Polybutadiene dynamic mechanical

Dynamic Mechanical Properties. The dynamic mechanical properties of branched and linear polyethylene have been studied in detail and molecular interpretation for various transitions have already been given, although not necessarily agreed upon in terras of molecular origin.(52-56) Transitions for conventional LDPE (prepared by free radical methods) when measured at low frequencies, are located around +70°C, -20°C and -120°C and are assigned to o, 5, and y transitions respectively. (53) Recently Tanaka et al. have reported the dynamic mechanical properties for a sample of HB which was also prepared by anionic polymerization, but contrary to our system the hydrogenation of the polybutadiene was carried out by a coordinate type catalyst.(12) The transitions reported for such a polymer at 35 Hz are very similar to those of LDPE.(12)... 

Three diblock copolymers of cis-1,4 polyisoprene (IR) and 1,4-polybutadiene (BR) have been studied in dynamic mechanical experiments, transmission electron microscopy, and thermomechanical analysis. The block copolymers had molar ratios of 1/2, 1/1, and 2/1 for the isoprene and butadiene blocks. Homopolymers of polybutadiene and polyisoprene with various diene microstructures also were examined using similar experimental methods. Results indicate that in all three copolymers, the polybutadiene and polyisoprene blocks are essentially compatible whereas blends of homopolymers of similar molecular weights and microstructures were incompatible. 

Dynamic Mechanical Properties. Figure 15 shows the temperature dispersion of isochronal complex, dynamic tensile modulus functions at a fixed frequency of 10 Hz for the SBS-PS specimen in unstretched and stretched (330% elongation) states. The two temperature dispersions around — 100° and 90°C in the unstretched state can be assigned to the primary glass-transitions of the polybutadiene and polystyrene domains. In the stretched state, however, these loss peaks are broadened and shifted to around — 80° and 80°C, respectively. In addition, new dispersion, as emphasized by a rapid decrease in E (c 0), appears at around 40°C. The shift of the primary dispersion of polybutadiene matrix toward higher temperature can be explained in terms of decrease of the free volume because of internal stress arisen within the matrix. On the other... 

Electron micrographs of compositions D and E are shown in Figures 9 and 10. It is evident that in E polybutadiene is the continuous phase (with some rubber in the polystyrene domains) while D represents a transition from lamellar to polybutadiene-continuous morphology. Again the dynamic mechanical data (Table II) are consistent with these obser-... 

In rubber-modified polystyrenes, the rubber is dispersed in the polystyrene matrix in the form of discrete particles. The two-phase nature of rubber-modified polystyrene was first suggested by Buchdahl and Nielsen [47] based on data on dynamic mechanical properties obtained with a torsion pendulum. The existence of two prominent loss peaks led to this conclusion, one at low temperatures which is due to the a relaxation of the rubber (e.g. 193 K for polybutadiene) and one at high temperatures which is due to the a relaxation of the matrix (e.g. 373 K for polystyrene). Later, microscopy provided proof of the existence of the rubber phase as a discrete dispersed phase in polystyrene [48]. 

Bates, F. S., Cohen, R. E., and Argon A. S. (1983) Dynamic mechanical properties of polystyrene containing micro spherical inclusions of polybutadiene influence of domain boundaries and rubber molecular weight, Macromolecules, 16, 1108 1114. 

F. De Candia, G. Romano, and V. Vittoria, Structure-Property Relationships in Some Composite Systems Visoelasticity, Rheol. Acta 16, 95 (1977). Polybutadiene/metha-crylic acid or magnesium methacrylate, simultaneously crosslinked and polymerized. Chemical/Physical IPN. Dynamic mechanical behavior and DSC studies. 

The temperature dependence of the relaxation activation energy of hydroxy-terminated polybutadiene-methyl methacrylate AB cross-linked polymer in the glass transition region is shown in Figure 4.8. The parameters C, = 8.77 °C, C2 = 85.07 °C and = 340 K were measured by means of the dynamic mechanical spectra 381 K was chosen as the reference temperature Tq. 

