Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-05-14
2004-06-29
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S291000, C526S318000
Reexamination Certificate
active
06756456
ABSTRACT:
DESCRIPTION
A subject-matter of the present invention is a process for the polymerization of chloroprene, the polychloroprenes obtained by the process and their use, in particular in adhesive mixtures.
More specifically, a subject-matter of the invention is a process for the polymerization of chloroprene in aqueous emulsion in the presence of copolymerizable surfactants, so that all or a large portion of the copolymerizable surfactant is found attached to the polymer chain.
In numerous fields of application, for ecological, health and safety reasons, there is a call for solvent adhesives to be substituted by aqueous adhesives.
Among its various uses, chloroprene rubber is sold for preparing solvent adhesives.
Numerous patents consequently disclose the means of obtaining latices of copolymerized or noncopolymerized polychloroprene in the form of an aqueous emulsion or an aqueous suspension in order to meet such a need.
Adhesive latices based on polychloroprene (CR) have to exhibit two main characteristics, which are good adhesiveness on numerous supports and rapid development of the cohesive forces of the film, obtained by a rapid rate of crystallization of the polymer.
The adhesive performance, measured starting from CR adhesive latices, in particular on nonporous supports, is poorer than that obtained with CR solvent adhesives.
The conventional formulation of an emulsion polymerization involves, inter alia, one or more amphiphilic compounds, known as “surfactants”, which make it possible simultaneously to stabilize the polymer particles and to control their size. These surfactant molecules are distributed between the surface of the polymer particles and the dispersing medium according to a complex adsorption/desorption equilibrium and can desorb under certain constraints. In the case of a film-forming polymer, such as CR, the consequences of this desorption phenomenon can be harmful. This is because some writers (Guyot A. and Tauer K., Advances in Polymer Science, 111, 43-45, 1994) have suggested that the surfactant thus desorbed is capable of migrating to the surface of the film, thus leading to the formation of hydrophilic domains. These regions of weakness are capable of detrimentally affecting the properties of the film, in particular its resistance to moisture, an important characteristic in the field of footwear, and thus its long term strength.
The industrial polymerization of chloroprene makes use, as stabilizers, of rosin salts. Simply adsorbed at the surface of the polymer particles, rosin salts have a tendency, during film formation, to group together in the form of domains, thus creating regions with a hydrophilic nature. It then becomes difficult to remove the water in a short time, which greatly reduces the advantage of adhesives of this type, in comparison with other adhesive latices, such as polyurethane-based latices.
One of the means for countering these disadvantages is to incorporate a surfactant which is copolymerizable with the CP, which surfactant will be found bonded to the polymer particles via a covalent chemical bond. It can therefore neither desorb from the surface of the polymer particles nor form hydrophilic regions during the film formation of the latex. This makes it possible to facilitate pathways for water to the surface of the adhesive film, thus reducing the drying time.
This alternative furthermore exhibits the advantage of making possible, during the destabilization of the latex for the purpose of using it as dry rubber, facilitated recycling of the aqueous wash liquor and reduced contamination by water.
The object of this present invention is to emulsion polymerize chloroprene, in the presence or absence of other comonomers, in the presence of a copolymerizable surfactant, in combination or not in combination with other known surfactants, so that all or a large portion of the copolymerizable surfactant is found attached via covalent bonds to the polymer chain.
The copolymerizable surfactant is, on its own, both a generator of micelles, because of its surfactant properties, and a comonomer, this being the situation within a wide pH and temperature range.
The copolymerizable surfactants are also known as reactive surfactants or surfmers (contraction of “surfactant monomer”), as they have a functional group capable of taking part in the propagation stage in the same way as the main monomer.
It is difficult to find, for a defined monomer, a surfactant capable of simultaneously acting as micelle generator (true surfactant) and as comonomer.
It is even surprising to find a micelle-generating copolymerizable surfactant which can, on its own, provide for the polymerization, without inhibiting it, and give rise to a stable latex.
This is because conventional copolymerizable surfactants known to date, such as reactive carboxylic acids, sodium styrenesulphonate and other products, only act as surfactants once copolymerized.
The reactive surfactants described in the literature include, inter alia, surfactants comprising reactive functional groups of acrylic or methacrylic type, but the latter do not make it possible, on their own, to form stable latices (Schoonbrood H. A.S. et al., Journal of Applied Polymer Science, 66, 1803-1820, 1997). This can be explained either by their high reactivity, leading to a high level of embedding, or by their affinity for the aqueous phase and the formation of polyelectrolytes. Whatever the true reason for it, the use of such surfactants does not make possible the preparation of stable latices, the polymer particles then being found to be without a significant fraction of the stabilizing carboxylic charges introduced by the surfactant.
Furthermore, it is difficult to find a surfactant which is copolymerizable with CP, given the high reactivity of chloroprene and its marked tendency towards homopolymerization.
The use of a sulphonated maleic surfactant, derived from sulphonated rosin or from a sulphonated fatty acid and synthesized according to a complex three-stage protocol, is disclosed in the Westvaco Patent U.S. Pat. No. 5,306,793, without an applicational example for chloroprene. This copolymerizable surfactant cannot be used alone and requires the parallel use of one or more conventional surfactants. Furthermore, the presence of sulphonate groups hinders the destabilization of the latex by the cold, which compromises the use of the polymer in the dry rubber form.
In its U.S. Pat. No. 4,446,282, Goodyear (U.S.) discloses the use of hemiesters and of hemiamides of certain dicarboxylic acids, such as 2-ethyl-1-hexyl maleic acid ester (EHMAE), but at basic pH and solely as comonomers, in combination with one or more true surfactants, for the sole purpose of preparing dry rubbers carrying carboxyl functional groups. Goodyear does not disclose the preparation of latex as such and gives no example of the polymerization of chloroprene.
In its patent EP 0 495 365, Bayer discloses a semi-continuous process which makes possible a homogeneous distribution of the carboxyl functional groups at the surface of the polymer particles, via the copolymerization of a non-surface-active acid comonomer. In comparison with a batch process, this process suffers, however, from complex processing.
The Applicant Company claims a process for the polymerization of chloroprene or of a mixture of chloroprene and of up to 20% by weight of a copolymerizable monomer, in aqueous emulsion in the presence of radical initiators, at a temperature of between 5° C. and 70° C., characterized in that the polymerization is carried out in the presence of one or more copolymerizable surfactants in agreement with the formula described below (I)
R
3
—Z—CO—C(R
1
)═C(R
2
)—COOM (I)
where: R
3
is a saturated or unsaturated, linear or branched and aliphatic or aromatic C
n
hydrocarbonaceous chain with n from 10 to 20;
R
1
and R
2
, which are identical or different, are chosen from H or
a C
1
-C
3
alkyl radical;
Z is chosen from —O— and —NH—;
M is chosen from alkali metals or NH
4
;
R
3
is preferably chosen from C
12
to C
18
alkyl radicals.,
Guyot Alain
Lima Romano
Maestri Piero
Masi Francesco
Sauterey François
Egwim Kelechi C.
Enichem Elastomeres France S.A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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