Crosslinking yield

Crosslinking yields can also be derived from the extent of swelling of the irradiated polymer (if the hydrodynamic interaction factor, X, between the polymer and the solvent is known accurately), or from stress relaxation measurements on elastomers. 

High Pressure. Irradiation under high pressure increases the crosslinking yield of some polymers (64-66). This has mechanistic implications which need to be further explored. 

Other gases—e.g., NO, N O, etc.—were found to affect crosslinking yields, but the mechanism of their action is not clear (9, 10). 

Due to the many possible reaction pathways after irradiation (including capturing of the reactive intermediates by the solvent) crosslinking yields are often low (<30%). Arguably, the popularity of the aryl azide moiety in PAL studies is based on its relative ease of preparation and incorporation rather than on its photochemical properties. 

Monosubstitution of wheat starch by acetyl or hydroxypropyl groups27 without crosslinking yields products with a reduced pasting temperature, and yields pastes with enhanced clarity and viscosity but with increased stringiness (Table 10.14). The usefulness of this product is somewhat limited and requires special applications. Amylose has been found to be hydroxypropylated —20% more than amylopectin in corn and potato starches at a molar substitution level of 0.1 (3.5% hydroxypropyl).425,426... 

More recently, Norimoto et al. [46] reported that etherification with PO and BO, in which the hydrophilic nature of the bulking agent is not counterbalanced by crosslinking, yielded high ASE values but increased mechanosorp-tive creep induced by moisture changes under load. 

In addition, a two-fold molar excess of SiH groups was used in order to achieve an optimum crosslinking yield (see below). As Fig. 4 shows, the mixture achieves its final storage modulus value after 1.5 h at a reaction temperature of 30 °C with a platinum concentration of 1.5 ppm, i.e., after this time the network is fiilly formed. 

In completion of above mentioned studies, the dependence between incident light intensity, la, and the crosslinking yield, was estimated. It has been found, that the dependence explored may be represented by the equation ... 

The effects of carbon blacks on vulcanization kinetics and crosslink yields are not discussed here, as they do not usually involve bonding of rubber to the surface. 

Copolymers of 2,3-epoxypropyl methacrylate and butadiene prepared by solution free radical polymerization were tested as potential candidates for electrom negative resists.The sensitivity of the copolymers to ionizing radiation was determined with a linear accelerator.The experimental data were treated according to the Saito-Inokuti statistical theory.The calculated crosslinking yield values, G(x),were dependent an... 

Radical formation, hydrogen production and crosslinking yield have been studied by Wilske and Heusinger [116] with samples irradiated at... 

Crosslinking and main-chain scission yields have been determined by many workers. Newtork formation is predominant. Typical values for crosslinking yields are given in Table 17. The various methods used, and the differences in purity, crystallinity and branching of the samples studied, explains the large scattering in the measured values. Most results in the literature show that main-chain scission also occurs, since a soluble fraction is always obtained even at very high doses. Early values of p0/q0 determined by Charlesby [297] and by Baskett and Miller [298] are, respectively, 0.35 and 0.18—0.20. A value of 0.3 independent of... 

Fig. 38. Arrhenius plot of crosslinking yields of polyethylene compiled from the literature data [285],...

TABLE 25 RADIOLYSIS OF POLYDIMETHYLSILOXANE [363], EFFECT OF TEMPERATURE ON THE CROSSLINKING YIELD ... 

For the liquid state between —40 and +150°C, good agreement is obtained between total gas yield and crosslinked yield. Furthermore, the correlation between total crosslink yield and the sum of the new interchain bonds is also satisfactory. The intermediate radicals were observed by ESR at 77°K. CH3 has been identified and other peaks have been assigned, respectively, to =Si—CHj and =Si ... 

Crosslinking occurs at high concentration in the usual solvents on irradiation, while cyclization is dominant at low concentrations. The crosslinking yield was low in solvents containing C=0 (butanone, acetone, cyclohexanone). This was attributed by Chapiro [441] to elementary processes (65) and (71). 

The relative amount of the PPF block also affects the mechanical properties of the crosslinked P(PF-co-EG). PPF is the only portion of the copolymer that can form covalent bonds for crosslinking, so more PPF block result in more possible crosslinks, yielding a stronger material [75]. Additionally the hydrophobic PPF moieties can interact with each other, forming secondary interactions that further... 

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