Patent Publication Number: US-2023148347-A1

Title: Thermally expandable microspheres prepared from bio-based monomers

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a U.S. National-Stage entry under 35 U.S.C. § 371 based on International Application No. PCT/EP2021/058757, filed Apr. 1, 2021 which was published under PCT Article 21(2) and which claims priority to European Application No. 20168102.0, filed Apr. 3, 2020, which are all hereby incorporated in their entirety by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to thermally expandable microspheres at least partially prepared from bio-based monomers and to a process of their manufacture. The present disclosure further provides expanded microspheres prepared from the thermally expandable microspheres. 
     BACKGROUND 
     Thermally expandable microspheres are known in the art, and are described for example in U.S. Pat. No. 3,615,972, WO 00/37547 and WO2007/091960. A number of examples are sold under the trade name Expancel®. They can be expanded to form extremely low weight and low density fillers, and find use in applications such as foamed or low density resins, paints and coatings, cements, inks and crack fillers. Consumer products that often contain expandable microspheres include lightweight shoe soles (for example for running shoes), textured coverings such as wallpaper, solar reflective and insulating coatings, food packaging sealants, wine corks, artificial leather, foams for protective helmet liners, and automotive weather strips. 
     Thermally expandable polymer microspheres usually comprise a thermoplastic polymeric shell, with a hollow core comprising a blowing agent which expands on heating. Examples of blowing agents include low boiling hydrocarbons or halogenated hydrocarbons, which are liquid at room temperature, but which vaporise on heating. To produce expanded microspheres, the expandable microspheres are heated, such that the thermoplastic polymeric shell softens, and the blowing agent vaporises and expands, thus expanding the microsphere. Typically, the microsphere diameter can increase between about 1.5 and about 8 times during expansion. Expandable microspheres are marketed in various forms, e.g. as dry free-flowing particles, as aqueous slurry or as a partially dewatered wet cake. 
     Expandable microspheres can be produced by polymerizing ethylenically unsaturated monomers in the presence of a blowing agent, for example using a suspension-polymerisation process. Typical monomers include those based on acrylates, acrylonitriles, acrylamides, vinylidene dichloride and styrenes. A problem associated with such thermoplastic polymers is that they are typically derived from petrochemicals, and are not derived from sustainable sources. However, it is not necessarily easy merely to replace the monomers with more sustainable-derived alternatives, since it is necessary to ensure that acceptable expansion performance is maintained. For example, the polymer must have the right surface energy to get a core-shell particle in a suspension polymerization reaction so that the blowing agent is encapsulated. In addition, the produced polymer must have good gas barrier properties to be able to retain the blowing agent. Further, the polymer must have suitable viscoelastic properties above glass transition temperature Tg so that the shell can be stretched out during expansion. Therefore, replacement of conventional monomers by bio-based monomers is not easy. 
     Expandable microspheres have been described, in which at least a portion of the monomers making up the thermoplastic shell are bio-based, being derivable from renewable sources. 
     WO2019/043235 describes polymers comprising lactone monomers with general formula: 
     
       
         
         
             
             
         
       
     
     where R1-R4 are each independently selected from H and C1-4 alkyl. 
     WO2019/101749 describes copolymers comprising itaconate dialkylester monomers of general formula: 
     
       
         
         
             
             
         
       
     
     where each of R1 and R2 are separately selected from alkyl groups. 
     US2017/0081492 describes heat-expandable microspheres in which the polymeric component comprises a methacrylate monomer and a carboxyl-containing monomer. Amongst many examples of methacrylate monomers that are suggested as being suitable is tetrahydrofurfuryl methacrylate, although no examples of polymers containing this monomer are provided, nor any properties of any such polymers or polymeric microspheres. 
     There remains a need for alternative thermoplastic expandable microspheres in which the thermoplastic polymer shell is, at least in part, derived from sustainable sources. 
     BRIEF SUMMARY 
     The present disclosure relates to thermoplastic polymeric microspheres comprising a thermoplastic polymer shell surrounding a hollow core, in which the thermoplastic polymer shell comprises a homopolymer or copolymer of a monomer of Formula 1: 
     
       
         
         
             
             
         
       
     
     Each of A1 to A11 are independently selected from H and from about C1 to about C4 alkyl, in which each C1-4 alkyl group can optionally be substituted with one or more substituents selected from halogen, hydroxyl and C1-4 alkoxy. 
     X is a linking group selected from —O—, —NR″—, —S—, —OC(O)—, —NR″C(O)—, —SC(O)—, —C(O)O—, —C(O)NR″—, and —C(O)S—. The group C(O) represents a carbonyl group, C═O. R″ is H or C1-2 alkyl optionally substituted with one or more substituents selected from halogen and hydroxy. 
     The present disclosure also relates to a process for preparing such thermoplastic polymeric microspheres, in which an organic phase comprising one or more monomers and one or more blowing agents is dispersed in a continuous aqueous phase, and polymerisation is initiated by a polymerisation initiator to form an aqueous dispersion of thermoplastic polymeric microspheres comprising a thermoplastic polymer shell surrounding a hollow core, the hollow core comprising the one or more blowing agents, wherein at least one monomer is a monomer of Formula 1. 
     The present disclosure further relates to uses of the thermoplastic polymeric microspheres, e.g. as low density fillers and/or as foaming agents. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein: 
         FIGS.  1 A and  1 B  are illustrations depicting single core and multiple core microspheres. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the disclosure or the application and uses of the subject matter as described herein. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. It is to be appreciated that all numerical values as provided herein, save for the actual examples, are approximate values with endpoints or particular values intended to be read as “about” or “approximately” the value as recited. 
     In the discussion below, the term “(meth)acryl-” is often used. This is intended to encompass both the term “acryl-” and the term “methacryl-”. For example “(meth)acrylate” encompasses “acrylate” and “methacrylate”, and “(meth)acrylamide” encompasses “acrylamide” and “methacrylamide”. 
     The thermoplastic polymeric microspheres according to the present disclosure are produced from monomers which are at least partially bio-based. By bio-based it is meant that the monomers are at least partially derived from biologically-derived sustainable and renewable sources, typically from plants or microorganisms. Consequently, they can be used to help increase the proportion of the microspheres that are derived from sustainable raw materials, and reduce reliance on monomers derived from non-renewable mineral sources such as crude oil. 
     The thermoplastic polymeric microspheres have a hollow core encapsulated by the thermoplastic polymer shell, which can contain one or more blowing agents, and can be made to expand on heating, i.e. the microspheres can be expandable. 
     For microspheres to be expandable, the thermoplastic polymer shell must be sufficiently impermeable to the blowing agent(s) to prevent them leaking out before use, while at the same time having properties that allow the microspheres to expand and increase their volume on heating, resulting in expanded microspheres of lower density than the pre-expanded material. 
     It has been found that polymers comprising monomers of Formula 1 (which can be produced from sustainable raw materials) are able to produce thermally expandable microspheres with the required properties. 
     [Polymeric Shell] 
     The thermoplastic polymer shell of the microspheres of the present disclosure is or comprises a polymer or copolymer of at least one monomer of Formula 1. In embodiments, the shell is or comprises a copolymer comprising more than one monomer of Formula 1. In embodiments, there can be one or more other ethylenically unsaturated co-monomers that are not of Formula 1, and which have a single non-aromatic C═C double bond. 
     In embodiments, the polymer is a copolymer of at least one monomer of Formula 1 and at least one additional monomer not of Formula 1. 
     Copolymers can be based on from about 2 to about 5 different comonomers, for example 2 to 3 comonomers, at least one of which is of Formula 1. 
     Suitable co-monomers not of Formula 1 include, for example (meth)acrylics, such as (meth)acrylic acid and (meth)acrylates; vinyl esters; styrenes (such as styrene and α-methylstyrene); nitrile-containing monomers (e.g. (meth)acrylonitrile); (meth)acrylamides; vinylidene halides (e.g. vinylidene halides, vinyl chloride and vinyl bromide); vinyl ethers (e.g. methyl vinyl ether and ethyl vinyl ether); maleimide and N-substituted maleimides; dienes (e.g. butadiene and isoprene); vinyl pyridine; itaconate dialkyl esters; lactones; and any combination thereof. 
     In embodiments, comonomers not of Formula 1 are selected from (meth)acrylonitrile, methyl (meth)acrylate, vinylidene dichloride, methacrylic acid, methacrylamide, itaconate dialkyl esters or any combination thereof. 
     By “(meth)acrylic monomers” it is meant a compound and isomers thereof according to the general formula: 
     
       
         
         
             
             
         
       
     
     wherein R can be selected from hydrogen and an alkyl containing from about 1 to about 20 (e.g. 1 to 12) carbon atoms and R′ can be selected from hydrogen and methyl. R can optionally comprise one or more heteroatoms, e.g. oxygen, as part of a substituent, e.g. in a hydroxy group, or incorporated into the alkyl backbone, e.g. as an ether link. Examples of (meth)acrylic monomers are acrylic acid and salts thereof, methacrylic acid and salts thereof, acrylic anhydride, methacrylic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, butyl methacrylate, propyl methacrylate, lauryl acrylate, 2-ethylhexylacrylate, ethyl methacrylate, isobornyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, polyethylene glycol (meth)acrylate or tetrahydrofurfuryl methacrylate. In embodiments, (meth)acrylic monomers include those where R is H or has from about 1 to about 4 carbon atoms (e.g. from 1 to 2 carbon atoms), for example methyl acrylate, methyl methacrylate and methacrylic acid. As used herein, the term “(meth)acrylic” refers to methacrylic and acrylic. As used herein, the term “(meth)acrylate” refers to acrylate and methacrylate. As used herein, the term “(meth)acrylic acid” refers to methacrylic acid and acrylic acid. 
     By vinyl ester monomers it is meant a compound and isomers thereof according to the general formula: 
     
       
         
         
             
             
         
       
     
     wherein R can be selected from an alkyl containing from about 1 to about 20 (e.g. 1 to 17) carbon atoms. In embodiments, R can optionally comprise one or more heteroatoms, e.g. oxygen, as part of a substituent, e.g. in a hydroxy group, or incorporated into the alkyl backbone, e.g. as an ether link. Examples of vinyl ester monomers include vinyl acetate, vinyl butyrate, vinyl stearate, vinyl laurate, vinyl myristate and vinyl propionate. 
     By nitrile containing monomers it is meant a compound and isomers thereof according to the general formula: 
     
       
         
         
             
             
         
       
     
     wherein R1 and R2 can be selected, separately from each other, from hydrogen and an alkyl containing from about 1 to about 17 (e.g. 1 to 4 or 1 to 2) carbon atoms, or a nitrile group. In embodiments, R1 and R2 can optionally comprise one or more heteroatoms, e.g. oxygen, as part of a substituent, e.g. in a hydroxy group, or incorporated into the alkyl backbone, e.g. as an ether link. Examples of nitrile-containing monomers include acrylonitrile (R1=R2=H), methacrylonitrile (R1=CH3, R2=H), fumaronitrile (R1=CH3, R2=CN), crotonitrile (R1=CH3, R2=CH3). In embodiments, nitrile containing monomers can be selected from acrylonitrile and methacrylonitrile. As used herein, the term “(meth)acrylonitrile” refers to acrylonitrile and methacrylonitrile. 
     By (meth)acrylamide monomers it is meant a compound and isomers thereof according to the general formula: 
     
