Polymer chain alignment

Apart from the tunable color emission covering the full visible range, there are several other aspects supporting the interest in PTs for PLEDs. PTs are examples of classical conjugated polymers with intrinsic one-dimensionality of the polymer chain. Alignment can induce anisotropy in macroscopic properties such as electron transport or optical properties. Polarized... 

Crystallinity refers to a regular, ordered, three-dimensional crystal lattice portion of a polymer (Kroschwitz, 1990) where the polymer chains align themselves in perfect parallel array. There are no purely crystalline polymers, as all polymers, even so-called crystalline polymers, have some portion of amorphous content. Nonetheless, crystalline regions of polymers can form up to 98% of the polymer structure (Rosen, 1993) and have consequent large impacts on mechanical behavior. 

We have proposed that crystallinity occurs when segments of linear polymer chains align and interact favorably with each other. When a crystalline polymer is cooled from the melt, some of the chains line up and form crystallites because it is thermodynamically favorable for them to do so. The extent of crystallinity depends upon a number of factors, including the polymer structure and the rate of cooling. 

Anisotropy generally strengthens a polymer specimen in, and weakens it perpendicular to, the direction of orientation. This effect has a simple molecular origin related to polymer chain alignment, as was discussed in Section 1 l.B.4. 

Beiermann BA, Kramer SLB, May PA, Moore JS, White SR, Sottos NR (2013) The effect of polymer chain alignment and relaxation on force-induced chemical reactions in an elastraner. Adv Funct Mater 24 1529-1537... 

At a molecular level, the development of the neck means that the stress apphed to the fiber is apparently rather high therefore it leads to the break up of the semi-crystalline structure with random orientation of the crystallites (i.e. the one shown in Figure 4.1 c). In the neck zone the structure rearranges since polymer chains align on stretching. As a result, the chains are eventually orientated as shown in Figure 4.3 a. So the fiber becomes anisotropic and therefore stronger. 

Cycloaliphatic LC PEAs based on commercially poly(l,4-cyclohexanedimelhylene terephthalate) (PCX) have also been synthesized with two cycloaliphatic diamines and a linear counterpart (1,6-hexamethylenediamine) (Figure 8.12) [55]. The compositions of the ester/amide units in the copolymers were varied up to 50% by the adjustment of the amounts of the diol and diamine in the feed. The introduction of amide linkages was found to induce nematic LC properties into the polyester backbone, which in turn increased the polymer chain alignment. Interestingly, the introduction of nematic LC phases into PCT was only possible when a low ratio of amide units (i.e., less than 25 mol%) was incorporated into the polymer backbone. 

Films of the conducting polymer, poly(p-phenylene vinylene), (PPV) are obtained from a water-soluble sulfonium-salt precursor polymer. Chain-aligned... 

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