Stepwise polycondensation

Initially PDPs were synthesized by stepwise polycondensation of linear activated depsipeptide [93]. In 1985, Helder, Feijen and coworkers reported the synthesis of PDPs by ROP of a morpholine-2,5-dione derivative (cyclic dimer of ot-hydroxy- and a-amino acid cyclodepsipeptide, cDP) [94, 95]. The ROP method gives an alternative type of PDP by homopolymerization and also allows the copolymerization with other monomers (lactones and cyclic diesters) including LA, GA, and CL to give a wide variety of functional biodegradable materials. The synthesis of PDPs as functional biomaterials has been recently reviewed [17]. 

The formation of oligo(alkylsilsesquioxanes) by hydrolysis of higher alkyltrichloro-silanes is assumed to result from consecutive, stepwise polycondensation... 

While condensation polymers account for only a modest fraction of all synthetic polymers, most natural polymers are of the condensation type. The first all-synthetic polymer, Bakelite, was produced by the stepwise polycondensation of phenol and formaldehyde. 

The kinetics for stepwise polycondensation reactions and the kinetics for monofunctional aminations and esterifications are similar. Experimentally, both kinetic approaches are... 

Chain scission is similar to the opposite of stepwise polycondensation where units are split apart in a random manner. 

Scheme 7. The stepwise polycondensation synthetic strategy to polycatenane.

The principle of the second synthetic approach to polycatenanes, i.e. stepwise polycondensation, has been proposed by Shaffer and Tsay, but not experimentally demonstrated [42, 43], This approach has the advantage over multifunctional polycondensation that a linear polymer is formed before cyclization (Scheme 7). However, the second step, which consists of the cyclization of n macrocycles along the polymer chain 19, is likely, again, to give rise to an undefined network, containing some rotaxane and catenane units 21, similar to the multifunctional polycondensation approach. 

An experimental attempt towards polycatenanes 9, based on a strategy related to the stepwise polycondensation approach, was reported in the seventies. Karagoumis et al. took advantage of the interface between a nonpolar phase (air, CC14) and a polar phase (H2O, Hg) to orient alkanes a,oj-disubstituted with polar groups (Scheme 9) [45], The successive addition of macrocycles of ring sizes 15-60 atoms and of difunctional species, susceptible to reaction with the a,o>disubstituted al-... 

Polyester, a condensation polymer, can be produced by chainwise, acid-catalyzed ring openings of cyclic ester (lactone) without expulsion of small molecules, and also by stepwise polycondensation of ohydroxycarboxylic acid. 

Molecular Weight Determination. As mentioned earlier, the GPC results for our samples are based on a polystyrene calibration curve. As such, all numbers must be regarded on a rel ati va basis. PS based weight average molecular weights, Mw, were about 10b for highly reacted samples. Actual Mw values may be lower even by a factor of 2, based on calculations for an stepwise polycondensation with 99% conversion (18). Mw versus DBTDL concentrations for a typical series are shown inTigure 13. As observed the effect of a hotter mold wall... 

Urea, formaldehyde Stepwise polycondensation Particle-board binder resin (60%), ... 

Melamine (trimerization of cyanamide), formaldehyde Stepwise polycondensation Dinnerware, table tops, coatings... 

There are numerous examples of the use of extruders to carry out chemical reactions in polymeric systems (Xan-thos, 1992). In genial, two types of reactions are carried out in extruders polymerization or depolymerization and polymer modification. In this section we illustrate the approach to modeling reactive extrusion by considering the stepwise polycondensation reaction of two species A and B in a singlescrew extruder. 

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