Semicrystalline, arrangement molecules

The crystalline plastics (basic polymers) tend to have their molecules arranged in a relatively regular repeating structure such as polyethylene (PE) and polypropylene (PP). This behavior identifies its morphology that is the study of the physical form or structure of a material. They are usually translucent or opaque and generally have higher softening points than the amorphous plastics. They can be made transparent with chemical modification. Since commercially perfect crystalline polymers are not produced, they are identified technically as semicrystalline TPs. The crystalline TPs normally has up to 80% crystalline structure and the rest is amorphous. 

Biopolymers such as proteins have a hierarchical structure (this can be compared to semicrystalline polymers. Section 2.7.2). The primary structure is simply the sequence of amino-acid residues in the polymer chain. This is created during the synthesis of each molecule, and is memorized , in other words it is not destroyed by thermal motion of the chain. Methods for determining primary structure have now been discovered, and even automated. The secondary structure of biopolymers results from hydrogen bonding between -CO and -HN groups. This leads to the so-called a and (3 structures of proteins. An a-helix and p-sheet are sketched in Fig. 6.13. The tertiary structure refers to the overall arrangement of the macromolecule, an example is shown in Fig. 6.14. 

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