Linear polyesters, structure

Lactomes may also be polymerized by ring-opening anionic polymerization techniques. While the five-membered ring is not readily cleaved, the smaller rings polymerize easily producing linear polyesters (structure 5.46). These polymers are commercially used as biodegradable plastics and in PU foams. 

Another important type of condensation polymer are the linear polyesters, such as poly (ethylene terephthalate) (PET) and poly (butylene terephthalate) (PBT). Copolymers of polyesters and PA have been studied in detail, and it has been shown that random copolyesteramides have a low structural order and a low melting temperature. This is even the case for structurally similar systems such as when the group between the ester unit is the same as that between the amide unit, as in caprolactam-caprolactone copolymers (Fig. 3.10).22 Esters and amide units have different cell structures and the structures are not therefore isomorphous. If block copolymers are formed of ester and amide segments, then two melting temperatures are present. 

A variation of the aromatic polyester structure was utilized by Hawker et al. when they described hyperbranched poly(ethylene glycol)s and investigated their use as polyelectrolyte media [76]. The highly branched structure implies that no crystallization can occur. Linear poly(ethylene) glycols usually crystallize, which has a detrimental effect on their use as polyelectrolyte media. 

Examples of crystalline polymers are nylons, cellulose, linear polyesters, and high-density polyethylene. Amorphous polymers are exemplified by poly(methyl methacrylate), polycarbonates, and low-density polyethylene. The student should think about why these structures promote more or less crystallinity in these examples. 

In equation 1, a dicarboxylic acid derivative called an anhydride (literally without water ) reacts with ethylene glycol, a di-alcohol, to form a linear polyester and the byproduct water. Ethylene glycol is the major ingredient in most automotive radiator fluids. In equation 2, the ethylene glycol is replaced with a tri-alcohol, glycerol. As the reaction proceeds, the polyester does not form linear chains, but rather becomes crosslinked as the three OH groups react with phthalic anhydride, building up a three-dimensional structure. 

BASF s Ecoflex and Novamont s Eastar Bio Ecoflex are aromatic-aliphatic co-polyesters based on butanediol, adipic acid, and terephthalic acid. BASF s products contain long-chain branching while Eastar Bio is highly linear in structure. 

The polyester structure has been adapted for use in radiation-cured coatings. Low molecular weight, linear polyesters have been made in which the terminal hydroxyl groups have been esterified with acrylic acid. These oligomers have low viscosity and are used increasingly in coatings cured by UV or electron-beam radiation (21). 

Highly compatible polymer blends of PPE and linear polyester resins provide beneficial improvements in the chemical resistance required for automotive applications. Such automotive applications include molded thermoplastic body panels. Foamable compositions of PPE resins are particularly suited as sources of lightweight structural substitutes for metals, especially in the automotive industry. 

The other macromolecule found only in certain wood species is suberin. This non-linear polyester contains very long aliphatic moieties which impart a characteristic hydrophobic feature to the natural material that contains it. Figure 1.7 shows a schematic structure of suberin. By far the most representative species containing this polymer in its very thick bark (the well-known cork) is Quercus suber, which grows in the Mediterranean area, but Nordic woods like birch, also have a thin film of suberin coating their trunks. The sources of suberin, as well as the corresponding structure and composition are described in Chapter 14, together with the use of its monomeric components for the synthesis of novel macromolecular materials. 

Poly(3-hydroxybutyrate) is a linear polyester with helical macromolecules. The secondary stracture of PHB is specified as left-hand 2j helix in a g g tt conformation, while the structure of oligolides consists of right-hand 3i helices [99]. The surface of the 3i(-l-) helix is covered by methyl groups, leading to the lipophilic nature of the macromolecule. The carbonyl bonds in the 2i(—) helix are placed perpendicularly, while in the 3i(-l-) counterpart, they are parallel to the helix axis. The latter is the reason for ability to form ionic complexes. 

Poly(Propylene Fumarate) (PPF) is a linear, unsaturated, hydrophobic polyester (Structure 12) containing hydrolyzable ester bonds along its backbone. PPF is highly viscous at room temperature and is soluble in chloroform, methylene chloride, tetrahydrofuran, acetone, alcohol, and ethyl acetate [66]. The double bonds of PPF can form chemical crosslinks with various monomers, such as W-vinyl pyrrolidone, poly(ethylene glycol)-dimethacrylate, PPF-diacrylate (PPF-DA), and diethyl fumarate [67,68]. The choice of monomer and radical initiator directly influence the degradative and mechanical properties of the crosslinked polymer. Once crosslinked, PPF forms a solid material with mechanical properties suitable for a range of bone engineering applications. 

Nuclear magnetic resonance (NMR) spectroscopy is one of the other basic methods for structural analysis. Aluri et al. [16] proposed a one-pot synthesis route to obtain two polymers of ABB for linear polyester and hyperbranched poly(ester-urethane)s based on multifunctional L-amino acid monomers using a temperature-selective melt... 

A different strategy providing access to linear polyesters derived from fatty acids in which their aliphatic sequences dangle from macromolecular chains (i.e., a type of structure very different to that of linear PE) has been described recently [73]. Various saturated fatty acid methyl esters were malonated to the corresponding methyl diesters, which were polymerised by transesterification with 1,6-hexanediol (Scheme 4.17). 

In this experiment, the syntheses of two polyesters (Experiment 46A), nylon (Experiment 46B), and polystyrene (Experiment 46C) will be described. These polymers represent important commercial plastics. They also represent the main classes of polymers condensation (linear polyester, nylon), addition (polystyrene), and cross-linked (Glyptal polyester). Infrared spectroscopy is used in Experiment 46D to determine the structure of polymers. 

Infrared spectroscopy is an excellent technique for determining the structure of a polymer. For example, polyethylene and polypropylene have relatively simple spectra because they are saturated hydrocarbons. Polyesters have stretching frequencies associated with the C=0 and C—O groups in the polymer chain. Polyamides (nylon) show absorptions that are characteristic for the C=0 stretch and N—H stretch. Polystyrene has characteristic features of a monosubstituted aromatic compound (see Technique 25, Figure 25.12). You may determine the infrared spectra of the linear polyester from Experiment 46A and polystyrene from Experiment 46C in this part of the experiment. Your instructor may ask you to analyze a sample that you bring to the laboratory or one supplied to you. 

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