Temperature polymerisation

CHROMATOGRAPHIC RESULTS OBTAINED USING L-PA IMPRINTED MIPs POLYMERISED AT DIFFERENT TEMPERATURES AND EVALUATED AT TWO TEMPERATURES 

(°C) Column temp. (°C) Resolution (Rs) Capacity factor (L-PA) (Cl) Separation factor (a) Solvent uptake (ml/g) Surface area (m /g) 

The polymers were prepared using acetonitrile as diluent and AIBN (60 C) or ABDV (40°C) as initiators. Polymerisation was started at the indicated temperatures and allowed to proceed for 24 h at each temperature. In the chromatographic evaluation the mobile phase was acetonitrile/acetic acid 90/10 (v/v). Each enantiomer (10 nmol) was injected separately. Data from [9]. 

More hydrophobic templates, such as 2,4-dichlorophenoxy acetic acid (Fig. 5.19), are best imprinted in combination with vinyl pyridine as functional monomer in 

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In production, anhydrous formaldehyde is continuously fed to a reactor containing well-agitated inert solvent, especially a hydrocarbon, in which monomer is sparingly soluble. Initiator, especially amine, and chain-transfer agent are also fed to the reactor (5,16,17). The reaction is quite exothermic and polymerisation temperature is maintained below 75°C (typically near 40°C) by evaporation of the solvent. Polymer is not soluble in the solvent and precipitates early in the reaction. 

Polyoxymethylene is obtained as a finely divided soHd. The bulk density of the product, which is very important for ease of handling in subsequent manufacturing steps, is influenced by many reaction variables, including solvent type, polymerisation temperature, and agitation. 

Fig. 4. Effect of polymerisation temperature on vinyl content at a 2 1 modifier 1itbium ratio.

Performing what is known as post-condensation. Most step polymerisations are exothermic and, consequently, the equilibrium constant K decreases with increasing temperature. Hence, one way to increase the molecular mass would be to decrease the polymerisation temperature, but kinetics prohibits using a too low temperature as it will lead to an excessively long residence time in the reactor and/or too high viscosities. Thus, in order to reach very high molecular... 

This is styrene-butadiene rubber polymerised at a temperature of 5 °C (41 °F) in contrast to the original polymerisation temperature of 50 °C (122 °F). It is also known as Low Temperature Polymer (LTP). Nitrile rubber can also be made by a low temperature process. Such polymers are characterised by improved processibility. 

These high energy species are extremely reactive, with themselves and with nucleophiles, and can generate runaway exotherms. With water, rapid evolution of carbon dioxide results. Some instances are reported [1], A compound of this class was resposible for the worst chemical industry accident to date. Di-isocyanates are extensively employed, with polyols, to generate polyurethane polymers. The polymerisation temperature should be held below 180°C or decomposition may occur which, in the case of foams, may induce later autoignition. 

PVDF is mainly obtained by radical polymerisation of 1,1-difluoroethylene head to tail is the preferred mode of linking between the monomer units, but according to the polymerisation conditions, head to head or tail to tail links may appear. The inversion percentage, which depends upon the polymerisation temperature (3.5% at 20°C, around 6% at 140°C), can be quantified by F or C NMR spectroscopy [30] or FTIR spectroscopy [31], and affects the crystallinity of the polymer and its physical properties. The latter have been extensively summarised by Lovinger [30]. Upon recrystallisation from the melted state, PVDF features a spherulitic structure with a crystalline phase representing 50% of the whole material [32]. Four different crystalline phases (a, jS, y, S) may be identified, but the a phase is the most common as it is the most stable from a thermodynamic point of view. Its helical structure is composed of two antiparallel chains. The other phases may be obtained, as shown by the conversion diagram (Fig. 7), by applying a mechanical or thermal stress or an electrical polarisation. The / phase owns ferroelectric, piezoelectric and pyroelectric properties. 

Die azeotrope Zusammensetzung fur lineare Copolymere aus Styrol und Fumarsaurediathylester entspricht bei einer Polymerisations-temperatur von 60 bzvv. 131° C einem Molenbruch Styrol von /oA- = 0,57... 

A decrease in the catalyst Al/Mt ratio and an increase in polymerisation temperature both result in a lower average polymer molecular weight and, in the case of stereospecific a-olefin polymerisation, decreased stereo regularity [22,107]. 

The symmetry of the metallocene and also the kind of procatalyst metal atom, the nature of the catalyst activator and the polymerisation temperature determine the polypropylene tacticity. The general stereoregulation behaviour of metallocene catalysts may be explained in terms of the local chirality, or chirotopicity, of the catalytic sites bonded to the same metal atom. For this analysis, the structure of metallocenes as catalysts should be considered. 

The solution process has been developed mainly for the manufacture of polyethylene. The term solution should not be taken literally since the polymer formed is often present in a molten state owing to maintenance of a high polymerisation temperature. In the solution process, a solvent such as... 

The gas-phase polymerisation of ethylene is typically carried out at 85-100 °C under a pressure of 20-25 atm. The ethylene monomer circulates, thus removing the heat of polymerisation and fluidising the catalyst bed. In order to keep the temperature of the process at values below 100 °C, gas conversion is maintained at 2-3 per pass [37], In the production of polypropylene by the gas-phase process, usually the polymerisation temperature is lower and ranges from about 50 to 85 °C, and the pressure range from ca 15 to 40 atm [553]. 

As regards a comparison of the relative effectiveness of titanium-and analogous zirconium-based catalysts in syndiospecific styrene polymerisation, the latter in general are less active than the former. Usually, polymer yields are lower, and a higher polymerisation temperature and reaction time as well as higher [Al(Me)01/transition metal compound ratios are required. Among the few zirconium compounds examined, only tetrabenzylzirconium activated with methylaluminoxane has relatively higher syndiospecific activity [10,48,56],... 

Cyclopentadienyltitanium alkoxides activated with methylaluminoxane are sensitive to various polymerisation conditions such as catalyst concentration, Al/Ti ratio, monomer concentration, dielectric constant of the reaction medium and polymerisation temperature. 

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