Simulation copolymerisation

Random ethylene copolymers with small amounts (4-10 wt-%) of 7-olefins, e.g. 1-butene, 1-hexene, 1-octene and 4-methyl- 1-pentene, are referred to as linear low-density polyethylene, which is a commercially relevant class of polyolefins. Such copolymers are prepared by essentially the same catalysts used for the synthesis of high-density polyethylene [241]. Small amounts of a-olefin units incorporated in an ethylene copolymer have the effect of producing side chains at points where the 7-olefin is inserted into the linear polyethylene backbone. Thus, the copolymerisation produces short alkyl branches, which disrupt the crystallinity of high-density polyethylene and lower the density of the polymer so that it simulates many of the properties of low-density polyethylene manufactured by high-pressure radical polymerisation of ethylene [448] (Figure 2.3). 

Several attempts have been made to simulate transport in realistic fully atomistic MD simulations of water/Nafion mixtures. Vishnyakov and Neimark [72-74] investigated alkali transport in aqueous and methanolic solution (and in mixed solvents) in the presence of Nafion. They found indications for the existence of the fluctuative bridging mechanism. The group by Kokhlov and Khalatur has also performed extensive yet unpublished studies of simple ion transport in Nafion. Goddard and coworkers [75] compared structural and dynamical properties of two different copolymerisation patterns, in order to estimate the effect of statistical vs. regular copolymerisation of TFE with the sulfonated vinyl ether. 

The reaction of the sodium salt of benzoic acid with methacryloyl chloride was shown to result in an anhydride which could be polymerised by a radical process or copolymerised with various percentages of ethylene glycol dimethacrylate to obtain crosslinked products. Hydrolysis reactions of the resulting polymers were carried out in various aqueous solutions and the rate of release of benzoic acid (used to simulate a drug) appeared to depend on both the percentages of crosslinking comonomer and the pH of the solution. A model is proposed for the delayed release of benzoic acid. 14 refs. 

An example of the copolymer composition produced in a batch reactor is shown in Figures 4.8 and 4.9 for a MMA-BA comonomer system. A seeded batch emulsion copolymerisation is simulated with a particle concentration Np of 2.6 x 10 ° particles per m water phase and an initial molar ratio of MMA and BA equal to one. The reactivity ratios and fBA used in the simulation are 2.24 and 0.414, respectively (Vicente, 2001). Partition coefficients, see Equation 4.21, were used to accoimt for monomer partitioning (Vicente, 2001). 

Figure 4.8 Simulated data for the seeded batch emulsion copolymerisation of MMA and BA, initial molar ratio of BA and MMA is one (a) instantaneous and cumulative copolymer composition (b) ratio of the concentration of monomer in the polymer particles referred to BA, %a = [BA]p/([BA]p + (MMA]p) (c) partial and overall conversions (d) rates of polymerisation.

The copolymer composition distribution can be calculated from the data collected in Figure 4.8 for the instantaneous composition and the time evolution of the overall conversion. Figure 4.9 displays the copolymer composition distribution for batch seeded emulsion copolymerisations of BA and MMA simulated with two initial monomer compositions one with 50mol% BA and 50mol% MMA and one with 90mol% BA and 10mol% MMA. 

Figure 4.11 shows simulated data for two-seeded semi-batch emulsion copolymerisations of BA and MMA carried out with feeding times of 3 and 6h, respectively. Figures 4.11(a) and (b) present the cumulative and instantaneous copolymer compositions. The results in the Figures 4.11(a) and (b) clearly demonstrate that the steady state is achieved in both cases. However, for the addition period of 6 h the fraction copolymer with a composition deviating from the desired composition of 0.5 is smaller than for the addition period of 3 h. Furthermore, the cumulative composition is closer to 0.5 for the 6 h addition period than for the 3 h addition. In comparison with the batch process, the composition drift is almost negligible as displayed in Figure 4.11 (d) which shows a very narrow chemical composition distribution (CCD) centred at 0.5. 

Figure 4.11 Simulated data for the starved feed semi-batch emulsion copolymerisation of BA and MMA. Initial molar ratio of BA and MMA is one. Instantaneous and cumulative copolymer composition for (a) 3 h and (b) 6 h monomer addition, respectively (c) polymerisation rates (d) CCD for 3 h addition.

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