Synthesis of PDMS Microspheres.
Novel Synthesis of Triblock PDMS-PS-PDMS Copolymers JONATHAN R
A variety of methods have been developed for polydimethylsiloxane (PDMS) elastomer surface functionalization, particularly for the improvement of hydrophilicity. However, in addition to difficulties in avoiding undesired physical changes to the modified surface, including surface cracking, “hydrophobic recovery” frequently leads hydrophilically modified surfaces to completely return over time to their hydrophobic nature, with accompanying loss of accessible functional groups. Thiol–ene chemistry provides a mild and robust technology for synthetic elaboration. We demonstrate the introduction of thiol groups onto the PDMS surface via base-catalyzed equilibration of MTS ((MeO)3Si(CH2)3SH). Thiols in the product elastomer were shown to be located primarily at the air interface using EDX, XPS, and fluorescence labeling initially, and after extended periods of time: total thiol concentrations at the surface and in the bulk were established by complementary chemical titrations with DTDP (4,4′-dithiodipyridine) and iodine titrations in different solvents. The surface density of thiols was readily controlled by reaction conditions: the rate of hydrophobic recovery, which led to incomplete loss of accessible functional groups, was determined. Thiol–ene click chemistry was then used to introduce a variety of hydrophilic moieties onto the surface including a silicone surfactant and maleic anhydride, respectively. In the latter case, molecular functionalization with both small (fluorescent labels) and polymeric nucleophiles (poly(ethylene glycol), chitosan) could be subsequently induced by simple ring-opening nucleophilic attack leading to permanently functional surfaces.
Polydimethylsiloxane - Wikipedia
Poly(urethane-dimethylsiloxane) anionomers (PUR-PDMS) were synthesized in two- and three-stage process, with the use of isophorone diisocyanate (IPDI) and poly(oxytetramethylene) diol (PTMG), partially replaced by polydimethylsiloxane diols (PDMS) with different chain structures. 2,2-bis(hydroxymethyl)propionic acid (DMPA) neutralized with triethylamine (TEA) was used as the ionogenic component built into the polyurethane chain and ethylenediamine (EDA) as the extender. Studies on the thermal degradation using TGA analysis in nitrogen or air atmosphere enabled us to investigate the decomposition process and to evaluate the effect of the presence of polysiloxanes on the thermal stability of PUR-PDMS anionomers. The degradation in nitrogen took place in two stages, while in air the decomposition mechanism was more complicated and involved four stages. It was observed that the temperature corresponding to the maximum rate of the second decomposition stage decreases with an increase in the content of PDMS built-into the polymer chain, which indicates a small increase in the thermal stability of polysiloxane-modified PUR anionomers. From the preliminary performance tests it appears that the hydrophobic fragments of the built-in polysiloxane have a tendency to migrate towards the polymer surface in the produced PUR-PDMS coatings, with the advantage of the increased hydrophobicity but at the expense of a decreased abrasion resistance of the coatings.