processing Temperatures

Total diol 100% CHDM 98% CHDM/2% BPA

Zone 1 processing T (°C) 230 210

Zone 2 processing T (°C) 230 220

Zone 3 processing T (°C) 235 220

Tensile Elongation 100% 63%

Holding pressure 6340 kPa 4820 kPa (920 psi) (700 psi)

Table II - The Effect of 4 Percent (%) Bisphenol A on RTPU Processing Temperature

Total diol 100% HDO 96% HDO/4% BPA

Zone 1 processing T (°C) 200 180

Zone 2 processing T (°C) 210 190

Zone 3 processing T (°C) 210 190

Tensile Elongation 137% 162%

Holding pressure 6200 kPa 4650 kPa (900 psi) (675 psi)

By comparison, 2 mole percent of the aliphatic monoalcohol, stearyl alcohol (SA), also reduced the processing temperature by about the same amount. In contrast, as illustrated in Comparison Table A, whereas the presence of 2 mole percent BPA reduced the deflection temperature under load (DTUL) for a formulation containing HDO by only 2C°, the same amount of SA reduced the DTUL by over 10C°. Similar results were observed when 4 mole percent BPA or SA was present in a formulation containing CHDM.

Comparison Table A - Comparison of Change in RTPU Deflection Temperatures Under Load: Stearyl Alcohol vs. Bisphenol A.

Formulation DTUL* (°C) DTUL (°C) 455 kPa (66 psi) 1820 kPa (264 psi)

100% HDO 89 76

96% HDO, 4% BPA 87 74

96% HDO, 4% SA 77 67

100% CHDM 134 119

98% CHDM, 2% BPA 132 118

98% CHDM, 2% SA 123 107

*as determined by ASTM D-648 using 0.32 cm thick specimens

Whereas the presence of the monofunctional alcohol diminished important physical properties, the presence of the aromatic diol improved processability without deleteriously affecting such properties. Although not bound by theory, it is believed that the presence of the monofunctional alcohol acted as a chain terminator in limiting molecular weight growth during polymerization; thus, a reduction of polymer processing temperature was accomplished by a reduction of polymer molecular weight, which can be detrimental to the physical properties of the polymer in some cases. The reduced processing temperatures coupled with virtually undiminished physical properties for the aromatic diol units can be explained as follows. The units of aromatic diols that were formed in the polymerization process (aromatic urethane units) were apparently more thermally labile than units of aliphatic diols (aliphatic urethanes). Thus, these aromatic urethanes cleaved at lower temperatures than the aliphatic urethanes, resulting in a less viscous polymeric material that was processable at lower temperatures without reduction in final polymer molecular weight.