Chain populations

P. E. Smith and B. M. Pettitt. Amino acid side-chain populations in aqueous and saline solution Bis(penicillamine) enkephalin. Biopolymers, 32 1623-1629,... 

Figure 12.5. (a) Lattice model showing a polymer chain of 200 beads , originally in a random configuration, after 10,000 Monte Carlo steps. The full model has 90% of lattice sites occupied by chains and 10% vacant, (b) Half of a lattice model eontaining two similar chain populations placed in contact. The left-hand side population is shown after 50,0000 Monte Carlo steps the short lines show the loeation of the original polymer interface (courtesy K. Anderson). 

We further characterized a sample by MALDI-TOF and SiNMR (run 5, Table 1). The MALDI TOF analysis shows the presence of multiple chain populations with different chain-ends, SiOH/SiOH (A), SiOH/SiOMe (B) and SiOMe/ SiOMe (C) (Fig. 5). A Si NMR spectrum of the same sample is given in Fig. 6, where it shows the presence of D, D, in addition to the linear polymer and the absence... 

The most extensive ESR studies of polymers under tensile load have undoubtedly been carried out on drawn crystalline fibres, and this work has been reviewed recently by Kausch and De Vries It is clear that the morpholines of oriented crystalline fibres, with extensive tie-chain populations and hn d rees of molecular uncoiling, strongly favour the incidence of molecular hracture under tensile stress. 

Z]/[Q]), so that R ranges from 0 to v as the molecules making up the system become more condensed. In systems in which finite chain and ring structures coexist, it is advisable to calculate an Rehains value for the chain population alone by subtracting the concentrations [T], [Z] and [Q] associated with cyclic molecules from the total concentrations of the T s, Z s and Q s respectively. 

The families of a,o)-dimethoxyl poly(methylphosphonates) for which p 2, alkyl polyphosphates for which p = 2, sodium polyphosphates for which p = 3 and aliphatic hydrocarbons for which p % 2 are examples of systems for which more than (v — 1) equilibrium constants are needed to represent the scrambling equilibria involving the chain population (since p > 1). 

Figtire 15.1, reproduced from the work of Rutledge and co-workers [6], illustrates the molecular picture of the inteiphase, in which three types of chain populations exist bridges that join two crystal lamellae, loops that have their entry and exit points on the same crystal lamellae, and tails that terminate in the amorphous phase. 

Being continuous, the advantage of CPF over the other techniques previously discussed lies in the fact that larger polymer samples can be fractionated in relatively shorter times. This is particularly important if large fractions with narrow MWD or CCD are required for the establishment of structure-property relationships or to remove, on a technical scale, chain populations that are imdesirable for a given application of specialty polymers. 

The application of Crystaf analysis for detecting blend composition is, of course, limited by cocrystalhzation, particularly if accurate quantitative information is required. As previously discussed, cocrystalUzation is found to be significant when two chain populations crystallize at relatively close temperature ranges (small A Tq), even for very slow CRs. Therefore, the use of Crystaf for determining blend compositions will be more adequate when the blend components have distinctly separated Crystaf peak temperatures (large ATc). Preferably, the difference between Crystaf peak temperatures should be more than 10 °C, particularly in the case where the blend components have similar molecular structures. 

In Chapter 3, evidence was cited which indicated that a Bence Jones protein is a homogeneous representative of the heterogeneous normal L chain population (6,7). Because of their homogeneity these proteins are suitable for amino acid sequence analyses the latter have conclusively shown that Bence Jones proteins are typical, although homogeneous, L chains. 

About two-thirds of the species investigated (all mammals) have unblocked H chains, comprising from 19 to 100% of the H chain population. Unblocked H chains were always homologous to human Vhui in sequence. 

The average monomer interpenetration depth of segments on the interdiffusing chains, jc(0, is obtained from an integration over the Gaussian segment density profiles of the inter-diffused minor chain population,(2i) such that... 

In free-radical polymerization, there are two chain populations inside the reactor radical chains and dead chains. Each population has a MWD. These distributions can be derived from mass balances of their respective species. For a radical chain having chain length r, we have... 

The radical chain population is very small compared with the dead-chain population ( P ] 10 -10" moll" vs. [M] 1-10 mol r ). In terms of polymer product, the dead-chain population represents the total polymer. Ecjuation [59] is important for polymer production, but not so for polymer applications. 

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