Vulcanizable compositions for forming nitrosamine-free sulfur-modified polychloroprene vulcanizates

Abstract

The present invention relates to vulcanizable compositions for forming nitrosamine-free sulfur-modified polychloroprene vulcanizates and methods for making the same.

Description

[Technical Field]

[0001] The present invention relates to nitrosamine-free sulfur-modified polychloroprene. In particular, the present invention relates to a vulcanizable composition for forming the nitrosamine-free sulfur-modified polychloroprene. Furthermore, the present invention relates to a method for producing the nitrosamine-free sulfur-modified polychloroprene vulcanizate. Finally, the present invention relates to the vulcanizate obtained thereby. [Background technology]

[0002] Sulfur-modified polychloroprene rubbers are used in a wide range of applications because they exhibit excellent dynamic properties.

[0003] Patent Document 1 discloses that sulfur-modified polychloroprene rubber can be peptized in latex using tetraalkylthiuram disulfide (TATD). However, TATD generates volatile n-nitrosamines, which are genotoxic and carcinogenic. TATD sulfur-modified polychloroprene rubber is produced with a relatively high molecular weight, which can then be masticated during compounding due to the combination of copolymerized sulfur and TATD. The reduction in Mooney viscosity during mixing provides excellent dispersion and promotes easy processability of the final product. TATD sulfur-modified polychloroprene rubber has been used for many years, and many vulcanizable mixtures have been developed to optimize the crosslinking rate of TATD sulfur-modified polychloroprene rubber to the requirements of the processing equipment used.

[0004] Nitrosamine-free sulfur-modified polychloroprenes are generally known in the art.

[0005] Patent Document 2 discloses that chloroprene / sulfur copolymers were peptized in alkaline dispersions with xanthogen sulfide, either alone or in combination with mercaptobenzothiazole, in the absence of nitrosamine-forming additives (e.g., octamine). Metal oxides are the usual curing agents. According to the method of Patent Document 2, copolymers of chloroprene and sulfur modified with diisopropylxanthogen disulfide (DIXD) are obtained. These chloroprene / sulfur copolymers have undesirably high Mooney viscosities. Furthermore, crosslinking of the resulting chloroprene / sulfur copolymers is slow and therefore inefficient.

[0006] Patent Document 3 discloses the peptization of chloroprene / sulfur copolymers polymerized in the presence of a modifier such as dialkylxanthogen disulfide by adding to an alkaline latex of such copolymer a modifier that is a thiol of the formula R-SH, where R includes, in particular, an arylthiazole to obtain mercaptobenzothiazole as a modifier. Residual mercaptan amounts in the final polymer (nDDM is classified as a dangerous substance) and should be avoided.

[0007] Patent Document 4 discloses a halogen-containing rubber composition in which a thiourea-based vulcanization accelerator is replaced with a special additive. This halogen-containing rubber composition is obtained by mixing a halogen-containing rubber with substituted or unsubstituted thiazolidinethione-2, an imidazole group, and, if necessary, a compound containing a diazabicyclo group. In particular, Patent Document 4 discloses chloroprene rubber that can be sulfur-modified, mercaptan-modified, or xanthogen-modified depending on the type of molecular weight modifier. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US Patent No. 9,475,895 B2 [Patent Document 2] U.S. Patent No. 5,483,006 [Patent Document 3] U.S. Patent No. 3,984,609 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-060550 Summary of the Invention [Problem to be solved by the invention]

[0009] Due to the adverse effects of nitrosamines on human health, there is a continuing need for further development of vulcanizable compositions for nitrosamine-free sulfur-modified polychloroprene that should overcome the problems of the prior art. There is a need for vulcanizable compositions for nitrosamine-free sulfur-modified polychloroprene that have improved crosslinking rates, compatibility with processing equipment, and exhibit good processability with respect to viscosity, while maintaining at least equivalent mechanical and / or physical properties in the vulcanizable composition and / or as the final composition as a vulcanizate.

