Mercaptan-Modified

The crystalliza tion resistance of vulcaniza tes can be measured by following hardness or compression set at low temperature over a period of time. The stress in a compression set test accelerates crystallization. Often the curve of compression set with time has an S shape, exhibiting a period of nucleation followed by rapid crystallization (Fig. 3). The mercaptan modified homopolymer, Du Pont Type W, is the fastest crystallizing, a sulfur modified homopolymer, GN, somewhat slower, and a sulfur modified low 2,3-dichlorobutadiene copolymer, GRT, and a mercaptan modified high dichlorobutadiene copolymer, WRT, are the slowest. The test is often mn near the temperature of maximum crystallization rate of —12° C (99). Crystallization is accelerated by polyester plasticizers and delayed with hydrocarbon oil plasticizers. Blending with hydrocarbon diene mbbers may retard crystallization and improve low temperature britdeness (100). 

If tertiary chlorine atoms are indeed critical to heat resistance, then reactions that consume them should improve polymer stabiUty. This is indeed the case. Post-reaction of polychloroprene with dodecyl mercaptan (111), use of higher levels of ethylene thiourea for curing (112), and inclusion of reactive thiols such as mercaptobenzimidazole in cure systems (113) all improve heat resistance. This latter technique is especially effective in improving the heat resistance of mercaptan modified polychloroprene. 

Mercaptan-modified polychloroprenes only contain sulphur at the ends of the polymer chain. Polymerization is carried out in the presence of a mercaptan to act... 

Mercaptan-inodified polychloroprenes provide lighter colour to solutions and are more resistant to discolouration than sulphur-modified polychloroprenes. Also mercaptan-modified polychloroprenes exhibit better ageing, and improved thermal and solution stability. 

Neoprene WHV-A. It is a non-peptizable and mercaptan-modified polychloro-prene elastomer. It is a slow-crystallizing, high molecular weight type and contains only 85% trans-, 4 structure. It is generally used in blends with low molecular weight crystallizing polychloroprene types to increase solution viscosity. 

The cross-linking efficiency of the more branched polychloroprene latex (mercaptan modified) has been found to be higher than the less branched sulfur-modified one. The latex dispersion is found to display higher rate of cross-linking than the coagulated and subsequently dried mbber films [386] due to higher concentration of radical in the former. 

PennvraltdP . [Atochem N. Am.] Tert. dodecyl mercaptan modifier in polymerization reactions, esp. fcM SBR and NBR. 

Beiistein Handbook Reference) AI3-08621 BRN 0507434 EINECS 203-674-6 1,3-Dibutylthiourea 1,3-Di-n-butyl-2-thiourea 1,3-Dibutyl-2-thiourea NSC 3735 Pennzone B Pennzone B 0685 Thiate U Thiourea, N,N -dibutyl- Urea, 1,3-dibutyl-2-thio- Urea, 1,3-di-N-butyl-2-thio- USAF EK-2138. Accelerator for mercaptan-modified chlotoprene rubber, an activator for ethylenepropylenediene terpolymers and natural nibber, an antidegradant for natural rubber-latex and thermoplastic styrene-butadiene rubber. Crystals mp = 63-65°. ElfAtochem N. Am. 

Beilstein Handbook Reference) AI3-14636 BRN 0773905 CCRIS 243 N,N -Diethyl-thiocarbamide 1,3-Diethylthiourea 1,3-Diethyl-2-thiourea N,N -Diethylthiourea N,N-Diethyl-2-thiourea EINECS 203-308-5 HSDB 4106 NCI-C03816 NSC 3507 Pennzone E Thiate H Thiourea, N,N -diethyl- U 15030 Urea, 1,3-diethyl-2-thio- USAF EK-1803. Accelerator for mercaptan-modified chloroprene rubber. Antidegradant for natural, nitrile-butadiene, styrene-butadiene, and chloroprene rubbers. Crystals mp = 78° bp dec. Xm = 234, 265 nm (c = 6310, 7244, MeOH) slightly soluble in CCI4, soluble in H2O (0.1 - 0.5 g/100 ml), EtOH, very soluble in Et20 LDso (rat orl) = 316 mg/kg. ElfAtochem N. Am. 

This synthesis is usually carried out in the presence of alkaline catalysts. The catalyst is neutralized and at least partially remains in the final product. Primary Cg-Cig long-chain alcohols are generally used for ethoxylation. The alcohols may be of synthetic (Ziegler or oxo alcohols), vegetable and animal origin. Other hydroxo compounds can be subjected to ethoxylation, for example diols, such as 2,4,7,9- tetramethyl-5-decyne-4,7-diol ( Surfinol ), vegetable sterols, lanoline fractions enriched by sterols and fatty alcohols [34]. Ethoxylated alcohols and mercaptanes modified by a subsequent addition of propylene oxide or ethoxylated and propoxylated alcohols mentioned before (section 1.2.2) are of some industrial importance. 

The amount of mercaptan modifier in an emulsion polymerization system for the production of a styrene-butadiene rubber can have an important effect upon some of the properties of the polymer obtained. This is illustrated by the results of Bebb et al. [17] for polymerizations carried out at 50 °C both the gel content of the polymer (see Figure 15.5a) and its plasticity (see Figure 15.5b) decrease sharply as the level of mercaptan increases indeed, if the modifier level is sufficiently high, the product is a very viscous liquid rather than an elastomer. The level of mercaptan in the reaction system can also affect the rate of polymerization. If the level of mercaptan is very low, the rate of pol)nnerization increases sharply with increasing mercaptan level. This effect is attributed to activation of the persulfate initiator in effect, a redox couple forms, the mercaptan being the reductam and the persulfate the oxidant At higher mercaptan levels, the rate of polymerization becomes insensitive to further mercaptan additicxi. 

Synonyms N,N -dibutyl-thiourea N,N-dibutylthiourea N,N -di-n-butylthiourea i,3-dibutyl-2-thiourea 1,3-dibutylthiourea Uses accelerator for mercaptan-modified chloroprene rubber activator for ethylene-propylene-diene terpolymers and natural rubber antidegradant for natural rubber latex and thermoplastic styrene-butadiene rubber A... 

Uses inhibitor of corrosion in metal pickling solutions accelerator for mercaptan-modified chloroprene rubber antidegradant for natural, nitrile-butadiene, styrene-butadiene, and chloroprene rubbers A... 

Description of Mercaptan- Modified Amido Modified Modified Modified Modified Modified Aromatic Modified... 

Mercaptan-modified Easy molecular weight control Not peptizable... 

N,N -Dibutylthiourea is a nitrosamine free accelerator, antidegradant, and corrosion inhibitor. Ultra-accelerator for mercaptan-modified CR. It is slightly safer than DETU. It is also used as a secondary accelerator for NR and synthetic rubbers. It disperses easily in rubber. It is non-staining and does not bloom. It is practically odorless. Antioxidant for NR, antiozonant for NR and SR, particularly SBR. 

A poor state of cure will also result if a mercaptan-modified neoprene such as Neoprene W is replaced with a sulfur-modified grade, which will severely retard the vulcanization. 

Mercaptan modified polychloroprene compounds vulcanised with a thiourea give superior heat ageing and compression set compared to... 

---