Grafting structure, styrene

Gauthier and M oiler [4] described in 1991 the use of anionic polymerization and grafting techniques to prepare poly(styrenes) with a dendritic structure. Styrene is well suited to be incorporated into a synthetic scheme aimed at producing... 

TABLE IV. Effect of Acid Structure in Methanol to Polyethylene.a Grafting of Styrene in ... 

The parameters which predominantly influence the acid effect in radiation grafting of styrene monomer to polyethylene film are the structure of solvent, the concentration of monomer and the dose rate. Because these three variables are inter-related, it is difficult to predict, a priori, the conditions required to yield an optimum in grafting. In this respect the type of solvent used is particularly important. 

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. 

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). 

PP/SBR PP grafted with Styrene useful as stand-alone structural materials. DeNicola and Conboy, 1994... 

PP with either SBR, SBS, or an acrylic elastomer, and PP grafted with styrene Stand-alone structural materials DeNicola and Conboy 1994... 

Acrylonitrile is also commonly found in impact modifiers, such as the acrylonitrile-butadiene-styrene (ABS) type, produced by emulsion polymerisation. Polybutadiene seed latex particles are grafted onto styrene and acrylonitrile in a seeded emulsion polymerisation process. As the styrene-acrylonitrile copolymer shell forms, polybutadiene domains are spontaneously separated within. The resulting impact modifier particles are subsequently compounded with polystyrene to product high impact polystyrene (HIPS). The impact modification properties of the latex particles may be optimised through varying the butadiene content, the particle size and structure, and the shell molecular weight. A basic formulation for an ABS impact modifier is given in Table 6. 

Hydrogen abstraction by alkoxy radicals at any of the allylic sites jdelds a site for styrene polymerization, resulting in a graft (282,283). Model studies based on styrene-butadiene block copolymers show a strong influence of graft structure on particle morphology (81,82). The double bonds in polybutadiene are much less... 

Whilst organic polymer seeds are quite readily encapsulated by a PDMS shell (due to surface tension issues), PDMS cores need to be crosslinked and the organic polymer layer made hydrophilic by charged monomers such as (meth)acrylic acid, in order safely to achieve the expected core-shell structure. The grafting of styrene/ acrylonitrile (St/AN) onto a poly(butadiene) shell led to a striking change in the structure of the particles, from core-shell to a flocculated, moon-like configuration. 

The structure of PP-g-polystyrene was studied by wide and narrow angle x-ray diffractometry. The polystyrene component formed discrete amorphous structures, which were identified after chloromethylation [143]. Structure of Rayon-Styrene graft copolymer was characterized by IR, wide angle x-ray, and SEM, grafting occurred mainly in the amorphous regions of rayon [1441. 

Problem 31.7 1 Irradiation of poly(-l,3-butadiene), followed by addition of styrene, yields a graft copolymer that is used to make rubber soles for shoes. Draw the structure of a representative segment of this styrene-butadiene graft copolymer. 

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