[0010] The above problems are addressed by the present invention. [Means for solving the problem]

[0011] In a first aspect, the present invention relates to a vulcanizable composition for forming a nitrosamine-free sulfur-modified polychloroprene vulcanizate, the vulcanizable composition comprising at least: a sulfur-modified polychloroprene copolymer polymerized from at least chloroprene, elemental sulfur, and xanthogen disulfide; at least one non-nucleophilic base, which is a bicyclic or polycyclic amine base containing two or more linked rings; Includes:

[0012] In a further aspect, the present invention relates to a method for making a nitrosamine-free sulfur-modified polychloroprene vulcanizate. a) polymerizing chloroprene in the presence of elemental sulfur and xanthogen disulfide to form sulfur-modified polychloroprene; b) vulcanizing the sulfur-modified polychloroprene formed in step a) in the presence of at least one non-nucleophilic base to form a nitrosamine-free sulfur-modified polychloroprene vulcanizate, wherein the non-nucleophilic base is a bicyclic or polycyclic amine base containing two or more linked rings; A method comprising: DETAILED DESCRIPTION OF THE INVENTION

[0013] For a thorough understanding of the present invention and its advantages, reference is made to the following detailed description.

[0014] It should be recognized that the various aspects and embodiments of the detailed description disclosed herein are descriptions of particular ways to make and use the invention, and do not limit the scope of the invention when considered in light of the claims and detailed description. It will also be recognized that features from different aspects and embodiments of the invention can be combined with features from different aspects and embodiments of the invention.

[0015] In a first aspect, the present invention relates to a vulcanizable composition for forming a nitrosamine-free sulfur-modified polychloroprene vulcanizate. a sulfur-modified polychloroprene copolymer polymerized from at least chloroprene, elemental sulfur, and xanthogen disulfide; at least one non-nucleophilic base, which is a bicyclic or polycyclic amine base containing two or more linked rings; 1. A vulcanizable composition comprising:

[0016] Polychloroprene (chloroprene rubber or CR) is a polymer of at least chloroprene (2-chloro-1,3-butadiene). Polychloroprene can be produced by emulsion polymerization of chloroprene, for example, as described in P.R. Johnson, Rubber Chemistry and Technology (1976), Vol. 49, Issue 3, pages 650-702, the teachings of which are incorporated herein by reference.

[0017] Polychloroprene is known for its mechanical and dynamic properties, resistance to aging and solvents, and its excellent flame retardancy. Sulfur-modified polychloroprene is also known in the art and offers additional benefits such as rebound resilience, excellent tear strength, and flex fatigue resistance.

[0018] The vulcanizable composition includes a sulfur-modified polychloroprene copolymer formed by polymerization of chloroprene and elemental sulfur via so-called free radical emulsion polymerization, followed by further bond cleavage via peptization using a chain transfer agent such as xanthogen disulfide. The chain transfer agent is added directly to the emulsion to control molecular weight and simultaneously act as a peptizer during and / or after emulsion polymerization and / or aging of the latex and formed solids.

[0019] The xanthogen disulfide may include a nonionic ether compound. The xanthogen disulfide may be a dialkyl xanthogen disulfide, such as diisopropyl xanthogen disulfide (DIXD). The sulfur-modified chloroprene copolymer is polymerized in the presence of xanthogen disulfide, which is present in an amount of ≦0.4 phm, particularly ≧0 phm, at the start of the polymerization reaction. This embodiment may allow for further reduction in Mooney viscosity, thereby further improving processability. In particular, when the xanthogen disulfide is present in the aforementioned specified amount of ≦0.4 phm at the start of the polymerization, a significant improvement in Mooney viscosity may be observed. However, since the viscosity remains high, good filler dispersion, processability, and mechanical properties can still be obtained. Since additional xanthogen disulfide is added at the end of the reaction, the xanthogen disulfide is present in an amount of <1 phm.

[0020] The at least one non-nucleophilic base is a bicyclic or polycyclic amine base containing two or more connected rings, and therefore a sterically hindered organic base that is a poor nucleophile. The at least one non-nucleophilic base can be present in an amount of ≥ 0.05 phr to ≤ 5 phr, preferably ≥ 1.5 phr to ≤ 2 phr. The minimum amount is necessary to reduce Mooney viscosity and adjust crosslink density and rate; a maximum amount is not suitable because it results in premature scorch. Optimal results are observed at an amount of ≥ 1.5 phr to ≤ 2 phr, which advantageously reduces Mooney viscosity, compression set, and crosslink rate, and increases crosslink density in the vulcanizate.

