[chel45]

Greetings!

For use with electrospinning, I need to synthesize a polyester polymer with polyurethane bonds by reacting diols, diisocyanates and diamines. The general concept of a reaction is in the attachment.

I use BDI as the isocyanate. I have a protocol and I tried to run the reaction, but the results were poor - looks like the polymerization was incomplete. So I need a couple of tips to optimize the process.

1) One of the identified problems was insufficient removal of water from the reaction components. At the first stage, the polymer was dissolved in DMSO. After that, toluene was added and the idea was to remove the water with toluene. I don't like it because it required finding the right combination of temperature and pressure. Requires dry air infiltration into the system. Now I would like to add 20% more DMSO instead of toluene and run a vacuum distillation for an hour. Is this enough to remove all the water?

2) Another thing I would like to do is to increase the amount of BDI a little and run the reaction with an excess of this substance. Previously, I used the ratio of components of polyester diol:BDI:diamine of 1:2:1. Should I change the ratio to 1:2,2:1?

Thanks in advance for advices)

[DrCMS]

It is no clear from what you have written so far how you are running this reaction and what if any in-process analysis you are doing. 

I suggest you focus on getting the standard reaction to work properly before you go making changes.

Do you adjust the formulation to account for the analysis of each batch of diol or just assume the centre point of the spec etc.
Do you have a measured water content for the diol and solvents used?
Do you have a purity measured on the BDI?
How did you run the first stage reaction - times temps etc.
Did you feed the diol into the isocyanate at the reaction temp or just mix all in-together and warm it up?
How did you determine the endpoint of the 1st stage?

I'd not worry too much about the chain extension part as amines react so quickly with isocyanates that those steps usually work fine if the 1st stage has been done right.

[chel45]

Thank you for the answer). I have a protocol which was used by other person to synthesize the polymer from other polyester diol (but with the same Mn). Now I need to make it work by myself. The problem is that I'm bioengineer not a chemist)

Do you adjust the formulation to account for the analysis of each batch of diol or just assume the centre point of the spec etc.

No.. Actually I have a new bottle of a custom synthesized polymer. But I checked it's certificate and Mn is more or less the same (1500 - 2000). It can be a problem?

Do you have a measured water content for the diol and solvents used?

I dissolve diol in DMSO and do distillation with toluene at 110 C for one our to remove water (with diaphragm pump and air intake though drying unit). But now I'm thinking to add 20% more of DMSO and do distillation under vacuum at 100 C.

Do you have a purity measured on the BDI?

I have 97% BDI but prior the reaction I've made distillation of the BDI and store at under argon atmosphere.

How did you run the first stage reaction - times temps etc.

3 hours under 75 C

Did you feed the diol into the isocyanate at the reaction temp or just mix all in-together and warm it up?
How did you determine the endpoint of the 1st stage?

Add isocyanate to diol. The endpoint is a time according to the protocol.

[chel45]

I'm stupid. Just found out that my polymer has lower Mn than expected. In it's certificate there were Mn according to specification and according to analysis. And I didn't notice it.

[DrCMS]

OK a lower molecular weight will make a big difference.  Even from the top to bottom of the spec range is a 25% or 33% difference in molecular weight depending on your start point.