Particles of hydrophobic polymers containing voids

Abstract

Polymer particles each containing at least one void and also a hydrophobic copolymeric surfactant and a hydrophilic copolymeric surfactant. The hydrophobic surfactant comprises long hydrophobic chains anchored in the particles and hydrophilic chains exposed to the voids. The hydrophilic copolymeric surfactant comprises hydrophobic portions anchored in the particles and hydrophilic chains exposed to the surroundings of the particles. The particles have a fine cell structure, are washable to remove unanchored surfactant and are easily dispersible in water. They are useful in coatings, plastics, cosmetics, paper and leather. Also a process for making the particles in which water is dispersed as droplets in monomer containing the hydrophobic surfactant and the dispersion is in turn dispersed in additional water containing the hydrophilic surfactant and the whole is subjected to a polymerisation which forms particles containing voids initially filled with water.

What we claim is: 
     
       1. A particle of a hydrophobic polymer containing at least one void and comprising an essentially hydrophobic surfactant in the region of the internal surfaces defining the voids and an essentially hydrophilic surfactant in the region of the external surface of the particle wherein a) the essentially hydrophobic surfactant is a block copolymer having a molecular weight of from 5,000 to 150,000 and comprising a hydrophobic chain and at least one hydrophilic chain which chain is present in an amount such that the hydrophilic portion of the block copolymer is from 5 to 45% of the weight of the block copolymer and   b) the essentially hydrophilic surfactant has a molecular weight of at least 2,000 and comprises at least one hydrophilic chain which chain is present in an amount such that the hydrophilic portion of the essentially hydrophilic surfactant is from 40 to 90 of the weight of the essentially hydrophilic surfactant, whereby the particle when dry is free-flowing in the presence of like particles and can be dispersed in water.   
     
     
       2. A particle according to claim 1 wherein the essentially hydrophobic surfactant has a molecular weight of from 10,000 to 40,000. 
     
     
       3. A particle according to claim 1 wherein the essentially hydrophobic surfactant comprises from 10 to 40 wt % of hydrophilic chains. 
     
     
       4. A particle according to claim 1 wherein the essentially hydrophobic surfactant comprises from 1 to 2 hydrophilic chains. 
     
     
       5. A particle according to claim 1 wherein the essentially hydrophilic surfactant has a molecular weight of from 3000 to 75,000. 
     
     
       6. A particle according to claim 1 wherein the essentially hydrophilic surfactant comprises from 50 to 80 wt % of hydrophilic chains. 
     
     
       7. A particle according to claim 1 wherein the essentially hydrophilic surfactant comprises from 1 to 3 hydrophilic chains. 
     
     
       8. Particles according to claim 1 wherein the number average particle size of the particles is from 0.3 to 100 μm. 
     
     
       9. Particles according to claim 8 wherein the number average particle size of the particles is from 0.5 to 50 μm. 
     
     
       10. Particles according to claim 8 having a number average particle size of below 10 μm. 
     
     
       11. Particles according to claim 8 containing voids wherein the number average diameter of the voids is from 0.1 to 10 μm.