Rhodium(I)-catalysed cross-linking of polysiloxanes conducted at room temperature

Self-Restructuring of Polyhydromethylsiloxanes by the Hydride Transfer Process: A New Approach to the Cross-Linking of Polysiloxanes and to the Fabrication of Thin Polysiloxane Coatings

The branching and cross-linking of siloxane polymers are important processes in silicone technology. A new type of such a process has been developed, which is a self-restructuring of linear polyhydromethylsiloxane (PHMS). This process involves the reorganization of the PHMS to form a highly branched siloxane polymer or finally a cross-linked siloxane network. It occurs through the transfer of a hydride ion between silicon atoms catalyzed by tris(pentafluoromethyl)borane. Its advantage over existing branching and cross-linking reactions is that it runs at room temperature without a low-molecular-weight cross-linker in the absence of water, silanol groups, or other protic compounds and it does not use metal catalysts. The study of this process was carried out in toluene solution. Its course was followed by ¹H NMR, ²⁹Si NMR and FTIR, SEC, and gas chromatography. A general mechanism of this new self-restructuring process supported by quantum calculations is proposed. It has been shown that a linear PHMS self-restructured to a highly branched polymer can serve as a pure methylsiloxane film precursor.

Block-copolymeric maltodextrin-based amphiphilic glycosilicones as surface-active systems

An efficient synthetic strategy that includes protection–modification–deprotection consequence was successfully developed to obtain novel water-soluble, amphiphilic, surface-active maltodextrin-based glycosilicones.

RECYCLING BEHAVIOR OF THERMOREVERSIBLY DIELS–ALDER CROSSLINKED EPM

The recyclability of thermoreversibly Diels–Alder (DA) crosslinked EPM has been studied. The retro DA reaction dominates over the dehydration–aromatization process of the DA adduct. Moreover, a negative influence of air occurred as a result of a crosslinking in air flow. Nevertheless, rubber compounds prepared from EPM-g-furan and carbon black can be recycled several times without losing mechanical strength, a feature attributed to a strong antioxidant effect of the carbon black.

Recyclability of Photoinduced Cross-Linked EPM Rubber with Anthracene-Grafted Groups: Problems and Their Solutions

In this paper, we present the formation of reversible covalently cross-linked networks in ethylene propylene rubber with grafted anthracene groups (EPM-g-AN) based on the principles of photoinduced anthracene dimerization. First, an industrial-grade EPM rubber grafted with maleic anhydride functional groups (EPM-g-MA) was modified with 9-anthracenemethanol. By irradiating EPM-g-AN with UV light (365 nm), the anthracene moieties dimerize via [4 + 4]cycloaddition, forming a covalent network. The network cleavage proceeds at high temperatures (>170 °C), even if with considerable (chemical) degradation. Furthermore, one of the degradation routes has been identified by ¹H NMR to occur via the ester bond cleavage releasing 9-anthracenemethanol. Nevertheless, the reversibility of cross-linking has been achieved by performing the reverse reaction in decalin. The UV-vis spectroscopy clearly shows that the de-cross-linking process in these conditions is due to the anthracene dimer cleavage. Although the recovery in mechanical properties upon recycling is yet to be optimized, the disclosed results pave the way toward the use of anthracene chemistry in thermally reversible networks with possible industrial perspective applications.

Fabrication and electrical study of large area free-standing membrane with embedded GaP NWs for flexible devices

Flexible optoelectronic structures are required in a wide range of applications. Large scale modified silicone-embedded n-GaP nanowire arrays of a record 6 µm thin membranes were studied. A homogeneous silicone encapsulation was enabled by G-coating using a heavy-load centrifuge. The synthesized graft-copolymers of polydimethylsiloxane (PDMS) and polystyrene demonstrated two times lower adhesion to Si compared to standard PDMS, allowing 3 square inch area high quality silicone/nanowire membrane mechanical release, preserving the growth Si substrate for a further re-use after chemical cleaning. The 90% transparent single-walled carbon nanotubes electrical contacts to the embedded n-GaP nanowires demonstrated mechanical and electrical stability. The presented methods can be used for the fabrication of large scale flexible inorganic optoelectronic devices.

A metal-free radical technique for cross-linking of polymethylhydrosiloxane or polymethylvinylsiloxane using AIBN

A new method was developed for the metal-free cross-linking of silicone rubbers. This process uses azobisisobutyronitrile (AIBN) to selectively react with Si-H and vinyl groups as a free-radical initiator for the thermal curing of polymethylhydrosiloxane (PMHS) and polymethylvinylsiloxane (PMVS). The AIBN-initiated curing reaction between the Si-H groups of PMHS generated Si-O-Si and Si-Si cross-links. In contrast, PMVS was cured via the formation of C-C bonds through "methyl-vinyl" and "vinyl-vinyl" mechanisms. Curing reactions were performed at 80-120 °C in air and confirmed by 13C and 29Si solid state NMR analyses and swelling trials.

Crystal structure of dichlorido(N-o-tolyl-1,1-di-p-tolylphosphanamine–κ1 P)-(methoxydi-p-tolylphosphane-κ1 P)palladium(II), C36H39Cl2NOP2Pd

C36H39Cl2NOP2Pd, orthorhombic, Pbca (no. 61), a = 19.209(13) Å, b = 15.144(11) Å, c = 24.011(19) Å, V = 6985(9) Å3, Z = 8, R gt(F) = 0.0292, wR ref(F 2) = 0.0867, T = 100 K.

The crystal structure of trans-carbonyl-(diphenylcyclohexyl-phosphine-κP)iodidomethyl-(2-oxopyridin-1(2H)-olato-κ2 O,O′)rhodium(III), C25H28INO3PRh

C25H28INO3PRh, monoclinic, P21/c (no. 14), a = 11.339(4) Å, b = 9.887(5) Å, c = 23.069(9) Å, β = 91.125(5)°, Z = 4, V = 2585.7(19) Å3, R gt(F) = 0.0463, wR ref(F 2) = 0.1093, T = 293(2) K.

Platinum-catalyzed reactions between Si-H groups as a new method for cross-linking of silicones

The platinum-catalyzed self-cross-linking of polymethylhydrosiloxane at RT in air was performed for the first time and proved by 1H, 13C, and 29Si SSNMR and swelling measurements. Quantum chemical modeling of possible structures was investigated. Platinum (0) and (ii) complexes were used as catalysts between the Si-H groups of polymethylhydrosiloxane. Karstedt's catalyst leads to Si-O-Si and Si-Si bond formation, but cis-[PtCl2(BnCN)2] generates predominantly Si-O-Si cross-links. cis-[PtCl2(BnCN)2] allows creating high-quality silicone rubbers without visible mechanical defects. This cross-linking approach can be used to obtain new Si-H-containing silicone materials.