Sciencemadness Discussion Board

how to determine average mw of a polymer ?

DubaiAmateurRocketry - 4-10-2013 at 03:28

I just received a KG of HTPB with MW 2300-2800.

a 500 is a big difference that can cause different mechanical properties if i cured it with 1:1 2200 or 1:1 2700 with MDI. If i do not know the mw of my HTPB.

How shall i determine the average mw of my HTPB then ?

[Edited on 4-10-2013 by DubaiAmateurRocketry]

bfesser - 4-10-2013 at 04:16

"KG" (wrong) = kg
MW = molecular weight (every chemist knows this)
HTPB = <a href="https://en.wikipedia.org/wiki/Hydroxyl-terminated_polybutadiene" target="_blank">Hydroxyl-terminated polybutadiene</a> <img src="../scipics/_wiki.png" />
MDI = <a href="https://en.wikipedia.org/wiki/Methylene_diphenyl_diisocyanate" target="_blank">Methylene diphenyl diisocyanate</a> <img src="../scipics/_wiki.png" />

What equipment and instrumentation do you have at your disposal? If I recall correctly, you can use something as simple as the viscosity of a solution to get a crude figure, or something as complex as a multi-instrumental analysis. (I'm out at the moment, but will refer to my polymer texts when I get home.)

DubaiAmateurRocketry - 4-10-2013 at 07:07

Quote: Originally posted by bfesser  
"KG" (wrong) = kg
MW = molecular weight (every chemist knows this)
HTPB = <a href="https://en.wikipedia.org/wiki/Hydroxyl-terminated_polybutadiene" target="_blank">Hydroxyl-terminated polybutadiene</a> <img src="../scipics/_wiki.png" />
MDI = <a href="https://en.wikipedia.org/wiki/Methylene_diphenyl_diisocyanate" target="_blank">Methylene diphenyl diisocyanate</a> <img src="../scipics/_wiki.png" />

What equipment and instrumentation do you have at your disposal? If I recall correctly, you can use something as simple as the viscosity of a solution to get a crude figure, or something as complex as a multi-instrumental analysis. (I'm out at the moment, but will refer to my polymer texts when I get home.)


Thank you very much, i would like to know both ways to figure out the mw.

Dany - 4-10-2013 at 08:10

See

http://en.wikipedia.org/wiki/Gel_permeation_chromatography

Dany.

BobD1001 - 4-10-2013 at 08:39

Mind PMing me the source for the HTPB? I am a model rocket enthusiast, and make my own composite propellants. I have been using PBAN, however HTPB is supposedly significantly easier to work with, and a much faster cure rate without the need for a heating chamber.

DubaiAmateurRocketry - 4-10-2013 at 08:47

Quote: Originally posted by BobD1001  
Mind PMing me the source for the HTPB? I am a model rocket enthusiast, and make my own composite propellants. I have been using PBAN, however HTPB is supposedly significantly easier to work with, and a much faster cure rate without the need for a heating chamber.


This is the company

http://www.qilong-chem.com/en/product/html/?99.html

bfesser - 4-10-2013 at 09:43

Quote: Originally posted by DubaiAmateurRocketry  
How shall i determine the average mw of my HTPB then ?
Quote: Originally posted by DubaiAmateurRocketry  

This is the company

http://www.qilong-chem.com/en/product/html/?99.html
New suggestion:
http://www.qilong-chem.com/en/page/contact/contact.php
Ask for Certificate of Analysis.

Next time, give all relevant details when asking a question; it makes all our lives easier.

[Edited on 4.10.13 by bfesser]

PHILOU Zrealone - 8-10-2013 at 00:10

Osmometry, differential tonometry also comes to mind to mesure average MW of a polymer.

Eblioscopy and cryoscopy would be too unsensitive because the weakest point is precise temperature measurements and temperature difference will be very small due to large MW.