Polymerisation diluents

Various transition metal-based catalysts not containing preformed metal-carbon bonds have been developed for the polymerisation of conjugated dienes [27-35, 150-158]. These catalysts include monometallic precursors such as Rh, Co and Ni salts and bimetallic precursors such as C0CI2-AICI3. Some of them are soluble in a polymerisation medium, e.g. Rh(N03)3 in protic solvents (ROH, H2O) [27,150-154] and C0CI2—AICI3 in aprotic solvents [155-157], and some others are insoluble in a polymerisation diluent, e.g. TiCL—Ni(PCl3)4 [158]. 

The radical chain will form a terminated macromolecule either by coupling with another radical or by disproportionation, or by hydrogen abstraction from the polymerisation diluent. Note that monomolecular termination, leading to Mt-H species according to scheme (7), which is characteristic of... 

Bisphenol A bis(2-hydroxypropyl methacrylate) was copolymerised with methyl derivatives of styrene (alphamethylstyrene, 4-methylstyrene and 60/40 3-methylstyrene/4-methylstyrene mixture) initiated by di-tert-butyl peroxide in the presence of 76 wt% of silica filler (quartz) at 150C-200C. The Raman bands of the carbon-carbon double bond stretching vibrations at 1630 and 1637/cm were found to be suitable for determining the conversion of double bonds of the styrene and methacrylate monomer simultaneously in dependence of the copolymerisation time. The carbonyl bands at 1702 and 1718 /cm were not suitable for assessing conversion of carbon-carbon double bonds. Relevance to polymerisable diluents for use with bisphenol A bis(2-hydroxypropyl) methacrylate) in dental applications like restorative composite materials, sealants and adhesives, is suggested. 18 refs. 

Fig. 6. Activity and isotacticity vs Al/donor ratio. Batch polymerisation occurs ia diluent hexane at 70°C and 0.7 MPa (7 bar) for 4 h with a superactive...

In the suspension process, which was the first method to be commercially developed, propylene is charged into the polymerisation vessel under pressure whilst the catalyst solution and the reaction diluent (usually naphtha) are metered in separately. In batch processes reaction is carried out at temperatures of about 60°C for approximately 1-4 hours. In a typical process an 80-85% conversion to polymer is obtained. Since the reaction is carried out well below the polymer melting point the process involves a form of suspension rather than solution polymerisation. The polymer molecular weight can be controlled in a variety of... 

Factors affecting laboratory polymerisation of the monomer have been discussed" and these indicate that a Ziegler-Natta catalyst system of violet TiCl3 and diethyl aluminium chloride should be used to react the monomer in a hydrocarbon diluent at atmospheric pressure and at 30-60°C. One of the aims is to get a relatively coarse slurry from which may be washed foreign material such as catalyst residues, using for example methyl alcohol. For commercial materials these washed polymers are then dried and compounded with an antioxidant and if required other additives such as pigments. 

Polymerisation may be carried out by techniques akin to those used in the manufacture of PTFE. The preparation of polymers in yields of up to 88% are described in one patent. Water was used as a diluent in concentrations of from one to five times the weight of the monomer, a gas with boiling point of -27.9°C. Solid polymers were formed with reaction temperatures of CL40°C at higher reaction temperatures liquid polymers are formed. 

In absence of diluent or other effective control of reaction rate, the sulfoxide reacts violently or explosively with the following acetyl chloride, benzenesul-fonyl chloride, cyanuric chloride, phosphorus trichloride, phosphoryl chloride, tetrachlorosilane, sulfur dichloride, disulfur dichloride, sulfuryl chloride or thionyl chloride [1], These violent reactions are explained in terms of exothermic polymerisation of formaldehyde produced under a variety of conditions by interaction of the sulfoxide with reactive halides, acidic or basic reagents [2], Oxalyl chloride reacts explosively with DMSO at ambient temperature, but controllably in dichloromethane at -60°C [3]. 

The components reacted violently 15 min after mixing at ambient temperature. This seems likely to have been a radical-initiated polymerisation of the alcohol (possibly peroxidised) in absence of diluent. 

Dimerisation is highly exothermic, the rate increasing rapidly with temperature, and may cause rupture of a closed uncooled container. The monomer may largely be prevented from dimerising by storage at — 80°C or below [1]. The polymerisation of the undiluted diene may become explosive within the range 0-40°C and at pressures above 2300 bar. The effect of diluents was also studied [2], A polymerisation was... 

