SynopsisConditions of epoxidation of unsaturated polymers were studied. Perphthalic monoacid appeared to be one of the most efficient epoxidation agents, particularly when the double bond is enriched with electrons. Some properties of the new polymers thus obtained were revealed and functional crosslinkings were achieved.Si certaines reactions d'oxydation des elastomeres! et en particulier du caoutchouc naturel,? ont fait l'objet de nombreux travaux, il ne semble pas que la creation de groupes epoxydes par reaction d'un peracide organique sur une double liaison ait ete clairement etudiee, En effet, les auteurs":" qui ont utilise les peracides dans les reactions de modification des polymeres n'ont pas mis en evidence les derives epoxydes, Ils obtiennent generalement des composes hydroxyles plus ou moins esterifies par les acides residuels. Quant a la chaine propre a I'elastomere, elle est fortement degrades.On a done utilise un reactif plus specifique des doubles liaisons polyiso-

On a étudié la fixation de carbonyles fortement électrophiles sur les polyènes macromoléculaires dont les doubles liaisons présentent une densité électronique élevée. Parmi les aldéhydes utilisés, il faut citer en premier lieu le chloral et le glyoxal. Le chloral se combine aux cis 1,4‐polyisoprènes en présence de AlCl3 ou de BF3 pour former des groupes latéraux —CHOH—CCl3 caractérisés par la spectrographie I.R. et l'analyse chimique. La cyclisation de la chaîne consécutive à l'action du catalyseur paraît être évitée dans le cas où l'on opère avec AlCl3, elle se manifesterait en présence de BF3. Le glyoxal se combine aux cis 1,4‐polyisoprènes en présence ou non d'acides de LEWIS pour donner des structures —CHOH—CHO. Le groupe aldéhyde libre de ces chaînes latérales est responsable de l'instabilité des polymères obtenus. D'autres structures aldéhydes ont été envisagées. Les résultats les plus favorables sont obtenus avec des carbonyles très électrophiles, parmi lesquels on peut citer le cas de l'aldéhyde glycidique.

In an earlier note the fixation of chloral onto cis-1,4-polyisoprene (natural or synthetic) in the presence of a catalyst such as AlCl3 or BF3 was discussed. A similar combination with glyoxal has already been mentioned. The fixation of chloral produces macromolecular products with a level of fixation of not higher than n=30 (n, number of reagent molecules attached to a chain of 100 C5H8 units). These compounds contain hydroxyl groups, the infrared bands of which appear at 3,300–3,500 cm−1, while the chlorines are identified at 570, 620, 680, 730, and 1,080 cm−1; these bands can be attributed to side chains —CHOH—CCl3. Also, the band which is characteristic for the cis configuration remains in the spectrum, but has decreased in comparison with the blank; the broadening of the peak at 1,640 cm−1 and the presence of a band at 860 cm−1 indicate the appearance of vinylidene double bonds not located in the chain. This observation is in agreement with our earlier work. The presence of side chains —CHOH—CCl3 is confirmed by the reactivity inherent to these functional groups. The expected reactions take place but are limited by the formation of a three dimensional network resulting in insoluble compounds. Thus, a modified polyisoprene (n=15) loses only 60% of its chlorine by heating to 130° C in xylene solution in presence of finely dispersed sodium. It is difficult to eliminate the remaining chlorine because the radicals formed by the —CCl3 groups produce crosslinking. Phenyllithium produces similar effects to those of sodium, in addition a certain number of phenyl groups are added and result in bands found at 1,495–1,580 cm−1. The presence of hydroxyl groups is also verified by reaction with acetyl chloride. Bifunctional reagents such as adipoyl dichloride or hexamethylene diisocyanate produce crosslinking reactions which become evident by rapidly increasing insolubility.

The cis-1,4-polyisoprenes are composed of 2-methyl-2-butene units, the double bonds of which must be favorable to the addition of strongly electrophylic reagents such as certain aldehydes. Chloral is of this type and its ionic reactions with various simple olefins has been described. We found it worth while to transpose these results to polyisoprenic macromolecules, either natural or synthetic. The ionic reactions generally create less modifications of the chain, such as fission or crosslinking, than would result from free radical reactions. Also, if the formation of free radicals is avoided, the possible fixation of chloral on the halogen carrying carbon (group —CCl2—CHO) becomes very unlikely. Pure anhydrous chloral is used as the reagent. A solution of 2% cis-1,4-polyisoprene (natural) in cyclohexane or decalin (free of peroxides) is heated under a nitrogen atmosphere with the reagent and in presence of a catalyst such as AlCl3 or BF3 at a concentration of 1–3% relative to the polyisoprene. The macromolecular product obtained is then subjected to a fractionation by the chloroform-methanol combination. After purification and desolvation of the main fraction an elemental analysis is made and the level of fixation n calculated based on the chlorine content. Table 1 relates some of the results obtained by using AlCl3 or BF3. In the absence of catalyst (Figure 1, A) the level of fixation is low: n=4 and therefore the nature of the reaction remains uncertain. In the presence of AlCl3 or of BF3, n increases rapidly in function of the temperature and of the relative molar concentration of the reagents, as shown by the curves B and C of Figure 1. The highest level of fixation obtained in these experiments is n=22. Figure 2 demonstrates this limit which is reached beyond the molar ratio of m=4, in the presence of AlCl3 (3%). Table 2 shows the particular action of AlCl3 which among all the catalysts tested proves to be as effective as BF3 without yielding any notable crosslinking of the macromolecular substance.