Grafting vinyl silanes

Grafting reaction Reaction of a monomer and a polymer to form a grafted polymer or copolymer Grafting vinyl silanes onto polyolefins for crosslinked polyolefins acrylic acids onto polyolefins for hydrophilicity maleic anhydride onto polyolefins for compatabilization... 

The synthesis of PDMS macromonomers with vinyl silane end-groups and their free-radical copolymerization with vinyl acetate, leading to poly(vinyl acetate)-PDMS graft copolymers, was described 346). The copolymers produced were later hydrolyzed to obtain poly(vinyl alcohol)-PDMS graft copolymers. 

Fig. 17 Dependence of the grafted amount of PVFA (yc) on the initial volume fraction of VFA used to graft on vinyl silane-functionalized silica particles (xVfa)...

Moad also notes that the most common grafting modifications made to polyolefins are via maleic anhydride, maleate esters, styrene, maleimides, acrylates and their esters, and vinyl silanes. Other polymer systems (Fink, 2005) that undergo grafting are polystyrene/maleic anhydride (useful for PA6/PS blends), PVC/butylmethacrylate (for improved processi-bility), PET/nadic anhydride, starch/vinyl acetate and starch/methyl acrylate (for improved water resistance). 

Vinyl silanes are another class of graft monomers. These materials or oligomers made from them are used as release agents which prevent adhesive materials from sticking to a film or substrate (Fig. 2). Grafted silanes have also found use in bio-medical applications and in the modification of fine inorganic particulates, such as silicas. 

Very low density PE (VLDPE), 52 Vinizene BP 5-5, 449 Vinyl alkoxysilanes, 172 Vinyl silanes, 172 Vinyl trimethoxysilane grafted polyethylene, 172 Vinyltriethoxy-silane, 194 Virgin plastics, 51 Viscoelastic behavior, 225 Viscoelastic fluid, 622 Viscoelastic materials, 631 Viscosity of polyethylene hot melts, 633 Viscosity of polymers, 620 Viscosity of water, 620 Viscosity, 622... 

Modern electron processors offer high speed (high dose-rate) curing of low viscosity liquid coatings so that surface modification of films becomes practicable. A process has been developed for grafting vinyl monomers to polyolefin film surfaces with the aid of functional silane primers using electron initiated polymerization. 

In the vinyl silane cross-linking process Sioplas process) developed by Dow, an easily hydrolysable trialkoxy vinyl silane, CH2=CHSi(OR)3, is grafted onto the polyethylene chain, the site activation having been achieved with the aid of a small amount of peroxide. The material is then extruded onto the wire. When exposed to hot water or low-pressure steam, the alkoxy groups hydrolyze and then condense to form a siloxane cross-link ... 

Cross-linking of the outer casing is achieved by grafting a vinyl silane to polyethylene by means of a peroxide as part of the cable extrusion process. The chemistry is shown in Scheme 2.1. When the cable is subsequently soaked in water, the alkoxy silanes hydrolyse and crosslink within the matrix. It is an unresolved question whether polymers that have been modified by a free radical mechanism will survive for the expected lifetime of underground cables (ca. 75 years). 

A newer chemical method is to melt-blend polyethylene with vinyl trialkoxy silane and peroxide, grafting the silane as side-groups onto the polyethylene chain (Fig. 3.69). As long as it is kept very dry, the alkoxysilane groups are stable. After the grafted polyethyl-... 

Ramar and Alagar [28] compared the dielectric strengths of non-clay-reinforced ethylene-propylene-diene-tris(2-methoxyethoxy)vinyl silane-grafted and ethylene-propylene-polymethyl methacrylate blends. The values of dielectric strength, volume resistivity, surface resistivity, and arc resistance increased with increasing... 

The basic chemistry of this process is that a silane such as tri-methoxy vinyl silane is grafted on to polyethylene and following extrusion the insulated wire or pipe is exposed to hot water or steam. The silane groups react with the water to form cross links with the elimination of methanol (Figure 12.13) [11]. A tin catalyst such as dibutyl tin dilaurate speeds up the crosslinking reaction. 

A one step process was developed by BICC with Maillefer for power cables which eliminated the compounding stage (the Monosil process) [15], in which all the additives were mixed with the polymer and grafting performed in the cable extruder. Direct injection has been used to inject a liquid mixture of silane, peroxide and tin catalyst into an add-on mixer to make cable [4] and hot water pipe [16]. The water pipes were steam autoclaved for four hours at 110 °C, which was well below the softening point of the HDPE used and the resulting crosslinked pipes withstood 1000 hours in water at 95 °C with a wall stress of 4.4 N/mm [ ] As with peroxides there are health and safety issues. Tri-methoxy vinyl silane is both very flammable and toxic. 

Polyethylene can be crosslinked by decomposition of organic peroxides, hydrolysis of vinyl-silane grafted polyethylene or by high-energy (P or y) irradiation. Design a suitable experiment to determine the crosslink density and present the relevant equations. 

The Sioplas process was developed in 1968 by Midland Silicones (Dow Corning), using peroxide-activated grafting of vinyl silane onto the polymer chain, usually in compounding units or twin-screw extruders. The liquid silane/peroxide mixture is added to the polymer melt by membrane or piston pumps, producing a grafted granular product which, after a catalyst has been added, can be processed to cable, pipe or other finished parts. 

Copolymers of vinyl silane VTMO can also be bonded to polymer chains by copolymerization, to produce vinyl silane thylene or vinyl silane ethylene butyl acrylate. These can be processed in granular form together with the appropriate catalyst master batch in conventional extruders. They can thus be regarded as alternatives to the grafted versions above but, due to their production process, they are only available as high pressure polyethylene grades. 

Gross-Linking. A variety of PE resins, after their synthesis, can be modified by cross-linking with peroxides, hydrolysis of silane-grafted polymers, ionic bonding of chain carboxyl groups (ionomers), chlorination, graft copolymerization, hydrolysis of vinyl acetate copolymers, and other reactions. 

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