Polymerization condensation process

Polymerization and depolymerization of sihcate anions and their interactions with other ions and complexing agents are of great interest in sol—gel and catalyst manufacture, detergency, oil and gas production, waste management, and limnology (45—50). The complex silanol condensation process may be represented empirically by... 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

The second general method, IMPR, for the preparation of polymer supported metal catalysts is much less popular. In spite of this, microencapsulation of palladium in a polyurea matrix, generated by interfacial polymerization of isocyanate oligomers in the presence of palladium acetate [128], proved to be very effective in the production of the EnCat catalysts (Scheme 3). In this case, the formation of the polymer matrix implies only hydrolysis-condensation processes, and is therefore much more compatible with the presence of a transition metal compound. That is why palladium(II) survives the microencapsulation reaction... 

Presumably, any type of strong base will react with cyclosilazanes to form amido species. If amido species are extremely susceptible to fragmentation then reactions such as reaction (11) would promote depolymerization rather than polymerization. Consequently, the only way polymeric species can form would be through a condensation process that leads to trisubstituted nitrogens and fused rings. 

Note 2 The earlier term polycondensation (namely, polymerization by a repeated condensation process, i.e., with elimination of simple molecules [1]) was synonymous with condensation polymerization . It should be noted that the current definitions of polycondensation and condensative chain polymerization were both embraced by the earlier term polycondensation . 

Recently Fujiwara et al. reported on the in vitro polymerization of trans-polyisoprene using the enzymes isopentenyl diphosphate isomerase (IDI) and fra 3-isoprenyl diphosphate synthase (IDS) [271]. IDI catalyzes the interconversion of IPP and DMAPP. IDS can now catalyze the polymerization of IPP from DMAPP as outlined above for the synthesis of natural rubber, and as outlined in Fig. 13a. However, the condensation process is inhibited due to hydrophobic interaction between IDS and hydrocarbon of the longer products. The hydrophobic chain of the elongating product does not readily protrude into the aqueous phase and it tends to interact with the enzyme. To achieve an efficient in vitro synthesis, the authors used an organic-aqueous two-liquid phase system to successfully synthesize (low molecular weight) fran.y-polyisoprene (see Fig. 13b). 

Only syntheses which involve the formation of new glycosidic linkages will be considered in this article. This restriction excludes many interesting examples of copolymerization in which only one of the monomers is a carbohydrate (or carbohydrate derivative), the polymerization of carbohydrate derivatives which contain a polymerizable group4 (such as acrylate), and the polymerization of sugar lactones.1 Many of these topics have already been discussed in reviews.1-8 Also outside the scope of this article is the chemical modification of naturally occurring polysaccharides thus, we have excluded the industrially important process of dextrini-zation,10 except as it may pertain to acid condensation processes. The radiation-catalyzed polymerization and modification of carbohydrate poly-... 

Because of the highly exothermic nature of acrylonitrile polymerization, bulk processes arc not normally used commercially. Howevei. a commercially feasible process lor bulk polymerization in a continuous stirred lank reactor has been developed. The heat nl reaction is controlled hy operating at relatively low conversion levels and supplementing the normal jacket cooling with reflux condensation of umcaclcd monomer... 

The polyamides trace their origin to the studies of W. H. Carothers, begun in 1928, on condensation polymerization, a process that involves the repetition many times of a reaction known to the organic chemist as a condensation reaction because it links two molecules together with the loss of a small molecule. Esterification and amidation are examples ... 

Polymers are made from the repeating units through two process. One process simply adds each succeeding monomer onto the chain through various methods, called addition polymerization. Condensation polymerization is the second process of adding monomers onto the chain to make large molecules. In condensation polymerization, small molecules like water are removed as the monomer unit is added onto the chain. 

In 1999, Muzafarov and coworkers published a preliminary report describing the synthesis of a hyperbranched poly(siloxane) from triethoxysilanol via a rapid, ammonia-catalyzed condensation process (Scheme 28)192. The authors acknowledged the potential difficulties of this process (e.g. head-head condensation leading to crosslinked products) but presented 29Si NMR data to support their conclusion that hyperbranched polymer was formed. The fact that no gel formation was observed also suggested that the polymerization proceeded as expected. The polymer, a transparent, yellow liquid, was characterized with NMR and IR spectroscopy, and GPC. 

The rate equation with strongly acidic catalysts is also second order in silanol and first order in catalyst (75). The mechanism is proposed to proceed via protonation of silanol, followed by an electrophilic attack of the conjugate acid on nonprotonated silanol. The condensation processes outlined in reactions 16a and 16b for sulfonic acids is also an applicable mechanism for the acid catalysis. The condensation polymerization in emulsion catalyzed by dodecylbenzenesulfonic acid is second order in silanol, but the rate has a complex dependence on sulfonic acid concentration (69). This process was most likely a surface catalysis of the oil-water interface and was complicated by self-associations of the catalyst-surfactant. 

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