[0021] At least one non-nucleophilic base is a bicyclic or polycyclic amine base, containing two (bicyclic) or more than two (polycyclic) linked rings (cyclic), for example, three, four, or even more than four linked rings. These rings are preferably formed primarily of carbon. However, the rings can contain at least one heteroatom. At least one heteroatom can be nitrogen. The bicyclic or polycyclic ring structure or substructure of each ring can include, for example, cycloalkanes, aromatics, and other types of rings. The rings are provided in combination with sizes of three or more atoms and bonds that form fusions and thus connect with edge-to-edge bonds. Furthermore, polycyclics can be bicyclic, tricyclic, or tetracyclic, i.e., contain more than one ring. Preferably, the bicyclic or polycyclic amine base comprises a diazabicyclic compound, which is formed as a bicyclic fused structure, with two nitrogen atoms included in the ring structure. Regarding the cyclic structure, particularly the partial cyclic structure, and thus each structure of the polycyclic ring, it is preferred that each partial cyclic structure is composed of 5 to 8 members, for example 6 to 7 members. Therefore, in the case of a diazacyclic structure, it may be preferred that each partial cyclic structure contains two nitrogen atoms as heteroatoms and the respective amounts of carbon atoms necessary to achieve the aforementioned specified amount or number of members of the cyclic structure. Regarding nitrogen atoms, it may be preferred that one or more nitrogen atoms are part of only one cyclic structure, or two or more cyclic structures. When the at least one non-nucleophilic base is an amide, it is preferably selected from lithium diisopropylamide. The at least one non-nucleophilic base is preferably di-tert-butylpyridine. The at least one non-nucleophilic base is preferably N,N-diisopropylethylamine. The at least one non-nucleophilic base is preferably selected from at least one of (1,4-diazabicyclo[2.2.2]octane) (DABCO), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN).

[0022] The vulcanizable composition can further include at least one crosslinking agent, which can be a metal oxide selected from the group consisting of zinc oxide, magnesium oxide, lead oxide, trimelead tetroxide, iron trioxide, titanium dioxide, calcium oxide, and hydrotalcite, or any combination thereof.

[0023] The vulcanizable composition may also include at least one additive or any combination thereof known to those skilled in the art. The at least one additive may be a heat aging stabilizer, a processing aid, a plasticizer, and a filler. The filler may be an inorganic filler, carbon black ranging from N110 to N990, carbon nanotubes, graphite, and aramid fiber. The at least one additive may be used in an amount of 0.5 phr to 200 phr.

[0024] The vulcanizable composition exhibits a reduced Mooney viscosity after mixing. This reduced Mooney viscosity can result in improved processability. Therefore, the significant advantages of the vulcanizable composition for forming nitrosamine-free sulfur-modified polychloroprene vulcanizates according to the present invention, and the vulcanizates obtained therefrom, facilitate their use in desired applications such as textile coating, calendaring, belting, anti-vibration shock absorbers, isolation, and foam products such as diving suits.

[0025] Apart from the reduction in Mooney viscosity, it was found that the resulting vulcanizates had at least equivalent mechanical properties desirable in the art, such as tensile strength, elongation at break, and compression set. Thus, the improved processability resulting from the reduction in Mooney viscosity is realized along with still advantageous mechanical properties.

[0026] Furthermore, controllable crosslink density can be advantageous in some applications (e.g., hoses, springs, etc., which require high crosslinking and low compression set) and can increase the cure rate, which is a further effective means of improving the properties of the resulting vulcanizates.

[0027] It has surprisingly been found that the present invention provides the above advantages.

[0028] The sulfur-modified polychloroprene copolymer vulcanizate can be formed in the presence of at least one accelerator. Thus, the vulcanizable composition can include at least one accelerator. The use of at least one accelerator can further reduce the Mooney viscosity and adjust the crosslink density and speed when forming the vulcanizate.

[0029] The at least one accelerator may be at least one of a thiazole compound, a carbamate compound, and a thiuram compound, or any combination thereof.

[0030] The thiazole compound may be a thiazole-based compound, such as MBT (2-mercaptobenzothiazole), MBTS (dibenzothiazyl disulfide), sodium, zinc, or copper salts of 2-mercaptobenzothiazole, cyclohexylamine salt, 2-(2,4-dinitrophenyl)mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinothio)benzothiazole. The thiazole compound is preferably mercaptobenzothiazole (MBTS).

