Add time:09/01/2019         Source:sciencedirect.com

[PdCl2(dppb)] is highly active in the catalytic CO-ethene copolymerization in H2O–H(CH2)nCOOH (n = 0, 1 or 2). The influence on the productivity, the limiting viscosity number and the average viscosity molecular weight MW¯v of the following reaction conditions is investigated: (i) solvent composition; (ii) temperature; (iii) CO and ethene partial pressure at a given pressure of one monomer; (iv) monomers ratio at a given total pressure; (v) total pressure at CO/ethene = 1/1; (vi) reaction time. The productivity passes through a maximum with a H2O molar fraction of 0.55–0.70 (14,800 gPK(g Pd h)−1 in H2O–HCOOH, H2O molar fraction = 0.58, 45 bar, CO/ethene = 1/1, 90 °C; LVN = 0.48 dLg−1, MW¯v = 21,194 Da). The productivity is in the order of the strength of the acid n = 0 > n = 1 > n = 2, whereas the activation energy is in the opposite order. These findings suggest that the protonation of the resting states β- and ɣ-chelate rings destabilizes them, thus favoring the chain-growing process. Proposed power rate laws fit the productivity data obtained at different monomer pressures. The productivity lowers with time, but in the first hour the rate remains almost constant. The morphology and crystallinity of selected PKs determined by solid state NMR is also discussed.

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