Condensation polymerization catalysts

Benzoin, [119-53-9] 2-hydroxy-2-phenylacetophenone, CgH CH(OH)COCgH (mp, 133—137°C bp, 343—344°C at 101.3 kPa), is formed by the self-condensation of benzaldehyde in the presence of potassium cyanide. It is used on a small scale as a polymerization catalyst in polyester resin manufacture. 

Polymerization of olefins such as styrene is promoted by acid or base or sodium catalysts, and polyethylene is made with homogeneous peroxides. Condensation polymerization is catalyzed by acid-type catalysts such as metal oxides and sulfonic acids. Addition polymerization is used mainly for olefins, diolefins, and some carbonyl compounds. For these processes, initiators are coordination compounds such as Ziegler-type catalysts, of which halides of transition metals Ti, V, Mo, and W are important examples. 

Process in wliich the addition of heat, catalyst or both, with or without pressure, causes the physical properties of the plastic to change through a chemical reaction. Reaction may be condensation, polymerization or addition reactions. 

Most of the compounds in this class have been prepared from preexisting crown ether units. By far, the most common approach is to use a benzo-substituted crown and an electrophilic condensation polymerization. A patent issued to Takekoshi, Scotia and Webb (General Electric) in 1974 which covered the formation of glyoxal and chloral type copolymers with dibenzo-18-crown-6. The latter were prepared by stirring the crown with an equivalent of chloral in chloroform solution. Boron trifluoride was catalyst in this reaction. The polymer which resulted was obtained in about 95% yield. The reaction is illustrated in Eq. (6.22). 

Acid catalysts, such as metal oxides and sulfonic acids, generally catalyze condensation polymerizations. However, some condensation polymers form under alkaline conditions. For example, the reaction of formaldehyde with phenol under alkaline conditions produces methy-lolphenols, which further condense to a thermosetting polymer. 

They find that heating cyclotri- and cyclotetrasilazanes with ammonium halide catalysts at temperatures of 160°C for 6-8 h results in a condensation polymerization process that evolves ammonia and leads to the formation of waxy polysilazanes. Analytical results suggest that these polysilazanes consist of rings linked by silyl bridges as illustrated by the following structure ... 

The conventional route to prepare I generally involves a high temperature melt polymerization of hexachlorocyclotriphosphazene, or trimer (IV). Recent studies have demonstrated the effectiveness of various acids and organometalllcs as catalysts for the polymerization of IV (8). Alternate routes for the preparation of chloro-polymer which do not involve the ring opening polymerization of trimer have been reported in the patent literature (9. 10). These routes involve a condensation polymerization process and may prove to be of technological importance for the preparation of low to moderate molecular weight polyphosphazenes. 

Unfortunately, the most favorable polymerization conditions (active catalyst, neat monomer) lead rapidly to solidified, high-viscosity reaction mixtures. Highly viscous media can severely inhibit condensation polymerizations, since inefficient removal of the small molecular weight product (in this case, hydrogen) slows approach of the reaction to completion. Raising the temperature to lower the viscosity is counterproductive, since cyclic formation becomes competitive at higher temperatures. 

Previously mentioned spacer mediated technique to obtain single site catalytic groups for enhanced catalytic efficiency was put to use by McKittrick M.W. et al. for the successful synthesis of a variety of site-isolated group 4 metal-olefm polymerization catalysts (Figure 24) [93]. This methodology was developed as an alternative to co-condensation and performed much more favorably than catalysts formed from grafting APTS and subsequent synthesis. 

PCH materials offer new opportunities for the rational design of heterogeneous catalyst systems, because the pore size distributions are in the supermicropore to small mesopore range (14-25A) and chemical functionality (e.g., acidity) can be introduced by adjusting the composition of the layered silicate host. The approach to designing PCH materials is based on the use of intercalated quaternary ammonium cations and neutral amines as co-surfactants to direct the interlamellar hydrolysis and condensation polymerization of neutral inorganic precursor (for example, tetraethylorthosilicate, TEOS) within the galleries of an ionic lamellar solid. 

Block copolymers may also be made by condensation polymerization. Elastomer fibers are produced in a three-step operation. A primary block of a polyether or polyester of a molecular weight of 1000-3000 is prepared, capped with an aromatic diisocyanate, and then expanded with a diamine or dihydroxy compound to a multiblock copolymer of a molecular weight of 20,000. The oxidative coupling of 2,6-disubstituted phenols to PPO is also a condensation polymerization. G. D. Cooper and coworkers report the manufacture of a block copolymer of 2,6-dimethyl-phenol with 2,6-diphenylphenol. In the first step, a homopolymer of diphenylphenol is preformed by copper-amine catalyst oxidation. In the second step, oxidation of dimethylphenol in the presence of the first polymer yields the block copolymer. 

Nafion-H has also been used as a catalyst for the oligomerization of styrene. The reaction was studied by Higashimura and co-workers.933,934 Hydroxy-terminated poly (alkylene)oxides were prepared by condensation-polymerization of 1,8-octanediol and 1,10-decanediol in the presence of Nafion-H.935 It showed higher activity than sulfuric acid consequently, polymerization could be carried out at lower temperature. 

As outlined earlier, three methods of polymerization have been established for the preparation of thiophenes, viz. electrochemical polymerization [189, 190], oxidative chemical polymerization using Lewis acid catalysts such as FeCl3 [191,192], and step-growth condensation polymerization using transition metal-catalyzed coupling reactions [lj]. 

The polysulfide then reacts by a condensation polymerization with the difunctional and trifunctional chloro compounds. It is also possible to react cyclic S8 with a mercaptan-capped molecule or dithiol in a condensation reaction in the presence of a basic catalyst. An example is the reaction with ethanedithiol (reaction (10)) 56... 

A variety of condensing agents, such as triphenylphosphite/pyridine [4,5] and DBOP/triethylamine [6], which are used in amounts equivalent to functional groups on monomers, had been developed by the 1980s, whereas new catalysts that promote condensation polymerization exactly with a catalytic amount were developed in the last decade. 

After the development of catalyst-transfer condensation polymerization of polythiophene, the block copolymer of polythiophene and PMA could be prepared more easily. As mentioned above, the vinyl-terminated polythiophene was first prepared. The vinyl group was converted to the 2-hydroxyethyl group by hydroboration, followed by esterification with 2-bromopropionyl bromide to give a macroinitiator for ATRP (Scheme 101)... 

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