Polymer, branched Drawing

Here we are drawing a hydrodynamic analogy between multi-tube reptation and polymer branching. deGennes s work indicates that a branched chain frictional coefficient should increase exponentially with the size or number of branches. 

Die-swell and draw-resonance ratio data for these polymers are presented in Table 13.2 and Table 13.3, respectively. According to these results, the influence of branching and molecular weight is significant. The extremely large increase in... 

In discussions of structure we must limit ourselves to the case of linear polymers, for with the branched polymers so far studied their complexity has defied analysis. Here, however, as I have discussed elsewhere [11], it is possible to draw up a rational classification of the types of structure as defined by the arrangements of hydrogen bonds taken as the main element in intra- and inter-chain linking. 

The fibrillar structure of crystalline polymers is determined by molecular characteristics, the initial morphology and orientation conditions. Recently, a complex investigation of the effect of molecular parameters (MW, MWD and degree of branching) and orientation parameters (temperature and draw ratio) on the morphology of PE and its thermomechanical behaviour has been reported 181 185). 

Branches occur on the branches also, so amylopectin has a treelike structure. Glycogen, the food reserve of animals, has a structure similar to that of amylopectin except that it has branches every 8 to 10 glucose units. The structures of these two polymers are represented schematically in the following drawings ... 

Hyperbranched polymers also possess a dendritic architecture, but with imperfect branching. The basic structural features present in these molecules are the same as in dendrimers, namely, a core surrounded by layers of BC capped with terminal units. The one-pot syntheses used to create these treelike stmctures also rely upon AB -type monomers (Scheme 30.1), but without protecting groups preventing simultaneous condensation reactions. The resulting polymers typically have broad MWD ( ) > 2), with multiple isomers and geometries. Because they are created in a single reaction step, hyperbranched polymers are more economical to produce than dendrimers as their synthesis is less time and resource intensive. This trait represents a major draw for industry and the development of commercial applications for dendritic polymers... 

Figure 2.17 I Differences between linear and branched polyethylene are illustrated. The left-hand panel shows hnear, or high-density polyethylene, and the right-hand panel shows the branched, or low-density form. In each case, the upper diagram illustrates the molecular structure for part of a polymer chain. The lower diagrams show the way that polymer chains would pack together to form the solid plastic. (Hydrogen atoms are omitted in those drawings ft)r clarity.) Branched chains cannot approach one another as closely, so the resulting material has a much lower density.

Fig. 9. Immature spherulites in a 5% blend of linear polyethylene in branched polymer (a) undeformed (b) drawn horizontally 4.5x at 75°C (c) detail revealing zigzags of rotated lamellae in phase parallel to the draw direction (d) detail of the extremity of an object as in (b), showing how individual lamellae have become disrupted giving an interrupted appearance. SEM images bar = 10 /xm. From Ref 124.

Lewis structures (Sect. 1.3) A drawing style in which the electrons take center stage, linear polymer (Sect. 27.6) A polymer that has only a minimal amount of branching or no branching at all. 

---