Direct copolymerization synthesis

Direct copolymerization techniques have also been employed in the s)m-thesis of sulfonated poly(aryl ether ketones),i i polyimides, i 5 and poly(benzoimidazoles). The synthesis of random disulfonated biphenol poly(arylene ether sulfone) copolymers (BPSH x where x represents the percentage of disulfonated diphenylsulfone moieties in the polymer versus unsulfonated diphenylsulfone moities) (14) is shown in Scheme 3.5. 

Figure 15. Synthesis of directly copolymerized wholly aromatic sulfonated poly(arylene ether sulfone), BPSH-ax, where XX is the ratio of sulfonated/unsulfonated activated halide.

Postsulfonation of polymers to form PEMs can lead to undesirable side reactions and may be hard to control on a repeatable basis. Synthesis of sulfonated macromolecules for use in PEMs by the direct reaction of sulfonated comonomers has gained attention as a rigorous method of controlling the chemical structure, acid content, and even molecular weight of these materials. While more challenging synthetically than postsulfonation, the control of the chemical nature of the polymer afforded by direct copolymerization of sulfonated monomers and the repeatability of the reactions allows researchers to gain a more systematic understanding of these materials properties. Sulfonated poly(arylene ether)s, sulfonated poly-(imide)s, and sulfonated poly(styrene) derivatives have been the most prevalent of the directly copolymerized materials. 

In a copolymerization system in which the product rxrz would exceed unity, the copolymer would contain sequences of like units in greater abundance than in a random copolymer of the same composition, and this tendency should be greater the larger the product rxrz (79). However to our knowledge no example of this case is known therefore the synthesis of copolymers with long uninterrupted stretches of a same monomer must be carried out by other methods than by direct copolymerization. In feet such copolymers have been synthesized their properties are more similar to those of a mechanical mixture of both homopolymers and differ markedly from those of a random copolymer. 

So far, theoretically, there have been two possible approaches for the synthesis of functional polyolefins, namely, (a) direct copolymerization of olefins with functional monomers using polymerization and catalyst technologies, and (b) post-polymerization reaction with polyolefins. 

In contrast to Group IV-based polymerization catalysts, late transition metal complexes can carry out a number of useful transformations above and beyond the polyinsertion reaction. These include isomerization reactions and the incorporation of polar monomers, which have allowed the synthesis of branched polymer chains from ethylene alone, and of functional polyolefins via direct copolymerization. The rational design of metallocene catalysts allowed, for the first time, a precise correlation between the structure of the single site catalyst and the mi-crostructure of the olefin homo- or copolymer chain. A similar relationship does not yet exist for late transition metal complexes. This goal, however, and the enormous opportunities that may result from new monomer combinations, provide the direction and the vision for future developments. 

J. Li, H. Yu, Synthesis and characterization of sulfonated poly(benzoxazole ether ketone)s by direct copolymerization as novel polymers for proton-exchange membranes, J. Polym. Sci. Part A Polym. Chem. 45 (11) (2007) 2273-2286. 

Interest in homogeneous olefin polymerization catalysts, especially group 4 metallocenes has caused a dramatic increase in the number of publications describing the synthesis of functionalized polyolefins by direct copolymerization. Many soluble metallocenes, such as bridged zirconocenes, have much better ability to incorporate higher a-olefins than do Ti-based Ziegler-Natta catalysts. This also makes them better suited for copolymerizations involving, often very bulky, functional comonomers. 

More recently, a variety of exciting new polymeric materials have been prepared in our group by the cationic copolymerization of soybean and other vegetable oils with a variety of alkene comonomers 18-35). These biopolymers possess industrially viable thermophysical and mechanical properties and thus may find structural applications. This chemistry takes advantage of the original C=C bonds of the soybean 18-27), tung 28,29), corn 30) and fish oils 31-35) to effect crosslinking. In this chapter, we shall focus primarily on the synthesis and characterization of soybean oil-based polymers, which result from the direct copolymerization of the C=C bonds of soybean oils with other comonomers via cationic polymerization 18-27). 

At present, many sulfonated derivatives of polymers such as poly(ether ether ketone), polysulfone, poly (ary lene ether snlfone), poly(styrene), and polyCphenylene sulfide) have been developed for fnel cells [10-14], More recently, the synthesis of sulfonated poly(arylene ether snlfone) and/or snlfonated poly(arylene ether ketone)s copolymers by direct copolymerization of biphenol, disnlfonated-activated aromatic halide monomers, and the precnrsor—activated aromatic halide monomer for fnel cell membrane applications— were carried ont [12,15],... 

