An experimental investigation on the evolution of the molecular weight distribution in styrene emulsion polymerization

Miller, Christopher M., Clay, Paul A., Gilbert, Robert G. and El-Aasser, M.S. (1997) An experimental investigation on the evolution of the molecular weight distribution in styrene emulsion polymerization. Journal of Polymer Science, Part A: Polymer Chemistry, 35 6: 989-1006. doi:10.1002/(SICI)1099-0518(19970430)35:6<989::AID-POLA2>3.0.CO;2-C

Author Miller, Christopher M.
Clay, Paul A.
Gilbert, Robert G.
El-Aasser, M.S.
Title An experimental investigation on the evolution of the molecular weight distribution in styrene emulsion polymerization
Journal name Journal of Polymer Science, Part A: Polymer Chemistry   Check publisher's open access policy
ISSN 0887-624X
Publication date 1997-04
Sub-type Article (original research)
DOI 10.1002/(SICI)1099-0518(19970430)35:6<989::AID-POLA2>3.0.CO;2-C
Volume 35
Issue 6
Start page 989
End page 1006
Total pages 18
Place of publication Hoboken, NJ, United States
Publisher John Wiley & Sons
Language eng
Formatted abstract
Styrene ab initio emulsion polymerizations were conducted at 70°C in an automated reaction calorimeter. Two polymerizations were performed, one above and the other below the critical micelle concentration (CMC) of the surfactant, thus ensuring differing polymerization kinetics between the two: the system below the CMC gave large particles that were expected to follow pseudobulk kinetics, while that above the CMC gave small particles that were expected to follow zero-one kinetics. The evolutions of the molecular weight distributions (MWDs) were characterized by removing samples periodically during the course of the reactions and analyzing with gel permeation chromatography. Interpretation of the data used average molecular weights, the GPC MWDs, and the number MWDs, as functions of conversion. It was found that all of the number MWDs (plotted as In (number of polymer chains) vs. molecular weight of polymer chains) were concave-up at low molecular weights and become nearly linear at molecular weights (≥3-4 × 106); this linearity is expected from theory. The slope of the high molecular weight region was consistent with theory for the dominant mode for chain stoppage: termination and transfer for the pseudobulk system and (predominantly) chain transfer to monomer for the zero-one system. The most likely explanation for the concavity of the number MWDs is a heterogeneity of radicals: some surface anchored with sulfate end groups and others (with hydrogen end groups arising from transfer to monomer and/or reentry) being more mobile. Thus, two types of termination are proposed: slow reaction-diffusion for the less mobile surface anchored chains, and rapid short-long (center of mass) termination for the more mobile hydrogen-terminated chains.
Keyword Emulsion polymerization
Molecular weight distribution
Free-radical polymerizations
Termination rate-processes
Rate coefficients
Low conversion
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ
Additional Notes Article first published online: 21 January 2000

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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