Chain architecture distribution

In some of these models (see Sec. Ill) the surfactants are still treated as flexible chains [24]. This allows one to study the role of the chain length and chain conformations. For example, the chain degrees of freedom are responsible for the internal phase transitions in monolayers and bilayers, in particular the hquid/gel transition. The chain length and chain architecture determine the efficiency of an amphiphile and thus influence the phase behavior. Moreover, they affect the shapes and size distributions of micelles. Chain models are usually fairly universal, in the sense that they can be used to study many different phenomena. 

Multiblock OBCs from chain shuttling polymerization have very different architectures. The overall chains and blocks within chains have distributions of molecular weights, with MJMn approaching 2.0. The statistical shuttling process produces chains with a distribution in the number of blocks per chain. The block junctions are precise since each block is grown on a different catalyst, and the compositions are homogeneous since the OBCs are produced at steady-state in a continuous reactor. 

This review demonstrated that research on diallyldimethylammoium chloride and its polymers have contributed to the general understanding of the polymerization of ionic monomers, the development of methods for the molecular characterization possibilities of cationic polyelectrolytes, and the understanding regarding polyelectrolyte behavior. However, in comparison to the industrial importance of diallyldimethylammonium chloride polymers, the level of fundamental knowledge is far from adequate. In particular, copolymerization processes with monomers other than acrylamide, the characterization of copolymers related to their chain architecture and charge distribution, the dependence of... 

The main feature of polymers is their MMD, which is well known and understood today. However, several other properties in which the breadth of distribution are important and influence polymer behavior (see Figure 1) include physical, the classical chain-length distribution chemical, two or more comonomers are incorporated in different fractions topological, polymer architecture may differ (e.g., linear, branched, grafted, cyclic, star or comb-like, and dendritic) structural, comonomer placement may be random, block, alternating, and so on and functional, distribution of chain functions (e.g., all chain ends or only some carry specific groups). Other properties the polymers may disperse (tacticity and crystallite dimensions) are not of the same general interest or cannot be characterized by solution methods. 

Linking processing to molecular architecture. Molecular mass distribution and chain architecture will be linked to a constitutive response. New chain architecture may be discovered which give processing advantage. 

Although quite complex hybrid block copolymer architectures can now be synthesized, obtaining these materials in a state of high purity typically requires additional measures. As discussed above, many of the hybrid copolymers contain homopolymer impurities, which must be removed by selective solvent extractions or fractional precipitation when possible. Since conventional NCA polymerizations also usually give polypeptide segments with large chain length distributions, these samples are ideally also fractionated... 

To obtain an unambiguous characterization of a particular material, it is often essential to fractionate a material (1-3). Synthetic polymers are rarely homogeneous chemical species, but have multivariate distributions in molecular weight, chemical composition, chain architecture, and functionality (4). For a precise characterization of a synthetic polymer, all the distributions need to be determined, which is a difficult, if not virtually impossible, task. Traditionally, fractionation has allowed separation of pol5miers on the basis of molecular mass or chemical composition (2). With proper techniques it is often possible to separate and characterize complex homo- and copolymer species on the basis of chemical heterogeneity and molar mass. 

The final system that is worth mentioning in this chapter on LRP in emulsion is the use of 1,1-diphenylethylene (DPE) (127). DPE adds to a growing radical and forms a radical with a reactivity too low for propagation. The exact mechanism is not elucidated, but the incorporation of DPE leads to a chain that allows chain extension or block copolymer formation. More or less similar to what was described about the xanthates in RAFT polymerization, here also the molar mass distributions are relatively broad. The greatest advantage of DPE-mediated polymerization is the fact that it results in minimal disturbance of the polymerization process. The product latex does not contain any unusual extractable material (like the catalyst in ATRP), or polymer-bound colored moieties (like the thiocar-bonylthio compound in RAFT). The obvious drawback is the limited control over chain architecture, and the limited understanding of the mechanistic details. 

The microstructure of the SAN copolymer with respect to the chain sequence distribution can be found from the first-order hidden Markov model. The HMM architecture is shown in Figures 11.1A and B. The conditional dyad probabilities... 

Consider the two strings S and T, with one of them, S, having a chain sequence distribution with a block architecture. 

MOLECULAR WEIGHT DISTRIBUTION AND CHAIN ARCHITECTURE (LINEAR OR STAR)... 

The molecular weight distribution and chain architecture for polymers prepared in these living polymerizations can be controlled by post-poljnnerization reactions, such as by the reaction of the "living ends" with compounds such as tin tetrachloride. 

We devoted special attention to characterize all the polymers that were prepared for this study. The characterization techniques listed in Table 4 were used for determining (1) comonomer composition, butadiene microstructure, and sequence distribution of the monomer units (2) molecular weight, molecular weight distribution, and chain architecture ... 

MOLECULAR WEIGHT MOLECULAR WEIGHT DISTRIBUTION CHAIN ARCHITECTURE... 

---