Polymerization methods polycondensation

As a variation on the base-catalyzed nucleopbilic displacement chemistry described, polysulfones and other polyarylethers have been prepared by cuprous chloride-catalyzed polycondensation of aromatic dihydroxy compounds with aromatic dibromo compounds. The advantage of this route is that it does not require that the aromatic dibromo compound be activated by an electron-withdrawing group such as the sulfone group. Details of this polymerization method, known as the Ullmaim synthesis, have been described (8). 

The main polymerization method is by hydrolytic polymerization or a combination of ring opening as in (3.11) and hydrolytic polymerization as in (3.12).5,7 9 11 28 The reaction of a carboxylic group with an amino group can be noncatalyzed and acid catalyzed. This is illustrated in the reaction scheme shown in Fig. 3.13. The kinetics of the hydrolytic polyamidation-type reaction has die form shown in (3.13). In aqueous solutions, die polycondensation can be described by second-order kinetics.29 Equation (3.13) can also be expressed as (3.14) in which B is die temperature-independent equilibrium constant and AHa the endialpy change of die reaction5 6 812 28 29 ... 

Interest in anionic polymerizations arises in part from the reactivity of the living carbanionic sites4 7) Access can be provided to polymers with a functional chain end. Such species are difficult to obtain by other methods. Polycondensations yield ro-functional polymers but they provide neither accurate molecular weight control nor low polydispersity. Recently Kennedy51) developed the inifer technique which is based upon selective transfer to fit vinylic polymers obtained cationically with functions at chain end. Also some cationic ring-opening polymerizations52) without spontaneous termination can yield re-functional polymers upon induced deactivation. Anionic polymerization remains however the most versatile and widely used method to synthesize tailor made re-functional macromolecules. 

The polymerization methods to PPV and PPV derivatives described in the previous section involve 1,6-polymerization of an immediately formed 1,4-xylyl-ene derivative. Aside frome this polymerization approach, a broad spectrum of polycondensation procedures (step-growth methods) to PPV and PPV derivatives has been developed. The methods can be classified as follows ... 

When discussing various methods for the synthesis of protein-like HP-copolymers from the monomeric precursors (Sect. 2.1), we pointed to the possibility of implementation of both polymerization and polycondensation processes. The studies of the potentials of the latter approach in the creation of protein-like macromolecular systems have already been started. The first published results show that using true selected reactions of the polycondensation type and appropriate synthetic conditions (structure and reactivity of comonomers, solvent, temperature, reagent concentration and comonomer ratio, the order of the reagents introduction into the feed, etc.) one has a chance to produce the polymer chains with a desirable set of monomer sequences. 

The arrangement of metal atoms at appropriate distances in the polymer backbone (type C) is achieved by the application of either the polymerization method or a combination of monomers. In the backbone of Pt-D1 and Pt-D2 polymers, for example, platinum atoms are regularly arranged at intervals of approximately 7.7 A and 12.1 A, respectively (Table 5). In the polymers prepared by the oxidative polycondensation method (Eq. 13), the metal atoms are arranged at intervals of approximately twice the distance compared with that formed in the dehydrohalogenation reaction (Eqs. 11 and 12). 

A4 the higher temperatures used in melt polycondensations it is necessary to remove the liberated hydrogen chloride by bubbling inert gas through the reaction medium. Side reactions are common, and this polymerization method is used only rarely. No major kinetic studies have been made. 

The capture of metal complexes is achieved in the synthesis of clusters within the porous network of zeolites, where the reactants are small enough to enter the large cavities, but the clusters formed are too large to escape ( ship- in-the-bottle synthesis). The cages limit the size of the cluster compounds that can be formed and the entrance to the porous channels prevents the departure from the cages. Other methods of encapsulating metal complexes utilize polymerization or polycondensation reactions such as the sol-gel process. The metal complex is dissolved in the medium to be polymerized and is therefore trapped in the matrix formed [93] (cf. Section 3.2.2). The limitations clearly arise from the porosity of the polymer formed. A pore structure with pores that are too wide cannot prevent the leaching of the complex, whereas a pore diameter that is too small results in mass-transfer limitations. 