       
         
         
             
             
         
       
     
     wherein R1, R2 and R3 can be selected, separately from each other, from hydrogen and an alkyl containing from about 1 to about 17 (e.g. 1 to 4 or 1 to 2) carbon atoms or hydroxyalkyl having from about 1 to about 17 carbon atoms (e.g. 1 to 4 or 1 to 2), for example acrylamide (R1=R2=R3=H), methacrylamide (R1=CH3, R2=R3=H), and N-substituted (meth)acrylamide monomers such as N,N-dimethylacrylamide (R1=H, R2=R3=CH3), N,N-dimethylmethacrylamide (R1=R2=R3=CH3), N-methylolacrylamide (R1=H, R2=H, R3=CH2OH). As used herein, the term “(meth)acrylamide” refers to methacrylamide and acrylamide. 
     By maleimide and N-substituted maleimide monomers is meant a compound according to the general formula: 
     
       
         
         
             
             
         
       
     
     wherein R can be selected from hydrogen, an alkyl containing from about 1 to about 17 carbon atoms, or halogen atom. 
     In embodiments, R is selected from H, CH3, phenyl, cyclohexyl and halogen, and in further embodiments R is selected from phenyl and cyclohexyl. 
     In embodiments, the ethylenically unsaturated monomers not of Formula 1 are substantially free from vinyl aromatic monomers (e.g. styrenes). If they are present, such vinyl aromatic monomers can be present at less than about 10 wt. %, for example less than about 5 wt. %, less than about 1 wt. % or less than about 0.1 wt % of the total weight of the polymer (which can be calculated from the weight of vinyl aromatic monomer in the mixture of monomers used in the synthesis). 
     In still further embodiments, monomers not of Formula 1 can be selected from bio-derived monomers described in WO2019/043235 and WO2019/101749. 
     Thus, in embodiments, the co-polymer can comprise a lactone monomer of general formula: 
     
       
         
         
             
             
         
       
     
     where R1-R4 are each independently selected from H and C1-4 alkyl. 
     In other embodiments, the copolymer can comprise an itaconate dialkylester monomer of general formula: 
     
       
         
         
             
             
         
       
     
     where each of R1 and R2 are separately selected from alkyl groups, for example C1-4 alkyl groups. 
     Use of such bio-derived monomers can help further increase the bio-derived content of the polymeric shell of the microspheres. 
     In embodiments, at least one of the one or more ethylenically unsaturated comonomers not of Formula 1 is selected from (meth)acrylic monomers (such as (meth)acrylic acid and (meth)acrylates), nitrile-containing monomers and itaconate dialkylester monomers. In further embodiments, at least one is selected from (meth)acrylic acid, (meth)acrylonitrile, C1-12 alkyl(meth)acrylates (e.g. C1-4 alkyl(meth)acrylates and methyl(meth)acrylates), and itaconate C1-4 dialkyl esters (e.g. itaconate C1-2 dialkyl esters). In embodiments, the comonomers are selected from acrylonitrile and dimethyl itaconate. 
     In embodiments, at least one of the one or more ethylenically unsaturated comonomers not of Formula 1 is selected from nitrile-containing monomers, such as (meth)acrylonitrile. Preferably, at least one of the one or more ethylenically unsaturated comonomers not of Formula 1 is acrylonitrile. 
     In embodiments, at least one of the one or more ethylenically unsaturated comonomers not of Formula 1 is selected from itaconate dialkylester monomers, such as dimethyl itaconate. 
     In embodiments, at least one of the one or more ethylenically unsaturated comonomers not of Formula 1 is selected from methyl (meth)acrylic monomers, such as methyl methacrylate or methylacrylate. 
     In further embodiments the one or more ethylenically unsaturated comonomers not of Formula 1 comprise nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile, and further comprise itaconate dialkylester monomers, such as dimethyl itaconate. 
     In further embodiments the one or more ethylenically unsaturated comonomers not of Formula 1 comprise nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile, and further comprise methyl (meth)acrylate. 
     In embodiments, the content of monomer of Formula 1 can be in the range of from about 1 to about 100 wt %. In embodiments, the content is in the range of from about 1 to about 85 wt %, from about 1 to about 60 wt %, or from about 1 to about 45 wt %. In further embodiments, the content of monomer of Formula 1 is at least from about 10 wt % or about 15 wt %, i.e. in the range of form about 10 to about 100 wt % or from about 15 to about 100 wt %, for example in the range of from about 10 to about 85 wt %, from about 15 to about 85 wt %, from about 10 to about 70 wt %, from about 10 to about 60 wt %, from about 15 to about 60 wt %, from about 10 to about 45 wt % or from about 15 to about 45 wt %, each based on the total polymer weight. 
     The content of co-monomers not of Formula 1 in the thermoplastic polymer can be in the range of from about 0 to about 90 wt.-%, or from about 0 to about 80 wt %, or from about 0 to about 50 wt %. Where used, their content in the thermoplastic polymer can be 5 wt % or more, for example 10 wt % or more, with example ranges being from about 5 to about 80 wt %, from about 10 to about 80 wt %, from about 5 to about 50 wt % or from about 10 to about 50 wt %, each based on the total polymer weight. 
     In embodiments, at least one of the one or more ethylenically unsaturated comonomers not of Formula 1 is selected from nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile, and the content of the nitrile-containing monomer, such as (meth)acrylonitrile, preferably acrylonitrile, is in the range of from about 5 to about 90 wt %, or from about 10 to about 90 wt.-%. Preferably, the content of the nitrile-containing monomer, such as (meth)acrylonitrile, preferably acrylonitrile, can also be from about 30 to about 90 wt.-%, such as from about 40 to about 90 wt.-%, from about 45 to about 80 wt.-%, or from about 50 to about 80 wt.-%, each based on the total polymer weight. 
     In embodiments, at least one of the one or more ethylenically unsaturated comonomers not of Formula 1 is selected from itaconate dialkylester monomers, such as dimethyl itaconate, and the content of the itaconate dialkylester monomers, such as dimethyl itaconate, is in the range of from about 1 to about 50 wt % or from about 2 to about 40 wt.-%. Preferably, the content of the itaconate dialkylester monomers, such as dimethyl itaconate, can also be from about 5 to about 30 wt.-%, such as from about 10 to about 20 wt.-%, each based on the total polymer weight. 
     In further embodiments, the ethylenically unsaturated comonomers not of Formula 1 comprise nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile, and further comprise itaconate dialkylester monomers, such as dimethyl itaconate, and the content of the nitrile-containing monomer, such as (meth)acrylonitrile, preferably acrylonitrile, is in the range of from about 5 to about 90 wt %, or from about 10 to about 90 wt.-%, or from about 30 to about 90 wt.-%, and the content of the itaconate dialkylester monomers, such as dimethyl itaconate, is in the range of from about 1 to about 50 wt % or from about 2 to about 40 wt.-%, or from about 5 to about 30 wt.-%, each based on the total polymer weight. 
     In a specific embodiment, the polymer is a copolymer, wherein the content of monomer of Formula 1 is in the range of from about 1 to about 85 wt %, from about 1 to about 60 wt %, from about 1 to about 45 wt %, from about 10 to about 45 wt %, or from about 15 to about 45 wt % and the ethylenically unsaturated comonomers not of Formula 1 comprise nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile, and further comprise itaconate dialkylester monomers, such as dimethyl itaconate, and the content of the nitrile-containing monomer, such as (meth)acrylonitrile, preferably acrylonitrile, is in the range of from about 5 to about 90 wt %, or from about 10 to about 90 wt.-%, or from about 30 to about 90 wt.-%, and the content of the itaconate dialkylester monomers, such as dimethyl itaconate, is in the range of from about 1 to about 50 wt % or from about 2 to about 40 wt.-%, or from about 5 to about 30 wt.-%, each based on the total polymer weight. 
     In a further specific embodiment, the polymer is a copolymer, wherein the content of monomer of Formula 1 is in the range of from about 1 to about 45 wt %, from about 10 to about 45 wt %, or from about 15 to about 45 wt % and the ethylenically unsaturated comonomers not of Formula 1 comprise nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile, and further comprise itaconate dialkylester monomers, such as dimethyl itaconate, and the content of the nitrile-containing monomer, such as (meth)acrylonitrile, preferably acrylonitrile, is in the range of from about 10 to about 90 wt.-%, or from about 30 to about 90 wt.-%, and the content of the itaconate dialkylester monomers, such as dimethyl itaconate, is in the range of from about 5 to about 30 wt.-%, each based on the total polymer weight. 
     In an even further specific embodiment, the polymer is a copolymer, wherein the content of monomer of Formula 1 is in the range from about 15 to about 45 wt % and the ethylenically unsaturated comonomers not of Formula 1 comprise (meth)acrylonitrile, preferably acrylonitrile, and further comprise dimethyl itaconate, and the content of the (meth)acrylonitrile, preferably acrylonitrile, is in the range of from about 30 to about 90 wt.-%, and the content of the dimethyl itaconate is in the range of from about 5 to about 30 wt.-%, each based on the total polymer weight. 
     In embodiments, the total bio-derived monomer content of the polymer is at least 10 wt %, for example at least 20 wt % or at least 30 wt %, for example in the range of from about 10 to about 90 wt %, for example from about 20 to about 80 wt % or from about 30 to about 70 wt %, each based on the total polymer weight. 
     In embodiments, the total content of monomers of Formula 1 and (meth)acrylate monomers not of Formula 1 of the polymer is less than about 50 wt %, particularly within the range of from about 1 to about 45 wt % or from about 15 to about 45 wt %, based on the total polymer weight. 
     The monomer content of the polymer can be calculated from the weight proportion of monomers used in the polymer synthesis, i.e. the weight percentage of the monomer in the total weight of monomers used. 
     In a specific embodiment, the thermoplastic polymer shell of the thermoplastic polymeric microspheres comprises a copolymer consisting of or including: 
     from about 10 to about 70 wt %, based on the total polymer weight, of monomers of Formula 1 as defined below: 
     
       
         
         
             
             
         
       
     
     from about 30 to about 90 wt %, based on the total polymer weight, of nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile; and 
     from about 0 to about 50 wt % (preferably at least 1 wt %), based on the total polymer weight, of itaconate dialkylester monomers (e.g. dimethyl itaconate) or methyl(meth)acrylate. 
     In a specific embodiment, the thermoplastic polymer shell of the thermoplastic polymeric microsphere comprises a homopolymer or a copolymer consisting of or including: 
     from about 10 to about 70 wt %, based on the total polymer weight, of monomers of Formula 2, Formula 3 or Formula 4 as defined below; 
     
       
         
         
             
             
         
