Polysiloxane-polyetherimide copolymers

These materials are developed from the polyetherimides introduced by General Electric (see also Section 18.14.2). At the time of writing one grade, Ultem Siltem STM 1500, is being offered. It is of particular interest as a material for wire and cable insulation, as it not only has excellent flame resistance coupled with low smoke generation but also avoids possible toxic and corrosion hazards of halogenated polymers. This can be of importance where there are possible escape problems in the event of a fire, such as in tunnels, aircraft and marine (particularly submarine) vessels. 

This polymer has a good strength for a flexible silicone polymer coupled with the good heat resistance which may be expected from its components, together with an outstanding value for the limiting oxygen index of 48. 

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Also of interest is the polysiloxane-polyetherimide copolymer marketed as Ultem Siltem STM1500, which is considered further in Chapter 29. 

Table 29.6 Some typical properties of a polysiloxane-polyetherimide copolymer (Ultem Siltem STM 1500)...

Information on the synthesis of the polyetherimide—polysiloxane block copolymers has not been disclosed. Many other synthetic methods for preparing block copolymers have been described (19,20,25) but are currendy not beheved to be commercially important. 

Polyether-polyester polyol hybrids, 25 472 Polyetherimide-polysiloxane block copolymers, 24 698, 704, 708... 

Polyetherimide-polysiloxane multiblock copolymers, 24 716 Polyetherimides (PEI), 10 217—218 Polyether impression materials, 8 332-333 Poly(ether ketones) (PEK), 10 197-199 Polyether polyols, 25 455-456,464,468t, 470 propylene oxide polymerization to, 20 793-794, 812 Poly ethers, 12 663... 

S—EB—S (compounds) polyurethane/elastomer block copolymers polyester/elastomer block copolymers polyamide/elastomer block copolymers polyetherimide/polysiloxane block copolymers polypropylene/EPDM or EPR blends polypropylene/EPDM dynamic vulcanizates polypropylene/butyl rubber dynamic vulcanizates polypropylene/natural rubber dynamic vulcanizates polypropylene/nitrile rubber dynamic vulcanizates PVC/ nitrile rubber blends... 

The polyetherimide—polysiloxane multiblock copolymers are relatively hard (about 70 on the Shore D scale). Their main application is flame-resistant wire and cable covering (24), where they combine very low flammability with a low level of toxic products in the smoke. This unusual and vital combination of properties justifies their relatively high price, about 37/kg, at a specific gravity of about 1.2. 

Besides the thermoplastic elastomers based on poly(styrene-6-elastomer- -styrene) block copolymers, five others are of commercial importance polyurethane/elastomer block copolymers, polyester/elastomer block copolymers, polyamide/elastomer block copolymers, polyolefin block copolymers, and polyetherimide/polysiloxane block copolymers. All five have the multiblock A-B-A-B. structure. The morphology of the polyurethane, polyester,... 

In the polyolefin-based block copolymers, the elastomeric segment is typically a copolymer of ethylene and 1-octene. It is nonpolar and very stable, as is the polysiloxane elastomer segment in the polyetherimide/polysiloxane block copolymers. 

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