Patent Publication Number: US-2022235192-A1

Title: Blowing agent blends for thermoplastic polymers

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national filing under 35 U.S.C. 371 of International Application No. PCT/US2020/035053 filed May 29, 2020, and claims priority of U.S. Provisional Application No. 62/854,177 filed May 29, 2019, the disclosures of which are incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates to blends of HFO-1336mzz-Z and cyclopentane, which are useful as blowing agents for thermoplastic polymers (e.g., polystyrene). 
     BACKGROUND 
     The production of various types of foams historically employed chlorofluorocarbons (i.e., CFCs) as the blowing agent. In general, the CFCs yield foams exhibiting good thermal insulation, low flammability, and excellent dimensional stability. However, despite these advantages the CFCs have fallen into disfavor due to their implication in the destruction of stratospheric ozone, as well as their, generally, high contribution to global warming. Thus, there is a need for blowing agents to have both low ODP (ozone depletion potential) and GWP (global warming potential). 
     SUMMARY 
     The present application provides, inter alia, processes for preparing a thermoplastic polymer foam, the process comprising: 
     (a) providing a foamable composition comprising a thermoplastic polymer and a blowing agent, wherein the blowing agent comprises from about 95% to about 1% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene and from about 1% to about 95% by weight cyclopentane; and 
     (b) expanding the foamable composition to produce the thermoplastic polymer foam. 
     The present application further provides thermoplastic polymer foam, comprising: 
     (a) a thermoplastic polymer selected from the group consisting of polystyrene homopolymer, a polystyrene copolymer, and styrene-acrylonitrile copolymer, or a blend thereof; and 
     (b) a blowing agent comprising from 95% to 1% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene and from 1% to 95% by weight cyclopentane. 
     In some embodiments, the thermoplastic polymer foams provided herein are prepared according to one or more of the processes described herein. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Methods and materials are described herein for use in the present invention; other, suitable methods and materials known in the art can also be used. The materials, methods, and examples are illustrative only and not intended to be limiting. All publications, patent applications, patents, sequences, database entries, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  compares the solubility, at 176° C., of a HFO-1336mzz-Z/cyclopentane blend containing 20 wt % cyclopentane in polystyrene homopolymer with melt flow index (MFI) ˜5.00 g/10 min at 200° C. (as determined in accordance with the procedure of ASTM D 1238 using a 5 kg weight on the molten polymer), to the solubility of neat HFO-1336mzz-Z in polystyrene. 
         FIG. 2  compares the solubility, at 176° C., of a HFO-1336mzz-Z/cyclopentane/HFC-152a blend containing 40 wt % HFO-1336mzz-Z, 40 wt % HFC-152a, and 20 wt % cyclopentane in polystyrene homopolymer with MFI 5.00 g/10 min at 200° C. (as determined in accordance with the procedure of ASTM D 1238 using a 5 kg weight on the molten polymer), to the solubility of a HFO-1336mzz-Z/HFC-152a blend (50 wt %/50 wt %) in polystyrene homopolymer. 
     
    
    
