Green Polymer Materials Polyketide Synthesis

Polyketone (poly-3-oxotrimethylene), alternating copolymer of ethene and carbon monoxide has attracted considerable interest from both academia and industry over the last decades since 1980'. Polyketone is predicted to be an environment-friendly synthetical material with perfect integrated properties, typical for generalplastic, engineeringplastic, fiber and film. The carbonyl groups containing in polymer backbone abundantly make the material photodegradable. Also, the carbonyl group can be used for derivatization to a variety of interesting new materials. The base materials are readily available, furthermore, considerable CO can be regained from industrial exhaust gases.In the paper, with Pd(AcO)₂DPPP as catalytic precursor, CO/C₂H₄ alternating copolymerization was studied deliberately from many aspects, the effects of various reaction conditions on copolymerization rate and molecular weight, polykeone structure, copolymerization. mechanism and environment-friendly property etc.Copolymerization reaction conditions, including stirrer speed, precursor concentration, DPPP:Pd, reaction temperature, pressure, water content, acid, solvents and reaction time, were investigated in detail, especaially effects on copolymerization rate and molecular weight. The following conclusions were obtained.(1) The copolymerization reaction involved simultaneous absorption of C₂H₄ and CO followed by a catalytic reaction leading to a solid product. Therefore, it was important to ensure that gas-liquid mass transfer steps (dissolution of C₂H₄ and CO) were not rate limiting. The experiments showed that rate of copolymerization was independent of stirrer speed beyond 300 rpm and linearly dependent on catalyst loading (from 0 to 0.24mmol/L of the precursor).It indicated copolymerization was in kinetic regime properly when stirre rate was 600～800rpm and precursor concentration was 0.04～0.1mmol/L.(2)An excess or less of diphosphine which depresses the catalytic activity, therefore the fitting ratio of DPPP:Pd was1.5.(3) Temperature was the most important factor in copolymerization. The apparent activation energy from the Arrhenius plot was evaluated as 51.9kJ/mol. Supposing constantpressure, the equation of temperature and rate was gained, InR= - 6242.4/T+19.Too high temperature involved precursor deactivation for precursor decomposition or reduction from Pd²⁺ to Pd⁺, Pd⁰ and Pd_met. Morever, increasing temperature led to molecular weight less. Rising temperature from 70℃ to 80℃, molecular weight dropped from 68894 to 32581.As a conclusion, polyketone was synthesized with molecular weight 16000 or so,it was better when temperature was 90～100℃, and the perfect was 95 ℃.(4) Adding pressure was in favor for the increase of rate and molecular weight, and corresponding CO ratio(mol/mol) should be 45～55%(5) Water content in methanol solvent was sensitive to copolymerization rate,as far as molecular weight was concerned, it made no difference. Copolymerization rate can be maintained higher in presence of 1～1.5%(w %) and when water content was1.15%, the highest copolymerization rate could be obtained.(6) Acid, as a co-catalyst, had an complicated effects on copolymerization rate. H₃PO₄ and CF₃COOH depressed the catalytic activity. While, TsOH, H₂SO₄and HClO₄ promoted catalytic activity and involved the increase of copolymerization rate, the effect of H₂SO₄ was the perfect .At the same time, the ratio of acid:Pd also played an important role. When the ratio of H₂SO₄:Pd=100, the highest copolymerization rate reached 11.21 kg/gPd·h. The effects of Acid on molecular weight was favoring, especially, the addition of HClO₄, the largest molecular weight was 34199,4 times than the blank one.(7) Solvent was not only thinner but also an important promoters.Experiments showed both methanol and acetic acid were available solvents. Copolymerization rate in methanol was as much as 1.9 times than the one in acetic acid. However, as for molecular weight, it was 16000 or so in methanol, less 60% than the one in acetic acid.(8) It was found that reaction half-life was 6h. When reaction time was 1.5h²h, the catalytic activity maintained active constantly. With reaction time prolonged, catalytic activity began to drop gradually.The structure and properties of polyketone were characterized by IR., ¹H-NMR and ¹³C-NMR. It indicated that the backbone chain of polyketone mainly consisted of constitutional-unit,-CH₂CH₂CO- and thimbleful fragmental unit, -CH₂CH₂CH₂CH₂CO-. The structures of end-groups were proved to be ester (-COOCH₃) and ketone(-COCH₂CH₃).In terms of experimental results and available research literatures, the machanism of CO/C₂H₄ alternating copolymerisation was considered that the copolymerisation was made up of chain initiation, chain propagation and chain termination.End group analysis of the CO/C₂H₄ copolymer by ¹³C NMR has demonstrated the presence of 50% ester (-COOCH₃) and 50% ketone (-COCH₂CH₃) groups. These observations explained by assuming two initiation and two termination mechanisms for polyketone formation. One initiation pathway produced ester end groups.It started with a palladium carbomethoxy species (PdCOOR). Alternatively, another activity species palladium hydride (PdH), produced a ketone end group.Two relevant termination mechanisms were proposed. One mechanism, protolysis of the palladium-alkyl bond, produced a saturated ketone end group. A second mechanism, the alcoholysis of the palladium-acyl bond, gived an ester end group.For CO/C₂H₄ copolymerization, the two alternating propagation steps were migratory insertion of CO into the palladium-alkyl bond and migratory insertion of ethene into the resulting palladium-acyl bond.Propagation "errors" (double ethene insertion) were also observed.Photodecomposition experiment were carried out in 18 days.It demonstrated polyketone was photodegradable by UV-irradiation, as far as molecular weight was concerned, its UV-photodecomposition half-time was 5days and it dropped from 26352 to 7892 in 18 days. As for structure, IR spectrum of polyketone was almost unchanged in contrast with the unirradiated sample. It demonstrated that the structue of polyketone was not destroyed during photodecomposition.Therefore, polyketone was an innovatory environment-friendly polymeric material.