Thermoplastic elastomer compositions rheology-modified using peroxides and free radical coagents

Abstract

Rheology-modified thermoplastic elastomer compositions comprising a melt blend of an ethylene/a-olefin polymer and a high melting polymer such as polypropylene or a propylene/a-olefin copolymer wherein the rheology modification is induced by a combination of a peroxide and a free radical coagent. The resulting compositions have an elastomeric phase, a non-elastomeric phase and certain physical properties that exceed those of a like composition that is rheology-modified by peroxide alone. The compositions can be used to make a variety of articles of manufacture, such as automotive instrument panel skins, via calendaring and thermoforming procedures.

1 . A rheology-modified, substantially gel-free thermoplastic elastomer composition comprising at least one elastomeric ethylene/alpha-olefin polymer or ethylene/alpha-olefin polymer blend and at least one high melting polymer selected from the group consisting of polypropylene homopolymers and propylene/ethylene copolymers, wherein the rheology modification is induced by a combination comprising a peroxide and a free radical coagent and the composition has a melt toughness of at least about 600 cNmm/s, a true ultimate tensile strength at 140° C. of at least about 3 MPa and an elongation to break at 140° C. of least about 400%.  
     
     
         2 . The composition of  claim 1  wherein the peroxide is an organic peroxide.  
     
     
         3 . The composition of  claim 2  wherein the organic peroxide is selected from the group consisting of α,α′-bis(t-butylperoxy)-diisopropylbenzene, dicumyl peroxide, di-(t-amyl)peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5(t-amyl peroxy-2-ethylhexonate), 2,5-dimethyl-2,5-di-(t-butyl peroxy)hexane, di-t-butylperoxide, 2,5-di(t-amyl peroxy)-2,5-dimethylhexane, 2,5-di-(t-butylperoxy)-2,5-diphenylhexane, bis(alpha-methylbenzyl)peroxide, t-butyl perbenzoate, benzoyl peroxide, 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane and bis(t-butylperoxy)-diisopropylbenzene.  
     
     
         4 . The composition of  claim 1  wherein the free radical coagent is selected from the group consisting of diallyl terephthalate, triallylcyanurate, triallylisocyanurate, 1,2-polybutadiene, divinyl benzene, trimethylolpropane trimethacrylate, polyethylene glycol dimethacrylate, ethylene glycol dimethacrylate, pentaerythritol triacrylate, allyl methacrylate, N,N′-m-phenylene bismaleimide, toluene bismaleimide-p-quinone dioxime, nitrobenzene, and diphenylguanidine.  
     
     
         5 . The composition of  claim 4  wherein the free radical coagent is selected from the group consisting of triallylcyanurate, 1,2-polybutadiene, divinyl benzene, and trimethylolpropane trimethacrylate.  
     
     
         6 . The composition of  claim 1 , wherein the ethylene/α-olefin polymer has polymerized therein at least one α-olefin comonomer, the α-olefin containing from 3 to 20 carbon atoms.  
     
     
         7 . The composition of  claim 6 , wherein the α-olefin contains from 3 to 10 carbon atoms.  
     
     
         8 . The composition of  claim 1 , wherein the ethylene/α-olefin polymer is a diene-modified polymer, the diene being selected from the group consisting of norbornadiene, dicyclopentadiene, 1,4-hexadiene, piperylene or 5-ethylidene-2-norbornene and mixtures thereof.  
     
     
         9 . The composition of  claim 1 , wherein the high melting polymer is a nucleated polymer.  
     
     
         10 . The composition of  claim 1 , further comprising a process oil in an amount within a range of from greater than 0 to about 50 weight percent, based on total composition weight.  
     
     
         11 . The composition of  claim 1  or  claim 10 , further comprising a filler in an amount within a range of from about 0 to about 70 weight percent, based on total composition weight.  
     
     
         12 . The composition of  claim 1  or  claim 10 , further comprising a blowing agent in an amount within a range of from greater than 0 to about 10 weight percent, based on total composition weight.  
     
     
         13 . The composition of  claim 11 , further comprising a blowing agent in an amount within a range of from greater than 0 to about 10 weight percent, based on total composition weight.  
     
