24 Nonuniform Emulsion Polymers Carbon-13 NMR Spectroscopy 1
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Downloaded by PENNSYLVANIA STATE UNIV on June 15, 2013 | http://pubs.acs.org Publication Date: October 7, 1981 | doi: 10.1021/bk-1981-0165.ch024
J. E. JOHNSTON, D. R. BASSETT, and T. B. MacRURY Technical Center, Union Carbide Corporation, South Charleston, WV 25303
With the advent of advanced characterization techniques such as multiple detector liquid exclusion chromatography and C Fourier transform nuclear magnetic resonance spectroscopy, the study of structure/property relationships in polymers has become technically feasible (1-6). Understanding the relationship between structure and properties alone does not always allow for the solution of problems encountered in commercial polymer synthesis. Certain processes, of which emulsion polymerization is one, are controlled by variables which exert a large influence on polymer infrastructure (sequence distribution, tacticity, branching, enchainment) and hence properties. In addition, because the emulsion polymerization takes place in an heterophase system and because the product is an aqueous dispersion, it is important to understand which performance characteristics are influended by the colloidal state, (i.e., particle size and size distribution) and which by the polymer infrastructure. In order to design experiments to test the influence of process variables on polymer infrastructure, a simple but general process design is needed. For these studies a new sequential feed polymerization process called "power-feed" was chosen (7-8,9). The advantage of this technique is that almost any conventional monomer feed profile can be simulated and described by an equation containing only three independent variables. In addition, a number of novel monomer composition profiles can also be constructed with this approach. The composition of the monomer feed to the reactor can be described by: 13
C = C - (C -C )(l - 0.50 with time
In Emulsion Polymers and Emulsion Polymerization; Bassett, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
Downloaded by PENNSYLVANIA STATE UNIV on June 15, 2013 | http://pubs.acs.org Publication Date: October 7, 1981 | doi: 10.1021/bk-1981-0165.ch024
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Figure 11. Correlation of calculated and measured triad fractions for the model copolymer described in Figure 10 (τ, = 0.16; r — 0.82; (A) EA-EA-EA; (U) EA-EA-STY = STY-EA-EA; (Φ) STY-EA-STY) 2
In Emulsion Polymers and Emulsion Polymerization; Bassett, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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EMULSION POLYMERS AND EMULSION POLYMERIZATION
A model has been developed in which the polymerization is described by two stages; a short first stage in which feed rate exceeds polymerization rate, and a second stage in which feed and polymerization rates are equal. The model requires the use of an additional "monomer tank" to simulate the residual monomer pool during this second stage. In addition, equivalent weights of monomer are entering and polymerizing during each portion of this stage; hence, the conversion is 100%. This model predicts the intermediate and final sequence distributions for a number of twotank power-feed systems. Downloaded by PENNSYLVANIA STATE UNIV on June 15, 2013 | http://pubs.acs.org Publication Date: October 7, 1981 | doi: 10.1021/bk-1981-0165.ch024
ABSTRACT A "model" latex copolymerization system consisting of styrene and ethyl acrylate has been studied using C nuclear magnetic resonance spectroscopy. Conventional semi-batch co polymers at five monomer ratios, a staged equimolar copolymer, and sequential, or "power-feed", copolymers of equimolar average composition have been prepared. Sequence distribution measure ments for these samples using C NMR spectroscopy clearly show differences arising from the use of different process designs. Triad sequence assignments have been made for ethyl acrylate -centered triads. Apparent reactivity ratios have been calculated for the semi-batch copolymers using run number theory. A model has been developed to describe the power-feed systems and predict the triad distributions in the incremental and final copolymer using the experimentally determined r and r values. 13
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ACKNOWLEDGMENTS The authors wish to thank Drs. K. L. Hoy, E. J. Derderian, and J. M. Whelan for their contributions to the progress of this work, and Mr. R. L. Pack for the C NMR measurements. 13
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In Emulsion Polymers and Emulsion Polymerization; Bassett, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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In Emulsion Polymers and Emulsion Polymerization; Bassett, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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