Cationic polymerization of butadiene and copolymerization of butadiene and styrene

Abstract

The cationic polymerization of butadiene with several Friedel‐Crafts catalysts has been described. Aluminum chloride and chlorosulfonic acid are active catalysts at −75°. The rate of polymerization at −75° is much faster than at the higher temperatures. Except for boron trifluoride etherate, which catalyzes the polymerization at −30°, the other catalysts (sulfuric acid, fuming sulfuric acid, stannic chloride, and boron trifluoride hydrate) produce appreciable amounts of polymer only at 0° or higher. The effect of variables, such as catalyst concentration, catalyst solvent, dilution, reaction time, etc., differs with each individual catalyst. In some cases, results were not conclusive due to lack of reproducibility. It was found that the presence of moisture is mainly responsible for this lack of reproducibility. Traces of water promote the polymerization with stannic chloride or boron trifluoride etherate, but inhibit the polymerization when an ethyl bromide solution of aluminum chloride is used as catalyst. Rubberlike polyhutadienes can be obtained with all catalysts except sulfuric and fuming sulfuric acids. However, the physical properties of these polymers show that the molecular weight is very low and that the polymer is not suitable as a rubber. Polymers ranging from viscous liquids to hard, brittle solids have also been obtained. In general, the solubility of the polymers is low. Approximately 60% of the butadiene enters the polymer chain by 1,4 addition. The copolymerization of butadiene and styrene at −75° with an ethyl bromide solution of aluminum chloride has also been studied. At conversions between 20 and 30% a soluble, rubberlike copolymer having a low molecular weight is formed. An insoluble, brittle polymer is obtained a t higher conversions. The soluble, cationic copolymer has a characteristic ultraviolet absorption curve which is different from that of GR‐S. It has a styrene content of approximately 50% by weight which demonstrates that the styrene is more active in cationic copolymerization than is butadiene.

Structural characterization of polybutadiene synthesized via cationic mechanism

“…Considerably, less attention is paid to the investigation of cationic polymerization of 1,3‐butadiene . This is consistent with the high sensitivity of the cationic polymerization to impurities in the monomer as well as with the complexity of the structure of cationic polybutadiene (CPB) . In previous works, the structure of CPB was investigated by infrared spectroscopy.…”

Cationic polymerization of butadiene using alkyl aluminum compounds as co-initiators: an efficient approach toward solid polybutadienes

“…Similar kinetic dependences were found earlier for the cationic polymerization of 1,3-pentadiene and isoprene co-initiated by AlCl 3 or alkylaluminum halides. 6–8,15,31–34 The reasons for such behavior are not clear to date. 13…”

“…On the other hand, the synthesis of LMWPB by cationic polymerization of butadiene has also been described in the literature. 5–19 The key advantages of cationic polymerization are a high reaction rate, the relatively low cost of catalytic systems and the possibility to prepare low molecular weight polymers without the necessity to regulate the molecular weight. The main drawback of the cationic polymerization of butadiene is the formation of a cross-linked, insoluble in organic solvents polymer due to the intensive chain transfer to the polymer.…”

“…In a series of early works, 6–10,14–16 it was shown that during the cationic polymerization of butadiene in the presence of AlCl 3 , AlBr 3 , SnCl 4 , TiCl 4 and BF 3 ·OEt 2 , completely soluble polybutadienes are formed only at low monomer conversions. The formation of an insoluble fraction (IF) was typically observed at high monomer conversions.…”

“…Cationic LMWPB synthesized in previous works 6–10,14–17 are typically viscous liquids. However, isolation, transportation and dosage of such polymers complicate the technology of their use and production.…”