End branch

A drawback of this approach is that it typically generates enormous and imwieldy synthesis trees which contain a large number of dead-end branches which are not worth further consideration. Furthermore, the chemist is forced to follow a rigid scheme during the planning process, alternating between the application of transforms, the derivation of new precursors, and again the application of further transforms to these precursors. 

For example, there was a dead-end branch, 12 in. in diameter and 3 m long, in a natural-gas pipeline operating at a gauge pressure of 550 psi (38 bar). Water and impurities colleeted in the dead-end, which corroded and failed. The escaping gas ignited at once, killing three men who were looking for a leak [4J. 

Design coverage is the square foot coverage per sprinkler and is the product of the distance between branch lines times the distance between sprinklers on branch lines. Also, the distances from end branch lines and end sprinklers on branch lines to wall must be checked to verify these distances do not exceed one-half the distance between branch lines or sprinklers on branch lines. This has a direct bearing on the coverage at the perimeter of the building. 

Transfer of the free radical to another molecule serves as one of the termination steps for general polymer growth. Thus, transfer of a hydrogen atom at one end of the chain to a free radical end of another chain is a chain transfer process we dealt with in Section 6.2 under termination via disproportionation. When abstraction occurs intramolecularly or intermolecularly by a hydrogen atom some distance away from the chain end, branching results. Each chain transfer process causes the termination of one macroradical and produces another macroradical. The new radical sites serve as branch points for chain extension or branching. As noted above, such chain transfer can occur within the same chain as shown below. 

To this end, branching has been determined conventionally in dilute solution by the ratio of intrinsic viscosities of branched and linear polymers having the same molecular weight, defined by (3) ... 

It is also interesting to note that the bipyridine complex 131 with a slightly smaller end-branched fluorocarbon chain forms only SmA and SmC phases. In the SmA phase the layer distance (d = 4.8 nm) is significantly shorter than the length... 

This result includes Eq. 10 of Johnson and Stewart (1965) and Eq. 2 of Satterfield and Cadle (1968) as special cases. Equation (3.4-11) predicts K = 1/3 for isotropic pore systems with no dead-end branches this value is accurate within a factor of 2 for many pelleted catalysts (Johnson and Stewart 1965 Brown et al. 1969 Horak and Schneider 1971). 

Structural defects and/or irregularities are weak points. They may function as initiation sites for degradation, and thus usually decrease the TTOS. Such weak points include chain ends, branches, chain backbone unsaturation (such as double bonds involving at least one atom of the chain backbone), and carbonyl groups incorporated in polymers (such as polyethylene) where they are not a part of the normal structure. 

Styryl-terminated Frechet-type dendrimers have been introduced as novel polymer crosslinkers by Seebach et al. [43-45]. They are constituted of four to 16 peripheral styryl units attached to aryl end branches of dendritic TADDOL, BINOL or Salen ligands and were copolymerised with styrene by suspension polymerisation. The catalytic performance of the polymer-bound catalyst was identical to that of the homogeneous analogues however, the supported catalysts could be used in many consecutive catalytic runs with only small loss in catalytic activity. A major drawback of fixing the catalytic unit in the core of the crosslinker is the poor loading capacity of the final polymer (0.13-0.20 mmol g 0> especially when high amounts of catalysts (10-20 mol%) are needed. 

Ethylene/propylene copolymers made with these nickel catalysts contain up to 6 mol % propylene. When the nickel catalysts were combined with supported chromium catalysts, branched polyethylene (5.0 methyl-ended branches per 1000 carbon atoms) was produced by the chromium copolymerizing ethylene with the a-olefins that were produced in situ by the nickel catalyst. Like the catalysts above, nickel catalysts with anionic ligands may themselves be supported on inorganic supports and polymeric supports. " ... 

The combination of amphiphilicity with distinct molecular shapes and topologies result in new modes of LC self-assembly, which are more complex than the simple and well-established sequence SmA-Cubv-Col-Cubi. For these end-branched molecules with a linear or slightly bent shape, a transition from micellar to a kind of vesicular-like self-assembly in Cubsj i phases takes place upon core elongation from compound 91 to 92 and 93 ( = 12-16) (Fig. 5.31). This work is important for the understanding of the nontrivial relation between self-assembly and molecular... 

Each data-line contains at the end branching ratios (in percents) of y-transitions to the levels situated below this excited state. In cases when there are many transitions from a certain initial state the corresponding horizontal line has a continuation in the Supplement (CD) where branching ratios of all known transitions are given. 

Referring to the standard ASTM D 883 again, a polymer is a substance consisting of molecules characterized by the repetition (neglecting ends, branch junctions and other minor irregularities) of one or more types of monomeric units. 

The T of these polyurethanes [81] followed classical trends in that, for the networks, the use of aromatic diisocyanates resulted in high values (about 100 C) associated with the stiffness of their moieties, whereas with the aliphatic counterparts, values around room temperature indicated much higher chain flexibility. The T s of the soluble fractions were much lower than those of their corresponding crosslinked materials, which is in tune with the presence of very mobile open-ended branches, generated by the insertion of monofunctional monomers into the polymer structure. 

Homopolymer (1946) n. High polymers consisting of molecules that contain (neglecting the ends, branch junctions, and other minor irregularities) either a single type of unit or two or more chemically different types in regular sequence. Odian GC (2004) Principles of polymerization. John Wiley and Sons Inc., New York. 

The number 2k - i is the number of paths that are not connected to the network matrix. The sum on i starts from 2 because i = 1 indicates that the branch point is the end branch point that has already been counted. The end groups do not contribute to elasticity of the network because they are free from external stress, but they contribute to the viscosity and the relaxation time of the network due to friction with the solvent molecules. 

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