Polymerization Temperature and Time

The rate of polymerization increases with increasing temperature within a given temperature range. At the maximum temperature limit, the catalyst gradually deactivates and the reaction rate declines. 

Some catalysts may hold the reaction rate steady for a long period of time after a short acceleration others may allow the reaction rate to decline with time after the induction period [35,36]. 

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In this paper we present a meaningful analysis of the operation of a batch polymerization reactor in its final stages (i.e. high conversion levels) where MWD broadening is relatively unimportant. The ultimate objective is to minimize the residual monomer concentration as fast as possible, using the time-optimal problem formulation. Isothermal as well as nonisothermal policies are derived based on a mathematical model that also takes depropagation into account. The effect of initiator concentration, initiator half-life and activation energy on optimum temperature and time is studied. 

These simulations clearly reveal the importance of considering M, in calculating the optimal temperature. is dependent on the heat of polymerization (-AH) as given by Eq. (13). Most monomers have heats of polymerization in the range of 50 to 80 KJ/mol. We thus decided to study the effect of (-AH) on optimal temperature and time for various half-life values of the initiator. The results are shown in Figme 5. 

Figure 5. Effect of Heat of Polymerization on Optimal Temperature and Time for Initiator with 10 hour half life at marked T.

High porosity carbons ranging from typically microporous solids of narrow pore size distribution to materials with over 30% of mesopore contribution were produced by the treatment of various polymeric-type (coal) and carbonaceous (mesophase, semi-cokes, commercial active carbon) precursors with an excess of KOH. The effects related to parent material nature, KOH/precursor ratio and reaction temperature and time on the porosity characteristics and surface chemistry is described. The results are discussed in terms of suitability of produced carbons as an electrode material in electric double-layer capacitors. 

The molecular weight of the polymers can be controlled (from ca. 50,000 to above 1,000,000) by changing the reaction temperature and time, the solvent, the concentration of the monomer, and the amount of base [39,40]. High molecular-weight polymers and a high content of trans double bonds are the reasons for the wide usage of Gilch polymerization in the synthesis of PPV homo- and copolymers. 

During the studies carried out on this process some unusual behavior has been observed. Such results have led some authors to the conclusion that SSP is a diffusion-controlled reaction. Despite this fact, the kinetics of SSP also depend on catalyst, temperature and time. In the later stages of polymerization, and particularly in the case of large particle sizes, diffusion becomes dominant, with the result that the removal of reaction products such as EG, water and acetaldehyde is controlled by the physics of mass transport in the solid state. This transport process is itself dependent on particle size, density, crystal structure, surface conditions and desorption of the reaction products. 

Carbon blacks have been reported to be capable of initiating the cationic polymerization of vinyl monomers such as vinyl ethers, indene, and acenaphthylene. The grafting sites of the polymer were based on carboxyl groups present on the surface [88]. The polymerization was inhibited by treatment of the carbon blacks with NaHCOs, CH2N2, pyridine, and DMF. Also, the degree of conversion was found to be dependent on temperature and time of polymerization [89]. 

Where r is about 50 times larger than rs. The inversion phenomenon, as one would expect from a kinetic point of view, is independent of polymerization temperature and is shown in Figure 11. 

The discussion of the recent results concerning the ethene polymerization on the Phillips catalyst demonstrates that temperature- and time-resolved FTIR spectroscopy (where both temperature and time change simultaneously during the experiment), together with an accurate control of the pressure conditions, has been decisive in clarifying the nature of the adsorbed species and of some of the precursor species present in the first stages of the polymerization reaction. Further advances in this direction may be achieved by increasing the sensitivity of the technique. 

The contribution of chain transfer with OAC in the case of TiCl4/MgCl2 is insignificant since the type and concentration of OAC do not influence the molecular mass of polyethylene >. Using titanium trichloride, the contribution of chain transfer with AlEtj increases with decreasing polymerization temperature, and at 50 °C chain transfer becomes the dominating process Mn propylene polymerization its contribution is several times lower... 

Whereas structure (113) prevails in cationic caprolactam polymers prepared at low temperature and short reaction periods, the fraction of amidine groups increases with temperature and time of polymerization. However, only small fractions of carboxyl groups were found in cationic polymers [180]. Only fractionated polymers contained equivalent amounts of basic and carboxylic groups which could also arise from hydrolysis of acyllactam groups [213]. 

The silicone matrix used for composite production was most favorable, as it allowed simple modifying adjustment of composite viscous and elastic properties according to composition, temperature, and time of polymerization. The presence of filler in the cured composition may... 

Polycrystalline samples of these racemates were irradiated, and the diastereomeric dimers were isolated and submitted to a careful mass-spectrometric analysis. The values of r were deduced from the ratios of the intensities of peaks corresponding to doubly deuteriated (55), partially deuteriated (RS + SR), and non-deuteriated dimers (RR). Parallel investigations of the dependence of r on temperature and time of irradiation have shown that no differential kinetic effect is operative in the dimerization of (RR) [or (55)] with respect to (RS). By applying this method to monomer (2) rapidly cooled from the melt we obtained values of r = I, suggesting a totally random distribution of the enantiomers along the polymerization axis. ... 

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