Polycondensation Routes

Polycondensation Routes.—Nylon 4,6 has been synthesized by melt-polycondensation and characterized by a variety of techniques, with emphasis on molecular structure determination. Routes to nylon 6,6 via phosphorylation of the salt in organic solvents in the presence of organic bases such as imidazole have been assessed. Similarly, the conditions for polycondensation of carboxylic acid difluorides with diamines in homogeneous aqueous organic media have been described.  

The synthesis of polyamides by in situ polycondensation of nylon salts or amino acids in the presence of aryl sulphites and imidazole or pyridine has also been studied and their catalytic activity evaluated. 

Specific preparations of polyamides containing units derived from A -malonic diesters of uracil and theophylline, aa -disubstituted adipate, succinate, and phenoxathiin have all been reported. A new water-soluble polyamide derived from ethylene glycol dimethoxycarbonylomethyl ether and hexamethylene-diamine has been described and conditions evaluated for the preparation of high molecular weight materials. 

Polyamides have been prepared by solution polymerization of aromatic and aliphatic diamines and active A A -diacyl-bis-2-benzothiazolones.  

Thionyl chloride has been reported as an activator in the synthesis of polyamides by direct polycondensation.  

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Nucleophilic Substitution Route. Commercial synthesis of poly(arylethersulfone)s is accompHshed almost exclusively via the nucleophilic substitution polycondensation route. This synthesis route, discovered at Union Carbide in the early 1960s (3,4), involves reaction of the bisphenol of choice with 4,4 -dichlorodiphenylsulfone in a dipolar aprotic solvent in the presence of an alkaUbase. Examples of dipolar aprotic solvents include A/-methyl-2-pyrrohdinone (NMP), dimethyl acetamide (DMAc), sulfolane, and dimethyl sulfoxide (DMSO). Examples of suitable bases are sodium hydroxide, potassium hydroxide, and potassium carbonate. In the case of polysulfone (PSE) synthesis, the reaction is a two-step process in which the dialkah metal salt of bisphenol A (1) is first formed in situ from bisphenol A [80-05-7] by reaction with the base (eg, two molar equivalents of NaOH),... 

Triarylamines have been employed in arylene vinylene AB copolymers 38 by Horhold et al. using a Homer polycondensation route of aldehydes and ketones 36 with fois-phosphonate 37 (Scheme 1-12) 164]. Phenylamines have remarkably low redox potentials and their charge transport properties have been investigated extensively [65]. EL devices comprising triarylamines have demonstrated low driving voltages. 

Referring to the ADMET mechanism discussed previously in this chapter, it is evident that both intramolecular complexation as well as intermolecular re-bond formation can occur with respect to the metal carbene present on the monomer unit. If intramolecular complexation is favored, then a chelated complex, 12, can be formed that serves as a thermodynamic well in this reaction process. If this complex is sufficiently stable, then no further reaction occurs, and ADMET polymer condensation chemistry is obviated. If in fact the chelate complex is present in equilibrium with re complexation leading to a polycondensation route, then the net result is a reduction in the rate of polymerization as will be discussed later in this chapter. Finally, if 12 is not kinetically favored because of the distant nature of the metathesizing olefin bond, then its effect is minimal, and condensation polymerization proceeds efficiently. Keeping this in perspective, it becomes evident that a wide variety of functionalized polyolefins can be synthesized by using controlled monomer design, some of which are illustrated in Fig. 2. 

We have synthesized such a material, which is called perfectly imperfect polyethylene, where each branch is a methyl group and its frequency along the backbone is controlled by the nature of the symmetrical diene used in the ADMET polycondensation reaction [37]. Equation 12 illustrates the chemistry used to produce polyethylene by a step polycondensation route rather than a chain propagation mechanism. 

Of particular interest was the reaction of two equivalents of potassium phthalimide with PFB using 18-crown-6 in refluxing acetonitrile. This reaction with either small molecules or the polymeric analogs represents a novel approach to arylimide synthesis via PTC. After 4 hr. under nonoptimized PTC reaction conditions, disubstitution afforded the bisimide 6 in ca. 50% yield. This shows that phthalimide anion, a considerably poorer nucleophile than either the phenoxide or thiophenoxide, is a strong enough nucleophile in the presence of 18-crown-6 to displace aryl fluoride with facility, and demonstrates that the synthesis of polyimides, an important class of thermally stable polymers, is feasible by this PTC polycondensation route. 

