Biocatalytic Synthesis of Silicone Polyesters

Abstract

The immobilized lipase B from Candida antarctica (CALB) was used to synthesize silicone polyesters. CALB routinely generated between 74-95% polytransesterification depending on the monomers that were used. Low molecular weight diols resulted in the highest rates of esterification. Rate constants were determined for the CALB catalyzed polytransesterifications at various reaction temperatures. The temperature dependence of the CALB-mediated polytransesterifications was examined. A lipase from C. rugosa was only successful in performing esterifications using carboxy-modified silicones that possessed alkyl chains greater than three methylene units between the carbonyl and the dimethylsiloxy groups. The proteases alpha-chymotrypsin and papain were not suitable enzymes for catalyzing any polytransesterification reactions.

Catalytic Systems for the Cross‐Linking of Organosilicon Polymers

“…Upon examination of the trypsin catalytic triad Ser-195,H is-57, and Asp-105, it became apparent that the serine's hydroxyl addition to the silane is the preferredr eactionp athway for this condensation, analogoustot raditional trypsin chemistry. [107b] With the use of immobilized lipase Bf rom Candida antartica (Novozym 435), Zelisko and his group were also able to synthesize silicone-polyesters [108] and silicone-polyamides [109] even at temperatures above the denaturation temperature of the free enzyme. The authors used in this case hydroxyalkyl-or aminoalkyl-terminated PDMS together with as iloxane-diester as cross-linker.O ther proteases like papain, a-chymotrypsin, or lipase from C. rugose showed poor or no cross-linking activity.…”

Biocatalysis in Silicon Chemistry

“…[83] There was, however, as trong correlation between the length of the alkyl chain lengthb etween the reactive carboxylate and the first silicon atom. [83,84] Despite our hopes that we couldc ontinueb yu sing CRL, we wereu nable to produce high-molecular-weightp olymers. This enzymeo nly had the capacity for producing di-and trimers.…”

Synthesis of polyesters containing disiloxane subunits: Structural characterization, kinetics, and an examination of the thermal tolerance of Novozym-435

“…Synthesis of 1,3-bis(3-carboxypropyl)-1,1,3,3-tetramethyldisiloxane dimethyl ester (5, CPr-TMDS-DME). Diester 5 was synthesized using previously published protocols [23]. Briefly, 5.01 g (16.34 mmol) of 1,3-bis(3-carboxypropyl)-1,1,3,3-tetramethyldisiloxane was refluxed in 15 mL of methanol in the presence of 5 mol% p-toluene sulfonic acid for 4 h to yield diester 5 as a clear and colourless liquid in 86% yield.…”

“…Disiloxane polyesters were prepared under solvent-free conditions using 5 wt.% N435 (with respect to the mass of the combined monomers) following previously provided protocols with minor modifications [23]. Typically, diol 4 was combined in a 1:1 mole ratio with diester 5, using approximately 0.5-0.75 g of the monomers.…”

“…The enzymatic synthesis of polyesters derived exclusively from siloxane-derived monomers has been described [23]. The number of siloxane units of the diol monomer did not affect the polymerization kinetics or the activation energy of the polymerization process [23].…”