Autoxidation: catalyst-free route to silicone rubbers by crosslinking Si–H functional groups

2019 ◽  
Vol 21 (23) ◽  
pp. 6483-6490 ◽  
Author(s):  
Michael Y. Wong ◽  
Alyssa F. Schneider ◽  
Guanhua Lu ◽  
Yang Chen ◽  
Michael A. Brook
Keyword(s):  
Functional Groups ◽  
Elevated Temperatures ◽  
Silicone Elastomers ◽  
Catalyst Free ◽  
Silicone Oils ◽  
Silicone Rubbers ◽  
Free Oxidation

Catalyst-free oxidation of HSi-containing silicone oils at elevated temperatures reliably produces silicone elastomers.

Polymer oxidation catalyst containing acidic functional groups

1981 ◽  
Vol 46 (5) ◽  
pp. 1237-1247
Author(s):  
Zdeněk Prokop ◽  
Karel Setínek
Keyword(s):  
Functional Groups ◽  
Elevated Temperatures ◽  
Redox Properties ◽  
Oxidation Catalyst ◽  
Carbon Clusters ◽  
Oxidation Activity ◽  
Redox Sites ◽  
Styrene Divinylbenzene ◽  
Proportional Decrease ◽  
Polymer Oxidation

The catalyst containing redox sites in addition to acid functional groups was prepared by sulphonation of a macroporous chloromethylated styrene-divinylbenzene copolymer with concentrated sulphuric acid at elevated temperatures. Its activity was tested for the oxidation of 2-propanol by molecular oxygen at 120 °C and was found to be comparable to that of the iridium on carbon catalyst.Neutralisation of acid functional groups by alkali metal led to proportional decrease in the oxidation activity. The results of EPR spectroscopic study of these catalysts show that the redox properties of the polymer are caused by carbon clusters which are capable of electron exchange.

scholarly journals The cumene/O2 system: a very simple tool for the radical chain oxidation of some functional groups

2017 ◽  
Vol 41 (15) ◽  
pp. 6981-6985 ◽  
Author(s):  
A. Malekafzali ◽  
K. Malinovska ◽  
F. W. Patureau
Keyword(s):  
Functional Groups ◽  
Radical Chain ◽  
Oxidation Method ◽  
Chain Oxidation ◽  
Metal Free ◽  
Radical Chain Oxidation ◽  
System A ◽  
Simple Tool ◽  
Free Oxidation

Just boil it in cumene! A general metal-free oxidation method is described.

Light Directs Monomer Coordination in Catalyst-Free Grignard Photopolymerization

2021 ◽  
Author(s):  
Eliot Woods ◽  
Alexandra Berl ◽  
Leanna Kantt ◽  
Michael Wasielewski ◽  
Brandon E. Haines ◽  
...  
Keyword(s):  
Conjugated Polymers ◽  
Radical Anion ◽  
Elevated Temperatures ◽  
Spectroscopic Studies ◽  
Computational Investigation ◽  
Catalyst Free ◽  
Active Layers ◽  
End Groups ◽  
Type Coupling

π-Conjugated polymers can serve as active layers in flexible and lightweight electronics, and are conventionally synthesized by transition-metal-mediated polycondensation at elevated temperatures. We recently reported a photopolymerization of electron-deficient heteroaryl Grignard monomers that enables the catalyst-free synthesis of n-type π-conjugated polymers. Herein we provide an experimental and computational investigation of the mechanism of this photopolymerization. Spectroscopic studies performed <i>in situ</i> and after quenching reveal that the propagating species is a radical anion with halide end groups. DFT calculations for model oligomers suggest a Mg-templated S<sub>RN</sub>1-type coupling, in which Grignard monomer coordination to the radical anion chain avoids the formation of free sp<sup>2</sup> radicals and enables C–C bond formation with very low barriers. We find that light plays an unusual role in the reaction, photoexciting the radical anion chain to shift electron density to the termini and thus favor productive monomer binding.

scholarly journals Evaluation of the influence of crosslink density and penetrant size on the diffusion properties of silicone oils into silicone elastomers

2019 ◽  
Author(s):  
Jonas Daenicke ◽  
Dirk W. Schubert ◽  
Mikael Hedenqvist ◽  
Erik Linde ◽  
Thomas Sigl ◽  
...  
Keyword(s):  
Crosslink Density ◽  
Silicone Elastomers ◽  
Silicone Oils ◽  
Diffusion Properties

Network Scission Processes in Peroxide Cured Methylvinyl Silicone Rubber

1967 ◽  
Vol 40 (2) ◽  
pp. 629-634
Author(s):  
D. K. Thomas
Keyword(s):  
Silicone Rubber ◽  
Elevated Temperatures ◽  
Main Chain ◽  
Methyl Groups ◽  
Chain Polymer ◽  
Filled Rubber ◽  
Oxidative Reactions ◽  
Silica Filler ◽  
Silicone Rubbers ◽  
Hydrolysis Of

