Determination of the Crosslinking Density of a Silicone Elastomer

Abstract

A laboratory experiment for the determination of the crosslinking density of silicone elastomers is described on the basis of swelling experiments and mechanical tests. In the experiment, the macroscopic swelling and mechanical behaviors of the elastomers were discussed as a function of the cross-linking density, which can be easily controlled by varying the base-to-curing-agent ratio during elastomer synthesis. The crosslinking density and the average molecular weight between cross-links were calculated from the swelling degree at equilibrium through the Flory− Rehner theory and from a simple mechanical model. The results have shown a good convergence of the average molecular weight between crosslinks calculated from the two methods, respectively. On a more general note, the suggested experiments and the associated results offered numerous opportunities for discussions on macromolecular architectures, interactions between polymers and solvents, and mechanical properties of elastomeric materials.

UV-Cured Transparent Silicone Materials with High Tensile Strength Prepared from Hyperbranched Silicon-Containing Polymers and Polyurethane-Acrylates

“…Therefore, the steady increment of pencil hardness of the UV-cured materials may be due to the increasing cross-linking density with the increasing TMP content of the PUAs. 39 It also can be seen that the surface water contact angle of these materials is 99.0−105.1°, which may be ascribed to the hydrophobicity of the HBP. The water absorption of these UVcured materials is as low as 0.5−0.9%, which may illustrate that the UV-cured materials have a fairly good water resistance performance.…”

“…The crosslinking density of UV-cured materials was evaluated by a swelling experiment similar to the reference shown in Table S3. 39 The higher the SD, the lower the cross-linking density of UV-cured materials will be. The samples were immersed in toluene for 72 h and SD expressed as SD = [m 0 /ρ e + (m − m 0 )/ρ s ]/(m 0 /ρ e ), where m 0 and m refer to the masses of the unswollen and swollen material (in g), respectively, and ρ e and ρ s refer to the density of the UV-cured material and toluene (in g cm −3 ), respectively.…”

New Bio‐Based Furanic Materials Effectively Absorb Metals from Water and Exert Antimicrobial Activity

“…This effect of crosslinker content may be explained by restrained mobility of the macromolecular chains in tighter gel structures. Another explanation for the lower swelling capacity of highly crosslinked resins (Figure 2 c) is that the increasing crosslink density lowers the average chain lengths between the crosslinks (Figure 2 f), thereby reducing the free spaces between macromolecular chains and interfering with their accessibility to the penetrating water molecules [14d, 32] . It should be noted that AAc/DAF‐1 and AAc/DADF‐1 are partially soluble in water (10–15 %), which can be attributed to the formation of star polymers with DAF or DADF cores and poly(AAc) arms [29] .…”

Facile Construction of Zn2+‐Carboxyl Salt‐Bonding as Sacrificial Unit in EPDM Rubber toward Mechanical and Sealing Resilience Performance Enhancement

“…The micro-morphologies of ZDMA/PZDMA were observed on JEOL JSM-5900LV SEM (Japan) and JEOL JEM 100CX II TEM (Japan) with acceleration voltage of 200 kV. The crosslinking density was calculated by equilibrium swelling method, [18][19][20] and the detailed information was described in Supporting Information.…”