     DETAILED DESCRIPTION 
     Incumbent agents with high global warming potentials (GWPs) for the expansion of thermoplastic foam, e.g. extruded polystyrene foam (XPS), are under regulatory pressure. Z-1,1,1,4,4,4-hexafluoro-2-butene (i.e., HFO-1336mzz-Z) could, in principle, be used as a low-GWP agent for the expansion of polystyrene (or other thermoplastic polymer) into foam with high thermal insulation capability. However, HFO-1336mzz-Z has low solubility in softened polystyrene under the operating conditions of the incumbent extrusion process. As a result, it would lead to suboptimal foam properties (e.g., higher than desirable foam density). 
     A blowing agent for the expansion of thermoplastic foam (e.g., polystyrene foam) must be sufficiently soluble in the molten thermoplastic polymer (e.g., polystyrene resin) under foam formation conditions so that an adequate volume of the blowing agent is available during the foam expansion and cooling phase to form cells and reduce the effective foam density to the target value. Expansion agent present in excess of its solubility could lead to foam defects. 
     As described herein, it has been found that, unexpectedly, blends of HFO-1336mzz-Z with cyclopentane can exhibit solubility in softened polystyrene that significantly exceeds the solubility of neat HFO-1336mzz-Z at the same conditions (see e.g.,  FIG. 1 ). For example, the solubility of neat HFO-1336mzz-Z in softened polystyrene homopolymer with a Melt Flow Index (MFI) of 5.0 g/10 min at 179° C. and 1374 psia is measured as 5.7 g per 100 g of polystyrene (or 5.7 phr, i.e, 5.7 parts of solute per hundred parts of resin by mass). In contrast, the solubility of an exemplary HFO-1336mzz-Z/cyclopentane blend containing 20 wt % cyclopentane has a solubility in the same polystyrene under the same temperature and pressure of 32.24 g per 100 g of polystyrene (i.e., 465.6% greater than the solubility of neat HFO-1336mzz-Z). 
     It has also been found that, unexpectedly, ternary blends of HFO-1336mzz-Z with cyclopentane and HFC-152a can exhibit solubility in softened polystyrene that significantly exceeds the solubility of a binary blend of HFO-1336mzz-Z and HFC-152a (50 wt %/50 wt % blend) at similar conditions (see e.g.,  FIG. 2 ). For example, the solubility of a HFO-1336mzz-Z/HFC-152a blend containing 50 wt % HFC-152a in softened polystyrene homopolymer with a Melt Flow Index (MFI) of 5.0 g/10 min at 179° C. and 2980 psia is measured as 11.8 g per 100 g of polystyrene (or 11.8 phr, i.e, 5.7 parts of solute per hundred parts of resin by mass). In contrast, the solubility of an exemplary HFO-1336mzz-Z/cyclopentane/HFC-152a blend containing 20 wt % cyclopentane and 40% HFC-152a has a solubility in the same polystyrene under the same temperature and approximately the same pressure (2968 psia) of 17.83 g per 100 g of polystyrene (i.e., 51.1% greater than the solubility of the 50 wt %/50 wt % HFO-1336mzz-Z/HFC-152a blend). 
     Accordingly, binary blends of HFO-1336mzz-Z and cyclopentane and ternary blends of HFO-1336mzz-Z, cyclopentane, and HFC-152a, each optionally in combination with at least one additional compound provided herein (e.g., an additional compound selected from the group consisting of HFOs, HCFOs, HFCs, HFEs, HCFCs, CFCs, CO 2 , N 2 , olefins, hydrochloroolefins, chlorinated hydrocarbons, organic acids, alcohols, hydrocarbons, ethers, aldehydes, ketones, water, methyl formate, ethyl formate, formic acid, and trans-1,2-dichloroethylene (DCE)) could be useful as blowing agents with low or moderate GWP for the expansion of thermoplastic foam, including extruded polystyrene foam. 
     Definitions &amp; Abbreviations 
     As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present). 
     Also, use of “a” or “an” is employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise. 
     As used herein, the term “about” is meant to account for variations due to experimental error (e.g., plus or minus approximately 10% of the indicated value). All measurements reported herein are understood to be modified by the term “about”, whether or not the term is explicitly used, unless explicitly stated otherwise. 
     As used herein, the term “consisting of” excludes any element, step, or ingredient not specified. If in the claim, such would close the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. When the phrase “consists of” or “consisting of” appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole. 
     As used herein, the term “consisting essentially of” is used to define a composition, method that includes materials, steps, features, components, or elements, in addition to those literally disclosed provided that these additional included materials, steps, features, components, or elements do not materially affect the basic and novel characteristic(s) of the claimed invention, especially the mode of action to achieve the desired result of any of the processes of the present invention. The term “consists essentially of” or “consisting essentially of” occupies a middle ground between “comprising” and “consisting of”. 
     When an amount, concentration, or other value or parameter is given as either a range, or a list of upper values and/or lower values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or value and any lower range limit or value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. 
     Global warming potential (GWP) is an index for estimating relative global warming contribution due to atmospheric emission of a kilogram of a particular greenhouse gas compared to emission of a kilogram of carbon dioxide. GWP can be calculated for different time horizons showing the effect of atmospheric lifetime for a given gas. The GWP for the 100-year time horizon is commonly the value referenced. 
     As used herein the term “Ozone depletion potential” (ODP) is defined in “The Scientific Assessment of Ozone Depletion, 2002, A report of the World Meteorological Association&#39;s Global Ozone Research and Monitoring Project,” section 1.4.4, pages 1.28 to 1.31 (see first paragraph of this section). ODP represents the extent of ozone depletion in the stratosphere expected from a compound on a mass-for-mass basis relative to fluorotrichloromethane (CFC-11). 
     The following abbreviations may be used herein: 
     CFC: chlorofluorocarbon 
     GWP: global warming potential 
     HCFC: hydrochlorofluorocarbon 
     HCFO: hydrochlorofluoroolefin 
     HFC: hydrofluorocarbon 
     HFE: hydrofluoroether 
     HFO: hydrofluoroolefin 
     HFC-152a: 1,1-difluoroethane 
     HFO-1336mzz-Z or 1336mzz-Z: Z-1,1,1,4,4,4-hexafluoro-2-butene 
     MFI: Melt Flow Index 
     ODP: Ozone depletion potential 
     PS: polystyrene 
     wt %: weight percent or percent by weight 
     Processes and Foams of the Invention 
     The present application provides processes for preparing a thermoplastic polymer foam. 
     In some embodiments, the processes provided herein comprise: 
     (a) providing a foamable composition comprising a thermoplastic polymer and a blowing agent, wherein the blowing agent comprises from about 95% to about 1% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene and from about 1% to about 95% by weight of cyclopentane; and 
     (b) expanding the foamable composition to produce the thermoplastic polymer foam. 
     In some embodiments, the blowing agent comprises about 1% to about 90% by weight cyclopentane, for example, about 1% to about 70%, about 1% to about 50%, about 1% to about 30%, about 1% to about 10%, about 10% to about 90%, about 10% to about 70%, about 10% to about 50%, about 10% to about 30%, about 30% to about 90%, about 30% to about 70%, about 30% to about 50%, about 50% to about 90%, about 50% to about 70%, or about 70% to about 90% by weight cyclopentane. 
     In some embodiments, the blowing agent comprises about 2% to about 45% by weight cyclopentane. In some embodiments, the blowing agent comprises about 10% to about 40% by weight cyclopentane. In some embodiments, the blowing agent comprises about 1% to about 30% by weight cyclopentane. In some embodiments, the blowing agent comprises about 15% to about 30% by weight cyclopentane. In some embodiments, the blowing agent comprises about 1% to about 25% by weight cyclopentane. In some embodiments, the blowing agent comprises about 5% to about 15% by weight cyclopentane. In some embodiments, the blowing agent comprises about 5% to about 10% by weight cyclopentane. 
     In some embodiments, the blowing agent comprises up to about 45% by weight cyclopentane, for example, up to about 40%, 30%, 25%, 20%, 15%, 10%, 5%, or 1% by weight cyclopentane. In some embodiments, the blowing agent comprises up to about 20% by weight cyclopentane. 
     In some embodiments, the blowing agent comprises about 90% to about 5% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene, for example, about 90% to about 10%, about 90% to about 30%, about 90% to about 50%, about 90% to about 70%, about 70% to about 5%, about 70% to about 10%, about 70% to about 30%, about 70% to about 50%, about 50% to about 5%, about 50% to about 10%, about 50% to about 30%, about 30% to about 5%, about 30% to about 10%, or about 10% to about 5% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     In some embodiments, the blowing agent comprises about 75% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprises about 75% to about 50% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprises about 60% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprises about 55% to about 35% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprises about 50% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprises about 40% to about 15% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprises about 30% to about 20% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprises about 30% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     In some embodiments, the blowing agent comprises up to about 95% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene, for example, up to about 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, or 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprises up to about 80% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     In some embodiments, the blowing agent comprises up to about 80% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene and up to about 20% by weight cyclopentane. 
     In some embodiments, the blowing agent consists essentially of Z-1,1,1,4,4,4-hexafluoro-2-butene and cyclopentane. In some embodiments, the blowing agent consists of Z-1,1,1,4,4,4-hexafluoro-2-butene and cyclopentane. 
     In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and cyclopentane in the polymer is greater than the solubility of the Z-1,1,1,4,4,4-hexafluoro-2-butene, alone, in the polymer. In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and cyclopentane in the polymer is improved by greater than about 10%, greater than about 25%, greater than about 50%, greater than about 100%, greater than about 100%, greater than about 200%, greater than about 300%, or greater than about 400% compared to the solubility of the Z-1,1,1,4,4,4-hexafluoro-2-butene, alone, in the polymer. In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and cyclopentane in the polymer is improved by about 400% to about 500% compared to the solubility of the Z-1,1,1,4,4,4-hexafluoro-2-butene, alone, in the polymer. In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and cyclopentane in the polymer is improved by about 450% to about 475% compared to the solubility of the Z-1,1,1,4,4,4-hexafluoro-2-butene, alone, in the polymer. In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and cyclopentane in the polymer is improved by about 460% to about 470% compared to the solubility of the Z-1,1,1,4,4,4-hexafluoro-2-butene, alone, in the polymer. 
     In some embodiments, the blowing agent provided herein further comprises HFC-152a. 
     In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 5% to about 75% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene, for example, about 5% to about 60%, about 5% to about 50%, about 5% to about 40%, about 5% to about 20%, about 5% to about 10%, about 10% to about 75%, about 10% to about 60%, about 10% to about 50%, about 10% to about 40%, about 10% to about 20%, about 20% to about 75%, about 20% to about 60%, about 20% to about 50%, about 20% to about 40%, about 40% to about 75%, about 40% to about 60%, about 40% to about 50%, about 50% to about 75%, about 50% to about 60%, or about 60% to about 75% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 75% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 75% to about 50% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 10% to about 50% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 30% to about 50% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 55% to about 35% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 30% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 15% to about 45% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 35% to about 45% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 20% to about 30% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 40% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 1% to about 45% by weight cyclopentane, for example, about 5% to about 95% by weight cyclopentane, for example, about 5% to about 80%, about 5% to about 50%, about 5% to about 25%, about 5% to about 10%, about 10% to about 95%, about 10% to about 80%, about 10% to about 50%, about 10% to about 25%, about 25% to about 95%, about 25% to about 80%, about 25% to about 50%, about 50% to about 95%, about 50% to about 80%, or about 80% to about 95% by weight cyclopentane. 
     In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 1% to about 50% by weight cyclopentane. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 2% to about 45% by weight cyclopentane. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 10% to about 40% by weight cyclopentane. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 15% to about 30% by weight cyclopentane. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 1% to about 25% by weight cyclopentane. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 10% to about 25% by weight cyclopentane. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 15% to about 25% by weight cyclopentane. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 5% to about 10% by weight cyclopentane. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 20% by weight cyclopentane. 
