Copolymerization chloral/isocyanates

Anionic copolymerization of isocyanates with chloral (67), cyanopropionalde-hyde (68), and acrolein dimer (69) is also known. For example, reaction of phenyl isocyanate with chloral in DMF at -68°C, using potassium cyanide as initiator, affords chloroform-soluble copolymers 10, which melt at about 230°C (67). 

Chloral, CChCHO, can be anionically or cationically polymerized. The polymerization is initiated above the ceiling temperature of 58° C and then allowed to proceed well below the ceiling temperature. Phosphines and lithium /-butoxide are especially suitable as anionic polymerization initiators, whereas tertiary amines only produce poly (chlorals) of low thermal stability. Anionic copolymerization of chloral with excess isocyanates produces alternating polymers, as is also the case for the cationic copolymerization of chloral with trioxan. 

Perhaloacetaldehydes copolymerize with each other, most prominently with chloral or with isocyanates. A typical copolymerization scheme with DCBA is given in Eqn. 9. 

Copolymerizations of aldehydes with isocyanates are well known and for perhaloacetaldehydes, aromatic isocyanates are the best comonomers. The polymerization of phenylisocynates with chloral has been most extensively studied. (21,22). The copolymerization of... 

BDCA is described in Eqn. 9 and the results of copolymerization of various perhaloacetaldehydes with phenyl-isocyanate are shown in Table 2. The copolymers are generally prepared with anionic initiators, for example with pyridine or Ph P, but LTB was also used as effective initiator, particularly for chloral copolymerizations. As in homopolymerizations, low temperature conditions must be employed for an effective copolymerization and yields of 30 % to nearly quantitative yields have been obtained. Most copolymers of a perhaloacetaldehyde and phenylisocyanate are insoluble when the copolymer contains only small amounts of phenylisocyanate, but polymers with more than 20 mole % of phenylisocyanate are normally soluble. A truly alternating copolymer of a perhaloacetaldehyde and phenylisocyanate has only been prepared with bromal as the monomer. Many attempts to prepare an alternating copolymer with chloral failed. This result seems to... 

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