1,4 Polybutadiene stress

B 1,481.2 1,4-Polybutadiene (low vinyl) 1,2-Polybutadiene (high vinyl) Polyethylene Polybutylene Improved material stress-strain properties... 

Fig. 10. Concentration dependence of a modulus in the region of low-frequency plateau (i.e. yield stress , measured by a dynamic modulus). Dispersion medium poly (butadiene) with M = 1.35 x 105 (7), silicone oil (2) polybutadiene with M = 1 x I04 (3). The points are taken from Ref. [6], The straight line through these points is drawn by the author of the present paper. In the original work the points are connected by a curve in another manner...

Some typical stress-strain curves for a carboxy-terminated polybutadiene proplnt (CTPB) containing 86% solids are given in Figure 8, and for a PBAA propellant (see Table 13) containing 83% solids in Figure 9 (Ref 52). The authors concluded that the CTPB proplnts studied were highly susceptible to humidity degradation... 

The influence of ambient aging at 70°F and accelerated aging at 160°F on the stress-strain behavior of carboxy-terminated polybutadiene, polybutadiene-acrylic acid, polybutadiene-acrylic acid-acrylonitrile, and hydroxy-terminated polybutadiene composite propints is shown in Figures 10 and 11. The elastomers and curative agents for these formulations are listed below... 

Under increasing strain the propint volume increases from the voids created around the unbonded solid particles. Nonlinearities in Young s modulus and Poisson s ratio then occur. Francis (Ref 50) shows this effect for a carboxy-terminated polybutadiene composite propellant with 14% binder as in Figure 12. He concludes that nonlinearities in low-temperature properties reduce the predicted stress and strain values upon cooling a solid motor, and therefore a structural analysis that neglects these effects will be conservative. However, when the predictions are extended to a pressurized fiberglas motor case, the nonlinearities in properties produce greater strains than those predicted with linear analysis... 

The correct explanation of the peculiar behaviour of the butadiene-styrene system was provided by O Driscoll and Kuntz 144). As stated previously, under conditions of these experiments butadiene is indeed more reactive than styrene, whether towards lithium polystyrene or polybutadiene, contrary to a naive expectation. This was verified by Ells and Morton 1451 and by Worsfold 146,147) who determined the respective cross-propagation rate constants. It is germane to stress here that the coordination of the monomers with Li4, assumed to be the cause for this gradation of reactivities, takes place in the transition state of the addition and should be distinguished from the formation of an intermediate complex. The formation of a complex ... 

In observing the time dependent changes in birefringence and stress-optical coefficient, for elongated samples at 25 C, it was found that the rate of crystallization of high trans SBR s was very much faster, some 10 times more rapid, than that for NR (8). This is consistent with the reported rates of isothermal crystallization for NR (2.5 hours at -26°C) and for 807. trans-1,4 polybutadiene (0.3 hours at -3°C) in the relaxed state (12). 

A new stress-relaxation two-network method is used for a more direct measurement of the equilibrium elastic contribution of chain entangling in highly cross-linked 1,2-polybutadiene. The new method shows clearly, without the need of any theory, that the equilibrium contribution is equal to the non-equilibrium stress-relaxation modulus of the uncross-linked polymer immediately prior to cross-linking. The new method also directly confirms six of the eight assumptions required for the original two-network method. 

Figure 3. Birefringence of triisocyanate cross-linked polybutadiene (B2) vs. stress...

Figures 6 and 7 give the data of Fukuda et al. (3) and that of Saunders (52). The variation of stress optical coefficient of the high cis and high trans, 1,4-polybutadiene is plotted against Me in Figure 6, where it is compared with...

Figure 6. PIP after Saunders, 1956. Stress optical coefficient as a function of molecular weight between cross-links (3, 52). PBD is polybutadiene. PIP is polyisoprene.

High-impact grades present better impact resistances even at low temperature, higher flexibility and environmental stress cracking resistance (ESCR). The butadiene-styrene block copolymers are transparent but the alloys made of polystyrene and polybutadiene are not. 

The stress relaxation properties of a high molecular weight polybutadiene with a narrow molecular weight distribution are shown in Figure 1. The behavior is shown in terms of the apparent rubber elasticity stress relaxation modulus for three differrent extension ratios and the experiment is carried on until rupture in all three cases. A very wide rubber plateau extending over nearly 6 decades in time is observed for the smallest extension ratio. However, the plateau is observed to become narrower with increasing extension... 

Figure 1. Stress relaxation curves for three different extension ratios. Uncross-linked high-vinyl polybutadiene with a weight average molecular weight of 2 million and a reference temperature of 283 K. G is the apparent rubber elasticity modulus calculated from classical affine theory. (Solid line is data from Ref. 1).

Graft copolymers are also used as compatibilizers to tie together different phases. HIPS contains PS grafted onto polybutadiene backbones. This allows stress or strain to be transferred from the PS to the polybutadiene phase transferring energy that might break the brittle PS to the more flexible polybutadiene phase. That is why HIPS is stronger than PS itself. 

The information on physical properties of radiation cross-linking of polybutadiene rubber and butadiene copolymers was obtained in a fashion similar to that for NR, namely, by stress-strain measurements. From Table 5.6, it is evident that the dose required for a full cure of these elastomers is lower than that for natural rubber. The addition of prorads allows further reduction of the cure dose with the actual value depending on the microstructure and macrostructure of the polymer and also on the type and concentration of the compounding ingredients, such as oils, processing aids, and antioxidants in the compound. For example, solution-polymerized polybutadiene rubber usually requires lower doses than emulsion-polymerized rubber because it contains smaller amount of impurities than the latter. Since the yield of scission G(S) is relatively small, particularly when oxygen is excluded, tensile... 

Figure 6. Relative stress decay vs. molecular weight between crosslinks of polybutadiene-polyurethane rubber at three temperatures...

Tristar polybutadienes prepared by the intermediacy of lithium acetal initiators were also converted to three dimensional networks in a liquid rubber formulation using a diisocyanate curing agent. Table IV shows normal stress-strain properties for liquid rubber networks at various star branch Hn s. It can be seen that as the branch Mn increases to 2920, there is a general increase in the quality of the network. Interestingly, the star polymer network with a star branch Mn of 2920 (Mc=5840) exhibits mechanical properties in the range of a conventional sulfur vulcani-zate with a Me of about 6000-8000. 

In l02) the authors describe the design of an experimental plant for studies of acoustic cavitation in flowable high polymers with the help of optic methods the plant employs a flat-slit transprent-wall capillary acoustic treatment of a polymer was carried out at a frequency of 17.8 kHz, and amplitude of vibration between 0 and 15 mcm. The study was conducted on 1,2 polybutadienes of narrow molecular-mass distribution tests were arranged at room temperature. It has been demonstrated that static mechanical stresses occur in a stationary (non-flowing) polymer under the action of acoustic treatment isochrome lines in the viscosimetric tank form a cellular structure with cell size of about 1-3 mm, and in the capillary the isochromes are observed in form of longitudinal strips (Fig. 19). The authors have also found that acoustic... 

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