Dilute Solution Theory of Polymer Crystal Growth: Fractionation Effects

Area of Science:

• Polymer Science
• Physical Chemistry
• Materials Science

Background:

• Polymer crystallization is influenced by molecular weight (MW).
• Understanding MW fractionation is crucial for controlling polymer properties.
• Previous theories often overlooked kinetic effects in fractionation.

Purpose of the Study:

• To formulate a nonequilibrium kinetic theory for polymer MW fractionation.
• To apply this theory to polyethylene crystallized from solution.
• To elucidate the influence of crystallization temperature and MW polydispersity on fractionation.

Main Methods:

• Development of a kinetic theory for polymer crystallization.
• Application to binary and multicomponent polyethylenes.
• Analysis of crystallization from unstirred xylene solutions.

Main Results:

• High MW polymer components crystallize preferentially.
• Fractionation is enhanced at higher crystallization temperatures.
• Crystal growth rates, not nucleation, govern MW fractionation.
• MW polydispersity can obscure the relationship between crystal thickness and MW.

Conclusions:

• A kinetic theory successfully describes polymer MW fractionation.
• Crystallization temperature significantly impacts fractionation efficiency.
• Crystal growth kinetics are the primary drivers of MW fractionation.
• Polydispersity complicates the interpretation of crystalline properties related to MW.