Polymerisation in solution

The technologies suitable for LLDPE manufacture include gas-phase fluidised-bed polymerisation, polymerisation in solution, polymerisation in a polymer melt under high ethylene pressure, and slurry polymerisation. Most catalysts are fine-tuned for each particular process. 

The Ticona materials are prepared by continuous polymerisation in solution using metallocene catalysts and a co-catalyst. The ethylene is dissolved in a solvent which may be the comonomer 2-norbomene itself or another hydrocarbon solvent. The comonomer ratio in the reactor is kept constant by continuous feeding of both monomers. After polymerisation the catalyst is deactivated and separated to give polymers of a low residual ash content and the filtration is followed by several degassing steps with monomers and solvents being recycled. 

The development of rubbers with a more closely controlled molecular structure. Such materials are made using anionic or Ziegler-Natta catalysts and are polymerised in solution (solution SBRs). 

Solution Polymerisation In solution polymerisation, the reaction is performed in the presence of a solvent such as ethyl benzene or toluene. 

In the mid-1960s the first measurements of propagation rate-constants for unsaturated monomers became available, from polymerisations initiated by y-radiation [5]. The circumstances of these experiments were such that it was immediately clear that these very high rate constants (106 to 108 1 mol"1 s 1) were those of unpaired cations, kp. All these reactions were carried out with bulk monomer, i.e., the polymerisations occurred in a medium of very low polarity (e c. 2 for hydrocarbons and 5 to 6 for alkylvinylethers). Unfortunately, the y-radiation method is not applicable to polymerisations in solution, especially in polar (usually alkyl halide) solvents. The methods which have been used to... 

The second-order rate-constants kp and kA for polymerisations in solution which we consider reliable are summarised in Table 12. The initiators used by the various investigators have not been listed, because by definition kp and Ep must be independent of these and there are insufficient data to permit any firm conclusions about the effects of the nature of the anion on and E. When considering the rate-constants in this Table it must be remembered that all of them, except those for isobutene, probably comprise a contribution from the polymer-complexed cation, p+p, greater or smaller according to circumstances (see Section 2.3), and correspondingly the activation energies would contain a term Ep+P and an enthalpy of complexation further, for the reason explained in Section 4.1.9, the kp from ionising radiation experiments are minimum values. 

Note. The results given in Table II were obtained from a series of experiments in which 5 cm styrene was polymerised in solutions of ethanol (50 cnr) and water containing 0.5 g PAA of molecular weight 27,000 and O.lg BzP at 78°C for 6 hours after which conversions to PST 100% in all cases). 

The major limitations of the feed forward control strategy presented here are that (i) it is only as good as the fundamental data which are used in the models and (ii) it can only be used for systems which conform to the conventionally accepted mode of behaviour of free radical chain polymerisation in solution. However, the same approach can be used with the appropriate models for any copolymerisation process. The range of application can be increased by making an arbitary assessment of the parameters necessary for the control models and/or by introducing a feedback loop which incorporates some state measurement device, e.g., an in-line gas chromatograph for measurement of residual monomers concentrations. Such a scheme is shown in Figure 21. 

Much of the discussion about solvent based solution polymerisation of acrylic monomers is also relevant to waterborne systems, where the monomers are polymerised in solution in a water soluble solvent, neutralised and then dispersed or inverted into water. 

Water based acrylics, for external applications, would be polymerised in solution in a similar manner to those intended for solvent based applications. Similar comonomers would be used except that a high level of either acrylic or methacrylic acid would be copolymerised with a resulting change in the ratio of the soft comonomers. The solvent... 

In 1915 and 1916, Ostromislensky (Ostromislensky, 1915, Ostromislensky, 1916, Talalay and Magat, 1945) carried out similar experiments with vinyl halides and discussed the advantages of the presence of an inert diluent. However, since there is no mention of the use of soap or other micelle-forming substances in his articles either, it seems that his observations also refer to uncatalyzed or photocatalyzed polymerisation in solution and suspension. 

The narrow particle size distribution, evident from Figure 3.6, is maintained with time as the droplets grow. This suggests that this growth occurs by fiirther polymerisation in solution, followed by deposition on existing droplets, without re-nucleation. Also, little or no coalescence or Ostwald ripening occurs in these emulsions. 

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