Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-12-12
2003-07-01
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S402210, C428S402000, C428S407000, C525S518000, C525S070000, C525S073000, C524S504000
Reexamination Certificate
active
06586097
ABSTRACT:
This invention relates to crosslinked microparticles defined by the process for producing them by dispersion polymerization in non-aqueous medium without using a polymeric stabilizer, to the associated process and to their uses in coating and moulding compositions, as reactive or non-reactive additives, and as regulators of the rheology and/or reinforcement and/or flexibilization of the host matrix.
Crosslinked microparticles, such as those described in the present invention, are also commonly denoted by the term “microgels”. These microgels are essentially characterized by a globular structure (from a new nm to a few microns) of a polymer of very high mass comprising intramolecular crosslinking nodes. Advances in Polymer Science (1998) vol. 136, pp. 139-234 presents a general bibliographical review of microgels, methods for preparing them and a number of applications.
The methods most commonly used for preparing crosslinked microparticles or microgels are, on the one hand, emulsion polymerzation in aqueous medium, and, on the other hand, dispersion polymerization in non-aqueous medium, of compositions of polymerizable compounds comprising, inter alia, a polymerizable compound having the function of a crosslinking agent. In both cases, the polymerization medium is non-solvent for the polymer formed, which precipitates in the form of polymer particles. The essential problem posed for these two preparation methods is the need to stabilize the particles formed during the polymerization in order to protect them against the strong interparticulate interactions which may lead, if they are not controlled, to aggregation and setting to a solid of the particles formed. This stabilization is an essential key parameter in controlling the size of the microparticles, in particular in the range below one micron. Most of the performance quality of the microparticles is directly associated with their specific structure and their size.
The steric stabilizers commonly used to prepare microgels by emulsion or by dispersion are essentially of polymeric structure, well defined and adapted to each case, according to the polymerization medium and the structure of the particle to be stabilized. Macromolecules 1996, 29, 8650-55 in particular describes microgels based on unsaturated polyesters of specific self-emulsifying structure (self-stabilized particles). U.S. Pat. No. 4,206,099 describes crosslinked microparticles obtained by polycondensation in non-aqueous medium, using grafted copolymers as steric stabilizers. U.S. Pat. No. 4,605,720 describes crosslinked acrylic macroparticles obtained by radical-mediated polymerization in dispersion in non-aqueous medium, using polymeric stabilizers.
Among the essential drawbacks of the crosslinked microparticles obtained with stabilizers of polymeric structure, mention may be made of:
the limited availability of the polymeric stabilizer adapted to each individual case as a function of the polymerization medium and the structure of the particle to be stabilized, which often requires the specific prior preparation of the stabilizing polymer in an additional separate step, thus complicating the method for gaining access to the target microparticles.
relatively high concentrations of stabilizing polymer are required to obtain particle sizes of less than one micron, which often poses problems of solubility of the polymer and of viscosity of the corresponding solution with a limitation on the choice of the couples [stabilizing polymer/solvent for the stabilizing polymer and the monomers, and non-solvent for the polymer of the particles formed].
although the high molecular mass and concentration of the stabilizing polymer are favourable to the steric stabilization of the particles formed during the polymerization, this presence of a steric barrier as an outer layer can pose problems of accessibility of the protected structure of the particle, thus creating, depending on the case, a reduction in the efficacy of the reactive functions borne by the particle or incompatibility with respect to the receiving moulding or coating composition, with negative repercussions on the final performance qualities of the coating or of the moulded product.
certain specific microparticle structures are difficult if not impossible to obtain given the fact that the essential presence of the stabilizing polymer automatically limits the possibilities in terms of the structure of the particle (core/shell/effective functionality) and the desirable physicochemical properties of the microparticle relative to the medium and to the intended application.
The present invention proposes to overcome these drawbacks in a simple manner with crosslinked microparticles between 10 and 300 nm in size, preferably between 10 and 200 nm and more particularly from 20 to 100 nm in size, obtained by dispersion polymerization, in non-aqueous medium which is non-solvent for the polymer formed, of a composition of ethylenically unsaturated polymerizable compounds, the said microparticles being characterized in that the said composition comprises:
at least one monomer A, comprising only one ethylenic unsaturation which can undergo radical-mediated polymerization, giving the microparticles formed in the said non-aqueous medium self-stabilization during and after polymerization, without any addition of polymer having the function of a stabilizing agent, either before, during or after polymerization,
at least one compound B comprising at least two ethylenic unsaturations which can undergo radical-mediated polymerization,
and optionally, depending on the case:
at least one compound C comprising only one ethylenic unsaturation which can undergo radical-mediated polymerization, which is different from A
and/or
at least one compound D which is different from A, B and C and comprising at least one ethylenic unsaturation which can undergo radical-mediated polymerization and at least one second reactive function f1 which is other than an ethylenic unsaturation.
The crosslinked microparticles of the present invention are obtained by radical-mediated dispersion polymerization, in non-aqueous medium which is non-solvent for the polymer formed, of a composition of ethylenically unsaturated polymerizable compounds comprising the compounds A, B, C and D as defined above, in the absence of any added polymer for stabilizing the microparticles, formed during the polymerization, either before, during or after the dispersion polymerization.
The compounds A are necessarily monomers with only one ethylenic unsaturation which can undergo radical-mediated polymerization, while the compounds B, C and D can be monomers and/or oligomers. These oligomers have molecular masses {overscore (Mn)} of less than 2500 and preferably less than 1500.
The monomers A giving the microparticles formed self-stabilization as defined above can be selected from monomers containing only one ethylenic unsaturation which can undergo radical-mediated polymerization, with a molecular mass {overscore (Mn)} of less than 600 and preferably less than 400, containing only one polymerizable ethylenic unsaturation selected from (meth)acrylates, maleates and vinyls and borne by a linear or branched aliphatic group or a substituted or unsubstituted monocyclic or polycyclic alicyclic group which can optionally bear at least one reactive function f2 which is different from the polymerizable ethylenic unsaturation. In general, the stabilizing function of the monomer A is associated with an adequacy of the solubility parameter of this monomer relative to that of the polymerization medium and that of the polymer formed. The term “(meth)acrylate” should be interpreted throughout as “acrylate and/or methacrylate”.
Preferably, the monomers A have a chemical structure corresponding to the general formula (I) below:
CH
2
═CR
1
—X—(R
2
—Y)
k
—R (I)
with R
1
=H, CH
3
X=ester —(C═O)O—, amide —(C═O)N(R
3
)—
Y=ester —O(O═C)—, amide —(R
3
)N(C═O)—, urethane —O(O═C)NH—
R
2
=C
2
-C
6
alkylene radical which can
Magny Benoit
Pascault Jean-Pierre
Valette Ludovic
Cray Valley S.A.
Whyte Hirschboeck Dudek SC
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