Process of heat treating structured polymer particles

Abstract

A process comprising heating an aqueous dispersion of first structured polymer particles at a temperature of at least about 155° C., optionally in the presence of a base and/or a swelling agent, to produce an aqueous dispersion of heat treated structured polymer particles.

1 . A process comprising heating an aqueous dispersion of first structured polymer particles at a temperature of at least about 155° C., optionally in the presence of a base and/or a swelling agent, to produce an aqueous dispersion of heat treated structured polymer particles. 
     
     
         2 . The process of  claim 1  wherein the first structured polymer particles are core-shell particles having an expandable core. 
     
     
         3 . The process of  claim 2  wherein the core-shell particles are expanded during the process. 
     
     
         4 . The process of  claim 1  wherein the heat treated structured polymer is a hollow latex particle upon drying. 
     
     
         5 . The process of  claim 1  wherein the heat treated structured polymer particle is a hollow particle and has an average wet void fraction of at least about 0.30. 
     
     
         6 . The process of  claim 1  wherein the first particles comprise a core-shell particle, and wherein heating is conducted under conditions sufficient to expand the first particle to produce a heat treated particle having an average wet void fraction of at least 0.30. 
     
     
         7 . The process of  claim 1  wherein the heating is conducted under conditions sufficient to expand the first particle to produce a heat treated particle having an average wet void fraction of at least 0.60. 
     
     
         8 . The process of  claim 2  wherein the core-shell particle comprises, in polymerized form, at least one monomer selected from the group consisting of (meth)acrylate monomers and vinyl carboxylic acid monomers. 
     
     
         9 . The process of  claim 8  wherein the core comprises at least 30 weight percent methyl methacrylate based on the weight of monomers used to make the core. 
     
     
         10 . The process of  claim 2  wherein the treatment is done in the presence of a base. 
     
     
         11 . The process of  claim 1  wherein the treatment is done in the presence of a swelling agent. 
     
     
         12 . The process of  claim 10  wherein the base comprises at least one of LiOH, KOH, and NaOH. 
     
     
         13 . The process of  claim 1  wherein the heating is conducted at a temperature of at least 160° C. 
     
     
         14 . The process of  claim 1  wherein a hollow latex is produced, the process comprising:
 A. forming a first structured particle by emulsion polymerizing a copolymer latex having:
 i) a core phase comprising, in polymerized form, at least one monomer selected from the group consisting of: methyl acrylate, methyl methacrylate, and allyl methacrylate; 
 ii) an optional intermediate shell comprising, in polymerized form, at least one monomer selected from the group consisting of: methyl acrylate, methyl methacrylate, and allyl methacrylate and/or divinyl benzene; and 
 iii) an outermost shell phase comprising a hydrophobic, crosslinked copolymer comprising, in polymerized form, at least one monomer selected from the group consisting of: styrene; methyl methacrylate; methacrylic acid; acrylic acid and allyl methacrylate or divinyl benzene; 
   B. exposing the copolymer latex to a base under conditions sufficient to produce a hollow latex.   
     
     
         15 . The process of  claim 1  further comprising cooling a hollow latex from at, or below, the peak heat treatment temperature to a temperature at or below the Tg of the shell polymer at a rate of not greater than about 2° C. per minute. 
     
     
         16 . The process of  claim 1  wherein the first structured polymer particles comprise at least 10 percent of polymerized acid monomer, based on the weight of the polymer in the particles. 
     
     
         17 . The process of  claim 14  wherein the heating at a temperature of at least about 155° C. occurs at least partially while polymerization is occurring. 
     
     
         18 . The process of  claim 1  wherein the differential between the maximum temperature of the heat treatment and the glass transition temperature of the shell is at least about 50° C. 
     
     
         19 . The process of  claim 1  wherein a hollow latex is produced, the process comprising:
 A. forming a first structured particle by emulsion polymerizing a copolymer latex having:
 iv) a core phase comprising, in polymerized form, at least one monomer selected from the group consisting of: acrylic acid, methacrylic acid and allyl methacrylate; 
 v) an optional intermediate shell comprising, in polymerized form, at least one monomer selected from the group consisting of: acrylic acid, methacrylic acid and allyl methacrylate and/or divinyl benzene; and 
 vi) an outermost shell phase comprising a hydrophobic, crosslinked copolymer comprising, in polymerized form, at least one monomer selected from the group consisting of: styrene; methyl methacrylate; methacrylic acid; acrylic acid and allyl methacrylate or divinyl benzene; 
   B. exposing the copolymer latex to a base under conditions sufficient to produce a hollow latex.   
     
     
         20 . A process comprising heating an aqueous dispersion of first structured polymer particles at a temperature of at least about 160° C. for at least one hour, optionally in the presence of a base and/or a swelling agent, under conditions sufficient to expand the particles in an aqueous dispersion. 
     
     
         21 . A hollow particle latex having an average wet void fraction of at least 0.60.