Other Polyesters

The above-mentioned results of the SSP of PET can be generally applied to other semicrystalline polyesters, such as poly(butylene terephthalate) (PBT), poly(tri-methylene terephthalate) PTT), polyethylene naphthalate) (PEN) or any other kind of semicrystalline co-polyester, as a result of their similar reaction behaviors. Most of the studies have been focused on PET and PBT due to their industrial importance. Meanwhile, the popularity of PEN is growing on account of the outstanding properties of this particular polymer. 

According to reports Po et al. [31] and Amoco [32], the reaction rate of PEN is lower than other polyesters. Considerations about this fact lead to the assumption that the structure-dependent reactivities of the acid and glycol components and their mobilities are responsible for the individual reaction rates of these polymers. Based on unpublished data, rigid or voluminous co-monomers result in reduced reactivities during melt polycondensation and SSP. The mobility of the component, as a result of its structure and stiffness, seems to explain this observation. 

Summarizing these results, it can be concluded that for PET the SSP reaction is a rate- and diffusion-controlled process whose physical aspects change with increased particle size and reaction time. Differentiation between the reactions which occur provides a better understanding of the SSP process. Based on this knowledge, calculations and predictions for engineering purposes thus become possible. 

The SSP process is obviously limited by tlie melting point of the prepolymer and the equilibrium temperature of the polymer process. The SSP reaction becomes too slow at temperamres below 190 °C in commercial processing. Temperatures below this level are only of scientific interest or applicable in the case of thermally sensitive polyesters. The increase in IV for tlie most common polyesters decreases in relation to the glycolic component, as shown in Eigure 5.15 however, this figure does not show the behavior of cyclohexane dimelhanol (CHDM) and PEN [30]. 

The monomers used to generate polyesters can be used to form many copolymers that will contain ester groups. The esters can be included in copolymers with other esters, with ether groups, amides, carbonates, etc. Some examples of such copolymers are listed in Table 10.1.9. 

Some thermosets are made with maleic anhydride only, or with other unsaturated 1,2-dicarboxylic acids or anhydrides such as itaconic acid or methylenesuccinic acid [7], chlorendic acid or 1,4.5,6,7,7-hexachloro-5-norbornene-2,3-dicarboxylic acid (or anhydride), 1,4.5,6,7-pentachloro-5-norbornene-2,3-dicarboxylic acid anhydride or 1,4.5,6-tetrachloro-5-norbornene-2,3-dicarboxylic acid anhydride. These norbomene derivatives can be obtained from the Diels-Alder condensation of the chlorinated cyclopenta-1,3-dienes and maleic anhydride, as shown in the following reaction  

The resulting anhydride can form polyesters with diols, and further form a thermoset by polymerization with styrene. 

Thermal decomposition of polyester copolymers is of considerable interest because of their common use in practice. A number of reports are available in literature describing either pyrolysis or slow thermal decomposition of polyester copolymers [57-60], etc. Some of these reports are summarized in Table 10.1.10. 

TABLE 10.1.10. Summary regarding literature information on thermal decomposition of several copolymers of esters [12]. 

The phenomenon has been observed with poly(4,4 -diphenylolpropane isophthalate) [118] 

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Used as fibres, particularly in textiles and film. Many other polyester polymers are of importance, e.g. unsaturated polyester resins from phthalic anhydride, propylene glycol and maleic anhydride used with reinforcement in boats, cars, etc. (alkyd resins). U.S. production 1983 1-7 megatonnes. 

Poly(ethylene terephthalate), the predominant commercial polyester, has been sold under trademark names including Dacron (Du Pont), Terylene (ICI), Eortrel (Wellman), Trevira (Hoechst-Celanese), and others (17). Other commercially produced homopolyester textile fiber compositions iaclude p oly (1,4-cyc1 oh exa n e- dim ethyl en e terephthalate) [24936-69-4] (Kodel II, Eastman), poly(butylene terephthalate) [26062-94-2] (PBT) (Trevira, Hoechst-Celanese), and poly(ethylene 4-oxyben2oate) [25248-22-0] (A-Tell, Unitika). Other polyester homopolymer fibers available for specialty uses iaclude polyglycoHde [26124-68-5] polypivalolactone [24937-51-7] and polylactide [26100-51-6],... 

Health Safety. PET fibers pose no health risk to humans or animals. Eibers have been used extensively iu textiles with no adverse physiological effects from prolonged skin contact. PET has been approved by the U.S. Eood and Dmg Administration for food packagiug and botties. PET is considered biologically iuert and has been widely used iu medical iaserts such as vascular implants and artificial blood vessels, artificial bone, and eye sutures (19). Other polyester homopolymers including polylactide and polyglycoHde are used iu resorbable sutures (19,47). 

Polycarbonate—polyester blends were introduced in 1980, and have steadily increased sales to a volume of about 70,000 t. This blend, which is used on exterior parts for the automotive industry, accounting for 85% of the volume, combines the toughness and impact strength of polycarbonate with the crystallinity and inherent solvent resistance of PBT, PET, and other polyesters. Although not quite miscible, polycarbonate and PBT form a fine-grained blend, which upon analysis shows the glass-transition temperature of the polycarbonate and the melting point of the polyester. 

