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.

Composite foams result from one-shot integration of unmodified lignin into a silicone pre-elastomer, where it performs as both crosslinker and reinforcing agent.

The exploitation of lignin, the second most abundant naturally occurring polymer on earth, has been hampered by its network structure, which makes it difficult to process. Hydrosilanes have previously been shown to convert aryl ethers to hydrolyzable silyl ethers in the presence of B­(C6F5)3. We demonstrate that the process is general and can be used to convert model lignin compounds to both aryl silyl ethers and alkanes. The relative reactivity of functional groups on model lignin compounds was found to be phenol > primary alcohol > methoxybenzene > alkyl silyl ethers. The process thus leads to cleavage of β-O-4, α-O-4, and methoxybenzene groups with concomitant silylation of phenolic and secondary alcohol groups. At longer time points provided sufficient silane was present, the full reduction of primary and secondary alcohols to alkyl groups was observed. Softwood lignin itself could only be partially solubilized (∼30%) even using excess hydrosilane and high catalyst loadings; the products were not characterized in detail. The lack of further degradation was attributed to its highly branched network structure containing 5-5, β-5, 4-O-5, and other linkages derived from coniferyl alcohol monomers that are not susceptible to reductive silylation. By contrast, over 95% of hardwood lignin was efficiently reduced/degraded into organosoluble products by the monofunctional hydrosilane HMe2SiOSiMe3 over a few hours at 50 °C. The molecular weight of the silylated products was consistent with oligomeric structures comprised of 3–8 linked aryl groups. This process holds promise to increase the accessibility to value-added products using lignin as a starting material.

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International audienceThe use of lignin as a filler for polymers to give composites provides both economic advantages and, in some cases, improved mechanical performance. The presence of lignin can also introduce certain advanced properties, including biodegradability, antimicrobial and antioxidant activity. Here we demonstrate that improved thermal insulation, thermal stability, and flame retardancy result when lignin is compounded with hydride-functionalized silicones to give elastomers and foams. In the absence of any additional inorganic flame retardant agent, the V-1 rating (UL-94) could be reached after chemical post-treatment of the materials with NH3 vapor to remove excess SiH groups (which were identified as a culprit for excessive flammability). The fire resistance was further improved to the V-0 rating (UL-94) by applying additional thermal post-treatment at 220 degrees C in air. These foams also demonstrated low thermal conductivity, which were comparable with pure silicone foams of similar density. The improved thermal stability is attributed to flame retardant silica char, lignin repolymerization and char and the ability of lignin to scavenge radicals