Polybutadiene rubbers molecular weight

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. 

Kraton G is a SEES thermoplastic elastomer with a middle block of hydrogenated polybutadiene and molecular weight of about 64,000. Vistalon is an EPDM rubber with a molecrdar weight of about 278,000. Paraloid is a methylmethacrylate-butadiene-st3rrene, MBS, elastomer with a core-shell structure. 

An unusual method for the preparation of syndiotactic polybutadiene was reported by The Goodyear Tire Rubber Co. (43) a preformed cobalt-type catalyst prepared under anhydrous conditions was found to polymerize 1,3-butadiene in an emulsion-type recipe to give syndiotactic polybutadienes of various melting points (120—190°C). These polymers were characterized by infrared spectroscopy and nuclear magnetic resonance (44—46). Both the Ube Industries catalyst mentioned previously and the Goodyear catalyst were further modified to control the molecular weight and melting point of syndio-polybutadiene by the addition of various modifiers such as alcohols, nitriles, aldehydes, ketones, ethers, and cyano compounds. 

The particle size of the dispersed phase depends upon the viscosity of the elastomer-monomer solution. Preferably the molecular weight of the polybutadiene elastomer should be around 2 x 10 and should have reasonable branching to reduce cold flow. Furthermore, the microstructure of the elastomer provides an important contribution toward the low-temperature impact behavior of the final product. It should also be emphasized that the use of EPDM rubber [136] or acrylate rubber [137] may provide improved weatherability. It has been observed that with an increase in agitator speed the mean diameter of the dispersed phase (D) decreases, which subsequently levels out at high shear [138-141]. However, reagglomeration may occur in the case of bulk... 

The polymerisation of butadiene results in a polymer with a narrow molecular weight distribution which can be difficult to process. Indeed, commercially available grades present a compromise between processibility and performance. Most polybutadiene rubbers are inherently difficult to break down during mixing and milling, have low inherent tack, and the inherent elasticity of the polymer gives poor extrudability. Peptisers can be used to facilitate breakdown and hence aid processing. 

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).

Berlin and coworkers (5,56) desired to obtain a material with an increased mechanical strength. They carried out a plasticization of bulk ami emulsion polystyrene molecular weight 80000 and 200000 respectively at 150-160° C, with polyisobutylene, butyl rubber, polychloroprene, polybutadiene, styrene rubber (SKS-30) and nitrile rubber (SKN 18 and SKN 40). The best results were obtained with the blends polystyrene-styrene rubber and polystyrene-nitrile rubber. An increase of rubber content above 20-25% was not useful, as the strength properties were lowered. An increase in the content of the polar comonomer, acrylonitrile, prevents the reaction with polystyrene and decreases the probability of macroradical combination. This feature lowers the strength, see Fig. 14. It was also observed that certain dyes acts as macroradical acceptors, due to the mobile atoms of hydrogen of halogens in the dye, AX ... 

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

Development of polybutadiene, polychloroprene and especially copolymers of butadiene andstyrene, as best replacements for natural rubber for tire-applications. Sodium used as catalyst Ring-opening polycondensation of caprolactam discovered by Schlack Formulation of the well-known Mark-Houwink equation for the viscometric determination of the molecular weight (mass)... 

Tlie rubber latex is usually produced in batch reactors. The rubber can be polybutadiene [9003-17-2] or a copolymer of 1,3-butadiene [106-99-0] and either acrylonitrile [107-13-1] or styrene [100-42-5]. The latex normally has a polymer content of approximately 30 to 50% most of the remainder is water. In addition to the monomers, the polymerization ingredients include an emulsifier, a polymerization initiator, and usually a chain-transfer agent for molecular weight control. 

V/hile analysing the composition of phases of the full separation of the emulsion it was fo xnd that the experimentally found concentrations of polymers in these solutions differ from those calculated for the case when each polymer is present in one phase only. It can be supposed that due to the partial compatibility in both emulsion phases there are both polymers present, but the "rubber" phase is a polybutadiene solution with the admixture of small quantity of PS, and the "polystyrene" phase represents a polystyrene solution with the admixture of PB, On the basis that in model emulsions of equal compositions the voliirae of rubber phase increases as the molecular weight of polystyrene decreases, and My of homopolystyrene in the polystyrene phase increases (table IIlJ we can draw a conclusion that low-molecular fractions of polystyrene migrate into the rubber phase. 

Low-molecular-weight (3,000-10,000) versions of such elastomers are used to produce liquid rubbers which can be shaped more easily than the conventional high-viscosity elastomers. The liquid rubbers can be vulcanized by reactions of their specific end groups. Hydroxyl-ended polybutadienes can be caused to grow in molecular size and to cross-link, for example, by reaction with isocyanates with functionalities > 2 (cf. reaction 1-12). 

Fig. 19a-d. Morphologies of four compliant particles in PS matrix a) KRO-1 resin particle b) HIPS particle c) concentric spherical shell (CSS) particle d) pools of low molecular weight polybutadiene as pure rubber particles (from Ref. [34] courtesy of Pergamon Press)... 

Polymer of hi molecular weight are in the main inccmq>atible, but it is often advantageous to compound two polymers in order to obtain a combination of new physical properties which either polymer alone cannot have. For example, EPDM rubber is inconq>atible with diene rubbers such as polyisrprene, polybutadiene,... 

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