## 3 Results and Discussion
### Mechanical Properties  
The mechanical tests are very important to characterize the virtually unexplored ductile properties of the products synthesized by inverse vulcanization. Consequently, it is possible to tune these materials for specific applications. All mechanical measurements were done with hot-pressed sulfur copolymers because it is often nearly impossible to reprocess the crude polymers into test specimens. Ductile experiments indicate that hot-pressed sulfur copolymers have better ductile properties than crude copolymers (Figure 10). They show a two to three times higher elongation. Hence, the remolded material has a higher stability for different applications. Attention should be paid to the heating time to prevent the formation of thermosets due to post cross-linking. Figure 10: Comparison of ductility experiments of crude and hot-pressed sulfur copolymers. The diagrams show copolymers with 15 wt % incorporated monomer content: (**a**) pS-DVB; (**b**) pS-DIB. Figure 9: Specific contact resistance of sulfur materials: (**a**) copolymers; (**b**) terpolymers. Measured after 0–3 months of synthesis. The Shore hardness of all sulfur copolymers (reprocessed with a hot press) has no clear correlation with the incorporated monomer content or cannot be detected due to the large standard deviations. The deviations of measurements are caused by inhomogeneities of the sulfur copolymers through air inclusions or the unsuccessful uniform reprocessing with the hot press. The values of the Shore hardness correspond to those of soft plastics or elastomers (Figure 11). Films of pS-DIB are relatively softer than those of pS-DVB (Shore \(D=13\)-67) below an incorporated monomer content of 30 wt %. Regarding the Shore hardness, the sulfur copolymer materials are softer than conventional hydrocarbon polymers like polystyrene (\(D=80\)), polymethylmethacrylate (PMMA) (\(D=87\)-88), polycarbonate (\(D=82\)-85), polypropylene (\(D=65\)-75), etc. [34]. Depending on the amount of styrene and DIB added to the DVB-based copolymer to form a terpolymer, a softer material is produced in contrast to conventional pS-DVB. Results of ductility experiments show that test specimens of pS-DVB act as ductile material with properties of amorphous plastomers. The curves of ductility experiments (Figure 12a) have a small elastic range and a large plastic range with no necking area. The ductile stress to stretch the polymer by the same factor increases with the decrease of the incorporated monomer content of the sulfur copolymer. This implies that a polymer with a lower incorporated monomer content has a higher stability. At a monomer content of 30-35 wt %, the polymers result in a sticky and viscous resin because a higher monomer content implies an autoacceleration (gel effect) that causes a temperature rise above 200 \({}^{\circ}\)C. The released exothermic energy decreases the viscosity by reducing the chain length when the temperature limit is exceeded to a value above 200 \({}^{\circ}\)C [3]. These materials cannot be processed into test specimens to carry out mechanical measurements. The \(E\)-modulus tends to decrease with an increase of added monomer content. The hardness of the exceptional copolymer with 15 wt % monomer content cannot be explained. Consequently, at a monomer content of 12.5 wt %, the hardness is highest in the plastic material. The stretching area of pS-DVBs extends up to 75%. Apparently, the fracture point decreases first with an increase of the incorporated monomer content, and then increases again at an incorporated monomer content of 25 wt %, when the viscosity of the products decreases (Figure 12b). Figure 11: Shore hardness of sulfur copolymers: (**a**) pS-DVB; (**b**) pS-DIB. The material of pS-DIB acts as amorphous plastomers with thermoplastic to duromeric properties, depending on the incorporated monomer content. The stress-strain diagram of pS-DIB shows a plastic region with a necking area (Figure 13a). The material has no elastic properties, since there is no linear elastic range in the stress-strain curve.