BATCH COPOLYMERISATION

Notably, this HP NMR investigation showed the formation of a transient binuc-lear p-H-p-CO complex, [Pd2(p-H)(p-CO)(dppf)2]OTs (5), and of the termination product [Pd(p-OH)(dppf)]2(OTs)2 (6) (Chart 7.1). Based on the in situ study, these compounds could be isolated, characterised and used to catalyse copolymerisation reactions. Both complexes proved to be active in batch copolymerisation reactions. However, the productivities in polyketone were significantly lower than those... 

Ethylene has a symmetrical monomer, so the concept of tacticity does not apply. Consequently, the crystallinity of polyethylene is controlled either by chain branching or by copolymerisation. Copolymers are classified into random and block copolymers (Fig. 2.7) depending on whether the monomer locations are random, or whether long blocks of each monomer exist. Polyethylene copolymers are random. The figure suggests that the local composition of a random copolymer is the same as that of the monomer mixture. However, in a batch copolymerisation, monomers tend to add to the end of a growing chain at different rates. The monomer ratio drifts as the polymerisation proceeds, so polymer formed at the end of the polymer-... 

As a necessary preliminary to the study of how compositional heterogeneity affects the properties of the polymers, compositionally heterogeneous and homogeneous co- and terpolymers had to be synthesised. It Is common in copolymerisations for the relative reactivity of the co-monomers to be different (5) so that during polymerisations carried out to high conversion In a free-running batch reactor, the Initially formed polymer Is richer In the more reactive monomer, whereas, at the end of the reaction the polymer produced contains a greater proportion of the less reactive monomer. In such circumstances, compositional... 

Compositionally uniform copolymers of tributyltin methacrylate (TBTM) and methyl methacrylate (MMA) are produced in a free running batch process by virtue of the monomer reactivity ratios for this combination of monomers (r (TBTM) = 0.96, r (MMA) = 1.0 at 80°C). Compositional ly homogeneous terpolymers were synthesised by keeping constant the instantaneous ratio of the three monomers in the reactor through the addition of the more reactive monomer (or monomers) at an appropriate rate. This procedure has been used by Guyot et al 6 in the preparation of butadiene-acrylonitrile emulsion copolymers and by Johnson et al (7) in the solution copolymerisation of styrene with methyl acrylate. 

Fig. 61. Diagram of hydrolytic cocondensation and preparation of the reactive mixture for copolymerisation in the production of SKTV 1,8- agitators 2, 3, 7 -batch boxes 4- hydrolyser 5, 6, 10 - collectors 9 - pump...

All the methods mentioned above use a mathematical model of the copolymerisation process in one way or another to arrive at a control policy for the production of compositionally homogeneous products. In this work use is made of a dynamic model of the process to control the feed rate of the more reactive monomer to a semi-batch reactor. Feedback from the process comes from an off-line model. The method is a general one and can be readily extended to accomodate feedback loops using on-line measurement devices with an experimental reactor. 

Experimental System The copolymerisation of styrene with methyl acrylate in toluene using azo-bis-iso- butyronitrile (AIBN) was selected as the model experimental system because the overall rate of reaction is relatively fast, copolymer analysis is relatively simple using a variety of techniques and the appropriate kinetic and physical constants are available in the literature. This monomer combination also has suitable reactivity ratios (i = 0.76 and r4 =0.175 at 80 C),(18) making control action essential for many different values if compositionally homogeneous polymers are to be prepared at higher conversions in a semi-batch reactor. 

The composition and quantity of styrene-maleic anhydride (SMA) copolymer resins were varied in emulsion copolymerisation of methyl methacrylate and n-butyl acrylate conducted by both batch and semicontinuous processes. The resulting particle sizes and levels of coagulum were measured to determine the optimum conditions for incorporation of the SMA resins into the resulting latexes. A semicontinuous process, in which no buffer was included and the SMA was added in a second stage comonomer emulsion, was found to produce coagulum-free latexes. 13 refs. 