[0031] Carbamate compounds include dithiocarbamates such as zinc dimethyldithiocarbamate (ZDMC), zinc diethyldithiocarbamate (ZDEC), zinc dibutyldithiocarbamate (ZDBC), zinc ethylphenyldithiocarbamate (ZEPC), zinc dibenzyldithiocarbamate (ZDBC), zinc pentamethylenedithiocarbamate (ZPD), zinc-N-pentamethylenedithiocarbamate (Z5MC), zinc dialkyldithiophosphate (ZDT), zinc-2-ethylhexanoate (ZEH), dinonyldithiocarbamate (ZDMC ... The dithiocarbamate may be zinc dithiocarbamate (ZNDNC), bismuth dimethyldithiocarbamate (BIDD), nickel dibutyldithiocarbamate (NDBC), selenium diethyldithiocarbamate (SeEDC), selenium dimethyldithiocarbamate (SeDMC), sodium diethyldithiocarbamate (SEDC), tellurium diethyldithiocarbamate (TeEDC), tellurium diethyldithiocarbamate (TeDEC), sodium dimethyldithiocarbamate (SMDC), and sodium dibutyldithiocarbamate (SBC).

[0032] The thiuram compound may be a thiuram disulfide, or a thiuram polysulfide may be used. The thiuram disulfide is preferably tetrabenzylthiuram disulfide (TBzTD). Thiuram polysulfides: dipentamethylenethiuram hexasulfide (DPTH), dipentamethylenethiuram monosulfide (DPTM), dipentamethylenethiuram disulphide (DPTD), N,N'-diethyl-N,N'-diphenylthiuram disulphide (EPTDM), and dimethyldiphenylthiuram disulphide (MPTD).

[0033] Preferably, the at least one accelerator is a combination of the thiazole compound mercaptobenzothoazole (MBTS) and the thiuram compound tetrabenzylthiuram disulphide (TBzTD).

[0034] The sulfur-modified polychloroprene copolymer may further include 2,3-dichloro-1,3-butadiene (DCB) monomer units. The amount of 2,3-dichloro-1,3-butadiene (DCB) is in the range of more than 0 to 10% by weight of the sulfur-modified polychloroprene copolymer. According to this embodiment, the 2,3-dichloro-1,3-butadiene (DCB) reduces the rate and degree of crystallization of the resulting copolymer, thereby allowing for a low-crystallinity grade for use at low temperatures.

[0035] Preferably, the sulfur-modified polychloroprene copolymer is formed in the presence of elemental sulfur in an amount of ≥ 0.2 phm at the beginning of the polymerization reaction. In other words, when forming the copolymer, and thus polymerizing the monomer units, elemental sulfur is added before or at the beginning of the polymerization reaction, for example, before the polymerization reaction begins. This embodiment can therefore exhibit the respective amount of sulfur-containing bonds in the final product. This embodiment can achieve a particularly effective reduction in Mooney viscosity. Furthermore, the mechanical properties of the copolymer are improved compared to embodiments in which sulfur is present in an amount of 0.2 phm or less. In particular, it has been found that tensile strength is improved when sulfur is present in the aforementioned specified amount at the beginning of polymerization.

[0036] With regard to sulfur supply, it is further preferred that the sulfur-modified chloroprene copolymer be prepared in the presence of elemental sulfur in an amount of ≦1 phm at the beginning of the polymerization reaction. Again, in other words, when forming the copolymer, and thus polymerizing the monomer units, elemental sulfur is added at or before the beginning of the polymerization reaction, e.g., before the beginning of the polymerization reaction. This embodiment can improve the reduction in Mooney viscosity due to peptization or milling (processability). However, the viscosity is still sufficiently high, so that good dispersion, processability, and mechanical properties are still obtained. Furthermore, this embodiment improves aging properties.

[0037] In a further aspect, the present invention relates to a method for making a nitrosamine-free sulfur-modified polychloroprene vulcanizate. a) polymerizing chloroprene in the presence of elemental sulfur and xanthogen disulfide to form a sulfur-modified polychloroprene; b) vulcanizing the sulfur-modified polychloroprene formed in step a) in the presence of at least one non-nucleophilic base to form a nitrosamine-free sulfur-modified polychloroprene vulcanizate, wherein the non-nucleophilic base is a bicyclic or polycyclic amine base containing two or more linked rings; A method comprising:

[0038] The above method can result in a composition that exhibits a reduced Mooney viscosity during step b), thereby improving the processability of the composition. Thus, the significant advantages of the nitrosamine-free sulfur-modified polychloroprene according to the present invention can be applied to multiple applications.

