Styrene high-conversion copolymerization

A method for calculating apparent reactivity ratios based on run number theory has been applied to "starved-feed" styrene/ ethyl acrylate systems. The reactivity ratios found are in agreement with those determined from solution polymerization data. The further confirmation of the observed agreement between reactivity ratios determined at low conversions and those determined by run number theory in "starved-feed" high conversion copolymerization requires the analysis of other comonomer pairs. 

At present, the kinetic parameters for prediction of copolymerization rates are scanty, except for a few low conversion copolymerizations of styrene and some acrylic comonomers. Engineering models of high conversion copolymerizations are, however, overdetermined, in the sense that the number of input parameters (kinetic rate constants, activation energies, enthalpies of polymerization, and so on)... 

With regards to the copolymerization, a recent kineuc study by Gruber and KneU (10 has indicated that styrene n-butyl methacrylate obeys the cla ical kinetic theory with regards to composition and sequence length to complete conversion. This theory is applied to high conversion to charau terize copolymer samples for GPC analysis. 

Corresponding data for the alternating radical copolymerization of styrene (Mi)-diethyl fumarate (M2)(n = 0.30 and r2 = 0.07) are shown in Figs. 6-6 and 6-7. This system undergoes azeotropic copolymerization at 57 mol% styrene. Feed compositions near the azeotrope yield narrow distributions of copolymer composition except at high conversion where there is a drift to pure styrene or pure fumarate depending on whether the initial feed contains more or less than 57 mol% styrene. The distribution of copolymer compositions becomes progressively wider as the initial feed composition differs more from the azeotropic composition. 

In such cases the polymerization can be taken to relatively high conversion without change in composition of the copolymer formed (see Example 3-37). In the copolymerization diagram the azeotrope corresponds to the intersection point of the copolymerization curve with the diagonal. For example, from Fig. 3.4 it may be seen that in the radical copolymerization of styrene and methyl methacrylate the azeotropic composition corresponds to 53 mol% of styrene. 

High conversions (close to 100%) can be obtained by the dispersion copolymerization of PEO-MA with butyl acrylate initiated by a water-soluble initiator (VA) [80]. The conversion curves have a shape similar to that for the dispersion copolymerization of PEO-MA with styrene. In runs with AIBN the final conversion was around 90% and/or the polymerization was very slow at high conversion. 

Maleate Surfmers were found to outperform methacrylic and crotonic compounds in the copolymerization of styrene, butyl acrylate and acrylic acid in seeded and nonseeded semicontinuous processes [17]. The maleate Surfmer achieved high conversion without homopolymerization in the aqueous phase which can result in emulsion instability. The methacrylate Surfmer was too reactive as opposed to the crotonate which was not sufficiently reactive. The reported dependence of the maleate Surfmer conversion on the particle diameter is consistent with a reaction at the particle surface. 

A free-radical polymerization mechanism can be excluded on the basis of the polymer microstructure and experiments with radical inhibitors. Rhodium(I)-spe-cies, formed by reduction of Rh " salts used as catalyst precursors by butadiene monomer, have been suggested as the active species. The catalyst is stable during the aqueous polymerization for over 30 h [23]. Catalyst activities are moderate with up to ca. 2x10 TO h [24, 25]. By contrast to industrially important free-radical copolymerization, styrene is not incorporated in the rhodium-catalyzed butadiene polymerization [26]. Only scarce data is available regarding the stability and other properties of the polymer dispersions obtained. Precipitation of considerable portions of the polymer has been mentioned at high conversions in butadiene polymerization [23, 27]. 

During copolymerization of styrene with divinylbenzene in the presence of a solvent, the polymer precipitates as it forms. At high conversion the polymer consists of submicroscopic fused polymer particles and solvent filled pores 122.231. Removal of the solvent leads either to collapse of the network or to permanent pores. Polymers with permanent porosity are called macropoFous or macroreticular. The more highly cross-linked e network, and the poorer the solvent used as diluent during polymerization, the more likely the product is to be macroporous. 

Few studies of reactivity ratios have been undertaken where the copolymerizations have been taken to high conversion. However, Johnson, Karmo, and Smith have demonstrated that the styrene-methyl methacrylate stem shows variations in the copolymer composition from that expected from the integrated copolymer equation. The deviations only occur during gelation or in the presence of precipitants, and the changes in and are reported. A comprehensive review of radical polymerization to high conversion has been produced in the form of a book by Gladysev. Many other comonomer pairs have been studied. ... 

Ito and Yamashita [7 , 75] have shown that Eqs. (11) —(13) can be condensed and simplified to obtain Eqs. (14) and (15), where is the reactivity ratio for the methacrylate monomer in the copolymerization system and where X is the ratio of styrene to methacrylate monomer in the copolymerization system used to prepare the copolymer studied. These equations are useful only for low conversion copolymers, but they can be integrated to predict resonance patterns for high conversion copolymers [75]. According to these equations, plots of 1/(1—Pa ) or 1 -h 2Pa/Pb vs. X should be linear and superimposable. We will term such plots I —Y plots. They can of course be used to evaluate a and... 

If crosslinking or copolymer precipitation occurs, bulk polymerization may be difficult to handle. A suspension process may then be the only feasible way in which the copolymerization can be carried out [4]. Suspension processes also provide a means of investigating copolymerization kinetics at high conversion. The monomer sequence in styrene-methyl methacrylate copolymers at high conversion have been found to differ from those observed at low conversion [77]. 

Zetterlund PB, Yamazoe H, Yamada B. Propagation and termination kinetics in high conversion free radical copolymerization of styrene/divinylbenzene investigated by electron spin resonance and Eourier-transform near-infrared spectroscopy. Polymer 2002 43 7027-7035. 

---