Acrylonitrile grafting effect

Effect of Substrate. Several comparisons were made to establish the effect of substrate on conversion of methylvinylpyridine and acrylonitrile. Relative effectiveness in the ethylene-propylene series were ethylene-propylene copolymer > polyethylene > polypropylene on a relativity scale of 4 3 2. The fact that chains terminated with polyethylene blocks are better substrates than polypropylene blocks suggests that random grafting on the backbone is not a major part of the reaction at low polymerization temperatures. The higher conversion on polyethylene... 

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

The theory of radiation-induced grafting has received extensive treatment. The direct effect of ionizing radiation in material is to produce active radical sites. A material s sensitivity to radiation ionization is reflected in its G value, which represents the number of radicals in a specific type (e.g., peroxy or allyl) produced in the material per 100 eV of energy absorbed. For example, the G value of poly(vinyl chloride) is 10-15, of PE is 6-8, and of polystyrene is 1.5-3. Regarding monomers, the G value of methyl methacrylate is 11.5, of acrylonitrile is 5.6, and of styrene is >0.69. 

An effective method of NVF chemical modification is graft copolymerization [34,35]. This reaction is initiated by free radicals of the cellulose molecule. The cellulose is treated with an aqueous solution with selected ions and is exposed to a high-energy radiation. Then, the cellulose molecule cracks and radicals are formed. Afterwards, the radical sites of the cellulose are treated with a suitable solution (compatible with the polymer matrix), for example vinyl monomer [35] acrylonitrile [34], methyl methacrylate [47], polystyrene [41]. The resulting copolymer possesses properties characteristic of both fibrous cellulose and grafted polymer. 

Results for the challenge of coated glass with S. aureus are shown in Table 1. The time of chlorination was a function of the hydrophilicity of the surface coating the poly(vinyl acetate oxazolidinone) polymers required the least amount of exposure to free chlorine. All of the surface coatings were effective against S. aureus in brief contact times. The grafted poly(acrylonitrile oxazolidinone) sample was not tested until 30 days after chlorination, but it still provided a 6-log inactivation of S. aureus in less than 10 min of contact. 

Fig. 2. Polymerization of acrylonitrile by vibromilling polyoxymethylene. Effect of milling time in hours on /) free polyacrylonitrile 2) nitrogen content of graft copolymer (28)...

The grafting of acrylonitrile and styrene on polycaprolactam was carried out in the liquid state (18,31). The more important parameters were monomer concentration and the milling time. In order to separate the effect of total liquid and of monomer concentration, the reactions were also conducted in solution. 

For low radiation doses, peroxides accumulate almost linearly with dose. However, after a certain dose has been reached, their concentration tends to level off. This conclusion can be derived from the observed change in the rate of graft copolymerization initiated by polymers subjected to increasing doses of preirradiation in air. Figure 2 illustrates this effect in the case of grafting acrylonitrile onto polyethylene (2). The drop in the yield of peroxide production presumably results from the efficient radiation-induced decomposition of these peroxides. Peroxides are known to decompose under free radical attack, and selective destruction of peroxides under irradiation has been established experimentally (8). This decomposition can become autocatalytic, and sometimes the concentration of peroxides may reach a maximum at a certain dose and decrease on further irradiation. Such an effect was observed in the case of poly (vinyl chloride). Figure 3 shows the influence of preirradiation dose on the grafting ratio obtained with poly (vinyl chlo-... 

The effectiveness of methacrylate-grafted latex rubbers for HIPS was unexpected because of the poor miscibility properties of these type of polymers (5). The situation is different in the case of acrylonitrile-butadiene-styrene (ABS) types that are miscible with methacrylate-grafted latex rubbers. 

Armstrong et al. have extensively studied the effect of this radiation on grafting butadiene, styrene, vinyl chloride, vinyl esters, acrylic, and methacrylic esters, acrylonitrile and other less common monomers on Nylon 66 fibers. They observed the influence of oxygen, water, methanol, acetic acid, dose of irradiation as well as temperature (160-163). 

Studies in the grafting of mixed monomers to cellulose have also been reported by Sakurada (113). Binary mixtures studied included butadiene with styrene or with acrylonitrile, and styrene with acrylonitrile. Remarkable increases in rate in the case of mixed monomer similar to those found by RAPSON were found in many cases. For example, about 10% of butadiene increased the grafting yield about ten fold. Similar results were found with the addition of acrylonitrile to butadiene and to styrene. Ternary mixtures of monomers were also investigated by both Rapson (109) and Sakurada (113). The large increases in rate with certain mixtures were interpreted by Sakurada as due to a particular balance of gd effects akin in many ways to popcorn polymerization. The effects were found also with polyvinyl alcohol but not with polyethylene where gel effects would perhaps be less prominent. 

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. 

Sonic Modulus. If crack or craze branching is the operative mech-nism in toughening, toughness should be directly related to the difference in sonic speeds in matrix and dispersed phases. Experiments to confirm this effect were undertaken using three commercial ABS resins. These were selected to represent the three main rubber types encountered commercially an acrylonitrile/butadiene copolymer rubber, a butadiene rubber with grafted styrene/acrylonitrile copolymer, and a block polymer of... 

The butadiene and butadiene-acrylic monomer systems polymerize when irradiated on PVC or vinyl chloride copolymer latex. The structure of the polymer obtained may be grafted if it can be proved that the copolymer properties are different from the blend properties. To elucidate the structure we studied a copolymer obtained by polymerizing butadiene-acrylonitrile on a PVC homopolymer lattice. Owing to practical reasons and to exclude the secondary effect of catalytic residues we used y radiation. However, we shall observe in a particular case the properties of peroxide-initiated graft copolymer. 

The concept of PO macroinitiators centers on the introduction of an initiation moiety into an olefinic polymer chain for polymerization. The most effective route for preparing PO macroinitiators is by employing functional polyolefins containing hydroxyl groups or other reactive groups. These functional POs are prepared by copolymerization of olefins with functional monomers and post-polymerization reaction, as mentioned above. In the case where an initiation moiety was at the chain-end of the polyolefins, a block type copolymer is produced. It has been reported that thiol-terminated PP was used as polymeric chain transfer agent in styrene and styrene/acrylonitrile polymerization to form polypropylene-b/odc-polystyrene (PP-b-PS) and polypropylene-btock-poly(styrene-co-acrylonitrile) (PP-b-SAN) block copolymer [19]. On the other hand, polymer hybrids with block and graft structures can be produced if initiation moieties are in the polymer chain. 

Effect of Grafting Acrylonitrile to Cotton Yarn Under Various Conditions on the Mechanical Properties. (Taken from Blouin etal.) Ref. 29. 

The effect of ceric ion concentration on the graft copolymerization of acrylonitrile onto bamboo is shown in Figure 3 As can be seen the grafting percentage increases to a maximum and then decreases with further increase in the concentration of the initiator. The optimum concentration of the initiator was found at around 0.15 M. 

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