Fig. 1 Representative methods of hydrogel formation. (A) Chemically cross-linked hydrogels are prepared from monomers, oligomers, or polymers in the presence of cross-linking agents. The chemical cross-linking proceeds via radical polymerization or polycondensation reaction. (B) Physically cross-linked hydrogels can be formed by ionic interactions, hydrophobic interaction, or hydrogen bonding.

Excellent heat and mass transfer characteristics of the SDR have been confirmed by the study of a phase-transfer-catalyzed Darzens reaction for preparing a drug intermediate. The SDR allowed for a 99.9% reduction in reaction time, 99% reduction of inventory and 93% reduction in the level of impurities [106]. Other possible applications of the SDR include polymerizations and polycondensations (in both cases considerable time savings and more uniform product) as well as precipitation/crystallization (smaller crystals with much narrower size distribution). Two large chemical companies have patented processes based on spinning-disc technology. SmithKline Beecham has claimed a method to epoxidize substituted... 

Many methods have been reported to synthesize hyperbranched polymers. These materials were first reported in the late 1980s and early 1990s by Odian and Tomalia [9], Kim and Webster [10], and Hawker and Frechet [11]. As early as 1952, Hory actually developed a model for the polymerization of AB -type monomers and the branched structures that would result, identified as random AB polycondensates [46], Condensation step-growth polymerization is likely the most commonly used approach however, it is not the only method reported for the synthesis of statistically branched dendritic polymers chain growth and ringopening polymerization methods have also been applied. 

Many synthetic procedures exist for the preparation of three-dimensional polymers. These are polymerization and polycondensation of bifunctional (polyfiinctional) monomers, connection of reactive ends of linear chains into an entire network, or crosslinking of preformed polymeric chains by involving their reactive functional groups or additional cross-agents. Each of these methods imparts a specific topology and, hence, special properties to a network. 

Polymerization plays a key role in chemical microencapsulation. The basic mechanism of this method is to put a polymer wall (can be multilayer) through polymerization on a core material, which is in a form of small liquid droplets, solid particles, or even gas bubbles or to embed the core material in a polymer matrix through polymerization. Interfacial polymerization is one of the most important methods that have been extensively developed and industrialized for microencapsulation. According to Thies and Salaun, interfacial polymerization includes live types of processes represented by the methods of emulsion polymerization, suspension polymerization, dispersion polymerization, interfacial polycondensation/polyaddition, and in situ polymerization. This chapter is only focnsed on interfacial polycondensation and polyaddition in a narrow sense of interfacial polymerization. 

Long polymer chains are synthesized from low molecular weight compounds that are monomers. There are two main methods of synthesis polymerization and polycondensation. 

PEAs have been synthesized by ring-opening polymerization and polycondensation methods. The first ones were mainly employed to get copolymers of a-hydroxy acids and a-amino acids (i.e., polydepsipeptides) and reported in the literature [4]. Recent works are focused to the use of enzymes (e.g., lipases) as new efficient catalysts for reaction of these morpholine-2,5-diones [5]. It has been demonstrated that the configuration of the a-amino acid moiety did not affect the enzyme-catalyzed polymerization, but in contrast, the configuration of the a-hydroxy acid moiety strongly in-flnenced the polymerization behavior. Unfortunately, ra-cemization of both units was demonstrated to take place dnring polymerization. 

Hyperbranched polymers are synthesized in a one-step method, often from AB monomers but also by combining A +B (x>3) monomers or variations of those. Polymerization methods have been applied that involve polycondensation, polyaddition, and ring-opening or self-condensing vinyl polymerization. Even though the one-pot synthetic approach leads to imperfectly branched structures because of uncontrolled growth, it is more suitable for the preparation on a larger scale and thus for commercial use. Nowadays, different... 

It is clearly a truism that for reducing the fire risk in the applications of plastics, their flammability should be diminished. This is achieved either by reactive flame-retardants incorporated during the preparation (polymerization, polyaddition, polycondensation) of the polymer or by additive flame-retardants admixed in the course of plastics processing. The flammability of plastics is sometimes reduced by surface protection. The most recent methods of reducing flammability are the modification of the macromolecular structure and the development of thermally resistant polymers (high-temperature plastics). 

Poly(alkylene H-phosphonate)s can be synthesized by polycondensation and polymerization methods. 

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