Polybutadiene rubber particles

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. 

From its architecture, ASA is closely related to ABS however, instead of polybutadiene rubber particles grafted with poly(styrene-acrylonitrile) (PSAN), poly(alkyl acrylate)-based graft rubber particles are used as the impact modifier (Figure 16.1). 

ABS resins are composed mainly of styrene (over 50 %) and varying amounts of acrylonitrile comonomer in the SAN polymer backbone and polybutadiene as a chemically grafted rubber dispersion. While the styrene units provide the rigidity and ease of processability, the acrylonitrile units contribute to the chemical resistance and heat stability. The polybutadiene rubber particles in ABS provide the toughness and impact strength. StmcturaUy, ABS itself is a two-phase polymer blend system with the dispersed polybutadiene rubber phase (0.1-1 pm) embedded in a continuous matrix of SAN copolymer. Thus, the composition of ABS resins can vary widely, allowing the production of several grades tailored for different end-use applications. 

The ABS terpolymer has two phases - a continuous phase of styrene-acrylonitrile (SAN) and a dispersed phase of polybutadiene rubber particles. The addition of the polybutadiene particles as an impact modifier increases the ability of the SAN continuous phase to withstand high speed impacts... 

Impact polystyrene contains polybutadiene added to reduce brittleness. The polybutadiene is usually dispersed as a discrete phase in a continuous polystyrene matrix. Polystyrene can be grafted onto rubber particles, which assures good adhesion between the phases. 

If high impact resistance is required, the PA can be modified with rubber particles.11,15 The blends are usually made by reactive compounding from maleic-anhydride-modified rubbers, such as, EPDM, EPR, polybutadiene, or SEBS. Partial amorphous PA with a high Tg combines to give a high dimensional stability and good solvent resistance with transparency. 

In a typical example (33) a fresh feed of 8% polybutadiene rubber in styrene is added with antioxidant, mineral oil, and recycled monomer to the first reactor at 145 lbs./hr. The reactor is a 100-gallon kettle at approximately 50% tillage with the anchor rotating at 65 rpm. The contents are held at 124°C and about 18% conversion. Cooling is effected via the sensible heat of the feed stream and heat transfer to the reactor jacket. In this reactor the rubber phase particles are formed, their average size determined and much of their morphology established. Particle size is controlled to a large measure by the anchor rpm. 

Block copolymers of polystyrene with rubbery polymers are made by polymerizing styrene in the presence of an unsaturated rubber such as 1,4 polybutadiene or polystyrene co-butadiene. Some of the growing polystyrene chains incorporate vinyl groups from the rubbers to create block copolymers of the type shown in Fig. 21.4. The combination of incompatible hard polystyrene blocks and soft rubber blocks creates a material in which the different molecular blocks segregate into discrete phases. The chemical composition and lengths of the block controls the phase morphology. When polystyrene dominates, the rubber particles form... 

Another major use of butadiene polymer is in the manufacture of HIPS. Most HIPS has about 4%i-12%i polybutadiene in it so that HIPS is mainly a PS-intense material. Here, the polybutadiene polymer is dissolved in a liquid along with styrene monomer. The polymerization process is unusual in that both a matrix composition of PS and polybutadiene is formed as well as a graft between the growing PS onto the polybutadiene is formed. The grafting provides the needed compatibility between the matrix phase and the rubber phase. The grafting is also important in determining the structure and size of rubber particles that... 

Most ABS is made by emulsion polymerization. A polybutadiene or nitrile rubber latex is prepared, and styrene plus acrylonitrile are grafted upon the elastomer in emulsion. The effect of rubber particle size in ABS graft copolymer on physical properties is the subject Chapter 22 by C. F. Parsons and E. L. Suck. Methyl methacrylate was substituted for acrylonitrile in ABS by R. D. Deanin and co-workers. They found a better thermoprocessability, lighter color, and better ultraviolet light stability. 

In an isotropic medium, cracks do not move faster than half the shear wave velocity Vu so the implications of the 0.8V curve in Figure 4 were not explored. In the two-phase ABS system, however, one can imagine cracks or crazes propagating rapidly in the matrix (V /2 <—B20 meters/sec), and thence into the rubber particle [at 23°C, polybutadiene (V /2 /—29 meters/sec)] where violent branching would occur. 

The rubber particles were examined with an electron microscope after the sample was treated with osmium tetroxide (27). The micrograph (Figure 7) clearly indicates the porous nature of the rubber phase and the occlusion of polystyrene. We therefore classify this type of rubber phase as filled graft rubber. Since grafting takes place before and after the rubber chain is coiled, therefore, for this case, the monomer is grafted onto the rubber both within and without the rubber phase. Polybutadiene is thus made more compatible to the polymer matrix surrounding the rubber phase and the polymer filling the rubber phase. Here we have an... 

We used a matrix copolymer system consisting of methyl methacrylate (MMA) and styrene (St) grafted on polybutadiene rubber. The variables investigated were latex particle size (360, 2000, and 5000 A), degree of grafting, rubber content, and the degree of particle dispersion. The following variables must be considered when a transparent impact polymer is prepared. 

Impact Properties. Chemical Nature of the Rubber. If the rubber is too compatible with the matrix, it will dissolve in the rigid material and disperse on a molecular scale. Little or no reinforcement will occur since the rubber particles become smaller than the radius of the tip of a stress-induced propagating crack. However if it is highly incompatible, good adhesion between rubber and matrix cannot be obtained. For example polybutadiene rubber adheres poorly to a styrene/acrylonitrile copolymer, but a nitrile rubber adheres well to the SAN copolymer. If grafting techniques are used however, compatibility is less of a problem since the rubber is chemically bonded to the matrix. 

Monomer compositional drifts may also occur due to preferential solution of the styrene in the rubber phase or solution of die acrylonitrile in die aqueous phase (72). In emulsion systems, rubber particle size may also influence graft structure so that die number of graft chains per unit of rubber particle surface area tends to remain constant (73). Factors affecting the distribution (eg, core-shell vs "wart-like" morphologies) of die grafted copolymer on die rubber particle surface have been studied in emulsion systems (74). Effects due to preferential solvation of die initiator by die polybutadiene have been described (75,76). 

To overcome the brittleness of GPPS, the material was modified by incorporation of polybutadiene. Impact-modified polystyrene (IPS) was invented by Ostromislensky [1] and has been commercialized since the 1950s. IPS consists of a polystyrene matrix with embedded cellular rubber particles. By rubber... 

Apart from pure polybutadiene rubbers, styrene-butadiene block copolymers are also used, enabling products having particle sizes of less than 1 xm to be produced. They have high gloss and high rigidity, but somewhat lower toughness for a comparable polybutadiene content. 

Other rubber systems have been commercially successful. Styrene block copolymers yield a HIPS product with a small particle size and provide high gloss. A mixed rubber system consisting of styrene-butadiene block rubber and/or ethylene-propylene diene modified (EPDM) rubber can be blended with the polybutadiene to form bimodal rubber particle size distribution for a... 

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