       
     
     wherein A1 is selected from H or C1-4 alkyl optionally substituted with hydroxy, such as H, methyl or methoxy, particularly H or methoxy; and more particularly H; 
     from about 30 to about 90 wt %, based on the total polymer weight, of nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile; and 
     from about 0 to about 50 wt % (preferably at least 1 wt %), based on the total polymer weight, of itaconate dialkylester monomers (e.g. dimethyl itaconate) or methyl(meth)acrylate. 
     In a further specific embodiment, the thermoplastic polymer shell of the thermoplastic polymeric microsphere comprises a copolymer consisting of or including: 
     from about 10 to about 60 wt %, based on the total polymer weight, of tetrahydrofurfuryl acrylate; 
     from about 30 to about 90 wt %, based on the total polymer weight, of nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile; and 
     from about 1 to about 50 wt %, based on the total polymer weight, of itaconate dialkylester monomers (e.g. dimethyl itaconate) or methyl(meth)acrylate. 
     In a still further specific embodiment, the thermoplastic polymer shell of the thermoplastic polymeric microsphere comprises a copolymer consisting of or including: 
     from about 10 to about 60 wt %, based on the total polymer weight, of tetrahydrofurfuryl acrylate; 
     from about 30 to about 80 wt %, based on the total polymer weight, of nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile; and 
     from about 5 to about 30 wt %, based on the total polymer weight, of itaconate dialkylester monomers (e.g dimethyl itaconate) or methyl(meth) acrylate. 
     In a preferred embodiment, the thermoplastic polymer shell of the thermoplastic polymeric microsphere comprises a copolymer consisting of or including: 
     from about 15 to about 45 wt %, based on the total polymer weight, of tetrahydrofurfuryl acrylate; 
     from about 30 to about 80 wt %, based on the total polymer weight, of nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile; and 
     from about 5 to about 20 wt %, based on the total polymer weight, of methyl(meth) acrylate. 
     In a further preferred embodiment, the thermoplastic polymer shell of the thermoplastic polymeric microsphere comprises a copolymer consisting of or including: 
     from about 20 to about 40 wt %, based on the total polymer weight, of tetrahydrofurfuryl acrylate; 
     from about 55 to about 75 wt %, based on the total polymer weight, of nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile; and 
     from about 5 to about 20 wt %, based on the total polymer weight, of methyl(meth) acrylate, 
     wherein the total amount of tetrahydrofurfuryl acrylate and methyl(meth) acrylate is from about 25 to about 45 wt %, based on the total polymer weight. 
     In another preferred embodiment, the thermoplastic polymer shell of the thermoplastic polymeric microsphere comprises a copolymer consisting of or including: 
     from about 15 to about 45 wt %, based on the total polymer weight, of tetrahydrofurfuryl acrylate; 
     from about 30 to about 80 wt %, based on the total polymer weight, of nitrile-containing monomers, such as (meth)acrylonitrile, preferably acrylonitrile; and 
     from about 5 to about 20 wt %, based on the total polymer weight, of itaconate dialkylester monomers (e.g. dimethyl itaconate). 
     [Crosslinking Multifunctional Monomers] 
     In embodiments, the polymer or copolymer can comprise one or more crosslinking multifunctional monomers having more than one ethylenically unsaturated C═C bond. Examples of groups comprising ethylenically unsaturated C═C bonds include vinyl and allyl groups. 
     In embodiments, such crosslinking multifunctional monomers can be selected from compounds comprising from 1 to 100 carbon atoms, including two or more ethylenically unsaturated C═C bonds. The compound can be a hydrocarbon, or can comprise one or more heteroatoms, such as O or N. 
     In embodiments, the compound comprises from about 1 to about 12 carbon atoms, for example divinyl benzene, triallyl isocyanurate, 1,4-butanediol divinyl ether and trivinylcyclohexane 
     In other embodiments, the compound can be selected from esters comprising one or more (meth)acrylate groups, for example comprising from about 1 to about 6 (meth)acrylate groups such as di, tri or tetra-esters. The ester groups can be attached to a hydrocarbon backbone comprising, for example, from about 1 to about 60 carbon atoms or from about 1 to about 40 carbon atoms, such as from about 1 to about 20 carbon atoms or from about 1 to about 10 carbon atoms. The hydrocarbon backbone can comprise one or more heteroatoms, for example one or more O or N atoms, for example in the form of ether, ester or amide linkages. Alternatively, or additionally, the hydrocarbon backbone can also comprise at least one ethylenically unsaturated C═C bond. For instance, in embodiments, the crosslinking multifunctional monomer can comprise a crosslinker comprising at least one ethylenically unsaturated C═C bond and attached to the crosslinker one more, preferably two, (meth)acrylate or (meth)acryloyl groups. 
     Examples of the crosslinking multifunctional monomers include one or more of ethylene glycol di(meth)acrylate, di(ethylene glycol) di(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, glycerol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, triallylformal tri(meth)acrylate, allyl methacrylate, trimethylolpropane tri(meth)acrylate, tributanediol di(meth)acrylate, PEG #200 di(meth)acrylate, PEG #400 di(meth)acrylate, PEG #600 di(meth)acrylate, acrylated epoxidized soybean oil (e.g. Ebecryl 860), 3-acryloyloxyglycol monoacrylate, triacryl formal, or any combination thereof. In embodiments, one or more crosslinking monomers that are at least tri-functional are used. The amounts of crosslinking functional monomers may be from about 0 to about 5 wt %, from about 0 to about 3 wt % or from about 0 to about 1 wt % of the total polymer weight, for example from about 0.1 to about 5 wt. %, from about 0.1 to about 3 wt. % or from about 0.1 to about 1 wt. %. The content can be calculated from the amount of cross-linking functional monomer present in the monomer mixture used to synthesise the thermoplastic polymeric microspheres. 
     [Monomer of Formula 1] 
     
       
         
         
             
             
         
       
     
     In Formula 1, each of A1 to A11 are independently selected from H and from about C1 to about C4 alkyl, in which each C1-4 alkyl group can optionally be substituted with one or more substituents selected from halogen, hydroxyhydroxy and C1-4 alkoxy. 
     X is a linking group selected from —OC(O)—, —NR″C(O)— and —SC(O)—. The group C(O) represents a carbonyl group, C═O. R″ is H or C1-2 alkyl optionally substituted with one or more substituents selected from halogen and hydroxy. In embodiments, X is selected from —OC(O)— and —NR″C(O)—. In particular preferred embodiments, X is —OC(O)—. 
     In embodiments, the total number of carbon atoms in A10 and A11 is from about 0 to about 12, for example from about 0 to about 6 carbon atoms. 
     In Formula 1, any of the following can apply:
         X is —OC(O)—   the optional substituent on the alkyl groups of A1 to A11 is hydroxy;   the alkyl groups of A1 to A11 are unsubstituted;   any or all of A1 to A11 are selected from H and optionally substituted C1-2 alkyl;   One of A10 and A11 is H and the other is H or C1-2 unsubstituted alkyl;   A10 and A11 are both H;   A8 is H and A9 is H or unsubstituted C1-2 alkyl;   A8 and A9 are both H;   any one or more of A1 to A7 are selected from H and C1-4 alkyl, for example C1-2 alkyl, where each alkyl optionally is optionally substituted with one or more hydroxy groups;   A1, A3, A5 and A7 are H, and A2, A4 and A6 are each independently selected from H and C1-2 alkyl, in which each alkyl is optionally substituted with one hydroxy group;   one of A1 to A7, e.g. A1, is monohydroxy-substituted C1-2 alkyl, such as CH2OH, and the rest are H;   no more than two of A1 to A7 are unsubstituted C1-2 alkyl, the rest being H;   all of A1 to A7 are H;   all of A1 to A9 are H;   all of A1 to A11 are H.       

     In embodiments, A2 to A9 are all H, i.e. where the monomer is of Formula 2. 
     
       
         
         
             
             
         
       
     
     In embodiments, X is —OC(O)—, for example where the monomer is of Formula 3. 
     
       
         
         
             
             
         
       
     
     In embodiments, in Formula 3, both A10 and A11 are H, such that the monomer is of Formula 4. 
     
       
         
         
             
             
         
       
     
