Copolymers of p-Methoxystyrene with 1,3-Dioxolane

When p-methoxystyrene (pMOSt) is polymerized in the presence of iodine (I2), iodoalkyl groups are formed and termination via proton transfer is not observed 107)  

PolypMOSt prepared in this way was used to initiate the polymerization of 1,3-dioxolane (DXL)108). A typical procedure was as follows pMOSt (0.5 mol l-1) was polymerized with iodine (10 mmole l-1) initiator at 0 °C or —15 °C in CC14. After completion of pMOSt polymerization, DXL containing a dissolved neutral salt of low nucleophilic anion (such as AgSbF6, AgBF4 or Bu4NC104) was added. After 64 hrs the polymerization was terminated and the polymer was precipitated in methanol. The conversion of DXL was unexpectedly high, 90%, in view of the equilibrium character of DXL polymerization ([M]e of DXL is 1.0 mole l-1 at 0 °C). 

The product was separated into methanol-soluble and methanol-insoluble fractions. The soluble fraction Mn = 5,000-9,000 by GPC with polystyrene standards was 

On the basis of these observations, block copolymer formation was claimed. It was reported, however, that some grafting also occurs when DXL is polymerized in the presence of preformed polypMOSt. Thus, when dead polypMOSt was added to the solution of living polyDXL, up to 70% of polyDXL was grafted by aromatic alkylation onto polypMOSt  

There is, however, still some doubt whether the alleged block copolymers are indeed copolymers and not predominantly a mixture of homopolymers containing some graft and block copolymers. The solubility criterion was mostly relied upon, and it was shown that 40 % of DXL entered the copolymer (60 % was isolated as methanol-soluble low-molecular-weight polyDXL). This criterion may be misleading as we already stressed, because, except for the very low-molecular-weight fraction, polyDXL is insoluble in methanol. Thus, the question whether or not block copolymers are formed in this system and if so, what is the efficiency of this reaction is still unresolved. 

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