FR2794462A1 - SULFUR MODIFIED POLYCHLOROPRENE HAVING IMPROVED SCREEN RESISTANCE - Google Patents

Abstract

Process for the preparation of polychloroprene modified with sulfur, in an alkaline aqueous emulsion and in the presence of radical initiators, characterized in that one or more organic polysulphides chosen from: 1) di or disulphides are added to the reaction mixture. tetraisobutylthiurams optionally additivated with (2) disulfides of di or tetraalkylthiurams in which the alkyl group is different from isobutyl and contains from 3 to 5 carbon atoms.

Description

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MODIFIED SULFUR POLYCHLOROPRENE
A RESISTANCE TO ENHANCED GRID
The present invention relates to an improved process for the preparation of sulfur-modified polychloroprene with improved roasting resistance without altering the optimum time of vulcanization.

 Sulfur modified chloroprene polymers are well known. They are obtained by polymerization of chloroprene, optionally with another unsaturated monomer, in the presence of elemental sulfur. The resulting polymer has a strongly crosslinked structure via polysulfide bonds and is difficult to work. To obtain a product of increased plasticity, the polymer is degraded with the aid of suitable agents which produce a rupture of the polysulfide bonds. This operation is known as peptisation.

 Methods of peptization in alkaline aqueous emulsion have been described, for example, in FR-A-1,376,314, FR-A-1. 392.446, FR-A-1.393.099, FR-A-1.398.602,

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 FR-A-2. 076,922, FR-A-2,089,811, US-A-3,318,832. According to these methods, the peptization is carried out after the polymerization by treatment of the polymer latex with an alkylthiuram disulfide associated or not with a dialkyldithiocarbamate or a xanthogen disulfide. These processes have the main disadvantage of the slowness of the peptization (several hours at 40 C). The reaction is continued during the treatment of the latex in order to remove the residual monomer as well as during the insulation phase of the rubber. Moreover, the plasticity of the rubbers obtained varies over time, which represents a serious drawback for their implementation and their transformation into manufactured products.

 It is also known, according to another technique, to increase the plasticity of sulfur-modified chloroprene polymers using modifying agents or chain transfer agents such as xanthogen disulfide, iodoform, or alkyl mercaptans. which are present during the polymerization and which act as molecular weight regulators. These methods are described, for example, in patents FR-A-1,457,004 and US-A-3,397,173. The modified copolymers obtained can be further peptized.

 Finally US-A-3,808,183 and EP-A-011. 029 describe a process for the preparation of sulfur-modified polychloroprene according to which the peptization is carried out directly during the polymerization and not after.

 The polysulfides that can be used belong to the class of plasticizer compounds described in the US-2 patent. 234,215. Of these, di- and tetraalkylthiuram disulfides in which the alkyl group contains from 3 to 5 carbon atoms are mentioned. These disulfides are introduced before the start of the polymerization in proportions of between 0.1 and 2 parts per 100 parts (by weight) of monomer charged.

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 The Applicant has found an improved process for the preparation of sulfur-modified polychloroprene according to which it is possible to obtain a sulfur-modified polychloroprene with improved roasting resistance without altering the optimum time of vulcanization.

 The process according to the invention is carried out by copolymerization of chloroprene with sulfur, the chloroprene being able to be replaced up to 20% by weight by other copolymerizable vinyl monomers, in aqueous alkaline emulsion and in the presence of radical initiators and is characterized in that one or more organic polysulfides chosen from: 1) disulphides of di or tetraisobutylthiuram optionally additivated with (2) di or tetraalkylthiuram disulfides in which the alkyl group is different from isobutyl and contains from 3 to 5 carbon atoms.

 In a preferred embodiment, the total charge of disulfides (1) and (2) is between 2.5 and 5.5 millimoles, preferably between 3.0 and 4.5 millimoles, per 100 parts by weight of monomer. charge.

The corresponding rate of decomposition products is between 0 and 2 millimoles phm.

 In one embodiment, from 20% to 40% of the molar loading of the disulfides (1) + (2) is carried out at the beginning of the reaction, the complement is introduced postpolymerization.

 With the term "di- and tetraalkylthiuram" is meant not only the above-mentioned compounds, but also their relative decomposition products, such as alkali metal dialkyldithiocarbamates. It is the same for polysulfide di- or tetraisobutylthiuram.

 If it is known that the isobutyl group in certain vulcanization accelerator such as monosulfide tetraisobutylthiuram (Rubber Chemistry and technology,

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 10/97 page 634-670, vol. 70) improves the safety during vulcanization, the Applicant is surprised to find that substituting a di- or tetraalkylthiuram disulfide and more specifically tetrabutylthiuram disulphide with a di- or tetraisoalkylthiuram disulphide and more particularly with the disulphide of diisobutylthiuram, leads to the production of polymers whose resistance to roasting is considerably improved without altering the optimum time of vulcanization; diisobutylthiuram disulfide may or may not be associated with a di- or tetraalkylthiuram disulfide in which the alkyl group contains from 3 to 5 carbon atoms.