     In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 5% to about 95% by weight HFC-152a, for example, about 5% to about 80%, about 5% to about 50%, about 5% to about 25%, about 5% to about 10%, about 10% to about 95%, about 10% to about 80%, about 10% to about 50%, about 10% to about 25%, about 25% to about 95%, about 25% to about 80%, about 25% to about 50%, about 50% to about 95%, about 50% to about 80%, or about 80% to about 95% by weight HFC-152a. 
     In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 5% to about 90% by weight HFC-152a. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 75% to about 85% by weight HFC-152a. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 50% to about 70% by weight HFC-152a. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 10% to about 55% by weight HFC-152a. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 20% to about 80% by weight HFC-152a. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 30% to about 50% by weight HFC-152a. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 1% to about 20% by weight HFC-152a. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 10% to about 50% by weight HFC-152a. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 35% to about 45% by weight HFC-152a. In some embodiments, the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a comprises about 40% by weight HFC-152a. 
     In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a in the polymer is greater than the solubility of a blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and HFC-152a in the absence of cyclopentane, in the polymer. In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a in the polymer is greater than the solubility of a blowing agent consisting essentially of Z-1,1,1,4,4,4-hexafluoro-2-butene and HFC-152a in the absence of cyclopentane, in the polymer. In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a in the polymer is greater than the solubility of a blowing agent consisting of Z-1,1,1,4,4,4-hexafluoro-2-butene and HFC-152a, in the polymer. 
     In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a in the polymer is improved by greater than about 10%, greater than about 20%, greater than about 30%, greater than about 40%, or greater than about 50%, compared to the solubility of a blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and HFC-152a, in the polymer. In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a in the polymer is improved by about 10% to about 60%, compared to the solubility of a blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and HFC-152a, in the polymer. In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a in the polymer is improved by about 40% to about 60%, compared to the solubility of a blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and HFC-152a, in the polymer. In some embodiments, the solubility of the blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a in the polymer is improved by about 45% to about 55%, compared to the solubility of a blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and HFC-152a, in the polymer. 
     In some embodiments, the blowing agent consists essentially of Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a. In some embodiments, the blowing agent consists of Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 10% to about 75% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 2% to about 45% by weight cyclopentane; and 
     about 90% to about 5% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 10% to about 50% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 5% to about 10% by weight cyclopentane; and 
     about 75% to about 85% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 10% to about 30% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 15% to about 30% by weight cyclopentane; and 
     about 50% to about 70% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 35% to about 55% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 10% to about 40% by weight cyclopentane; and 
     about 50% to about 70% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 50% to about 75% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 10% to about 40% by weight cyclopentane; and 
     about 10% to about 55% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 30% to about 50% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 10% to about 30% by weight cyclopentane; and 
     about 30% to about 50% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 35% to about 45% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 15% to about 25% by weight cyclopentane; and 
     about 35% to about 45% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 40% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 20% by weight cyclopentane; and 
     about 40% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 10% to about 40% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 50% to about 10% by weight cyclopentane; and 
     about 50% to about 85% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 10% to about 40% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 6% to about 9% by weight cyclopentane; and 
     about 54% to about 81% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 25% to about 35% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 1% to about 10% by weight cyclopentane; and 
     about 60% to about 70% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 25% to about 30% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 5% to about 10% by weight cyclopentane; and 
     about 60% to about 65% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 28% to about 30% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 6% to about 8% by weight cyclopentane; and 
     about 63% to about 65% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 29% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene; 
     about 7% by weight cyclopentane; and 
     about 64% by weight HFC-152a. 
     In some embodiments, the blowing agent comprises: 
     about 80 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene and about 20 wt % cyclopentane; or 
     about 80 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 15 wt % cyclopentane, and about 5 wt % HFC-152a; or 
     about 80 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 10 wt % cyclopentane, and about 10 wt % HFC-152a; or 
     about 80 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 5 wt % cyclopentane, and about 15 wt % HFC-152a; or 
     about 70 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene and about 30 wt % cyclopentane; or 
     about 70 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 20 wt % cyclopentane, and about 10 wt % HFC-152a; or 
     about 70 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 10 wt % cyclopentane, and about 20 wt % HFC-152a; or 
     about 70 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 5 wt % cyclopentane, and about 25 wt % HFC-152a; or 
     about 60 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene and about 40 wt % cyclopentane; or 
     about 60 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 30 wt % cyclopentane, and about 10 wt % HFC-152a; or 
     about 60 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 20 wt % cyclopentane, and about 20 wt % HFC-152a; or 
     about 60 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 10 wt % cyclopentane, and about 30 wt % HFC-152a; or 
     about 60 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 5 wt % cyclopentane, and about 35 wt % HFC-152a; or 
     about 50 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene and about 50 wt % cyclopentane; or 
     about 50 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 40 wt % cyclopentane, and about 10 wt % HFC-152a; or 
     about 50 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 30 wt % cyclopentane, and about 20 wt % HFC-152a; or 
     about 50 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 20 wt % cyclopentane, and about 30 wt % HFC-152a; or 
     about 50 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 10 wt % cyclopentane, and about 40 wt % HFC-152a; or 
     about 50 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 5 wt % cyclopentane, and about 45 wt % HFC-152a. 
     about 40 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 55 wt % cyclopentane, and about 5 wt % HFC-152a; 
     about 40 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 50 wt % cyclopentane, and about 10 wt % HFC-152a; or 
     about 40 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 40 wt % cyclopentane, and about 20 wt % HFC-152a; or 
     about 40 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 30 wt % cyclopentane, and about 30 wt % HFC-152a; or 
     about 40 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 20 wt % cyclopentane, and about 40 wt % HFC-152a; or 
     about 40 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 10 wt % cyclopentane, and about 50 wt % HFC-152a; or 
     about 40 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 5 wt % cyclopentane, and about 55 wt % HFC-152a. 
     In some embodiments, the blowing agent comprises about 80 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene and about 20 wt % cyclopentane. 
     In some embodiments, the blowing agent comprises about 40 wt % Z-1,1,1,4,4,4-hexafluoro-2-butene, about 20 wt % cyclopentane, and about 40 wt % HFC-152a. 
     Without being bound by theory, it is believed that blowing agent blends having lower HFO-1336mzz-Z content would serve as lower-cost, low-GWP replacements of incumbent XPS blowing agents, while maintaining foam quality including thermal resistance), whereas compositions containing higher HFO-1336mzz-Z content would serve as low-GWP XPS blowing agents to enable higher foam thermal resistance while maintaining other foam quality attributes. 
     In some embodiments, the processes of the invention further comprise heating the polymer and blowing agent in the presence of one or more additives. Exemplary additives include, but are not limited to, nucleating agents, cell stabilizer agents, surfactants, preservative colorants, antioxidants, reinforcing agents, fillers, antistatic agents, IR attenuating agents, extrusion aids, plasticizers, and viscosity modifiers, or any combination thereof, in an amount to obtain the effect desired. 
     In some embodiments, the blowing agents provided herein are substantially free of additives. In some embodiments, the blowing agents comprise one or more additives (e.g., one, two, three, four, or five additives). 
     In some embodiments, the processes of the invention are performed in the presence of a nucleating agent. In some embodiments, the nucleating agent is selected from talc, graphite, and magnesium silicate. 
     In some embodiments, the foamable compositions further comprise a flame retardant. In some embodiments, the flame retardant comprises a polymeric flame retardant or a halogenated flame retardant. In some embodiments, the flame retardant is a brominated flame retardant or a chlorinated flame retardant. In some embodiments, the flame retardant is PolyFR. 
     In some embodiments, the foamable compositions further comprise an Infrared Attenuating Agent. 
     As used herein, the term “molten composition” refers to a foamable composition. The amount of blowing agent in the molten composition will depend on the amount of additives other than blowing agent and the density desired in the foamed product. In some embodiments, the amount of blowing agent in the foamable composition is from about 5 to about 20 wt %. In some embodiments, the amount of blowing agent in the foamable composition is from about 5 to about 15 wt %, based on the weight of the foamable composition. It is understood that the weight percentage of the blowing agent in the foamable composition can be adjusted based on the desired density of the foam, and the ratio of components in the blowing agent. 
     In some embodiments, the blowing agent is from about 5 parts to about 25 parts per hundred parts of polymer by mass, for example, about 5 to about 20, about 5 to about 15, about 5 to about 10, about 10 to about 25, about 10 to about 20, about 10 to about 15, about 15 to about 25, about 15 to about 20, or about 20 to about 25 parts per hundred parts of polymer by mass. In some embodiments, the blowing agent is from about 7 parts to about 18 parts per hundred parts of polymer by mass. 
     In some embodiments, the thermoplastic polymer provided herein is an alkenyl aromatic polymer. As used herein, the term “alkenyl aromatic polymer” refers to a polymer formed from alkenyl-aromatic monomer units. In some embodiments, the alkenyl-aromatic monomer unit is a C 2-6  alkenyl-C 6-10  aryl monomer unit. In some embodiments, the alkenyl-aromatic monomer unit is a C 2-6  alkenyl-phenyl monomer unit, wherein the phenyl is optionally substituted. In some embodiments, the alkenyl aromatic polymer is polystyrene. 
     The polystyrene can be styrene homopolymer or can contain copolymerized monomer other than styrene (i.e., polystyrene copolymer). In some embodiments, the thermoplastic polymer comprises a blend of polystyrene and an additional thermoplastic polymer. In some embodiments, the additional thermoplastic polymer is a copolymer of styrene with a monomer other than styrene (e.g., acrylonitrile). 
     In some embodiments, the thermoplastic polymer is selected from polystyrene, polyethylene, polyethylene copolymer, polypropylene, polypropylene copolymer, acrylonitrile butadiene styrene, styrene acrylonitrile copolymer, and blends thereof. In some embodiments, the thermoplastic polymer is selected from polystyrene, polyethylene, and polypropylene. In some embodiments, the thermoplastic polymer is a polyethylene-polypropylene copolymer. In some embodiments, the thermoplastic polymer is polystyrene. 