     In embodiments, in Formula 2, 3 or 4, A1 is H or C1-4 alkyl optionally substituted with a hydroxyl group, e.g. C1-2 alkyl optionally substituted with a hydroxyl group. In embodiments, A1 is H, methyl or methoxy, for example being selected from H or methoxy. 
     In a specific embodiment, the thermoplastic polymer shell of the thermoplastic polymeric microsphere comprises a homopolymer or copolymer of a monomer of Formula 4 wherein A1 is H. The monomer of Formula 4 is then tetrahydrofurfuryl acrylate (THFA). 
     In embodiments where the thermoplastic polymer shell of the thermoplastic polymeric microsphere comprises a copolymer of a monomer of Formula I which is tetrahydrofurfuryl acrylate (THFA), the copolymer may further comprise one or more ethylenically unsaturated co-monomers that are not of Formula 1, such as a (meth)acrylic monomer (e.g. tetrahydrofurfuryl methacrylate, methyl methacrylate or methacrylate), a (meth)acrylonitrile monomer (e.g. acrylonitrile) and/or an itaconate dialkylester monomer (e.g. dimethyl itaconate). 
     The monomers of Formula 1 can be produced from biomass via different routes. For example, they can be prepared from furfural, which is a by-product of many agricultural and other plant-based products such as corn cobs, oats, wheat bran, rice hulls, sugarcane and sawdust. 
     Furfural, or correspondingly substituted analogues, can be converted to monomers of Formula 1 by first producing a corresponding tetrahydrofurfuryl alcohol compound, e.g. by hydrogenation, using techniques described in U.S. Pat. No. 2,838,523 or WO2014/152366 for example. This alcohol compound can then be used, optionally after suitable conversion of the —OH functional group, to produce a monomer of Formula 1, e.g. through condensation reactions. 
     As an example, where X is —OC(O)—, esters of Formula 1 can be formed by acid catalysed esterification using corresponding unsaturated carboxylic acids, acyl halides or carboxylic acid anhydrides, as described for example in U.S. Pat. No. 3,458,561 or Lal &amp; Green, J. Org. Chem., 1955, 20, 1030-1033. Alternatively, they can be made by creating an ester with a hydroxycarboxylic acid, followed by dehydration to produce the C═C double bond in the group attached to X, as described for example in U.S. Pat. No. 5,250,729. In further examples, transesterification can be used, as described for example in US475213. 
     [Microsphere and Polymer Shell Characteristics] 
     The polymer shell softens at or above the glass transition temperature (Tg) of the polymer that constitutes the polymer shell. The blowing agent(s) within the core of the polymer shell is typically selected so that it begins to vapourise below the Tg of the thermoplastic polymer in the shell, thus causing expansion of the microsphere when the polymer is heated to above its softening temperature, i.e. above the Tg. It is also possible to select a blowing agent such that its boiling point is higher than the Tg of the polymer, but below its melting temperature, such that the shell softens first, before vapourisation takes place. However, this is less desirable, as the microspheres can become distorted, which potentially causes inhomogeneous and less efficient expansion. 
     The temperature at which the expansion starts is called Tstart, while the temperature at which maximum expansion is reached is called Tmax. In some applications it is desirable that the microspheres have a high Tstart and high expansion capability, so as to be used in high temperature applications like foaming of thermoplastic materials in e.g. extrusion or injection moulding processes. Tstart for the expandable microspheres is in embodiments from about 50 to about 250° C., for example from about 60 to about 200° C., or from about 70 to about 150° C. Tmax for the expandable microspheres is in embodiments in the range of from about 70 to about 300° C., most preferably from for example from about 70 to about 230° C. or from about 75 to about 160° C. 
     The Tg of the polymer, or at least one of the polymers, that constitutes the polymer shell can be the same as or below the Tstart. 
     Tmax is typically below the melting point of the polymer that constitutes the polymer shell, to avoid collapse of the expanded microspheres. 
     The expandable microspheres preferably have a volume median diameter from about 1 to about 500 μm, more preferably from about 3 to about 200 μm, most preferably from about 3 to about 100 μm. 
     The term expandable microspheres as used herein refers to expandable microspheres that have not previously been expanded, i.e. unexpanded expandable microspheres. 
     In the expandable polymeric microspheres, the thermoplastic polymer shell surrounds a hollow core or cavity, which contains the blowing agent. The microsphere ideally comprises just a single core, as opposed to so-called multi-core microspheres. These are illustrated in  FIGS.  1 A and  1 B , where 1 indicates the thermoplastic polymer, and 2 indicates hollow regions that contain blowing agent. In  FIG.  1 B , there is no polymeric shell as such, the structure more being representative of a polymeric bead comprising pockets of blowing agent in a foam- or cellular-type structure. Therefore, the term “core-shell” distinguishes the single core microspheres from the foam/cellular structure that is associated with multiple core microspheres. 
     Single core microspheres have significantly improved expansion characteristics compared to multi core microspheres or foams, because they tend to comprise more blowing agent per unit mass of polymer. Thus, in embodiments, in a given batch or collection of expandable microspheres, at least 60% by mass are single core microspheres (with a core/shell structure as opposed to a foam/cellular structure), and in further embodiments at least 80% by mass, such as at least 90% or at least 95% by mass. 
     [Expansion of Expandable Microspheres] 
     Expansion is achieved by heating the expandable microspheres at a temperature above Tstart. The upper temperature limit is set by when the microspheres start collapsing and depends on the exact composition of the polymer shell and the blowing agent. The ranges for the Tstart and Tmax (defined further below) can be used for finding a suitable expansion temperature. 
     The density of the expanded microspheres can be controlled by selecting temperature and time for the heating. Heating can be by any suitable mechanism, for example using devices as described in EP0348372, WO2004/056549 or WO2006/009643. 
     The expandable microspheres can be expanded by heating, either in a dry form or in a liquid suspending medium, which in embodiments is an aqueous medium. In embodiments, the resulting expanded microspheres may contain less blowing agent. This is because, on microspheres expansion, the thermoplastic polymer shell becomes thinner, which can make it more permeable to the more blowing agent. 
     The expansion typically results in a particle diameter from about 1.5 to about 8, for example from about 2 to about 5 times larger than the diameter of the unexpanded microspheres. After expansion, the density of the microspheres is typically less than about 0.6 g/cm3. In preferred embodiments, the density of the expanded microspheres is 0.06 or less, for example in the range of from about 0.005 to about 0.06 g/cm3. Typically, where the density of the heated particles is 1 g/cm3 or more, then either the microspheres have not expanded, or there is substantial agglomeration of the microspheres. 
     The volume median diameter of the expanded microspheres is typically 750 μm or below, for example 500 μm or below or, more usually, 300 μm or below. The volume mean diameter of the expanded microspheres is also typically 5 μm or more, for example 7 μm or more, 10 μm or more, or 20 μm or more. Example ranges include from about 5 to about 750 μm, from about 5 to about 500 μm, from about 5 to about 300 μm, from about 7 to about 750 μm, from about 10 to about 300 μm, from about 20 to about 750 μm, from about 20 to about 500 μm or from about 20 to about 300 μm 
     [Blowing Agent] 
     In embodiments, the blowing agent, sometimes referred to as a foaming agent or a propellant, is selected such that it has a sufficiently high vapour pressure at temperatures above the Tg of the thermoplastic shell to enable expansion of the microspheres. 
     In embodiments, the boiling temperature (at atmospheric pressure) of the blowing agent, or at least one of the blowing agents, is not higher than the Tg of the polymer constituting the thermoplastic polymer shell. In embodiments, the boiling point at atmospheric pressure of the blowing agent can be in the range of from about −50 to about 250° C., for example from about −20 to about 200° C., or from about −20 to about 100° C. In embodiments, the amount of the blowing agent in the expandable microspheres is at least 5 wt % or in embodiments at least 10 wt %. In embodiments, the maximum amount of blowing agent in the microspheres is 60 wt. %, for example 50 wt. %, 35 wt. % or 25 wt %, based on the total weight of the microspheres. Example ranges include from about 5 to about 60 wt %, from about 5 to about 50 wt %, from about 5 to about 35 wt %, from about 5 to about 25 wt %, from about 10 to about 60 wt %, from about 10 to about 50 wt %, from about 10 to about 35 wt % and from about 10 to about 25 wt %. 
     The blowing agent can be a hydrocarbon, for example a hydrocarbon with from about 1 to about 18 carbon atoms, such as from about 3 to about 12 carbon atoms, and in embodiments from about 4 to about 10 carbon atoms. The hydrocarbon can be a saturated or unsaturated hydrocarbon. The hydrocarbon can be aliphatic or aromatic, typically aliphatic (which includes branched, linear and cyclic hydrocarbons). Aliphatic hydrocarbons are typically unsaturated. In embodiments, the hydrocarbon is selected from about C4 to about C12 alkanes, for example linear or branched alkanes such as n-butane, isobutane, n-pentane, isopentane, cyclopentane, neopentane, hexane, isohexane, neo-hexane, cyclohexane, heptane, isoheptane, octane, isooctane, decane, dodecane and isododecane. In embodiments, the hydrocarbon is selected from about C4 to about C10 alkanes. 
     Further examples of blowing agents include dialkyl ethers and halocarbons, e.g. chlorocarbons, fluorocarbons or chlorofluorocarbons. The dialkyl ether can comprise two alkyl groups each selected from about C2 to about C5 alkyl groups, for example C2-C3 alkyl groups. The halocarbon can be a C2 to C10 halocarbon comprising one or more halogen atoms that are, in embodiments, selected from chlorine and fluorine. In embodiments, the halocarbon is a haloalkane, such as a C2 to C10 haloalkane. The alkyl or haloalkyl groups in the dialkyl ethers and haloalkanes can be linear, branched or cyclic. 
     The blowing agent can be a single compound or a mixture of compounds. For example, mixtures of any one or more of the above-mentioned blowing agents can be used. 
     In embodiments, for environmental reasons, the one or more blowing agents are selected from (di)alkyl ethers and hydrocarbons, for example alkanes. In further embodiments the one or more blowing agents are selected from alkanes. Haloalkanes are preferably avoided, due to their potential ozone depletion properties, and also due to their generally higher global warming potential. Saturated hydrocarbons are preferred over unsaturated hydrocarbons, because the latter could potentially undergo side reactions with the monomers that are used to prepare the thermoplastic polymeric shell. This can reduce the blowing agent quantity in the hollow core, or even disrupt formation of the polymeric microspheres. 
     [Production of Microspheres] 
     The microspheres can be prepared in a suspension polymerisation process. In the process, an aqueous dispersion (or emulsion) of organic droplets comprising monomer and blowing agent is polymerised in the presence of a free-radical initiator, where at least one of the monomers is according to Formula 1. 
     Typical ways of doing this include processes described in U.S. Pat. Nos. 3,615,972, 3,945,956, 4,287,308, 5,536,756, EP0486080, U.S. Pat. No. 6,509,384, WO2004/072160 and WO2007/091960. 
     In a typical process of suspension polymerization, the monomer(s) and the blowing agent(s) are mixed together to form a so called oil-phase or organic phase. The oil-phase is then mixed with an aqueous mixture, for example by stirring or other mechanism of agitation, to form a fine dispersion of droplets, which can be in the form of an emulsion. The droplet size of the emulsion or dispersion can be manipulated, and they typically have a median diameter of up to 500 μm, and typically in a range of from about 3-about 100 μm. The dispersion or emulsion may be prepared by devices known in the art. 
     The dispersion or emulsion may be stabilised with so called stabilising chemicals, or suspending agents, as known in the art such as surfactants, polymers or particles. 
     [Emulsion Stabilisers] 
     In embodiments, an emulsion is formed. In further embodiments, the emulsion is stabilised by a so-called “Pickering Emulsion” processes. Stabilisation of the emulsion droplets is preferred for a number of reasons; without stabilisation a coalescence of the emulsion droplets containing the monomers and the blowing agents may occur. Coalescence has negative effects; such as, a non-uniform emulsion droplet size distribution resulting in undesirable proportions of emulsion droplets with different sizes, which in turn leads to undesirable properties of thermally expandable microspheres after polymerization. Furthermore, stabilisation prevents aggregation of thermally expandable microspheres. In addition, stabilisation may prevent formation of non-uniform thermally expandable microspheres and/or the formation of a non-uniform thermoplastic shell and an incomplete thermoplastic shell of the thermally expandable microspheres. The suspending agent is preferably present in an amount of up to 20 wt. %, for example from about 1 to about 20 wt % based on the total weight of the monomer(s). 
     In some embodiments, the suspending agent is selected from salts, oxides and hydroxides of metals such as Ca, Mg, Ba, Zn, Ni and Mn, for example one or more selected from calcium phosphate, calcium carbonate, magnesium hydroxide, magnesium oxide, barium sulphate, calcium oxalate, and hydroxides of zinc, nickel and manganese. These suspending agents are suitably used at a high pH, preferably from about 5 to about 12, most preferably from about 6 to about 10. Preferably magnesium hydroxide is used. However, sometimes alkaline conditions need to be avoided, for example where the monomer of Formula 1 or the resulting polymer may be prone to hydrolysis. 
     Therefore, in embodiments, it may be advantageous to work at a low pH, for example in the range of from about 1 to about 6, such as in the range of from about 3 to about 5. A suitable suspending agent for this pH range is selected from starch, methyl cellulose, hydroxypropyl methylcellulose, hydroxypropyl methylcellulose, carboxy methylcellulose, gum agar, silica, colloidal clays, oxide and hydroxide of aluminium or iron. In preferred embodiments, silica is used. 
     Where silica is used, it can be in the form of a silica sol (colloidal silica), which is typically an aqueous silica sol comprising silica particles. 
     The silica particles can provide a stabilising protective layer at the interface between the organic and aqueous phase during the polymerisation process, which prevents or reduces coalescence of the suspended or emulsified organic-phase droplets. 
     The silica particles can be combined with one or more co-stabilisers, for example as disclosed in U.S. Pat. No. 3,615,972. The co-stabilisers can be selected from: metal ions (such as Cr(III), Mg(II), Ca(II), Al(III) or Fe(III)) and flocculants (such as a poly-condensate oligomer of adipic acid and diethanol amine) optionally with a reducing agent. 
     In embodiments, the surface of the colloidal silica particles can be modified with one or more metal ions to produce so-called “charge-reversed” silica sols. Such surface modification includes modification with moieties that comprise elements that formally adopt a +3 or +4 oxidation state. Examples of such modifying elements include boron, aluminium, chromium, gallium, indium, titanium, germanium, zirconium, tin and cerium. Boron, aluminium, titanium and zirconium are particularly suitable for modifying the silica surface, especially aluminium-modified aqueous silica sols. These can be prepared using known methods, for example as described in U.S. Pat. Nos. 3,007,878, 3,139,406, 3,252,917, 3,620,978, 3,719,607, 3,745,126, 3,864,142 and 3,956,171. 
     In embodiments, the surface can comprise one or more organic groups, for example after being modified with one or more organosilane compounds. Typical organosilane groups which can be on the silica surface include those described in WO2018/011182 and WO2018/213050. Thus, the organosilane moiety can be represented by group E-Si≡, where —Si≡ is a silicon atom from the silane moiety that is bound to the surface of the silica particle via one or more siloxane (—Si—O—Si) bonds. 
     E is an organic group that can be selected from alkyl, epoxy alkyl, alkenyl, aryl, heteroaryl, C1-6 alkylaryl and C1-6 alkylheteroaryl. These can optionally be substituted with one or more groups selected from —Ra or -LRa. L, when present, is a linking group selected from —O—, —S—, —OC(O)—, —C(O)O—, —C(O)OC(O)—, —C(O)OC(O)—, —N(Rb)—, —N(Rb)C(O)—, —N(Rb)C(O)N(Rb)- and —C(O)N(Rb)-. 
     Ra can be selected from hydrogen, F, Cl, Br, alkyl (e.g. C1-6 alkyl), alkenyl (e.g. C1-6 alkenyl), aryl (e.g. C5-8 aryl), heteroaryl (e.g. C5-8 heteroaryl comprising at least one heteroatom selected from O, S and N); C1-3 alkyl-aryl and C1-3 alkyl-heteroaryl. Alkyl groups can be C1-6 alkyl. Aryl groups can be those with a 5 to 8 membered ring. Heteroaryl groups can those with a 5-8 membered rings, comprising at least one heteroatom selected from O, S and N. The Ra groups can optionally be substituted with one or more groups selected from OH, F, Cl, Br, epoxy, —C(O)ORb, —ORb and —N(Rb)2. Rb is H or C1-6 alkyl. 
     In embodiments, E can comprise one or more groups selected from hydroxy, thiol, carboxyl, ester, epoxy, acyloxy, ketone, aldehyde, (meth)acryloxy, amino, mercapto, amido and ureido. In embodiments, E can comprise an epoxy group or one or more hydroxy groups. 
     In specific examples, E can be selected from one or more groups selected from C1-6 alkyl optionally substituted with an epoxy group, a (meth)acrylamido group or one or more hydroxy groups. In embodiments, E can be —Rc-O-Rd, where Rc is C1-6 alkyl and Rd is a C1-6 alkyl optionally modified with an epoxy group or one or more hydroxy groups. 
     Specific examples of E include 3-glycidoxypropyl, dihydroxypropoxypropyl [e.g. HOCH2CH(OH)CH2OC3H6-], and methacrylamidopropyl. 
     Organosilane-modified colloidal silica can be made using procedures described in US2008/0245260, WO2012/123386, WO2004/035473 and WO2004/035474. 
