Having trouble synthesizing Amphoteric Polyacrylamide (PAM). Need advice on monomer reactivity and blending.
Hi everyone,
I am currently working on synthesizing polyacrylamide (PAM) in our lab via semi-batch solution polymerization (monomer dropping method) and ran into an issue with an amphoteric formulation.
We successfully synthesized individual anionic and cationic PAMs previously:
- Anionic: Acrylamide (AM) + Methacrylic Acid (MAA) -> Success
- Cationic: Acrylamide (AM) + Acryloyloxyethyltrimethyl ammonium chloride (DAC) -> Success
However, when we tried to synthesize an amphoteric PAM using a premix of all three monomers, we failed.
Our Method:
We prepared a monomer premix of AM, MAA, and DAC, and dropped it into water containing the initiator.
Approximate Formulation (by weight):
- Water: 64%
- Acrylamide (50% aq. soln): 32%
- MAA: 1%
- DAC: 3%
The Problem:
Upon analyzing the final polymer, the anionic functionality (MAA) was practically undetectable, and the cationic charge density (DAC) was much lower than our theoretical estimates.
Question 1: Why is the amphoteric synthesis failing like this? Could it be due to the drastically different reactivity ratios between MAA and DAC when mixed together, or perhaps the formation of an ionic monomer complex (monomer pair) in the premix that alters the polymerization kinetics? What should I adjust (e.g., pH, dropping sequence, or alternative monomers) to fix this?
Additional Observation & Question 2 (Blending vs. Co-polymerization):
When we physically blended our pure cationic PAM and anionic PAM together in solution to check the charge, the solution turned highly turbid/opaque (white haze), though both charges were detected. We assume this turbidity is due to the formation of a polyelectrolyte complex (PEC).
Interestingly, we have a commercial amphoteric PAM benchmark sample from a supplier. It is not clear/transparent; it is a turbid, viscous liquid (suspension/emulsion-like appearance).
Question 2: Given that our pure copolymer blend turned turbid, is it possible that this commercial "amphoteric" sample is actually just a physical blend of anionic and cationic PAMs rather than a true copolymer? Or is it normal for a true amphoteric PAM copolymer to be turbid in solution due to intra/inter-molecular salt-and-pepper interactions?
Would love to hear insights from polymer engineers or anyone experienced with water-soluble polymers/flocculants. Thanks in advance!