Polymer Bulletin 25, 641-648 (1991) ro~i~i~ BulleUn Springer-Verlag 1991 Photoinitiated cationic bulk polymerization of mesogenic vinyl ethers H. Jonsson, H. Andersson, P.-E. Sundell, U. W. Gedde, and A. Hult* Department of Polymer Technology, Royal Institute of Technology, S-10044 Stockholm, Sweden SUMMARY Mesogenic vinyl ethers have been bulk polymerized cationically in the liquid crystalline phase, using onium salt redox systems for photochemical initiation. High molecular mass polymers (Mn<41 000) with a narrow molecular mass distribution (around 2) were obtained at high temperatures (<80~ Apparently the polymerization system stabilizes the propagating cation and thus reduces the tendency for chain transfer to occur. Highly ordered thin (30- 50 ~m) films were produced by the polymerization of monomers oriented in their nematic phase. Despite the fact that they were in the SAphase, the t-rims were completely transparent. INTRODUCTION One part of the vast field of mesomorphic polymers that has received quite a lot of attention are polymerizations performed in the liquid crystalline (LC) phase (1-2). Nevertheless, know- ledge of the effects this type of polymerization has on e. g. polymer structure and morphology and on polymerization kinetics, is rather limited. The reported results also differ remarkably and one example of this is the effect on polymerization rate. Hoyle et al. reported a rate enhance- ment in the LC phase upon photo-polymerization of cholesterol containing acrylate and meth- acrylate monomers (3-4). The reverse, a decrease, was described by Perplies et al. for the ther- mally initiated polymerization of Schiff base based acrylates and methacrylates (5). Mesophase polymerization of styrene monomers carrying Schiff base moieties gave, on the other hand, no change in rate compared to polymerization in the isotropic phase, according to Paleos and Labes (6). It is apparently difficult to compare direcdy systems with different monomers, initiators, mesophases etc. at this level of understanding. A very interesting application of mesophase polymerization is the in situ photopolymeri- zation of oriented LC mono- and bifunctional acrylates described by Broer et al. (7-10). The monomers were oriented in their mesophase by conventional techniques used for low molar mass liquid crystals and then polymerized with uv-radiation with subsequent freezing-in of the structure. In this way, oriented thin films were produced with a higher degree of order than films resulting from the ordering of polymers. Thin macroscopically ordered polymer films are a very important group of materials for the realization of several proposed applications for func- tional LC polymers such as non-linear optics. In a previous paper (11) we showed that thermally initiated cationic polymerization of vinyl ethers in the LC phase produced high molecular mass polymers (Mn<83 000) with a narrow molecular mass distribution (around 2) at, for cationic polymerization very high temperatures (<120~ This paper presents data on the sulfoninm salt initiated photopolymerization of phenyl- benzoate based LC vinyl ethers. It also shows how macroscopically ordered thin films of well- defined polymers can be made by polymerization of monomers preoriented in their LC state. *To whom offprint requests should be sent