Inclusion polymerizations

The trick used in asyrmnetric inclusion polymerization is to perform the reaction in a rigid and chiral environment. With more specific reference to chirality transmission, the choice between the two extreme hypotheses, influence of the starting radical (which is chiral because it comes from a PHTP molecule), or influence of the chirality of the channel (in which the monomers and the growing chain are included), was made in favor of the second by means of an experiment of block copolymerization. This reaction was conducted so as to interpose between the starting chiral radical and the chiral polypentadiene block a long nonchiral polymer block (formed of isoprene units) (352), 93. The iso-prene-pentadiene block copolymer so obtained is still optically active and the... 

CONTENTS Preface. George W. Gokel. Cryptophanes Receptors for Tetrahedral Molecules, Andre Collett, Jean-Pierre Dutasta and Benedict Lozach. Inclusion Polymerization in Steroidal Canal Complexes, Kiichi Takemoto, Mikiji Miyata. Functionalized Tetraazamacrocycles Ligands with Many Aspects, Thomas A. Kaden. Calixarenes as the Third Supramolecular Host, Seiji Shinkai, Kyushu University, Japan. Fluorescent Chemosensors for Metal and Non-Metal Ions in Aqueous Solutions Based on the Chief Paradigm, Anthony W. Czamik. Index. 

When butadiene and 2,3-dimethylbutadiene are included in the channels of urea and thiourea, respectively, 1,4 addition invariably results to yield polymers with chemical and stereo regularities (Scheme 39). Note that addition in the 1,2 fashion is prevented sterically by the narrow channel. Similarly, high selectivity was obtained when butadiene, vinyl chloride, and styrenes were polymerized in the channels of cyclophosphazenes. Syndiotac-tic polymer alone is obtained from vinyl chloride included in urea channels this is apparently the first example of inclusion polymerization of a vinyl polymer in which control is exerted over the steric configuration of the developing tetrahedral carbon atom (Scheme 39). Highly isotactic polymer is obtained from 1,3-pentadiene when it is included in a perhydrotriphenylene matrix (Scheme 39). Note that addition could occur at either end (i.e., Q to... 

Chiral solid matrices are used for asymmetric synthesis polymerization of 1,3-dienes (inclusion polymerization), although the matrix reaction is not exactly a catalytic synthesis [40,41]. (R)-trans-anti-trans-anti-trans-Perhydrotriphenylene (13) [42,43], deoxyapocholic acid (14) [44,45], and apocholic acid (15) [46,47] are known as effective matrices for the... 

Polyrotaxanes Prepared by Inclusion Polymerization (Polythiophene Polyrotaxanes)... 

Encapsulation chemistry similar to that described above (exchange of anilinium, followed by oxidation with peroxydisulfate) was foimd to produce polyaniline not only in zeolite Y, but also in montmorillonite clay. 5 Spectral features (UV-VIS, IR and EPR) of the products were indicative of emeraldine salt and base formation, respectively. The change in basal spacing of the montmorillonite upon intercalation provided additional evidence for the inclusion polymerization. 

Keywords Cyclodextrin, Cyclodextrin complex, Hydrophilic hosts, Inclusion, Polymerization... 

Crystalline inclusion compounds containing unsaturated monomers are effective reactive systems for the production of linear polymers (1-6). This process belongs to the wider class of solid state polymerization, but possesses some specific features which make it worthy of a separate description. Throughout this article, the polymerization in inclusion compounds will be referred to as "inclusion polymerization" (other names currently used in the scientific literature are channel, canal or tunnel polymerization), and the terms "clathrate" will be used as synonymous with "inclusion compound". When there is no risk of confusion, the more general term of "adduct" will be used for clathrate in principle a... 

In inclusion polymerization a monomeric clathrate is transformed into a polymeric one (where monomeric and polymeric refer to the nature of the guest molecules)(Fig. 1) or into a mixture of polymer and host when the polymer does not possess the steric requirements for inclusion. 

