Polyether block copolymers, elastomeric

Thermoplastic elastomeric behavior requires that the block copolymer develop a microheterogeneous two-phase network morphology. Theory predicts that microphase separation will occur at shorter block lengths as the polarity difference between the A and B blocks increases. This prediction is borne out as the block lengths required for the polyether-polyurethane, polyester-polyurethane, and polyether-polyester multiblock copolymers to exhibit thermoplastic elastomeric behavior are considerably shorter than for the styrene-diene-styrene triblock copolymers. 

T nterest in polyether-ester block copolymers that are both thermoplastic - and elastomeric continues at a sustained pace (1-9). Most of the recent communications have dealt with the tetramethylene terephthalate/ poly(tetramethylene ether) terephthalate copolymers which are continuing to find increased use in commercial applications requiring thermoplastic elastomers with superior properties. 

The work reported here is concerned with the syntheses and properties of polyether-ester block copolymers containing poly (tetramethylene ether) units of molecular weight of approximately 1000 as the amorphous polyether blocks and a variety of esters as the crystallizable hard segments. The purpose of this study is to correlate changes in synthesis and properties of these thermoplastic and elastomeric copolymers with changes in the concentration and nature of the ester segments, particularly the types of diol and diacid. 

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. 

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. 

Thomas et al. [1986] studied the effect of gamma irradiation (1,10,100 and 500 kGy) on PVC/TPE = 100 0, 75 25, 50 50, 25 75 and 0 100 blends (Table 11.9). As TPE a thermoplastic, elastomeric polyether-ester block copolymer of 1,4-butane-diol-polybutylene and glycol-terephthalic acid copolymer (ElytreF ), was used. The blends were prepared in an internal cam-type mixer at 80 rpm, 180°C, mixing time 7 min. TPE was added first,... 

Segmented block copolymers have been demonstrated by degrading cellulose triacetate and coupling it to low-molecular-weight polyesters or polyethers capped with isocyanate end groups and spinning from methylene chloride to make Spandex type elastomeric fibers [111,112]. 

Further research showed that the most viable approach to production of an elastomeric nylon via block copolymer technology was through the combination of a polyamide and a polyether. Such reactions, using various chemical means to join the polyether and polyamide, had been documented. However, apparently none of these methods resulted in the production of a commercially viable thermoplastic elastomer. 

The combination of the hard polyamide segment and the soft polyether siegment yields a block copolymer that exhibits a two phase structure a crystalline phase due to the polyamide and an amorphous phase due to the polyether. The crystalline phase allows the copolymer to behave as a thermoplastic and the amorphous phase imparts elastomeric qualities. 

This effort bore fruit in 1968, with the production (under the direction of Bill Witisiepe) of the material known today as HYTREL - a polyether-ester copolymer which has excellent thermal and melt stability, and combines desirable elastomeric properties with thermoplastic processability. Because this completely new resin was a block copolymer of randomized hard and soft segments, it offered a combination of resilience and strength that had never been seen in any thermoplastic. And it is this combination that today positions polyester elastomers perfectly for economic replacement of parts currently made from other flexible materials. 

Polyamide TPEs are usually either polyester-amides, polyetherester-amide block copolymers, or polyether block amides (PEBA) (see Fig. 3.7). PEBA block copolymer molecular architecture is similar to typical block copolymers. The polyamide is the hard (thermoplastic) segment, whereas the polyester, polyetherester, and polyether segments are the soft (elastomeric) segment. ... 

A different method is based on the possibility of having block copolymers as a dispersed phase between PBT and elastomeric polyethers. The blends and the copolymers are obtained directly during the polymer-... 

Wolfe J R Jr (1977) Elastomeric polyether-ester block copolymers. I. Structure-property relationships of tetramethylene terephthalate/polyether terephthalate copolymers. Rubber Chem Technol 50 688-703. 

Segmented polyurethanes (PUs) are typical representatives of linear block copolymers of the type (A-B)jj and an important class of thermoplastic elastomers. They are composed of short alternating blocks of soft (SS) and hard segments (HS). The SS impart elastomeric character to the copolymer, whereas the HS form a solid phase (HS microdomains) through intermolecular association and impart dimensional stability to the array of macromolecules. Low molecular mass polyethers and polyesters are typically used as SS, while HS normally consist of an aromatic diisocyanate that has been chain extended with a low molecular weight diol or diamine to form an oligomeric aromatic urethane or urethane urea segment [1-3]. 

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