Correlation between Locally Ordered (Hydrogen-Bonded) Nanodomains and Puzzling Dynamics of Polymethysiloxane Derivative

Abstract

We examined the behavior of poly­(mercaptopropyl)­methyl­siloxane (PMMS), characterized by a polymer chain backbone of alternate silicon and oxygen atoms substituted by a polar pendant group able to form hydrogen bonds (−SH moiety), by means of infrared (FTIR) and dielectric (BDS) spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and rheology. We observed that the examined PMMS forms relatively efficient hydrogen bonds leading to the association of chains in the form of ordered lamellar-like hydrogen-bonded nanodomains. Moreover, the recorded mechanical and dielectric spectra revealed the presence of two relaxation processes. A direct comparison of collected data and relaxation times extracted from two experimental techniques, BDS and rheology, indicates that they monitor different types of the mobility of PMMS macromolecules. Our mechanical measurements revealed the presence of Rouse modes connected to the chain dynamics (slow process) and segmental relaxation (a faster process), whereas in the dielectric loss spectra we observed two relaxation processes related most likely to either the association–dissociation phenomenon within lamellar-like self-assemblies or the sub-Rouse mode (α′-slower process) and segmental (α-faster process) dynamics. Data presented herein allow a better understanding of the peculiar dynamical properties of polysiloxanes and associating polymers having strongly polar pendant moieties.

Supramolecular structures of self-assembled oligomers under confinement

“…Namely, PMMS has the ability to form H-bonding via thiol moieties that are attached to its backbone. 39 In contrast, PMMS- g -HMA is a graft copolymer based on PMMS and extended with the hexylmethacrylate (HMA) group, which forbids the formation of H-bonding between these oligomers (see Fig. 1(a) and Fig.…”

Is a Dissociation Process Underlying the Molecular Origin of the Debye Process in Monohydroxy Alcohols?

“…Herein, it should also be added that in hydroxyl-terminated poly(propylene glycol) and poly(dimethylsiloxane) derivatives, E a ∼ 5.8–9.1 kJ/mol, 31 whereas for urazole-functionalized entangled polyisoprene and poly(mercaptopropyl)methylsiloxane, E a ∼ 25–29 kJ/mol. 32 , 44 …”

“…Herein, it should also be added that in hydroxyl-terminated poly(propylene glycol) and poly-(dimethylsiloxane) derivatives, E a ∼ 5.8−9.1 kJ/mol, 31 whereas for urazole-functionalized entangled polyisoprene and poly(mercaptopropyl)methylsiloxane, E a ∼ 25−29 kJ/mol. 32,44 Having the values of E a estimated from dielectric data for both examined MA, we decided to compare them to the respective ones calculated from FTIR investigations. One can assume that the agreement between E a determined from both experimental techniques could be further evidence that the appearance of the D-process is related to the continuous dissociation/association between MA molecules creating longer self-assemblies (of approximately "supramolecular" structures) and affecting the dipole moment (as well as the polarization), as proposed by the TCM approach.…”

“…This probably means that the most valuable information on the dissociation (or association) processes occurring in alcohols can be obtained from fitting the data measured in the vicinity of T g to the Rubinstein model. Herein, it should also be added that in hydroxyl-terminated poly­(propylene glycol) and poly­(dimethylsiloxane) derivatives, E a ∼ 5.8–9.1 kJ/mol, whereas for urazole-functionalized entangled polyisoprene and poly­(mercaptopropyl)­methylsiloxane, E a ∼ 25–29 kJ/mol. , …”

The impact of H/D exchange on the thermal and structural properties as well as high-pressure relaxation dynamics of melatonin

“…It is worth mentioning that they regulate various chemical (e.g., water association), physical (e.g., phase transitions), and biochemical (e.g., the formation of the DNA double helix responsible for transferring genetic information during replication) processes 1 . Furthermore, HBs play a significant role in molecular self-assembly mechanism by governing and stabilizing the structural organization of associating liquids (such as water 2 and alcohols 3 or more complex systems (i.e., liquid and plastic crystals 4 , 5 , polymers 6 , etc.). The issue of molecular self-organization is interesting but far from completely established and explained.…”