Just like most I've created my account with a question in mind
I've been doing some exploratory work on acrylamide polimerization using AIBN in organic solvents, with the goal to obtain short length chains of about 20 amide units or less. I'm no polymer scientist myself, so I mainly base myself on what I can find in literature. I'm not sure if the following concept makes any sense at all:
Currently the polymerization takes place in pure ethanol just below boiling pt. A typical screening test uses ~100:1 monomer:initiator (molar) and 2.5:1 EtOH:monomer molar ratio.
At a certain point in time the polymer starts to gradually precipitate into a white bulky mass (preceded by the hazy phase). I'm assuming the polymerization degree gets too high (positive mixing Gibbs) and the growing chain is no longer being able to dissolve in pure Ethanol? From what I find in literature, typical commercial PAAm (MW~10,000) only dissolves into <50% EtOH (aq.) as the solvophobic interaction is too great.
If this is mainly what's happening, could anyone roughly estimate (or point me to some literature) on the MW that can be expected when precipitation occurs? Simply put, at what chain length does a PAAm no longer dissolve properly in Ethanol (branching not taken into account, if I can assume so(?))
And can I trigger precipitation at a lower MW by using a less polar solvent (e.g., IPA or higher alcohols?) that are still compatible with the monomer?
I currently quench the reaction with cold solvent once I see precipitation, followed by filtration and drying. Could I expect significant branching/crosslinking up to this point? We're talking of precipitation after ~10-15min.
Additionally, do I need to quench, or can I just let the reaction continue and don't have to worry about an increase in chain length of the already precipitated polymer? In literature I find that in solution polymerization generally the propagation, which continues in the precipitated swollen particle, doesn't exert a strong effect on the MW of the product (e.g., styrene in benzene), assuming the polymer is not or partially soluble in the solvent. Is that the case here as well?
Thanks in advance, and if there are any additional pointers on getting my desired low MW PAAm in a controlled way, I'm happy to hear it