Polymers structural arrangements

Prevalence of the head-to-tail arrangement in vinyl polymers is abundantly confirmed by determinations of polymer structures. Staudinger and Steinhofer found that destructive distillation of polystyrene at about 300° yielded 1,3-diphenylpropane, 1,3,5-triphenyl-pentane, and 1,3,5-triphenylbenzene... 

Structural arrangements in polymers can be exceedingly complex. Crystals are rare, but not unknown. By first growing monomer crystals of diacetylene molecules, and then photo-polymerizing them, large optical-quality polydi-acety-lene crystals can be made, for example. 

The most common of all natural polymers is cellulose. It is ubiquitous in plant life in various molecular modifications and structural arrangements. Large quantities are found in the trunks, branches and leaves of trees as well as in... 

It is noteworthy that the value of g is different from zero and relatively large. This result suggests that the electric and magnetic contributions to the nonlinearity are essentially of the same order of magnitude. This large value of the magnetic contributions is probably due to the near centrosym-metric arrangement of the monomer units in the helical polymer structure... 

The variation in polymer structures is observed when the backone of the polymer molecule contains a carbon atom attached to two different side groups. Such polymers can have different configurational arrangements or tacticity. 

The polymer prepared from same monomer is called homopolymer. If more than one monomer is used, the polymer obtained is called copolymer which may be of following four types depending on their structure arrangements ... 

Descriptions of polymer structures revealed by studies of physical properties focus attention on the distribution of local arrangements present in the molecules, and terms useful in this context are defined in this section. (The terms defined here in relation to complete polymer molecules can also be applied to sequences and to blocks, as in Ref. 2, Definition 3.14.)... 

After a listing of some general definitions relating to crystalline polymers (Section 1), the subject is divided into sections dealing, successively, with local structural arrangements at the scale of a few bond lengths (Section 2), morphological aspects (Section 3), molecular conformation within polymer crystals (Section 4) and, finally, kinetic aspects of crystallization (Section 5). An alphabetical index of terms is provided for the convenience of the reader. 

This type of arrangement (III) is usually referred to as a head-to-tail (H-T) or 1,3-placement of monomer units. An inversion of this mode of addition by the polymer chain propagating alternately via Eqs. 3-9 and 3-8 would lead to a polymer structure with a 1,2-placement of substituents at one or more places in the final polymer chain. 1,2-Placement is usually... 

Polymers are unlike low-molecular-weight compounds in that they have no uniform structure and are a mixture of macromolecules of diflFerent length and diflFerent structural arrangements, even when derived from a single monomer. 

Lithium and alkyllithiums in aliphatic hydrocarbon solvents are also used to initiate anionic polymerization of 1,3-butadiene and isoprene.120,183-187 As 1,3-butadiene has conjugated double bonds, homopolymerization of this compound can lead to several polymer structures. 1,4 Addition can produce cis-1,4- or tram-1,4-polybutadiene (19, 20). 1,2 Addition results in a polymer backbone with vinyl groups attached to chiral carbon atoms (21). All three spatial arrangements (isotactic, syndiotactic, atactic) discussed for polypropylene (see Section 13.2.4) are possible when polymerization to 1,2-polybutadiene takes place. Besides producing these structures, isoprene can react via 3,4 addition (22) to yield polymers with the three possible tacticites ... 

Morphology is the order or arrangement of the polymer structure. The possible order between a molecule or molecule segment and its neighbors can vary from a very ordered highly crystalline polymeric structure to an amorphous structure (i.e., a structure in greatest disorder or random). The possible range of order and disorder is clearly depicted on the left side of Fig. 1.14. For example, a purely amorphous polymer is formed only by the non-... 

The potential of block copolymers in forming supramolecular structures on surfaces has been studied in great detail by Stupp and co-workers [36]. Their studies have concentrated on the supramolecular properties of diblock and triblock rod-coil polymers which consist of one or two components that are conformationally flexible and one component with a more rod-like character at one of the ends of the polymer chain ( c in Figure 4.25). This latter component can be crystallized and is expected to yield well-defined structural arrangements. The Stupp-type copolymers are based on diblock styrene-b-isoprene coils combined with various rod-like components. The synthesis of such materials is carried out in two stages. In the first step, the diblock coil part is produced, as shown in Figure 4.26. The... 

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