Step- growth condensation

Step-growth condensation reactions, for water- soluble polymers, 20 441 Step-growth copolymerization, 7 611, 632-635... 

Step-growth condensation polymers, such as polyesters and polyamides, are formed by reversible reactions. In the case of PET, the commercial synthesis is essentially carried out by two reactions. The first is the formation of bishydroxyethyl terephthalate by esterification of a diacid with a glycol or by transesterification of a diester with a glycol. The second is the formation of the polymer by a polycondensation reaction. 

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]. 

Know the meaning of and illustrate the difference between chain-growth (addition) and step-growth (condensation) polymerization. 

An interesting thing is that the polyether with low polydispersity from chain-growth condensation polymerization possessed higher crystallinity than the one with broad molecular weight distribution from conventional step-growth condensation polymerization. The XRD pattern of the former polymer showed a stronger intensity, and the DSC profile showed the... 

Let us emphasise that the driving force for acyclic diene metathesis, which is a step-growth condensation polymerisation, is the release and removal of a small condensate molecule. The polycondensation is performed preferably under bulk conditions (no solvent used), since acyclic diene metathesis is thermally neutral and there is no need to remove the heat of the reaction, in contrast to exothermic cyclic olefin ring-opening metathesis polymerisation. 

Heck-type step-growth condensation polymerisation involves mainly palladium-based catalysts, although nickel-based catalysts are also effective. It is worth noting that this polycondensation requires a change in the oxidation state of the metal (e.g. Pd) [schemes (30) and (31)] [71], which is in contrast to chain growth polymerisation, such as ethylene/carbon monoxide alternating copolymerisation promoted by Pd-based catalysts [schemes (82) and (83) in Chapter 3], for which the preservation of the oxidation state of palladium, Pd(II), is typical [83-85] ... 

In a step-growth polymerization, any two monomers having the correct functionality can react with each other, or two polymer chains can combine. Most step-growth polymers are condensation polymers, bonded by some kind of condensation (bond formation with loss of a small molecule) between the monomers or the polymer segments. The most common condensations involve the formation of amides and esters. Dacron polyester is an example of a step-growth condensation polymer. 

Electrophoresis protein separation membranes have been prepared by step-growth condensation of water-soluble polyvinyl alcohol with selected water-soluble difunctional crosslinking agents. These membranes have broad pore size ranges, restricted pore size distribution, greater resistance to hydrolysis in an alkaline medium, and improved gel clarity when higher amounts of crosslinkers are used. 

ADMET differs from ROMP in one major respect. Whereas ROMP is a chain-growth polymerization, ADMET is a step-growth, condensation process.58 Manifestation of this difference lies in both the molecular weights and the molecular weight distributions of polymer chains that result from the two path-... 

The first substituted PTV derivatives poly(3-methoxy-2,5-thienylene vinylene) and poly(3-ethoxy-2,5-thienylene vinylene) 84 were synthesized by Elsenbaumer in the late 1980s [125], The method employed was a step-growth condensation using a nickel-mediated cross-coupling reaction between a Grignard reagent and a dichloroethene (Scheme 1-27). The materials obtained were deep blue solids, but the majority of the sample was insoluble in common organic solvents. End-... 

Synthetic polymers are used in a number of areas of life and range from the nylon used in various articles of clothing to the polyvinyl chloride (PVC) used in plumbing and other applications. Synthetic polymerization of organic monomers can take place by addition polymerization or by step-growth (condensation) polymerization. Polystyrene is a common product of addition polymerization, and nylon is a common product of step-growth polymerization. 

Table 5.1 Comparison of Step-Growth and Chain-Growth Polymerizations Step-growth/condensation polymerization Chain-growth/addition polymerization...

Step-growth/condensation polymerization Chain-growth/addition polymerization... 

Step growth condensation reactions involving multifunctional reactants. More or less densely crosslinked products such as epoxy and phenol-formaldehyde resins may be prepared by the reaction of multifunctional monomers or prepolymers with each other or with other appropriate molecules. 

Another advantage of the DPE functionalization methodology is that it can be used to prepare condensation macromonomers, 34, which are polymers with two polymerizable ftmctional groups at one chain end. This type of macromonomer can participate in step-growth (condensation) polymerization with other diftmctional monomers to form model comb-type, branched condensation copolymers. 

A cure reaction yielding volatile products, such as water in step-growth condensation reactions, should always be examined in sealed pans withstanding high internal pressure to obtain accurate kinetic data. In pans with loose fitting lids, the endothermic evaporation of volatile products is sometimes sufficiently large to compensate for the exothermic heat of reaction. Moreover, it is impossible to obtain quantitative data when sample mass is continuously changing by loss of volatile products. 

Step-growth condensation copolymerisations give rise to additional experimental difficulties, with respect to the former reactions studied, due to the continuous release of e.g. water. Indeed, the evaporation of water produced by the reaction may obscure the detection of the cure process and prohibit a reliable quantification of the reaction heat and the reaction conversion. To illustrate how condensation polymerisations can be studied by MTDSC, the post-cure condensation reactions of melamine-formaldehyde (MF) resins will be discussed [91]. 

The free energy change in step growth condensation, AF = A// — TA5 = RT In K. By plotting In K against reciprocals of absolute temperatures, one obtains roughly a linear relationship. Sawada wrote, therefore,... 

Step-growth polymer (See also Condendsadon polymer. Section 17.12 and Specif Topic C in WileyPLUS)-. A polymer produced when bifunctional monomers (or potentially bifunctional monomers) react with each other through the intermolecular elimination of water or an alcohol. Polyesters, polyamides, and polyurethanes are all step-growth (condensation) polymers... 

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