Styrene polymerization catalysts

The most commonly applied variation of the a-ligands in mono-Cp H styrene polymerization catalysts is the introduction of alkoxy/aryloxy groups, which generally leads to catalysts with increased activity and syndioselectivity. Campbell et al. determined the order of deceasing... 

MAO and boron compounds are expensive chemicals that increase the cost of the SPS production. However, the cocatalyst is an indispensable compound for the titanium complexes used as styrene polymerization catalysts. The roles of the cocatalyst are supposed to reduce the valence of the titanium compounds by forming the precursor of the active site, to activate the precursor, and subsequently to stabilize the active site by weak coordination. TIBA reacts with the transition metal and reduces Tl(IV) to 11(111), and this may be the precursor of the active site. Yabunouchi found that the catalytic activity in the styrene polymerization increased by the addition of a small amount of ((R )3CO)n-Al-(R )3 n to the styrene monomer, even if the amount of MAO is decreased [17]. One of these compounds is [(C6Hs)3CO](i-C4H9)2Al (Fig. 3.8). The catalytic activitiy was increased more than two times by the addition of a small amount of [(C6H5)3CO](i-C4H9)2Al to a mixture consisting of Tl MAO TIBA = 1 50 25 in molar ratio. 

Only very few rare-earth-based nonmetaUocene compounds were used as styrene polymerization catalysts (Fig. 7.7). 

With the recent advent of truly homogeneous isospecific styrene polymerization catalysts [14,33], new perspectives for the stereoselective polymerization of styrene, such as stereoblock polystyrene, appear to be within reach. 

Thermoplastic resins produced from pure monomers such as styrene, alkyl-substituted styrenes, and isobutylene are produced commercially. An advantage of these resins is the fact that they are typically lighter in color than Gardner 1 (water-white) without being hydrogenated. Among the earliest resins in this category were those made from styrene and sold as Piccolastic. Styrene and alkyl-substituted styrenes such as a-methylstyrene are very reactive toward Friedel-Crafts polymerization catalysts. 

Another appHcation for this type catalyst is ia the purification of styrene. Trace amounts (200—300 ppmw) of phenylacetylene can inhibit styrene polymerization and caimot easily be removed from styrene produced by dehydrogenation of ethylbenzene using the high activity catalysts introduced in the 1980s. Treatment of styrene with hydrogen over an inhibited supported palladium catalyst in a small post reactor lowers phenylacetylene concentrations to a tolerable level of <50 ppmw without significant loss of styrene. 

Beaded acrylamide resins (28) are generally produced by w/o inverse-suspension polymerization. This involves the dispersion of an aqueous solution of the monomer and an initiator (e.g., ammonium peroxodisulfates) with a droplet stabilizer such as carboxymethylcellulose or cellulose acetate butyrate in an immiscible liquid (the oil phase), such as 1,2-dichloroethane, toluene, or a liquid paraffin. A polymerization catalyst, usually tetramethylethylenediamine, may also be added to the monomer mixture. The polymerization of beaded acrylamide resin is carried out at relatively low temperatures (20-50°C), and the polymerization is complete within a relatively short period (1-5 hr). The polymerization of most acrylamides proceeds at a substantially faster rate than that of styrene in o/w suspension polymerization. The problem with droplet coagulation during the synthesis of beaded polyacrylamide by w/o suspension polymerization is usually less critical than that with a styrene-based resin. 

Addition of styrene to a green solution of naphthalene" Na+ in tetrahydrofuran leads to an instantaneous change of color from green to red. Styrene polymerizes rapidly and quantitatively within a few seconds, and when the reaction is completed, addition of water converts the red solution of polystyryl carbanions into colorless solution of polystyrene. After precipitation of the polymer it was shown spectroscopically25 that the residual solution contains an amount of naphthalene equal to that used in the preparation of the initiating catalyst. This observation confirms the proposed mechanism of initiation of the polymerization. 

Paraplex Propallants. A series of JATO proplnts (the PF-series) developed by the Aerojet Engrg Corp, Azusa, Calif using Paraplex P-10 resin-styrene mixt as a fuel ingredient in the amt of approx 26.5%. Other ingredients are AN or K perchlorate, 73.0%, and small amts of t-butyl-hydroperoxide or benzoylperoxide, 0.1 to 0.5% (as a polymerization catalyst) (Ref 2)... 

Paraplex Resin-Bonded Explosive. Usually consists of Paraplex P-43/RDX/Al/Styrene monomer/ Lupersol DDM (as a polymerization catalyst) in the following percentages, viz 6.0/65.0/ 20.0/9.0/0.5. Density 1.65g/cc. The material is mixed and polymerized using the usual procedure for polyester resins and Plastic Bonded Expls (see in this Vol)... 

