Photocured Simultaneous and Sequential PDMS/PMMA Interpenetrating Polymer Networks

Abstract

Photocured interpenetrating polymer networks (IPNs) of PDMS and PMMA were synthesized through a sequential route to form semi-IPNs and a simultaneous route to form graft IPNs. Experiments were designed to understand the effect of network architecture and PMMA concentration on IPN microstructure, thermal properties, mechanical properties, and chemical structure. At PMMA concentrations above 10 wt %, the microstructure in both IPN architectures consisted of a dispersed PMMA phase in a PDMS continuous phase, where the domain size and shape were found to depend on both the synthetic route and the PMMA concentration. The PMMA glass transition temperature in sequential IPNs was nearly unaffected by PMMA concentration, indicating that the PMMA and PDMS phases were poorly mixed. In contrast, the PMMA glass transition region in the simultaneous IPNs was complex. This was interpreted to indicate the presence of both mixed PDMS/PMMA and pure PMMA phases, the ratio of which depends on PMMA concentration. PeakForce Tapping was used to directly determine how differences in the extent of mixing impact the mechanical properties of the dispersed phases. In the simultaneous IPNs, the number of cross-links between the PDMS and PMMA networks was found to increase as a function of PMMA concentration. The PMMA molecular weight distribution remained constant with PMMA concentration in the sequential IPNs, whereas increasing PMMA concentration in the simultaneous IPNs substantially increased polydispersity and led to a bimodal molecular weight distribution. PMMA concentration also appears to play a minor role in determining PMMA stereoregularity in the simultaneous IPNs. Overall, this study demonstrates how structure/process relationships can be used to control properties in these hybrid elastomers.

Role of Nanoscale Heterogeneity in the Mechanical Performance of Hybrid Elastomers

“…These spherical domains have characteristic length scales on the order of 50–100 nm. While there is significant mechanical contrast observed between these domains, there still exists a degree of PDMS/PMMA mixing in both phases, as investigated in our prior work . The PDMS/PIBoMA graft-IPN in Figure b shows a qualitatively different morphology than that of the PDMS/PMMA material, with significantly smaller domain sizes and a lower degree of phase contrast between the PIBoMA-rich domains and the underlying matrix.…”

“…This understanding of the AFM phase data has been supported by the elemental contrast seen in electron microscope images, as reported in our previous work on PDMS/PMMA IPNs. 10 A constant phase angle range was used in the three images to highlight quantitative differences in phase contrast between the images. An inset where the phase angle range was reduced has also been added to the PDMS/PIBoMA graft-IPN image in Figure 2b to highlight local differences in tip−sample energy dissipation.…”

“…While there is significant mechanical contrast observed between these domains, there still exists a degree of PDMS/ PMMA mixing in both phases, as investigated in our prior work. 10 The PDMS/PIBoMA graft-IPN in Figure 2b shows a qualitatively different morphology than that of the PDMS/ PMMA material, with significantly smaller domain sizes and a lower degree of phase contrast between the PIBoMA-rich domains and the underlying matrix. The lower phase contrast could indicate a higher degree of polymer−polymer mixing in the 75/25 PDMS/PIBoMA graft-IPN, with the PIBoMA-rich phases having significant amounts of PDMS.…”

Correlating Nanomechanical Mapping and Single-Molecule Localization Microscopy for Local Properties in Interpenetrating Network Elastomers

“…In another study, we also investigated mixing in IPNs using dynamic mechanical thermal analysis (DMTA) for PDMS/PMMA IPNs with different synthesis routes and compositions. IPNs exhibited either a broad tan-delta peak in the PMMA glass transition range, suggesting that all dispersed domains consist of a mixture of PDMS and PMMA, or two peaks, suggesting that some domains are a mixture and others are pure PMMA . These studies provide a macroscopic perspective by averaging over a large sample volume, but there is minimal information at the local nanoscale level.…”

Multimorphic Materials: Spatially Tailoring Mechanical Properties via Selective Initiation of Interpenetrating Polymer Networks

“…[ 24 ] In another recent example, Beebe and coworkers demonstrated that semi‐IPNs (e.g., one cross‐linked and one uncross‐linked network) prepared from sequential polymerization of poly(siloxanes) and poly(methyl methacrylate) were better mixed than the chemically identical IPNs prepared using simultaneous polymerizations, which enabled moduli tunability of 2.5× (i.e., 20–50 MPa). [ 25,26 ] In these examples, the reliance on a single stimulus for initiation (e.g., light or heat, respectively) precluded the ability to spatially control morphology.…”