[polyista]

Hi I'm new to this forum! My aim is to build better understanding in chemistry/material science by asking questions which I have been bit hesitant before. Hope I can get *delete me*

My question is, how can I get information about crystallinity of polymer based on its chemical structure? I'm analysing at the moment during biomaterials course poly(ethylene glycol-co-lysine-co-D,L lactide) to PLLA and trying to identify crystallinity differences based on the structures.

[Corribus]

Crystallinity has to be experimentally determined. It is not an intrinsic polymer property. The same polymer will have different crystallinity depending on how it is processed and what additives are in it.

The most common methods to measure polymer crystallinity include x-ray diffraction and differential scanning calorimetry, but there are a few others as well.

[jeffmoonchop]

Think about what groups will interact to form motifs, for example hydrogen bonding between acid groups. But you cant predict the overall crystal structure, as there are likely many polymorphs.

[polyista]

Hey thanks for the answers!

I did some further reading from book Integrated Biomaterials Science, and it states: "The ability of a material to crystallise is determined by the regularity of its molecular structure. A regular structure is potentially capable of crystallinity while an irregular structure will tend to give amorphous polymers. Generally, the crystallisation is limited to linear or slightly branched polymers with high structural regularity. "

So if I read this correctly, from molecular structure it is possible to gain insight into materials ability to crystallise even without experimental tests. So if this logic holds, I need to analyse poly(ethylene glycol-co-lysine-co-D,L lactide) vs PLLA structures to see differences in regularity and branches. What do you think?

[Corribus]

You can gain insight into a substance's tendency to crystallize from its molecular structure, but everything I wrote still stands. Factors that have nothing to do with structure also play a big role in crystallization, like cooling rate and presence of impurities. Sure, if you control every other factor that influences crystallinity, you might be able to make a generalize statement of which polymers have more crystallinity than others, but that's about the best you can do.

[polyista]

You can gain insight into a substance's tendency to crystallize from its molecular structure, but everything I wrote still stands. Factors that have nothing to do with structure also play a big role in crystallization, like cooling rate and presence of impurities. Sure, if you control every other factor that influences crystallinity, you might be able to make a generalize statement of which polymers have more crystallinity than others, but that's about the best you can do.

Agreed, thank you for pointing these out! Learnt lot of new regarding polymer crystallization.