In addition to sulfone, phenyl units, and ether moieties, the main backbone of polysulfones can contain a number of other connecting units. The most notable such connecting group is the isopropylidene linkage which is part of the repeat unit of the well-known bisphenol A-based polysulfone. It is difficult to clearly describe the chemical makeup of polysulfones without reference to the chemistry used to synthesize them. There are several routes for the synthesis of polysulfones, but the one which has proved to be most practical and versatile over the years is by aromatic nucleophilic substitution. This polycondensation route is based on reaction of essentially equimolar quantities of 4,4,-dihalodiphenylsulfone (usually dichlorodiphenylsulfone (DCDPS)) with a bisphenol in the presence of base thereby forming the aromatic ether bonds and eliminating an alkali salt as a by-product. This route is employed almost exclusively for the manufacture of polysulfones on a commercial scale. 

Thermoplastic Polymers and Copolymers, One-step solution polycondensation routes were used to prepare a variety of thermoplastic DiSiAn-derived polymers and copolymers (Schemes I and II, respectively). 

Other polymetallocenes with short spacers via polycondensation routes... 

A step-growth polycondensation route has been succesfully devised to prepare novel nickel polymers 207 with arene spacer groups. The procedure involved the polycondensation of the fluorinated dilithiated species 206 and an Ni(ii) complex (Equation (75))." " The rod-like structure of these polymers was established by dilute-solution viscosity measurements, and the results were similar to those reported for the related platinum polyyne polymers 166 (M = Pt(P Bu3)2 x = 2) (Section 12.06.5.2.3). 

As another interesting variant on materials with M-C linkages, formally conjugated polymers 210 and 211 have been prepared via polycondensation routes and have been characterized in the solid state.In the case of the intriguing metal-carbyne polymers 211, the materials are fluorescent at room temperature," unlike monomeric species such as (RO)3W=GR (R = alkyl or aryl). Polymers such as 210 and 211 and analogs" represent very exciting targets for future study. 

The mechanism of formation is similar to the Gilch polymerization route. The resulting polymers exhibit a significantly higher molecular weight and have less structural defects as those prepared by the polycondensation route. 

Other Polymetallocenes with Short Spacers Obtained by Polycondensation Routes... 

Polyferrocenylphenylphosphines 3.29, analogous to those previously synthesized by polycondensation routes (Section 3.2.2), have also been prepared by thermal ROP of phosphorus-bridged [l]ferrocenophanes 3.28 (Eq. 3.13) [72]. The solubility of the materials was observed to increase when the cyclopentadienyl rings were substituted with n-butyl or trimethylsUyl groups. Sulfurization was carried out in order to facilitate their characterization by GPC, as the polyferrocenylphosphine... 

Khan, A. and S. Hecht. 2004. Microwave-accelerated synthesis of lengthy and defect-free poly(m-phenyleneethynylene)s via AB and A(2) -I- BB polycondensation routes. Chem Commun 300. 

Nucleophilic Substitution Route. Commercial synthesis of poly(arylethersulfone)s is accomplished via the nucleophilic substitution polycondensation route. This synthesis route, discovered at Union Carbide in... 

The polymers derived from lactic acid by the polycondensation route are generally referred to as poly(lactic acid) and the ones prepared from lactide by ring-opening polymerization as polylactide [9], Both types are generally referred to as PL A. 

Previous work involved the s3mthesis and physical characterization of linear uranyl polyesters obtained from both interfacial and aqueous solution polycondensation routes. Uranyl ion complexation, i.e. removal, was effected to a 10" molar (concentration in aqueous solution) level. 

Poly(lactic acid) (PLA) is a biodegradable polymer that has a variety of applications. It has been widely used in the biomedical and pharmaceutical fields for several decades due to its biocompatibility and biodegradability in contact with mammalian bodies. For many years, however, the application of PLA was very limited, due to the high cost of synthesis in the laboratory. For the most part, the direct polycondensation route (see Figure 8.1) was employed to produce PLA from lactic acid. The resultant PLA had a low molecular weight and poor mechanical properties. 

Route 1 Dire(4 polycondensation Route 2 Ring opening polymerization... 

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