Amphiphilic core-shell latexes

• US 6,573,313 B2
• Filed: 01/16/2001
• Issued: 06/03/2003
• Est. Priority Date: 01/16/2001
• Status: Active Grant

• Current Assignee: Hong Kong Polytechnic University
• Original Assignee: Hong Kong Polytechnic University
• Inventors: Zhu, Jun Min, Harris, Frank W, Li, Pei
• Primary Examiner(s): Cain, Edward J.
• Application Number:
  US09/759,242
• Publication Number:
  US 20020143081A1
• Time in Patent Office: 868 Days
• Field of Search: 523/201
• US Class Current: 523/201
• CPC Class Codes: C08F 251/00 Macromolecular compounds obtained by polymerising monomers on to polysaccharides or derivatives thereof
• CPC Class Codes: C08F 265/04 on to polymers of esters
• CPC Class Codes: C08F 271/00 Macromolecular compounds obtained by polymerising monomers on to polymers of nitrogen-containing monomers as defined in group C08F26/00
• CPC Class Codes: C08F 279/02 on to polymers of conjugated dienes
• CPC Class Codes: C08F 285/00 Macromolecular compounds obtained by polymerising monomers on to preformed graft polymers
• CPC Class Codes: C08F 291/00 Macromolecular compounds obtained by polymerising monomers on to macromolecular compounds according to more than one of the groups C08F251/00 - C08F289/00

Abstract

Amphiphilic latex nanoparticles comprise a core and shell, The core contains hydrophobic vinylic grafted copolymer and hydrophobic vinylic homopolymer, and the shell to which the hydrophobic vinylic polymer is grafted is a hydrophilic, nitrogen-containing polymer. Typically the particles are made by a process which involves generating radicals on the nitrogen atoms of said hydrophilic polymer, and then initiating free-radical polymerisation of said vinylic monomer, hydrophobic vinylic polymer separating to form latexes of highly monodispersed core-shell particles with the hydrophobic polymer as the core and said hydrophilic polymer as the shell.

Claims

1. A process of forming a well-defined amphiphilic core-shell emulsion polymer, the process comprising treating a water-soluble polymer containing amino groups with a small amount of alkyl hydroperoxide in the presence of a vinylic monomer.

2. The process as defined in claim 1, comprising generating radicals on nitrogen atoms of the water-soluble polymer, and then initiating free-radical polymerization of said vinylic monomer, whereby a vinylic polymer separates to form a latex of highly monodisperse core-shell particles with a hydrophobic polymer as the core and a hydrophilic polymer as the shell.

3. The process as defined in claim 2, wherein the core of said amphiphilic core-shell emulsion polymer comprises a hydrophobic grafted copolymer and a hydrophobic homopolymer, and said shell to which said hydrophobic polymer is grafted is a hydrophilic, nitrogen-containing polymer.

4. The process as defined in claim 3, wherein the nitrogen of said hydrophilic, nitrogen-containing polymer is present as an amino group.

5. The process as defined in claim 1, wherein said water-soluble polymer is selected from natural and synthetic water-soluble polymers containing amino groups.

6. The process as defined in claim 3, wherein said hydrophilic, nitrogen-containing polymer is selected from the group consisting of polyethyleneimine, and other synthetic amino polymers;

chitosan and other N-acetyl sugars; and

casein, gelatine, bovine serum albumin and other proteins.

7. The process as defined in claim 2, wherein the monomer forming the core portion of the core-shell particles is selected from the group consisting of a hydrophobic vinylic monomer, an acrylate monomer, an acrylamide monomer, polymerizable nitrile, acetate, and chloride monomers, a styrenic monomer, and a diene monomer;

where the weight % of the monomer is from 25 to 95% of the total core-shell emulsion polymer weight.

8. The process as defined in claim 1, wherein said vinylic monomer has the formula R¹R²C═

CH₂, where R¹ is hydrogen or alkyl and R² is alkyl, aryl, heteroaryl, substituted aryl, halo, cyano, or another suitable hydrophobic group.

9. The process as defined in claim 1, wherein said vinylic monomer has the formula CH₂═

CR³COOR⁴, where R³ is hydrogen or alkyl and R⁴ is alkyl or substituted alkyl or another suitable hydrophobic group.

10. The process as defined in claim 1, wherein said vinylic monomer is of formula CH₂═

CR³COONHR⁴, where R³ is hydrogen or alkyl and R⁴ alkyl or substituted alkyl, or another suitable hydrophobic group such that the monomer is water insoluble.

11. The process as defined in claim 1, wherein said vinylic monomer is of the formula CH₂═

CR¹—

CH═

CH₂, where R¹ is hydrogen, alkyl, or chloro.

12. The process as defined in claim 1, wherein a particle size of the amphiphilic core-shell particles is less than 200 nm, measured as D_n, a number average diameter.

13. The process as defined in claim 1, wherein the amphiphilic core-shell particles has a narrow size distribution, where D_v/D_n is in the range of 1.1 to 1.2.

14. The process as defined in claim 7, wherein the polymerized vinylic monomer has a polydispersity, M_w/M_n, in the range 1.5 to 3.

15. The process as defined in claim 1, wherein a hydrophobic polymer is formed in an amount of from 25 to 95% by weight, based on total core-shell emulsion polymer weight.

16. The process as defined in claim 1, wherein the water-soluble polymer containing amino groups is present in an amount of from 5 to 75% by weight, based on total core-shell emulsion polymer weight.

17. The process as defined in claim 7, wherein the free radical polymerization is accomplished via an amine/peroxide redox initiation.

18. The process as defined in claim 17, wherein the peroxide is an alkyl hydroperoxide.

19. The process as defined in claim 18, wherein a molar ratio of vinylic monomer to peroxide is more than 5000:

1.

20. The process as defined in claim 1, where polymerization is achieved in the absence of a surfactant.