Synthesis, elastomer copolymerization

Copolymerization allows the synthesis of an almost unlimited number of different products by variations in the nature and relative amounts of the two monomer units in the copolymer product. A prime example of the versatility of the copolymerization process is the case of polystyrene. More than 11 billion pounds per year of polystyrene products are produced annually in the United States. Only about one-third of the total is styrene homopolymer. Polystyrene is a brittle plastic with low impact strength and low solvent resistance (Sec. 3-14b). Copolymerization as well as blending greatly increase the usefulness of polystyrene. Styrene copolymers and blends of copolymers are useful not only as plastics but also as elastomers. Thus copolymerization of styrene with acrylonitrile leads to increased impact and solvent resistance, while copolymerization with 1,3-butadiene leads to elastomeric properties. Combinations of styrene, acrylonitrile, and 1,3-butadiene improve all three properties simultaneously. This and other technological applications of copolymerization are discussed further in Sec. 6-8. 

The growing importance of thermoplastic elastomers is clearly evident from the papers presented at this Symposium. The majority of papers on elastomer synthesis deal with these types of block copolymers. The papers by Quirk and Tung describe the triblock copolymers based on -methylstyrene-butadiene and styrene-a-methylstyrene-diene systems, respectively. Anionic block copolymerization of hexamethyl- and hexaphenylcyclotrisiloxane is discussed in the paper (not included in this book) by Ibemesi, Gvozdic, Keumin, Lynch and Meier,... 

Chloroprene (2-chloro-1,3-butadiene), [126-99-8] was first obtained as a by-product from tbe synthesis of divinylacetylene (1). Wben a mbbery polymer was found to form spontaneously, investigations were begun tbat prompdy defined tbe two methods of synthesis that have since been the basis of commercial production (2), and the first successbil synthetic elastomer. Neoprene, or DuPrene as it was first called, was introduced in 1932. Production of chloroprene today is completely dependent on the production of the polymer. The only other use accounting for significant volume is the synthesis of 2,3-dichloro-l,3-butadiene, which is used as a monomer in selected copolymerizations with chloroprene. 

The synthesis of elastomers by step, chain, and ring-opening polymerizations is reviewed. These reactions are characterized as to the process variables which must be controlled to achieve the synthesis and crosslinking of an elastomer of the required structure. Both radical and ionic chain polymerizations are discussed as well as the structural variations possible through copolymerization and s tereoregularity. 

Kennedy, J. P. and Chou, T. Poly(isobutylcnc-co-(J-Pinenc) A New Sulfur Vulcanizable, Ozone Resistant Elastomer by Cationic Isomerization Copolymerization. Vol. 21, pp. 1-39. Kennedy, J. P. and Delvaux, J. M. Synthesis, Characterization and Morphology of Poly(buta-diene-g-Styrene). Vol. 38, pp. 141-163. 

The following protocols (6-10) describe the synthesis of some cholesterol-based acrylates and their photopolymerization in an aligned cholesteric phase. The protocols utilize a modification of a system previously described by Shannon. 5 6 ip ie absence of a diacrylate comonomer, the cholesteric phase produced initially on copolymerization is not stable and reverts to a smectic phase on a single cycle of heating and cooling. In the presence of the diacrylate the first-formed phase is stable. This is one example of how crosslinking can stabilise the liquid crystal phase in liquid crystalline elastomers, others include, the so-called, polymer-stabilized liquid crystals and those described in the later protocols. 

The synthesis of isobutene copolymers containing conjugated double bonds was accomplished only a few years ago by copolymerizing the isoolefin with suitable trienes. The results, largely unpublished, permit to compare the behaviour of these two classes of copolymers which display several analogies. The presence of the conjugated double bond functionalities gives rise to several possibilities of post-modification reactions which extend widely the utilization of these classes of synthetic elastomers. 

