Thermoplastics elastomers, segmented polyester

Celia R.J., Morphology of segmented polyester thermoplastic elastomers, J. Polym. Set Symp., 42, 727, 1973. 

Witsiepe, W.K., Segmented polyester thermoplastic elastomers, Adv. Chem. Ser., 129, 39, 1973. Srichatrapimuk V.W. and Cooper S.L., Infrared thermal analysis of pol3furethane block polymers, J. Macromol. Set Phys. B, 15, 267, 1978. 

Witsiepe W K (1973) Segmented polyester thermoplastic elastomers, Adv Chem Ser 129 39-60. 

Among the polyurethane, polyester, and polyamide thermoplastic elastomers, those with polyether-based elastomer segments have better hydrolytic stabihty and low temperature flexibiUty, whereas polyester-based analogues are tougher and have the best oil resistance (43). Polycaprolactones and aUphatic polycarbonates, two special types of polyesters, are used to produce premium-grade polyurethanes (12). 

It is important to note that any molecular architecture that provides a thermoplastic block chemically bonded to an elastomeric block, which is in turn bonded to another thermoplastic segment, should exhibit the properties of a thermoplastic elastomer. For example, grafting thermoplastic branches onto an elastomeric backbone produces thermoplastic elastomer behavior [285, 298]. Other examples are the segmented-type polymers—[AB] — with alternating hard and soft segments thus, a variety of segmented polyesters and polyurethanes with polyether or polyester soft segments exhibit properties of thermoplastic elastomers [263,298,299]. 

The permeability of water vapor through PET is higher than that of polyolefins but lower than that of polycarbonate, polyamide, and polyacetal. Antioxidants are necessary to prevent to the oxidation of polyether segments in thermoplastic polyester elastomer. Chemical resistance of PET is generally good to acids, alkalis, and organic solvents. 

The phase separation of semicrystalline thermoplastic elastomers is often controlled by the extent of crystallization of the domain forming polar segments. The domain forming segments of polyurethane and polyether-polyester thermoplastic elastomers are generally smaller... 

Polyester thermoplastic elastomers are block copolymers made up of alternating hard and soft segments. The hard segments are alkylene terephthalate blocks and the soft segments are poly(alkylene ether) terephthalate... 

The term polyester thermoplastic elastomers is widely used for segmented poly(ether-ester) block copolymers with alternating/random length sequences... 

Thermoplastic copolyester elastomers are generally block copolymers produced from short-chain aUphatic diols, aromatic diacids, and polyalkjlene ether-diols. They are often called polyesterether or polyester elastomers. The most significant commercial product is the copolymer from butane-l,4-diol, dimethyl terephthalate, and polytetramethylene ether glycol [25190-06-1J, which produces a segmented block copolyesterether with the following stmcture. 

Fig. 2. Sphemlitic moiphology of thermoplastic elastomer where the heavy lines represent polyester segments (184).

A smaller but rapidly growing area is the use of PTMEG ia thermoplastic polyester elastomers. Formation of such polyesters iavolves the reaction of PTMEG with diacids or diesters. The diols become soft segments ia the resulting elastomeric materials. Examples of elastomeric PTMEG polyesters iaclude Hytrel (Du Pont) and Ecdel (Eastman Chemicals). 

In thermoplastic polyurethanes, polyesters, and polyamides, the crystalline end segments, together with the polar center segments, impart good oil resistance and high upper service temperatures. The hard component in most hard polymer/elastomer combinations is crystalline and imparts resistance to solvents and oils, as well as providing the products with relatively high upper service temperatures. 

In Chapters 3 and 11 reference was made to thermoplastic elastomers of the triblock type. The most well known consist of a block of butadiene units joined at each end to a block of styrene units. At room temperature the styrene blocks congregate into glassy domains which act effectively to link the butadiene segments into a rubbery network. Above the Tg of the polystyrene these domains disappear and the polymer begins to flow like a thermoplastic. Because of the relatively low Tg of the short polystyrene blocks such rubbers have very limited heat resistance. Whilst in principle it may be possible to use end-blocks with a higher Tg an alternative approach is to use a block copolymer in which one of the blocks is capable of crystallisation and with a well above room temperature. Using what may be considered to be an extension of the chemical technology of poly(ethylene terephthalate) this approach has led to the availability of thermoplastic polyester elastomers (Hytrel—Du Pont Amitel—Akzo). 

Random block copolymers of polyesters (hard segments) and amorphous glycol soft segments, alloys of ethylene interpolymers, and chlorinated polyolefins are among the evolving thermoplastic elastomers. 

Thermoplastic polyurethane elastomers are normally based on polyester prepolymers. The properties of these polymers can be systematically varied by tailoring the nature and ratio of the hard and soft segments. The stiffness of a polyurethane elastomer increases as the proportion of hard blocks increases. As the stiffness increases, the extensibility of the material decreases. 

Condensation polymerization and stepwise addition polymerization are, for example, applied for the preparation of block polyesters. The synthesis concepts are different from those of chain polymerization in that at least one monomer is an oligomer with one or two functional end groups, for example polytetrahy-drofurane with a molecular weight of several hundred and OH-end groups (see Example 3-23). If this oligomer partially replaces butandiol in the condensation polymerization with terephthalic acid (compare examples 4-1 and 4-2), a po-ly(ether ester) is obtained with hard ester segments and soft ether segments and with the properties of a thermoplastic elastomer. 

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