Polycondensation reaction scheme

Ferrocene polymers with nonlinear optical properties were also prepared via Knoevenagel polycondensation reactions. " Scheme 32 shows the reaction of monomer 123 with 124 to give the accordion polymer 125 with values ranging from 9100 to 26,600." A mixture of A and Z isomers was initially obtained however, an isomerically enriched polymer (98% E isomer) could be isolated through selective precipitation. 

Synthetic strategies for the preparation of polymers according to the AB or AA + BB type of polycondensation reactions (Scheme 11.6), combined with endcapping processes, can also be applied here, provided that a sufficient separation of the generated oligomers is feasible. Mullen and coworkers [214] published a... 

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 ... 

Wang and coworkers first reported the use of these monomers as a novel elastomeric material for potential application in soft tissue engineering in 2002. The molar ratio of glycerol to sebacic acid they used was 1 1. The equimolar amounts of the two monomers were synthesized by polycondensation at 120°C for three days. The reaction scheme is shown in Scheme 8.1. To obtain the elastomers, they first synthesized a prepolymer and then poured an anhydrous 1,3-dioxolane solution of the prepolymer into a mold for curing and shaping under a high vacuum. 

The fabrication of colloidal silica and optical glasses by the sol-gel process has attracted a great deal of attention (8). The process relies on the hydrolytic polycondensation reactions of alkoxysilanes, usually (EtO)4Si, in which the reactive silanols (EtO)4 Si(OH)n (n = 1-4) are formed. These then undergo acid- or base-catalyzed condensation with both water and alcohol formation, as shown in Scheme 2. 

Acyclic diene metathesis (ADMET) is a step-growth polycondensation reaction for the polymerization of o -dienes 729 The process is catalyzed by the same metal alkylidene initiators used for ROMP, and is driven by the removal of ethylene from the system (Scheme 13). Both molybdenum and ruthenium-based initiators have been used to prepare a variety of materials including functionalized polyethy-... 

The 1,2-O-cyanoethylidene method also became the basis for a polycondensation reaction, which allowed the synthesis of many polysaccharides [37]. When both the O-trityl and cyanoethylidene groups are present in the same molecule as in 31, polycondensation takes place under glycosidation conditions giving a polysaccharide chain, for example 32 (Scheme 5.11). 

Esterification is the first step in PET synthesis but also occurs during melt-phase polycondensation, SSP, and extrusion processes due to the significant formation of carboxyl end groups by polymer degradation. As an equilibrium reaction, esterification is always accompanied by the reverse reaction being hydrolysis. In industrial esterification reactors, esterification and transesterification proceed simultaneously, and thus a complex reaction scheme with parallel and serial equilibrium reactions has to be considered. In addition, the esterification process involves three phases, i.e. solid TPA, a homogeneous liquid phase and the gas phase. The respective phase equilibria will be discussed below in Section 3.1. 

Many studies on the modelling of esterification, melt polycondensation, or solid-state polycondensation refer to the reaction scheme and kinetic data published by Ravindranath and co-workers. Therefore, we will examine the data sources they have used over the years. The first paper concerned with reactor modelling of PET production was published by Ravindranath el al. in 1981 [88], The reaction scheme was taken from Ank and Mellichamps [89] and from Dijkman and Duvekot [90], The kinetics for DEG formation are based on data published by Hovenkamp and Munting [60], while the kinetics for esterification were deduced... 

The new polymers 9-28 were synthesized by the Pd-catalyzed reaction of (4,4 - or 5,5 -dibromo-2,2 -bipyridine)-bis(4,4 -terf-butyl-2,2 -bipyridine or 2,2 -bipyridine)ruthenium(II) complexes 5-8 and diethynylarenes (Table 2) in a step-growth polycondensation mechanism (Scheme 4). The typical reaction conditions used for the synthesis of the polymers involved stirring the argon-... 

The use of HMF or the corresponding dialdehyde precursors obviously applies to the synthesis of monomers for polycondensation reactions as shown by the examples given in Scheme 2. ITiese difimctional structures again mimic the corresponding well-known aliphatic and aromatic counterparts used in the preparation of polyesters, polyamides, polyurethanes, etc. 

Galbis et al. described a variety of carbohydrate-based linear polyesters 61 of the poly(alkylene dicarboxylate) type that were obtained by polycondensation reactions of the alditols 2,3,4-tri-(9-methyl-L-arabinitol (9) and 2,3,4-tri-O-methyl-xylitol (10), and the aldaric acids 2,3,4-tri-(9-methyl-L-arabinaric acid (26) and 2,3,4-tri-(9-methyl-xylaric acid (27), butanediol, and adipic acid were also used as comonomers [28]. Copolyesters of the poly(aIkylene-c )-arylene dicarboxylate) type were obtained using bisphenols as comonomers (Scheme 1). Chemical polycondensation reactions were conducted in bulk or in solution. Enzymatic polycondensation reactions of adipic acid with the above-mentioned alditols were carried out successfully using Lipozyme and Novozyme 435. The hydrolytic degradations of some of these polyesters were also described. 

