Polycondensation polymerization contrasted

Polycondensation In contrast to polyaddition and polymerization adhesives, a byproduct, for example, water, develops during curing. Apart from the application of heat, adequate pressurizing of the adherends is required (see autoclave). 

Since such a polyaddition proceeds mechanistically like a condensation polymerization, many authors refer to it as an addition polycondensation, in contrast to the substitution polycondensation of Equation (lS-2). 

AS) close to zero, so that even a low reaction enthalpy suffices to promote the polycondensation. In contrast, polyaddition is characterized by a large negative reaction entropy, so that a highly exothermic reaction is needed to effect the polymerization. The requirement of a highly exothermic reaction strongly limits the number of addition reactions suited for a successful polymerization. In the case of polycondensations even a reaction enthalpy around zero may allow for the synthesis of a high molar mass polymer, when the byproduct is transferred into another phase (e.g., evaporization of CO2 or crystallization of NaCl). From the thermodynamic point of view polycondensations of cyclic monomers represent an intermediate case, as discussed in Chap. 9. 

We now report a convenient method for the interfacial polycondensation of 1,1 -bis(3-aminoethyl)ferrocene (1) with a variety of diacid chlorides and diisocyanates, leading to ferrocene-containing polyamides and polyureas. In some instances, we have been able to observe film formation at the interface. Moreover, the polymerization reactions can be conveniently conducted at ambient temperatures in contrast to earlier high-temperature organometallic condensation... 

In contrast to template polycondensation or ring-opening polymerization, template radical polymerization kinetics has been a subject of many papers. Tan and Challa proposed to use the relationship between polymerization rate and concentration of monomer or template as a criterion for distinguishing between Type I and Type II template polymerization. The most popular method is to examine the initial rate or relative rate, Rr, as a function of base mole concentration of the template, [T], at a constant monomer concentration, [M]. For Type I, when strong interactions exist between the monomer and the template, Rr vs. [T] shows a maximum at [T] = [M]q. For type II, Rr increases with [T] to the critical concentration of the template c (the concentration in which template macromolecules start to overlap with each other), and then R is stable, c (concentration in mols per volume) depends on the molecular weight of the template. 

In contrast to the process of creating a secondary dispersion as was used for the preparation of, e.g., polyurethanes and epoxide resins, it was shown that the miniemulsion polymerization process allows one to mix monomeric components together, and polyaddition and polycondensation reactions can be performed after miniemulsification in the miniemulsified state [125]. 

Step-growth polymerizations at high temperatures produce nearly random copolymers because of end-group interchange reactions like (5-14) between macromolecules. Interfacial and low-temperature solution polycondensations are conducted under essentially irreversible conditions, by contrast. In these cases the average copolymer composition and blocklike character of the product may depend on the reaction conditions and relative reactivity of the functional groups involved in the polymerization. 

The products contain the metal in a five-coordinated environment, with a chelating amide carbonyl group (CONMe2) for the latter. Reactions (c) and (d) occur at — 78°C at ambient temperature and, in contrast to group IVB derivatives MesMNMcz, even a trace of amide caused polymerization or polycondensation of the acetylenedicarboxylic ester. 

In interfacial polymerization a pair of immiscible liquids is employed, one of which is usually water while the other is a hydrocarbon or chlorinated hydrocarbon such as hexane, xylene, or carbon tetrachloride. The aqueous phase contains the diamine, diol, or other active hydrogen compound and the acid receptor or base (e.g., NaOH). The organic phase, on the other hand, eontains the acid chloride. As the name suggests, this type of polymerization occurs interfacially between the two Hquids. In contrast to high-temperature polycondensation reactions, these reactions are irreversible because there are no significant reactions between the polymer product and the low-molecular-weight by-product at the low... 

In contrast to addition polymerization, low-molar mass compounds are evolved in polycondensation (condensation polymerization). 

PEAs have been synthesized by ring-opening polymerization and polycondensation methods. The first ones were mainly employed to get copolymers of a-hydroxy acids and a-amino acids (i.e., polydepsipeptides) and reported in the literature [4]. Recent works are focused to the use of enzymes (e.g., lipases) as new efficient catalysts for reaction of these morpholine-2,5-diones [5]. It has been demonstrated that the configuration of the a-amino acid moiety did not affect the enzyme-catalyzed polymerization, but in contrast, the configuration of the a-hydroxy acid moiety strongly in-flnenced the polymerization behavior. Unfortunately, ra-cemization of both units was demonstrated to take place dnring polymerization. 

Bresler expected that polycondensation should take place between stearic aldehyde 27 at the interface and either of the amines 28 or 29 which was present in the subphase, to produce polyaminals 30. > The former combination was supposed to produce 2-D Hnear polymers (The authors a linear polymer in 2-D confinement), and actually gave rise to a product that exhibited no elastic properties and only an increased viscosity. In contrast, the latter combination afforded a product which behaved as a brittle soUd that was ascribed to a 2-D network (The authors an irregularly crosslinked monolayer in 2-D confinement). The copolymerization of pepsin with either formaHn or a diamine was also studied, and this resulted in elastic, rubber-like films. In none of these cases were any details of degree of polymerization nor any structural analysis of the products provided, however. 

The van der Waals bonds between monomer molecules are replaced by covalent bonds between the monomeric units in polymerization. Since van der Waals bond lengths are about 0.3-0.5 nm and covalent bond lengths are, in contrast, about 0.14-0.19 nm, a general contraction occurs. The contraction increases with decreasing monomer molecule size, since more van der Waals bonds per unit mass must be eliminated. Thus, ethylene contracts by about 66%, vinyl chloride by about 34%, styrene by about 14%, and W-vinyl carbazole by as little as about 7.5%. Polymerization of ethylene oxide leads to a volume contraction of 23%, of tetrahydrofuran to one of about 10%, but that of octamethyl cyclotetrasiloxane, however, to a contraction of only 2%. Some strained bicyclic ring systems even polymerize with an expansion. With polycondensation, the volume contraction is smaller with decreasing size of eliminated residue. Polycondensation of hexamethylene diamine with adipic acid leads to a contraction of 22% (water elimination), that of hexamethylene diamine and dioctyl phthalate, on the other hand, to one of 66% (elimination of octanol). 

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