[0039] Apart from the reduction in Mooney viscosity, the nitrosamine-free sulfur-modified polychloroprene vulcanizates formed by the above method have been found to have at least equivalent mechanical properties such as tensile strength, elongation at break and compression set. Thus, the improved processability resulting from the reduction in Mooney viscosity is realized along with still desirable mechanical properties.

[0040] Apart from this, it has further been found that the crosslink density and cure rate can be adjusted by the described method, which provides a more effective means for improving the properties of the vulcanizable product.

[0041] It may further be preferred that the sulfur-modified polychloroprene copolymer is formed in the presence of at least one accelerator selected from at least one of a thiazole compound, a carbamate compound, and a thiuram compound, as described above, or any combination thereof.

[0042] More preferably, sulfur is present in an amount of ≥ 0.2 phm, particularly < 1 phm, at the start of the polymerization reaction. In particular, the respective amount of sulfur is added to the polymerization mixture before the polymerization reaction begins. According to this embodiment, mixing with a non-nucleophilic base can particularly effectively reduce the Mooney viscosity, thereby providing particularly favorable processability. Apart from this, the mechanical properties of the copolymer are improved compared to an embodiment in which sulfur is present in a lower amount, such as an amount of 0.2 phm or less. In particular, improved tensile strength may be observed when sulfur is present in the aforementioned specified amount at the start of polymerization.

[0043] In a further embodiment, step a) is carried out in the presence of dichloro-2,3-butadiene (DCB) as an additional monomer unit. This allows the sulfur-modified chloroprene copolymer to be a copolymer containing dichloro-2,3-butadiene (DCB) monomer units. For example, the copolymer present in the vulcanizable composition may be a terpolymer consisting of the aforementioned named monomer units, i.e., sulfur, chloroprene, and dichloro-2,3-butadiene.

[0044] Furthermore, the xanthogen disulfide can be present preferably in an amount of ≦0.4 phm at the start of the polymerization reaction. For example, the xanthogen disulfide can be added to the polymerization mixture before the start of the polymerization reaction. In this embodiment, the Mooney viscosity can be reduced, thereby providing particularly good processability.

[0045] The at least one non-nucleophilic base may be as described above.

[0046] The at least one non-nucleophilic base may be present in an amount of ≧0.05 phr to ≦5 phr, preferably in an amount of ≧1.5 phr to ≦2 phr, before the vulcanization reaction.

[0047] To allow for the formation of nitrosamine-free polychloroprene rubber, the process is carried out without the use of nitrosamine-forming compounds, i.e., conventional accelerators.

[0048] With regard to further advantages and features of the method for forming nitrosamine-free sulfur-modified polychloroprene, it is referred to in the vulcanizable compositions, vulcanizates, and examples.

[0049] The vulcanizates formed from the vulcanizable compositions or by the methods described above will now be further described.

[0050] For example, the vulcanizates of the present invention have improved processability, making them useful for a wide range of applications. This is particularly evident in the high viscosity at the beginning of mixing, which allows for effective filler dispersion, and the low viscosity at the end, which allows for easy calendaring, textile coating, and other applications. Furthermore, cure characteristics are improved over standard chloroprene / sulfur copolymers. For example, when cured with conventional metal oxide curatives, peptized copolymers without nitrosamine precursors exhibit slower cures. Furthermore, the final copolymers do not achieve the same cure state. Scorch is undesirable because it initially leads to undesirably rapid vulcanization, which narrows the processing window and clogs processing equipment, resulting in inefficient processability.

[0051] The invention is illustrated by the following non-limiting examples. [Example]

[0052] "phr" means parts per hundred parts by weight of rubber in the case of vulcanizates. The total of all elastomer components, including chloroprene rubber, equals 100 phr.

[0053] "phm" means parts per hundred of monomer. When used in a polymerization recipe, the amount of monomer (i.e., chloroprene and optional comonomer) is equivalent to 100 phm.

[0054] The crosslink density (MDR) was determined using a moving die rheometer (MDR 2000E) at 170°C for 40 minutes using an angle of 0.5° and an oscillation frequency of 1.7 Hz.