Abstract In what appeared to be a complex system it transpires that network scission in methylvinyl silicone rubbers at temperatures below 250° C is due largely to hydrolytic reactions in the main chain polymer. At temperatures of 250° C and above there are indications that a significant amount of scission arises from oxidative reactions in the crosslinks, and that this reaction is catalyzed by acidic residues in the rubber. There is no indication that acidic byproducts of the vulcanization reaction catalyze the hydrolysis of siloxane bonds in the polymer. In conventional heat aging tests in which the rubber remains in an unstrained condition the effects of hydrolysis will only be observed if the concentration of water in the system is allowed to rise. Under these circumstances softening will occur because of a shift in the position of equilibrium in the reaction ∼Si—O—Si—O∼ + H2O→∼Si—OH+ HO—Si—O∼ On aging the material in a well ventilated situation the effects of hydrolysis are not seen and the silicone rubber becomes brittle after long exposure at high temperature. This embrittlement must result from additional crosslinking caused by oxidative reactions in the methyl groups of the main chain polymer. When the rubber is used in compression or tension, hydrolytic scission will affect performance, and in applications of this sort it is important to dry the rubber before use and prevent access of moisture to the component during use. With filled rubber the silica filler is a further source of moisture and drying needs to be carried out at elevated temperatures immediately before use. In order to improve the confined heat aging performance of silicone rubber an alternative filler to fine silica is needed which does not have the same affinity for water. It may be, however, that ability to reinforce silicone rubber and affinity for water are inseparable.

Solvent- and catalyst-free, quantitative protection of hydroxyl, thiol, carboxylic acid, amide and heterocyclic amino functional groups

2016 ◽  
Vol 18 (23) ◽  
pp. 6209-6214 ◽  
Author(s):  
Mia L. Jawor ◽  
Basil M. Ahmed ◽  
Gellert Mezei
Keyword(s):  
Carboxylic Acid ◽  
Functional Groups ◽  
Acid Amide ◽  
Waste Materials ◽  
Carboxylic Acid Amide ◽  
Catalyst Free

Various substrates are quantitatively protected by 3,4-dihydro-2H-pyran at 125 °C in the absence of any additional chemicals, without generating any waste materials.

Influence of Fiber’s Surface State on Mechanical Properties and Fiber-Matrix Interaction of CFRP

2013 ◽  
Vol 690-693 ◽  
pp. 323-328
Author(s):  
J. J. Sha ◽  
Y.X. Zhang ◽  
J. Li ◽  
J. X. Dai ◽  
Z. Q. Wei ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Flexural Strength ◽  
Functional Groups ◽  
Carbon Fibers ◽  
Surface State ◽  
Elevated Temperatures ◽  
Fiber Surface ◽  
Flexural Test ◽  
Matrix Interaction ◽  
Fiber Matrix

In order to investigate the influence of carbon fiber’s surface state on the mechanical properties and the fiber-matrix interaction of CFRP, the change of surface state was achieved by thermal treatment of carbon fibers at elevated temperatures, and the surface state was characterized by XPS. The mechanical properties were measured from the flexural test. The CFRP reinforced with 600 °C treated fabrics containing the highest reactive functional groups, showed the highest flexural strength and modulus. But in the case of CFRP reinforced with 1500 °C treated fabrics containing the lowest reactive functional groups, exhibited the lowest flexural strength and modulus. Combining the mechanical properties with the microstructure analysis, the results indicated that the fiber-matrix interaction (strong or weak) depends on the relative percentage of reactive functional groups present on the carbon fiber surface.

PIFA-Mediated Oxidative Cyclization Reactions of α-Acyl Acrylamides: A Synthetic Route to Substituted Isoxazol-3(2H)-ones

Synthesis ◽  
2018 ◽  
Vol 50 (09) ◽  
pp. 1875-1882 ◽  
Author(s):  
Rui Zhang ◽  
Dewen Dong ◽  
Jingwen Yuan ◽  
Chitturi Rao ◽  
Qian Zhang ◽  
...  
Keyword(s):  
Intramolecular Cyclization ◽  
Oxidative Cyclization ◽  
Metal Catalyst ◽  
Synthetic Route ◽  
Cyclization Reactions ◽  
Reaction Conditions ◽  
Catalyst Free ◽  
Free Oxidation

An intramolecular cyclization of various α-acyl β-amino acrylamides in the presence of PIFA and TFA is described. This transformation features mild reaction conditions, simple execution, high chemo­selectivity, and metal catalyst-free oxidation, and thereby, provides not only an alternative protocol for the construction of N–O bond, but also an efficient and straightforward synthesis of substituted isoxazol-3(2H)-ones from readily available α-acyl acrylamides.

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