Furthermore, LCEs have been prepared by block copolymerization and hydrogen bonds (Cui et al., 2004 Li et al., 2004). Li et al. (2004) proposed a musclelike material with a lamellar structure based on a nematic triblock copolymer (Components 8a-c, Fig. 3.10). The material consists of a repeated series of nematic (N) polymer blocks and conventional rubber (R) blocks. The synthesis of block copolymers with well-defined structures and narrow molecular-weight distributions is a crucial step in the production of artificial muscle based on triblock elastomers. Talroze and coworkers studied the structure and the alignment behavior of LC networks stabilized by hydrogen bonds under mechanical stress (Shandryuk et al., 2003). They synthesized poly[4-(6-acryloyloxyhexyloxy)benzoic acid], which... 

Problem of creation of multi-phase reaction systems with developed surface of phase contact is especially actual under polymer synthesis. In particular at the stages of reaction mixture formation under emulsion [1, 80] and suspension [142] copolymerization, halogenation of elastomers [55, 143], decomposition and removal of electrophilic catalysts and Ziegler-Natta catalytic systems out of polymer [1], saturation of solvent by monomers [78, 79], formation of heterogeneous and micro-heterogeneous Ziegler-Natta catalytic systems [144] and so on. 

Polyaddition of organosilicon dihydrides, mainly dihydro(poly)siloxanes to dialkenyl-substituted organic compounds also known as hydrosilylation copolymerization, leads to polycarbosiloxanes with functionalized organic segments (359). Platinum-catalyzed polymerization hydrosilylation of a,allyl-substituted bisphenols, imides, or amides leads to the synthesis of block copolymers that are useful thermoplastic elastomers (Scheme 40). 

Here, we report on the synthesis and characterization of PMMA-poly(/i-butylacrylate)-PMMA (MBuM) symmetric triblock copolymers, as a new family of thermoplastic elastomers. These compounds have be prepared by a novel route based on controlled radical polymerization [4]. Compared to classical anionic living polymerization [5], this new route, sketched in Scheme la, appears particularly appealing since the triblock copolymers are prepared in a two-step process instead of the usual three steps required in anionic polymerization. In the latter case, as butylacrylate cannot be polymerized via a living process, the MBuM symmetric triblocks have to be synthesized by sequential copolymerization of er butylacrylate (tBuA) and MMA followed by the transalcoholysis of the tBu esters with n-butanol... 

Another commercially important reaction is du Pont s synthesis of 1,4-hexadiene. This is converted to synthetic rubber by copolymerization with ethylene and propylene, which leaves the polymer with unsaturation. Unsaturation is also present in natural rubber, a 2-methylbutadiene polymer 12.13, and is necessary for imparting elastomer properties and permitting vulcanization, a treatment with Sg that cross-links the chains via C-S-C units and greatly hardens the material. 

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. 

As mentioned in Section 3, typical aramid-6-polyether elastomers are synthesized by the polycondensation reaction of polyether diol with the aramid compound I in the presence of transesterification catalysts. Under these conditions, the synthesis of aramid-6-polyester elastomers gave only low molecular weight elastomers with a broad segment length distribution due to transesterification reactions of the polyester segments. This result inidicated that in the obtaining of aramid-6-polyester elastomers, transesterification catalysts should be avoided. Later, a method for the obtaing of this type of elastomers was developed, which consisted in the copolymerization of an activated acyl lactam-terminated aramid compound II with polyester diols in the molten state, in the absence of transesterification catalysts [40,42]. Compound II was obtained by the reaction of N-(p-aminobenzoyl) caprolactam with terephthaloyl chloride, as shown in Scheme 8 [61]. 

The anionic arm-first methods can also be applied to the synthesis of star block copolymers [59]. The procedure is identical except that living diblock copolymers (arising from sequential copolymerization of two appropriate monomers, added in the order of increasing nucleophilicity) are used as living precursor chains. The active sites subsequently initiate the polymerization of a small amount of a bis-unsaturated monomer (DVB in most cases) to generate the cores. If polystyrene and polyisoprene (or polybutadiene) are selected, the resulting star block copol)miers behave as thermoplastic elastomers because of their different glass transition temperatures. 

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