Poly isotactic polymer synthesis

The synthesis of isotactic polymers of higher a-olefins was discovered in 1955, simultaneously with the synthesis of isotactic PP (1,2) syndiotactic polymers of higher a-olefins were first prepared in 1990 (3,4). The first commercial production of isotactic poly(l-butene) [9003-29-6] (PB) and poly(4-methyl-l-pentene) [9016-80-2] (PMP) started in 1965 (5). 

It is the purpose of this article to review studies which have been carried out along these lines in the laboratories of the authors, at Universities Pierre et Marie Curie (France) and Laval (Canada). For the sake of completion, studies carried out in other laboratories will also be mentioned. More specifically, the methods of synthesis used for a- and 3-substituted poly(3-propiolactones) will be discussed. It will be seen that the synthesis of the corresponding high optical purity monomers is particularly difficult, and tedious. The principal thermal properties of the polymers obtained will also be discussed, along with the properties of racemic mixtures obtained from two isotactic polymers having the same chemical structure but different chiralities. 

An interesting aspect of the benzofuran cationic polymerization was uncovered by Natta, Farina, Peraldo and Bressan who reported in 196160,61 that an asymmetric synthesis of an optically active poly(benzofuran) could be achieved by using AlCl2Et coupled with (-)j3-phenylalanine, (+)camphorsulphonic acid or with (-)brucine. The optical activity was definitely due to the asymmetric carbon atoms in the polymer chain, indicating that at least some of the polymer s macromolecules possessed a di-isotactic structure, v/ z.62 ... 

The synthesis of isotactic and syndiotactic polymers has been achieved for a number of polymers. For example poly (methyl methacrylate) can be prepared in either isotactic or syndiotactic configurations depending on the details of the polymerisation conditions. 

First, the short chain length PHAs, poly(HASCL), are composed of monomeric units containing up to 5 carbon atoms. The most well-known representatives are poly(3-hydroxybutyrate) (PHB), and its copolymers with hydroxyvalerate. Of all the PHAs, PHB is by far the most commonly encountered in nature [18]. It is the simplest PHA with respect to chemical structure, having a methylene (-CH3) group as the pendent R-unit in Fig. 1. Owing to its enzymatic synthesis, PHB has an exceptional stereochemical regularity. The chains are linear and the chiral centers all are in the R-stereochemical conformation, which implies that this polymer is completely isotactic. 

Another result of great importance—the conformational asymmetric polymerization of triphenylmethyl methacrylate realized in Osaka (223, 364, 365)— has already been discussed in Sect. IV-C. The polymerization was carried out in the presence of the complex butyllithium-sparteine or butyllithium-6-ben-zylsparteine. The use of benzylsparteine as cocatalyst leads to a completely soluble low molecular weight polymer with optical activity [a]o around 340° its structure was ascertained by conversion into (optically inactive) isotactic poly(methyl methacrylate). To the best of my knowledge this is the first example of an asymmetric synthesis in which the chirality of the product derives finom hindered rotation around carbon-carbon single bonds. 

Production of materials in which the daughter polymer and the template together form a final product seems to be the most promising application of template polymerization because the template synthesis of polymers requiring further separation of the product from the template is not acceptable for industry at the present stage. Possible method of production of commonly known polymers by template polymerization can be based on a template covalently bonded to a support and used as a stationary phase in columns. Preparation of such columns with isotactic poly(methyl methacrylate) covalently bonded to the microparticulate silica was suggested by Schomaker. The template process can be applied in order to produce a set of new materials having ladder-type structure, properties of which are not yet well known. A similar method can be applied to synthesis of copolymers with unconventional structure. 

Catalysts based on the Hf pyridyl amine complexes 126-128 have been used for the preparation of ethylene/ propylene co-polymers as well as of ethylene/propylene/l-octene terpolymers. These co-polymers are characterized by having at least 60 wt% propylene units, Mw around 300000, and Mw/Mn in the range 2.0-2.4. The NMR analysis of these co-polymers showed that the propylene sequences are remarkably isotactic mm > 90%) and showed the presence of regioirregularly inserted propylene units(<0.5% mol). The most interesting property of catalysts based on 126-128 is their high thermal stability.1119 Using modifications of isospecific bis(phenoxy-amine)-based catalysts, such as complex 164, the controlled synthesis of iPP- /orjf-poly/E-co-P) diblock co-poly-mers has been achieved. This is a remarkable result since iPP and PE are both polymeric materials of extreme industrial relevance.1206... 

Poly(vinyl alcohol) is very high in head-to-tail structures, based on NMR data. It shows the presence of only a small amount of adjacent hydroxyl groups. The polymer prepared from amorphous poly(vinyl acetate) is crystalline, because the relatively small size of the hydroxyl groups permits the chains to line-up into crystalline domains. Synthesis of isotactic poly(vinyl alcohol) was reported from isotactic poly(vinyl ethers) like poly(benzyl vinyl ether), TOly(f-butyl vinyl ether), poly(trimethylsilyl vinyl ether), and some divinyl compounds. ... 

Lactic acid is currently produced by fermentation of carbohydrates and is rme of the high potential and versatile biomass-derived platform chemicals, leading to various useful polymer products. PLA is produced by ROP of lactide (derived from lactic acid) and exhibits mechanical properties similar to poly(ethylene terephthal-ate) and polypropylene. Representative examples discussed herein included the synthesis of highly stereo-controlled PLAs, such as isotactic, heterotactic, and syndiotactic PLA materials, rendered by different catalyst/initiator systems. 

Various metal complex systems of Ziegler type are widely applied within industry for the production of high-density polyethylene, isotactic polypropylene, 1,4-c/s-and 1,4- rans-polymers of isoprene and 1,2-poly butadiene, and many other types of copolymers, such as ones based on ethylene and propylene, which could not be produced earlier based on traditional methods of synthesis. 

Abe H, Doi Y, Kumagai Y (1994a) Synthesis and characterization of poly[(R,S)-3-hydroxybu-tyrate-b-6-hydroxyhexanoate] as a compatibilizer for a biodegradable blend of poly[(R)-3-hydroxybutyrate] and poly(6-hydroxyhexanoate). Macromolecules 27 6012-6017 Abe H, Dd Y, Satkowski MM, Noda I (1994b) Miscibility and morphology of blends of isotactic and atactic poly(3-hydroxybutyrate). Macromolecules 27 50-54 Abe H, Matsubara I, Doi Y (1995) Physical properties and enzymic degradability of polymer blends of bacterial poly[(R)-3-hydroxybutyrate] and poly [(R,S)-3-hydroxybuty rate] stereoisomers. Macromolecules 28 844-853... 

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