Random polymerization

Figure 8.5 illustrates the sort of separation this approach predicts. Curve A in Fig. 8.5 shows the weight fraction of various n-mers plotted as a function of n. Comparison with Fig. 6.7 shows that the distribution is typical of those obtained in random polymerization. Curve B shows the distribution of molecular weights in the more dilute phase-the coacervate extract-calculated for the volumes of the two phases in the proportion 100 1. The distribution in the concentrated phase is shown as curve C it is given by the difference between curves A and B. 

Analysis of DSC experiments on various alkyl-substituted trimers gave even more disappointing results. Although more thermally resilient, these macrocycles polymerized with very broad exotherms. For the hexyl-substituted trimer, melting occurred around 150 °C, while polymerization extended from ca. 170 to 230°C. This pattern was thought to be indicative of a random polymerization process. Overall, polymerization of trimeric macrocycles occurred at sufficiently high temperatures that the resultant materials were intractable brown tars. 

Transformation of the initially deposited remains of living organisms started in the water columns and in the upper layers of bottom sediments of ancient seas. Random polymerization and condensation reactions of degraded biopolymers are believed to have formed the initial geopolymers, which contain humin, fulvic and humic acids. Until now these compounds (very typical for soil humus as well) are... 

Free-radical initiation of emulsion copolymers produces a random polymerization m which the trans/ds ratio cannot be controlled. The nature of ESBR free-radical polymerization results in the polymer being heterogeneous, with a broad molecular weight distribution and random copolymer composition. The microstructurc is not amenable to manipulation, although the temperature of the polymerization affects the ratio of trans to cis somewhat... 

There is another way to confirm that the triad distribution cannot result from a random polymerization. The observed relative proportion of the triad structure in Figure Id is (l) (.93) (.26). The corresponding distribution for the triad structure for, 266 mole fraction VCI2 would be (l) (,36) (.13) Obviously, this comparison confirms from just a consideration of the triad distribution that the polymer does not conform to Bernoullian statistics. 

Synthesis of silica-based materials with controlled skeleton structures, such as zeolites, requires controlling the structure of oligomeric silicate species at the first reaction step. Organic quaternary ammonium ions, which are known as organic templates in zeolite synthesis (1 ), have a role in making up the specific structures of silicate anions, whereas silicate anions randomly polymerize in aqueous solutions containing alkali metal ions, resulting in the presence of silicate anions with different structures. 

The multibridging complexes shown in Fig. 7 can be connected to each other by adding suitable transition metal ions as linking elements, however, in most of the cases this procedure leads to insoluble, random polymeric materials. A better control was achieved by employing suitable metal complexes as ending elements in... 

This reasoning predicts that a reactivity ratio or an r V2 product greater than unity will decrease with increasing temperature and vice versa. The tendency for random polymerization will increase and the tendency for monomer alternation will decrease with increasing reaction temperature, so long as the same copolymerization mechanism predominates over the experimental temperature range. 

Random polymerization of diphenyl-4-styrylphosphine 42 with 12 mol. equiv. of N-isopropylacrylamide 43 in the presence of 4mol% of AIBN gave 44 in 89% yield. Complex 41 was synthesized by self-assembly of 44 and (NH4)2PdCU (45) [45]. The catalyst could be reused ten times without a significant reduction in its activity. 

We have carried out contact angle and XPS studies of the various polymers indicated in Table I and have found significant differences in their behavior. Apparently PS serves to protect the surface to a large extent when present in block form. However, styrene/ butadiene copolymers which are randomly polymerized are attached by ozone approximately as efficiently as pure butadiene. 

The formation of 2,2-biquinoline from pyrolysis of quinoline suggest that the main reaction mode is thermal cracking and subsequent random polymerization to heavier molecules. 

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 ... 

Diamino derivatives of carbohydrates have been employed for polycondensation reactions with carboxyl-activated aliphatic and aromatic dicar-boxylic acids. The resulting polyamides are of the AABB type (nylons-m,n analogs), and therefore, the regio- and stereoregularity in the polyamide chain is determined by the configuration of the carbohydrate precursor. When such a molecule lacks a C2 axis of symmetry, random polymerization leads to nonstereoregular polyamides. 

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