Crosslink densities, poly

Figure 1 Left illustration of the application of a mask to produce different samples . Right FT-IR images of the carbonyl band of poly(vinyl cinnamate), showing different levels of crosslink density as revealed from a decrease in conjugated carbonyls. Reproduced from Rafferty et al. [9], Copyright 2002, with permission from the Society for Applied Spectroscopy.

The variation of the domain sizes with crosslink density was recognized by Yeo et al. [28], investigating cross-poly(n-butyl acrylate)-inter-cross-polystyrene. Figure A shows the morphology of 50/50 compositions as a function of network I crosslinking level. The cellular structures are gradually transformed to finer, and more obviously cylindrical or worm-like shapes with increasing crosslink density. 

Figure 12. Radius of poly(dimethyl slloxane) phase as a function of weight fraction In cross-poly(dimethyl slloxane)-Inter-cross-polystyrene sequential IPN s with three different crosslink densities of network I. Broken lines are theoretical values from...

An example of the model prediction is shown by the solid line in Fig. 5 for poly(AMsopropylacrylamide) gel at 1 atm. In this case, three parameters were adjusted to fit the experimental data the cohesive energy density of the gel, the crosslink density and the interaction energy. However, the first two are within 2% and 6%, respectively, of independently measured experimental values. Hence, the model prediction is based on a single fitted parameter, the interaction... 

The comparative effect of the polystyrene and poly-2,6-dichlorosty-rene fillers on the tensile strength of a polybutadiene vulcanizate is shown in Figure 6. Despite the large difference in Tg values for these fillers, there is no difference in their effect on the vulcanizate. This is illustrated further by the failure envelope plot shown in Figure 7, where the data points for the two fillers, at equal volume fraction, appear to coincide quite well. The fact that all the points fall on the same envelope is a good indication of the constant crosslink density for these vulcanizates. Thus, the similarity in effect of these two fillers appears to be more related to their similar modulus values. 

Carbon black filled NR vulcanisates have been studied by high-resolution solid-state 13C NMR at 75.5 MHz. It is shown that the detection of poly- and mono-sulfidic crosslinks with 13C MAS spectroscopy is also possible in the case of carbon black filled NR vulcanisates. Quantitative results suggest that the addition of carbon black leads to a decrease in crosslink density with increasing filler content [55]. 

Figure 10.3 Mean molecular mass between chemical crosslinks and trapped chain entanglements Mc+e in a cured mixture of a poly(ethylene glycol) diacrylate (PEGDA) and 2-ethylhexyl acrylate (EHA) as a function of the EHA content [52]. Mc+e values were determined from (1/T2s)max and the plateau modulus (see Figure 10.2). A substantial difference in Mc+e value, as determined by these two methods at low crosslink density, is caused by the effect of network defects which decrease volume average network density determined by DMA (see Section 10.3). The molecular mass of PEGDA (Mn = 700 g/mol) is indicated by an arrow. The molecular mass of network chains in cured PEGDA is about three times smaller than that of the initial monomer. The molecular origin of this difference is discussed in Section 10.3...

The strongest residual dipolar couplings were also edited in a non-rotating crosslinked poly(isoprene) series by exciting DQ and triple-quantum coherences in the short time regime [62,63]. From this, the dynamic order parameters of the methylene and methyl groups were estimated and correlated with the crosslink density. Essentially the same behaviour was found as for SBR. 

Having established the validity of Eq. 14, this relationship can now be used, in rearranged form (Eq. 16), to calculate the crosslink density (1/k) of poly(Sty-co-DVB) polymers, the swelling ratio of which was already reported or otherwise determined by any other method, provided that C and k0 for the sorbed liquid are known. 

A more critical test of the gravimetric method for determination of crosslink density (1/7.) would be a comparison of results obtained on the basis of Eq. 16 for poly(Sty-co-DVB) samples made via free-radical polymerization in various... 

Table 1. Correlation of observed crosslink density for poly(sty-co-DVB) with the corresponding observed carbon-13 line-width...

Precrosslinked poly(organosiloxane) particles are composed of crosslinking trifunctional and linear difunctional siloxane units (T and D units, respectively) [5]. The molar ratios of D and T units can be varied without restrictions thus, hard spheres (fillers) as well as soft, elastic silicone particles are accessible. In this study, the siloxane particles were synthesized in emulsion. The particle size was controlled by emulsifier concentration and crosslink density highly crosslinked particles were obtained with particle diameters ranging from 20-50 nm the size of elastic particles could be varied between 70 and 150 nm. The composition of precrosslinked poly(organosiloxane) particles is summarized in Scheme 1 further, organic radicals R which can be incorporated into the partieles are listed [6,7]. 

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