Molecular Insights into Sequence Distributions and Conformation-Dependent Properties of High-Phenyl Polysiloxanes

Abstract

The excellent performance and wide applications of phenyl polysiloxanes are largely due to their phenyl units and monomer sequences. However, the relationship between molecular structure and material properties has not been explicitly elucidated. In this work, the sequence distribution and microstructure of random copolymers were quantitatively investigated by means of a molecular dynamics (MD) simulation combined with experimental verification. The results of 29Si NMR showed that the large number of phenyl units not only shortened the length of the dimethyl units, but also significantly increased the proportion of consecutive phenyl units. The simulation results indicated the attraction between adjacent phenyl groups that were effectively strengthened intra- and inter- molecular interactions, which determined the equilibrium population of conformations and the dynamics of conformational transitions. Furthermore, the evolution of bond angle distribution, torsion distribution, and mean-squared displacements (MSD) shed light on the conformational characteristics that induce the unique thermodynamics properties and photophysical behavior of high-phenyl polysiloxanes. Differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), spectrofluorimetry, and laser scanning confocal microscopy (LSCM) were performed to verify the conclusions drawn from the simulation. Overall, the complementary use of MD simulations and experiments provided a deep molecular insight into structure–property relationships, which will provide theoretical guidance for the rational design and preparation of high-performance siloxanes.

Effect of Diphenyl Content on Viscoelasticity of Poly(dimethyl-co-diphenyl)siloxane Melt and Network

“…The properties of the PDMS- co -PDPS copolymer are greatly dependent on the amounts of diphenyl component . Zhu et al showed that incorporation of a high mole percentage of phenyl components changes the atomic structures significantly . Other structural changes have also been observed in other copolysiloxanes. − Moreover, our recent molecular simulation study clarified the structure–property interplay of the PDMS- co -PDPS copolymer and showed that the increase of the diphenyl component greatly slows down microscopic relaxation, which can affect the bulk viscoelasticity of the copolymer according to the literature …”

“…26 Zhu et al showed that incorporation of a high mole percentage of phenyl components changes the atomic structures significantly. 27 Other structural changes have also been observed in other copolysiloxanes. the PDMS-co-PDPS copolymer and showed that the increase of the diphenyl component greatly slows down microscopic relaxation, which can affect the bulk viscoelasticity of the copolymer according to the literature.…”

Application of Multi-Vinyl Silicon-Containing Cross-Linkers in Free-Radical Cross-Linked Thermosets with Ultra-Low Dielectric Loss

“…Additionally, the flexibility of the Si−C and Si−O−Si structures in the cross-linkers increases the mobility of the cross-linked network, thereby reducing the material's T g . 34 Although this property of silanes and siloxanes is beneficial for producing flexible materials such as elastomers, it poses a disadvantage for electronic packaging applications. Nonetheless, the T g of these three cross-linked samples has reached the level of commonly used high-T g epoxy-based FR-4 substrates, 35 indicating that the materials obtained in this study can still meet typical application requirements.…”

“…This is first due to the lower functional group content of the silicon-containing cross-linkers (two functional groups per molecule) compared to the two control cross-linkers (three or more functional groups per molecule), resulting in a relatively lower cross-link density of the products. Additionally, the flexibility of the Si–C and Si–O–Si structures in the cross-linkers increases the mobility of the cross-linked network, thereby reducing the material’s T g . Although this property of silanes and siloxanes is beneficial for producing flexible materials such as elastomers, it poses a disadvantage for electronic packaging applications.…”

Investigating structure and dynamics of unentangled poly(dimethyl-co-diphenyl)siloxaneviamolecular dynamics simulation

“…Recently, Zhu et al showed the influence of the phenyl units on the atomic structures of the methyl- co -phenyl polysiloxane, with moderately high phenyl ratios of 31.6 mol% and 30.7 mol% for PDMS- co -PMPS and PDMS- co -PDPS, respectively. 33 However, most of the previous works focus on exploring the structural and mechanical properties separately and pay less attention to their connection. Consequently, the interplay between the two properties is not well understood, especially for cases with high phenyl content, thus leaving an understanding of the influence of the phenyl content on the properties of the copolymer somewhat unclear.…”