Connectivity between repeating units

A limitation of the freely jointed chain model is that the bond angle 9 linking polymer repeat units is constant (e.g., 9 = 109.5 for tetrahedrally connected carbons), which results in some degree of correlation between repeat unit orientations. A model termed the freely rotating chain model fixes the bond angle between repeat units, but allows free rotation about bonds connecting them (Figure 7.5). In this case, it can be shown that... 

Polyalkenes form by linking carbon atoms in a free radical polymerization. The polymer structure is constructed by connecting monomer units. The polymerization process converts the bonds of the monomers to a bonds between polymer repeat units. 

As we have explained in the previous two chapters, polymers are long chains of repeat units connected by bonds. One consequence of these long chains is the high number of intermolecular forces present between polymer molecules. The character of the bonds in a polymer will partially define the strength of the intermolecular interactions between the molecules. 

The conformational mobility of a chromophoric main-chain polymer is often connected to its electronic structure. Therefore, changes in the UV-visible absorption spectra and/or chiroptical properties are spectroscopically observable as thermo-, solvato-, piezo-, or electrochromisms. It is widely reported that o-conjugating polysilanes exhibit these phenomena remarkably clearly.34 However, their structural origins were controversial until recently, since limited information was available on the correlation between the conformational properties of the main chain, electronic state, and (chir)optical characteristics. In 1996, we reported that in various polysilanes in tetrahydrofuran (THF) at 30°C, the main-chain peak intensity per silicon repeat unit, e (Si repeat unit)-1 dm3 cm-1, increases exponentially as the viscosity index, a, increases.41 Although conventional viscometric measurements often requires a wide range of low-dispersity molecular-weight polymer samples, a size exclusion chromatography (SEC) machine equipped with a viscometric detector can afford... 

As mentioned above, in this simulation, one repeating unit located in the middle of the center stack is selected and modeled. In the middle of the center stack, the boundaries between the single unit and adjacent units are regarded to be thermally adiabatic. Hence, for the thermal boundary conditions at the surfaces of the solid part connecting the next units, adiabatic boundary conditions are employed. In a practical cell stack, the fuel and air are introduced into the channel through man-... 

PFSA membrane is better connected than that in Nafion. This signature of better coimectivity of aqueous domains in SSC at intermediate hydration level shown for the small molecular weight chains (trimers), is also observed for the simulations of the chains composed of 15 repeat units as depicted in Fig. 10. In Fig. 9(c), the high value of Ro (4.5 A) has shifted all the curves to larger cluster sizes. Still, where there is a difference between the two polymer electrolytes, SSC PFSA membrane shows a more connected aqueous domain. 

Fig. 13 Above Schematics of a hairy-rod polymer consisting of a stiff backbone and flexible covalently connected side chains. N, Zk, and v are the number of segments, the segment length (the Kuhn length), and the volume of the beds of the side chains, respectively M, Zu, L, and d are the number of the repeat units, distance between grafting points (the unit length) and the length and diameter of the rod, respectively. Below. End-on schematics of (a) nematic (Nem) and (b) hexagonal (Hex) phase of hairy-rod molecules. Adapted from [24]...

---