Ring-opening polymerization of glycidylic compounds: influence of the glycidylic oxygen in the coordinative mechanism

Abstract

A series of oxiranic monomers was synthesized and polymerized by four of the most common aluminium-based coordinative initiators: (C 2 H 5 ) 3 Al/H 2 O (mole ratio 1 : 0.6) named Vandenberg catalyst, (C 2 H 5 ) 3 Al/CH 3 COCH 2 COCH 3 /H 2 O (mole ratio 1 : 1 : 0.5) named Vandenberg chelate catalyst, (i-PrO) 2 Al1O1Zn1O1Al(i-PrO) 2 named Teyssié catalyst and (i-PrO) 3 Al/ZnCl 2 (mole ratio 1 : 0.5) named Price catalyst. They all have a different Lewis acid character. The influence of a second oxygen (glycidylic or not) on the characteristics of the polymers and conversions was studied and rationalized on the basis of a coordinative mechanism. The differences in the polymerization rate and regioregularity of the polymers obtained are related to the electronic and coordination effects of the neighbouring oxirane substituents. The new polymers were also thermally characterized.

Synthesis of New Reactive Polyethers: Poly(-bromoalkyl-1-glycidylether)s

“…The spectrum of poly(10-bromo-1,2-epoxydecane) shows two signals at 77.8 and 73.8 ppm which correspond to a methine and a methylene carbon respectively. These signals, according to previous studies, [18] are assignable to irregular linkages and point to an outstanding difference in the microstructure of both kinds of polymers. It must be pointed out that these signals can also be observed in the spectra described by other authors, [46] in which, however, no assignment was made.…”

“…According to our previous work, [18] this unusually high percentage of irregular linkages must be attributed to the absence of the glycidylic oxygen. As we mentioned above, this second coordinating point allows a highly stable chelate adduct to form which fixes the monomer position in the initiator complex, thus favoring the nucleophilic attack at the less hindered position and producing normal heat to tail linkages.…”

“…The methine carbon appears as a triplet centered at 79.4 ppm corresponding to the mm, mr + rm and rr triads, and the methylene carbon signalappears as a quadruplet centered at 72.2 ppm corresponding to mm, mr, rm and rr triads. This higher stereosequence sensitivity of the methylene main chain carbon is characteristic of polyoxiranes with no b-heteroatoms relative to the oxiranic ring such as poly(1,2-epoxybutane), [44,45] poly(1,2-epoxyoctane), [46] poly(4-phenyl-1,2-epoxybutane) [18] and poly(4phenoxy-1,2-epoxybutane). [18] The degree of tacticity calculated from the relative intensities of the different triads was very close to the one calculated for the poly(x-bromoalkyl-1-glycidylether)s ( Table 6 and 7).…”

“…Moreover, in this case the nucleophilic ring-opening is not so easy as in the case of arilglycidylethers, in which a considerable electronic activation of the oxiranic ring must be considered. [18] Among the three alkylaluminium-based initiators some differences were observed. The Vandenberg catalyst (V) Scheme 2. gave the faster polymerization and no monomer was detected after one day, but it also gave a considerable oligomeric fraction which diminished the final polymer conversion.…”

“…Another advantage of these new monomers is that they should polymerize in higher conversions and with higher regioregularity than x-haloalkyloxiranes since, according to our previous studies, the glycidylic oxygen favorably participates in the coordination step. [18] Full Paper: A set of x-bromoalkyl-1-glycidylethers were synthesized by reacting epichlorohydrin (ECH) and various x-bromo-1-alkanols. The starting alcohols were readily obtained in good yields from the inexpensive 1, xalkanediols.…”