Polyether blocks, chemical structure

Elastomeric polyether-ester block copolymers were prepared by melt transesterification of poly(tetramethylene ether) glycol of molecular weight approximately 1000 with a variety of diols and esters. The ease of synthesis and the properties of these thermoplastic copolymers have been related to the chemical structure and concentration of the ester hard segments. 

PEBA exhibit a two-phase (crystalline and amorphous) structure and can be classified as a flexible nylon. Physical, chemical, and thermal properties can be modified by appropriate combination of different amounts of polyamide and polyether blocks [149], Hydrophilic PEBAs can be prepared which can have specific applications in medical devices. Similarly to other thermoplastic elastomers, the poiyamide-based ones find applications in automotive components, sporting goods conveyor belting, adhesives, and coatings [150]. In recent years the world consumption was approximately 6400 tons per year with about 80% in Western Europe and the rest equally split between the United States and Japan [143],... 

A small part of the -NCO groups of diisocyanate reacts with the terminal hydroxyl groups of polyethers and forms a block copolymer structure, having a polyurea segment chemically linked to a polyether segment, which plays the role of a nonaqueous dispersant and assures the excellent stability of the resulting polyurea dispersion (reaction 6.20) [67, 68]. 

Figure 13.2 Chemical structures of (a) polyamide and (b) polyether blocks polyamide block could be PA6 (x = 5) or PA12 (x = 11) and polyether block could be polyfethylene oxide) (PEO, y = 2) or polyftetramethylene oxide) (PTMO, y = 4)...

Table 5.102 shows chemical resistance of polyether block amides as a function of their chemical structure. With increasing soft phase content, i.e., decreasing hardness, chemical resistance decreases, 1. e., the increasing amide content (hard phase contents) improves chemical resistance. 

Thermoplastic elastomers are most commonly formulated from elastomeric polyurethane or block copolymers of polystyrene-elastomer, polyamide-elastomer, or polyether-elastomer bases. Thermoplastic elastomers are provided as a raw material in pelletized form for subsequent compounding. The internal domain structure that is required for thermoplastic-elastomeric performance has been established by specific considerations of blending and structural-chemical interactions. In compounding operations, specific temperature ranges are required to assure that phase separation does not occur in the TPE base polymer. 

As indicated in the literature [4,6], although the (3 peak shows only little variation with the PA/PE ratio, the a peak decreases in temperature for lower PA/PE ratios and a shorter polyamide block length as observed in Figure 10. Such a lowering of the a peak is attributed to an internal plasticization coming from oligoether miscible components inside the polyamide-rich regions. Another possible interpretation could be that, since the immiscible polyamide and polyether components are linked by chemical bonds, the structure and mobility of each block affect the others [15]. 

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