Stress Relaxation of End-Linked Polydimethylsiloxane Elastomers with Long Pendent Chains

Abstract

Two important issues in the area of stress relaxation in elastomers are addressed experimentally in this paper. The first deals with the dependence of the terminal relaxation time on the number of entanglements that a chain tethered to a network makes with the network, and the second deals with the validity of the empirical Chasset-Thirion equation. By carefully end-linking PDMS chains to form networks with few defects besides the controlled amount of long pendent chains, our results show a much weaker exponential dependence of the terminal relaxation time on number of entanglements per tethered chain than predicted by the Doi-Kuzuu theory for a fixed entanglement network but closer to the exponential dependence predicted by lattice calculations with a harmonic potential. The ChassetThirion equation is found to hold only in an intermediate time regime of the relaxation spectrum.

Novel Michael Addition Networks Containing Poly(propylene glycol) Telechelic Oligomers

“…The resulting model networks are considered more well‐defined than typical sulfur or peroxide vulcanized rubbers and often possess better mechanical properties due to the presence of fewer dangling ends 13,14. Crosslinking telechelic oligomers to form model networks was previously accomplished with polysiloxanes via hydrosilation of vinyl‐terminated and SiH‐terminated oligomers,15–21 but other efforts involve telechelic polyethers,22–24 polyisobutylenes,25 polyurethanes,26 and polyimides 27…”

A rheological study on non-rubber component networks in natural rubber

“…Second, to pick out the non-rubbers, the rubber chain peaks assignment are listed below. [38] 1 H-NMR The 1 H-NMR spectrums of NR, DPNR and TEDPNR were shown in Fig.2, and a small amount of residual chloroform peak was detected at 7.28ppm. Then, the recession of characteristic peaks of protein at 1663 and 1546cm -1 [35] is obviously observed in DPNR compared with NR, and the peaks of C=O in phospholipid at 1738cm -1 [36] in TEDPNR.…”

“…And the relaxation time of all samples was displayed in the histogram in Fig.8. [38] Similarly, in the unvulcanized rubber, the relaxation units were also constrained by the natural network, and then displayed a decrease in relaxation time. In vulcanized rubber, the relaxation time decreases with increasing crosslinking density, which can be interpreted as the crosslinking point restriction.…”

Damping elastomer with broad temperature range based on irregular networks formed by end‐linking of hydroxyl‐terminated poly(dimethylsiloxane)

“…However, since the damping properties depend on the glass transition, the effective damping temperature region (tan δ > 0.3) by these methods was not sufficiently broad. In recent years, a novel damping elastomer, based on irregular networks with dangling chains, has attracted much attention . As only one end of the pendant chains was linked to the permanent networks, the irregular networks have many relaxation modes with different relaxation times .…”