Experiments and Simulations: Enhanced Mechanical Properties of End-Linked Bimodal Elastomers

• Published in: Macromolecules Vol. 41; no. 21; pp. 8231 - 8241
• Main Authors: Genesky, Geoffrey D, Aguilera-Mercado, Bernardo M, Bhawe, Dhananjay M, Escobedo, Fernando A, Cohen, Claude
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 11.11.2008
• Subjects: Applied sciences; Exact sciences and technology; Inorganic and organomineral polymers; Physicochemistry of polymers; Properties and characterization; Dimethylsiloxane polymer; Structure effect; Monte Carlo method; Tensile stress; Swelling; Computer simulation; Stress strain relation; Mechanical properties; Experimental study; Silicone elastomer
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma801065x

We report on stress−strain and swelling results for polydimethylsiloxane bimodal networks, studied both experimentally and via Monte Carlo simulations. These end-linked networks were formed with negligible extent of soluble fractions, and reasonable agreement is found between experimental results and simulation data. We examine the variation in microstructure for networks with different concentrations of short chains. When the concentration of short chains is low, these chains aggregate during the end-linking process and lead to a heterogeneous network structure, while networks formed with higher short chain concentrations are more homogeneous. Short chains that are long enough to initially have a Gaussian conformation also produce the characteristic stress upturn and enhanced toughness previously reported in bimodal networks with non-Gaussian short chains. We find that it is the limited extensibility of the short chains at high concentrations and not the cluster formation of short chains at low concentrations that leads to the enhanced mechanical properties of these elastomers.