 In general, the use of agents improving the safety of the roasting of polymers leads to increase the optimum time of vulcanization which leads to reducing the productivity of the workshops and increasing the cost of the process.

 According to the invention, it is surprisingly found that the optimum vulcanization times are not affected and that the mechanical and dynamic properties of the polymers thus produced are of excellent level, whereas the safety in the implementation of the polymers is significantly improved.

 The polymerization process according to the invention is carried out in a known manner in aqueous alkaline emulsion in the presence of free radical generators, such as hydrogen peroxide, organic peroxides, cumyl peroxide, dibenzoyl peroxide, alkali metal ferricyanides or dibenzoyl peroxide. ammonium, and preferably the persulfates of alkali metals or ammonium.

 As emulsifiers, it is possible to use any compound or mixture of usual compounds such as the water-soluble salts of acids derived from crude, disproportionated, hydrogenated or partially polymerized rosin,

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 deriving from gem, wood and tall oil. The emulsion generally contains a certain amount of dispersing and stabilizing agents such as sulphates of fatty alcohols, alkyl sulphates and sulphonates, the alkaline salts of alkyl aryl sulphonic acids and more particularly the alkaline salts of methylene bis-naphthalene acid. sulfonic acid. Small amounts of a conventional chain transfer agent can also be added.

 Chloroprene can be replaced up to 20% of its weight by another copolymerizable monomer. Among the monomers copolymerizable with chloroprene, mention may be made of vinylaromatic compounds, such as styrene, vinyltoluenes and vinylnaphthalenes, acrylic acids, methacrylic acids and their ester and nitrile derivatives, such as ethyl acrylate, butadiene and isoprene, 2,3-dichloro-1,3-butadiene and 2,3-dimethyl-1,3-butadiene, vinyl ethers and ketones such as methyl vinyl ether, vinyl acetate and methyl vinyl ketone.

 The concentration of the monomer (s) in the emulsion is generally between 30 and 60% by weight relative to the total weight of the emulsion.

 The sulfur content can range from 0.1 to 0.6% by weight relative to chloroprene or the monomer mixture.

 The polysulfides that can be used according to the invention are introduced into the reaction medium on the one hand at the same time as the other reactants before starting the polymerization and on the other hand in postpolymerization.

 It takes for 100% of millimoles of peptizer charged in total, put at least 60% of millimoles of tetraisobutylthiuram disulphide. The balance consists of di- or tetraalkylthiuram disulfide in which the alkyl group has from 3 to 5 carbon atoms (excluding the isobutyl group).

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 In general, relative to the total amount of peptizer charged, 20% to 40% of the molar charge is made at the beginning of the reaction, the complement is introduced postpolymerization.

 The polymerization temperature may vary from 10 ° C. to 80 ° C., but it is preferably between 40 ° C. and 60 ° C.

 The pH of the emulsion during the polymerization is greater than 10, and preferably between 11 and 13.

 The final conversion level is not constrained and may vary from 50% to 90%, and preferably from 70% to 80%.

 The polymerization can be stopped at any time by addition of a conventional polymerization inhibiting agent. The residual monomer is removed by flash distillation and the rubber is isolated from the latex by any known means.

 The chloroprene polymers obtained have a Mooney viscosity of between 20 and 100, preferably between 35 and 70. This value is stable and does not change during the storage of the latex and the treatment of the rubber. The desired value can be set by those skilled in the art by means of some preliminary tests depending on the amount of sulfur, the nature and level of peptizing agent as well as the polymerization conditions.

 The polychloroprenes can be vulcanized with the vulcanization systems usually used for sulfur-modified polychloroprenes, without the addition of accelerators derived from thiourea, and in the same way as the polychloroprenes conventionally peptized with thiurams. The vulcanized products have excellent properties.

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 The invention is illustrated by the following examples in which parts are by weight.

EXAMPLE 1
A sulfur-modified polychloroprene latex is prepared using an aqueous emulsion system of the following composition:
Chloroprene 100
Resin acids (disproportionated rosin) 4.0
Sulfur 0.3
Tetraisobutylthiuram disulfide 0.2
Sodium dibutyldithiocarbamate 0.2
Water 100
Sodium hydroxide (100%) 0.79
Sodium salt of methylene bis alkylnaphthalene sulfonic acid (100%) 0.80
Catalyst solution
Sodium persulfate 1
Water 99
The polymerization is carried out at 50 ° C. under a nitrogen atmosphere at a pH of 12.9 and the catalyst solution is added continuously so as to obtain a regular polymerization rate (the total amount introduced is about 3 parts by weight). ).

