Aqueous dispersions of crystalline polymers and uses

Details Aqueous dispersions of crystalline polymers and uses Aqueous dispersions of crystalline polymers and uses

2001-01-18

2003-04-01

Lankford, Jr., Leon B. (Department: 1651)

Drug, bio-affecting and body treating compositions

Effervescent or pressurized fluid containing

Organic pressurized fluid

C524S556000

Reexamination Certificate

active

06540984

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to aqueous dispersions of crystalline polymers, methods for making such dispersions and the use of such dispersions for coating substrates.
It is known to use certain organic polymers to provide coatings on a wide variety of substrates, including hair (see U.S. Pat. Nos. 4,196,190; 4,452,216; 4,834,968 and 4,983,383); fabrics (see U.S. Pat. Nos. 3,644,241; 3,833,393 and 4,780,499); and seeds and other organisms (see U.S. Pat. No. 5,129,180). It is also known to set a fabric by impregnating the fabric with a monomer component, and polymerizing the monomer while maintaining the fabric in a desired configuration (see U.S. Pat. No. 4,401,688).
One class of polymers which has been used for coating substrates comprises side-chain crystalline (“SCC”) polymers. However, the known coating compositions containing SCC polymers have the disadvantage that the polymer is dissolved in an organic solvent. Organic solvents are expensive, require environmental controls, and are particularly undesirable for application to human hair or to an organism.
Attempts have been made to prepare aqueous dispersions of SCC polymers (see
British Polymer Journal
20, 521-524 (1988), U.S. Pat. Nos. 5,506,307 and 5,516,865, and Japanese Patent Document No. 6-192341), but the results have been poor and/or the techniques expensive.
SUMMARY OF THE INVENTION
We have discovered, in accordance with the present invention, that very valuable results can be achieved by coating substrates with aqueous dispersions of polymeric particles in which the polymer is a crystalline polymer containing units derived from at least one hydrophobic monomer and preferably also from a lesser amount of units derived from at least one hydrophilic monomer. Particularly useful results are obtained when the substrate is a seed or other organism, or a fibrous material. We have also discovered, in accordance with the invention, novel aqueous dispersions of crystalline polymers and methods of making such dispersions.
In one of its embodiments, this invention provides a substrate having a solid polymeric coating thereon, the coating having been obtained by:
(1) applying to the substrate an aqueous dispersion of solid particles comprising a crystalline polymer, the polymer (a) having a melting point T
m
and (b) comprising units derived from a hydrophobic monomer, and
(2) evaporating water from the dispersion to form the solid polymeric coating;
the coating having at least one of the following characteristics:
(A) at temperatures below T
m
, the coating is substantially impermeable to water (as hereinafter defined), and at temperatures above T
m
, the coating is substantially permeable to water (as hereinafter defined);
(B) the polymer is a crosslinked polymer having a gel content of at least 50%,
(C) the polymer is derived from a monomer component comprising:
(i) a hydrophobic monomer component comprising a first hydrophobic monomer, the first hydrophobic monomer being such that a homopolymer thereof is crystalline and has a melting point T
c
, and
(ii) a hydrophilic monomer component comprising a hydrophilic monomer, the ratio by weight of the hydrophobic monomer component to the hydrophilic monomer component being 10:1 to 50:1;
(D) the polymer is derived from a monomer component comprising a hydrophobic monomer component comprising (i) a first hydrophobic monomer, the first hydrophobic monomer being such that a homopolymer thereof is crystalline and has a melting point T
c
, and (ii) a second hydrophobic monomer which
(a) is such that a homopolymer thereof is amorphous and has a glass transition point T
g
which is less than T
c
, and
(b) is present in amount such that T
m
is (T
c
−5)° C. or less;
(E) the polymer is derived from a monomer component comprising a hydrophobic monomer component comprising (i) a first hydrophobic monomer, the first hydrophobic monomer being such that a homopolymer thereof is crystalline and has a melting point T
c
, and (ii) a second hydrophobic monomer which
(a) is such that a homopolymer thereof is amorphous and has a glass transition point T
g
which is more than T
c
, and
(b) is present in amount such that the coating has a tack at (T
c
+10)° C. which is less than the tack at (T
c
+10)° C. of a coating formed under the same conditions from a composition which is identical except that the crystalline polymer does not contain units derived from the second hydrophobic monomer;
(F) the polymer is derived from a monomer component comprising:
(i) a hydrophobic monomer component comprising a hydrophobic monomer, the hydrophobic monomer being such that a homopolymer thereof is crystalline and has a melting point T
c
;
(ii) a hydrophilic monomer component comprising a hydrophilic monomer; and
(iii) a crosslinking monomer having at least two polymerizable groups;
(G) the polymer is derived from a monomer component comprising one or more monomers containing carboxyl groups, at least 75% of the carboxyl groups having been neutralized;
(H) the polymer is crosslinked by an external crosslinker (as herinafter defined);
(I) the particles of the dispersion have coalesced to form a continuous coating, but retain a particulate character;
(J) the coating contains less than 1% of unreacted monomer, based on the weight of the polymer; and
(K) at least some of the particles comprise a core comprising said crystalline polymer and a coating around the core comprising a substantially amorphous polymer.
In describing the invention below, unless otherwise noted, parts, percentages and ratios are by weight. The monomers from which the crystalline polymer is derived are important. The term hydrophobic monomer is used herein to denote a monomer whose solubility in water at 25° C. is less than 2%. The term hydrophilic monomer is used herein to denote a monomer whose solubility in water at 25° is 2% or more. More than one hydrophobic monomer can be used, and the term hydrophobic monomer component is used herein to denote all the hydrophobic monomers collectively, and is often abbreviated herein to “BMC.” More than one hydrophilic monomer component can be used, and the term hydrophilic monomer component is used herein to denote all the hydrophilic monomers collectively, and is often abbreviated herein to “PMC.” The monomers from which the crystalline polymer is derived can include one or more monomers which contain two or more polymerizable groups, so that the polymer is crosslinked. Such monomers (which may be hydrophobic or hydrophilic) are referred to herein as crosslinking monomers; and the term crosslinking monomer component is used herein to denote all the crosslinking monomers collectively, and is often abbreviated herein to “XLC.” Except where otherwise noted, percentages of monomers given herein (both as starting materials, and as residual monomers) are based on the total weight of the monomer starting material. As further discussed below, the monomers used in preparing the crystalline polymers are preferably n-alkyl acrylates or methacrylates. The abbreviation CnA and 'CnMA are used to denote n-alkyl acrylates and n-alkyl methacrylates, respectively, in which the n-alkyl group contains x carbon atoms. For example C4A denotes butyl acrylate, and C12MA denotes lauryl methacrylate.
Crystalline melting points given herein (T
m
and T
c
) are the peak of a curve produced using a differential scanning calorimeter (DSC) at a heating rate of 10° C. per minute, and using the second heat cycle. The onset of melting (T
o
) is taken from the same curve. T
o
, T
m
and T
c
are measured in the conventional way well known to those skilled in the art. Thus T
m
and T
c
are the temperature at the peak of the DSC curve, and T
o
is the temperature at the intersection of the baseline of the DSC peak and the onset line, the onset line being defined as the tangent to the steepest part of the DSC curve below the peak. Tack values given herein are measured as follows. The latex is applied to a polymeric film (a polyester film available from DuPont under t

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