Crystallization in polymer systems actually is a process that transfers the entangled melts into a semi-crystallinelayered structure. Whether or not a chain disentangles may result in different crystallization mechanism. When compared tothe crystal thickness (dc)

the volume occupied by the chain in the melt

i.e.

the radius of gyration (Rg)

plays a veryimportant role in polymer crystallization. When dc≤Rg

crystallization does not necessitate a chain disentangling. The entanglements are just shifted into the amorphous regions.However

as dc>Rg

i.e.

as the crystal thickness gets larger than the radius of gyration of the chain in the melt

it becomes necessary for a chain to disentangle.Then a change of crystallization mechanism occurs.Such change has been experimentally observed in the crystallization of poly(1-butene).A change in the crystal morphologies from spherulite to quadrangle

is seen via PLM

as crystallization temperatures increase.Even more

such a change is molecular weight dependent

and shifts to lower temperature as molecular weight decreases.There exists a jump of crystal thickness and crystallinity associated with morphological change

as seen via SAXS.A change of crystallization kinetics and crystallinity is further evidenced via dilatometry.The unique feature of plb crystallization has been discussed based on the radius of gyration of chain in the melt(Rg)

and very good agreement is obtained.