Polymerisation under pressure

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... 

In order to compensate for shrinkage, special techniques are required in the manufacture of rod. In one process, vertical aluminium tubes are filled with syrup and slowly lowered into a water bath at 40°C. As the lowest level of syrup polymerises, it contracts and the higher levels of syrup thus sink down the tube, often under pressure from a reservoir of syrup feeding into the tubes. 

High molecular weight polymers are produced by an adiabatic bulk polymerisation process ° using di-tert-butyl peroxide (0.02%) and 2,2 -azo-bisdi-isobutyronitrile (0.01%) as initiators and pressurised with N2. Heating to 80-90°C causes an onset of polymerisation and a rapid increase in temperature. After the maximum temperature has been reached the mass is allowed to cool under pressure. A typical current commercial material (Luvican M.170) has a A -value of about 70 (as assessed in a 1% tetrahydrofuran solution). 

Presence of zeolites with 5 A, which were used to dry ethylene under pressure and catalysed the polymerisation. The installation was destroyed. The zeolites with 3 A do not play any catalytic role. 

Can polymerise, but its main danger iies in its propensity to dimerise by the Diels-Alder reaction. This reaction takes piace at a temperature starting at 0-40°C, under pressure, if the dimerisation is not controlled, the storage equipments temperature and pressure rise very quickly, which leads to their destruction. Storage temperatures of -80°C have been recommended. 

Condensation of the reactants at 180°C under pressure to give 1,1,2-trichloro-2,3,3-trifluorocyclobutane was effected smoothly several times in a 1 1 autoclave. Scaling up to a 3 1 preparation led to uncontrollable polymerisation which distorted the larger autoclave. 

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. 

PVC may be formed by the polymerisation of vinyl chloride emulsion under pressure, using a peroxide catalyst. Polyvinyl chloride is found as UPVC (unplasticised PVC), plasticised PVC or as an impact modified PVC. 

A very efficient method to avoid a long induction period is to obtain an activated masterbatch of DMC catalyst. Thus, a quantity of DMC catalyst, 10-20 times higher than for normal PO polymerisation, is suspended in a purified polyether polyol used as starter (for example a polyether triol with a MW = 650-700 daltons) [51, 52]. To this suspension of DMC catalyst is added a quantity of PO, and the mixture is stirred under pressure (200-400 MPa), at 105-120 °C, until the pressure begins to decrease rapidly. A concentrated suspension of an activated DMC catalyst was obtained. By using a part of this activated masterbatch in normal PO polymerisation, the PO consumption starts immediately, without any induction period (see Figure 5.4). 

Vegetable oil-based polyamides are usually prepared either by the crosscondensation polymerisation of diacids with suitable diamines (hexameth-ylene diamine for nylon 6,10 and nylon 6,9), or by the self-condensation polymerisation of amino-acids (o)-aminoundecanoic acid for nylon 11). Cross-condensation is usually a two-step reaction in which the alcoholic salt solution of the reactants is heated under pressure at a high temperature to obtain the desired polyamide. The self-condensation reaction of amino acids is usually carried out in an autoclave. The melted reactant is polymerised under relatively high pressure and temperature. In both the cases the reaction is performed under the blanket of an inert atmosphere. 

Before discussing the various forms of polymers which may be encountered it is pertinent to describe briefly the basic structure of water-based polymer dispersions(ll). The starting point is a monomer which forms droplets in water. Aqueous surfactants are adsorbed at the droplet surface to stabilise the emulsion before an initiator is added to cause polymerisation under controlled conditions of pressure, temperature and stirring rate. The latex is thus an aqueous dispersion of small discrete polymer particles to which is added a range of additives, such as coalescents, anti-foaming agents, bacteriocide and anti-oxidants, to improve shelf life and properties related to its end use. 

The system involved in the bulk polymerisation process is the simplest from the point of view of composition and is used for large-scale radical polymerisation. In this process, the initiator is mixed with the monomer, usually under pressure of an inert gas, and the mixture is heated to induce generation of free radicals by thermal decomposition of the initiator. Depending on whether the monomer is a gas or a liquid, the system can be homogenous or heterogeneous... 

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