Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-08-07
2004-02-24
Short, Patricia A. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S453000
Reexamination Certificate
active
06696528
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a low molecular weight engineering thermoplastic polyurethane and blends thereof. More particularly the invention relates to a dispersion of a low molecular weight engineering thermoplastic polyurethane in a polyarylene ether matrix.
Polyarylene ethers (PAEs) are a class of thermoplastic resins with excellent mechanical and electrical properties, heat resistance, flame retardancy, low moisture absorption, and dimensional stability. These resins are widely used in automobile interiors, particularly instrument panels, and electrical as well as electronic applications.
PAEs are very difficult to process (for example, by injection molding) as a result of their high melt viscosities and their high processing temperature relative to their oxidative degradation temperature. Consequently, PAEs are commonly blended with compatible polymers such as polystyrene (WO 97/21771 and U.S. Pat. No. 4,804,712); polyamides (U.S. Pat. No. 3,379,792); polyolefins (U.S. Pat. No. 3,351,851); rubber-modified styrene resins (U.S. Pat. Nos. 3,383,435 and 3,959,211, and Ger. Offen. No. 2,047,613); and mixtures of polystyrene and polycarbonate (U.S. Pat. Nos. 3,933,941 and 4,446,278). Unfortunately, improvements in processing have generally been obtained at the expense of flexural modulus, flexural strength, or heat distortion temperature.
Epoxy resins have also been investigated as a reactive solvent for the PAE. (See Venderbosch, R. W., “Processing of Intractable Polymers using Reactive Solvents,” Ph.D. Thesis, Eindhoven (1995); Vanderbosch et al.,
Polymer
, Vol. 35, p. 4349 (1994); Venderbosch et al.,
Polymer
, Vol. 36, p. 1167 (1995a); and Venderbosch et al.,
Polymer
, Vol. 36, p. 2903 (1995b)). In this instance, the PAE is first dissolved in an epoxy resin to form a solution that is preferably homogeneous. An article is then shaped from the solution, and the solution is cured at elevated temperatures, resulting in a phase separation that can give a continuous PAE phase with epoxy domains interspersed therein. The properties of the finished article are primarily determined by the PAE; however, the use of an epoxy resin as a reactive solvent for the PAE is not practical in a continuous melt process like injection molding because the epoxy resin needs a curing agent to set. The curing agent will, over time, accumulate in the injection molding barrel, thereby fouling the machine. Furthermore, the cure and subsequent phase separation has to take place at at least 150° C., which is impractical in a molder environment.
In view of the deficiencies in the art, it would be desirable to find a reactive solvent that would solve the processing problems inherent in some reactive solvents for PAE, without deleteriously affecting the physical properties of the PAE.
SUMMARY OF THE INVENTION
The present invention addresses a need in the art by providing a composition that comprises a single phase melt containing 1) a polyarylene ether and 2) an engineering thermoplastic polyurethane having a) a T
g
of at least 50° C. and b) a number average molecular weight of not greater than about 10000, and not less than 2000 amu; wherein the polyarylene ether is represented by the formula:
where Ar is a substituted or unsubstituted aromatic nucleus and n is an integer of at least 10.
In another aspect, the present invention is a two-phase composite that comprises 1) a polyarylene ether and 2) an engineering thermoplastic polyurethane having a) a T
g
of at least 50° C. and b) a number average molecular weight of not greater than about 10,000, and not less than 2000 amu; wherein the polyarylene ether is represented by the formula:
where Ar is a substituted or unsubstituted aromatic nucleus and n is an integer of at least 10, and wherein the composite is further characterized by having a first T
g
within 5° C. of the T
g
of the pure engineering thermoplastic polyurethane and a second T
g
within 10° C. of the T
g
of the pure polyarylene ether.
In a third aspect, the present invention is a composition comprising an engineering thermoplastic polyurethane having a T
g
of at least 50° C. and a number average molecular weight of not more than 10,000 and not less than 3000 amu (Daltons).
The low molecular weight engineering thermoplastic polyurethanes (ETPUs) are depolymerizable at advanced temperatures, resulting in a dramatic decrease in melt viscosity, and repolymerizable at reduced temperatures. Moreover, the ETPU and PAE form a homogeneous melt at advanced temperatures below the degradation temperature of the PAE, and form a heterogeneous dispersion of the ETPU in a PAE matrix phase at reduced temperatures. Consequently, the blend of the PAE and ETPU melt processable at temperatures below the degradation temperature of the PAE, yet retain the properties of the unadulterated PAE at the reduced temperatures.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is a dispersion comprising a PAE and an ETPU having a T
g
of at least 50° C. and a number average molecular weight of not more than 10,000, preferably not more than 7,000, and more preferably not more than 5500 amu; and not less than 1000, preferably not less than 2000, and more preferably not less than 3000 amu. The PAE is represented by the following formula:
where Ar is a substituted or unsubstituted aromatic nucleus and n is an integer of at least 10. The aromatic nucleus can be, for example, phenylene, alkylated phenylene, chlorophenylene, bromophenylene, and naphthalene. Ar is preferably 2,6-dimethyl-1,4-phenylene,2-methyl-6-ethyl-1,4-phenylene,2,6-diethyl-1,4-phenylene, and 2,3,6-trimethyl-1,4-phenylene; Ar is more preferably 2,6-dimethyl-1,4-phenylene. Preferred PAEs are poly(2,6-dimethyl-1,4-phenylene) ether and the copolymer obtained by the polymerization of 2,6-dimethyl phenol and 2,3,6-trimethyl phenol, with poly(2,6-dimethyl-1,4-phenylene) ether being more preferred.
The low molecular weight ETPUs contain structural units formed from the reaction of a polyisocyanate, a diol chain extender, a monofunctional chain stopper, and optionally, a high molecular weight polyol. The polyisocyanate that is used to form the TPU is preferably a diisocyanate, which may be aromatic, aliphatic, or cycloaliphatic. Representative examples of these preferred diisocyanates can be found in U.S. Pat. Nos. 4,385,133, 4,522,975, and 5,167,899, the disclosure of which diisocyanates are incorporated herein by reference. Preferred diisocyanates include 4,4′-diisocyanatodiphenyl-methane, p-phenylene diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-diisocyanatocyclohexane, hexamethylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3′-dimethyl-4,4′-biphenyl diisocyanate, 4,4′-diisocyanatodicycl, and 2,4-toluene diisocyanate, or mixtures thereof. More preferred are 4,4′-diisocyanatodicyclohexylmethane and 4,4′-diisocyanatodiphenylmethane.
As used herein, the term “diol chain extender” refers to a low molecular diol having a molecular weight of not greater than 200. Preferred chain extenders include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, neopental glycol, 1,4-cyclohexanedimethanol, and 1,4-bishydroxyethylhydroquinone, and combinations thereof. Particularly preferred difunctional chain extenders include 1,6-hexanediol and mixtures of 1,4-butane diol and diethylene glycol, 1,4-butane diol and triethylene glycol, and 1,4-butane diol and tetraethylene glycol.
As used herein, the term “monofunctional chain stopper” refers to an aliphatic, cycloaliphatic, or aromatic monoalcohol, monoamine, or monothiol. In general, the type and the concentration of the monofunctional chain stopper is preferably selected so that the final composite has two T
g
s, one of which is within 10° C., more preferably within 5° C., of the T
g
of the PAE, and the other of which is within 5° C., more preferably within 2° C., of the ETPU. The monofunctional chain stopper is preferably a monoalcohol, more pr
D'Hooghe Edward Louis
Moses Paul J.
van Pelt Wilfred
Short Patricia A.
The Dow Chemical Company
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