 After 4.5 hours, the monomer conversion is 70%. The polymerization was stopped by addition of 0.01 part of p-tert-butylcatechol and 0.01 part of phenothiazone as an emulsion. 1.3 parts of tetraisobutylthiuram disulphide are then added in the form of a solution in chloroprene. The latex is then treated with steam to remove the residual monomer and then cooled.

 After isolation of the polymer by coagulation on a cold drum, the measurement of the Mooney viscosity (ML1 + 4 at 100 ° C.) gives the value of 41 points.

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 The main safety features in the implementation of the elastomer and rheometric are given in Tables 1 and 2.

COMPARATIVE EXAMPLES
Chloroprene / sulfur copolymers are produced under the same conditions as in Example 1, only the amounts and the nature of the peptizing agents (and associated decomposition products) vary.

 The safety features of implementation and rheometric are given in Tables 1 and 2.

EXAMPLES 2-5
Chloroprene / sulfur copolymers are produced under the same conditions as in Example 1, only the amounts and the nature of the peptizing agents (and associated decomposition products) vary.

 The safety features of implementation and rheometric are given in Tables 1 and 2.

 In Tables 1a and 1b, the amounts of peptizer are expressed in mmol.

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TABLE 1A

<tb> Pept. <SEP> in <SEP> polym. <SEP> Ex.1 <SEP> Ex.2 <SEP> Ex <SEP> 3 <SEP> Ex.4 <SEP> Ex.5 <SEP> Ex.6 <SEP> Ex.7 <SEP> Ex.8 <SEP> C.1 <SEP> C.2 <SEP> C.3 <SEP> C.4 <SEP> C. <SEP> 5
<tb> TBTDS <SEP> 0.735 <SEP> 0.735
<tb> TiBTDS <SEP> 0.49 <SEP> 0.71 <SEP> 0.61 <SEP> 0.69 <SEP> 0.54 <SEP> 0.49 <SEP> 0.49 <SEP> 2 , 24 <SEP> 0.735 <SEP> 0.73 <SEP> 0.61
<tb> DBDNa <SEP> 0.88 <SEP> 0.44 <SEP> 0.88 <SEP> 0.88 <SEP> 1.76 <SEP> 0.88 <SEP> 0.88 <SEP> 0 , 88 <SEP> 0.88
<tb> DiBDNa <SEP> 0.88 <SEP> 0.44 <SEP> 0.88 <SEP> 0.88
<tb> Pept. <SEP> in <SEP> postpol.
<Tb>

TETDS <SEP> 0.07 <SEP> 4 <SEP> 4
<tb> TBTDS <SEP> 0.12 <SEP> 3.2
<tb> TiBTDS <SEP> 3.2 <SEP> 2.7 <SEP> 3.1 <SEP> 3.3 <SEP> 3.9 <SEP> 3.2 <SEP> 3.2 <SEP> 3 , 2 <SEP> 0.12 <SEP> 6.1
<Tb>

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TABLE 1B

<tb> Ex.l <SEP> Ex.2 <SEP> Ex <SEP> 3 <SEP> Ex.4 <SEP> Ex.5 <SEP> Ex.6 <SEP> Ex.7 <SEP> Ex.8 <SEP> C.1 <SEP> C.2 <SEP> C.3 <SEP> C. <SEP> 4 <SEP> C. <SEP> 5
<tb> Sum <SEP> TiBTDS <SEP> 3.69 <SEP> 3.41 <SEP> 3.71 <SEP> 3.99 <SEP> 4.44 <SE> 3.69 <SE> 3.69 <SEP> 5.44 <SEP> 0 <SEP> 0 <SEP> 0.735 <SEP> 0.85 <SEP> 6.71
<tb> Sum <SEP> peptizer <SEP> 1,4 <SEP> 1,6 <SEP> 1,5 <SEP> 1,6 <SEP> 1,4 <SEP> 2,3 <SEP> 1,4 <SEP> 2.2 <SEP> 1.6 <SEP> 1.6 <SEP> 1.6 <SEP> 1.6 <SEP> 1.5
<tb> in <SEP> poly.
<Tb>