In the sol-gel procedure for the preparation of hybrids, polymeric acid catalysts such as poly (styrene sulfonic acid) were also used instead of hydrogen chloride [14]. The polymeric acid catalyst was effective for the preparation of hybrids at a similar level to that of hydrogen chloride catalyst. In some cases, the increased modulus was observed due to the higher extent of reaction. No difference was observed in morphologies between the hybrids prepared with polymeric and small molecule acid catalysts. The method using polymeric acid catalyst may depress the ion-conductive property, characteristic to the mobile acidic small molecules. Polymeric catalyst may also influence the rheology of the resulting hybrids. 

Peaking and Non-isothermal Polymerizations. Biesenberger a (3) have studied the theory of "thermal ignition" applied to chain addition polymerization and worked out computational and experimental cases for batch styrene polymerization with various catalysts. They define thermal ignition as the condition where the reaction temperature increases rapidly with time and the rate of increase in temperature also increases with time (concave upward curve). Their theory, computations, and experiments were for well stirred batch reactors with constant heat transfer coefficients. Their work is of interest for understanding the boundaries of stability for abnormal situations like catalyst mischarge or control malfunctions. In practice, however, the criterion for stability in low conversion... 

Thus, this polymerization catalyst yields more random copolymers with styrene, while still maintaining a low vinyl content and high trans-1,4 content. 

The Dow corporation has recently developed constrained geometry addition polymerization catalysts (CGCT), typically Me2Si(C5Me4)(NBut)MCl2 (M = Ti, Zr, Hf) (141) activated with MAO. The homo-polymerization of a-olefins by CGCT afford atactic or somewhat syndiotactic (polypropylene rr 69%) polymers. The metal center of the catalyst opens the coordination sphere and enables the co-polymerization of ethylene to take place, not only with common monomers such as propylene, butene, hexene, and octene, but also with sterically hindered a-olefins such as styrene and 4-vinylcyclohexene [202]. 

Buna [Butadien natrium] The name has been used for the product, the process, and the company VEB Chemische Werke Buna. A process for making a range of synthetic rubbers from butadiene, developed by IG Farbenindustrie in Leverkusen, Germany, in the late 1920s. Sodium was used initially as the polymerization catalyst, hence the name. Buna S was a copolymer of butadiene with styrene Buna N a copolymer with acrylonitrile. The product was first introduced to the pubhc at the Berlin Motor Show in 1936. Today, the trade name Buna CB is used for a polybutadiene rubber made by Bunawerke Hiils using a Ziegler-Natta type process. German Patent 570, 980. 

The use of palladium(II) sulfoxide complexes as catalyst precursors for polymerization has met with mixed results thus a report of a palla-dium(II) chloride-dimethyl sulfoxide system as a catalyst precursor for phenylacetylene polymerization suggests similar results to those obtained using tin chloride as catalyst precursor (421). However, addition of dimethyl sulfoxide to solutions of [NH fPdCh] decreases the activity as a catalyst precursor for the polymerization of butadiene (100). Dimethyl sulfoxide complexes of iron have also been mentioned as catalyst precursors for styrene polymerization (141). 

As an extension of the previous work, copolymers based on partially sulfonated ethylene—styrene pseudorandom interpolymers have also been employed instead of the block copolymers (Figure Due to the unique nature of the polymerization catalyst, styrene residues are separated by at least one ethylene residue and the acid groups are distributed randomly along the chain. This material provides an economical and unique counterpoint to the sulfonated SEES PEMs, where the sulfonic acid groups are bunched together in the styrene blocks. Controlling the styrene content in each material provides a route to control the level of sulfonation and resultant ion exchange capacity of the PEM. 

As an example, styrene polymerizes at ordinary temperatures and the rate of polymerization increases as temperature increases. The reaction is exothermic and becomes violent as it is accelerated by its own heat. Inhibitors are added to prevent the initiation of dangerous polymerization. When the styrene is used to fabricate materials, e.g., fiberglass resin, a catalyst may be added in the manufacturing process to initiate polymerization at a controlled rate. Any unbalance of these reactions in terms of quantities or temperatures could cause hazardous fire conditions. 

Styrene Polymerization Palygorskite, kaoUnite, and montmorillonite Weakest catalyst is montmorillonite... 

Indenylidene compounds VIII, K, XXI, XXIII, XXVIIIa and XXVIIIb act as atom transfer radical polymerization catalysts for the polymerization of methyl methacrylate and styrene in high yields and with good control (Table 8.7). The catalytic activity can be dramatically improved by transforming the complexes into cationic species by treatment with AgBp4 [61]. 

Scheme 8.4 Various zinc(ii)salphens have been coordinated to mPy-BIAN (PdMe), forming active catalysts for CO/styrene polymerization reactions.

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