Copolymers, containing poly butylene

Having established the rates and types of motion that occur in the poly (butylene terephthalate) homopolymer (5), it is of interest to extend these studies to the investigation of the types of motions that occur in segmented copolymers that contain poly (butylene terephthalate) as the hard segment. The structure of such a polymer is shown below, where m and n refer to the "hard" and "soft" segments, respectively. (This structure also illustrates the sites of the deuterium labels.)... 

The results presented here show that there are two distinct motional environments for the "central" deuterons of poly (butylene terephthalate) in the segmented copolyesters containing poly (butylene terephthalate) as the hard segment. One of the motional environments is identical to that observed in the poly (butylene terephthalate) homopolymer, in which Helfand-type motions (6) about three bonds occur with a correlation time of 7 x 10-6 s at 20 °C. The Tj for these deuterons is ca. 60 ms at 20 °C. Approximately 90% of the hard segments reside in these organized lamellar environments in the segmented copolymer with 0.87 mole fraction hard segments. 

Poly(butylene terephthalate) and Poly(butylene terephthalate)-Containing Segmented Copolymers... 

Figure 4. Solid state deuterium NMR spectra of (a) poly (butylene terephthalate) (b) segmented co-polyester containing 0.96 mole fraction of poly (butylene terephthalate) hard segments and (c) segmented copolymer containing 0.87 mole fraction hard segments. (See text for specific deuterium labeling patterns.) All spectra were obtained with the quadrupole echo pulse sequence at 20 °C and 55.26 MHz, using 30 ts at the tj quadrupole echo delay time.

It is of interest to estimate the amount of hard segment which gives the sharp line, and further, to determine if the poly (butylene terephthalate)-like broad line represents deuterons which undergo motions which are identical to those observed in the poly(butylene terephthalate) homopolymer. These points are addressed for the copolymer containing 0.87 mole fraction hard segments, by the solid state deuterium NMR spectra shown in Figure 6. 

Jelinski LW, Dumais JJ, Watnick PL Engd AK, Sefcik MD (1983) HMR relaxation in poly(butylene terephthalate) and poly(butylene terephthalate)-containing s mented copolymers. Macromolecules 16 409... 

The oxidation stability of poly( butylene isophthalate-co-terephthalate) copolyesters has been shown to decrease steadily with isophthalate unit content [26]. As expected, GC-MS analyses show that oxidation takes place mainly in the butylene units, through the same mechanism as before. Small-molecule products of a copolyester containing 25 mol% isophthalate included THF, butyrolactone, 3-buten-2-one, 2-propenal, and various other cyclised and carbonyl fragments, along with acetic acid. As has been observed for most polyesters, thermal and thermo-oxidative reactions occur simultaneously, and the lower stability of butylene-isophthalate units is most probably responsible for the lower overall stability of copolymers containing this structure, even under the oxidation conditions used. 

A newer type of (AB) block copolymer, known as the poly(ether-ester) elastomers and sold as Hytrel , contains alternating blocks of poly(butylene oxide) and butylene terephthalate as the soft and hard blocks, respectively (144-147) ... 

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