Graft acrylates and siloxane copolymer latexes were prepared by batch process via simultaneous radical and ring-opening copolymerisation. Vinyl septamethyl cyclotetrasiloxane was used as a coupling agent to form chemical bonds between polyacrylates and polysiloxane. The occurrence of graft copolymerisation was confirmed by Soxhlet extraction and by the dynamic mechanical properties of latex polymer. 7 refs. 

European Polymer Journal 32, No.9, Sept. 1996, p. 1139-43 KINETIC STUDIES ON EMULSION COPOLYMERISATION OF VINYLACETATE AND ACRYLICS IN THE BATCH PROCESS Tang L-G Weng Z-X Pan Z-R Hangzhou,Zhejiang University... 

The batch emulsion copolymerisation of vinyl acetate and acrylic acid, methyl acrylate and acrylamide was investigated at 25C with a redox initiator system and a complex emulsifier. The kinetic behaviour of the copolymerisation and the structure of the resulting copolymers, as well as the particle size and number density of the latexes, were studied as a function of the conversion and the reaction time. 10 refs. 

Monodisperse copolymer particles from 1.1 to 2.6 micrometers in diameter were obtained by unseeded batch dispersion copolymerisation of styrene and butyl acrylate in an ethanol-water medium. A two-level factorial design using bottle polymerisations was initially carried ont including the following variables stabiliser concentration, initiator concentration, polarity of the dispersion medium, initial monomer concentration, and temperature. Once the region of experimental conditions in which monodisperse latexes can be prepared was identified, further effort was devoted to analyse the effect of other variables. 51 refs. 

The ultimate goal of most of the investigations on emulsion copolymerisation is to be able to control the process in such a way as to produce a copolymer product (latex or coagulate) with desired properties. For this purpose the semi-continuous (sometimes called semi-batch) emulsion copolymerisation process is widely used in industry. The main advantages of this process as compared with conventional emulsion batch processes include a convenient control of emulsion polymerisation rate in relation with heat removal and control of chemical composition of the copolymer and particle morphology. These are important features in the preparation of speciality or high performance polymer latexes. 

Van Doremaele (1990) applied a more pragmatic approach a method which can be applied without actually calculating n t) or n(fp) and may therefore be more generally applicable. This method was applied to the emulsion copolymerisation of styrene (S) and methyl acrylate (MA). The batch emulsion copolymerisation of S and MA is known to often produce highly heterogeneous copolymers (styrene being the more reactive and less water-soluble monomer). 

With the further development of online Raman spectroscopy, the controlled composition reactor seems to become realistic. In Figure 3.7 the CCD of a copolymerisation of butyl acrylate and veova 9 is depicted, for both batch and a Raman-controUed reaction. For a more extensive discussion of process strategies see Chapter 4. 

This chapter focuses on key features to understand the emulsion copolymerisation kinetics and on the influence of operation on the copolymer composition of the final latex products. Focus is on batch and semi-batch or semi-continuous operation, see Figure 4.1. Only the free-radical emulsion copolymerisation of two monomers is considered but the concepts can be directly applied for formulations containing more than two monomers. The reacting monomers usually having different reactivities, polymerise simultaneously. The reactivities and the individual concentrations of the monomers at the locus of polymerisation, that is, the particle phase, govern the built-in ratio into the polymer chains at a certain time. 

Characteristic features of emulsion copolymerisation appear when discussing the copolymerisation process in a perfectly mixed batch reactor. In a batch process no materials enter or leave the reactor during the polymerisation, see Figure 4.1. For monomer i the following... 

Figure 4.2 Typical example of the conversion time history (a) and chemical composition distribution (b) of a batch emulsion copolymerisation of styrene and methyl acrylate. Initial overall molar ratio of styrene and methyl acrylate is 0.33. Styrene is the more reactive monomer. 0 overall monomer conversion O-partial conversion of styrene partial conversion of methyl acrylate. Note the fast homopolymerisation of methyl acrylate when styrene is vanished.

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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