Distribution of repeat units

Because of the random nature of the distribution of repeat units, each contribution to the left-hand side of this expression is equal and... 

Random copolymers are a special type of statistical copolymer in which the distribution of repeat units is truly random (some words of caution are necessary here because older textbooks and scientific papers often use the term random copolymer to describe both random and non-random statistical copolymers). A section of a truly random copolymer is represented below ... 

There are several examples of random copolymers of methacrylates (R-l to R-3). MMA/nBMA copolymerization was carried out with a copper catalyst, but the products were of low molecular weight because this study was directed to mechanistic studies.263 Random copolymers of MMA and nBMA (R-l) were also obtained in emulsion (MJMn = 1.2—1.3).254 Two monomers were consumed almost simultaneously to give a random or statistical distribution of repeat units along the chains. Copolymerization of MMA... 

Strictly speaking, random copolymers are copolymers in which the distribution of repeating units is truly random. They should be considered only as a special type of statistical copolymer, because the term statistical copolymer includes all copolymers in which the sequential distribution of the repeating units may follow different statistical laws such as zero-, first- or second-order Markov, depending on the specific reactants and the method of synthesis. However, most literature references use the terra random copolymer independent of the type of statistical distribution, which is seldom known.)... 

Chemical heterogeneity in synthetic polymers offers a challenge to the analytical chemist to devise sensitive techniques for the characterization of these chemical distributions. It is well known that many synthetic copolymers consist of a collection of polymer chains that differ in their individual compositions. This distribution of repeat-unit composition from chain to chain can influence the physical properties of synthetic polymers significeuitly. Consequently, a thorough characterization of a copolymer sample would include a description of the average composition eUid its compositional distribution. 

The polymerization of D3 was followed by GC/MS. After 36 h, the reaction was quenched by the introduction of trimethylchlorosilane. About 92% of the D3 had been converted, while the amount of unconverted D/ had not changed significantly. Si NMR analyses allowed the determination of the sequence distribution of repeat units, which showed no random copolymerization of D/ and D3 as in the case of diblock copolymers prepared by sequential anionic copolymerization of D3 extended with D/. Because the polymerization of the first monomer could not be carried out to completion (<100% conversion) without increasing the molecular weight distribution, the second monomer (with faster propagation rates) had to be introduced before the equilibration reaction became established. Therefore, unreacted monomer from the first step was still in solution when the second monomer was added. The risk of random copolymerization can be suppressed if the second monomer has far higher reactivity towards polymerization than the first monomer. The block formed in the second step contained only a few methylvinylsiloxane units, i.e. the block purity was very high. 

I. Introduction n. Chemical Composition in. Sequence Distribution of Repeat Units... 

In the previous sections, it was shown that racemic and isotactic polymers of PMEPL have been prepared. The former is made of chains having a random distribution of repeat units of S and R configurations whereas the latter consists only of units of R or S configurations. Two sorts of isotactic chains can, therefore, be synthesized, plus one racemic chain ... 

Copolymers often have different properties than either of their corresponding homopolymers. A list of some common copolymers and their apphcations is presented in Table 27.3. Copolymers are often classified based on the order in which the monomers are joined together. Alternating copolymers contain an alternating distribution of repeating units, while random copolymers contain a random distribution of repeating units. 

Alternating copolymers contain an alternating distribution of repeating units, while random copolymers contain a random distribution of repeating units. 

The pronounced upfield shift of the dibrominated adjacent ring allowed an estimation of the distribution of repeating units in copolymers VI and XII since the characteristic peak only occurred when the dlbromo ring preceded the other type of ring. The relative intensities of shifted cind unshifted pe dcs for all samples Indicated a random distribution. 

Effects of Repeat Unit Sequence Distribution and Specific Interactions. Most theories and quantitative structure-property relationships for Tg only consider the case of a random distribution of repeat units along the polymer chains in treating copolymers. They give equations which predict a monotonic change of Tg between the Tg values of the homopolymers of the constituent repeat... 

Random copolymers, in which the distribution of repeating units is random ... 

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