Materials are methyl and butyl methycrylate and a photoinitiator (TPO or TPO-L). Light source is a UV Laser with 405nm. With intesities lower than 1mW polymerization needs about 2 hours. Speeding up the polymerization by using higher light intensities does not have any effect. The monomer stays liquid.
Does anyone has an answer for that?
Although the inhibitor of the monomers and the initiator can affect the reaction, I would say it is incontrovertibly due to the dissolved oxygen. So, degas the solution by purging it with N2 and seal it under the inert atmosphere. In addition, try to use a reaction vessel with least free space!
Hello, I agree with above mentioned answer,
and there are might be also other reasons: 1) initial monomers should be purified from inhibitor of polymerization hydroquinone etc via distillation under reduced pressure. 2) there may be some special glass or the glass wall is too thick which partially cut off light power.
TPO and TPO-L are very weakly absorbing at 405 nm. You may not be generating enough radicals to overcome the presence of inhibitors or oxygen. Can you shift the initiation wavelength shorter? Here are data sheets on TPO-L and TPO
www.lambson.com/wp-content/uploads/2014/07/TPO-Technical-Data-Sheet-Rev-2.pdf
www.lambson.com/wp-content/uploads/2014/07/TPO-L-Technical-Data-Sheet-Rev-2.pdf
Monomers are usually provided with a small amount of inhibitor added to prevent auto-initiation. You can distill the monomer or pass the monomer through a short column of silica gel (you can make it yourself or buy pre-packed columns from monomer provider) - the inhibitors tend to adhere more strongly than the monomer itself. Removal of oxygen will also improve polymerization - if you are not doing this in a vessel, providing a blanket of N2 over a substrate will help.
Thanks a lot to all of you.
I was using an inhibitor remover before polymerization. So this shouldn't be a problem.
I made a test using a closed vessel with monomer-initiator mixture and filled with nitrogen. Indeed, polymerization was reduced to a third of the prior polymerization time. I think this is the right way. Next step will be to increase light intensity to get to even shorter reaction times.
- Badges
- Science topic