Historically, companies produce Styrene Butadiene Rubber (SBR) without monitoring what happens inside the polymer reactor. Many manufacturers employ chromatography measurements once the reaction is complete or intermittently during production or R&D. Thus, there is a lack of realtime data which results in reactions running longer than required to mitigate against off-spec rubber polymer batches. Such a process consumes more energy, operator time and equipment availability than is required. Conversely, ACOMP, an innovative product available from Fluence Analytics, yields continuous, realtime measurements on critical polymer properties during the production and R&D of SBR.
By providing realtime insights, Fluence Analytics is disrupting the standard production processes for polymers used in rubber applications. ACOMP continuously generates realtime data streams with molecular weight, viscosity, composition, residual monomer and monomer conversion measurements.
Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP) was used to continuously measure the anionic polymerization of Styrene Butadiene Rubber (SBR) at the 20 L scale. The following application note details ACOMP successfully demonstrating that it can track conversion, along with weight average molecular weight (Mw), and low and high shear reduced viscosities (RV). After the initial reaction, the effects of the coupling agent were directly monitored by ACOMP. This showed a doubling in Mw over time and increases in RV commensurate with what one expects for random coils in a good solvent.
ACOMP yields continuous data on these important characteristics of the reaction and resulting polymers. These polymer properties include conversion, molecular weight, reduced viscosity, and shear thinning viscosity. It is important to note that ACOMP is not a chromatographic method. Thus, it yields continuous average values, such as Mw, rather than the intermittent molecular weight distributions (MWD) provided by GPC. The work below, conducted in conjunction with Bridgestone Research Americas, outlines results obtained from the application of ACOMP to SBR reactions.
The UV signal in Figure 1 does not return to its solvent value, due to scattering and absorption by the polymer that has formed. The true fractional conversion, f, is found by a procedure developed by Fluence Analytics, and the true conversion found by this procedure is shown on the right-hand y-axis. The signals in Figure 1 are all normalized to a scale of 1. The decay of the UV 265 nm signal shows the conversion of the styrene into polymer. The light scattering at 90o increases with respect to the increasing polymer mass, and it reaches a plateau during the first phase. When the reaction begins, both viscosity signals increase until a plateau is reached. The addition of the coupling agent causes strong increases in both viscometers.
Figure 2 shows Mw and low and high shear RV as a function of time, including the coupling reaction. Mw was obtained from angular extrapolation (five angles; 45, 65, 90, 115, 135) to zero angle. Figure 2 reveals several features. First, Mw and both low and high shear RV increase monotonically in the first phase. In contrast, in free radical reactions, chains are initiated, propagate, and terminate quickly, so that Mw decreases versus time. Examining the first and second plateau values gives Mw,2/Mw,1=1.94 +/- 0.06. Similarly, high and low shear RV increase in the first phase, again exhibiting ‘living’ type behavior of the reaction and increase after coupling.
ACOMP can directly monitor and characterize polymer conversion, Mw, and RV of the polymers produced during a living, anionic solution based SBR polymerization process. This information is directly important with respect to characterizing the macromolecular polymer properties of Mw and RV, and it is also useful in providing insights into production rates and efficiencies, such as improving cycle time and yields while achieving product consistency from batch to batch. This information also provides complementary information on the polymers produced which may lead to further correlations to important rheological properties of polymer end products such as Mooney and tanδ.
ACOMP has also successfully monitored other types of rubber. These include EPDM, Solution Styrene Butadiene Rubber (SSBR), Emulsion Styrene Butadiene Rubber (ESBR), Styrene Isoprene Rubber (SIR), Acrylonitrile Butadiene Styrene (ABS), Nitrile Butadiene Rubber (NBR), Butyl Rubber, and Acrylonitrile Styrene Acrylate (ASA).
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