     Whether the thermoplastic polymer being foamed is polystyrene or blends of polystyrene with other thermoplastic polymer, in some embodiments, styrene is the dominant polymerized monomer (unit) in the thermoplastic polymer being foamed. In some embodiments, the polymerized units of styrene constitute at least 70 mol %, at least 80 mol %, at least 90 mol %, or at least 100 mol % of the polymerized monomer units of the thermoplastic polymer. 
     When the thermoplastic polymer contains styrene copolymer, the amount of the additional monomer copolymerized with the styrene is such that the styrene content of the copolymer is at least 60 mol % of the copolymer, at least 70 mol %, at least 80 mol %, or at least 90 mol % of the copolymer, based on the total number of moles (i.e., 100%) of the copolymer. It is understood that these ratios apply whether the styrene copolymer is the only styrene-containing polymer in the thermoplastic polymer or is a blend with other thermoplastic polymer, such as styrene homopolymer or other styrene copolymer. 
     In some embodiments, the thermoplastic polymer comprises styrene homopolymer (i.e., polystyrene homopolymer). When the thermoplastic polymer is a blend of polystyrene and other thermoplastic polymer as described above, the polystyrene component of this blend, in some embodiments, is styrene homopolymer comprising at least 80 wt % of the combined weight of polystyrene and other thermoplastic polymer. 
     The molecular weight of the thermoplastic polymer comprising polystyrene being foamed is sufficiently high to provide the strength necessary for the requirements of the foam application. The strength requirement determines the minimum density of the foamed product. The high molecular weight of the thermoplastic polymer comprising polystyrene also contributes to the strength of the foamed product. An indicator of molecular weight is the rate at which the molten polymer flows through a defined orifice under a defined load. The lower the flow, the higher the molecular weight. Measurement of the melt flow rate is determined in accordance with ASTM D 1238 at 200° C. and using a 5 kg weight on the molten polymer. The weight of molten polymer flowing through the orifice in a defined amount of time, enables the melt flow rate to be reported in g/10 min. In some embodiments, the melt flow rate of the thermoplastic polymer comprising polystyrene is no greater than 20 g/10 min, no greater than 15 g/10 min, or no greater than 10 g/10 min. In some embodiments, the minimum melt flow rate for all the melt flow rates disclosed herein is at least 1 g/10 min, whereby the melt flow rate ranges disclosed herein include, but are not limited to, 1 to 25, 1 to 20, 1 to 15, and 1 to 10 g/10 min. In some embodiments, the melt flow rate is about 25 g/10 min or less, as determined in accordance with the procedure of ASTM D 1238 at 200° C. using a 5 kg weight on the molten polymer. 
     The references to thermoplastic polymer comprising polystyrene also apply to polystyrene by itself. Thus, for example, the disclosure of thermoplastic polymer comprising polystyrene in the preceding paragraph can be replaced by the disclosure polystyrene. 
     In some embodiments, the process of the invention further comprises extruding the thermoplastic polymer to form a thermoplastic polymer foam comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and optionally HFC-152a. 
     In some embodiments, the extruding is performed at a die temperature of from about 100° C. to about 150° C., for example, about 100° C. to about 140° C., about 100° C. to about 130° C., about 100° C. to about 120° C., about 100° C. to about 110° C., about 110° C. to about 150° C., about 110° C. to about 140° C., about 110° C. to about 130° C., about 110° C. to about 120° C., about 120° C. to about 150° C., about 120° C. to about 140° C., about 120° C. to about 130° C., about 130° C. to about 150° C., about 130° C. to about 140° C., or about 140° C. to about 150° C. In some embodiments, the extruding is performed at a die temperature of from about 110° C. to about 140° C. In some embodiments, the extruding is performed at a die temperature of from about 120° C. to about 130° C. 
     In some embodiments, the processes of the invention are performed in an extruder to 1) form the foamable composition into a desired form; and 2) to extrude the foamable composition to form a thermoplastic polymer foam comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and, optionally, HFC-152a. 
     When the process of the invention is performed in an extruder, the thermoplastic polymer forms the feed to the extruder. In some embodiments, the blowing agent and co-blowing agent are fed into the extruder at a location intermediate to the feed and extrusion ends of the extruder, typically into the foamable composition that is created as the extrusion screw advances the feeds along the length of the extruder. Additional additives may be added where convenient and as may be dictated by the state of the additive. For example, solid additives can be conveniently be added to the feed end of the extruder, possibly as a mixture with the polymer feed in particulate form to the extruder. The resulting foamable composition within the extruder is extruded through a die, thereby allowing the foamable composition to expand into the foamed product of a desired shape (e.g., a sheet, a plank, a rod, or a tube) and subsequently cooled. 
     The “melt mixing region” is the region within the extruder where the composition is melted to form the molten composition. This melting occurs by the input of heat and the heat developed in the mixing process forming the melt. In some embodiments, the temperature of the melt mixing region is at least 185° C., at least 190° C., at least 200° C., or at least 210° C. In some embodiments, the maximum temperature for all the melt mixing temperatures disclosed herein is 250° C. The melt mixing temperatures disclosed herein are the temperatures of the melt in the mixing zone at the time of mixing. In some embodiments, the pressure under which the melt mixing is carried out is at least 1750 psi, at least 2000 psi, at least 2500, at least 3000 psi (207 Bar), at least 3500 psi (241 Bar), or at least 4000 psi (276 Bar). In some embodiments, the maximum value for all the minimum pressures disclosed under which the melt mixing is carried out is no greater than 5000 psi (345 Bar). The pressures disclosed herein are gauge pressures. 
     In the region within the extruder where the molten composition is extruded, the molten composition is cooled so that the temperature at which the extrusion is carried out is, in some embodiments, at least 105° C., at least 110° C., or at least 125° C. In some embodiments, the maximum value for all the minimum extrusion temperatures disclosed herein is no greater than 140° C. The extrusion temperatures disclosed herein are the temperature of the melt at the time of extrusion. 
     In some embodiments, the extrusion is performed with a pressure of at least 750 psi, at least 1000 psi, at least 1250 psi, 1500 psi (103 Bar), or at least 1600 psi (110 Bar). The maximum value for the minimum extrusion pressures disclosed herein is, in some embodiments, no greater than 2000 psi (138 Bar). The extrusion pressure is the pressure inside the extrusion die. 
     In some embodiments, the process is performed at a pressure just before foaming of from about 100 psi to about 5000 psi, for example, about 100 psi to about 4000 psi, about 100 psi to about 3000 psi, about 100 psi to about 2000 psi, about 100 psi to about 1000 psi, about 750 psi to about 1250 psi, about 1000 psi to about 5000 psi, about 1000 psi to about 4000 psi, about 1000 psi to about 3000 psi, about 1000 psi to about 2000 psi, about 2000 psi to about 5000 psi, about 2000 psi to about 4000 psi, about 2000 psi to about 3000 psi, about 3000 psi to about 5000 psi, about 3000 psi to about 4000 psi, or about 4000 psi to about 5000 psi. In some embodiments, the process is performed at a pressure just before foaming of from about 500 psi to about 4000 psi. In some embodiments, the process is performed at a pressure just before foaming of from about 800 psi to about 3000 psi. In some embodiments, the process is performed at a pressure just before foaming of from about 1000 psi to about 2500 psi. 
     The disclosures of multiple ranges for melt flow rate, temperature and pressure above can be used in any combination in the practice of the present invention to obtain the particular foamed structure desired. For example, melt mixing pressures of 3000 to 5000 psi (207 to 345 Bar) are used for achieving low foam densities of the foamed product, and this pressure range can be used with any of the melt mixing and extrusion temperature ranges to form any of the smooth-skin, closed cell foam product densities disclosed herein. The same is true for the melt extrusion pressure range of 1500 to 2000 psi (103 to 138 Bar) together with the 3000 to 5000 psi (207 to 345 bar) pressure range for melt mixing. In some embodiments, the two pressure ranges for melt mixing (207 to 345 Bar) and extrusion (103 to 138 bar) are used together. The melt flow rates for the polymer being foamed (e.g., at least 1 and no greater than 25, 20, 15, or 10 g/10 min) can be used with any combinations of pressure and temperatures, depending on the foamed product result desired. 
     When the process of the invention is performed in an extruder, the thermoplastic polymer (i.e., the foamable composition) is cooled such that the temperature at which the extrusion is performed is, in some embodiments, at least 125° C. or at least 130° C. In some embodiments, the temperature at which the extrusion is performed is a temperature less than the first temperature of the process of the invention. In some embodiments, the maximum value for all the minimum extrusion temperatures disclosed herein is about 150° C. or less. In some embodiments, the extruding is performed at a temperature of from about 100° C. to about 150° C. In some embodiments, the extruding is performed at a temperature of from about 110° C. to about 140° C. 
     In some embodiments, the extrusion temperature disclosed herein is the temperature of the polymer melt at the time of extrusion. 
     When the process of the invention is performed in an extruder, the extrusion is, in some embodiments, performed with a pressure of at least 750 psi or at least 1000 psi or at least 1250 psi or at least 1500 psi (103 Bar) or at least 1600 psi (110 Bar). The maximum value for the minimum extrusion pressures disclosed herein is, in some embodiments, no greater than 2000 psi (138 Bar). In some embodiments, the extruding is performed at a pressure of from about 1500 psi to about 2000 psi. In some embodiments, the extrusion pressure disclosed herein is the pressure inside the extrusion die. 
     In some embodiments, the extruding is performed at a pressure of from about 100 psi to about 5000 psi, for example, about 100 psi to about 4000 psi, about 100 psi to about 2000 psi, about 100 psi to about 1000 psi, about 750 psi to about 1250, about 1000 psi to about 5000 psi, about 1000 psi to about 4000 psi, about 1000 psi to about 2000 psi, about 2000 psi to about 5000 psi, about 2000 psi to about 4000 psi, or about 4000 psi to about 5000 psi. 
     In some embodiments, the extruding is performed at a pressure of from about 500 psi to about 4000 psi. 
     In some embodiments, the extruding is performed at a pressure of from about 750 psia to about 3000 psia. 
     In some embodiments, the extruding is performed at a pressure of from about 900 psia to about 2750 psia. 
     In some embodiments, the present application provides a foam product (e.g., a thermoplastic polymer foam) prepared according to one or more of the processes described herein. 
     In some embodiments, the foam comprises: 
     (a) a thermoplastic polymer selected from the group consisting of polystyrene homopolymer, a polystyrene copolymer, and styrene-acrylonitrile copolymer, or a blend thereof; and 
     (b) a blowing agent provided herein (i.e., a blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and, optionally, HFC-152a). 
     In some embodiments, the foam comprises: 
     (a) a thermoplastic polymer selected from the group consisting of polystyrene homopolymer, a polystyrene copolymer, and styrene-acrylonitrile copolymer, or a blend thereof; and 
     (b) a blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene and cyclopentane as provided herein. 
     In some embodiments, the foam comprises: 
     (a) a thermoplastic polymer selected from the group consisting of polystyrene homopolymer, a polystyrene copolymer, and styrene-acrylonitrile copolymer, or a blend thereof; and 
     (b) a blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a as provided herein. 
     In some embodiments, the foam provided herein further comprises one or more additives described herein. 
     It is understood that the blowing agent blends, additives, melt flow rates, temperatures, pressures, and other process parameters described herein can be used in any combination in the practice of the present invention to obtain the particular foamed structure desired. 
     In some embodiments, the thermoplastic polymer foams provided herein comprise one or more of the following properties:
         Closed cells—at least 70%, at least 80%, at least 90%, or at least 95% closed cells. Closed cell content can be measured according to ASTM method D6226-05.   Average Cell Size: From about 0.005 mm to about 5 mm (i.e., 5 μm to about 5000 μm), for example, about 0.01 mm to about 5 mm, about 0.05 mm to about 5 mm, about 0.05 mm to about 0.5 mm. In some embodiments, the average cell size is from about 0.01 mm to about 1 mm. In some embodiments, the average cell size is from about 0.02 mm to about 0.5 mm. In some embodiments, the average cell size is from about 0.1 mm to about 0.3 mm.   Density: No greater than about 60 kg/m 3 , no greater than about 45 kg/m 3 , no greater than about 40 kg/m 3 , no greater than about 35 kg/m 3 , or no greater than about 23 kg/m 3 . Density can be measured according to ISO method 845 85.   Smooth skin.   Substantially free of blowholes.       

