Copolymers of 1,3-Dioxepane and 1,2-Dimethoxyethylene

As described in the previous section, under suitable reaction conditions one can prepare living polyacetals (poly-l,3-dioxolane and poly-1,3-dioxepane) in almost quantitative yields having well defined molecular weights (DPn = ([M]0 — [M]e)/[I]0), and a low content of cyclic fraction (a few percent). 

Living bifunctional poly-l,3-dioxepane (polyDXP) was used as initiator for the polymerization of 1,2-dimethoxyethylene (DME) to prepare ABA-type block copolymers 121)  

In the first stage, DXP was polymerized with (CF3S02)20 initiator in CH2C12 solvent at —78 °C. After the completion of DXP polymerization, a sample was taken for DPn determination of polyDXP and then a solution of DME was added. The system was kept at —78 °C for several hours and then the polymerization was terminated by sodium methanolate. The precipitated polymer was isolated, dried and characterized (yield, DPh, NMR). Results of typical experiments are given in Table 15.10. The molecular weights were close to the values calculated by assuming that each dicationic living polyDXP initiated DME polymerization. 

GPC analysis showed that the precipitated copolymer had a unimodal molecular weight distribution, and the corresponding peak has shifted towards higher molecular weights as compared to the starting polyDXP. GPC analysis also showed that prior to precipitation with methanol, the copolymer contained some low-molecular-weight 

it seems that polymerization of DME during the second stage is accompanied by some transfer, and in addition to copolymer a certain amount of low-molecular-weight products (probably DME homopolymer) are also formed. 

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