[0055] For tensile strength (TS), 2 mm sheets were prepared by vulcanizing the vulcanizable mixture at 170°C. Dumbbell-shaped test specimens were punched out from these sheets. Tensile strength and elongation at break (EB) were determined according to ASTM D2240-81.

[0056] Hardness was determined using a durometer according to ASTM D2240-81.

[0057] Compression set (CS) was determined according to DIN ISO 850 Part A.

[0058] Goodrich test (MTS) DIN 53533 T3-88 Goodrich; 400Hz-Elastomer-Pruefsystem 831.20; manufactured by MTS Systems GmbH.

[0059] The Mooney viscosity was determined according to DIN ISO 289-1 at ML1+4 / 100°C.

[0060] [Table 1]

[0061] CR-1: 1668 g of deionized water was added to a mixture of 98.06 g of rosin acid potassium salt (55%) (Sylvaros RS 200) in water, 32.55 g of Baykanol PQ (naphthalenesulfonic acid, polymer with formaldehyde, sodium salt, CAS 9084-06-4 in water (30%)), and 3.78 g of Marlon A350 (benzenesulfonic acid, C10-13-alkyl derivative, sodium salt, CAS 68411-30-3 in water (60%)) and stirred. Subsequently, 10.41 g of KOH prill (87% purity) was added under continuous stirring to form the so-called aqueous phase. When the solution was clear, 0.9 g of anthraquinone disulfonic acid sodium salt was added, and the mixture was deoxygenated with nitrogen for at least 8 hours.

[0062] 2.25 g of diisopropyl xanthogen disulfide (DIXD) was dissolved in 1500 g of chloroprene. This solution was introduced into a 6-liter double-jacketed nitrogen-flushed reactor together with the aqueous phase. The reactor contents were mixed under stirring to 44 °C. As soon as the reactor temperature stabilized, 11.56 g of a sulfur dispersion in water (52% sulfur content) was added along with 120 g of water. Polymerization was immediately initiated by adding an initiator (3 wt. % potassium persulfate in water). The addition flow rates were selected to achieve 75% monomer conversion within approximately 3 hours of reaction time. Once 75% monomer conversion was achieved, the addition of the potassium persulfate solution was stopped, and 1.1 g of hydroquinone in 20 ml of deionized water was added to the reactor. The reactor temperature was then lowered to 20 °C. Next, an emulsion of 8.25 g of DIXD in 74.5 g of chloroprene in 82.5 g of aqueous phase was added to the reactor. Unreacted monomer was removed by steam distillation in a cyclone under reduced pressure (150 mbar).

[0063] The monomer-free latex was neutralized with 0.1 M HCl in water to pH=7.5, frozen at −20° C., and lyophilized to obtain solid polychloroprene.

[0064] CR-2: Same as CR 1, except that the amount of sulfur dispersion added before the start of polymerization was 8.67 g, and the DIXD / chloroprene / water emulsion added after the end of polymerization contained an additional 2.81 g of sulfur dispersion.

[0065] CR-3: Same as CR 1, except that the amount of sulfur dispersion added before the start of polymerization was 5.78 g, and the DIXD / chloroprene / water emulsion added after the end of polymerization contained an additional 5.76 g of sulfur dispersion.

[0066] CR-4: Same as CR 1 except that the amount of DIXD in chloroprene at the start of the reaction was 1.50 g.

[0067] CR-5: Same as CR 1 except that the amount of sulfur dispersion added before the start of polymerization was 28.85 g.

[0068] CR-6: Same as CR-1 except the monomer mixture consisted of 1455 g of chloroprene and 45 g of dichloro-2,3-butadiene.

[0069] CR-7: Same as CR-1 except the monomer mixture consisted of 1395 g chloroprene and 105 g dichloro-2,3-butadiene.

[0070] CR-8: Same as CR 1 except that the amount of DIXD in chloroprene at the start of the reaction was 6.00 g.

[0071] Preparation, vulcanization, and characterization of rubber compositions A Harburg Freudenberger internal mixer GK1.5 was used with a filling rate of 65%, the set temperature was 30°C and mixing was carried out at 40 rpm.

[0072] The following steps were identified: 0-0.5 min = polymer addition 0.5-3.0 min = Carbon black, MgO, stearic acid 3 minutes = Wash and add ZnO. Slow addition avoids scorch. 4 minutes = end

[0073] All further additives were added on a Troester mixed roll system (WNU3) with rollers cooled to 30° C. The roller diameter was 200 mm. The roller rotation speed and friction ratio were controlled to obtain a stable sheet.