     EXAMPLES 
     The invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes and are not intended to limit the invention in any manner. 
     Example 1. Solubility of an HFO-1336mzz-Z/Cyclopentane Blend in Softened Polystyrene Homo-Polymer 
     This example demonstrates the enhanced solubility of Z-1,1,1,4,4,4-hexafluoro-2-butene (i.e., HFO-1336mzz-Z)/cyclopentane blends in softened polystyrene compared to the solubility of neat HFO-1336mzz-Z in softened polystyrene. 
     The solubility of HFO-1336mzz-Z and an HFO-1336mzz-Z/cyclopentane blend containing 20 wt % cyclopentane in softened polystyrene was determined by the following procedure: Approximately 78 g polystyrene was loaded into a 125 cc stainless steel Parr© reactor. The reactor was weighed, mounted to inlet/outlet piping, immersed in an oil bath and evacuated. An HIP pressure generator (made by High Pressure Equipment Company) was used to load an amount of blowing agent in excess of its expected solubility into the evacuated reactor. The oil bath was heated and maintained at a temperature of 179° C. for 30 minutes before the final pressure was recorded. The Parr© reactor was removed from the oil bath and cooled to room temperature. The reactor (with re-solidified polystyrene inside) was weighed after excess (non-dissolved in the polystyrene) blowing agent was drained or vented. The weight gain was recorded as solubility according to the following equation: 
       solubility (wt %)=(resin weight gain×78)×100.  Equation 1.
 