     In terms of the proportion of surface modification, this can be expressed in units of μmol modifying group per square metre of colloidal silica surface. In embodiments, the surface coverage from the one or more organic groups is in the range of from about 0.35 to about 3.55 μmol/m2, for example from about 0.35 to about 2.82 μmol/m2, or from about 0.77 to about 2.82 μmol/m2. 
     [Co-Stabilisers] 
     In order to enhance the effect of the suspending agent, it is also possible to add small amounts of one or more co-stabilisers. In embodiments, the amount of co-stabiliser is present in amounts of up to 1 wt %, for example from about 0.001 to about 1 wt %, based on the total weight of the monomer(s). Co-stabilisers can be organic materials which can be selected, for example, from one or more of water-soluble sulfonated polystyrenes, alginates, carboxymethylcellulose, tetramethyl ammonium hydroxide or chloride or water-soluble complex resinous amine condensation products such as the water-soluble condensation products of diethanolamine and adipic acid, the water-soluble condensation products of ethylene oxide, urea and formaldehyde, polyethylenimine, polyvinylalcohol, polyvinylpyrrolidone, polyvinylamine, amphoteric materials such as proteinaceous, materials like gelatin, glue, casein, albumin, glutin and the like, non-ionic materials like methoxycellulose, ionic materials normally classed as emulsifiers, such as soaps, alkyl sulphates and sulfonates and long chain quaternary ammonium compounds. 
     [Proportions] 
     In a suitable, typically batch-wise, procedure for preparing the expandable microspheres, the polymerization is conducted in a reaction vessel. In embodiments, the procedure includes preparing a mixture comprising or consisting of 100 parts of the monomer phase, which includes the monomer(s), the blowing agent(s); from about 0.1 to about 5 parts of a polymerisation initiator; from about 100- to about 800 parts of the aqueous phase; and from about 1 to about 20 parts of a suspending agent. The mixture is then homogenised. The droplet size of the monomer phase determines the size of the final expandable microspheres, in accordance with the principles described in e.g. U.S. Pat. No. 3,615,972, which can be applied for all similar production methods with various suspending agents. The required pH depends on the suspending agent used, as described above. 
     [Initiator] 
     The emulsion obtained is subjected to conventional radical polymerization using at least one initiator. Typically, the initiator is used in an amount from about 0.1 to about 5 wt. % based on the weight of the monomer phase. Conventional radical polymerization initiators are selected from one or more of organic peroxides such as dialkyl peroxides, diacyl peroxides, peroxy esters, peroxy dicarbonates, or azo compounds. Suitable initiators include dicetyl peroxydicarbonate, di(4-tert-butylcyclohexyl) peroxydicarbonate, dioctanyl peroxide, dibenzoyl peroxide, dilauroyl peroxide, didecanoyl peroxide, tert-butyl peracetate, tert-butyl perlaurate, tert-butyl perbenzoate, tert-butyl hydroperoxide, cumene hydroperoxide, cumene ethylperoxide, diisopropylhydroxy dicarboxylate, 2,2′-azo-bis(2,4-dimethyl valeronitrile), 2,2′-azobis(2-methylpropionate), 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and the like. It is also possible to initiate the polymerization with radiation, such as high energy ionising radiation, UV radiation in combination with a photoinitiator or microwave-assisted initiation. 
     When the polymerization is essentially complete, microspheres are normally obtained as an aqueous slurry or dispersion, which can be used as such or dewatered by any conventional mechanism, such as bed filtering, filter pressing, leaf filtering, rotary filtering, belt filtering or centrifuging to obtain a so called wet cake. It is also possible to dry the microspheres by any conventional mechanism, such as spray drying, shelf drying, tunnel drying, rotary drying, drum drying, pneumatic drying, turbo shelf drying, disc drying or fluidised bed drying, to produce powdered microspheres. Microspheres can be provided in suspended (e.g. as an aqueous suspension), wet (e.g. wet-cake) or dry (e.g. powdered) form. They can be provided either in pre-expanded or in expanded form. 
     [Residual Monomer Reduction] 
     If appropriate, the microspheres may at any stage be treated to reduce or further reduce the amount of residual unreacted monomers, for example by any of the procedures described in WO2004/072160 or U.S. Pat. No. 4,287,308. 
     The presence of residual monomers is undesirable, as their reactivity can make the microspheres less desirable for applications such as food, drink and pharmaceuticals packaging. 
     Use of monomers of Formula 1 in preparing the polymer or copolymer shell of the microsphere can help reduce the amount of residual monomer remaining in the polymer. 
     For instance, the microspheres may be treated with an agent such as certain oxo acids of sulfur, or salts or derivatives thereof to reduce or further reduce the amount of residual unreacted monomers, such as one or more of acrylonitrile, methacrylonitrile and monomers according to formula 1, such as tetrahydrofurfuryl acrylate. 
     In one embodiment, the microspheres are treated with an agent reacting directly or indirectly with at least part of said residual monomers, wherein said agent is selected from oxo acids of sulfur, salts and derivatives thereof, comprising at least one sulfur atom having at least one free electron pair and binding three oxygen atoms or comprising at least two sulfur atoms which are linked via a peroxide group. It has surprisingly been found that with such treatment the residual amount of monomer in the microspheres can be reduced to less than about 2,000 ppm, such as for instance less than about 1,000 ppm, particularly less than about 500 ppm. 
     According to a preferred embodiment, the microspheres are treated with an agent selected from oxo acids of sulphur, salts and derivatives thereof, comprising at least two sulfur atoms which are linked together via a peroxide group. Particular preferred are persulfates. It has surprisingly been found that with such persulfate treatment the residual amount of monomer in the microspheres can be further reduced to less than about 500 ppm, such as for instance less than about 300 ppm, particularly less than about 200 ppm and even less than about 100 ppm. Surprisingly, the persulfate treatment may reduce in particular the amount of residual acrylonitrile in the microspheres to less than about 500 ppm, such as for instance less than about 300 ppm, particularly less than about 200 ppm and even less than about 100 ppm or less than about 50 ppm. 
     The agent may be added as such or be formed in situ through one or more chemical reactions from a precursor. 
     Suitable agents for the agent selected from oxo acids of sulfur, salts and derivatives thereof, comprising at least one sulfur atom having at least one free electron pair and binding three oxygen atoms include bisulfites (also called hydrogen sulfites), sulfites and sulfurous acid, of which bisulfites and sulfites are preferred. Suitable counter ions include ammonium and mono- or divalent metal ions such as alkali metal and alkaline earth metal ions. Most preferred are sodium, potassium, calcium, magnesium and ammonium. Also organic compounds comprising any of the above groups may be used, such as alkyl sulfites or dialkyl sulfites. Particularly preferred agents are dimethyl sulfite, sodium bisulfite, sodium sulfite, and magnesium bisulfite. Most preferred is sodium bisulfite. 
     Examples of precursors include sulfur dioxide, sulfonyl chloride, disulfites (also called metabisulfites or pyrosulfites), ditionites, ditionates, sulfoxylates, e. g. of sodium, potassium or other counter ions as defined above. Preferred precursors are sulfur dioxide, disulfites and ditionites. Particularly preferred precursors are sodium metabisulfite, potassium metabisulfite and sodium ditionite. To the extent corresponding acids exist, they are also useful. The precursors can easily react to form an active agent as defined above, e. g. by redox reactions and/or by simply being dissolved in an aqueous medium. 
     Suitable agents for the agent selected from oxo acids of sulfur, salts and derivatives thereof, comprising at least two sulfur atoms which are linked via a peroxide group include persulfates, such as for instance sodium persulfate, potassium persulfate or ammonium persulfate. Preferred is sodium persulfate. To the extent corresponding acids exist, they are also useful. 
     It has been found that an agent as defined above reacts directly or indirectly with monomers without negatively affecting important properties of the microspheres, such as the degree of expansion that can be achieved. Furthermore, reaction products remaining on or in the microspheres are less toxic than e. g. acrylonitrile and do not cause any significant problem of discolouration. 
     During the step of contacting the microspheres with the agent for reacting with residual monomers, the microspheres are preferably in the form of an aqueous slurry or dispersion, preferably comprising from about 0.1 to about 50 wt % microspheres, most preferably from about 0.5 to about 40 wt % microspheres, while the agent is preferably dissolved in the liquid phase, preferably at a concentration from about 0.1 wt % up to the saturation limit, most preferably from about 1 to about 40 wt %. However, the microspheres could alternatively be suspended in any other liquid medium which dissolves the agent, or mixtures thereof. Preferably, the slurry or dispersion originates from the polymerisation mixture in which the microspheres have been produced. 
     Without being bound to any theory, it is believed that addition of an agent or precursor as earlier defined result in a solution comprising sulphite, bisulfite, or persulfate which in turn reacts with the monomers. 
     The amount of agent, expressed as moles sulfur atoms having at least one free electron pair and binding three oxygen atoms or moles peroxide groups linking two sulfur atoms, compared to the molar amount of residual monomers, is preferably at least about equimolar, more preferably from about equimolar to about 200% excess, most preferably from about equimolar to about 50% excess on a molar basis, particularly most preferably from about equimolar to about 25% excess on a molar basis. If the slurry or dispersion originates from the polymerisation mixture and thus contains residual monomer also in the liquid phase, these monomers have to be taken into account in addition to those present in or on the microspheres. 
     The agent or precursor for the agent reacting with residual monomers may be added during the production of the microspheres, optionally when the polymerisation still is running, although it is preferred that at the time for addition of the agent or precursor the polymerisation is almost complete and less than about 15% preferably less than about 10% residual monomers remain. The agent or precursor is preferably added when the microspheres has formed but still are in a slurry or dispersion and most preferably when they still are in the same reaction vessel as the polymerisation has been conducted in. 
     Alternatively, the agent or precursor may be added to the microspheres in a separate step after the microspheres have been removed from the polymerisation reactor, optionally after any of subsequent operations such as dewatering, washing or drying. The non-treated microspheres comprising residual monomers could then be regarded as an intermediate product, which optionally can be transported to another location and there being brought into contact with the agent for removing residual monomers. 
     In any of the above options, the agent or precursor may be added all at once or in portions. 
     The pH during the step of contacting the microspheres with the agent is preferably from about 3 to about 12, most preferably from about 3.5 to about 10. The temperature during said step is preferably from about 20 to about 100 C, most preferably from about 50 to about 100 C, particularly most preferably from about 60 to about 90 C. 
     The pressure during said step is preferably from about 1 to about 20 bar (absolute pressure), most preferably from about 1 to about 15 bar. The time for said step is preferably at least about 5 minutes, most preferably at least about 1 hr. There is no critical upper limit, but for practical and economic reasons the time is preferably from about 1 to about 10 hours, most preferably from about 2 to about 5 hours. After said step, the microspheres preferably are dewatered, washed and dried by any suitable conventional mechanism. 
     [Uses of Microspheres] 
     The expandable and expanded microspheres of the present disclosure are useful in various applications, typically as a foaming agent and/or as a low density filler. 
     Examples of applications where the microspheres can be used include the production of foamed or low density resins, paints, coatings (e.g. anti-slip coatings, solar reflective, insulating coatings and underbody coatings), adhesives, cements, inks (e.g. printing inks such as waterborne inks, solvent borne inks, plastisol inks, thermal printer paper, and UV curing inks), paper and board, porous ceramics, non-woven materials, shoe soles such as sports shoe soles, textured coverings, artificial leather, food packaging, crack fillers, putties, sealants, toy-clays, wine corks, explosives, cable insulations, foams for protective helmet liners, and automotive weather strips. Microspheres can also be used in the in the treatment or processing of natural leather, for example to remove defects, to improve the aesthetic appearance, or to increase thickness. 
     The microspheres can also be used in producing polymer or rubber materials. Examples include thermoplastics (e.g. polyethylene, polyvinyl chloride, poly(ethylene-vinylacetate), polypropylene, polyamides, poly(methyl methacrylate), polycarbonate, acrylonitrile-butadiene-styrene polymer, polylactic acid, polyoxymethylene, polyether ether ketone, polyetherimide, polyether sulfone, polystyrene and polytetrafluoroethylene), thermoplastic elastomers (e.g. styrene-ethylene-butylene-styrene copolymer, styrene-butadiene-styrene copolymer, thermoplastic polyurethanes and thermoplastic polyolefins); styrene-butadiene rubber; natural rubber; vulcanized rubber; silicone rubbers; and thermosetting polymers (e.g. epoxies, polyurethanes and polyesters). 
     In some of these applications expanded microspheres are particularly advantageous, such as in putties, sealants, toy-clays, genuine leather, paint, explosives, cable insulations, porous ceramics, and thermosetting polymers (like epoxies, polyurethanes and polyesters). In some cases it is also possible to use a mixture of expanded and expandable microspheres of the present disclosure, for example in underbody coatings, silicone rubbers and light weight foams. 
     EXAMPLES 
     The present disclosure will be further described in connection with the following, non-limiting examples. If not otherwise stated, all parts and percentages are weight parts or weight percentages. 
     [Analysis Details] 
     The expansion properties were evaluated on dry particles on a Mettler Toledo TMA/SDTA851e thermomechanical analyser, interfaced with a PC running with STARe software. The sample to be analysed was prepared from 0.5 mg (+/−0.02 mg) of the thermally expandable microspheres contained in an aluminum oxide crucible with a diameter of 6.8 mm and a depth of 4.0 mm. The crucible was sealed using an aluminum oxide lid with a diameter of 6.1 mm. Using a TMA Expansion Probe type, the temperature of the sample was increased from about 30° C. to about 240° C. with a heating rate of 20° C./min while applying a load (net.) of 0.06 N with the probe. The displacement of the probe vertically was measured to analyze the expansion characteristics. 
     Initial temperature of expansion (Tstart): the temperature (° C.) when displacement of the probe is initiated, i.e. the temperature at which the expansion start; 
     Maximum temperature of expansion (Tmax): the temperature (° C.) when displacement of the probe reaches its maximum, i.e. the temperature at which maximum expansion is obtained; 
     Maximum displacement (Lmax): the displacement (μm) of the probe when displacement of the probe reaches its maximum; 
     TMA density: sample weight (d) divided by volume increase of the sample (dm3) when displacement of the probe reaches its maximum. The lower the TMA density, the better the microspheres expand and a lower TMA-density usually indicates more desirable expansion properties. A TMA density of 0.2 g/cm3 or lower is considered to be desirable and a TMA density of at least 0.15 g/cm3 or lower is considered to be particularly desirable. 
     The particle size and size distribution was determined by laser light scattering on a Malvern Mastersizer Hydro 2000 SM apparatus on wet samples. The median particle size is presented as the volume median diameter, D(50). The span is calculated from [D90−D10]/D50, where D90 is the diameter which encompasses 90% of the microspheres, and D10 is the diameter which encompasses 10% of the microspheres, on a volume basis. 
     The amount of the blowing agent was determined by thermal gravimetric analysis (TGA) on a Mettler Toledo TGA/DSC 1 with STARe software. A11 samples were dried prior to analysis in order to exclude as much moisture as possible and if present also residual monomers. The analyses were performed under an atmosphere of nitrogen using a heating rate at 25° C. min-1 starting at 30° C. and finishing at 650° C. 
     The amount of residual monomers in the obtained microsphere slurry was determined after solvent extraction using gas chromatography using a Gas Chromatograph (GC) equipped with a Flame Ionization Detector (FID) and a polar separation column. A defined aliquot of microsphere slurry, along with a defined amount of internal standard is extracted with acetone under stirring for 3 hours. The extracted sample is centrifuged, and a part of the supernatant is transferred in to a GC sample vial. The residual concentration of each monomer in the slurry sample is analyzed with GC-FID (Gas Chromatograph equipped with a Flame Ionization Detector) where the different monomers are separated on a polar Agilent InnoWax column. The amounts of residual monomers determined for the microspheres of some examples before and after treatment with sodium bisulfite or sodium persulfate are specified in Tables 6 and 7 below. 
     [Synthetic Procedure] 
     Thermoplastic core/shell microspheres were prepared according to the following general procedure using the components and amounts specified in Tables 1-3 below. 
     An organic phase was prepared by mixing monomers, cross linking agent and blowing agent(s) in a stirring vessel. This was then mixed with an aqueous phase that comprised stabiliser, the polymerisation initiator, sodium hydroxide and acetic acid, these last two components being added to ensure the pH of the aqueous phase was approximately 4.5. 
     In a typical experiment, the content of the aqueous phase was as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Added water: 
                 362.5 g 
               