[0074] To achieve homogenization, the sheet was cut three times on the left and three times on the right, then folded five times. Mixing was then terminated and the product was removed from the rollers in the form of a blanket. The blanket was vulcanized in a press at 170°C for 40 minutes.

[0075] The following materials were used as provided:

[0076] Baypren® 616 VP - copolymer of chloroprene and sulfur peptized with diisopropyl xanthogenate disulfide (xanthogen disulfide), Mooney viscosity 48 MU (CAS: 9010-98-4).

[0077] Baypren® 611 - TETD peptized copolymer of chloroprene and sulfur, Mooney viscosity 48 MU (CAS: 9010-98-4).

[0078] Non-nucleophilic base - Rhenogran® XLA-60 - a synergistic combination of 60% activated amine and retarder, 40% acrylic copolymer and dispersant (CAS-Number: 6674-22-2), supplied by Rheinchemie (DBU concentration ≥ 25% by weight). <wt.-40%)。

[0079] Non-nucleophilic base - 1,4-diazabicyclo[2.2.2]octane (DABCO), obtained from Sigma Aldrich (CAS number: 280-57-9).

[0080] Additive - Regal SRF - Cabot carbon black (CAS number: 1333-86-4) approved to the objectives of ASTM N772.

[0081] Crosslinker - Maglite® DE - Magnesium oxide (CAS number: 1309-48-4) commercially available from CP Hall.

[0082] Crosslinker - Zinc Oxide Red Seal (CAS number: 1314-13-2) from Grillo-Werke AG.

[0083] Edenor C18 98-100 - Stearic Acid (CAS Number: 57-11-4) from Oleo solutions.

[0084] Accelerator - Rhenogran® MBTS-80 - 80% dibenzothiazyl disulfide (CAS number: 120-78-5) supplied by Rheinchemie.

[0085] Accelerator - Rhenogran® TBzTD-70 - 70% (CAS number: 10591-85-2) supplied by Rheinchemie.

[0086] EXAMPLES: All examples in the table below were characterized. * is according to the present invention.

[0087] [Table 2]

[0088] [Table 3]

[0089] By using a non-nucleophilic base (DABCO or XLA-60), a reduction in Mooney viscosity was observed in the examples of the present invention. When an accelerator such as MBTS or TBzTD is used in addition to the non-nucleophilic base (DACBO or XLA-60), the reduction in Mooney viscosity is further improved. In terms of the evaluation, + means good and ++ means excellent.

[0090] [Table 4]

[0091] The combination of a non-nucleophilic base and sulfur copolymerized chloroprene rubber with DIXD not only reduces the Mooney viscosity but also increases the crosslink density and cure rate for the samples of the present invention, whereas the combination of a non-nucleophilic base and sulfur copolymerized chloroprene rubber with TETD does not change the crosslink density.

[0092] [Table 5]

[0093] The use of a non-nucleophilic base in combination with sulfur copolymerized chloroprene rubber with DIXD reduces compression set (Example 4 vs. 3), while the use of a non-nucleophilic base in combination with sulfur copolymerized chloroprene rubber with TETD increases compression set (Example 2 vs. 1). M indicates the tensile curve representation, which is the stress value of elongation in % (number shown).

[0094] [Table 6]

[0095] The combination of a non-nucleophilic base and chloroprene rubber copolymerized with sulfur and loaded with DIXD results in a lower internal temperature rise but a smaller temperature rise (Example 4 vs. 3), whereas the combination of a non-nucleophilic base and chloroprene rubber copolymerized with sulfur and loaded with TETD results in a higher internal temperature and an increased temperature rise (Example 2 vs. 1).

[0096] [Table 7]

[0097] The amount of sulfur added during initiation was varied from 0.4 phm to 0.3 phm and 0.2 phm for CR-1 to 3, while CR-5 was polymerized with 1 phm of sulfur added during initiation.

[0098] [Table 8]

[0099] The amount of sulfur added during initiation is important for the increase in Mooney viscosity along with the non-nucleophilic base. Above 0.2 phm, the decrease in Mooney viscosity is as shown in Experiment 13. * , 14 * , 16 * , and 17 * The Mooney viscosity of chloroprene polymerized with 1 phm of sulfur added during initiation is very low, resulting in a sticky material that is difficult to process. In Tables 7 and 8, Experimental Examples 19 and 20 are examples. * and 20 is 20 * is.