Potentially very explosive, it may be handled and transferred by low temperature distillation. It should be stored at —25°C to prevent decomposition and formation of explosive polymers [1]. The critical pressure for explosion is 0.04 bar, but presence of 15-40% of diluents (acetylene, ammonia, carbon dioxide or nitrogen) will raise the critical pressure to 0.92 bar [2], Further data on attenuation by inert diluents of the explosive decomposition of the diyne are available [3], During investigation of the cause of a violent explosion in a plant for separation of higher acetylenes, the most important finding was to keep the concentration of 1,3-butadiyne below 12% in its mixtures. Methanol is a practical diluent [4], The use of butane (at 70 mol%) or other diluents to prevent explosion of 1,3-butadiyne when heated under pressure has been claimed [5], It polymerises rapidly above 0°C. 

In some processes, a diluent, like benzene or chlorobenzene are used as the solvent. At high pressure and temperature, both the polyethylene and the monomers dissolve in these solvents so that the reaction occur in a solution phase. In a typical process, 10-30 per cent of the monomer is converted to polymer per cycle. Rest of monomer is recycled. Extensive chain transfer reactions take place during polymerisation to yield a branched polyethylene. Apart from long branches it is also having a large number of short branches of unto 5 carbon atoms formed by intramolecular chain transfer reactions. A typical molecule of Low density polyethylene is having a short branch for about every 50 carbon atoms and one or two long branches per molecule. 

Polymerisations in alkyl chlorides. In Figure 3 of Reference 43 it was shown that the DP of the polymers at first increased with monomer concentration, and then fell off steeply to a quite low value characteristic of the polymerisation of undiluted monomer. The exact nature of the diluent ( alkyl halide ) and catalyst were not disclosed, but it is now known that the diluent was methyl chloride and the catalyst aluminium chloride. Kennedy and Thomas have investigated in some detail this interesting phenomenon [56] Experiments were carried out at -78° in a dry-box To 7.1 g of isobutene and the appropriate quantity... 

The experiment with CS2 showed up another extremely interesting effect. Over almost the whole range of compositions the DPs obtained were very significantly greater than those obtained without carbon bisulphide - with methyl chloride as sole diluent. This CS2 effect has been reported previously for the cationic polymerisation of a-methylstyrene [57] and of isobutene [50]. It seems likely that it is due (at least partly) to the fact that CS2 does not act as a transfer agent, whereas most alkyl halides do. 

This group of compounds is widely used in industry as a radical source for initiation of polymerisation. They are available from several manufacturers in a very wide range of formulations in various diluents to reduce operational hazards. These were classified into 6 hazard levels and of the many materials available, the first list below of 6 compounds (all dry and unformulated except for that suffixed, which is water-wetted) were included in the highest risk category. This specified the material as being sensitive to friction or mechanical shock equivalent to the dissipation of 1 kg m or less of energy within the sample. 

Slurry processes in which dissolved ethylene is polymerised to form solid polymer particles suspended in a hydrocarbon diluent... 

One of the drawbacks associated especially with slurry and solution CSTR processes is the necessity of removing the solvent or diluent in a post-production step. In a gas phase reactor the polymerisation takes place in a fluidised bed of polymer particles. Inert gas or gas mixture is used for fluidisation. The gas flow is circulated through the polymer bed and a heat-ex-changer in order to remove the polymerisation heat. Gaseous ethylene and comonomer are fed into the fluidisation gas line of the reactor, and a supported catalyst is added directly to the fluidised bed (Fig. 7). Polymerisation occurs at a pressure of about 20-25 bar and a temperature of about 75-110 °C. The polymer is recovered as a solid powder which is, however, usually pelletised. Due to the limited cooling capacity of the fluidising gas, reactor... 

The type of solvent or diluent should be specified in reporting a Ziegler-Natta catalyst system. Alkene polymerisations are usually carried out in inert solvents, such as aliphatic or aromatic hydrocarbons (e.g. some gasoline fractions or toluene). The use of protic or aprotic polar solvents or diluents instead of the hydrocarbon polymerisation medium can drastically alter the reaction mechanism. This usually results in catalyst deactivation for alkene coordination polymerisation. Modern alkene polymerisation processes are carried out in a gas phase, using fluidised-bed catalysts, and in a liquid monomer as in the case of propylene polymerisation [28,37]. 

The slurry process is the oldest and still widely used method for manufacturing polymers of ethylene, propylene and higher a-olefins. In this process, the monomer dissolves in the polymerisation medium (hydrocarbon diluent) and forms a solid polymer as a suspension containing ca 40 wt-% of the polymer the polymerisation occurs below the melting point of the polymer. In slurry polymerisation, the temperature ranges from 70 to 90 °C, with the ethylene pressure varying between 7 and 30 atm. The polymerisation time is 1-4 h and the polymer yield is 95-98 %. The polymer is obtained in the form of fine particles in the diluent and can be separated by filtration. Removal of the catalyst residues from the polymer can be achieved by the addition of alcohol (isopropanol, methanol), followed by recovery and extraction of the catalyst residues. The polymer is freed from diluent by centrifuging and then dried. In the case of polypropylene manufacture, the atactic fraction remains in the diluent [28,37]. 

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