     
         14 . A process for preparing a rheology-modified, substantially gel-free TPE composition, the process comprising: a) adding at least one peroxide and at least one free radical coagent to a molten polymer blend that comprises an elastomeric ethylene/alpha-olefin polymer and a high melting polymer selected from the group consisting of polypropylene homopolymers and propylene/ethylene copolymers; and b) maintaining the polymer blend in a molten state while subjecting it to conditions of shear sufficient to disperse the peroxide and coagent throughout the molten polymer blend, effect rheology modification of the polymers and substantially preclude formation of insoluble polymer gels, sufficient rheology modification being measured by a melt toughness of at least about 600 cNmm/s, a true ultimate tensile strength at 140° C. of at least about 3 MPa and an elongation to break at 140° C. of least about 400%.  
     
     
         15 . A process for preparing a rheology-modified, substantially gel-free TPE composition, the process comprising: a) adding at least one peroxide and at least one free radical coagent to at least one component of a polymer blend that comprises an elastomeric ethylene/alpha-olefin polymer and a high melting polymer selected from the group consisting of polypropylene homopolymers and propylene/ethylene copolymers; and b) converting the polymer blend to a molten polymer blend while subjecting the blend to conditions of shear sufficient to disperse the peroxide and coagent throughout the molten polymer blend, effect rheology modification of the polymers and substantially preclude formation of insoluble polymer gels, sufficient rheology modification being measured by a melt toughness of at least about 600 cNmm/s, a true ultimate tensile strength at 140° C. of at least about 3 MPa and an elongation to break at 140° C. of least about 400%.  
     
     
         16 . A process for preparing a rheology-modified, substantially gel-free thermoplastic elastomer article of manufacture, the process comprising: a) adding at least one peroxide and at least one free radical coagent to a molten elastomeric ethylene/alpha-olefin polymer or elastomeric ethylene/alpha-olefin polymer blend to provide a rheology-modified ethylene/alpha-olefin polymer or ethylene/alpha-olefin polymer blend; b) adding to the rheology-modified polymer or polymer blend a high melting polymer selected from the group consisting of polypropylene homopolymers and propylene/ethylene copolymers to form a composite polymer blend; and c) converting the composite polymer blend into the article of manufacture, the article of manufacture having a melt toughness of at least about 600 cNmm/s, a true ultimate tensile strength at 140° C. of at least about 3 MPa and an elongation to break at 140° C. of least about 400%.  
     
     
         17 . The process of any of claims  14 - 16 , wherein the melt toughness of the rheology-modified composition is at least 700 cNmm/s.  
     
     
         18 . The process of  claim 17 , wherein the melt toughness of the rheology-modified composition is at least 800 cNmm/s.  
     
     
         19 . An article of manufacture having at least one component thereof fabricated from the composition of  claim 1 .  
     
     
         20 . The article of  claim 19 , wherein the composition further comprises at least one additive selected from the group consisting of process oils, fillers and blowing agents.  
     
     
         21 . The article of  claim 20 , wherein the process oil is present in an amount within a range of from greater than 0 to about 50 percent by weight, based on total composition weight.  
     
     
         22 . The article of  claim 20 , wherein the filler is selected from the group consisting of glass, silica, carbon black, metal carbonates, metal sulfates, talc, clay and graphite fibers.  
     
     
         23 . The article of  claim 20 , wherein the filler is present in an amount within a range of from greater than 0 to about 70 percent by weight, based on total composition weight.  
     
     
         24 . The article of  claim 20 , wherein the blowing agent is present in an amount within a range of from greater than 0 to about 10 percent by weight, based on total composition weight.  
     
     
         25 . The process of  claim 14  or  claim 15 , wherein a sequential step c) follows b), and step c) comprises converting the rheology modified polymer blend into an article of manufacture.  
     
     
         26 . The process of  claim 25  further comprising sequential intermediate steps b1) and b2) that precede step c), step b1) comprising recovery of the rheology modified polymer blend as a solid and step b2) comprising conversion of the solid to a melt state sufficient for fabricating the article of manufacture.