On the critical molecular chain length of polydimethylsiloxane

Abstract

SYNOPSISBecause a study of the results reported for the chain dimensions of polydimethylsiloxane (PDMS) , critical for the onset of this polymer's non-Newtonian flow behavior, obtained from the viscosity-molecular weight relationships available from the literature, clearly revealed that considerable differences exist between the reported data, a detailed analysis of these data was performed together with an additional examination of 10 new PDMS samples that were selected so as to have molecular weights that would fill the gaps observed in the polymer viscosity-chain length relationship constructed from the accepted literature data. The results obtained were analyzed by using several different procedures integrated into a recently described comparative method that could allow for determination of what is called the most realistic critical value, Zwc. The latter was determined as 930 PDMS main-chain atoms, which corresponds to this polymer's degree of polymerization of 464.5 and the weight-average molecular weight of 34,500. It is not only shown that after elimination of some clearly erroneous data points from the previously reported relationships the obtained critical chain-length values could very well fit the earlier relationships, but also that appropriate "master" relationships were constructed including 48 pairs of the old and 10 pairs of the new data points. It is suggested that this relationship be accepted as the bestfit viscosity-polymer chain-length dependence for PDMS, and it is pointed out that the obtained PDMS critical chain-length value ranks this polymer's macromolecules as the most flexible of the corresponding long-chain molecules presently known. 0 1993

Structural characterization and thermal behaviour of block copolymers of polydimethylsiloxane and polyamide having trichlorogermyl pendant groups

“…Polydimethylsiloxanes (PDMSs) have good electrical properties, low surface energy, the ability to withstand damage, resistance to contamination and very low glass transition temperatures of the order of − 123 °C. Their low surface tension, low solubility and low dielectric constant are due to chain flexibility and weak intermolecular forces 1–3. They are used in making high‐voltage insulators as well as coatings on porcelain and glass in order to improve the hydrophobic characteristics.…”

Polymer Chain Mobility under Shear—A Rheo-NMR Investigation

“…In contrast, the high-molecular-weight sample exhibits a bi-exponential decay, clearly showing heterogeneity of the molecular motion, which is explained by the presence of entanglements. The molecular weight is well above the reported entanglement molecular weight of PDMS of about 35,000 g/mol [17]. Entanglements of the polymers leads to restricted motion and thus less averaging of the dipolar coupling and, therefore, shorter T 2 .…”

Polysiloxane/Polystyrene Thermo-Responsive and Self-Healing Polymer Network via Lewis Acid-Lewis Base Pair Formation

“…Moreover, the zero-shear viscosity ( η 0 ), determined as the complex viscosity ( η *) at low shear-rates ( Figure S7 ), is much higher (47,300 Pa·s) compared to that of the free-flowing parent vinyl-terminated PDMS (0.1 Pa·s). Remarkably, the molecular weight of the PDMS-PY employed in this study ( M n = 9620 Da) was well below the critical molecular weight of PDMS (reported at M c = 34,500 Da, approximate DP > 400, [ 45 ]); therefore, we can postulate that the rheological observations are not due to the entanglement of the linear PDMS chains, but mostly due to the reversible crosslinks between the PDMS/PS in the form of Lewis pairs.…”