Synthesis Of Polyacrylonitrile Via Living/Controlled Radical Polymerization

Polyacrylonitrile (PAN) is an important polymer precursor that possesses outstanding chemical and physical properties. Narrow polydispersity is an essential requirement for synthesis of high-performance PAN. The living/controlled radical polymerization proves to be the desired polymerization technique for PAN with low polydispersity, since it provides a route to the facile synthesis of well-defined polymers with definite architecture, predetermined molecular weight and narrow molecular weight distribution. In this ariticle, narrow polydispersity PAN was synthesized via activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP) and single electron transfer living radical polymerization (SET-LRP), respectively. The conversion was determined gravimetrically. The molecular weight and polydispersity index (PDI) of polymers were measured by gel permeation chromatography (GPC). The end-group of PAN was investigated via 1HNMR.Narrow polydispersity PAN was prepared via AGET ATRP in homogeneous system. The polymerization was conducted with acrylonitrile (AN) as the monomer, carbon tetrachloride (CCl₄) as the initiator, copper bromide (CuBr₂)/iminodiacetic acid (IDA) as the catalyst precursor and ascorbic acid (VC) as the reducing agent in solvent N,N-dimethylformamide (DMF). The first order kinetic plot demonstrated the features of living/controlled polymerization as evidenced by a linear increase of molecular weight with respect to monomer conversion and narrow molecular weight distribution. The effects of the amount of ligand, catalyst, initiator as well as reducing agent and polymerization temperature on the polymerization were also investigated. The experiments results showed that the ratio of [AN]:[CCl₄]:[CuBr₂]:[IDA]:[VC]=200:1:1:2:0.75 gave the best control on the polymerization with PDI at 1.25. The polymerization rate increased with increasing the polymerization temperature. The apparent activation enthalpy was calculated to be 35.9 kJ/mol.Narrow polydispersity PAN was prepared via AGET ATRP in in homogeneous system. The polymerization was carried out with AN as the monomer, CCl₄ as the initiator, ferric trichloride (FeCl₃)/lactic acid (LA) as the catalyst precursor and VC as the reducing agent in solvent DMF. The first order kinetic plot demonstrated the features of living/controlled polymerization as evidenced by a linear increase of molecular weight with respect to monomer conversion and narrow molecular weight distribution. The effects of the amount of ligand and initiator, polymerization temperature and different ligands on the polymerization were also studied. When the ratio of [AN]:[CCl₄]:[FeCl₃]:[LA]:[VC]=200:1:1:2:0.75, the polymerization showed the best control over the molecular weight distribution and PDI=1.20. Increasing the polymerization temperature could enhance the polymerization rate. The apparent activation enthalpy was calculated to be 32 kJ/mol.Narrow polydispersity PAN was prepared via AGET ATRP in emulsion using the procedure of"two-step". The polymerization was conducted with AN as the monomer, CCl₄ as the initator, copper chloride (CuCl₂)/hexamethylenetetramine (HMTA) as the catalyst, VC as the reducing agent and polyoxyethylene lauryl ether (Brij 35) as the surfactant. The first order kinetic plot demonstrated the features of living/controlled polymerization as evidenced by a linear increase of molecular weight with respect to monomer conversion and narrow molecular weight distribution. The effects of the amount of ligand and monomer as well as polymerization temperature on the polymerization were also discussed. The experiments results demonstrated that the suitable crude ratio of [AN]:[CCl₄]:[CuCl₂]:[HMTA]:[VC] was 200:2:1:2:1.5. The polymerization rate increased with the increase of polymerization temperature. The apparent activation enthalpy was calculated to be 65 kJ/mol.Narrow polydispersity PAN was prepared via SET-LRP in heterogeneous system. The polymerization was carried out with AN as the monomer, Cu(0) power as the catalyst, CCl₄ as the initiator and HMTA as the ligand in solvent DMF or mixture of DMF and H₂O at 25°C or 65°C. The first order kinetic plots at both temperatures demonstrated the features of living/controlled polymerization as evidenced by a linear increase of molecular weight with monomer conversion and narrow molecular weight distribution. The effects of the amount of ligand, catalyst, initiator and solvent on the polymerization were also probed. The experiments results demonstrated that monomer conversion increased with the increase of ligand. Almost no polymerization occured in the absence of ligand due to the poor disproportionation reaction of Cu(I). The polymerization rate exhibited an increase with the increase of the amount of catalyst Cu(0)/HMTA. Better control on the molecular weight distribution was produced with the addition of CuCl₂. The polymerization rate increased with increasing the amount of CCl₄. H₂O enhanced the polarity of mixted solvent, and further led to the increase of polymerization rate.