DPN

Gray cast iron is the most commonly used cast iron and is the least expensive. It is the easiest to cast and machine. The tensile strength of gray cast iron ranges from 155 to 400 N/mm (10 to 26 ton/in. ). The tensile modulus ranges from 70 to 140 kN/mm and the hardness from 130 to 300 DPN. 

White cast iron is very hard (from 400 to 600 DPN) and brittle. All white cast irons are very difficult to machine and usually are finished by grinding. Table 3.3 gives properties of the four principal types of white cast irons. 

BSI Designation Purity (% min.) Degree of Cold-Work Typical Mechanical Properties Tensile Strength Hardness (N/mm2) (DPN) ... 

BSl Designation Main Alloy Elements Heat Tensile Treatment Strength Condition (N/mm ) Hardness (DPN)... 

Density (g/cm2) Melting Point (°C) Coefficient of Expansion X IQ-6 (°C) Thermal Conductivity (W/m °C) Vield Tensile Strength Modulus (N/mm2) (N/mm2) Hardness (DPN)... 

Keeping the composition of copolymerization media constant the total comonomer concentration of which is varied. The absorbed dose was kept constant at 0.14 KGy for the AM-AANa and at 0.35 KGy for the AM-DAEA-HCl systems. The results are shown in Figs. 4 and 5, which show the rate of polymerization, Rp, the degree of polymerization, and the intrinsic viscosity increase with increasing monomer concentration. At comonomer concentration >2.1 M/L, DPn decreases with increasing comonomer concentration. From the logarithmic plots, exponents of the comonomer concentration for the AM-AANa system were determined to be [17,54]. 

A correction is needed, however, if parameters relating to the number of moles of reactants are introduced (e.g. p or the degree of polymerization DPn). 

Assuming that no intramolecular or side reactions take place and that all groups are equireactive, the polydispersity index, 7P, of hyperbranched polymers obtained by step-growth polymerization of ABX monomers is given by Eq. (2.2), where pA is die conversion in A groups.196 Note that the classical Flory relationship DPn = 1/(1 — pa) holds for ABX monomer polymerizations ... 

When prepared by thermal condensation of the respective alkoxides and carbonates in hydrocarbon media such as decalin, these catalysts yielded living poly-e-capro-lactone. Its living nature was demonstrated by the increase of DPn with conversion and by the validity of the relation... 

Some of these bi-metallic oxyalkoxides are able to polymerize oxiranes to high-molecular weight poly-ethers8 b) (M.W. of the order of 106 ). The resulting polymers reveal a quasi-living character, their DPn increases with conversion and is further... 

For such systems the lifetime of living polymers is determined by kd only, independently of [M], although the maximum DPn achieved in such a system does depend on [M], However, when propagation proceeds through intermediates, e.g.,... 

The latter seem to be more reactive than the former, and hence the shift of the equilibrium leads to an increase in the polymerization rate. This explanation was verified by investigating the polymerization initiated by monofunctional initiators31), as well as by difunctional poly-a-methyl styrene of DP 70 and 270 32). No curvature was observed in the first case, neither in the second provided that the DPn of the initiator was sufficiently large. 

Barium and strontium salts of polystyrene with two active end-groups per chain were prepared by Francois et al.82). Direct electron transfer from tiny metal particles deposited on a filter through which a THF solution of the monomer was percolated yields the required polymers 82). The A.max of the resulting solution depends on the DPn of the formed oligomers, being identical with that of the salt of polymers with one active end-group per chain for DPn > 10, but is red-shifted at lower DPn. Moreover, for low DPn, (<5), the absorption peak splits due to chromophor-chromophor interaction caused by the vicinity of the reactive benzyl type anions. 

Our investigations agree with arguments in earlier articles by other authors, namely that empirical reactivity indices provide the best correlation with the goal values of the cationic polymerization (lg krel, DPn, molecular weight). On the other hand, the quantum chemical parameters are often based on such simplified models that quantitative correlations with experimental goal values remain unsatisfactory 84,85>. But HMO calculations for vinyl monomers show, that it is possible to determine intervals of values for quantum chemical parameters which reflect the anionic and cationic polymerizability 72,74) (see part 4.1.1) as well as grades of the reactivity (see part 3.2). 

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