Sum <SEP> Overall <SEP> 4.57 <SEP> 4.36 <SEP> 4.59 <SEP> 4.99 <SEP> 5.32 <SEP> 5.45 <SEP> 4.57 <SEP> 5.44 <SEP> 5.615 <SEP> 4.815 <SEP> 5.615 <SEP> 1.73 <SEP> 7.59
<tb> peptisant
<tb>% <SEP> TiBTDS <SEP> loaded <SEP> 80.7 <SEP> 78.2 <SEP> 80.8 <SEP> 80 <SEP> 83.5 <SEP> 67.7 <SE> 80 , 7 <SEP> 100 <SEP> 0 <SEP> 0 <SEP> 13.1 <SEP> 49.1 <SE> 88.4
<tb>% <SEP> peptizer <SEP> in <SEP> 30 <SEP> 36.5 <SEP> 32.5 <SEP> 31.5 <SEP> 26.7 <SEP> 41.3 <SEP> 30 <SEP> 41.2 <SEP> 28.8 <SEP> 33.5 <SE> 28.8 <SE> 93.1 <SE> 19.6
<tb> poly ..
<Tb>

Sum <SEP> DBDNa <SEP> or <SEP> 0.88 <SEP> 0.88 <SEP> 0.88 <SEP> 0.88 <SEP> 0.88 <SEP> 1.76 <SEP> 0, 88 <SEP> 0 <SEP> 0.88 <SEP> 0.88 <SEP> 0.88 <SEP> 0.88 <SEP> 0.88
<tb> DiBDNa
<Tb>

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 Legend: TBTDS tetrabutylthiuram disulfide TiBTDS tetraisobutylthiuram disulfide DBDNa sodium dibutyldithiocarbamate DiBDNa sodium diisobutyldithiocarbamate TETDS tetraethylthiuram disulfide Polymer (100 phr), MgO (4 phr), stearic acid (0.5 phr), SRF black (30 phr), aromatic oil (5 phr), zinc oxide (5 phr).

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TABLE 2

<tb> Ex.l <SEP> Ex.2 <SEP> Ex <SEP> 3 <SEP> Ex. <SEP> 4 <SEP> Ex. <SEP> Ex. <SEP> 6 <SEP> Ex.7 <MS> Ex. <SEP> 8 <SEP> C.1 <SEP> C. <SEP> 2 <SEP> C.3 <SEP> C. <SEP> 4 <SEP> C.5
<tb> Screening <SEP> T10 <SEP> 110 <SEP> 101 <SEP> 86 <SEP> 93 <SEP> 96 <SEP> 99 <SEP> 118 <SEP> 109 <SEP> 65 <SEP> 76 <SEP > 61 <SEP> 70 <SEP> 95
<tb> Rheometer <SEP> TS2 <SEP> 6, <SEP> 1 <SEP> 6 <SEP> 6 <SEP> 5.9 <SEP> 6 <SEP> 5.8 <SEP> 6.1 <SEP> 6.7 <SEP> 4.5 <SEP> 4.7 <SEP> 4 <SEP> 4.3 <SEP> 5.8
<tb> T90 <SEP> 11.8 <SEP> 11.2 <SEP> 11 <SEP> 11 <SEP> 10.9 <SEP> 11.5 <SEP> 12.8 <SE> 12.9 <SEP > 11.5 <SEP> 12.9 <SEP> 11.7 <SEP> 11 <SEP> 16.5
<Tb>

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Experimental values show that the optimum amount of TiBTDS is between 2.5 and 5.5 millimoles phm. The use of 0.735 millimole phm (comparative example 3) or 0.85 millimole phm (comparative example 4) does not lead to a significant improvement in the resistance to roasting since it is found that values identical to those obtained with 0 millimole phm of TiBTDS (Comparative Example 1).

 A larger amount of TiBTDS as described in Comparative Example 5 (6.72 millimoles phm) results in longer times for T90 vulcanization times that are too long.

Claims (5)

Process for the preparation of sulfur-modified polychloroprene, the chloroprene which can be replaced up to 20% by weight by other copolymerizable vinyl monomers, in aqueous alkaline emulsion and in the presence of radical initiators, characterized in that one or more organic polysulfides selected from: 1) disulphides of di or tetraisobutylthiuram optionally additivated with (2) di or tetraalkylthiuram disulphides in which the alkyl group is different from isobutyl and containing from 3 to 5 atoms is added to the reaction mixture; of carbon.  2. Method according to claim 1, characterized in that the total sum of disulfides (1) and (2) is between 2.5 and 5.5 millimoles per 100 parts by weight of charged monomers.  3. Method according to claim 2, characterized in that the total sum of the disulfides (1) and (2) is between 3.0 and 4.5 millimoles per 100 parts by weight of charged monomers.  4. Method according to claim 1, characterized in that from 20% to 40% of the molar loading of the disulfides (1) + (2) is carried out at the beginning of the reaction, the complement is introduced postpolymerization.  5. Method according to claim 1, characterized in that, for 100% moles of (1) + (2), at least 60% is tetraisobutylthiuram disulphide