Cold emulsion polymerization

TYPICAL POLYMERIZATION RECIPES FOR HOT AND COLD EMULSION POLYMERIZED STYRENE-BUTADIENE RUBBERS... 

Method of synthesis emulsion polymerization in water medium initiated by peroxide or peroxydisulfate also solution polymerized grades are available typically produced by cold emulsion polymerization Dube, M A Li, L, Polym. Plast. Technol. Eng., 49,648-56, 2010 Godoy, J L Minari, R J Vega, J R Marchetti, J L, Chemomelrics Intelligent Lab. Systems, in press, 2011. 

Cold emulsion polymerization uses typical emulsion recipes containing various combinations of t-dodecyl mercaptan, diisopropylbenzene monohydroperoxide, potassium pyrophosphate, ferrous sulfate, the tetrasodium salt of ethylenedi-amine-tetraacetic acid (EDTA), and sodium formaldehyde sulfoxylate in an aqueous soap emulsion at a reaction temperature of only 5 °C. 

Uses Emulsifier for cold emulsion polymerization of SBR latex foaming agent for NR, SBR latex, NBR, CR rubbers Priolene 6905 [Croda Inc Croda Chem. Europe Ltd]... 

Uses Emulsifier for cold emulsion polymerization of SBR latex lubricant corrosion... 

Chem. Desaip. Oleic acid CAS 112-80-1 EINECS/ELINCS 204-007-1 Uses Emulsifier for cold emulsion polymerization of SBR latex Properties Acid no. 197-202 iodine no. 87-92 sapon. no. 199-204 cloud pt. 8 C max. 

Chem. Descrip. Disp. of alcohols, fatly soaps, and surfectanls Uses Defbamer preventing air entrainment during latex monomer stripping in SBR cold emulsion polymerization, PVAC, PVA, and acrylic latexes, aq. effluent systems... 

The original SBR process is carried out at. 50° C and is referred to as hot polymerization. It accounts for only about 5% of aU the mbber produced today. The dominant cold polymerization technology today employs more active initiators to effect polymerization at about 5°C. It accounts for about 85% of the products manufactured. Typical emulsion polymerization processes incorporate about 75% butadiene. The initiators are based on persulfate in conjunction with mercaptans (197), or organic hydroperoxide in conjunction with ferrous ion (198). The rest of SBR is produced by anionic solution polymerization. The density of unvulcanized SBR is 0.933 (199). The T ranges from —59" C to —64 C (199). 

Simplified nitrile mbber polymerization recipes are shown in Table 2 for "cold" and "hot" polymerization. Typically, cold polymerization is carried out at 5°C and hot at 30°C. The original technology for emulsion polymerization was similar to the 30°C recipe, and the redox initiator system that allowed polymerization at lower temperature was developed shortiy after World War II. The latter uses a reducing agent to activate the hydroperoxide initiator and soluble iron to reactivate the system by a reduction—oxidation mechanism as the iron cycles between its ferrous and ferric states. 

Among the polyesters that are used for PVC, the copolymers of butadiene with ethyl fumarates and ethyl acrylates deserve mention. They have been produced by Badische Anilin-und Sodafabrik (BASF) under the commercial name Palamoll. Palamoll I consists of 75% diethyl fumarate and 25% butadiene Palamoll II contains equal parts of butadiene and ethyl acrylate. In combination with the same amount of liquid plasticizers (such as DOP), films with cold resistance down to — 60°C. can be produced. These products are especially important for cable insulation because of their good dielectric properties. The Palamoll products are produced by emulsion polymerization and can be directly combined with emulsions of PVC. 

Redox systems are used for polymerizations at lower temperatures. Many of these redox initiator couples were developed for the emulsion copolymerization of butadiene and styrene, since the 5-10"C cold recipe yields a better rubber than the hot SO C emulsion polymerization. 

The target polymerization temperature will usually be chosen to optimize production rates or product quality. Cold SBR, which is made near S C, is an interesting case in this regard. The cold product is superior as a rubber to hot (60°C emulsion polymerization) SBR, because it contains less low-molecular-weight polymer which cannot be reinforced with carbon black. There is also less branching and more tra/) -l,4 units in the cold SBR. Hot SBR is easier to mill and extrude because of its low-molecular-weight fraction and is used mostly for adhesive applications while cold SBR, which is made mainly for tires, accounts for about 90% of all production of this polymer. 

In addition to the polymer viscosity, polymerization temperature also plays an important role in shaping the processability. Emulsion-polymerized SBR grades produced at low polymerization temperatures have less chain branching than those produced at higher temperatures. At an equivalent viscosity, cold polymerized E-SBR is normally easier to process than hot polymerized E-SBR, and this applies particularly... 

In large-scale industrial applications, emulsion polymerization is carried out in kettles that have adequate means of agitation and are equipped with reflux condensers. If one of the monomers is a gas or a low-boiling liquid, the polymerization is performed in a closed system capable of sustaining the pressure developed as a consequence of the increased temperature. An interesting method to control the temperature is to start with only a part of the batch in the kettle after the reaction has started and the liberated heat of the reaction has caused an increase of the temperature of the kettle content, additional cold monomer emulsion or water is gradually added to keep the temperature at the desired level. 

By the way, it is interesting to note that the type of poly(vinyl alcohol) most conveniently dissolvable in cold water contains 10-30% residual poly(vinyl acetate). The compatibility of the poly(vinyl acetate) blocks with latex particles may explain the suitability of these grades of poly(vinyl alcohol) in vinyl acetate emulsion polymerizations [145]. 

Styrene-butadiene rubber is the largest volume synthetic elastomer commercially available. It ean be produced by free-radical emulsion polymerization of styrene and butadiene either at 50 to 60°C (hot emulsion SBR) or at about 5°C (cold emulsion SBR). The two kinds of SBR have sigmfieantly different properties. The hot emulsion SBR process, which was developed st, leads to a more branehed polymer than the cold emulsion process. Cold SBR has a better abrasion resistance and, eonsequently, provides better tread wear and dynamic properties. 

Since poly(vinyl acetate) is usually used in an emulsion form, it is manufactured primarily by free-radical-initiated emulsion polymerization. The polymer is too soft and shows excessive cold flow, which precludes its use in molded plastics. The reason is that the glass transition temperature of 28°C is either slightly above or (at various times) below the ambient temperatures. 

Standard SBR materials are made from an emulsion polymerization process and are available in more than 100 grades, but only a few are used as a base for adhesives. The two basic processes for producing these many grades can be either a hot or cold process, depending on the polymerization temperature, with hot polymerization being the preferred process. Hot polymerized SBR typically yields a lower molecular weight polymer, but with a wider molecular weight distribution which provides for a more balanced polymer. The styrene content can also be varied to enhance certain properties. Emulsion process polymers are often called random SBR because there is no control of the attachment sites for the styrene monomer when polymerized. These polymers are often blended with other polymers to lower cost and increase compatibility with various resins, plasticizers, and fillers. 

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