Thermal transitions and physical structures

Propagation is a chain reaction involving very rapid addition of monomer to the radicalized chain. 

It is possible that a radicalized chain abstracts a hydrogen from an adjacent polymer molecule and that the reactive site is then moved from one molecule to another (chain transfer). This leads in most cases to the formation of a molecule with a long-chain branch. The chain transfer reaction may also be intramolecular, which is a well-known mechanism giving branches in high-pressure polyethylene. 

Both anionic and cationic polymerization include both initiation and chain-wise propagation but with one important difference from radical polymerization  

It is useful to divide the polymers into two main classes the fully amorphous and the semicrystal-line. The fully amorphous polymers show no sharp, crystalline Bragg reflections in the X-ray diffracto-grams taken at any temperature. The reason why these polymers are unable to crystallize is commonly their irregular chain structure. Atactic polymers, statistical copolymers and highly branched polymers belong to this class of polymers (Chapter 5). 

The semicrystalline polymers show crystalline Bragg reflections superimposed on an amorphous 

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