               
                   
                 NaOH (1M) 
                  15.8 g 
               
               
                   
                 Acetic Acid (10%) 
                  25.3 g 
               
               
                   
                 Stabiliser (Silanized Colloidal Silica) 
                  32.0 g 
               
               
                   
                 Initiator (35% Dicetyl peroxydicarbonate) 
                  7.5 g 
               
               
                   
                 Rinse water 
                  50.0 g 
               
               
                   
                   
               
            
           
         
       
     
     Rinse water refers to water that was used to flush the inlet pipes to the reactor after the various components had been added. 
     The mixture was stirred vigorously using a propellor mixer to form a homogeneous dispersion. The oil (organic) phase content of the mixture was 40 wt %. The monomer mixtures of the various Examples are shown in Table 1. The oil phase composition is shown in Table 2, and the aqueous phase composition is shown in Table 3. 
     Examples 1-15 
     The monomers used in these Examples are acrylonitrile, dimethyl itaconate, and tetrahydrofurfuryl acrylate. The aqueous and organic phases were transferred to a 1 L volume rotator/stator reactor. Under constant stirring, polymerisation was initiated by raising the temperature to 57° C. and holding at that temperature for 5 hours. The reactor temperature was then raised to 63° C., and the temperature held for 4 hours, under the same mixing conditions. A 20 wt % aqueous solution of sodium bisulfite was then added at a temperature of 70° C. in order to reduce levels of any residual unreacted monomer. The amount added was selected to ensure that the amount of sodium bisulfite (on a dry basis) was 14 wt % of the total organic phase. The temperature was then held for 4.5 h, before being allowed to cool to room temperature. 
     The slurry was filtered through a 63 μm filter, to remove agglomerated particles. The resulting microspheres were then analysed for density, particle size, expansion characteristics, amount of filtered agglomerated material, and long term-stability (i.e. expansion characteristics after 4 months). 
     Comparative Example 16 
     Microspheres based on dimethyl itaconate, acrylonitrile and methylacrylate monomers were prepared according to an analogous procedure to that described above for Examples 1 to 15. 
     Example 17 
     The microspheres of Example 17 were prepared according to an analogous procedure as set forth about for Examples 1-15 with the only modification that the amount of sodium bisulfite added was selected to ensure that the amount of sodium bisulfite (on a dry basis) was 5.7 wt % of the total organic phase. 
     Example 18-21 
     The microspheres of Examples 18-21 were prepared according to an analogous procedure as set forth about for Examples 1-15 with the only modification that instead of sodium bisulfite a 25 wt % aqueous solution sodium persulfate was added at a temperature of 73° C. in order to reduce levels of any residual unreacted monomer. The amount added was selected to ensure that the amount of sodium persulfate (on a dry basis) was 5.7 wt % of the total organic phase. 
     Example 22-32 
     The microspheres of Examples 22-32 were prepared according to an analogous procedure as set forth about for Examples 1-15 with the only modification that instead of sodium bisulfite a 25 wt % aqueous solution sodium persulfate was added at a temperature of 73° C. in order to reduce levels of any residual unreacted monomer. The amount added was selected to ensure that the amount of sodium persulfate (on a dry basis) was 2.5 wt % of the total organic phase. In Examples 23, 26, and 28-31 methyl methacrylate (MMA) was added as further monomer. In Example 27, methyl acrylate (MA) was added as further monomer. 
     Various properties of the microspheres are presented in Tables 4 and 5. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Monomer Composition of Organic Phase (1) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 
                 ACN (2) 
                 DMI (3) 
                 THFA (4) 
                 MA (5) 
                 MMA (6) 
               
