Reversible amine solubilization of cured siloxane polymers

Abstract

SynopsisWe report that aliphatic primary and secondary amines completely solubilize crosslinked silicone resins and rubber compositions at room temperature. The solubilization is attributed to nucleophilic cleavage of Si-0 bonds by amines, which apparently occurs selectively at crosslinking sites. The selectivity may reflect the presence of three oxygen atoma at such sites, which are expected to enhance the electrophilicity of silicon. On evaporation of amine, crosslinks are apparently regenerated as evidenced by solubility characteristics as well as f i l m properties of the reclaimed silicones. In addition to their theoretical interest, these results are potentially important from the standpoint of commercial applications as well, including the possible reclaiming of silicone-constituted furniture molds and the coating of heat-sensitive materials.During the course of studies on the application of solubility parameter methods for swelling cured we have found that aliphatic primary and secondary amines completely solubilize crosslinked siloxane polymers at room temperature. A major objective of this research was the development of solvent-based methods for facilitating the recovery of spores from plastic and rubbery materials utilized in spacecraft components. This goal was conveniently accomplished in high yields in the case of representative silicones by treatment with amines followed by plate counting methods (these results will be submitted elsewhere). Nevertheless, the unexpected finding of complete solubilization of cured silicones by amines prompted further studies on the nature of this interaction. The results are reported herein which indicate that amines react selectively at Si-0 crosslinking sites by nucleophilic substitution, as illustrated in eq. (1). Furthermore, the reversibility of this reaction is evidenced by the reformation of crosslinked sites on evaporation of amine. In addition to their theoretical interest, these results are potentially important from a technological standpoint as well, including the possible applications of reclaiming silicone-constituted furniture molds and coating of heat-sensitive materials.Initial studies were conducted with Dow Corning DC 840 silicone resin, which possesses a phenyl methyl polysiloxane backbone. The prepolymer also contains silanol (Si-OH) sites which are converted into Si-0-Si crosslinkages during curing. After curing at 24OOC for 1 hr, 50-mg samples (as cubes approximately 3 mm on a side) were suspended in 2 ml m i n e solvent

Characterization of ethanolysis products of poly(dimethylsiloxane) species by electrospray ionization tandem mass spectrometry

“…Sample partial degradation is a popular way of simplifying molecules to be mass‐analyzed, providing that the treatment is sufficiently controlled to allow the structure of the original polymer to be reconstructed . With the aim of recycling room temperature vulcanized silicone rubbers, Pappas and co‐workers developed an aminolysis process enabling a complete dissolution of the cross‐linked silicone network . These highly insoluble materials were transformed into smaller, hence soluble, linear species, using a chemical treatment that specifically cleaved bonds at branching points.…”

“…[9][10][11][12][13] With the aim of recycling room temperature vulcanized silicone rubbers, Pappas and co-workers developed an aminolysis process enabling a complete dissolution of the cross-linked silicone network. [14,15] These highly insoluble materials were transformed into smaller, hence soluble, linear species, using a chemical treatment that specifically cleaved bonds at branching points. The specific bond cleavage of tri-and/or tetra-functional siloxane units (respectively named T and Q according to the Si nomenclature) of cross-linked polymers was proposed to occur through a nucleophilic substitution of the amine, leading to both hydroxy-and amino-terminated polysiloxane oligomers.…”

Polysiloxane depolymerization with dimethyl carbonate using alkali metal halide catalysts

“…Many depolymerization reagents have been reported, such as alcohol [1][2][3], hydrogen chloride [4,5], thionyl chloride [6][7][8][9] and amines [10][11][12][13][14][15]. Alcohol is the most common reagent.…”

A New Route for Preparation of Hydrophobic Silica Nanoparticles Using a Mixture of Poly(dimethylsiloxane) and Diethyl Carbonate

“…Commercial poly(dimethylsiloxanes) (code name: PDMS-100, linear, -CH3 terminated, viscosity 95-105 mm 2 /s molecular weight ~6000 Da and degree of polymerization 35-65), (code name: PDMS-50, linear, -CH3 terminated, viscosity 45-55 mm 2 /s, molecular weight ~3500 Da and degree of polymerization [23][24][25][26][27][28] and poly(dimethylsiloxane) (code name: PDMS-20, linear, -CH3 terminated, viscosity 18-22 mm 2 /s, molecular weight ~2000 Da and degree of polymerization [13][14][15]. Diethyl carbonate containing ≥99.0 wt % of (C2H5O)2CO, n-hexane containing ≥99.0 wt % of C6H6 and hexamethyldisilazane (HMDS) was obtained by Sigma Aldrich (Hamburg, Germany).…”