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Polymers based on renewable monomers are projected to have a significant role in the sustainable economy, even in the near future. Undoubtedly, the cationically polymerizable β-pinene, available in considerable quantities, is one of the most promising bio-based monomers for such purposes. In the course of our systematic investigations related to the catalytic activity of TiCl4 on the cationic polymerization of this natural olefin, it was found that the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl4/N,N,N′,N′-tetramethylethylenediamine (TMEDA) initiating system induced efficient polymerization in dichloromethane (DCM)/hexane (Hx) mixture at both −78 °C and room temperature. At −78 °C, 100% monomer conversion was observed within 40 min, resulting in poly(β-pinene) with relatively high Mn (5500 g/mol). The molecular weight distributions (MWD) were uniformly shifted towards higher molecular weights (MW) in these polymerizations as long as monomer was present in the reaction mixture. However, chain–chain coupling took place after reaching 100% conversion, i.e., under monomer-starved conditions, resulting in considerable molecular weight increase and MWD broadening at −78 °C. At room temperature, the polymerization rate was lower, but chain coupling did not occur. The addition of a second feed of monomer in the polymerization system led to increasing conversion and polymers with higher MWs at both temperatures. 1H NMR spectra of the formed polymers indicated high in-chain double-bond contents. To overcome the polarity decrease by raising the temperature, polymerizations were also carried out in pure DCM at room temperature and at −20 °C. In both cases, rapid polymerization occurred with nearly quantitative yields, leading to poly(β-pinene)s with Mns in the range of 2000 g/mol. Strikingly, polymerization by TiCl4 alone, i.e., without any additive, also occurred with near complete conversion at room temperature within a few minutes, attributed to initiation by adventitious protic impurities. These results convincingly prove that highly efficient carbocationic polymerization of the renewable β-pinene can be accomplished with TiCl4 as catalyst under both cryogenic conditions, applied widely for carbocationic polymerizations, and the environmentally benign, energy-saving room temperature, i.e., without any additive and cooling or heating. These findings enable TiCl4-catalyzed eco-friendly manufacturing of poly(β-pinene)s, which can be utilized in various applications, and in addition, subsequent derivatizations could result in a range of high-added-value products.

Highly efficient carbocationic polymerization of styrene was achieved under environmentally advantageous conditions in benzotrifluoride, BTF (α,α,α-trifluorotoluene, TFT), an environmentally benign solvent at room temperature, that is without any energy consumption for cooling or heating, with even better yields than that in the usually applied volatile and harmful, widely used chlorinated solvent, dichloromethane (DCM). The polymerization was initiated by 1-phenylethyl chloride in conjunction with the TiCl4/TMEDA (N,N,N′,N′-tetramethylethylenediamine) catalyst (coinitiator) system. Within a very short reaction time (5 min), higher conversion values were obtained in BTF (89%) than in DCM (76%), that is the TiCl4/TMEDA combination proved to be a powerful catalyst for the carbocationic polymerization of styrene even in BTF. The molecular weight distributions of the synthesized polymers were relatively narrow in both solvents (Mw/Mn = 1.29–1.65). The effect of the increasing reaction temperature (up to room temperature) was also investigated. With increasing reaction temperature, the polydispersity decreased and Mn close to the theoretical one was obtained in BTF at room temperature. Structural analysis with 1H NMR revealed that the major chain breaking reaction in this polymerization is indanyl ring formation between the penultimate monomer unit and the propagating carbocation. These results indicate that BTF can be utilized as a unique, inert, non-volatile, environment friendly solvent with medium polarity for cationic polymerization of styrene, a nonfluorous monomer, and based on these results, presumably it may be also applied effectively as a quite universal solvent for a large array of various polymerizations and copolymerizations for not only fluorinated, but also for nonflourous monomers, and other chemical reactions as well.