               
                   
               
               
                 1 
                 30 
                 20 
                 50 
                   
                   
               
               
                 2 
                 40 
                 20 
                 40 
                   
                   
               
               
                 3 
                 40 
                 20 
                 40 
                   
                   
               
               
                 4 
                 50 
                 20 
                 30 
                   
                   
               
               
                 5 
                 50 
                 20 
                 30 
                   
                   
               
               
                 6 
                 60 
                 20 
                 20 
                   
                   
               
               
                 7 
                 60 
                 20 
                 20 
                   
                   
               
               
                 8 
                 60 
                 20 
                 20 
                   
                   
               
               
                 9 
                 60 
                 20 
                 20 
                   
                   
               
               
                 10 
                 50 
                 20 
                 30 
                   
                   
               
               
                 11 
                 50 
                 20 
                 30 
                   
                   
               
               
                 12 
                 50 
                 20 
                 30 
                   
                   
               
               
                 13 
                 50 
                 20 
                 30 
                   
                   
               
               
                 14 
                 50 
                 20 
                 30 
                   
                   
               
               
                 15 
                 50 
                 20 
                 30 
                   
                   
               
               
                 17 
                 50 
                 20 
                 30 
                   
                   
               
               
                 18 
                 50 
                 20 
                 30 
                   
                   
               
               
                 19 
                 50 
                 20 
                 30 
                   
                   
               
               
                 20 
                 50 
                 20 
                 30 
                   
                   
               
               
                 21 
                 60 
                 10 
                 30 
                   
                   
               
               
                 22 
                 50 
                 20 
                 30 
                   
                   
               
               
                 23 
                 70 
                   
                 20 
                   
                 10 
               
               
                 24 
                 70 
                 10 
                 20 
                   
                   
               
               
                 25 
                 50 
                 20 
                 30 
                   
                   
               
               
                 26 
                 70 
                   
                 20 
                   
                 10 
               
               
                 27 
                 60 
                   
                 30 
                 10 
                   
               
               
                 28 
                 65 
                   
                 25 
                   
                 10 
               
               
                 29 
                 75 
                   
                 20 
                   
                  5 
               
               
                 30 
                 60 
                   
                 20 
                   
                 20 
               
               
                 31 
                 70 
                   
                 20 
                   
                 10 
               
               
                 32 
                 60 
                 20 
                 20 
               
               
                   
               
               
                 Comparative Example 
                 ACN (2) 
                 DMI (3) 
                   
                 MA (5) 
                   
               
               
                   
               
               
                 16 
                 43 
                 40 
                   
                 17 
                   
               
               
                   
               
               
                 (1) Amounts are in % weight of total monomer (excluding cross-linking agent) 
               
               
                 (2) ACN = Acrylonitrile 
               
               
                 (3) DMI = Dimethyl itaconate 
               
               
                 (4) THFA = Tetrahydrofurfuryl acrylate 
               
               
                 (5) MA = Methyl acrylate 
               
               
                 (6) MMA = Methyl methacrylate 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Content of Organic Phase (1) 
               
            
           
           
               
               
               
               
            
               
                   
                 Amount  
                 Crosslinking Agent  
                 Blowing Agent/ 
               
               
                 Example 
                 Monomer 
                 Amount (2) 
                 Amount (3) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 100 
                 0.40 
                 iB/21 
               
               
                 2 
                 100 
                 0.40 
                 nB/21 
               
               
                 3 
                 100 
                 0.40 
                 iB/21 
               
               
                 4 
                 100 
                 0.40 
                 nB/21 
               
               
                 5 
                 100 
                 0.40 
                 iB/21 
               
               
                 6 
                 100 
                 0.33 
                 nB/21 
               
               
                 7 
                 100 
                 0.33 
                 iP/10 + nB/10 
               
               
                 8 
                 100 
                 0.33 
                 iP/10 + nB/10 
               
               
                 9 
                 100 
                 0.33 
                 iP/21 
               
               
                 10 
                 100 
                 0.40 
                 iB/11 + iP/10 
               
               
                 11 
                 100 
                 0.40 
                 iB/14.7 + iO/6.3 
               
               
                 12 
                 100 
                 0.40 
                 iB/14.7 + iP/6.3 
               
               
                 13 
                 100 
                 0.60 
                 iB/14.7 + iP/6.3 
               
               
                 14 
                 100 
                 0.80 
                 iB/14.7 + iP/6.3 
               
               
                 15 
                 100 
                 1.20 
                 iB/14.7 + iP/6.3 
               
               
                 17 
                 100 
                 0.60 
                 iB/14.7 + iP/6.3 
               
               
                 18 
                 100 
                 0.40 
                 iB/14.7 + iP/6.3 
               
               
                 19 
                 100 
                 0.80 
                 iB/14.7 + iP/6.3 
               
               
                 20 
                 100 
                 0.40 
                 iB/17 + iP/6.3 
               
               
                 21 
                 100 
                 0.40 
                 iB/21 
               
               
                 22 
                 100 
                 0.28 
                 iB/21 
               
               
                 23 
                 100 
                 0.20 
                 iB/14.7 + iP/6.3 
               
               
                 24 
                 100 
                 0.20 
                 iB/14.7 + iP/6.3 
               
               
                 25 
                 100 
                 0.19 
                 iB/21 
               
               
                 26 
                 100 
                 0.20 
                 iB/10.0 + iO/11.0 
               
               
                 27 
                 100 
                 0.40 
                 iB/21 
               
               
                 28 
                 100 
                 0.20 
                 iB/14.7 + iP/6.3 
               
               
                 29 
                 100 
                 0.20 
                 iB/10.0 + iO/11.0 
               
               
                 30 
                 100 
                 0.40 
                 iB/21 
               
               
                 31 
                 100 
                 0.20 
                 iB/14.7 + iP/6.3 
               
               
                 32 
                 100 
                 0.40 
                 iB/14.7 + iP/6.3 
               
               
                 16 
                 100 
                 0.50 
                 iB/25 
               
               
                   
               
               
                 (1) Amounts in weight parts, in addition to 100 weight parts monomer 
               
               
                 (2) Crosslinking agent = trimethylolpropane trimethacrylate 
               
               
                 (3) Charged amount (in weight-%) of the organic phase, i.e. monomers, blowing agent and crosslinker; iB = isobutane; nB = n-Butane; iP = isopentane; iO = isooctane 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Amount of charged silanized colloidal silica (g silica/1 organic phase) 
               
            
           
           
               
               
               
            
               
                 Example 
                 Silica A (1) 
                 Silica B (2) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 0 
                 60 
               
               
                 2 
                 96 
                 0 
               
               
                 3 
                 0 
                 60 
               
               
                 4 
                 96 
                 0 
               
               
                 5 
                 0 
                 60 
               
               
                 6 
                 96 
                 0 
               
               
                 7 
                 96 
                 0 
               
               
                 8 
                 96 
                 0 
               
               
                 9 
                 96 
                 0 
               
               
                 10 
                 0 
                 60 
               
               
                 11 
                 0 
                 60 
               
               
                 12 
                 0 
                 60 
               
               
                 13 
                 0 
                 60 
               
               
                 14 
                 0 
                 60 
               
               
                 15 
                 0 
                 60 
               
               
                 17 
                   
                 60 
               
               
                 18 
                   
                 60 
               
               
                 19 
                   
                 60 
               
               
                 20 
                   
                 60 
               
               
                 21 
                   
                 60 
               
               
                 22 
                   
                 60 
               
               
                 23 
                   
                 60 
               
               
                 24 
                   
                 60 
               
               
                 25 
                   
                 60 
               
               
                 26 
                   
                 60 
               
               
                 27 
                   
                 60 
               
               
                 28 
                   
                 60 
               
               
                 29 
                   
                 60 
               
               
                 30 
                   
                 60 
               
               
                 31 
                   
                 60 
               
               
                 32 
                   
                 60 
               
               
                 16 
                 74 
                 0 
               
               
                   
               
               
                 (1) Silica A = 50 wt % aqueous colloidal silica with volume average particle size of 60 nm, and which is surface modified with glycidoxypropylsilane and propylsilane in a 60:40 molar ratio, with a total surface coverage of 2.37 μmol/m2 of silica surface. 
               
               
                 (2) Silica B = 50 wt % aqueous colloidal silica with a volume average particle size of 32 nm, and which is surface modified with glycidoxypropoxysilane and propylsilane in a 50:50 molar ratio, with a total surface coverage of 2.37 μmol/m2 of silica surface. 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Expandable Microsphere Properties 
               
            
           
           
               
               
               
               
               
            
               
                   
                 D 
                   
                 Volatile  
                 Residual  
               
               
                   
                 (μm) 
                 Span 
                 Content 
                 Monomer 
               
               
                 Example 
                 (1) 
                 (2) 
                 (wt %) (3) 
                 (ppm) (4) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 1 
                 8.9 
                 1.0 
                 10.2 
                 801 
               
               
                 2 
                 10.1 
                 1.1 
                 14.9 
                 1114 
               
               
                 3 
                 9.7 
                 1.0 
                 14.2 
                 1370 
               
               
                 4 
                 11.0 
                 1.0 
                 20.0 
                 475 
               
               
                 5 
                 9.4 
                 1.2 
                 12.5 
                 989 
               
               
                 6 
                 10.2 
                 1.0 
                 14.1 
                 48 
               
               
                 7 
                 10.4 
                 0.8 
                 13.0 
                 22 
               
               
                 8 
                 12.9 
                 0.9 
                 22.2 
                 35 
               
               
                 9 
                 10.4 
                 0.8 
                 12.1 
                 368 
               
               
                 10 
                 9.4 
                 1.1 
                 18.6 
                 987 
               
               
                 11 
                 10.8 
                 1.0 
                 17.2 
                 471 
               
               
                 12 
                 10.2 
                 1.1 
                 19.5 
                 388 
               
               
                 13 
                 9.9 
                 1.0 
                 18.7 
                 832 
               
               
                 14 
                 11.1 
                 1.2 
                 17.1 
                 709 
               
