1. Polymer Institute of the Slovak Academy of Sciences, , 845 41 Bratislava, Slovakia;2. International laser centre, , 841 04 Bratislava, Slovakia;3. Department of Chemical Engineering, Dupuis Hall, Queen's University, , Kingston, Ontario, K7L 3N6 Canada;4. Institute of Physical Chemistry, University of Goettingen, , 37077 Goettingen, Germany
Abstract:
Pulsed‐laser polymerization with subsequent analysis of the polymer molar mass distribution by size‐exclusion chromatography, PLP–SEC, is used to measure the propagation rate coefficient, kp, of N‐vinylpyrrolidone (NVP) in a series of organic solvents, varying the NVP concentration from 5 to 100 wt% and varying the temperature between –5 and +80 °C. In contrast to the 20‐fold increase observed in aqueous solution upon decreasing the NVP concentration from bulk to dilute conditions, the kp values of NVP in butyl acetate, iso‐propyl acetate, N‐ethylpyrrolidone, and N‐ethylformamide stay within 20% of the bulk value and exhibit no significant dependence on monomer concentration. The kp behavior of NVP in methanol and n‐butanol is intermediate between the one in water and in the other organic solvents, with kp increasing by about a factor of 2 upon lowering the monomer concentration from bulk to 5 wt% NVP. The activation energies for propagation in organic solvents agree within experimental uncertainty with the value reported for bulk NVP. The data demonstrate that hydrogen bonding is responsible for the increase in kp upon dilution, with this effect being much stronger in an aqueous environment than in a solution of alcohol.