Syntheses of phenoxy-substituted polynaphthylimides and polyperyleneimides were carried out in accordance with Scheme 5.4 [37, 38]. All polycondensation reactions were carried out under high-temperature solution polycondensation conditions in phenolic solvents (w-cresol, m- or p-chlorophenols) using benzimidazole and benzoic acid as catalysts. All the reactions proceeded homogeneously and led to the formation of deeply coloured polymers. General properties of the polymers are listed in Table 5.6. 

Recently, a number of studies have been aimed at expanding the scope of palladium- and nickel-catalyzed polycondensation reactions through new twists on established routes or the advent of entirely new reaction pathways. The Ni(0)-catalyzed homo-coupling polymerization of triflate-substituted benzenes 17, as shown in Scheme 22, was utilized to synthesize a number of PPP derivatives [74-76]. Structural characterization indicated that these polymers are para-linked,... 

The mechanism snfficiently explains how prodnctive condensation metathesis occms since terminal alkenes are contained in every step of the productive cycle (Scheme 5). In this kinetically controlled regime (high concentration of terminal alkene present), alkylidene reactions with unsubstituted (terminal) alkenes are favored over interchain redistribution reactions or other degenerate eqnilibria. However, when terminal alkene concentration decreases near the end of the polycondensation reaction, competing... 

Scheme III. Use of end-capped siloxane oligomers. R is C2Hs- The polycondensation reaction is not balanced stoichiometrically.

Figure 5. Reaction scheme of polycondensation of cardanyi acrylate (CA) with m-Phenylene Diamine (MPDA) and Furfural (FF) in the presence of acid as the catalyst.

For anti-Hib vaccine, s)mthetic chemistry was compelled to reach the efficiency level attained during the production of the glycoconjugate vaccine from natural CPS. The contribution of several groups [149] to the synthesis of Hib-oligosaccharides paved the way for further improvement. A simplified synthesis of the repeating disaccharide unit and chain elongation process in one step through a polycondensation reaction were essential achievements before further developments and clinical evaluation were possible (see O Scheme 6). The synthetic... 

Other synthesis methods have also been developed but may not be practiced on a large commercial scale as compared to those indicated above. Examples of syntheses that begin from liquid phase precursors include the sol-gel, hydrothermal, and Pechini methods. In the course of these reaction schemes, polycondensation or precipitation occurs, and the volatile components are removed, often by thermal methods. Other synthesis routes to ceramic materials include the nitridation of metals to form metal nitrides and the carbothermal reduction of oxides to form carbides and borides. 

Given these rigorous demands for the success of a polycondensation reaction, there are several reasons why olefin metathesis is particularly well suited for polycondensation. The first is that although olefin impurities are detrimental to ADMET, other more common synthetic impurities are not, unless they react with the catalyst. Secondly, like most polycondensations, ADMET is a reversible process and removal of the condensate will shift the equilibrium towards higher molecular weight polymer. The condensate molecule for ADMET, ethylene, is a gas at room temperature and is thus readily removed from the reaction mixture to drive the reaction to high conversion (Scheme 6.4). 

As with all polycondensation reactions, the formation of cychc ohgomers by ADMET is possible and has been demonstrated in a variety of cases [31-33]. This occurs by intramolecular back-biting metathesis of an active metal carbene with an internal olefin of the polymer (Scheme 6.5) to hberate cyclooctadiene, for example, from ADMET polybutadiene, although larger cychcs have also been observed. A related undesired cyclization is the intramolecular cyclization of the monomer by RCM. 

Thus we will consider coke formation on the surface of the adsorbent/catalyst as the polycondensation of starting organic substances or the products of an earlier reaction of these substances which are capable of further reactions [13]. The process of formation of polycondensation products cannot be presented by only one chemical reaction (Scheme 1 illustrates only the general mechanism of coke formation.) This process can be imagined as a multitude of different polycondensation reaction processes leading to hypermolecular structure of the condensation products. 

The possibility of insertion of aquo- and amine-copper(II) complexes or chromium(III) complexes into a PMS matrix during the synthesis was discussed [40,41]. Tetraamino complexes of copper such as [Cuen2(H20)2] and hexa- and penta-amino complexes of chromium [Cren3] + and [Cr(NEt3)5Cl] were used. The synthesis of the adsorbents was performed in aqueous solutions at pH 9-10, in which amino complexes of transition metals undergo alkaline hydrolysis forming hydroxo-complexes. The presence of hydroxyl groups in the coordination sphere of the metal allowed a polycondensation reaction between the complex and hydrolysis products of sodium methylsiliconate (see Scheme 7). 

The enantioselective alkynylation of ketones catalyzed by Zn(salen) complexes has been reported [24]. Polymeric salen ligand 30 was prepared with a polycondensation reaction and subsequently used as a polymeric chiral ligand of Zn. The polymeric Zn(salen) complex (prepared by 30) was then used as a catalyst of asymmetric addihon of phenylacetylene to aldehyde in the presence of 2 equivalents of Et/Zri. Subsequent asymmetric alkynylahon of 31 gave 33 in 96% yield and 72% ee (Scheme 3.9) [25]. 

The lack of dependence of the reaction rate for polycondensation on the extent of reaction (to a first approximation) allows a simple bimolecular reaction mechanism to be employed. Noting, from the previous section, that the reaction mechanism for simple esterification reactions (Scheme 1.1) had as the rate-determining step the second reaction, namely... 

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