Abstract
The free-radical homopolymerization of 1,3-bis(N,N,N-trimethylammonium)-2-propylmethacrylate dichloride (di-M) and 1,3-bis(N,N,N-trimethylammonium)-2-propylacrylate dichloride (di-A) in aqueous solution yields cationic polyelectrolytes (PEL) with theoretical/structural charge spacing of only ≈0.12 nm. The high charge density causes condensation of ≈82% of the chloride counterions. The high level of counterion condensation reduces the ionic strength in the polymerizing batch when the monomer molecules connect to PEL chains. This has the consequence that the hydrodynamic and excluded volume of the PEL molecules will change. Studies of the free radical polymerization revealed non-ideal polymerization kinetics already at low conversion and additionally autoacceleration above a certain monomer concentration and conversion. Similar autoacceleration was not observed for monomers yielding PEL with charge spacing of 0.25 or 0.5 nm. Coulomb interactions, monomer association, steric effects, and specific features of the monomer constitution have been evaluated concerning their contributions to the concentration dependence and conversion dependence of kinetic parameters. The different backbone constitutions of di-M and di-A not only influence the polymerization kinetics but also equip poly(di-M) with higher hydrolytic stability. The experimental results confirm the impact of electrochemical parameters and the necessity to reconsider their inclusion in kinetic models.
Highlights
Polyelectrolytes (PEL) can be produced either by chemical modification of neutral macromolecules or by polymerization of ionic/charged monomers [1]
As reported for diallyldimethylammonium chloride (DADMAC) [2] and other cationic monomers [1,3], the charge density has a strong impact on the polymerization behavior
This paper presents the systematic examination of the free-radical polymerization (FRP) of the cationic double-charged
Summary
Polyelectrolytes (PEL) can be produced either by chemical modification of neutral macromolecules or by polymerization of ionic/charged monomers [1]. It is known and generally accepted that the polymerization of ionic monomers in aqueous solution is affected by electrostatic forces/Coulomb interactions. As reported for diallyldimethylammonium chloride (DADMAC) [2] and other cationic monomers [1,3], the charge density has a strong impact on the polymerization behavior. Interaction of the PEL backbone charges with counterions, repulsion between the charges at the polymer backbone, and repulsion between the charge at the growing polymer radical and the ionic monomer, are all influenced by the ionic strength and can cause significant deviation from ideal polymerization behavior.
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