Natural rubber/cw-1,4-polybutadiene (NR/BR) blends (70/30 mass ratio) have been widely used in the tire industry. Many nanocomposites based on organo-montmorillonite (OMMT)/rubber blends have been investigated. However, relatively little attention had been paid to binary rubber hybrids/ montmorillonite nanocomposites, and according to Zheng Gu et ah, no studies existed dealing with OMMT/NR/BR nanocomposites. So, the authors described the preparation of OMMT/NR/BR nanocomposites by direct mechanical blending and determined the cure characteristics, static mechanical properties, dynamic mechanical properties, and thermal stability of the nanocomposites. OMMT/NR/BR nanocomposites had exactly the same onset decomposition temperature and lower thermal degradation rate as the NR/BR blends. 

Figure 8.29 Dynamic mechanical behavior of polystyrene-Wocfc-polybutadiene-Woc/f-polystyrene, a function of the styrene-butadiene mole ratio (123,124).

In Figure 10, dynamic mechanical properties of random copolymer SBR 1011 (Ameripol 1011, BF Goodrich Rubber Co.) and block copolymer SBS (Kraton DllOl, Shell Chemicals Co.) are examined. SBR 1011 has only one tan 8 peak maximum temperature at —45°C due to its random structure however, Kraton DllOl has two tan 8 peak temperatures at -90°C and 100°C. The tan 8 peak at -90°C corresponds to polybutadiene domains (rubber domains) and the tan 8 peak at 100°C to polystyrene domains (end blocks) in the block copolymer. In the case of SBR random copolymer, the tan 8 peak temperature changes depending on the styrene concentration in the rubber. 

The influence of the vinyl content on the viscoelastic behaviour of polybutadienes is shown in Figure 4. Measurements of tan S, the phase angle between stress and strain under sinusoidal deformation, have been performed by Dynamic Mechanical Spectrometry (Rheometrics). Looking at the shift along the temperature axis due to the different vinyl content, a maximum vinyl content of 72% has been chosen, since beyond this limit the polymer can hardly be regarded as a rubber. 

In addition to the normal 1,4- and 1,2-structures of polybutadiene, the use of certain polar modifiers, e.g. TMEDA and tetrahydrofuran (THF), can result in the formation of vinylcyclopentane units (Fig. 2) 13-16 cyclic structure can be as high as 45wt% in VBRs prepared by the addition of butadiene at a rate such that intramolecular cyclization can compete effectively with chain propagation. No appreciable amounts of cyclic structure are found in VBRs prepared by batch polymerization. " How this cyclic structure influences the dynamic mechanical properties needs to be studied. 

Figure 13.15 Storage (O) and loss ( ) moduli of 10 wt% 1.24 MDa polybutadiene in 1 or 1.5 kDa phenyl-terminated polybutadiene as measured with a dynamic mechanical spectrometer, using time-temperature superposition with a 100 K temperature range, based on data of Tapadia and Wang(26). Solid lines are stretched exponentials and sums of two power-law decays.

Zom, R., McKenna, G. B., WUlner, L., Richter, D. Rheological investigation of polybutadienes having different microstructures over a large temperature range. MacromoL (1995) 28, pp. 8552-8562 Stern, D. M., Berge, J. W., Kurath, S. F. Sakoonkim, C., Ferry, J. D. Dynamic mechanical properties of concentrated solutions of polymethyl methacrylate in diethyl phthalate./ CoU. Sci., (1962) 17, pp. 409 17... 

Ferry and co-workers observed that polyisobutylene exhibits double loss peaks in dynamic mechanical studies as a function of temperature and as a function of reduced frequency - "fast" Tg and "slow" T>Tg loss peaks. Similar mechanical loss peaks were reported for cis-trans- iny polybutadiene, both as a function of temperature " and frequency by Sidorovitch and co-workers. 

The dynamic viscoelasticity and the thermal behaviour of films of Thermoelastic 125 cast from solutions in four solvents - toluene (T), carbon tetrachloride (C), ethyl acetate (E), and methyl ethyl ketone (M) — have been studied by Miyamato133 The mechanical loss tangent (tan 8) and the storage modulus E dependences exhibit two transitions at —70 °C and 100 °C which have been attributed to onset of motion of polybutadiene and polystyrene segments, respectively. The heights of the polybutadiene peaks on tan 6 curves decrease in the order C > T > E > M, while for polystyrene the order is reversed C < T < E < M. These phenomena have been related to the magnitude of phase separation of the polystyrene and polybutadiene blocks. 

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