Rubber grafting

Adam G., Sebenik A., Osredkar U., Ranogajec F., and Veksli Z. The possibility of using grafted waste rubber—photochemically induced grafting. Rubber Chem. TechnoL, 64, 133, 1991. 

The rubber content of the ABS polymer, is expressed in terms of the weight of the original rubber feed, rather than of the grafted rubber produced during polymerization. This is not necessarily the same as that charged to the reaction mixture. 

ABS compositions with bimodal particle size distributions of the grafted rubber can be prepared by emulsion graft polymerization techniques. The preparation of ABS types by emulsion polymerization consists in brief of (13) ... 

H. Keskkula, D.R. Paul, K.M. McCreedy, and D.E. Henton, Methyl methacrylate grafted rubbers as impact modifiers for styrenic polymers, Polymer, 28(12) 2063-2069, November 1987. 

Figure 1. Two phases. Small graft rubber particles suspended in a hard matrix.

Graft Resin, % Transmission, % Haze, % Graft Rubber Resin... 

The importance of the graft handle on a 62/38 butadiene-methyl methacrylate rubber can be illustrated by its effect on the optical properties of the polyblend. From Table II it can be seen that the reduction in percent haze is dramatic for an increase of methyl methacrylate graft from 0 to 27% by weight, while there is no apparent change in the light transmission. The blend resin in this polyblend system was an 88-12 methyl methacrylate-styrene copolymer, and the total resin to backbone rubber ratio was kept at 2.5-1.0. The measured refractive indices are included for each component (the graft rubber and the blend resin). The difference in refractive index amounts to no more than 0.004 unit for any of the components. 

Figure 2 shows the variation with time of the amount of grafted rubber measured on the basis of the amount of n-heptane-extractable rubber at 60 °C. The behavior is asymptotic, and for ethylene-propylene copolymers the yield of grafted rubber never exceeds 60%. 

The data in Table III concern materials prepared at 70°C by Procedure B and indicate that with respect to the corresponding runs carried out at 70°C by Procedure A see Table II) significant variations of the non-extractable rubber content may be observed. Table IV summarizes some results obtained by studying crude polymerizates prepared at 65 °C according to Procedure A with respect to the runs carried out at 70°C (Table III) reduced amounts of suspender and initiator were used. The data suggest that under these conditions both the monomer conversion and conversion of the initial rubber to grafted rubber are slower. 

The influence of temperature and of initiator type on the amount of grafted rubber present in the reaction crude products were studied by a series of tests the results are summarized in Table V. In all runs, the monomer conversion was allowed to progress to about 80-90%. 

The amount of grafted rubber is influenced only slightly by the type of initiator used this suggests that grafting probably takes place on the active centers formed on the rubber by transfer reactions between the growing chains of PVC and the elastomer chains. 

The polymerization reaction in aqueous suspension of vinyl chloride in the presence of an ethylene-propylene saturated elastomer occurs with the formation of poly (vinyl chloride) homopolymer and rubber-poly (vinyl chloride) grafted copolymers. The first grafting reaction proceeds as far as diffusion of the monomer inside the particles in suspension is possible afterwards, some chain branching of grafted PVC is possible. Under our experimental conditions the amount of grafted rubber does not exceed 60% of the initial rubber and is little influenced by the type of initiator used. 

Graft Blends. The properties of ABS-type polymers involving mixtures of terpolymer resins and graft rubbers are shown in Table IV. As with the nitrile rubber types, there is a pronounced gain in impact strength at a given rubber level when DBPF is present in both phases (Blends 1 vs. 3 and 2 vs. 4). 

Table IV. Blends of Styrene—Acrylonitrile—DBPF Resins with Graft Rubbers 7...

Rubber-resin heterophase systems are classified as (1) resin as the disperse phase, (2) rubber as the disperse phase, (3) grafted rubber latex particles as the disperse phase, and (4) filled graft rubber as the disperse phase. Adhesion mechanisms related to these systems are discussed. Special emphasis is made on the last two systems which involve grafting. The graft rubber isolated from the fourth system is characterized. The graft rubber is shown to function as a compatibilizer and as an adhesive or a coupling agent for the rubber-resin interface. 