     It has been found that, unexpectedly, a blend of HFO-1336mzz-Z with cyclopentane exhibits solubility in softened polystyrene that significantly exceeds the solubility of neat HFO-1336mzz-Z at the same conditions ( FIG. 1 ). For example, the solubility of neat HFO-1336mzz-Z in softened polystyrene homopolymer with a Melt Flow Index (MFI) of 5.0 g/10 min at 179° C. and 1,374 psia was estimated as 5.7 g/100 g of polystyrene (5.7 phr). In contrast, the solubility of an HFO-1336mzz-Z/cyclopentane blend containing 20 wt % cyclopentane exhibited a solubility in the same polystyrene, at the same temperature and pressure, of 32.24 g/100 g of polystyrene, or 465.6% higher solubility than the solubility of neat HFO-1336mzz-Z. 
     Example 2. Solubility of an HFO-1336mzz-Z/HFC-152a/Cyclopentane Blend in Softened Polystyrene Homo-Polymer 
     This example demonstrates the enhanced solubility of Z-1,1,1,4,4,4-hexafluoro-2-butene/HFC-152a/cyclopentane blends in softened polystyrene compared to the solubility of HFO-1336mzz-Z/HFC-152a blends in softened polystyrene. 
     The solubility of an HFO-1336mzz-Z/HFC-152a (50 wt %/50 wt %) blend and an HFO-1336mzz-Z/HFC-152a/cyclopentane blend containing 40 wt % HFO-1336mzz-Z, 40 wt % HFC-152a, and 20 wt % cyclopentane in softened polystyrene was determined according to the procedures described in Example 1. 
     It was been found that, unexpectedly, a blend of HFO-1336mzz-Z with HFC-152a and cyclopentane exhibits solubility in softened polystyrene that significantly exceeds the solubility of a binary blend of HFO-1336mzz-Z and HFC-152a at similar conditions ( FIG. 2 ). For example, the solubility of the binary HFO-1336mzz-Z/HFC-152a blend (50 wt %/50 wt %) in softened polystyrene homopolymer with a Melt Flow Index (MFI) of 5.0 g/10 min at 179° C. and 2980 psia was estimated as 11.8 g/100 g of polystyrene (11.8 phr). In contrast, the solubility of an HFO-1336mzz-Z/HFC-152a/cyclopentane blend containing 40 wt % HFO-1336mzz-Z, 40 wt % HFC-152a, and 20 wt % cyclopentane exhibited a solubility in the same polystyrene, at the same temperature and a similar pressure (2968 psia) of 17.83 g/100 g of polystyrene, or 51.1% higher solubility than the solubility of the binary HFO-1336mzz-Z/HFC-152a blend. 
     Example 3. Polystyrene Foam Extrusion Using HFO-1336mzz-Z/HFC-152a/Cyclopentane Blend as the Blowing Agent 
     This example demonstrates the reduction in XPS foam density resulting from the addition of cyclopentane in a blowing agent blend containing HFO-1336mzz-Z and HFC-152a. The polystyrene was styrene homo-polymer (Total Petrochemicals, PS 535B) having a melt flow rate of 4 g/10 min. A nucleating agent (talc) was present with the polystyrene and blowing agent in the molten composition formed within the extruder. 
     A 50 mm twin screw laboratory extruder was used with 9 individually controlled, electrically heated zones. The first four zones of the extruder were used to heat and soften the polymer. The remaining barrel sections, from the blowing agent injection location to the end of the extruder, were set at selected lower temperatures. A rod die with a 3 mm opening was used for extruding foamed rod specimens. Results are summarized in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Extruder Operating Parameters and Foam Density Achieved 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Run 
                 Run 
                 B vs A 
               
