ST. PENCZEK, J. FEJGIN, W. SADOWSKA, and M. TOMASZEWICZ spezhchen Oberflachen (ca. 25 m2/g). Polymerisationsansatze mit Polyathern sind selbst bei einem Gehalt von 60 Gew.-% an festem Copolymeren noch fliissig. Eine monomolekulare Schicht von Polyathern (z. T. als Blockcopolymeres, z. T. nur adsorbiert) auf der Oberflache der Polyacetal-Partikel scheint auszureichen, urn die beschriebenen Phlnomene hervorzurufen. Diese Schicht verhindert das Agglomerieren der Polyacetal-Partikel.

SynopsisI n the cationic polymerization of 3,3-bis(chloromethyl)oxetane induced by BTI. 3 the solvent polarity (toluene, methylene chloride, ethylene chloride, nitrobenzene, and nitromethane) does not influence the k,,/k, ratio, where k,, stands for the rate constant of chain transfer to polymer. Increase of the overall polymerization rate is due mainly to the increase of ki. The application of the steady-state conditions in which the slow formation of the active centers is compensated by the unimolecular chain transfer to polymer allowed the determination of k,/k, ratios for several chain-transfer agents of low molecular weight.It was established that the k,,/k, ratio is a linear function of -pK, of the chain-transfer agents.Alcohols and ethers of different basicities were used.

Polymerization of several cyclic monomers has been recently described in terms of living polymerization introduced originally by SZWARC~).Living polymers of tetrahydrofuran were obtained with R,Al-cocatalysts 2), Ph,CeMeeXn3), SbCl,, BF3-cocatalysts4) and other systems. According to some authors the heterogeneous polymerization of trioxane bears also resemblance to living polymerization5), although in this case the possibility of immobilization of active centers should be taken into account6y7). I n this case as well as in the case of propylene oxide/R2Zn/H20 systemE and propylene oxide/R,Al/H,O system9) the chain transfer to polymer, accompanied with active center stabilization (with or without chain scission or cyclization), had introduced important deviations from the true living system.