Electrosteric stabilization with poly(acrylic) acid in emulsion polymerization: Effect on kinetics and secondary particle formation

Vorwerg, Lars and Gilbert, Robert G. (2000) Electrosteric stabilization with poly(acrylic) acid in emulsion polymerization: Effect on kinetics and secondary particle formation. Macromolecules, 33 18: 6693-6703. doi:10.1021/ma0003607


Author Vorwerg, Lars
Gilbert, Robert G.
Title Electrosteric stabilization with poly(acrylic) acid in emulsion polymerization: Effect on kinetics and secondary particle formation
Journal name Macromolecules   Check publisher's open access policy
ISSN 0024-9297
1520-5835
Publication date 2000-09-01
Sub-type Article (original research)
DOI 10.1021/ma0003607
Volume 33
Issue 18
Start page 6693
End page 6703
Total pages 11
Place of publication Washington, DC, United States
Publisher American Chemical Society
Language eng
Abstract A kinetic study of seeded emulsion polymerization using seed latices electrosterically stabilized with poly(acrylic) acid was performed. Data were obtained at 50 °C for the steady-state rate of polymerization initiated with persulfate and for the non-steady-state relaxation initiated using γ-radiolysis; conditions were chosen so the system obeyed `zero-one' kinetics (when entry of a radical into a particle already containing a growing radical leads to instantaneous termination). The relaxation data directly measure the rate coefficient k for radical exit (desorption) from particles, which in combination with the steady-state rate then yields the rate coefficient for radical entry, ρ. Electrosterically stabilized particles were synthesized from well-characterized seed (made with ionic surfactant) by second-stage polymerization of a small amount of styrene and acrylic acid. Two degrees of surface coverage were employed using 5 and 15 wt % acrylic acid. The low-coverage particles were much more colloidally stable than the polystyrene latices stabilized by initiator fragments and adsorbed surfactant but the behavior of k and ρ was the same as that of the ionically stabilized seed. The colloidal stability of the high-coverage latices was strongly pH-dependent, with high stability at high pH. These latices exhibited strongly reduced k (by a factor of about 3) at low pH but ρ was only slightly lower compared to the ionically stabilized seed. At high and neutral pH, kinetic parameters could not be determined for the highly covered particles because of secondary nucleation; however, a decreased rate was observed with increasing pH, despite an increase in particle number, indicating a reduced ρ. Thus, extensive electrosteric stabilizer seems to reduce entry and exit rate coefficients, although to a lesser extent than reported in an earlier preliminary study. For sparsely electrosterically stabilized particles, the dependences of ρ and k on particle size and (for ρ) initiator concentration were in accord both with those observed for ionically stabilized ones and with the values predicted from models for these processes (transfer diffusion for k and `propagation to z-mer' for ρ).
Keyword Free-radical Polymerization
Latex-particles
Polyacrylic-acid
Butyl Acrylate
Styrene
Surface
Entry
Diffusion
Water
Hydrogels
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemistry and Molecular Biosciences
Centre for Nutrition and Food Sciences Publications
 
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Created: Tue, 08 Mar 2011, 01:59:14 EST