Numbering of Chains

The first four members of the alkane series (methane, ethane, propane, butane) are irregular subsequent members are named systematically by attaching -ne to the list of numerical prehxes given in Table 3.1. 

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Short chains of amino acid residues are known as di-, tri-, tetrapeptide, and so on, but as the number of residues increases the general names oligopeptide and polypeptide are used. When the number of chains grow to hundreds, the name protein is used. There is no definite point at which the name polypeptide is dropped for protein. Twenty common amino acids appear regularly in peptides and proteins of all species. Each has a distinctive side chain (R in Figure 45.3) varying in size, charge, and chemical reactivity. 

The amount of branching introduced into a polymer is an additional variable that must be specified for the molecule to be fully characterized. When only a slight degree of branching is present, the concentration of junction points is sufficiently low that these may be simply related to the number of chain ends. For example, two separate linear molecules have a total of four ends. If the end of one of these linear molecules attaches itself to the middle of the other to form a T, the resulting molecule has three ends. It is easy to generalize this result. If a molecule has v branches, it has v 2 chain ends if the branching is relatively low. Branched molecules are sometimes described as either combs or... 

Can branching be ruled out, since it would obviously make the number of chain ends per molecule an unknown quantity ... 

With either S or H as additives, two different kinds of chain are present A BAB. .. ABAB and A BABAB. . . ABABAA with S or B BABAB. . . ABAB with H. In these cases the total number of acid and base groups counts the total number of chain ends. There are two equivalents of total chain ends per mole of chains. Therefore, for S, [total ends] = 39.9 + 2.4 = 42.3 and... 

We need to know the number of chains per unit volume and must calculate the result on this basis ... 

Not only does this calculation overcount the number of chains involved, but it makes no attempt to consider any compensation from the perpendicular direction. 

Note that as M the absolute number of chain ends per unit volume decreases, as does the chain-end correction. 

The effect of branching is to increase the number of chain ends and, therefore, free volume, which decreases Tg. Conversely, crosslinking ties together separate molecules, decreases the number of loose ends, and raises Tg. Copolymers show different effects on T, depending on the microstructure... 

The number average degree of polymerization is given by dividing the number of repeat units by the number of chains, or... 

One distinction that should be pointed out involves the comparison of Eqs. (5.1) and (5.40). In the former we considered explicitly the AB monomer, while the latter is based on the polymerization of AA and BB monomers. In both instances is obtained by dividing the total number of monomer molecules initially present by the total number of chains after the reaction has occurred to extent p. Following the same procedure for different reaction... 

Telomerization Reactions. Butadiene can react readily with a number of chain-transfer agents to undergo telomerization reactions. The more often studied reagents are carbon dioxide (167—178), water (179—181), ammonia (182), alcohols (183—185), amines (186), acetic acid (187), water and CO2 (188), ammonia and CO2 (189), epoxide and CO2 (190), mercaptans (191), and other systems (171). These reactions have been widely studied and used in making unsaturated lactones, alcohols, amines, ethers, esters, and many other compounds. 

The final step of the oxidation process is the formation of CO2, and this also occurs by a number of chain sequences such as... 

In which X is the average monomer interpenetration distance, L is the contour length of interdiffused chains and n(t) is the number of chains diffused at time t. The time and molecular weight dependence of these molecular properties are given in Table 1. 

Since L and X are constant, in the absence of brush-like ordering. Pc Xc, which represents a critical number of chains required to build up the network above the percolation level. Hence we have... 

A set of flexible chains is considered in the canonical NVT ensemble. The density of chains, pch = - ch/ (- ch is a chosen number of chains), is the parameter of simulation. The system of flexible chains in question has been equilibrated, then during the productive part of the simulation run the pair... 

Only one polymer molecule is produced per mole of inhibitor. The inhibitor must be at least equimolar with the number of chains formed. Concentrations must be chosen (usually very low) to give the desired molecular weight. 

Reaction conditions should usually be chosen such that the fraction of initiator-derived chains (should be greater than or equal to the number of chains formed by radical-radical termination) is negligible. The expressions for number average degree of polymerization and molecular weight (eqs. 13 and 14) then simplify to eqs. 15 and 16 ... 

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