Chain transfer agent grafted polymer

If a linear mbber is used as a feedstock for the mass process (85), the mbber becomes insoluble in the mixture of monomers and SAN polymer which is formed in the reactors, and discrete mbber particles are formed. This is referred to as phase inversion since the continuous phase shifts from mbber to SAN. Grafting of some of the SAN onto the mbber particles occurs as in the emulsion process. Typically, the mass-produced mbber particles are larger (0.5 to 5 llm) than those of emulsion-based ABS (0.1 to 1 llm) and contain much larger internal occlusions of SAN polymer. The reaction recipe can include polymerization initiators, chain-transfer agents, and other additives. Diluents are sometimes used to reduce the viscosity of the monomer and polymer mixture to faciUtate processing at high conversion. The product from the reactor system is devolatilized to remove the unreacted monomers and is then pelletized. Equipment used for devolatilization includes single- and twin-screw extmders, and flash and thin film evaporators. Unreacted monomers are recovered for recycle to the reactors to improve the process yield. 

Mention may finally be made of graft polymers derived from natural rubber which have been the subject of intensive investigation but which have not achieved commercial significance. It has been found that natural rubber is an efficient chain transfer agent for free-radical polymerisation and that grafting appears to occur by the mechanism shown in Figure 30.8. 

Fig. 5.8 Examples of polymers grafted from nanocarbons, (a) An ATRP initiator covalently attached to RGO via nitrene and carbodiimide chemistry was used for the growth of poly(2-(ethyl (phenyl)amino)ethyl-methacrylate). (b) A RAFT chain transfer agent is covalently attached to GO prior to polymerization of vinylcarbozole.

Finally, the ASA graft copolymer is prepared. To the alkyl acrylate rubber polymer obtained as described just above, styrene and acrylonitrile are added in the desired quantities. Dodecylmercaptan and potassium persulfate are added as chain transfer agent and radical initiator, respectively. An ASA copolymer with a mean diameter of 550 nm is obtained. 

Graft ABS polymers were prepared by the reaction of an approximate azeotropic mole ratio of styrene-acrylonitrile monomer mixture in the presence of different weights of diene substrate latex. Initiator, chain transfer agent, and soap levels were constant. Grafting reactions were... 

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. 

Returning to Vollmert s patent (18), we apply the more complete spectrum of operations to his example 1. In this case butyl acrylate and acrylic acid are dissolved in acetone with azoisobutyronitrile (initiator) and dodecyl mercaptan (chain transfer agent), polymerized, and the acetone is evaporated to form polymer 1. Separately, styrene and 1,4-butanediol monoacrylate are bead polymerized with benzoyl peroxide to form polymer 2. Polymers 1 and 2 are mechanically blended with the simultaneous addition of 1,4-butanediol followed by heating to promote grafting and crosslinking. These steps can be represented in some detail by ... 

Graft Polymer Studies on Model System. Methyl methacrylate/ styrene ratio, chain transfer agent level, and type of initiator system were evaluated in graft polymer using Firestone 2004 polybutadiene latex as a model. 

Table II. Effect of Level of Chain Transfer Agent on Impact of Graft Polymer...

A wide variety of polymer microspheres can be made by dispersion polymerization. A key component in all of these systems is the stabilizer (dispersant) both during particle formation and for the stability of the resulting colloidal particles. Functionality can be introduced into colloidal particles in various ways by copolymerization of functional monomers (like HEMA), or incorporation of functional dispersants, initiators, chain transfer agents, or macromonomers. Many different types of macromonomer are prepared and used to prepare functional microspheres. Amphiphilic macromonomers provide a particularly versatile component in these systems, being the source of both stabilizer and functional residue. They act as stabilizer because they are covalently grafted onto the particles surface by copolymerization with main monomers, and form tightly bound hairy shells on the particles surface. 

Considerable work has been done on the initiation of the vinyl fluoride by ionizing radiation much as y-radiation from a °Co source. A selection of references on this research includes Usmanov and other authors [4,48-62], Of these, Usmanov et al. [4] deal with the graft copolymerization of vinyl fluoride to some natural and synthetic polymers. Usmanov et al. [53] discuss the formation of branched polymers during radiation-induced polymerization. Gubareva et al. [54] deal with solution polymerizations. Nakamura et al. [58, 59, 61] deal with emulsion polymerizations of vinyl fluoride by radiation initiations. Usmanov et al. [60,61] discuss the effects of chain-transfer agents during radiation-initiated polymerization. Some copolymerization studies are described in Usmanov et al. [55]. 

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