Clathrate polymerization

Living radical polymerization (atom transfer radical pol5mierization) has been developed which allows for the controlled polymerization of acrylonitrile and comonomers to produce well defined linear homopolymer, statistical copolymers, block copolymers, and gradient copolymers (214-217). Well-defined diblock copolymers with a polystyrene and an acrylonitrile-styrene (or isoprene) copolymer sequence have been prepared (218,219). The stereospecific acrylonitrile polymers are made by solid-state urea clathrate polymerization (220) and organometallic compounds of alkali and alkaline-earth metals initiated polymerization (221). 

The degree of crystallinity in poly(vinyi chloride) has attracted much attention because of its low degree of crystallinity. Commercial samples have values about 5—10 % but the urea-clathrate polymerized material was about 65 % crystalline, and also highly syndiotactic. ... 

Polymerization in confined space usually includes polymerization of inclusion compounds (clathrates), polymerization of monomer crystals, polymerization in nanolayers, or in dispersed systems. 

Another example of such a behavior is provided by the interesting polymerization of butadiene molecules imprisoned in tubes of clathrates of urea.9 Of course, the configuration of the resulting polymer is strongly influenced by the order introduced in the assembly of monomers and thus all trans polybutadiene is formed. 

Acetylene, clathrate in hydroquinone, 7 hydrate thermodynamic data and lattice constants, 8 Acrylamides, polymerization of, 181 Acrylonitrile, 155 Activity coefficients, 125... 

Carbon tetrachloride-hydrogen sulfide-water ternary system, 49, 51, 52 Carboniuin ion polymerization, 158 Carboxylic groups initiator, 174 Catalyst clathrates equilibrium, 35 Cell partition function, in calculation of thermodynamic quantities of clathrates, 26... 

Configurational energy for clathrates, 12 Configurations, superposition of, 258 Conformal solution theory, 137 Coordination polymerization, 148, 162, 170... 

Styrene polymerization, 175 Suicide monomer, 180 Sulfur dioxide clathrate, 2 in hydroquinone, 7... 

Bulk polymerization of //r/ .v-2-melhyI-1,3-pcntadiene lead only to 1,4-trans addition polymer, however it allows randomization of the trans structure, leading to an atactic polymer. The polymerization of the clathrate of rraw.v-2-mclhyl-1,3-pcntadiene yielded an isotactic 1,4-trans addition polymer. The polymer formed from the bulk had a molecular weight of 20,000 (240 monomer units), and that formed from the clathrate had a molecular weight of 1000 (12 monomer units). Similar results were obtained for other dienes, and the results are summarized in Table 4. It can be concluded that polymerization of dienes in the clathrate lead exclusively to a 1 A-lrans addition polymer, except in the case of 1,3-cyclohexadiene. For this monomer, although the polymer is formed entirely by 1,4-addition, the polymer formed is essentially atactic. In bulk polymerization, the polymerization proceeds in most cases through 1,4-addition (both trans and cis), but in the case of butadiene and 1,3-cyclohexadiene 1,2-additions were also observed. Actually, in the case of the bulk /-induced polymerization of 1,3-cyclohexadiene the 1,2-addition process was favoured over the 1,4-addition process by a ratio of 4 3. 

One of the first reactions to be studied systematically in a channel-type clathrate was the polymerization of olefins or diolefins. The ordering of the monomers within the clathrate lattice leads to stereoregular products that are not available by other techniques (232-234). Such radiation-induced stereospecific polymerization has been reported for a number of clathrate hosts (235). 

Clathrate hydrates can be formed not only with neutral organic molecules but also with alkylammonium salts with small anionic counteranions [37] and with guests involving polymeric anions [38]. 

Finally we have the completely three-dimensionally joined structure with hydrogen bonds, which is characteristic of all the polyhydroxy compounds from glycerol to the sugars, and by extension even the polymerized sugars, the carbohydrates (Fig. 9). A particularly interesting subsection of this type of structures is that in which the hydrogen-bonded framework is continuous, but extended, leaving holes in which the other types of atom molecule can be placed. These are the clathrate compounds already discussed. 

The compounds M(NH3)2Ni(CN)4 (M = Zn or Cd), which consist of two-dimensional polymeric sheets of tetracyanonickelate ions bridged by coordinating diamminemetal(II) cations, function as host lattices for clathration of small aromatic molecules such as thiophene, furan, pyrrole or pyridine IR studies indicate the presence of hydrogen bonding between the host lattice ammonia and the aromatic guest molecules.132,133 A crystal structure determination of the related clathrate Cd(en)Ni(CN)4(pyrrole)2 has been reported.134 Similarly, the complex Cd(py)2Ni(CN)4 consists of polymeric [Cd—Ni(CN)4] layers held together by Cd-bound pyridine.135... 

For some multimeric proteins, hydrophobic patches on the surface of subunits serve as interaction sites that favor polymerization in aqueous solutions. To allow polymerization to occur, the organized clusters ( clathrates ) of water around the hydrophobic sites must be removed. This process requires an input of thermal energy to melt the clathrates. Thus, the... 

A somewhat unique situation has been studied in the free radical polymerization in urea 70) and thiourea (77) clathrates. Several monomers have been found for which all conditions for solid state polymerization to a stereoregular equilibrium crystal outlined above are fulfilled. The radicals are protected from termination by neighboring radicals by the urea or thiourea walls of the canals. The proper approach of the monomer molecules is achieved in thiourea by stacking the monomer... 

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