Dear,

I am doing suspension polymerization of methyl methacrylate
BPO-DMPT is used as initiator at room temp (~5.5wt % of monomer)
PVA (I tried 99% and 88% hydrolized) as suspending agent (1wt% of water)
monomer:water : 1:3.6

I fail to obtain the bead but an aggregated mass for 99% PVA and soft clumps for 88% PVA
Please advice how to overcome this and obtain PMMA in beads.

Thank you for your time
Best regards

How are you dispersing the initiator?

the initiator is mixed with the monomer, briefly stirred, then added to the water/PVA solution

If you are not dispersing the initiator in discrete sites in the suspension fluid, or dispersing the monomer in discrete sites, or somehow mixing it into the suspension fluid to distribute it in some kind of dispersion...then why would you not expect the monomer to self-attract into lumps?

hmmm...I was following a procedure. So..your point is each component should b added separately to the suspension solution?

Well...not necessarily. I'd just assme that to create beads, you would need some type of mechanical dispersion to seperate the momomer into discrete drops. Unless there is something happening chemically that causes PVA to disperse the PMMA...or some additive not mentioned that causes this.

Oh I see what you mean, I didn't mention a 600-700 rpm mechanical stir in the PVA solution.

PVA is the dispersant. In emulsion polymerization the initiator is generally in the water. To form large beads the initiator would probably be in the monomer because it will not diffuse that far. Degree of agitation is critical. Agitation must break-up the monomer into droplets, but once the droplets start to polymerize the agitation must be gentle so that the droplets do not stick together. The PVA forms a delicate "skin" on the droplets to prevent sticking. This skin needs to be broken to reduce the droplets to the desired size early in the agitation, but then care must be taken to not break this "skin" during polymerization.

hmm...Thanks for your input. So the suggestion is to lower the agitation during polymerization? Can you let me know if there is a specific relationship or something time-based on that (so I can adjust it)?

There's a nice overview here: http://en.wikipedia.org/wiki/Suspension_polymeriza...

I've tried to dissolve PVA 99 and 86% in water and it's not so easy. Did yours dissolve completely? 86% should be better than the 99% hydrolysed. What you want is a water soluble polymer that has some portions that want to adsorb to the hydrophobic monomer droplet so 99% is no good, it's all hydrophilic and doesn't want to adsorb to the droplets where it can work to prevent them agglomerating. Look online for other recipes using PEG or PVP as the stabilizer.

Chris DeArmitt - PhD FRSC CChem
Plastic & Additives Webinars
Instant Downloads & Inexpensive
www.plastictraining.com