Dicyclopentadiene sulfur

Results. Pure elemental sulfur applied between 120 and 160 °C hardly penetrated into construction sand. Dicyclopentadiene-sulfur mixtures produced negligible penetration at concentrations of 3-9% at 120-160°C. Above 9%, the penetration depths ranged from 3 to 11 mm at 130-160°C. Above 140 °C, the dicyclopentadiene-sulfur reaction is exothermic and extremely difficult to control. When uncontrolled, the material was extremely viscous and the penetration was negligble. 

Sulfur can be fully plasticized by using the modifiers dipentene, styrene, and dicyclopentadiene. Sulfur can be plasticized with dicyclo-pentadiene at two minimum concentrations, as indicated in Table III 13% at reaction temperatures of < 140°C and 6% at reaction temperatures > 140 °C. This effect probably results from cracking of the dicyclopentadiene dimer molecule, which doubles the molecules available for reaction. The higher percentage dicyclopentadiene mixture was initially flexible. Upon aging, both plasticized materials became brittle. The reaction is exothermic and very difficult to control above 140 °C. When uncontrolled, extreme viscosity increases were encountered. 

Ethylene—Propylene Rubber. Ethylene and propjiene copolymerize to produce a wide range of elastomeric and thermoplastic products. Often a third monomer such dicyclopentadiene, hexadiene, or ethylene norbomene is incorporated at 2—12% into the polymer backbone and leads to the designation ethylene—propylene—diene monomer (EPDM) mbber (see Elastomers, synthetic-ethylene-propylene-diene rubber). The third monomer introduces sites of unsaturation that allow vulcanization by conventional sulfur cures. At high levels of third monomer it is possible to achieve cure rates that are equivalent to conventional mbbers such as SBR and PBD. Ethylene—propylene mbber (EPR) requires peroxide vulcanization. 

Sulfur Polymer Cement. SPC has been proven effective in reducing leach rates of reactive heavy metals to the extent that some wastes can be managed solely as low level waste (LLW). When SPC is combined with mercury and lead oxides (both toxic metals), it interacts chemically to form mercury sulfide, HgS, and lead sulfide, PbS, both of which are insoluble in water. A dried sulfur residue from petroleum refining that contained 600-ppm vanadium (a carcinogen) was chemically modified using dicyclopentadiene and oligomer of cyclopentadiene and used to make SC (58). This material was examined by the California Department of Health Services (Cal EPA) and the leachable level of vanadium had been reduced to 8.3 ppm, well below the soluble threshold limit concentration of 24 ppm (59). 

Figure 2. Change in stress-strain behavior with time, with dicyclopentadiene polymerized sulfur...

Two percent by weight of dicyclopentadiene (DCPD) was added to the sulfur, followed by the aggregate, which was 75% of the SC. 

With larger amount of propylene a random copolymer known as ethylene-propylene-monomer (EPM) copolymer is formed, which is a useful elastomer with easy processability and improved optical properties.208,449 Copolymerization of ethylene and propylene with a nonconjugated diene [EPDM or ethylene-propylene-diene-monomer copolymer] introduces unsaturation into the polymer structure, allowing the further improvement of physical properties by crosslinking (sulfur vulcanization) 443,450 Only three dienes are employed commercially in EPDM manufacture dicyclopentadiene, 1,4-hexadiene, and the most extensively used 5-ethylidene-2-norbomene. 

Although both linear polyethene and isotactic polypropene are crystalline polymers, ethene-propene copolymers prepared with the aid of Ziegler catalysts are excellent elastomers. Apparently, a more or less random introduction of methyl groups along a polyethene chain reduces the crystallinity sufficiently drastically to lead to an amorphous polymer. The ethene-propene copolymer is an inexpensive elastomer, but having no double bonds, is not capable of vulcanization. Polymerization of ethene and propene in the presence of a small amount of dicyclopentadiene or 1,4-hexadiene gives an unsaturated heteropolymer, which can be vulcanized with sulfur in the usual way. 

The rationale in using these particular dienes is that only the strained double bond of dicyclopentadiene and the terminal double bond of 1,4-hexadiene undergo polymerization with Ziegler catalysts. Consequently the polymer chains contain one double bond for each molecule of dicyclopentadiene or 1,4-hexadiene that is incorporated. These double bonds later can be converted to cross-links by vulcanization with sulfur (Sections 13-4 and 29-3). 

