Graft emulsion polymerisation

Transparency is often required. This is achieved by arranging that the particle size of the modifier to be below that of the wavelength of visible light (0.4-0.8 pm). This can normally be achieved by emulsion polymerisation, e.g., polybutadiene, polystyrene. Adhesion and surface compatibility between the polymer and modifier can be achieved by surface grafting of polar groups, e.g., acrylonitrile, various acrylates, onto the impact modifier surface before blending. 

The size distribution of the PVCL microgel particles synthesised by a batch emulsion polymerisation was monomodal and reasonably narrow [177], regardless of the choice of the emulgator, SDS (El, E2) or macromonomer (E3, E4). The size distributions remain monomodal upon subsequent grafting. A typical size distribution of a PVCL microgel (El) at 20 °C is presented in Fig. 17, as well as the effect of grafting, as a second step, on the hydrodynamic size (El-g). 

Graft copolymers are obtained by subsequent radical emulsion polymerisation of olefinic unsaturated monomers in the presence of functionalized siloxane particles. Scheme 3 illustrates that the graft... 

Most reports on emulsion polymerisation have been limited to commercially available surfactants which, in many cases, are relatively simple molecules such as sodium dodecyl sulphate and simple nonionic surfactants. However, studies on the effects of surfactant structure on latex formation have revealed the importance of the structure of the molecule. Block and graft copolymers (polymeric surfactants) are expected to be better stabilisers when compared to simple surfactants. The use of these polymeric surfactants in emulsion polymerisation and the stabilisation of the resulting polymer particles is discussed below. 

A novel graft copolymer of hydrophobically modified inuhn (INUTEC SPl) has been used in the emulsion polymerisation of styrene, MMA, butyl acrylate, and several other monomers [8]. All lattices were prepared by emulsion polymerisation, using potassium persulphate as initiator, and the z-average particle size was determined using PCS electron micrographs were also recorded. 

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. 

The possibility of producing latex particles whose molecular architecture seems to be thermodynamically unfavourable by combining free-radical and emulsion polymerisation mechanistic knowledge is discnssed. Examples of unusual new materials created using this approach are illustrated. They include extensively grafted copolymers based on isoprene and dimethylaminoethyl methacrylate, spatially-homogeneous copolymers and composite aniline-styrene polymer colloids. 29 refs. AUSTRALIA... 

A superabsorbent nanocomposite based on partially neutralised acrylic acid, recycled PS foam and Na-MMT was prepared via emulsion polymerisation [65]. The results indicated that the acrylic acid monomer had successfully grafted onto the PS chains and the layers of Na-MMT were exfoliated after copolymerisation. Moreover, the addition of Na-MMT not only improved the thermal stability of the samples, but also increased the content and rate of water absorbency. 

The second major process used for making rubber-modified plastics depends on the separate preparation of the elastomer phase and the glassy polymer phase. Much of the ABS plastics are made via this process. The key step is emulsion polymerization of butadiene monomer to produce rubber particles of the desired size, before grafting. There is an extensive literature devoted to emulsion polymerisation science and technology as before, only the features unique to rubber-modified plastics are discussed. 

To produce the Type 2 polymers, styrene and acrylonitrile are added to polybutadiene latex and the mixture warmed to about 50°C to allow absorption of the monomers. A water-soluble initiator such as potassium persulphate is then added to polymerise the styrene and acrylonitrile. The resultant materials will be a mixture of polybutadiene, polybutadiene grafted with acrylonitrile and styrene, and styrene-acrylonitrile copolymer. The presence of graft polymer is essential since straightforwsird mixtures of polybutadiene and styrene-acrylonitrile copolymers are weak. In addition to emulsion processes such as those described above, mass and mass/suspension processes are also of importance. 

The idea of the preparation of porous polymers from high internal phase emulsions had been reported prior to the publication of the PolyHIPE patent [128]. About twenty years previously, Bartl and von Bonin [148,149] described the polymerisation of water-insoluble vinyl monomers, such as styrene and methyl methacrylate, in w/o HIPEs, stabilised by styrene-ethyleneoxide graft copolymers. In this way, HIPEs of approximately 85% internal phase volume could be prepared. On polymerisation, solid, closed-cell monolithic polymers were obtained. Similarly, Riess and coworkers [150] had described the preparation of closed-cell porous polystyrene from HIPEs of water in styrene, stabilised by poly(styrene-ethyleneoxide) block copolymer surfactants, with internal phase volumes of up to 80%. 

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