Theoretical analysis of hydrolysis of polydimethylsiloxane (PDMS)

Abstract

Silicones (polydimethylsiloxane, PDMS) are the materials currently used in most breast implants. ICP and FTIR analysis of the tissue capsule around aged breast implants and in vitro models show that Si-containing material is leaking from the PDMS implants. In this study, the hydrolysis of PDMS has been theoretically modeled using a semiempirical quantum mechanical method called AM1. The activation barrier for removing a methanol monomer was found to be +82 Kcal/mol while the removal of a methane monomer was +41 Kcal/mol. Using the same AM1 method, hydrolysis of the identical to Si-O-Si identical to bond also has been modeled for pentasilicic acid and, in this study, for 1,1,3,3,-fetramethyldisiloxane-1,3-diol. The barrier to the removal of a silicon-containing tetrahedron for both studies was found to be +27 Kcal/mol. This is approximately one and a half times smaller than the energy of that needed to remove a methyl group. The pentacoordinated silicon-activated transition state for hydrolysis of PDMS may provide an energetically favorable pathway for development of a surface that will enhance chemisorption of charged protein molecules, and such a pathway may show up in NMR studies of the hydrolysis of PDMS.

Kinetics of Ultraviolet and Plasma Surface Modification of Poly(dimethylsiloxane) Probed by Sum Frequency Vibrational Spectroscopy

“…In the future, it will be interesting to use SFG spectroscopy on isotope-labeled PDMS samples to elucidate detailed mechanistic pathways since it is possible that multiple multistep chemical reactions may be occurring at the same time. At the present time, we can only speculate on possible mechanisms for regeneration of CH 3 groups on the basis of our results and published literature. − , It has been suggested that the attack of radicals containing CH 3 groups, the reorientation of PDMS molecules at the surface during modification, and migration of PDMS molecules (or oligomers) from the bulk during modification could all contribute to CH 3 group regeneration. In our SFG experiments, we observe no significant change in reorientation of PDMS molecules at the surface during modification.…”

Long-Term Thermal Aging of Modified Sylgard 184 Formulations

“…These can be produced from a proposed reaction mechanism involving water interacting with Si–H groups; although the hydrosilylation reaction is an addition reaction between Si–H and vinyl groups in the presence of a catalyst, notably Pt, water can also attack Si–H to form Si-OH in the presence of the same catalyst [ 17 , 34 ]. Additionally, siloxanols can be created from the hydrolysis of PDMS, where a water molecule attacks a siloxane chain, resulting in a chain scission and two hydroxyl-terminated chains [ 74 , 75 , 76 ]. If a siloxanol encounters a silane, a new crosslink will form between the two moieties and H 2 gas will be produced.…”

Controllable Silane Water-Cross-Linking Kinetics and Curability of Ethylene−Propylene Copolymer by Amine Compounds

“…The AM1 calculation could yield to molecular structures, heats of formation, and transition-state energies. According to the procedure recommended by West et al, − the conformations of an intermediate for the hydrolysis and condensation were built by binding the oxygen atom of a nucleophilic complex to the silicon atom of an alkoxysilane and hydroxysilane, respectively, and then minimizing the energy with AM1 unrestricted Hartree−Fock (UHF). These UHF AM1-optimized geometries then were submitted to MOPAC saddle-point calculations to predict the transition state.…”