We are specifically interested in the system in which a liquid-solid interface reaction has taken place. An example of this type of reaction is the chemical grafting of a rubber with a monomer at the interface. The function of the grafted rubber as an adhesive has been postulated (II, 29, 46, 64) but has never been proved. Since the grafted rubber is the key to bridging two incompatible polymers together, we devoted a major portion of our experimental work to the characterization of the grafted polymer as an adhesive at the interface. 

Grafted rubber latex particles as the disperse phase... 

Grafted Rubber Latex Particles as the Disperse Phase. ABS polymers or acrylonitrile-butadiene-styrene polymers, can be generally made by piggy-back grafting of a polybutadiene latex with styrene and... 

Filled Graft Rubber as the Disperse Phase. Rubber-modified polystyrene is generally obtained by polymerization grafting of a rubber in the presence of styrene monomer. The polymerization is carried out totally or partially in mass with the aid of shearing agitation, as patented by Amos et al. (1). The study on the initial stage of this type of polymerization was first published by Bender (5), and phase inversion similar to that discovered for the two-phase pressure-sensitive adhesives was observed. The mechanism of particle formation has also been reviewed (47). 

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... 

Since these rubber particles are highly filled with a homopolymer or a copolymer, the rubber is already reinforced with a resin to give a higher modulus particle than the grafted rubber latex. On the basis of the uniqueness of these rubber particles, this process is also more appropriate in manufacturing high-strength medium-impact ABS polymer (31), or rubber-reinforced styrene-methyl methacrylate copolymer (32). The... 

The styrene-acrylonitrile copolymers were prepared in the form of a thin film. The graft polybutadiene solution was coated on a glass slide. But, for the graft polymer containing acrylonitrile, it was undesirable to use the glass slide because of the induced orientation, therefore, we used a Mylar film to support a thick smooth film of the graft rubber. 

A zero or negative interfacial tension also implies the compatibiliza-tion of two phases (12). An inter-diffusion at the molten stage can take place under this condition. We could expect the graft side chain to diffuse into the polymer phase and the grafted rubber main chain to diffuse into the rubber phase as shown in Figure 6. On the whole, we can conclude that grafting tends to make rubber more compatible with the polymer phase. 

ABS and HIPS. The yield stress vs. W/t curves of ABS and HIPS are very similar. They are somewhat surprising because the yield stresses reach their respective maximum values near the W/t (or W/b) where plane strain predominates. This behavior is not predicted by either the von Mises-type or the Tresca-type yield criteria. This also appears to be typical of grafted-rubber reinforced polymer systems. A plausible explanation is that the rubber particles have created stress concentrations and constraints in such a way that even in very narrow specimens plane strain (or some stress state approaching it) already exists around these particles. Consequently, when plane strain is imposed on the specimen as a whole, these local stress state are not significantly affected. This may account for the similarity in the appearance of fracture surface electron micrographs (Figures 13a, 13b, 14a, and 14b), but the yield stress variation is still unexplained. 

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. 

Material. Optically clear films (about 5 mils thick) of three SA (saturated acrylic) plastics (3) that contained 25, 33, and 50% of an acrylic graft rubber (referred to as SA-1, SA-2, and SA-3) were compression molded. The acrylic graft rubber latices were latex blended with a resin latex composed primarily of methyl methacrylate, and the blend was coagulated. The compositions of these three polymers are as follows SA-1, 79/17/4 wt %—methyl methacrylate/butyl acrylate/styrene SA-2, 72/23/5 wt %—methyl methacrylate/butyl acrylate/styrene SA-3, 59/34/7 wt %—methyl methacrylate/butyl acrylate/styrene. All three graft rubbers contained low levels of a crosslinking comonomer (less than 1.0 wt %). 

Laser fight scattering was described by one of us (2) for measuring the phase structure of an MBAS plastic as a function of graft rubber concentration. The data were analyzed with the Debye-Bueche expression (I, 2)... 

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