               
                 15 
                 11.9 
                 1.0 
                 14.8 
                 2356 
               
               
                 17 
                 9.9 
                 1.0 
                 18.7 
                 1012 
               
               
                 18 
                 11.2 
                 0.9 
                 16.6 
                 102 
               
               
                 19 
                 11.5 
                 1.0 
                 15.3 
                 88 
               
               
                 20 
                 18.0 
                 1.3 
                 18.8 
                 61 
               
               
                 21 
                 18.7 
                 0.9 
                 17.3 
                 152 
               
               
                 22 
                 17.0 
                 0.9 
                 20.4 
                 677 
               
               
                 23 
                 20.4 
                 1.1 
                 13.5 
                 1143 
               
               
                 24 
                 21.9 
                 1.1 
                 14.5 
                 1180 
               
               
                 25 
                 19.1 
                 0.9 
                 20.6 
                 1156 
               
               
                 26 
                 21.8 
                 0.9 
                 21.0 
                 809 
               
               
                 27 
                 18.3 
                 1.0 
                 16.9 
                 1118 
               
               
                 28 
                 23.8 
                 1.2 
                 6.8 
                 2395 
               
               
                 29 
                 19.3 
                 1.1 
                 21 
                 1051 
               
               
                 30 
                 18.0 
                 1.3 
                 7.6 
                 439 
               
               
                 31 
                 21.0 
                 1.1 
                 11.8 
                 226 
               
               
                 32 
                 15.7 
                 1.1 
                 14.8 
                 55 
               
               
                 16 
                 13.0 
                 2.1 
                 4.6 
                 36660 
               
               
                   
               
               
                 (1) Volume median particle size of unexpanded microspheres 
               
               
                 (2) [D90-D10]/D50 
               
               
                 (3) Volatile content of the microspheres, measured by TGA in weight %; based on the total weight of the microspheres 
               
               
                 (4) Sum of all remaining unreacted monomer in the polymer shell, measured by GC 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Expansion Characteristics 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 TMA 
                   
                   
                 TMA 
                   
                   
               
               
                   
                 Density 
                 Tstart 
                 Tmax 
                 Density 
                 Tstart 
                 Tmax 
               
               
                   
                 (g L−1) 
                 (° C.) 
                 (° C.) 
                 (g L−1) 
                 (° C.) 
                 (° C.) 
               
            
           
           
               
               
               
            
               
                 Example 
                 Directly after synthesis 
                 After 4 months&#39; storage 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 1 
                 43.1 
                 95 
                 98 
                 (1) 
                 (1) 
                 (1) 
               
               
                 2 
                 32.9 
                 77 
                 86 
                  25.3 
                 77  
                 89  
               
               
                 3 
                 12.6 
                 94 
                 101 
                  12.4 
                 93  
                 102  
               
               
                 4 
                 12.4 
                 108 
                 113 
                  17.7 
                 85  
                 113  
               
               
                 5 
                 14.8 
                 94 
                 113 
                  14.6 
                 93  
                 113  
               
               
                 6 
                 17.4 
                 103 
                 124 
                  16.1 
                 95  
                 123  
               
               
                 7 
                 27.2 
                 105 
                 123 
                 (1) 
                 (1) 
                 (1) 
               
               
                 8 
                 9.5 
                 128 
                 132 
                  10.9 
                 104  
                 132  
               
               
                 9 
                 26.3 
                 118 
                 151 
                 (1) 
                 (1) 
                 (1) 
               
               
                 10 
                 8.5 
                 116 
                 121 
                 (1) 
                 (1) 
                 (1) 
               
               
                 11 
                 11.1 
                 105 
                 119 
                 (1) 
                 (1) 
                 (1) 
               
               
                 12 
                 10.5 
                 106 
                 116 
                 (1) 
                 (1) 
                 (1) 
               
               
                 13 
                 11.5 
                 101 
                 113 
                 (1) 
                 (1) 
                 (1) 
               
               
                 14 
                 14.7 
                 99 
                 114 
                 (1) 
                 (1) 
                 (1) 
               
               
                 15 
                 21 
                 101 
                 114 
                 (1) 
                 (1) 
                 (1) 
               
               
                 17 
                 11.5 
                 101 
                 113 
                 (1) 
                 (1) 
                 (1) 
               
               
                 18 
                 12.3 
                 105 
                 115 
                 (1) 
                 (1) 
                 (1) 
               
               
                 19 
                 17.3 
                 102 
                 114 
                 (1) 
                 (1) 
                 (1) 
               
               
                 20 
                 10.8 
                 86 
                 123 
                 (1) 
                 (1) 
                 (1) 
               
               
                 21 
                 11.7 
                 91 
                 123 
                 (1) 
                 (1) 
                 (1) 
               
               
                 22 
                 9.4 
                 86 
                 120 
                 (1) 
                 (1) 
                 (1) 
               
               
                 23 
                 15.2 
                 93 
                 137 
                 (1) 
                 (1) 
                 (1) 
               
               
                 24 
                 13.3 
                 96 
                 139 
                 (1) 
                 (1) 
                 (1) 
               
               
                 25 
                 10.4 
                 89 
                 118 
                 (1) 
                 (1) 
                 (1) 
               
               
                 26 
                 11.8 
                 97 
                 139 
                 (1) 
                 (1) 
                 (1) 
               
               
                 27 
                 21.4 
                 85 
                 119 
                 (1) 
                 (1) 
                 (1) 
               
               
                 28 
                 19.7 
                 95 
                 135 
                 (1) 
                 (1) 
                 (1) 
               
               
                 29 
                 19.2 
                 98 
                 140 
                 (1) 
                 (1) 
                 (1) 
               
               
                 30 
                 18.9 
                 96 
                 136 
                 (1) 
                 (1) 
                 (1) 
               
               
                 31 
                 18.6 
                 91 
                 134 
                 (1) 
                 (1) 
                 (1) 
               
               
                 32 
                 11.8 
                 92 
                 130 
                 (1) 
                 (1) 
                 (1) 
               
               
                 16 
                 103.3 
                 99 
                 112 
                 (1) 
                 (1) 
                 (1) 
               
               
                   
               
               
                 (1) Not measured. 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Residual monomer amounts before  
               
               
                 treatment with sodium persulfate (in ppm) 
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 
                 ACN (1) 
                 THFA (2) 
                 DMI (3) 
                 MMA (4) 
                 MA (5) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 20 
                 2210 
                 1190 
                 339 
                   
                   
               
               
                 22 
                 1610 
                 1690 
                 80 
                   
                   
               
               
                 23 
                 2790 
                 2100 
                   
                 8 
                   
               
               
                 27 
                 1570 
                 1020 
                   
                   
                 622 
               
               
                   
               
               
                 (1) ACN = Acrylonitrile 
               
               
                 (2) THFA = Tetrahydrofurfuryl acrylate 
               
               
                 (3) DMI = Dimethyl itaconate 
               
               
                 (4) MMA = Methyl methacrylate 
               
               
                 (5) MA = Methyl acrylate 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Residual monomer amounts after treatment with  
               
               
                 sodium bisulfite or sodium persulfate (in ppm) 
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 
                 ACN (1) 
                 THFA (2) 
                 DMI (3) 
                 MMA (4) 
                 MA (5) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 11 
                 77 
                 20 
                   
                   
               
               
                 10 
                 5 
                 940 
                 42 
                   
                   
               
               
                 12 
                 18 
                 360 
                 10 
                   
                   
               
               
                 13 
                 20 
                 802 
                 10 
                   
                   
               
               
                 14 
                 15 
                 684 
                 10 
                   
                   
               
               
                 17 
                 200 
                 802 
                 10 
                   
                   
               
               
                 18 
                 38 
                 54 
                 10 
                   
                   
               
               
                 19 
                 24 
                 54 
                 10 
                   
                   
               
               
                 20 
                 15 
                 26 
                 20 
                   
                   
               
               
                 21 
                 21 
                 40 
                 91 
                   
                   
               
               
                 22 
                 342 
                 273 
                 62 
                   
                   
               
               
                 23 
                 797 
                 341 
                   
                 5 
                   
               
               
                 24 
                 890 
                 270 
                 20 
                   
                   
               
               
                 25 
                 468 
                 620 
                 68 
                   
                   
               
               
                 26 
                 592 
                 212 
                   
                 5 
                   
               
               
                 27 
                 622 
                 233 
                   
                   
                 263 
               
               
                 28 
                 1890 
                 500 
                   
                 5 
                   
               
               
                 29 
                 796 
                 250 
                   
                 5 
                   
               
               
                 30 
                 348 
                 71 
                 20 
                   
                   
               
               
                 31 
                 140 
                 81 
                   
                 5 
                   
               
               
                 32 
                 15 
                 20 
                 20 
               
               
                   
               
               
                 (1) ACN = Acrylonitrile 
               
               
                 (2) THFA = Tetrahydrofurfuryl acrylate 
               
               
                 (3) DMI = Dimethyl itaconate 
               
               
                 (4) MMA = Methyl methacrylate 
               
               
                 (5) MA = Methyl acrylate 
               
            
           
         
       
     
     By way of further comparison, reference can be made to the disclosures of WO2019/043235 and WO2019/101749, in particular the disclosed comparative examples. 
     In WO2019/043235, attempts were made to prepare microspheres from caprolactone/acrylonitrile and lactic acid/acrylonitrile copolymers (Examples 31-42, as described at page 25, line 15 to page 28, line 4). Caprolactone and lactic acid are both bio-derived monomers. These attempts were unsuccessful. 
     Similarly, in WO2019/101749, attempts were made to prepare microspheres from acrylonitrile/methyl acrylate/dimethyl maleate and acrylonitrile/methyl acrylate/diethylmaleate copolymers (Examples 25-30, as described at page 24, line 16 to page 26, line 5). Dimethyl maleate and diethyl maleate are bio-derived monomers. These attempts were also unsuccessful. 
     The results presented herein demonstrate that monomers of Formula 1 can successfully be used to produce expandable thermoplastic polymeric microspheres, and therefore can be used to improve the content of sustainably-sourced material in such microspheres. Such a result is unexpected, in view of the comparative examples mentioned above. 
     The results also show that the microspheres can still successfully be expanded after several months storage, showing that they have good shelf-life, and good blowing agent retention characteristics. 
     The results further show that reduced residual monomer content in the microspheres can be achieved by use of monomers of Formula 1 in the thermoplastic polymer shell. 
     Moreover, the results show that a treatment of the microspheres with an agent selected from oxo acids of sulphur, salts and derivatives thereof, comprising at least one sulfur atom having a least one free electron pair and binding three oxygen atoms or comprising at least two sulfur atoms which are linked via a peroxide group reduces the amount of residual monomers in the microspheres. In particular, treatment of the microspheres with an agent selected from oxo acids of sulphur, salts and derivatives thereof, comprising at least two sulfur atoms which are linked via a peroxide group may significantly reduce the amounts of residual monomers, for instance to less than 100 ppm. The reduction of the amount of residual acrylonitrile is particularly pronounced when using such persulfate treatment. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the various embodiments in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment as contemplated herein. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the various embodiments as set forth in the appended claims.