Copolymerization of Lactones with Cyclic Ethers

The basicity of esters is similar to that of related ethers, therefore, in copolymerization random structures could be expected. THF (pKb = 5.0) and BCMO (pKb = 5.65) were copolymerized with e-caprolactone (eCL pKb = 5.31) and P-propiolactone (PPL, pKb = 10.06), eCL and cyclic ethers enter the copolymer with nearly the same rates. The reactivity ratios determined by the Mayo-Lewis method are rt(BCMO) = 0.24, r2(eCL) = 0.44 and rt(THF) = 0.7, r2(eCL) = 0.3 4C). r, should be higher for THF(Mj) because the reversibility of THF polymerization has not been taken into account (cf. Sect. 15.1.3.1). rt and r2 values suggest the formation of nearly random copolymers. The microstructure of BCMO-eCL copolymers was studied by NMR spectroscopy, and the new signals B and A due to heterodyad appeared [cf. Eq. (15-41)]. Simultaneously the ratio of signals C/D decreased from 2 to a lower value  

When THF was used above its equilibrium concentration ([THF]0 [THF],) mostly its homopolymer was formed. Only when [THF], reaches [THF]e does PPL start to polymerize. Under these conditions one obtains two consecutive THF units separated by a number of PPL units, depending on the PPL content. 

4 Attempted Copolymerization of Monomers that Belong to Different Classes of Chemical Compounds 

Typical vinyl monomers, like styrene or its derivatives, are much less basic than heterocyclics. Thus attempts to prepare random vmyl/heterocyclic copolymers 

The less nucleophilic acetals copolymerize with vinyl compounds more readily. Perhaps, in these systems the alkoxycarbenium ions (... —OCH ) that coexist in equilibrium with oxonium ions facilitate copolymerization with vinyl compounds. Styrene copolymerizes with trioxane 51,52) and tetraoxane53). The latter system yields polytrioxane and trioxane-styrene copolymer together with 1,4-phenyl-1,3-dioxane. It was formed in 25% yield in ethylene dichloride at 30 °C after 1 hr using [BF3 OEtj] = 10-2 mol l-1, [styrene], = [tetraoxane = 0.5 mol l-1. The proposed mechanism of 4-phenyl- 1,3-dioxane formation is shown below (cf. also Chap. 7)  

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