1,2-Polybutadiene fractions

Figure 2. The calibration relation M(Vp) and effective relations M (V) of broad MWD 1,2-polybutadiene fractions.

A separate polymerization was carried out under identical conditions but, for this experiment, the polybutadiene fraction was separated by the double precipitation described in the Experimental section. As expected, the apparent degree of grafting was in general 50% lower than that... 

The determination of the microstructure of polybutadiene, i.e., the distribution of cis and frans-1,4-polybutadiene, as well as that of trans-XA- and 1,2-polybutadiene in polystyrene presents an analytical challenge. Fig. 5.1-12 shows the spectrum of a mixture of polystyrene and polybutadiene, obtained in CS2 solution. Difference spectroscopy with pure polystyrene as a standard affords the spectrum of the polybutadiene fraction, from which the microstructure can easily be determined (Peitscher, 1979). 

Table 9.22 Analysis of Hydroxy-Terminated Polybutadiene Fractions ...

Fig. 16.7 Experimental and theoretical sequence length distribution in homogeneously hydrogenated polybutadienes. Fractions of units hydrogenated (a) 0.088 (b) 0.442 (c) 0.674 (d) 0.778 n = number of units hydrogenated / = fraction of hydrogenated units...

Peak analysis of the active centre kinetic inhomogeneity distribution curves reveals that Type I AC (responsible for the polybutadiene fraction with a MW in the range of 2400) only exist in traditional polymerisation processes disappearing by polymerisation time = 20 min. Type II AC are also deactivated by this time. Type V AC (which are responsible for the high MW fraction of a polymer) become active by the polymerisation time of 60 min ( 15% conversion). The pattern of the polybutadiene MWD curves is evidently influenced by the wide range of different types of AC, which affect the polymerisation process at all stages. 

Among the techniques employed to estimate the average molecular weight distribution of polymers are end-group analysis, dilute solution viscosity, reduction in vapor pressure, ebuUiometry, cryoscopy, vapor pressure osmometry, fractionation, hplc, phase distribution chromatography, field flow fractionation, and gel-permeation chromatography (gpc). For routine analysis of SBR polymers, gpc is widely accepted. Table 1 lists a number of physical properties of SBR (random) compared to natural mbber, solution polybutadiene, and SB block copolymer. 

The crude product from the above reaction mixt was fractionated into a distilled product (bp 200°/0.3 Torr) with an average molecular weight of 514 and a residue with an average molecular weight of 940. These were evaluated as catalysts and compared to prior art ferrocenes in a standard carboxy-terminated polybutadiene formula cured with MAPO. The results are shown in Table 31... 

One characteristic of shear banded flow is the presence of fluctuations in the flow field. Such fluctuations also occur in some glassy colloidal materials at colloid volume fractions close to the glass transition. One such system is the soft gel formed by crowded monodisperse multiarm (122) star 1,4-polybutadienes in decane. Using NMR velocimetry Holmes et al. [23] found evidence for fluctuations in the flow behavior across the gap of a wide gap concentric cylindrical Couette device, in association with a degree of apparent slip at the inner wall. The timescale of these fluctuations appeared to be rapid (with respect to the measurement time per shear rate in the flow curve), in the order of tens to hundreds of milliseconds. As a result, the velocity distributions, measured at different points across the cell, exhibited bimodal behavior, as apparent in Figure 2.8.13. These workers interpreted their data... 

The amount of both low and high molecular weight polymer produced, as a function of polymerization temperature, can be seen in Figure 7. In this Figure, the MWD s of polybutadienes prepared with barium t-butoxide-hydroxide and BuLi in toluene at 30°C and 5°C are compared. Although both polymers show a broad MWD, the fraction of low molecular weight polymer present in the polybutadiene prepared at 5°C is greatly decreased. 

Therefore, at room temperature Fluoro-PSB-II a thermoplastic elastomer with a soft polymer phase (fluorinated block) and a hard phase (PS-block), similar to the parental polystyrene-6-polybutadiene block copolymer. Depending on the relative volume fraction of both components and the continuity of the phases, the resulting bulk material is rubbery or a high-impact solid. 

Table 1 shows the gel fractions of 1,2-polybutadiene film containing mono or diazido compound which were irradiated by ultraviolet radiation. The results show that the gel fractions for diazides are 0.77 - 0.82, and 1,2-polybutadiene was crosslinked by dinitrene which was formed by the photodecomposition of diazide. The gel fractions for monoazides have lower values than those for diazides. This means that the crosslinking with monoazides is less effective than that with diazides. 

Table 1 Gel fractions of 1,2-polybutadiene containing azido compound after irradiated with the ultraviolet light...

Boron is one of the essential materials for obtaining high specific impulse of a ducted rocket However, the combustion efficiency of boron-containing gas-generating pyrolants is low due to incomplete combustion of the boron particles in the ramburner.[i3-i l Fig. 15.20 shows the combustion temperature ofa boron-containing pyrolant with and without boron combustion as a function of air-to-fuel ratio, 8. A typical boron-containing pyrolant is composed of mass fractions of boron particles b(0-30), ammonium perchlorate ap(0.40), and carboxy-terminated polybutadiene ctpb(0-30). If the boron particles burn completely in the ramburner, the maximum combustion temperature reaches 2310 K at 8 = 6.5 and v = Mach 2 p =... 

---