Mixed-dihalide systems

Use of a mixed dihalide monomer feed in a conventional polymerization will produce random copolymers. A block copolymer cannot be prepared by a stepwise addition of the monomers. During copolymerization interchange takes place, resulting in randomization. To prepare block copolymers, it is best to prepare individual mercaptan-terminated polymers, blend them in the desired proportion, and then process the blended system by conventional techniques. 

The method has been extended to the preparation of difunctional compounds. Dihalides Including the mixed variety are formed in 90 to 98% yields. Primary unsaturated bromides of the type RCH=CHCH,Br have been formed from the corresponding alcohols by the action of phosphorus tribromide and pyridine at a low temperature without any apparent rearrangement. However, the corresponding secondary-carbinol system, RCHOHCH=CH is very susceptible to allylic isomerization. The formation of a, -acetylenic bromides from acetylenic alcohols and phosphorus tribromide is common (40-70%). An acetylenic-allenic isomerization has been observed, viz.,... 

Michaelis-Arbuzov reactions have been carried out with tribenzyl phosphite and mixed alkyl dibenzyl phosphites (PhCH20)2P0R. A trace of an alkyl halide causes the former to isomerize to the predicted dibenzyl benzylphosphonate, but when the mixed phosphites are treated with the halide R X, loss of benzyl halide occurs with the formation of (PhCH20)(R0)P(0)R. The high reactivity of the systems led to the formation of several oligophosphonates. Carbohydrate-like 1,2-oxaphosphori-nanes have been prepared from 2,3-dimethoxybutane 1,4-dihalides and PhP(OEt)2 as mixtures of diastereoisomers (compare the formation of 57) ... 

Based on the similar crystal structure one might expect extended solid solutions between Cdl2-type dihalides and Bila-type trihalides, as well as between CdCl2-type and AlCla-type halides. This, however, appears not to be the case. The systems MgCl2—CrCla, FeCl2—CrCla and MnCl2—CrCla were found to be similar to eutectic-type systems [906]. Moreover, the different anion stacking is sufficient to prevent mixed-crystal formation between CrCla and FeCla [906]. 

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