On the contrary, the phase structure and the thermal history do not have important effects on the location and intensity of the /3 relaxation. This relaxation is very broad in all the samples and overlaps the y relaxation. The activation energy of the /3 peak is about 85 kJ mol for the three samples, of the same order of magnitude as that of other polyesters [38,40]. Finally, the y relaxation is found in the three samples of PTEB with no remarkable influence of the thermal history. 

Step-growth polymer (Sections 21.9, 31.4) A polymer in which each bond is formed independently of the others. Polyesters and polyamides (nylons) are examples. 

More definitive evidence of enzymatic attack was obtained with 1 1 copolymers of e-caprolactone and 6-valerolactone crosslinked with varying amounts of a dilactone (98,99). The use of a 1 1 mixture of comonomers suppressed crystallization and, together with the crosslinks, resulted in a low-modulus elastomer. Under in vitro conditions, random hydrolytic chain cleavage, measured by the change in tensile properties, occurred throughout the bulk of the samples at a rate comparable to that experienced by the other polyesters no weight loss was observed. However, when these elastomers were implanted in rabbits, the bulk hydrolytic process was accompanied by very rapid surface erosion. Weight loss was continuous, confined to the... 

The effects of a series of added tertiary amines on the rate of chedn scission of other polyesters, including poly( e-caprolactone-co-lactic acid), has been studied and found to be equally great (65). The mechanism with tertiary amines can only be general base catalysis for the effectiveness of the amines was not related to their pK values or lipophilicities. The acceleration of the hydrolysis of the polyesters was used as a strategy for controlling the drug release rate. 

From this perspective it would be interesting to discover if there is a relationship between the substrate used and the concentration of free CoA under conditions of unlimited growth. If there is, depending on the source of carbon and energy used and the K value of the 3-ketothiolase for CoASH, cell multiplication and poly(3HB) accumulation can occur simultaneously [60,61]. If this enzyme is not involved, poly(3HB) [29] and other polyesters [28,29] can also be synthesized during growth. 

The incorporation of comonomers into PET and other polyesters, with the intent that these comonomers would then serve as the site for additional, postpolymerization reactions, has not been widely explored. A potential difficulty in such an approach is that the reactive comonomer cannot react under PET synthesis conditions of ca. 285 °C/2h/Lewis acid catalyst if the modification is to be effective. Two such systems, stable under PET synthesis, and then subjected to post-polymerization reactions, have been recently reported. 

It should additionally be noted that a number of the paths of the schemes above have received some confirmation in a number of literature reports dealing with the photolysis and photo-oxidation of other polyesters [32-35], Because these reports investigated poly(butylene terephthalate) (PBT), poly(ethylene naphthalate) and poly(butylene naphthalate), however, they may not have direct application to understanding of the processes involved in PET and PECT and so have not been discussed in this present chapter. All do contain support for the formation of radicals leading to CO and C02 evolution, as well as the hydrogen abstraction at glycolic carbons to form hydroperoxides which then decompose to form alkoxy radicals and the hydroxyl radical. These species then were postulated to undergo further reaction consistent with what we have proposed above. 

Other polyesters of commercial importance are polycarbonates, liquid crystal polyesters, unsaturated polyesters, and copolymers (Secs. 2-8e, 2-14g, 2-12, 2-13). 

Polymerization of esters to produce polyesters is an important commercial process. Polyethylene terephthalate or PET is one of the most common plastics used in food containers (Table 15.4). This ester is formed by the reaction of ethylene glycol and terephthalic acid (Figure 15.17). PET and other polyesters consist of esters linked together. Notice that both terephthalic acid and ethylene glycol have two carboxyls and two hydroxyls, respectively. When a polyester such as PET is formed, a monomer con-... 

Gases o2-n2 Mol Sieve 5A u bility than DEGS or other polyesters Will not elute CO2... 

Polycarbonate-polyester blends are used on extenor parts for the automotive industry. Such blends combine the toughness and impact strength of polycarbonate with die crystallinity and inherent solvent resistance of PBT, PET. and other polyesters. 

The sole representative of this class is l-(4,6-dimethoxy-l,3,5-triazin-2-yl)pyrene (67), [3271-22-5], which gives a bluish white brightening effect on polyester substrates it is employed chiefly in combination with other polyester brighteners such as 38. Compound 67 is obtained by the Fricdel-Crafts reaction of cyanuric chloride with pyrene with subsequent replacement of the remaining chlorines with methoxyl groups [117],... 

This group of polyesters is made by the opening of the caprolactam ring. Caprolactam is also used in the production of nylon. Their structure appears to provide a degree of protection from hydrolytic attack. They are formed by the reaction shown in Figure 2.13 (Barbier-Baudry and Braachais, 2003). Their hydrolytic properties fall between those of PTMEG and other polyesters. 

Another way to control the release of biocides is to entrap them into a matrix that is slowly hydrolyzed, e.g., into polylactic acid or other polyesters [104, 105] or degradable polyelectrolyte multilayers [106], By choosing a matrix that is degradable by a specific enzyme, the location of release in the body can be controlled. An example of this approach, which is very common for drug release but rarely used for biocides, is fluoroquinolone-modified biodegradable polyurethane that releases the antibiotic ciprofloxazin upon degradation catalyzed by the enzyme cholesterol esterase [107],... 

The fiber softens at about 200°C and melts at 225°C. It is said to have a silk-like hand and appearance and other properties comparable to those of other polyesters. 

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