End-Linked Poly(dimethylsiloxane) Elastomers:  ²H-Nuclear Magnetic Resonance Investigations of Compression-Induced Segment Anisotropy

Abstract

2 H-NMR spectroscopy is applied to measure strain-induced orientational anisotropy of polymer segments in three environments in poly(dimethylsiloxane) (PDMS) elastomers: elastic chains, pendant chains, and PDMS(d) chains dissolved in the network. The elastomers were prepared with systematically-varied structures and selective deuterium labeling. Network features were inferred from macroscopic measurements using statistical and thermodynamic models. The segment order parameter, S, was found to be proportional to λ 2 -λ -1 , where λ is the compression ratio, for the three environments in uniaxially-compressed PDMS networks: elastic chains, pendant chains, and dissolved probe chains. Furthermore, all three environments show the same dependence of the ratio S/(λ 2 -λ -1 ) on the elastic modulus, in the range 0.089-0.29 MPa. These results agree with the recent theoretical predictions of Brereton and Ries (Macromolecules 1996, 29, 2644) and thus support the premise that the excluded volume (entropic) interactions between segments subjected to deformation cause anisotropic averaging of the quadrupolar interaction and thus cause a 2 H-NMR line splitting.

Effects of structural imperfections on the dynamic mechanical response of main‐chain smectic elastomers

“…38 Even the optimal networks have w sol values substantially higher than the accepted range for ''model'' networks, which can have w sol < 1.0 mass %. 39,41,44,45 Thus, although the ''optimal'' samples are presumed to have a lower concentration of architectural defects than the ''imperfect'' networks, they cannot be fairly described as ''model'' networks. The high soluble fractions may be attributed to intramolecular cyclization reactions, encouraged by the presence of solvent during crosslinking and by the flexibility of the oligosiloxane connectors.…”

Indentation fracture of silicone gels

“…[9][10][11] The network of the gels was formed from vinyl-terminated polydimethylsiloxane (PDMS) prepolymers with a molecular weight of either 800 (V1) or 28,000 g/mol (V28). From these networks, 14 sample types were prepared, as listed in Table I.…”

Crosslinked Elastomers: Structure–Property Relationships and Stress-Optical Law

“…Besides mechanical measurements, many different experimental approaches have been used in order to study elastomer networks. These include techniques to measure segmental orientation, such as optical birefringence [ 26 , 27 ], fluorescence polarization [ 28 ], infrared dichroism [ 29 ], and H NMR [ 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. Small angle scattering techniques have been used as well [ 37 , 38 , 39 , 40 , 41 , 42 ].…”