Polyamide block copolymers

Multiblock Copolymers. Replacement of conventional vulcanized mbber is the main appHcation for the polar polyurethane, polyester, and polyamide block copolymers. Like styrenic block copolymers, they can be molded or extmded using equipment designed for processing thermoplastics. Melt temperatures during processing are between 175 and 225°C, and predrying is requited scrap is reusable. They are mostiy used as essentially pure materials, although some work on blends with various thermoplastics such as plasticized and unplasticized PVC and also ABS and polycarbonate (14,18,67—69) has been reported. Plasticizers intended for use with PVC have also been blended with polyester block copolymers (67). 

A wide range of polyether-polyamide block copolymers were first offered by Atochem in 1981 under the trade name Pebax. These are made by first producing a low molecular weight polyamide using an excess of dicarboxylic acid at a temperature above 230°C and under a pressure of up to 25 bar. This is then combined with a polyether by reaction at 230-280°C under vacuum (O.l-lOTorr) in the presence of a suitable catalyst such as Ti(OR)4. 

Table 18.16 Selected properties of polyether-polyamide block copolymers of the Pebax type (After Deleens, 1987)...

Polystyrene-polyamide block copolymer synthesis 63> also involves some kind of site transformation. The polystyrene precursor is fitted at chain end with a function... 

Polyamide/rubber blends, 20 361 Polyamide block copolymers, 24 704, 708 Polyamide composite membranes, 21 633 Polyamide-elastomer block copolymers, 24 698... 

Polyamide block copolymer with polyether/polyester PVC... 

In contrast, organophilic PV membranes are used for removal of (volatile) organic compounds from aqueous solutions. They are typically made of rubbery polymers (elastomers). Cross-linked silicone rubber (PDMS) is the state-of-the-art for the selective barrier [1, 43, 44]. Nevertheless, glassy polymers (e.g., substituted polyacetylene or poly(l-(trimethylsilyl)-l-propyne, PTMSP) were also observed to be preferentially permeable for organics from water. Polyether-polyamide block-copolymers, combining permeable hydrophilic and stabilizing hydrophobic domains within one material, are also successfully used as a selective barrier. 

Table 4.4 Carbon dioxide (A)/nitrogen (B) permselectivity characterization for polyimide, polyurethane and polyamide block-copolymers containing polyether segments.

By a similar degradation and graft copolymer formation mechanism block copolymers could be obtained by reactive extrusion. A prerequisite is the presence of functional groups and the interaction of these groups with immiscible polymers during melt processing. Several polyamide block copolymers are synthesised by a melt-modification process. 

The use of modified PTFE micropowder in combination with the mechanism of the controlled degradation of polyamide and the utilisation of melt-mixing devices like a lab melt mixer or twin-screw extruders are the basis of the reactive compa-tibilisation of the completely immiscible polymers. On the basis of the discussed mechanism PTFE polyamide block copolymers are formed by reactive extrusion ... 

Reaction mechanism of PTFE polyamide block copolymer formation by transa-midation... 

In order to form PTFE polyamide block copolymers high shear rates are necessary under melt processing conditions, to receive a good distribution and a further break down of PTFE micropowder particles. The particle size of the added PTFE micropowder is in the order of 2-8 pm. The crucial point for a successful coupling reaction is the contact between the carboxylic acid groups on the surface of the PTFE microcrystals and the amide groups of the molten polyamide matrix. As a result, a very homogeneous distribution of PTFE in the PA matrix is observed after reactive extrusion [21-23]. 

Lehmann D, Hupfer B, Lappan U, Pompe G, HauBler L, Janke A, Jehnichoi D, GeiBler U, Reinhardt R, Lunkwitz K, Franke R, Kunze K (2001) New PTFE polyamide compounds by reactive extmsion, synthesis and characterization of PTFE polyamide block copolymers, PPS 2001 Regional meeting, Antalya, 22-24 October 2001... 

The membrane material is decisive for the removal efficiency. Urkiaga et al. [129] tested different commercially available membranes on their adsorption characteristics for MTBE showing that sihcone rubber was more efficient than polyether-polyamide block-copolymer membranes (PEBA) and polyoctyl methyl siloxane membranes (POMS) at MTBE concentrations of 250mg/L and 1250 mg/L. The studies by Keller et al. [128] and Vane et al. [130] used polypropylene and silicone rubber membranes, respectively. 

Singhal, J.P. and Raya, A.R. 2002. Synthesis of blood compatible polyamide blocks copolymers. Biomaterials. 23 1139-1145. 

Louie JS, Pinnau I, Ciobanu I, Ishida KP, Ng A, and Reinhard M, Effects of polyether-polyamide block copolymer coating on performance and fouling of reverse osmosis membranes, Journal of Membrane Science 2006, 280, 762-770. 

Polyether-polyamide block copolymers have been found to meet these criteria very fine precipitates in the region of 0.5 to 2.0 xm have been observed. 

Permanent antistats do not depend on the relative humidity and they do not lose their effectiveness in a short time. One type is exemplified by the use of polyether-polyamide block copolymers combined with an intrinsically conducting substance, and another class consists of neoalkoxytitanates or zirconates. These compounds form non-blooming, bipolar layers, producing a surface and volume electron-transfer circuit, which produces a permanent antistatic effect. They are independent of atmospheric moisture and compatible with a wide range of polymers, including polyolefins, polyesters, polystyrene and PVC. Inherently conducting polymer additives such as sulfonated polyanilines are also used. They are discussed further in Chapter 5. 

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