Molecular weight temperature dependence

In a typical adiabatic polymerization, approximately 20 wt % aqueous acrylamide is charged into a stainless steel reactor equipped with agitation, condenser, and cooling jacket or coils. To initiate the polymerization, an aqueous solution of sodium bisulfite [7631-90-5] is added, followed by the addition of a solution of ammonium persulfate [7727-54-0] N2HgS20g. As the polymerization proceeds, the temperature rises to about 90°C, and then begins to fall at the end of the polymerization. The molecular weight obtained depends primarily on the initiator concentration employed. 

If the degree of polymerization is controlled principally by chain termination so that Xn is proportional to the kinetic chain length, the temperature coefficient of the average molecular weight will depend... 

Notice the similarity between the relationship for liquid viscosity [Eq. (4.7)] and that for gaseous viscosity [Eq. (4.6)]. They both have a square root dependence on temperature and molecular weight and depend on the inverse square of the collision diameter [can you prove this for Eq. 4.7) ]. So, at least in principle, there is a fundamental relationship between the structure of a liquid and its viscosity. 

Thus, one may conclude that, in the region of comparatively low frequencies, the schematic representation of the macromolecule by a subchain, taking into account intramolecular friction, the volume effects, and the hydrodynamic interaction, make it possible to explain the dependence of the viscoelastic behaviour of dilute polymer solutions on the molecular weight, temperature, and frequency. At low frequencies, the description becomes universal. In order to describe the frequency dependence of the dynamic modulus at higher frequencies, internal relaxation process has to be considered as was shown in Section 6.2.4. 

For a given polymer in a given solvent the sedimentation coefficient is dependent on polymer concentration, molecular weight, temperature and pressure. 

Extensional viscosity is obviously dependent on average molecular weight, temperature and rate of extension. Apparently, also the tensile strain (degree of extension) is important. 

Description A variety of polymers are produced on these large reactors for various applications. The melt index, polymer density and molecular weight distribution are controlled with temperature profile, pressure, initiator and comonomer concentration. Autoclave reactors can give narrow or broad molecular weight distribution depending on the selected reactor conditions, whereas tubular reac-... 

The adsorption of polymeric surfactants is more complex, since in this case the process is irreversible and produces a high-affinity isotherm with a steep rise in the adsorption value at low polymer concentrations (in this region most of the molecules are completely adsorbed). Subsequently, the adsorbed amount remains virtually constant, giving a plateau value that depends on the molecular weight, temperature and solvency of the medium for the chains (this topic was discussed in detail in Chapter 6). 

In the above discussed papers monofunctional polystyrenes with Mn = 2,000 to 4,000 were used. The block copolymers had Mn = 12,000 to 100,000. The molecular weight distribution was quite narrow for directly brominated polystyrenes (Mw/Mn = 1.04) and was slightly broader for xylylene dibromide modified polystyrenes (Mw/Mn = 1.15) (at—10 °C with PF counterion). The molecular weight distribution depended on both temperature and counterion 139). 

That is, in terms of reaction rates, the molecular weight of polyolefins is given by the ratio between the overall rate of propagation (Rp) and the sum of all rates of chain release (Rr) reactions this means that the molecular weight is dependent on the type of catalyst and the kinetics of the process, that is, the polymerization conditions (polymerization temperature, monomer concentration, catalyst/cocatalyst ratio). Hence, understanding the details of the mechanisms of chain release reactions is the key to molecular weight control in metallocene-catalyzed olefin polymerization. Here, chain release reactions (usually referred to as termination or transfer reactions) are all those steps that cause release of the polymer chain from the active catalyst, with the formation of a new initiating species (see section... 

Precipitation Polymer insoluble in monomer or monomer miscible with precipitant for polymer Physical state of system permits easy agitation Relatively low temperatures employed Separation of product difficult and expensive Catalyst systems are special and need careful preparation Molecular weight distribution depends on type of catalyst... 

In general, a miscible blend of two polymers is likely to have properties somewhere between those of the two unblended polymers. The relative miscibility of polymers controls their phase behavior, which is of crucial importance for final properties. Polymer-polymer miscibility depends on a variety of independent variables, viz., composition, molecular weight, temperature, pressure, etc. 

The above described technique seems to be prospective for fabrication of polymer based optical devices. The method is simple, free of disadvantages of conventional techniques. It gives highly reproducible results and is suitable for production of high-quality pol)nner waveguides. However, it should be noted, that the response to external electric field is not the same for different pol)nners. Apparently the quality and the shape of the structures created by the effect of the external electric field depend on the polymer type, its molecular weight, temperature of flow, molecular structure ect. Therefore the conditions of pattern preparation must be optimalized for each particular case. 

Gaseous vinyl chloride monomer is polymerised under high pressure conditions. Since polyvinyl chloride polymer is insoluble in its own monomer, the reaction kinetics do not follow the classical emulsion polymerisation kinetics. During polymerisation, chain transfer to monomer is extensive, and molecular weight development depends upon the reaction temperature rather than the initiator concentration. Consequently, lower reaction temperatures are needed to reach higher molecular weights. A typical formulation for the suspension polymerisation of polyvinyl chloride is given in Table 5. 

The Huggins constant k is independent of the molecular weight but depends on the specific polymer/solvent pair and temperature. The value of k is about... 

Values offJB and a/fB, which on the latter basis may be identified simply with fg and OLf, are included in Table 11-11, together with Aa and the characteristic temperature Tco of equation 26. Since the data are all for polymers with reasonably high molecular weight, the dependence of Tg on molecular weight when the latter is low (mentioned in Section D) is avoided. For the great majority of systems,... 

The application of equations 67 and 68 to blends of samples of the same polymer with widely different molecular weights or broad molecular weight distributions depends on the hypothesis that the free volumes of the different species are additive in their volume fractions. A rather good confirmation of these equations was obtained from shear creep measurements by Ninomiya, Ferry, and Oyanagi on a series of poly(vinyI acetate) fractions and their blends. 24 First,was determined from the temperature dependence of ot for a sample of very high molecular weight and equation 34 (with B = 1). Then fu was evaluated for each sample and blend from equation 68 and experimental data in the transition zone which provided log oo log To it was found to be always consistent with equation 34 and the temperature... 

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