Isotactic polymers chloral

Isocyanophosphonates, aldol reactions, 227 Isoquinoline synthesis, enamide reactions, 33 Isomerization allylic amines, 9, 95 olefins, 118, 171 see also specific compounds Isopulegol, 102 Isotactic polymers, 174 chloral, 182 photoirradiation, 347 methacrylates, 181 propylene, 174 Isotacticity, 177... 

Aldehyde Polymers Asymmetric anionic polymerization can lead trichloroacetalde-hyde (chloral) to a one-handed helical, isotactic polymer having a 4/1-helical conformation with... 

Asymmetric anionic polymerization can convert trichloroacetaldehyde (chloral) to a one-handed helical, isotactic polymer (44) having a 4/1-helical conformation with high optical activity ([oi]d +4000° in film).28114-118 Anionic initiators such as 45,115 46,115 and 47117 and Li salts of optically active carboxylic acids or alcohols are used for the polymerization. Although the polymers are insoluble in solvents and their conformation in solution cannot be directly... 

The polymerization of bulky aldehydes such as chloral using enantiopure lithium alkoxides (7,8) gives insoluble, isotactic polymers that exhibit optical activity in the sohd state (Scheme 6) [8,50,51]. The solution and solid-state hel-... 

It has earlier been established that chloral can only be polymerized to crystalline, apparently isotactic polymer, no soluble fraction, even of low molecular weight, has ever been observed. ( ) Fluoral has been known to exist also in a soluble form.(9) It has become very desirable to establish clearly the space filling size of trihalomethy1 sustituent of the per-haloacetaldehyde (which after polymerization becomes the side group of the polyacetal chain) that is necessary to form isotactic polymer and isotactic polymer only. 

Chloral was known to give only insoluble, presumably isotactic polymer, fluoral could be polymerized to insoluble and soluble presumable atactic polymer. 

In the presence of chiral lithium alkoxides as initiators, chloral forms completely isotactic, crystalline polymers that are insoluble in all solvents (Scheme 71) (166). The polychloral film displays rotation values as high as 3000-5000°. The stereoregular helicity comes about at the stage of the trimer (167). A pure enantiomer of a tert-butoxy-initiated, acetate end-capped pentamer of chloral, which has 4r-helical conformation in both chloroform solution at 35 °C and in the crystalline state, can be obtained by HPLC resolution on a chiral stationary phase (168). 

The purely isotactic oligomers of chloral provides unique and ideal models for the quantitative investigation of the properties of helical polymers because the oligomers have a high tendency to crystallize and have very simple H and 13C NMR spectra. As far as we are aware, there is no other analogue of linear low-molecular compounds showing such slow interconversion between enantiomeric helical states. 

Poly(chloral) is predominantly isotactic and insoluble in all solvents. Thus, shaped articles can only be produced by the monomer molding technique or by cutting and drilling. The polymer is very resistant to chemical attack, but thermally decomposes to its inflammable monomer above a temperature of 200° C. It is not produced commercially. 

Poly(chloral), which is predominately isotactic, has a 4 helical conformation in the crystalline state. It is insoluble in all solvents, and thus can only be worked under restraint (by sawing or drilling). Alternatively, molded shapes can be prepared by the monomer molding technique. Poly(chloral) is stable to fuming nitric acid. It does not melt or drip, although above 200°C it decomposes into inflammable monomers. The polymer itself has a LOI of 100. The mechanical properties of the unipolymer, or the copolymer with a little isocyanate, approximate those of PMMA or PS. 

---