Polymers acid terminated

Using excess ethylene glycol is the usual practice because it drives the equilihrium to near completion and terminates the acid end groups. This results in a polymer with terminal -OH. When the free acid is used (esterification), the reaction is self catalyzed. However, an acid catalyst is used to compensate for the decrease in terephthalic acid as the esterification nears completion. In addition to the catalyst and terminator, other additives are used such as color improvers and dulling agents. For example, PET is delustred hy the addition of titanium dioxide. 

Figure 1.35 The complex structure of an asparagine-linked polysaccharide. Note the branched nature of polymer with terminal sialic acid residues on each chain. 

Fatty acids have also been converted to difunctional monomers for polyanhydride synthesis by dimerizing the unsaturated erucic or oleic acid to form branched monomers. These monomers are collectively referred to as fatty acid dimers and the polymers are referred to as poly(fatty acid dimer) (PFAD). PFAD (erucic acid dimer) was synthesized by Domb and Maniar (1993) via melt polycondensation and was a liquid at room temperature. Desiring to increase the hydrophobicity of aliphatic polyanhydrides such as PSA without adding aromaticity to the monomers (and thereby increasing the melting point), Teomim and Domb (1999) and Krasko et al. (2002) have synthesized fatty acid terminated PSA. Octanoic, lauric, myristic, stearic, ricinoleic, oleic, linoleic, and lithocholic acid acetate anhydrides were added to the melt polycondensation reactions to obtain the desired terminations. As desired, a dramatic reduction in the erosion rate was obtained (Krasko et al., 2002 Teomim and Domb, 1999). 

Polyoxypropylene urethane polymer, mercaptan-terminated, 22 40-41 Polyparabanic acid (PPA) tape material, 17 836... 

A variety of these physisorbed molecules were used as anchor points for covalent immobilization in a so-called hybrid approach [16]. That is the case of bifunctional pyrenes (i.e. 1 -pyrenebutanoic acid sucdnimidyl ester, pyrene maleimide) or polymers with terminal amine/carboxylic groups that have been used to covalently immobilize proteins, functionalized oligonucleotides, and so on, (Figure 3.9) [43,44]. 

Starting from a hyperbranched polyester based on 4,4 -bis(hydroxyphenyl)valeric acid, terminal -OH groups were derivatized to yield the hyperbranched macroinitiator. The Hgand precursor was introduced as the first block in the grafting from reaction, followed by 2-methyl-2-oxazoHne polymerization to give the second block and allow for water-soluble polymers. The triphenylphosphine-functionalized am-phiphihc star block copolymer was obtained after transformation of the iodoaryl... 

Newkome GR, Young JK, Baker GR, Potter RL, Audoly L, Cooper D, Weis CD, Morris K, Johnson CS Jr. Cascade polymers. 35. pH dependence of hydrodynamic radii of acid-terminated dendrimers. Macromolecules 1993 26 2394-2396. 

Of particular importance in describing the difference between these two families of resins are the locations of die reactive unsaturation. In the polyester resin, these groups are located along the backbone of die polymer with terminal hydroxyl or carboxylic acid groups. The vinyl ester resins contain no significant acidity but terminate in reactive vinyl ester groups. Because of the location of these reactive sites, the vinyl ester resins will homopolymerize as well as coreact with various vinyl monomers. 

A related series of hyperbranched polymers possessing high molecular weight (20,000-50,000 amu) was also created 20,21 by the melt condensation of 5-acetoxy- (8) or 5-(2-hydroxyethoxy)-(9) isophthalic acids (Scheme 6.3). Polymerization of diacid 8 was effected in two stages (1) melting at 250 °C combined with removal of acetic acid with the aid of an inert gas, and (2) application of a vacuum at the onset of solid state formation. Refluxing the resultant acid-terminated, ester-linked polymer 10 in THF/H20 decomposed the labile anhydride cross-links, which were generated under the reaction conditions. 

Isophthalic acid 9, prepared by ethoxylating the phenolic group of 5-hydroxyisophtha-lic acid with ethylene oxide, was polymerized at 190°C using Bu2SnAc2 as the catalyst. The resulting carboxylic acid terminated hyperbranched polymer (not shown) was readily soluble in typical organic solvents. Due to a lower condensation temperature than that employed for the polymerization of diacid 8, evidence of anhydride bond formation was not observed. 

Reichert and Mathias prepared related branched aramids, to those of Kim,t5-34] from 3,5-dibromoaniline (23) under Pd-catalyzed carbonylation conditions (Scheme 6.7). These brominated hyperbranched materials (24) were insoluble in solvents such as DMF, DMAc, and NMP, in contrast to the polyamine and polycarboxylic acid terminated polymers that Kim synthesized, which were soluble. This supports the observation that surface functionality plays a major role in determining the physical properties of hyperbranched and dendritic macromolecules J4,36 A high degree of cross-linking could also significantly effect solubility. When a four-directional core was incorporated into the polymerization via tetrakis(4-iodophenyl)adamantanc,1371 the resultant hyperbranched polybromide (e.g., 25) possessed enhanced solubility in the above solvents, possibly as a result of the disruption of crystallinity and increased porosity. 

Scheme 6.6. Procedures for the preparation of poly(aryl amide) polymers. The carboxylic acid terminated polymers exhibited lyotropic liquid crystalline behavior.

Polyanhydrides have been modified by incorporating amino acids into im-ide bonds. The imide with the terminal carboxylic acids is activated with acetic anhydride and copolymerized with sebacic acid or CCP. Poly(anhydride-imides) increase the mechanical properties of the polyanhydrides. Degradation of poly(anhydride-imide)s is similar to that of polyanhydrides (i.e., surface erosion). Two different cleavable bonds (anhydride and ester) in the polymer chains have been included in polyanhydrides. Carboxylic acid-terminated e-caprolactone oligomers or carboxylic acid-terminated monomers (e.g., salicylic acid) have been polymerized with activated monomers (e.g., SA). 

Other functionalizations of polyisobutene have been performed 78) by means of the inifer technique and subsequent reaction at the chain end. Polymers bearing terminal carboxylic acid or anhydride functions can also be considered as potential starting materials for the synthesis of polyisobutene macromonomers. 

Once the number of antennae is established, further extension is possible through addition of backbone polymers and terminal structures similar to those found on mucin-type glycans. LacNAc polymers can be added to any of the aforementioned GlcNAcs (Fig. 4A, w-x). Similarly, these polymers can be elaborated with fucose, sulfate, and sialic acid added in the same linkages described for mucin-type structures (Fig. 4A, y-z). Most fucosyltransferases and sulfotransferases, as well as the sialyltransferases that cap polyLacNAc, are capable of modifying both O-linked and A-linked glycans some exhibit a preference for one or the other. These biases are likely a result of differences in enzyme localization. 

More carbon dioxide is formed during polyamidation at high temperatures than would be expected from the simple cleavages just described. Most likely this additional carbon dioxide is formed by decarboxylation of acid-terminated polymer chains. 

The exchange reactions involving amine-terminated or acid-terminated polymer molecules proceed at a faster rate than exchange reactions between amide linkages. Korshak et al. [94b] showed that formation of block copolymers from mixed homopolyamides having chemically blocked end groups was much slower than when the homopolyamides had free carboxyl and free amine end groups. 

---