Polyethylene terephthalate repeating unit

Those polymers which are the condensation product of two different monomers are named by applying the preceding rules to the repeat unit. For example, the polyester formed by the condensation of ethylene glycol and terephthalic acid is called poly(oxyethylene oxyterphthaloyl) according to the lUPAC system, as well as poly (ethylene terephthalate) or polyethylene terephthalate. 

Poly (ethylene Terephthalate). Polyethylene terephthalate) is prepared by the reaction of either terephthalic acid or dimethyl terephthalate with ethylene glycol, and its repeating unit has the general structure. 

N(backbone ester) s L 1C number of ester (-COO-) groups in the backbone of the polymeric repeat unit, which is defined as described in Section 2.D. For example, N one ester) 0 for poly(vinyl acetate) and for poly(methyl methacrylate), 1 for poly(e-caprolactone) and for poly(glycolic acid) (see Figure 2.4), and 2 for polyethylene terephthalate). 

The three-phase structures 12, 13, and 14 are of particular interest because of the even more severe violation of the phase rule. At constant pressure, in equilibrium, only one-phase areas should be stable. Drawn fibers of poly(ethylene terephthalate) (PET) are discussed as three-phase sttucture with Figs. 5.68-72 and 5.113-115. As in polyethylene, the drawing to fibers or films orients the amorphous nanophase and achieves an arrested mesophase order, proven with Fig. 5.72. Since the drawing of PET fibers is much less efficient in extending the molecules than gel-spinning, there remains a sizeable portion of the amorphous phase, as shown in Fig. 5.71. The mobile mesophase of PET has not been found as a stable phase, as in polyethylene. Copolymers of PET with stiffer repeating units, such as oxybenzoate, however, have stable mesophases (see Chap. 7). 

These polymers have only one type of repeating unit. Polyethylene, poly(vinyl chloride), poly(ethylene terephthalate), etc. are a few examples of this class of polymers. 

Polyethylene terephthalate (PET) is the material used to manufacture polyester film capacitors. Its molecular structure is based on the repeat unit... 

The poly(ethylene terephthakte) analyzed was about 75% cr5retalline. The cr tal structure is triclinic with the moleculEu chains in an almost planar conformation. The poly(ethylene sebacate) was about 57% crystalline with a nomoclinic crystal structure with the molecular chains also in a planar conformation, in fact quite similar to the polyethylene crystal structure. The two repeating units, however, do not cocrystallize since the repeating unit lengths in the chain direction do not match. The copolymers thus show only poly(ethylene terephthalate) crystallinity. The 80/20 copolymer was about 22% crystalline, while the 60/40 copolymer was about 15% cr5retalline. 

Instead of the addition pol)nnerization described above, some polymers are formed by a chemical reaction between two monomers that produces the repeating units together with a byproduct. This process is called condensation or step reaction polymerization. An example would be the reaction between dimethyl terephthalate and ethylene glycol to produce polyethylene terephthalate (PET) and methyl alcohol as a byproduct. The nylons and polycarbonates are linear chain pol)nners that also pol)nnerize by the condensation process. 

The polymer has a Tg of about —20°C and is a tough material at room temperature. We now compare polyethylene terephthalate with polyethylene. The former has a phenyl group on every repeat unit and, as a result, has stiffer chains (and, hence, higher Tg) compared to polyethylene. 1,4-Polybutadiene has a double bond on the backbone and similarly has a higher Tg. 

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