Cross-linked polybutadienes

Polybutadiene is readily cross-linked by heating with 1% dicumyl peroxide for 10 min at 145°C. If the product is first extracted with C2CI4 to remove any non-cross-linked material and then placed in eontact with WCl6/EtA.lCl2/EtOH in C2CI4 at 45°C, it rapidly goes into solution (Hummel 1970 Kumar 1981). An added acyclic olefin assists this process but is not essential. It is clear that the network can be readily broken down by the occurrence of either intramolecular or intermolecular metathesis reactions. 

For heavily cross-linked polymers Q 0.3), there is always an insoluble residue after metathetical degradation. As the degradation proceeds, volatiles analyzable by GC are produced, together with a certain amount of low-molecular-weight extractable polymer, the proportion of which rises to a maximum and then declines as metathesis proceeds towards completion (Ast 1977b Kumar 1982). 

The degradations of vulcanized polybutadienes (Bozkurt 1989 Ziimreoglu 1992 Hummel 1993a) and of cross-linked blends with ethene/propene copolymer (Hummel 1987b) have also been studied. 

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The term ABS was originally used as a general term to describe various blends and copolymers containing acrylonitrile, butadiene and styrene. Prominent among the earliest materials were physical blends of acrylonitrile-styrene copolymers (SAN) (which are glassy) and acrylonitrile-butadiene copolymers (which are rubbery). Such materials are now obsolete but are referred to briefly below, as Type 1 materials, since they do illustrate some basic principles. Today the term ABS usually refers to a product consisting of discrete cross-linked polybutadiene rubber particles that are grafted with SAN and embedded in a SAN matrix. 

Since the excellent work of Moore and Watson (6, who cross-linked natural rubber with t-butylperoxide, most workers have assumed that physical cross-links contribute to the equilibrium elastic properties of cross-linked elastomers. This idea seems to be fully confirmed in work by Graessley and co-workers who used the Langley method on radiation cross-linked polybutadiene (.7) and ethylene-propylene copolymer (8) to study trapped entanglements. Two-network results on 1,2-polybutadiene (9.10) also indicate that the equilibrium elastic contribution from chain entangling at high degrees of cross-linking is quantitatively equal to the pseudoequilibrium rubber plateau modulus (1 1.) of the uncross-linked polymer. 

Figure 2. Glass transition temperature from DSC in cross-linked polybutadiene as a function of...

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

Tensile Strength Data from Electron Beam Cross-Linked Polybutadiene and Its Copolymers... 

Valentine,R.H. Viscoelastic properties of linear and cross-linked polybutadienes. Ph. D. thesis, University of Wisconsin, 1967. 

The radical concentration is strongly dependent on the presence of molecular anchorages, notably cross-links. Mead studied cross-linked polybutadienes deformed plastically below Tg. Pre-strains of different magnitudes were applied above... 

A variant of rubber toughening involves the use of preformed core-shell rubbers comprising a highly cross-linked polybutadiene core with a grafted shell of a vinylic polymer. In this case, the particles are small, typically ca. 0.1 pm, and thus have little effect on the observed viscosity of the epoxy. One of the principal advantages of this over simple rubber toughening is the ability to produce predetermined controllable morphology in the cured polymer. " ... 

Extracting hydrophobic gels prepared by swelling cross-linked polybutadiene with solutions of 4-acylpyrazol-5-one (HL) in toluene, chloroform, and carbon tetrachloride were used for copper extraction studies [192]. The metal distribution curves, close to those obtained in the pure liquid-liquid extraction systems, show that the polymer has no effect on the thermodynamics of the liquid-gel extraction, as shown in Fig. 43. Kinetic studies... 

Figure 17. Cross-polarization magic angle sample spinning of cis-polybutadiene with 5phr ROOR. Spectrum (A) cross-linked polybutadiene obtained in dry state. Spectrum (B) same as (A) except swollen in benzene to equilibrium swelling, S artifact of rotor.

Recently, an interesting article was published about the behavior of elastomers, such as cross-linked polybutadienes, at cryogenic temperatures (6). Their results are contrary to the common belief that the fracture energy would decrease to nothing at these temperatures. In fact, the fracture energy increases - presumably due to craze formation. If the same result holds true for the rubber-... 

This book has been divided into three areas chemical detection, biological detection, and decontamination. The subject matter in the chapters include cross-linked divinyl benzene-substituted methacrylate polymers (Chapter 2), porous silicon (Chapter 3), reactive glass surfaces (Chapter 4), polycarbosilanes (Chapter 5), non-aqueous, chemically cross-linked polybutadiene gels (Chapter 6), conducting polyaniline nanofibers (Chapter 7), organically doped polystyrene and polyvinyltoluene (Chapter 8), electroplated polymer cast resins (Chapter 9), self assembled monolayers (Chapter 10), amphiphilic functionalized norbomene polymers (Chapter 11), transition metal substituted polyoxometalates (POMs) (Chapter 12), cross-linked divinyl-benzamide phospholipids (Chapter 13), and silica and organo silyl polymers (Chapter 14). 

Figure 2. Swelling of cross-linked polybutadiene in solvents with varying solubility parameters. Solubility parameter has units of MPa. ...

Fig. 4. Loss tangent of a chemically cross-linking polybutadiene as function of reaction time (48). Data were taken at several frequencies. The GP is marked by the instant at which the loss tangent is independent of frequency. All data are taken at low frequencies where the self-similar behavior prevails.

Finally, there are several papers concerned with cross-linked systems. A relaxation study of poly(vinyltrichloroacetate) (PVTCA) cross-linked with either poly(methyl acrylate) or poly(methyl methacrylate) showed that although phase separation occurred, the mobility of the cross-linking component was altered by attachment to the PVTCA. Rowland and Labun have observed a marked decrease in H Ti values consequent on cross-linking polybutadiene, an effect attributed to a broad distribution of correlation times for protons near the cross-link. 

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