Influence of the Polymerization Temperature

FIGURE 1.6 Influence of the polymerization temperature on the porosity of polyfglycidyl methacrylate-co-ethylene dimethacrylate) monoliths determined by MIP. (a) Differential pore size distribution curves of the polyfglycidyl methacrylate-co-ethylene dimethacrylate) rods, prepared by 22 h polymerization at a temperature of 55°C ( ), 12 h at 70°C ( ), and a temperature increased during the polymerization from 50°C to 70°C in steps by 5°C lasting 1 h each and kept at 70°C for another 4h ( ). (Reprinted with permission from Svec, F. and Frechet, Chem. Mater., 1, 707, 1995. Copyright 1995, American Chemical Society.) (b) 

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Figure 7.1.8 demonstrates the influence of the polymerization temperatures on the molecular weight distribution. It can be seen from this figure that the block efficiency increases with increasing polymerization temperature. 

Figure 13 Influence of the polymerization temperature on separation factors (a) for polymers measured at different temperatures. Flow rate, lmlmin mobile phase, 0.05% hexa-methylenediamine in chloroform. Injection amounts were 8 ig (48.5 nmol) in 40 pL injection volume. (From Ref [76].)...

The temperature dependency of 1,2 content shown in Table II is also consistent with complex formation between polybutadienyl-lithium and the oxygen atom in the lithium morpholinide moleculre. One can visualize an equilibrium between noncom-plexed and complexed molecules which would be influenced by temperature. Higher temperatures would favor dissociation of the complex and, therefore, the 1,2 content of the polymer would be lower than that from the low temperature polymerization. This explanation is supported by the polymerization of butadiene with lithium diethylamide, in which the microstructure of the polybutadiene remains constant regardless of the polymerization temperature (Table IV). This is presumably due to the fact that trialkylamines are known to be poor... 

The mechanism is complicated by the possibility of anti-syn-isomerization and by n - a-rearrangements (it - r 3-allyl Act - r 1 -allyl). In the case of C2-unsubstituted dienes such as BD the syn-form is thermodynamically favored [646,647] whereas the anti-isomer is kinetically favored [648]. If monomer insertion is faster than the anti-syn-rearrangement the formation of the czs- 1,4-polymer is favored. A higher trans- 1,4-content is obtained if monomer insertion is slow compared to anti-syn-isomerization. Thus, the microstructure of the polymer (czs-1,4- and frazzs-1,4-structures) is a result of the ratio of the relative rates of monomer insertion and anti-syn-isomerization. As a consequence of these considerations an influence of monomer concentration on cis/trans-content of BR can be predicted as demonstrated by Sabirov et al. [649]. A reduction of monomer concentration results in a lower rate of monomer insertion and yields a higher trans-1,4-content. On the other hand the czs-1,4-content increases with increasing monomer concentration. These theoretical considerations were experimentally verified by Dolgoplosk et al. and Iovu et al. [133,650,651]. Furthermore, an increase of the polymerization temperature favors the formation of the kinetically controlled product and results in a higher cis- 1,4-content [486]. l,2-poly(butadiene) can be formed from the anti- as well as from the syn-isomer. In both cases 2,1-insertion occurs [486]. By the addition of electron donors the number of vacant coordination sites at the metal center is reduced. The reduction of coordination sites for BD results in the formation of the 1,2-polymer. In summary, the microstructure of poly(diene) depends on steric factors on the metal site, monomer concentration and temperature. 

The minimum in degradation rate found for subsaturation PVC obtained around 55°C becomes less obvious if the monomer concentration at the reaction site is used as variable instead of the relative monomer pressure, P/PQ. The observed behavior is mainly due to the influence of the polymerization conditions on the formation of thermally labile chlorine, i.e. tertiary chlorine and internal allylic chlorine. Tertiary chlorine is associated with ethyl, butyl and long chain branches. The labile structures are formed after different inter-and intramolecular transfer reactions. Generally, the content increases with decreasing monomer concentration and increasing temperature in accordance with the proposed mechanisms. The content of internal double bonds instead decreases with increasing temperatures. 

Following these previous results, we investigated in this study the influence of the polymerization conditions(monomer concentration and polymerization temperature) on the structure of poly(divinyl formal). 

Still another new approach was the combined use of fractionation, osmometry and viscometry to study the influence of the polymerization conditions Ctemperature, extent of polymerization, solvent) on the infrastructure of addition polymers it was originally exemplified with three polystyrene samples prepared at different temperatures but has since been used in refined form and with such improved fractionation techniques (GPC) to study such problems as branching, stereoregulation and grafting. 

The influence of temperature on the copolymerization was investigated at constant absorbed dose of 0.12 and 0.16 KGy for copolymerization of AM-AANa [17,54] and AM-DAEA-HCl [22], respectively. The results are shown in Figs. 9 and 10, which show that the Rp values increase while the intrinsic viscosity and the degree of polymerization decrease with increasing the polymerization temperature. However, the increase in the temperature of the polymerization medium increases the swell-... 

Thus, at constant temperature and at a constant sweep rate, the influence of the cathodic overpotential (tjc) on the peak overpotential (t]p) of the voltammogram obtained under conformational relaxation control of the polymeric structure is described by... 

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