Propylene oxide monomer

The propylene oxide complex was rather unstable and dissociated partially to its components in solution as shown by the molecular weight determined cryoseopically in benzene. This instability corresponds to the low electron donating power of the propylene oxide monomer as well as to the low electron accepting power of the catalyst. 

A final example of a stereoselective heterogeneous catalytic system is the work of Laycock, Collacott, Skelton and Tchir.17 Layered double hydroxide (LDH) synthetic hydrotalcite materials were used to stereospecifically polymerize propylene oxide [PO] to crystalline isotactic and liquid atactic poly(propyleneoxide) [PPO]. These authors suggest that the LDH surface acts as other inorganic or organometallic coordination initiators or catalysts by providing specific surface orientations for propylene oxide monomer. X-ray powder diffraction showed some loss of crystallinity after calcination and X-ray photoelectron spectroscopy showed an enhancement of Mg/Al content due to restructuring of the Mg and A1 surface atoms. The surface was also rich in Cl ... 

The polymeric chains are assumed to grow on sites available for propylene oxide monomer but not on oxygen adsorption sites. 

On the basis of the above assumptions one can write the following transient mass balances for gaseous propylene oxide, adsorbed propylene oxide monomer and sites covered by i-mer respectively ... 

The enumeration and geometry of the possible stereoregular structures of polypropylene oxide illustrate the value of the above concepts of symmetry. Propylene oxide monomer has a truly asymmetric carbon, and the repeat unit in the polypropylene oxide chain can be either of the two optical isomeric... 

Anionic polymerization of a substituted epoxide such as propylene oxide yields only low molecular weight (< 5000) polymers as chain growth is severely restricted by chain transfer to monomer. The transfer reaction becomes more prevalent as the substituent group possesses hydrogen atoms on the a-carbon atom. The chain transfer to propylene oxide monomer occurs by proton abstraction from the methyl group attached to the epoxide ring (Young and Lovell, 1990) ... 

Studies using a deuterated version of 9 revealed that the non-coordinating l-methoxypropan-2-olate groups initiated the polymerization by attack on the propylene oxide monomer, whereas the coordinated l-methoxypropan-2-olate groups provided the chiral structure, which remained unchanged during the polymerization. When these... 

This order is quite different from the one found for the corresponding propylene oxide monomer, although the former roughly runs inversely parallel to the latter, as shown in Figure 3. 

The polymerization kinetics were studied in detail. It appeared that the rate of reaction decreased as the concentration of complex increased. This anomalous behavior was explained in terms of the ability of all the zinc atoms in the complex to form coordination complexes with propylene oxide monomer, but only the inner methoxyls were effective in opening the oxirane ring of monomer coordinated with the central zinc atom. In support of this explanation, it is noted that neither diethylzinc alone nor ethylzinc methoxide initiate propylene oxide polymerization under the conditions described here however, both will form complexes with propylene oxide, about two methyl oxiranes per zinc. Addition of either zinc alkyl to Tsuruta Catalyst/... 

In the presented simulations we started from a homogeneous solution, then quenched the solution to the proper Flory Huggins values for the inhomogeneous system. During the subsequent collective diffusive relaxation, the free energy goes down and order parameters go up. The indicated results (Figure 7.3) are snapshots of the isodensity surfaces of the propylene oxide monomer... 

---