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ABSTRACT:The monomer reactivity ratios for styrene/ 2-ethylhexylacrylate in bulk at 80°C were investigated by studying the resulting copolymer composition via 1 H-NMR. Composition results were summarized and various methods were employed to estimate the reactivity ratios including the use of the Error-in-Variables-Model (EVM) approach by using the Mayo-Lewis model. The estimates of the reactivity ratios from the EVM method are found to be r s ϭ 0.979 and r EHA ϭ 0.292. The resulting copolymer has a tendency toward alternation with an azeotrope of f(styrene) ϭ 0.972.

Published online in Wiley InterScience (www.interscience.wiley.com).Although much work has been published about the dn/dc values for homopolymers, including ␣-methyl styrene (AMS) and methyl methacrylate (MMA) 1,2 there has been little in the way of published work to determine the dn/dc values for copolymers. It is generally accepted that the dn/dc value for a homopolymer is almost entirely dependent on the monomer and weakly dependent on (or independent of) molecular weight. 2Copolymers may be very different, however. Because molecular weight and composition can be closely linked (especially for systems with depropagating monomers like AMS and to a lesser extent MMA), some correlation may be present. Another factor that affects molecular weight, besides the reaction conditions, is the feed fraction of monomers. Will this have an effect on the dn/dc values obtained?From the Polymer Handbook 2 there is a historical recording of dn/dc values primarily at wavelengths below 633 nm, with new data appearing for 633 nm He-Ne lasers, but with none at the wavelength that current equipment uses: 670 nm. Another incentive to embark on this work is to show whether the assumption of a linear relationship between dn/dc and copolymer composition is valid 2-6 and whether the relationship works better for the mole or weight fraction composition.To determine the dn/dc of the copolymers and of the two homopolymers, a GPC setup, including a Waters solvent/ sample delivery system (Waters, Milford, MA) with an inline degasser (model AF), 515 HPLC pump, and 717plus autosampler, was used. The detectors on the system were from Viscotek (Houston, TX), contained in the TDA 302 quad detector package that incorporates RALS/LALS (670 nm), differential refractive index (DRI), viscometer, and UV (model 2501) detectors. The analysis software OmniSEC v2.0 (Viscotek) was included with the detectors.The samples analyzed in this study were produced by free-radical polymerizations at temperatures ranging from 100 to 140°C. Consequently, the AMS content in the copolymer reached a maximum of about 20%. To produce a polymer with a higher AMS content we would have to greatly sacrifice both yield and molecular weight, making the polymer undesirable for practical applications.To determine dn/dc it is possible to use this equipment along with the following expression based on the DRI response:where RI cal is the calibration constant for the RI detector, established by analyzing samples of known dn/dc and known concentrations; RI i is the measured response from the detector; C i is the sample concentration; and n 0 is the refractive index of the solvent. Because we already have the RI cal , and we know C i and n 0 , then the dn/dc can be calculated for the sample. Alternatively, the dn/dc can be calculated by plotting the RI area (integrated from the RI signal) versus C i . Because RI area is assumed directly proportional to the refractive index of the sample in solution, the slope of this line will be dn/dc. For the work discussed here, this second techni...

The kinetics of the copolymerization of α‐methyl styrene and methyl methacrylate (MMA) have been revisited for the bulk system. Reactivity ratios and other kinetic parameter estimates based upon a copolymerization model developed by Kruger et al. (Makromol Chemie 1987, 188, 2163–2175) have been determined for a range of temperatures (60–140 °C). An interesting phenomenon has been uncovered, which shows that there is a distinct difference in copolymer composition predicted by the model when compared with experimental data at feed ratios of MMA below a critical value. This deviation also appears to be influenced by the reaction temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3868–3877, 2005