Electrochemical synthesis of polyesters and polyamides. A study of the polymerisation of lactams, lactones and the anhydride/propylene oxide system by direct electrolysis of their conducting solutions

Preliminary experiments describe the electroinitiated polymerisation of phthalic anhydride/propylene oxide, maleic anhydride/propylene oxide, caprolactam, laurolactam and E-caprolactone in N,N-dimethylformamide (DMF), acetonitrile and tetrahydrofuran (THF) using alkali metal salts or quaternary ammonium salts as supporting electrolytes. Electrolysis were performed in the single and divided cell under an atmosphere of purified nitrogen. Polymerisation of propylene oxide/phthalic anhydride occurred in both cells. In the case of the divided cell the polymerisation occurred in both compartments but the yield and molecular weight of products were low. Similarly polymerisation of propylene oxide/maleic anhydride occurred in both cells and in the case of t.he divided cell in both compartments when using DMF as solvent. Polymerisat:lon of caprolactam and laurolactam did not occur in either of DMF or acetonitrile solution. In DMF/alkali metal salts polymerisation of E-caprolactone occurred readily in the cathode compartment only whereas polymerisation in DMF /quaternary ammonium salts polymerisation occurred in both compartments. The conversion of E-caprolactone in the single cell was very low when using DMF/alkali metal salts but in the case of divided cell the conversion in the cathode compartment was 100%. The rate of disappearance of E-caprolactone with time was determined by gas-liquid chromatography. The gas-liquid chromatographic analysis showed that three oligomeric products were formed apart from polymer which were identified by the use of ·various analytical techniques. A detailed investigation into the kinetics and mechanism of electropolymerisation of E-caprolactone in DMF and using LiCl or KNO3 as supporting electrolyte was undertaken. In the case of both supporting electrolytes it was found that the initial rate of polymerisation was directly proportional to the initial monomer concentration and the current. Further experiments showed that two initiating species were produced during the electrol:y.sis of DMF/LiCl. An acceleration in the rate of polymerisation was apparent which considered to be due to the formation of second type of initiating species. Some transfer to solvent took place. The molecular weight and % yield was independent of the current. The kinetics and mechanism of electropolymerisation of E-caprolactone in THF and NaBPh4 was studied. The results showed a "living" system but it was found that the increase of initial monomer concentration, the molecular weight did not increase. It was also found that calculated molecular weights and molecular weights obtained by viscosity measurement showed a remarkable agreement. In this system some oligomeric products were formed apart from polymer but there was no dimer peak present in the GLC trace as in the case of DMF alkali metal salts. Block copolymerisation of styrene and E-caprolactone was attempted by preparing living polystyryl anions electrochemically followed by the addition of E-caprolactone. The analysis by differential scanning calorimetry and gel permeation chromatography showed that the attempted block copolymer was composed of entirely mixtures of two homopolymers. The poly (E-caprolactone) produced was found to be highly crystalline and crystallite size was also calculated. The other properties were found to be similar to those reported in the literature. Cyclic voltammetry experiments showed that the monomer is not reduced directly but instead alkali metal ions are reduced to alkali metals which either react with the monomer to produce radical anions which dimerise very quickly or react with DMF to produce some active species which are believed to be DMF dianions.

URI

https://bradscholars.brad.ac.uk/handle/10454/20283

Type

Thesis

Qualification name

PhD