Commercially significant polymeric

The neat resin preparation for PPS is quite compHcated, despite the fact that the overall polymerization reaction appears to be simple. Several commercial PPS polymerization processes that feature some steps in common have been described (1,2). At least three different mechanisms have been pubUshed in an attempt to describe the basic reaction of a sodium sulfide equivalent and -dichlorobenzene these are S Ar (13,16,19), radical cation (20,21), and Buimett s (22) Sj l radical anion (23—25) mechanisms. The benzyne mechanism was ruled out (16) based on the observation that the para-substitution pattern of the monomer, -dichlorobenzene, is retained in the repeating unit of the polymer. Demonstration that the step-growth polymerization of sodium sulfide and /)-dichlorohenzene proceeds via the S Ar mechanism is fairly recent (1991) (26). Eurther complexity in the polymerization is the incorporation of comonomers that alter the polymer stmcture, thereby modifying the properties of the polymer. Additionally, post-polymerization treatments can be utilized, which modify the properties of the polymer. Preparation of the neat resin is an area of significant latitude and extreme importance for the end user. 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Some polymers from styrene derivatives seem to meet specific market demands and to have the potential to become commercially significant materials. For example, monomeric chlorostyrene is useful in glass-reinforced polyester recipes because it polymerizes several times as fast as styrene (61). Poly(sodium styrenesulfonate) [9003-59-2] a versatile water-soluble polymer, is used in water-poUution control and as a general flocculant (see Water, INDUSTRIAL WATER TREATMENT FLOCCULATING AGENTs) (63,64). Poly(vinylhenzyl ammonium chloride) [70304-37-9] h.a.s been useful as an electroconductive resin (see Electrically conductive polya rs) (65). 

Miscellaneous Copolymers. VP has been employed as a termonomer with various acryUc monomer—monomer combinations, especially to afford resins usehil as hair fixatives. Because of major differences in reactivity, VP can be copolymerized with alpha-olefins, but the products are actually PVP grafted with olefin or olefin oligomers (151,152). Likewise styrene can be polymerized in the presence of PVP and the resulting dispersion is unusually stable, suggesting that this added resistance to separation is caused by some grafting of styrene onto PVP (153). The Hterature contains innumerable references to other copolymers but at present (ca 1997), those reviewed in this article are the only ones known to have commercial significance. 

Poly(butadiene- (9-acrylonitrile) [9008-18-3] NBR (64), is another commercially significant random copolymer. This mbber is manufactured by free-radical emulsion polymerization. Important producers include Copolymer Rubber and Chemical (Nysyn), B. F. Goodrich (Hycar), Goodyear (Chemigum), and Uninoyal (Paracdl). The total U.S. production of nitrile mbber (NBR) in 1990 was 95.6 t (65). The most important property of NBR mbber is its oil resistance. It is used in oil well parts, fuels, oil, and solvents (64) (see Elastomers, synthetic— nitrile rubber). 

Distribution of the monomer units in the polymer is dictated by the reactivity ratios of the two monomers. In emulsion polymerization, which is the only commercially significant process, reactivity ratios have been reported (4). IfMj = butadiene andM2 = acrylonitrile, then = 0.28, and r2 =0.02 at 5°C. At 50°C, Tj = 0.42 and = 0.04. As would be expected for a combination where = near zero, this monomer pair has a strong tendency toward alternation. The degree of alternation of the two monomers increases as the composition of the polymer approaches the 50/50 molar ratio that alternation dictates (5,6). Another complicating factor in defining chemical stmcture is the fact that butadiene can enter the polymer chains in the cis (1), trans (2), or vinyl(l,2) (3) configuration ... 

The (9-cresol novolaks of commercial significance possess degrees of polymerization, n, of 1.7—4.4 and the epoxide functionaUty of the resultant glycidylated resins varies from 2.7 to 5.4. Softening points (Durran s) of the products are 35—99°C. The glycidylated phenol and o-cresol—novolak resins are soluble in ketones, 2-ethoxyethyl acetate, and toluene solvents. The commercial epoxy novolak products possess a residual hydrolyzable chlorine content of <0.15 wt% and a total chlorine content of ca 0.6 wt % (Table 2). 

The principal reactions with commercial significance include polymerization, oxidation, and addition including halogenation, alkylation, oligomerization, hydration, and hydroformylation. 

The new knowledge and understanding of radical processes has resulted in new polymer structures and in new routes to established materials many with commercial significance. For example, radical polymerization is now used in the production of block copolymers, narrow polydispersity homopolymers, and other materials of controlled architecture that were previously available only by more demanding routes. These commercial developments have added to the resurgence of studies on radical polymerization. 

Surface fluorination changes the polymer surface drastically, the most commercially significant use of polymer surface direct fluorination is the creation of barriers against hydrocarbon permeation. The effectiveness of such barriers is enormous, with reductions in permeation rates of two orders of magnitude. Applications that exploit the enhanced barrier properties of surface-fluorinated polymers include (1) Polymer containers, e.g., gas tanks in cars and trucks, which are produced mostly from high-density polyethylene, where surface fluorination is used to decrease the permeation of fuel to the atmosphere and perfume bottles. (2) Polymeric membranes, to improve selectivity commercial production of surface-fluorinated membranes has already started.13... 

The more significant commercial catalytic polymerization processes have proved to be phosphoric acid processes and sulfuric acid processes. 

At the present time, no significant commercialization of polymeric electro-optic modulators exists. However, that situation appears be changing rapidly. Pacific Wave Industries now offer a variety of broad bandwidth modulators for purchase and firms such as Radiant Research, IPITEK and Lumera Corporations are dramatically expanding their activities. Figure 35 shows the PWI40 GHz modulator fabricated from CLD-l/APC polymer material. 

Inisurfs, Transurfs and Surfmers may be used to reduce/avoid the use of conventional surfactants in emulsion polymerization. However, when Inisurfs and Transurfs are used, the stability of the system cannot be adjusted without affecting either the polymerization rate (Inisurfs) or the molecular weight distribution (Transurfs). Furthermore, the efficiency rate of Inisurfs is low due to the cage effect. It is therefore not obvious yet that these classes will become commercially significant. 

Currently this technology is of minor commercial significance, but stereoregular forms of numerous polyacrylates have been prepared and characterized These include poly(/-butyl acrylate) (138—141), poly(isopropyl acrylate) (142), and poly(isobutyl acrylate) (143,144). Carefully controlled reaction conditions are usually required to obtain polymers with some measurable degree of crystallinity. In nonpolar solvents the anionic polymerization of acrylates generally yields isotactic polymer, whereas in polar solvents syndiotactie polymerization is favored. The physical and chemical properties of the various forms are often quite different. A general review covers these and other aspects of the anionic polymerization of acrylates (145). 

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