L. H. William, Ph.D. Thesis, Synthesis and characterization of sulfonated poly(arylene ether sulfone) copolymers via direct copolymerization candidates for proton exchange membrane fuel cells. Hampton University, Virginia, USA, 2002. 

Fig. 16 Hydrodynamic radii versus the scattering angle measured directly after synthesis for two batches of copolymerizations with different molar ratios of PEG macromonomer to FBMA black, filled squares nM/npBMA = 0.01 red open squares nw/npEMA = 0.026). Blue half-filled squares are electrostatically stabilized poly(FBMA) particles synthesized for reference (cf. [69]). The particle size remains constant after centrifugation and freeze-thaw processing as shown for one batch red triangles and circles) which is indicative of stericaUy stabilized particles. Reproduced from [69] with permission...

Wiles, K.B., Wang, F., McGrath, J.E. (2005) Directly copolymerized poly(arylene sulfide sulfone) disulfonated copolymers for PEM-based fuel cell systems. 1. Synthesis and characterization. Journal of Polymer Science Part A Polymer Chemistry, 43, 2964-2976. 

In general, the preparation of ionomers is a straightforward procedure. The particular acid group of interest can be introduced onto the hydrocarbon backbone either by direct copolymerization or post-synthesis reaction. The following five important groups of ionomers illustrate the various methods of preparation. These ionomer families are ethylene-based materials, ionic elastomers, modified polystyrenes, perfluorinated resins and halato-telechelic polymers. 

Wang, R, Hickner, M., Ji, Q., Harrison, W., Mecham, J., Zawodzinski, T. A., and McGrath, J. E. 2001. Synthesis of highly sulfonated poly(arylene ether sulfone) random (statistical) copolymers via direct copolymerization. Macromol. Symp. 175 387-395. 

FIGURE 5.11 Synthesis of (a) sulfonated monomer and (b) sulfonated poly(arylene ether)s with pendant sulfoalkyl groups by direct copolymerization. 

FIGURE 5.12 Synthesis of SPEKs by direct copolymerization of (a) sodium 6,7-dihydroxy-2-naphthalenesulfonate and (b) sulfonated hydroquinone. 

The slower, more controlled hydrolysis of silicon-methoxy bonds enables the synthesis of a material diat is processable and extremely tough, yet flexible, with the degree of flexibility a direct result of the molar feed ratio of die two monomers since both are incorporated equally in the ADMET copolymerization. Therefore, a series of materials can be made where the properties are adjusted... 

The insertion of unsaturated molecules into metal-carbon bonds is a critically important step in many transition-metal catalyzed organic transformations. The difference in insertion propensity of carbon-carbon and carbon-nitrogen multiple bonds can be attributed to the coordination characteristics of the respective molecules. The difficulty in achieving a to it isomerization may be the reason for the paucity of imine insertions. The synthesis of amides by the insertion of imines into palladium(II)-acyl bonds is the first direct observation of the insertion of imines into bonds between transition metals and carbon (see Scheme 7). The alternating copolymerization of imines with carbon monoxide (in which the insertion of the imine into palladium-acyl bonds would be the key step in the chain growth sequence), if successful, should constitute a new procedure for the synthesis of polypeptides (see Scheme 7).348... 

However, the practical, direct synthesis of functionalized linear polyolefins via coordination copolymerization olefins with polar monomers (CH2 = CHX) remains a challenging and industrially important goal. In the mid-1990s Brookhart et al. [25, 27] reported that cationic (a-diimine)palladium complexes with weakly coordinating anions catalyze the copolymerization of ethylene with alkylacrylates to afford hyperbranched copolymers with the acrylate functions located almost exclusively at the chain ends, via a chain-walking mechanism that has been meticulously studied and elucidated by Brookhart and his collaborators at DuPont [25, 27], Indeed, this seminal work demonstrated for the first time that the insertion of acrylate monomers into certain late transition metal alkyl species is a surprisingly facile process. It spawned almost a decade of intense research by several groups to understand and advance this new science and to attempt to exploit it commercially [30-33, 61]. 

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