The Influence of Graft Rigidity on the Dynamical Behavior of PMMS-Based Polymer Brushes at Ambient and High Pressures
Year: 2024
Type: article
Abstract: In this paper, we investigated the molecular dynamics of polymer brushes based on poly(mercaptopropyl)methylsiloxane (PMMS), in which the thiol group was grafted with different homologous flexible acrylates (acrylate-based PMMS copolymers) and more rigid methacrylate (methacrylate-based PMMS copolymers) monomers of varying lengths of alkyl chain under ambient and elevated pressure conditions. It was found that the glass transition temperature, T g, of PMMS homopolymer is significantly lower compared to the other systems. Moreover, surprisingly, in the methacrylate-grafted copolymers, there are two relaxation processes (α and α′), while in the systems grafted with various acrylates, only a single process is present in the supercooled phase. Complementary rheological investigations indicated that the faster α process comes from the segmental motions, while α′ is not detected in the mechanical response. Further high-pressure experiments showed that there is a superposition between segmental and α′ modes irrespective of applied pressure, p, in methacrylate-based PMMS copolymers. This result suggests that the latter process might be considered as a sub-Rouse mode, or alternatively, it may originate from the dielectric active relaxation of the rigid polar side chain (grafts). Moreover, analysis of the high-pressure data allowed us to estimate the pressure coefficient of the glass transition temperature, d T g /d p, which was much higher for polymer brushes with respect to the PMMS homopolymer. Interestingly, the values of d T g /d p for methacrylate-grafted copolymers are slightly higher compared to acrylate-based PMMS copolymers, which may be due to the different flexibility/rigidity of both groups of materials as all examined materials have the same degree of polymerization of homopolymer backbone ( N bb ∼ 12) and side chain ( N sc = 1). However, for both groups of studied systems, d T g /d p values did not scale with chain length. This unexpected result must be related to the structure of the studied grafted copolymers and the character of grafts, derivatives of acrylates/methacrylates. The data presented here extend our knowledge of the influence of the architecture of different molecules on the dynamics of polymers at ambient and high pressures.
Source: Macromolecules
Institution: University of Silesia in Katowice
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,500
Award: G376568738
OpenAlex ID: W4404405221