Sulfur Modified with Dicyclopentadiene. The beneficial use of dicyclopentadiene to modify sulfur has been reported by a number of workers including Currell et al. (3), Sullivan et al. (4), and also Diehl (5). Currell et al. showed that the interaction of dicyclopentadiene and elemental sulfur at 140 °C gives a mixture of polysulfides and free elemental sulfur which, even after standing for 18 mo, is held as a mixture of presumably monoclinic and noncrystalline sulfur. Sullivan et al. reported that the minimum concentration of dicyclopentadiene required to stop permanently the embrittlement of elemental sulfur is 13% if the reaction temperature is less than 140°C and only 6% if the reaction temperature is greater than 140 °C. Presumably the polysulfide reaction products form a solid solution with the unreacted sulfur from which orthorhombic sulfur cannot crystallize. 

Table II summarizes the initial results of a further study on the modification of sulfur by dicyclopentadiene at 140°C. The efficiency of dicyclopentadiene in inhibiting the formation of orthorhombic sulfur is...

We can confirm the reports of Sullivan et al. that the reaction between dicyclopentadiene and sulfur is exothermic. If the temperature rises above 150 °C, the extreme viscosity increase causes the mixture to become almost solid and the reaction difficult to control. Diehl (5) and Bordoloi and Pearce (6,7) have reported quantitative studies of these viscosity changes. They show that there are large viscosity increases as the amount of dicyclopentadiene added, reaction temperature, and reaction time are increased. Our results show that these increases in viscosity are caused by the formation of high-molecular-weight polysulfides. 

Figure 3. Structure obtained by x-ray diffraction of cyclic pentasulfide formed by interaction of sulfur and dicyclopentadiene...

Figure 5. Shore D hardness vs. log time plots of modified sulfur materials. Samples are identified by percentage of modifier used (w/w sulfur) and heating time at 140°C. The onset of sample shattering is indicated by X. (a) Sulfur (b) 5% dicyclo-pentadiene, 3 hr (c) 10% dicyclopentadiene, 3 hr (d) 25% dicyclopentadiene, 3 hr (e) 5% styrene, 3 hr (f) 10% styrene, 3 hr (g) 25% styrene, 3 hr (h) 25% myrcene, 0.8 hr.

Increases in the UTS of the polypropylene fabric by impregnation with sulfur materials ranged from 24 to 87% the highest increases were obtained with dicyclopentadiene-modified sulfur materials. Merely heat-... 

Plastic Sulfur Stabilization by Copolymerization of Sulfur with Dicyclopentadiene... 

Liquid sulfur-dicyclopentadiene (DCP) solutions at 140°C undergo bulk copolymerization where the melt viscosity and surface tension of the solutions increase with time. A general melt viscosity equation rj == tj0 exp(aXH), at constant temperature, has been developed, where tj is the viscosity at time t for an S -DCP feed composition of DCP mole fraction X and rj0 (in viscosity units), a (in time 1), and b (a dimensionless number, -f- ve for X < 0.5 and —ve for X > 0.5) are empirical constants. The structure of the sul-furated products has been analyzed by NMR. Sulfur non-crystallizable copolymeric compositions have been obtained as shown by thermal analysis (DSC). Dodecyl polysulfide is a viscosity suppressor and a plasticizer for the S8-DCP system. 

Sulfur is used directly in sulfur-additive solutions which are used as coatings (3, 4, 5, 6). Dicyclopentadiene is a potentially cheap material that can form copolymers with liquid sulfur. The patent literature reports applications of the sulfur-dicyclopentadiene system in sprayable coatings, rubber vulcanizates, etc. However, very little has been written on the chemistry, characterization, and properties of this system. 

Dicyclopentadiene (boiling point for both the isomers is 170°C) is soluble in liquid sulfur at 140°C in all proportions, and the melt viscosity of the sulfur-DCP solution increases with time because of a copolymerization reaction. The DSC thermograms of sulfur-DCP mixtures are shown in Figure 1. The exothermic reaction clearly becomes evident with a feed of about 20% DCP with the exotherm starting at about 140°C. 

Figure 6. NMR spectrum of the sulfurated products of endo-dicyclopentadiene (almost an equimolar mixture of cis-exo and trans addition products as shown) in CSe using TMS as internal standard...

The behavior of melt viscosity of sulfur-dicyclopentadiene solutions is of obvious interest from the point of sprayable coatings. The melt viscosity behavior has been reported recently, but only qualitatively and over a narrow range of compositions (18). The viscosity of sulfur measured by the capillary method by Bacon and Fanelli (19, 20) is considered to be the best (21). Recently, however, the viscosity of sulfur has been measured by an apparatus containing an electric motor and a rotating cylinder (22). Viscosity of the sulfur-DCP solutions are measured here with the help of a Brookfield synchro-lectric viscometer, which is of the later kind. Viscosity measurements have been carried out to follow the copolymerization reaction and to analyze the viscosity behavior. 

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