I've recently started playing with PAM as a bubble polymer. It looks promising but needs more investigation.
The PAM (Polyacrylamide) family is an important group of industrial polymers with an international trade value of several billion dollars annually. They come in 4 main varieties: Nonionic, Cationic, Anionic, and Cross-linked. I'm ignoring the Nonionic and Cationic varieties for now because I've yet to find a vendor with a minimum order less than 1 ton! The anionic variety I'm familiar with because the use of this in water treatment was the subject of my Ph.D. thesis, but it is not readily available for domestic use. This leaves the cross linked variety which is both readily available and cheap.
Cross linked PAM can absorb large volumes of water and is widely used in agriculture for conditioning soil. You will find it in gardening stores labelled 'water retaining crystals', or something similar, but most varieties have been heavily cross linked to make them insoluble in water. The one that I've been using is sold as 'the dirty gardener water retention granules' and is less than $10 for a 1lb bag (enough for 1000 gallons of bubble juice). I've attached a photo so you can check that you are getting the right thing. Since I originally wrote this post we have found that a number of different products have similar descriptions and labelling and it's easy to buy the wrong one. Here is a link to one source of the right stuff. (When you order it, specify that you want the fine-grained WATER SOLUBLE PAM to be sure they send you the right one. The right stuff has a grain size like table sugar).
Using PAM water retention granules (PAM wrgs):
Mixing: It is very slow to dissolve but you don't need a slurry. I've been making my stock solution at 1gram per litre thus: Add the PAM first to the jug or mixing bowl then pour in the water. Leave to stand for 8 hours or so then give it a good mix with an egg whisk. Leave to stand for another 8 hours and then mix agin until it is uniform. You can then add a small quantity of this stock solution to your detergent mix to get the polymer concentration you need.
In bubble juice: so far it looks as though the optimum quantities are similar to PEO - somewhere between 0.01 and 0.1 g/L. The attached photo was 0.05 g/L. To get .01 g/L you would add 10mL of your stock PAM solution to each liter of bubble juice. For 0.1 g/L you would add 100mL of stock solution.