A discussion of inclusion polymerization within the frame of solid state polymerization requires the specification of the points which distinguish the two processes. In inclusion polymerization the solid phase consists of two components, host and guest. The former is a crystalline substance which possesses a strong tendency to polymorphism. Generally hosts are able to crystallize in... 

The most common hosts for inclusion polymerization are urea, thiourea, perhydrotriphenylene (PHTP), deoxycholic acid (DCA), apocholic acid (ACA) and tris(o-phenylenedioxy)cyclotriphosphazene (TPP)(Fig. 2). They have the common feature of forming channel-like clathrates, but differ in many specific properties. For instance, urea and thiourea have a rigid structure in which the host molecules are connected by hydrogen bonds and possess a high selectivity towards the guests. In urea channels are rather narrow whereas in thiourea they are wider as a consequence, linear molecules include only in urea and branched or cyclic molecules in thiourea. On the contrary, chainnels existing in PHTP clathrates are very flexible and can accomodate linear, branched and cyclic molecules. 

Figure 1. Schematic drawing of Inclusion polymerization. (Reproduced with permission from reference 12. Copyright 1982 Huthlg and Wepf Verlag, Basel.)...

Apocholic acid ACA Figure 2. Hosts used In Inclusion polymerization. 

A topochemical condition for polymerization is the proper approach of successive monomers at the growing chain-end within the channels. In this respect, conjugated dienes like butadiene, isoprene, etc. possessing reactive atoms in terminal positions, are very suited to inclusion polymerization. However, even bulkier monomers such as substituted styrenes or methyl methacrylate can polymerize if the space available inside the channels permits a favorable orientation and/or conformation of the monomer. The most studied examples are butadiene, vinyl chloride, bromide and fluoride, and acrylonitrile in urea 2,3-dimethylbutadiene and 2,3-dichlorobutadiene in thiourea butadiene, isoprene, cis- and trans-pentadiene, trans-2-methylpentadiene, ethylene and propylene in PHTP butadiene, cis- and trans-pentadiene, cis- and trans-2-methylpentadiene in DCA and ACA butadiene, vinyl chloride, 4-bro-mostyrene, divinylbenzene, acrylonitrile and methyl methacrylate in TPP. 

PHTP is a chiral host which can be resolved into enantiomers DCA and ACA are (or derive from) naturally occurring optically active compounds. Using these hosts inclusion polymerization can be performed in a chiral environment and can be used for the synthesis of optically active polymers. This line of research has been very fruitful, both on the synthetic and on the theoretical plane. It has been ascertained that asymmetric inclusion polymerization occurs by a "through space" and not by a "through bond" induction only steric host-guest interactions (physical in nature) and not conventional chemical bonds are responsible for the transmission of chirality (W). 

All the important aspects of inclusion polymerization have been reviewed several times in recent years (3-6). Interested readers can refer to the literature cited in order to have a more complete knowledge of the specific examples. In the next pages, we shall discuss some points which have been recently developed in our laboratory. 

The temperature dependence of the regioselectivity observed in isoprene inclusion polymerization was investigated between -60 amd +70 C. As expected, the number of defects increases with increasing temperature and ramges from 8 to 26%, expressed as fraction of inverted units. If we plot log Pjjj/Ppp 11 18... 

Finally, we wish to comment briefly on a recent development in inclusion polymerization. As already discussed, this reaction can be carried out on the pure clathrate or in the presence of an excess monomer. Consequently, the vapor pressure of a volatile monomer during polymerization ranges from the decomposition pressure of the clathrate to the vapor pressure of the saturated solution of the host in the guest, which is generally very close to that of the pure liquid monomer. For example, the vapor pressure... 

We succeeded in polymerizing ethylene in PHTP in a steel tube at 20 C and 50 atm and propylene at 20 C and 10 atm. As far as we know these are the first examples of inclusion polymerization performed under high pressure. 

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