Styrene, alternating copolymerization

Other miscellaneous compounds that have been used as inhibitors are sulfur and certain sulfur compounds (qv), picryUiydrazyl derivatives, carbon black, and a number of soluble transition-metal salts (151). Both inhibition and acceleration have been reported for styrene polymerized in the presence of oxygen. The complexity of this system has been clearly demonstrated (152). The key reaction is the alternating copolymerization of styrene with oxygen to produce a polyperoxide, which at above 100°C decomposes to initiating alkoxy radicals. Therefore, depending on the temperature, oxygen can inhibit or accelerate the rate of polymerization. 

Using the r and tz values from Table 6-2, construct plots showing the initial copolymer composition as a function of the comonomer feed composition for the radical copolymerizations of methyl acrylate-methyl methacrylate and styrene-maleic anhydride. Are these examples of ideal or alternating copolymerization ... 

Radical Copolymerization of Styrene with Maieic Anhydride (Alternating Copolymerization)... 

Scheme 12. Alternating copolymerization of styrene and CO in [C6py][NTf2].

In contrast to the radical-monomer interaction in the transition state proposed by Mayo and Walling (62, 63), the formation of a molecular complex between the electron donor monomer and the electron acceptor monomer—i.e., monomer-monomer interaction—has been proposed as the contributing factor in the free radical alternating copolymerization of styrene and maleic anhydride (8) as well as sulfur dioxide and mono-or diolefins (6, 9, 12, 13, 25, 41, 42, 43, 44, 61, 79, 80, 88). Walling and co-workers (83, 84) did note a relationship between the tendency to form molecular complexes and the alternating tendency and considered the possibility that alternation involved the attack of a radical on a molecular complex. However, it was the presence in the transition state of polar resonance forms resembling those in the colored molecular complexes which led to alternation in copolymerization (84). 

There exist many alternating copolymerizations ethylene or propene with alkyl acrylates [244], vinyl acetate with maleic anhydride [245], styrene with acrylonitrile [246], styrene with fumaronitrile [247], vinyl carbazol with fumaronitrile, vinyl ferrocenne with diethylfumarate [248], and further pairs or systems of three monomers [238, 249-253]. External conditions can support or hinder alternation. At not too high temperatures, vinyl acetate forms a donor—acceptor complex with maleic anhydride. Under these conditions (and in the presence of a radical initiator), an alternating copolymer is formed. The concentration of the complex decreases with increasing temperature above 363 K the complex cannot exist. Under these conditions, copolymerization yields a statistical copolymer whose composition depends on the composition of the monomer mixture [245]. 

The t-BOC protected copolymers were prepared both by copolymerization of the t-BOC protected hydroxyphenylmaleimide monomer with styrene and by modification of preformed phenolic copolymers of various molecular weights as shown in Scheme I. In both cases the copolymer compositions were foxmd to be 1 1 based on NMR results and elemental analyses. The NMR and IR spectra obtained from copolymers from both routes were identical. The 13C and IH NMR spectra of the modified polymer are shown in Figures 1 and 2. These data substantiate the completeness of the protection reaction of the preformed phenolic copolymer. The copolymers are presumed to be predominately alternating since these comonomers represent an example of the classic general alternating copolymerization case of an electron rich comonomer (styrene) and an electron poor comonomer (N-substituted maleimide) (13). 

In general, an alternating eopolymer is formed over a wide range of monomer compositions. It has been reported that little chain transfer occurs, and in some cases, conventional free radical retarders are ineffective. Reaction occurs with some combinations, like styrene-acrylonitrile, when the monomers are mixed with a Lewis acid, but addition of a free-radical source will increase the rate of polymerization without changing the alternating nature of the copolymer. Alternating copolymerizations can also be initialed photochemically and electrochemically. The copolymerization is often accompanied by a cationic polymerization of the donor monomer. 

Via metal catalysis, cyclic monomers such as TV-substituted maleimides M-40, M-41, and M-42 do not homopolymerize but can copolymerize with vinyl monomers, among which alternating copolymers can be obtained with styrene via a radical mechanism. The 1-13 (X = Br)/CuBr/L-l system induced alternating copolymerizations with styrene to give controlled molecular weights and narrow MWDs (Mw/Mn =1.1 — 1.4) in the bulk or anisole at 80—110 °C.219-222... 

Polyketones formed by the palladium-catalyzed alternating copolymerization of styrene and CO have become the subject of a great deal of attention [43]. Almost concurrently, two papers appeared describing this reaction in ionic liquids [44,45]. Seddon et al. used [Pd(bipy)2][PFs] in a variety ofionic liquids (Scheme 7-1) [44]. The complex was active in methanol [ca. 17.4 kg (g Pd) ], but the product polyketone was contaminated with palladium. In the ionic liquids the activity of the catalyst was dependent on the nature of the anion, decreasing in the order [N(S02CFj)2]"... 

The tendency for alternation increases as the difference in polarity between two monomers increases. Styrene is an electron donor monomer, while maleic anhydride is an electron acceptor. Consequently, alternating copolymerization between both monomers is facilitated. Notice that r,r2 for the monomers is 0.0006. 

Alternating copolymerization of styrene with maleic anhydride is also explained by donor... 

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