Polymerization of methacrylates with bulky substituents with a catalyst system of the ziegler‐natta type

Abstract

The field of the synthesis of polymers with photosensitive and mesogenic (capable of forming the liquid-crystalline state) groups is being rapidly developed. For the solution of this problem the well-known polymerization of vinyl monomers has been used, particularly that of the acrylic series',2), occurring virtually only by the radical mechanism.To obtain stereoregular polymers, it is advisable to use Ziegler-Natta catalysts, but the use of these systems for the polymerization of polar monomers is still limited.Previously some of the present authors have proposed a catalytic system tris(acety1acetonato)chromium/triisobutylaluminium/2,2-bipyridyl used in the polymerization of methyl-and butyl met ha cry late^^).In this work we attempted to extend the action of this system to methacrylates with bulky groups: cholesteryl methacrylate (ChMA) and 9-anthrylmethyl methacrylate (9-AMMA). Experimental PartExperiments were carried out under conditions precluding the presence of moisture and air. Toluene, triisobutylaluminium (AliBu,), 2,2'-bipyridyl (BPy), and chromium acetylacetonate (Cr(acac),) were purified and synthesized by published methods".Cholesteryl methacrylate (ChMA) was synthesized from cholesterol and methacryloyl chloride in benzene by a method described previously4? The purity of ChMA was checked by thin layer chromatography". ChMA was used in toluene solution.Polymerizations were carried out in dilatometers and ampoules by a method already described3? Polymers were purified by repeated precipitation from toluene or chloroform solutions into methanol.Homopolymers were removed from the copolymers of methyl methacrylate (MMA) and ChMA by using the selective solubility of poly(methy1 methacrylate) (PMMA) and poly(cholestery1 methacrylate) (PChMA) in cyclohexane and acetonitrile.Analyses of copolymers were carried out by IR spectroscopy using the changes in the intensity ratios of absorption bands in the range of 1740 and 2880 cm-' depending on the contents of the ChMA units in the copolymer.In the preparation of copolymers of MMA and ChMA with 9-anthrylmethyl methacrylate (9-AMMA) the latter was applied in ''label'' amounts, i. e., one 9-AMMA unit per 500-1 OOO units of MMA or ChMA. The content of 9-anthrylmethyl groups in the copolymers was determined from the absorptance (optical density) of their solutions in dichloroethane or toluene for one of the absorption bands of the 9-anthranyl group in the range of 350-400 nm').A Specord UVVIS spectrophotometer (DDR) was used to measure the UV absorption spectra. The viscosities of PChMA and of the copolymers of MMA and ChMA were determined in toluene and chloroform at 25 "C. Molecular masses of PChMA were determined osmometrically with a Hewlett-Packard high speed membrane osmometer-502. Toluene was used as solvent, at 37 "C.

Investigation of Methyl Methacrylate and Vinyl Acetate Polymerization Promoted by Al(iBu)3/2,2‘-Bipyridine and Al(iBu)3/2,2‘-Bipyridine/TEMPO Complexes

“…Among the number of systems which provide “living” anionic polymerization of methacrylic monomers in the presence of aluminum derivatives in conjunction with a cocatalyst/co-initiator, − Ikeda et al suggested 20 years ago that polymerization of methacrylates in toluene at room temperature with R 3 Al and Lewis base adduct (e.g., 2,2‘-bipyridine, triphenylphosphine) proceeds according to an anionic coordinative mechanism. Korshun and Mazurek reported that methacrylate monomers were polymerized within temperature range from +25 to −60 °C in the presence of R 3 Al/BIPY/Cr(acac) 3 with M n increasing linearly with conversion. “Long-lived” anionic active centers are invoked, and block copolymers were prepared.…”

“…Ikeda et al 22 suggested 20 years ago that polymerization of methacrylates in toluene at room temperature with R 3 Al and Lewis base adduct (e.g., 2,2′-bipyridine, triphenylphosphine) proceeds according to an anionic coordinative mechanism. Korshun and Mazurek23 reported that methacrylate…”