Protective space coatings: a ceramer approach for nanoscale materials

Macro Chemistry & Physics

2008

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A synthetic route was developed to prepare thermosetting methyl, cyclopentyl, and cyclohexyl substituted polysiloxanes with epoxide or amino end groups. Cycloalkene (cyclopentene or cyclohexene) and dichlorosilane gas were reacted at 180 °C, and at high pressure (2 MPa) to produce dicycloaliphatic dichlorosilane. Hydrolytic condensations of the dichlorosilanes were performed affording low molecular weight cyclic siloxane oligomers. Base catalyzed ring opening polymerization of the cyclic oligomers afforded the hydride‐terminated polysiloxanes. The hydride‐terminated polysiloxanes were then functionalized with glycidyl epoxide or aliphatic amine groups via hydrosilation reactions. The oligomers and polymers were characterized by 1H NMR, 13C NMR, 29Si NMR, FTIR, and GPC. The molecular weight of polydimethylsiloxane, polydicyclopentylsiloxane, and polydicyclohexylsiloxane oligomers were $\overline M _{\rm n}$ = 1 000, 1 200, and 1 500, respectively. The polydispersity index of all the cyclic oligomers was ≈1.15. Differential scanning calorimetry (DSC) was used to evaluate the crosslinking reaction and the glass transition temperature of the thermally cured systems. Crosslinking occurred at 120 °C and the Tg of the methyl, cyclopentyl, and cyclohexyl functionalized siloxanes were found to be at −104, −93, and −82 °C, respectively.magnified image

Section: Full Papermentioning

confidence: 99%

Synthesis of Amine and Epoxide Telechelic Siloxanes

Chakraborty

Macro Chemistry & Physics

2008

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“…The average time to obtain a 13 C spectra was 2 h and 20 min. Hexamethylbenzene (HMB) methyl peak was used as an internal standard and referenced to d % 17.3 ppm for 13 C spectra and 29 Si used 3-(trimethylsilyl)-1-propanesulfonic acid sodium salt (DSS) referenced to d ¼ 1.46 ppm relative to TMS at d ¼ 0 ppm.…”

Section: Solid-state 13 C and 29 Si Nmr Analysismentioning

confidence: 99%

“…for Si-O-Si and Si-OH fragments within a sol-gel material, however no information was presented on the overall network structure. [13] In addition, the physical and mechanical properties of these modified materials were found to be appreciably different from the unmodified components. [9][10][11] In this study, a mixed metal-oxo hybrid material will be investigated with a cycloaliphatic epoxide and triethoxysilane functionalized polysiloxane of high molecular weight as the continuous phase.…”

Section: Introductionmentioning

confidence: 99%

“…Methyl, cyclopentyl, and cyclohexyl substituted polysiloxanes were formulated with a variety of sol-gel precursors (tetraethylorthosilicate oligomers, titanium(IV) iso-propoxide, zirconium(IV) propoxide, and zinc acetate). Phase-modulated FT-IR, X-ray photoelectron spectroscopy, solid state 29 Si NMR, and solid state 13 C NMR were used to investigate the internal structure of the mixed metal-oxo/silicon-oxo colloids prepared within the cured polysiloxane matrix. Results indicate that the cycloaliphatic groups inhibit the complete hydrolysis and condensation of the pendant triethoxysilane group and reaction of the sol-gel precursors.…”

Section: Introductionmentioning

confidence: 99%

“…[8][9][10][11][12] Also, application of hybrid materials in the aerospace industry could provide protection against radiation as well as high energy particles that are present in a space environment. [13] In addition to the metal alkoxides reacting with each other, the polymer can be modified with pendant alkoxy silane groups, which can act as a coupling agent nucleating the development of metal-oxo-cluster growth. Thus, the in situ formed systems are well dispersed in comparison with post-added nanoparticles.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Mixed Sol‐Gel Precursors on the Metal‐Oxo Phase Within a UV‐Curable Silicone Hybrid Material

Dworak

Macro Chemistry & Physics

2006

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Summary: An inorganic hybrid material was produced using a polysiloxane binder and metal‐oxo‐clusters which were derived from sol‐gel precursors. The continuous phase is composed of an elastomeric polysiloxane functionalized with cycloaliphatic epoxide groups. Pendant alkoxy silane groups serve as a coupling agent to form a network between the metal‐oxo‐clusters and the crosslinked polysiloxane. Methyl, cyclopentyl, and cyclohexyl substituted polysiloxanes were formulated with a variety of sol‐gel precursors (tetraethylorthosilicate oligomers, titanium(IV) iso‐propoxide, zirconium(IV) propoxide, and zinc acetate). Phase‐modulated FT‐IR, X‐ray photoelectron spectroscopy, solid state 29Si NMR, and solid state 13C NMR were used to investigate the internal structure of the mixed metal‐oxo/silicon‐oxo colloids prepared within the cured polysiloxane matrix. Results indicate that the cycloaliphatic groups inhibit the complete hydrolysis and condensation of the pendant triethoxysilane group and reaction of the sol‐gel precursors. Analysis also indicated that the metal‐oxo‐clusters were comprised of mixed species of sol‐gel precursors resulting in hetero‐bonded (SiOMetal) colloids.Possible network compositions of the cured material (a) specific metal‐oxo‐clusters, (b) hetero‐bonded metal‐oxo‐clusters, and (c) core/shell type metal‐oxo‐cluster configuration.magnified imagePossible network compositions of the cured material (a) specific metal‐oxo‐clusters, (b) hetero‐bonded metal‐oxo‐clusters, and (c) core/shell type metal‐oxo‐cluster configuration.

Mechanical and film properties of thermally curable polysiloxane

Chakraborty

J of Applied Polymer Sci

2009

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Telechelic glycidyl epoxide siloxanes substituted with either methyl, cyclopentyl, or cyclohexyl groups were cured thermally with corresponding telechelic aliphatic amine. Also, the three glycidyl epoxide functionalized siloxanes were homopolymerized via a photoinitiated cationic mechanism. Both the UV and thermal curing were performed by formulating with reactive diluents. The mechanical properties, viscoelastic behavior, and coatings properties of the thermally cured siloxanes were studied. In addition, the X-ray measurements were performed. The rate of polymerization increased with the increasing size of substituent on the siloxane backbone. The hardness, adhesion, and solvent resistance increased as the bulk of the substituent increased in the siloxane backbone. The release properties for adhesion and readhesion increased with increase in steric bulk of the backbone substituents. Crosslink density reduced and oxygen permeability increased with increase in siloxane substituent size. There was also an increase in the advancing and the receding contact angles with the increase in substituent size. The inverse dependency of substituent size and free volume was observed in the d-spacing of the X-ray data.