               
                   
                 Units 
                 A 
                 B 
                 (%) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 HFO-1336mzz-Z mass flow 
                 phr* 
                 3.3 
                 3.2 
                   
               
               
                 Cyclopentane mass flow 
                 phr 
                 0 
                 0.9 
                   
               
               
                 HFC-152a mass flow 
                 phr 
                 4.6 
                 4.3 
                   
               
               
                 HFO-1336mzz-Z in Blowing Agent 
                 wt % 
                 41.8 
                 38.1 
                   
               
               
                 Cyclopentane in Blowing Agent 
                 wt % 
                 0 
                 10.7 
                   
               
               
                 HFC-152a in Blowing Agent 
                 wt % 
                 58.2 
                 51.2 
                   
               
               
                 HFO-1336mzz-Z/HFC-152a mass 
                   
                 0.72 
                 0.74 
                   
               
               
                 ratio 
                   
                   
                   
                   
               
               
                 Extruder screw rotational speed 
                 rpm 
                 40 
                 40 
                   
               
               
                 Polystyrene flow rate 
                 kg/h 
                 20 
                 20 
                   
               
               
                 Nucleator (talc) proportion in the  
                 wt % 
                 0.35 
                 0.35 
                   
               
               
                 solids feed 
                   
                   
                   
                   
               
               
                 Die Temperature 
                 ° C. 
                 134 
                 131 
                   
               
               
                 Die Pressure 
                 psi 
                 1630 
                 1380 
                   
               
               
                 Effective Foam Density 
                 kg/m 3   
                 44 
                 38 
                 −13.6 
               
               
                   
               
               
                 *parts (by mass) per hundred parts of polystyrene resin 
               
            
           
         
       
