Polymerization degree, polycondensation

The second category of polymerization reactions does not involve a chain reaction and is divided into two groups poly addition and poly condensation [4]. In botli reactions, tire growth of a polymer chains proceeds by reactions between molecules of all degrees of polymerization. In polycondensations a low-molecular-weight product L is eliminated, while polyadditions occur witliout elimination ... 

Thus, ESR data confirm (a) the lower-ring polycondensation and polymerization degree of HAs and FAs from organic amendments with respect to soil HAs and FAs and (b) the partial incorporation of the amendment on these structural properties into native soil HAs and FAs. 

The bottleneck in the origin of life is the formation of the functional biopolymers— enzymes and nucleic acids. The answer cannot be the random polycondensation from a chaotic mixture of the monomers, as this process would afford an astronomic number of different chains—ca. 10 for chains with a polymerization degree of 60. Given that, the probability that the same chain is produced more than once by a random polymerization process is in first approximation equal to zero the single active individual macromolecule, even if formed, would decompose before it could be made again by another chance event. How then can active macromolecules be formed ... 

Stringent purity conditions are required in carrying out polymerizations. In the free radical polymerization of styrene, no more than a few ppm oxygen is needed to terminate or prevent polymerization. In polycondensation, 1% of monofunctional impurities may limit the average degrees of polymerization to below 100 (see 17.2.2.). 

Molar mass averages and polydispersity can be calculated theoretically for various polymerization reactions. In the case of polycondensation of monomer type a-R-b (e.g., hydroxy acid) or the equimolar mixture of monomers a-Ri-a and b-Ri-b the average polymerization degrees are as follow ... 

Polyanhydrides have been synthesized by various techniques such as melt polycondensation, ring-opening polymerization, interfacial polycondensation, dehydrochlorination, and dehydrative coupling (13,14). The most widely used technique for polyanhydride synthesis is melt polycondensation, which occurs in two steps. In the first step, dicarboxylic acid monomers react with excess acetic anhydride to form acetyl-terminated anhydride prepolymers (1) with a degree of polymerization (DP) ranging from 1 to 20 (eq. 1). 

Effects of the solvent, polymerization time, intrinsic viscosity and pH on the degree of the specific rotation of polyhexamethylene-c -tartaramide were investigated. From the results of hydrolysis of the polymer, it was found that c/-tartaric acid is not racemized during condensation polymerization. Interfacial polycondensation of diamines with r/-tartaric acid derivatives failed. 

Poly(oxysilicon phthalocyanine)s (27) have been synthesized with polymerization degrees between 10 and 200 by the polycondensation of dihydroxy silicon, phthalocyanine (26) at 350-400 °C and 1 kPa (lOmbar) (equation i3).22o-222... 

The structure of the -(GT-6-P04-6-PA) - macromolecule can be regarded as a copoly (ether-6-ester) chain, -(GT-6-P04) -, in which some of the tereph-thalate groups (T) are replaced by PA blocks. A characteristic feature of the preparation of -(GT-6-P04-6-PA)n- (similarly to the synthesis of -(GT-6-P04)n-) is the formation of the ester block during the polycondensation step. This enables the control of the polymerization degree of this block through the change in the dimethyl terephthalate (DMT) mole fraction with respect to the other reactants. The PA/PO weight ratio can be used to affect the distribution of these blocks in the macromolecule. However, one should bear in mind that the terpoly(ester-6-ether-6-amide)s are random block polymers. 

The concept of functionaUty and its relationship to polymer formation was first advanced by Carothers (15). Flory (16) gready expanded the theoretical consideration and mathematical treatment of polycondensation systems. Thus if a dibasic acid and a diol react to form a polyester, assumiag there is no possibihty of other side reactions to compHcate the issue, only linear polymer molecules are formed. When the reactants are present ia stoichiometric amouats, the average degree of polymerization, follows the equatioa ... 

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