Analysis of the Propoxylation of Zinc-Cobalt Double Metal Cyanide Catalysts with different active Surfaces and Particles Sizes

The action of three different Co/Zn double-metal-cyanide (DMC) catalysts in the propoxylation of polyols was made comparable in a kinetic study, using pulse-wise feeding of propylene oxide (PO). Key insights...


Supporting Catalyst descriptions
showing a sharp reflex at 2θ of 23.7° [3].The XRD pattern of DMC C is consistent with the usual cubic Prussian blue structure type, but intensity and shape of the peaks indicate that parts of the framework have collapsed [4].The XRD pattern of DMC A shows a resemblance to reported dimorphic cubic and hexagonal structures, in which the zinc metal (M) is octahedral respectively tetrahedral coordinated as it shows considerable reflexes at 2θ = 9.9 and 14.4°, belonging to a semi-crystalline Zn 3 [Co(CN) 6 ] phase [3].The reflexes at 2θ of 11.3, 16.5 and 21.7° can be assigned to a hexagonal phase (Zn 3 Co 2 -H) [5], [6].

Reaction profile and experimental data in pulse-decay experiments
Figure S4 Temperature-and pressure profiles and conversion of PO during pulse-decay experiment including drying procedure, activation phase and pulsed PO additions.

Table S1
Parameters and determined reaction rates of all feeding-step experiments with DMC A.

Diffusion and M w dependent Viscosity of the reaction mixture at 120 °C
The self-diffusion of PPGs is quite well-documented, in particular at lower temperatures and smaller molecular masses.[10][11][12][13][14][15] The diffusion constant D may be expected to scale exponentially with molecular mass with a mass dependent exponent between -0.6 (M w (bulk) of ± 2000 Da) to -0.75 (M w (bulk) of 4200 Da).Diffusion constants extrapolated to higher temperatures give molecular weight dependent values of about 10 -11 m 2 /s.Beyond the critical molecular mass of about 7000 Da, D will progressively decrease stronger (exponent reaching down to -2) as entanglements become an issue and mass diffusion becomes more and more determined by reptation [16], [17].The importance of transient networks between PPGs with molecular weights of this study and at the temperature above 100 °C will be negligible [18], [19].
The diffusion of small molecules in PPGs on the other hand is hardly reported upon, a study with camphor quinone (CQ) showed that the Stokes-Einstein dependence reduces to , i.e. the diffusion constant decreases more slowly with viscosity than theoretically.This observation was related to rotation-translational coupling to movements of polymer segments.The viscosity of PPG products at e.g. 120 °C scales with an exponent of 1.07 (± 0.03) with the molecular weight (s.suppl between M w = 2250-16,000 Da).Assuming that similar holds true for PO, leading to , polymer and monomer will deviate increasingly in diffusivity with increasing molecular mass.This is also the result from  On the linearity of (and ) and 1/T under diffusion influenced rates

Attainable PDIs in the set-up
A broadening of a molecular weight distribution can also originate from the reactor set-up.The viscosity of the PPG is increasing with its molecular weight (thus increasing the Kolmogorov smallest domain).making it also more and more challenging to distribute the PO uniformly into the reaction mixture [21].This effect could be traced using a propeller stirrer in the reactor while propoxylating with DMC A (Figure S9(l)).Latter stirrer is less effective at higher viscosities than an anchor stirrer.Now a tail of high molecular weight products is readily formed.broadening the PDI (Figure S9(m)).The effects are even more pronounced when the dosing of PO is faster with possible higher local gradients of PO concentration.These results are in accordance with the usual observations [21], [22], [23].An anchor stirrer is more effective and a narrow distribution is maintained (Figure S9(r)).

Figure S2
Figure S2 Isotherm of DMC A resulted by adsorption measurements with nitrogen.

1 Figure S5
Figure S5 Arrhenius plots of reaction system with from left to right DMC A, DMC B and DMC C showing 95 % prediction band (light grey) and 95 % confidence band (grey).

Figure S6
Figure S6 Eyring plots of reaction system with from left to right DMC A, DMC B and DMC C showing 95 % prediction band (light grey) and 95 % confidence band (grey).Information for Figure 4, S5, S6 DMC/Data displayed used in the regression A All data Data T < 130°C B Data [ROH] > 0.55 mol/L Data [ROH] > 0.55 mol/L C All data All data calculations on data acquired at 7 °C: correcting for the different radii of gyration of CQ (0.35 nm) and PO (~ 0.1 nm), PO would have about 1.5 times the diffusion constant of PPG with M w of 2000 Da and 3 times for a PPG of 4000 Da[10],[18],[20].The viscosity of PPG increases with the weight average mass with exponent of about 1 at the relevant range of temperature and molecular mass (FigureS7; measurements by Dr. Szopinski at our institute).

Figure S7
Figure S7 Dynamic viscosity on theoretical weight average molecular weight of PPGs.

Figure S9
Figure S9 Broadening of the distribution as function of the stirrer geometry or enhanced PO addition rate using DMC A (50 ppm initially) and PPG 2000 as starter at 120 °C.

Table S2
TableS3Parameters and determined reaction rates of all feeding-step experiments with DMC C.

(s•mg DMC •mol)
ln    ln     Calculations were carried out on the linearity of " " in the context of derivation that the

20 kJ/mol 120 kJ/mol 127 kJ/mol 135 kJ/mol T / °C [OH]/k mPO k s (T) k s •K k s (T) k s •K k s (T)
Values for [OH]/k mPO and k s •K are given in 10 -6 mol•s/L and 10 -6 L 2 /(s•mg DMC •mol) Figure S8 Plot of and vs 1/T for activation energies of 120, 127 and 135 kJ/mol.ln   ln

Table S5
Action of single DMC crystals at the first pulse (PPG 2250 mol/L).