     
     The results in Table 1 show that use of a Z-HFO-1336mzz/HFC-152a/cyclopentane blend containing 10.7 wt % cyclopentane as the blowing agent enables the formation of extruded polystyrene foam with a density about 13.6% lower than the density achieved with a blowing blend containing Z-HFO-1336mzz and HFC-152a in a mass ratio (about 0.72) similar to the mass ratio of Z-HFO-1336mzz and HFC-152a (about 0.74) in the Z-HFO-1336mzz/HFC-152a/cyclopentane blend. 
     OTHER EMBODIMENTS 
     1. A process for preparing a thermoplastic polymer foam, the process comprising: 
     (a) providing a foamable composition comprising a thermoplastic polymer and a blowing agent, wherein the blowing agent comprises from about 95% to about 1% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene and from about 1% to about 95% by weight cyclopentane; and 
     (b) expanding the foamable composition to produce the thermoplastic polymer foam. 
     2. The process of embodiment 1, wherein the solubility of the blowing agent in the polymer is greater than the solubility of the Z-1,1,1,4,4,4-hexafluoro-2-butene, alone, in the polymer. 
     3. The process of embodiment 1 or 2, wherein the blowing agent comprises about 75% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     4. The process of embodiment 1 or 2, wherein the blowing agent comprises about 50% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     5. The process of any one of embodiments 1 to 4, wherein the blowing agent comprises about 2% to about 45% by weight cyclopentane. 
     6. The process of any one of embodiments 1 to 4, wherein the blowing agent comprises about 15% to about 25% by weight cyclopentane. 
     7. The process of embodiment 1 or 2, wherein the blowing agent comprises up to about 80% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene and up to about 20% by weight cyclopentane. 
     8. The process of any one of embodiments 1 to 7, wherein the blowing agent consists essentially of Z-1,1,1,4,4,4-hexafluoro-2-butene and cyclopentane. 
     9. The process of any one of embodiments 1 to 8, wherein the blowing agent further comprises HFC-152a. 
     10. The process of embodiment 9, wherein the solubility of the blowing agent in the polymer is greater than the solubility of the Z-1,1,1,4,4,4-hexafluoro-2-butene, alone, in the polymer. 
     11. The process of embodiment 9 or 10, wherein the blowing agent comprises about 75% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     12. The process of embodiment 9 or 10, wherein the blowing agent comprises about 50% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     13. The process of any one of embodiments 9 to 12, wherein the blowing agent comprises about 2% to about 45% by weight cyclopentane. 
     14. The process any one of embodiments 9 to 13, wherein the blowing agent comprises about 5% to about 90% by weight HFC-152a. 
     15. The process any one of embodiments 9 to 13, wherein the blowing agent comprises about 75% to 85% by weight HFC-152a. 
     16. The process any one of embodiments 9 to 15, wherein the blowing agent consists essentially of Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a. 
     17. The process of any one of embodiments 1 to 16, wherein the thermoplastic polymer is an alkenyl aromatic polymer. 
     18. The process of any one of embodiments 1 to 16, wherein the thermoplastic polymer is selected from the group consisting of polystyrene, polyethylene homopolymer, polyethylene copolymer, polypropylene homopolymer, polypropylene copolymer, acrylonitrile butadiene styrene, and styrene acrylonitrile copolymer, and blends thereof. 
     19. The process of any one of embodiments 1 to 16, wherein the thermoplastic polymer is selected from the group consisting of a polystyrene homopolymer, a polystyrene copolymer, styrene-acrylonitrile copolymer, and blends thereof. 
     20. The process of any one of embodiments 1 to 19, wherein the process is performed at a pressure just before foaming of from about 100 psi to about 5000 psi. 
     21. The process of any one of embodiments 1 to 19, wherein the process is performed at a pressure just before foaming of from about 1000 psi to about 2500 psi. 
     22. The process of any one of embodiments 1 to 21, further comprising extruding the thermoplastic polymer to form the thermoplastic polymer foam. 
     23. The process of embodiment 22, wherein the extruding is performed at a die temperature of from about 100° C. to about 150° C. 
     24. The process of embodiment 22, wherein the extruding is performed at a die temperature of from about 110° C. to about 140° C. 
     25. The process of embodiment 22, wherein the extruding is performed at a die temperature of from about 120° C. to about 130° C. 
     26. The process of any one of embodiments 1 to 25, wherein the polymer foam is a closed cell polymer foam. 
     27. The process of any one of embodiments 1 to 26, wherein the polymer comprises at least 70% closed cells. 
     28. The process of any one of embodiments 1 to 27, wherein the polymer foam is a smooth skin polymer foam. 
     29. The process of any one of embodiments 1 to 28, wherein the polymer foam is substantially free of blowholes. 
     30. The process of any one of embodiments 1 to 16 to 19 to 29, wherein the polymer is a polystyrene homopolymer. 
     31. The process of any one of embodiments 1 to 30, wherein the foamable composition further comprises nucleating agent. 
     32. The process of embodiment 31, wherein the nucleating agent is selected from the group consisting of talc, graphite, and magnesium silicate. 
     33. The process of any one of embodiments 1 to 32, wherein the foamable composition further comprises a flame retardant. 
     34. The process of embodiment 33, wherein the flame retardant comprises a polymeric flame retardant or a halogenated flame retardant. 
     35. The process of embodiment 33, wherein the flame retardant is a brominated flame retardant or a chlorinated flame retardant. 
     36. The process of embodiment 33, wherein the flame retardant is PolyFR. 
     37. The process of any one of embodiments 1 to 36, wherein the foamable composition further comprises an Infrared Attenuating Agent. 
     38. The process of any one of embodiments 1 to 37, wherein the blowing agent is from about 5 parts to about 25 parts per hundred parts of polymer by mass. 
     39. The process of any one of embodiments 1 to 37, wherein the blowing agent is from about 7 parts to about 18 parts per hundred parts of polymer by mass. 
     40. The present application further provides a thermoplastic polymer foam, comprising: 
     (a) a thermoplastic polymer selected from the group consisting of polystyrene homopolymer, a polystyrene copolymer, and styrene-acrylonitrile copolymer, or a blend thereof; and 
     (b) a blowing agent comprising from 95% to 1% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene and from 1% to 95% by weight cyclopentane, 
     41. The thermoplastic polymer foam of embodiment 40, wherein the blowing agent comprises about 75% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     42. The thermoplastic polymer foam of embodiment 40, wherein the blowing agent comprises about 50% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     43. The thermoplastic polymer foam of embodiment 40, wherein the blowing agent comprises about 25% to about 15% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     44. The thermoplastic polymer foam of any one of embodiments 40 to 43, wherein the blowing agent comprises about 2% to about 45% by weight cyclopentane. 
     45. The thermoplastic polymer foam of any one of embodiments 40 to 43, wherein the blowing agent comprises about 15% to about 25% by weight cyclopentane. 
     46. The thermoplastic polymer foam of embodiment 40, wherein the blowing agent comprises up to about 80% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene and up to about 20% by weight cyclopentane. 
     47. The thermoplastic polymer foam of any one of embodiments 40 to 46, wherein the blowing agent consists essentially of Z-1,1,1,4,4,4-hexafluoro-2-butene and cyclopentane. 
     48. The thermoplastic polymer foam of embodiment 40, wherein the blowing agent further comprises HFC-152a. 
     49. The thermoplastic polymer foam of embodiment 48, wherein the blowing agent comprises about 75% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     50. The thermoplastic polymer foam of embodiment 48, wherein the blowing agent comprises about 50% to about 10% by weight Z-1,1,1,4,4,4-hexafluoro-2-butene. 
     51. The thermoplastic polymer foam of any one of embodiments 48 to 50, wherein the blowing agent comprises about 2% to about 45% by weight cyclopentane. 
     52. The thermoplastic polymer foam of any one of embodiments 48 to 51, wherein the blowing agent comprises about 5% to about 90% by weight HFC-152a. 
     53. The thermoplastic polymer foam of any one of embodiments 48 to 51, wherein the blowing agent comprises about 75% to 85% by weight HFC-152a. 
     54. The thermoplastic polymer foam of any one of embodiments 48 to 53, wherein the blowing agent consists essentially of Z-1,1,1,4,4,4-hexafluoro-2-butene, cyclopentane, and HFC-152a. 
     55. The thermoplastic polymer foam of any one of embodiments 40 to 54, wherein the polymer has a density of less than about 64 kg/m 3 , according to ISO method 845-85. 
     56. The thermoplastic polymer foam of any one of embodiments 40 to 54, wherein the polymer has a density of less than about 48 kg/m 3 , according to ISO method 845-85. 
     57. The thermoplastic polymer foam of any one of embodiments 40 to 54, wherein the foam has a density of less than about 40 kg/m 3 , according to ISO method 845-85. 
     58. The thermoplastic polymer foam of any one of embodiments 40 to 54, wherein the polymer has a density of less than about 35 kg/m 3 , according to ISO method 845-85. 
     59. The thermoplastic polymer foam of any one of embodiments 40 to 54, wherein the polymer has a density of less than about 29 kg/m 3 , according to ISO method 845-85. 
     60. The thermoplastic polymer foam of any one of embodiments 40 to 54, wherein the polymer has a density of less than about 25 kg/m 3 , according to ISO method 845-85. 
     61. The thermoplastic polymer foam of any one of embodiments 40 to 60, wherein the polymer has a melt flow rate of less than about 25 g/10 min. 
     62. The thermoplastic polymer foam of any one of embodiments 40 to 61, which is a closed cell polymer foam. 
     63. The thermoplastic polymer foam of any one of embodiments 40 to 62, which is a smooth skin polymer foam. 
     64. The thermoplastic polymer foam of any one of embodiments 40 to 63, wherein the polymer foam is substantially free of blowholes. 
     65. The thermoplastic polymer foam of any one of embodiments 40 to 64, wherein the foam comprises at least 70% closed cells. 
     66. The thermoplastic polymer foam of any one of embodiments 40 to 65, wherein the average cell size of the foam is from about 1 micrometers to about 5,000 micrometers. 
     67. The thermoplastic polymer foam of any one of embodiments 40 to 66, wherein the average cell size of the foam is from about 10 micrometers to about 5,000 micrometers. 
     68. The thermoplastic polymer foam of any one of embodiments 40 to 66, wherein the average cell size of the foam is from about 100 micrometers to about 300 micrometers. 
     69. The thermoplastic polymer foam of any one of embodiments 40 to 68, wherein the foam is a polystyrene foam. 
     70. The thermoplastic polymer foam of any one of embodiments 40 to 68, wherein the foam is a styrene/acrylonitrile copolymer foam. 
     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims. It should be appreciated by those persons having ordinary skill in the art(s) to which the present invention relates that any of the features described herein in respect of any particular aspect and/or embodiment of the present invention can be combined with one or more of any of the other features of any other aspects and/or embodiments of the present invention described herein, with modifications as appropriate to ensure compatibility of the combinations. Such combinations are considered to be part of the present invention contemplated by this disclosure.