[0100] [Table 9]

[0101] A sulfur content between 0.2 phm and 1 phm of sulfur added at the start of polymerization provides good tensile strength and compression set.

[0102] [Table 10]

[0103] [Table 11]

[0104] [Table 12]

[0105] Addition of 3 and 7 phm of DCB during polymerization is combined with chloroprene and 0.4 phm of sulfur.

[0106] [Table 13]

[0107] Similar behavior can be seen for polymers containing sulfur, chloroprene, and DCB with non-nucleophilic bases: the Mooney viscosity decreases.

[0108] [Table 14]

[0109] The crosslinking rate and density are comparable for all polymers and are independent of DCB content. The mechanical properties of all polymers are excellent.

[0110] Having thus described the present invention and its advantages, it should be understood that the various aspects and embodiments of the invention disclosed herein are merely illustrative of specific ways to make and use the invention.

[0111] The various aspects and embodiments of the present invention do not limit the scope of the invention in light of the appended claims and the above detailed description.

[0112] The desire for Letters Patent protection is set forth in the following claims.

Claims

1. 1. A vulcanizable composition for forming a nitrosamine-free sulfur-modified polychloroprene vulcanizate, comprising: a sulfur-modified polychloroprene copolymer polymerized from at least chloroprene, elemental sulfur, and xanthogen disulfide; a non-nucleophilic base, which is a bicyclic or polycyclic amine base containing two or more connected rings; wherein said linked rings are formed from carbon and optionally contain at least one heteroatom, said heteroatom being nitrogen; Vulcanizable compositions.

2. 10. The vulcanizable composition of claim 1, wherein the sulfur-modified polychloroprene vulcanizate is formed in the presence of at least one accelerator selected from a thiazole compound, a carbamate compound, and a thiuram compound, or any combination thereof.

3. 3. The vulcanizable composition of claim 1 or 2, wherein the non-nucleophilic base is selected from the group consisting of 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,4-diazabicyclo[2.2.2]octane, and 1,5-diazabicyclo[4.3.0]non-5-ene, or any combination thereof.

4. The vulcanizable composition of any one of claims 1 to 3, wherein the sulfur-modified polychloroprene copolymer further comprises 2,3-dichloro-1,3-butadiene.

5. The vulcanizable composition of any one of claims 1 to 4, further comprising a vulcanizing agent.

6. 1. A method for producing a nitrosamine-free sulfur-modified polychloroprene vulcanizate, comprising: a) polymerizing chloroprene in the presence of elemental sulfur and xanthogen disulfide to form a sulfur-modified polychloroprene; b) vulcanizing the sulfur-modified polychloroprene formed in step a) in the presence of a non-nucleophilic base to form the nitrosamine-free sulfur-modified polychloroprene vulcanizate, wherein the non-nucleophilic base is a bicyclic or polycyclic amine base containing two or more linked rings; wherein said linked rings are formed from carbon and optionally contain at least one heteroatom, said heteroatom being nitrogen.

7. 7. The method of claim 6, wherein step b) is carried out in the presence of a promoter.

8. The method of claim 7, wherein the accelerator is selected from at least one of a thiazole compound, a carbamate compound, and a thiuram compound.

9. 9. The method of any one of claims 6 to 8, wherein the non-nucleophilic base is selected from the group consisting of 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,4-diazabicyclo[2.2.2]octane, and 1,5-diazabicyclo[4.3.0]non-5-ene, or any combination thereof.

10. 10. The method of any one of claims 6 to 9, wherein in step a) sulfur is present at the initiation of the polymerization reaction in an amount of ≥ 0.2 phm.

11. The method of claim 10, wherein in step a), sulfur is present in an amount of <1 phm at the start of the polymerization reaction.

12. 12. The method of any one of claims 6 to 11, wherein in step a), the xanthogen disulfide is present in an amount of ≦0.4 phm at the start of the polymerization reaction.

13. 13. The process according to any one of claims 6 to 12, wherein step a) is carried out in the presence of dichloro-2,3-butadiene as a further monomer unit.

14. A vulcanizate formed from the vulcanizable composition of any one of claims 1 to 5, or a vulcanizate formed by the method of any one of claims 6 to 13.

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