K. Alyürük

Fractionation of partially stereoregular poly(propylene oxide)

Abstract Partially stereoregular poly(propylene oxide) samples were synthesized via reactions catalysed by a preformed analytically defined trimethylaluminium hydrolysate. These samples were fractionated into two contrastingly different fractions. 1. (i) D-polymers: This fraction constituted the major part (up to 90%). It mainly contained cyclic low molecular weight oligomers (MW 2. (ii) K-polymers: This fraction was high molecular weight stereoregular polymer. Stepwise thermal precipitation from dilute isooctane solution of K-polymers yielded a succession of fractions which differed in melting point. It appears that the phase equilibria during the thermal precipitations were not controlled by the molecular weights of species.

Polymerization of propylene oxide by the Pruitt-Baggett catalyst

Abstract The Pruitt-Baggett adduct (PBA) which formed from the reaction of FeCl3 with propylene oxide (PO) was hydrolysed in diethyl ether (ether) solutions at different r = H 2 O Fe mole ratios. Although the hydrolysates were insoluble in ether they could be converted into PO-soluble form (PBC) by a thermal treatment providing that the r value was kept smaller or equal to unity. PBC polymerized PO concurrently into a mixture of high molecular weight crystalline polymer with low molecular weight non-crystallizable oligomers. The traces catalytic activity shown by PBA substantially enhanced as the hydrolysis ratio r, increased from 0 to 0.5. Although the PBC obtained at r = 0.50 gave maximum yield of polymer, the maximum stereoregular yield (crystalline polymer/oligomer mass ratio) was observed at r = 2 3 mole ratio.

Column fractionation of partially stereoregular poly(propylene oxide)

Abstract A column packed with glass beads has been used to fractionate partially stereoregular poly(propylene oxide) (PPO). PPO was first crystallized onto the glass beads from isooctane solution by stepwise lowering the column temperature. Each layer of PPO, which was deposited at different temperature ranges, was extracted by washing the beads with several columns full of isooctane. Thus several fractions differing in both stereoregularity and molecular weight were obtained by progressively increasing the extraction temperature and the solvent residence time in the column. It is concluded that in the procedure described above PPO can be fractionated on the basis of structural and steric regularity. The observed steady increase in the molecular weight of fractions with extraction temperature was interpreted as being due to the fact that the stereoregularity of chains increases with their molecular weight.

Stereoregular polymerization of propylene oxide by bis-dimethylaluminium oxide

Stereoregular polymerization of propylene oxide (PO) by bis-dimethylaluminum oxide (BMAO) was studied. It is found that at 80°C a relatively high initial rate of the process rapidly dies away. By measuring and identifying the evolved by-product gases of the polymerization it was concluded that the decay of the rate is due to the transfer of a proton from the methyl (Me) group of PO, to the Me-Al groups of BMAO, by forming an aluminium allylalkoxide bond and a methane molecule. However, this transformation (and also the alcoholysis of Me groups of BMAO with several alcohols) apparently increases the stereoregular yield of the process. The polymerization process as well as the ionization of BMAO and the transport properties of ions were studied in the presence and absence of solvents, additives and monomer. Although BMAO extensively ionizes in the polymerization solution, the stereoregular yield of process increases as the dielectric constant of the media decreases. On the basis of present data the mechanism of polymerization was discussed.

Monomer-bound ion pairs in the stereoregular polymerization of propylene oxide by the Pruitt-Baggett catalyst

Abstract The Pruitt-Baggett adduct (PBA) (MW = 438 g mol−1) that formed from the reaction of FeCl3 with propylene oxide (PO) was hydrolysed in diethyl ether (ether) solutions at different r = H 2 O Fe molar ratios. The hydrolysates ( PBH r ), which were insoluble in ether, could be converted into catalytically active form ( PBC r ) by a thermal treatment. PBC r (r was soluble in etheric solvents and in pyridine. These solutions, in contrast to PBA and PBH r , were electrical conductors. Profound differences in the electrical conductivity of PBC r was observed by varying the hydrolysis ratio r. The observed conductivity decayed and finally vanished with a kinetically second-order process. This is explained by the free ions, formed from PBC 0.67 (MW = 4400 g mol−1), being bound together with an ether (or PO) molecule to yield ether- (or PO-) bound ion pairs (PBCB). PBC 0.67 and the electrical conductivity of its freshly prepared solutions could be retrieved by ‘driving off’ (by drying under vacuum at 40°C) the ‘binding molecule’ (ether or PO) from PBCB. In contrast to this system, the electrical conductivity of solutions of PBC 0.20 (which shows inferior catalytic activity) did not change with ageing.

Polymerization of propylene oxide and copolymerization of carbon disulphide and propylene oxide with xanthate salts

Abstract Anionic polymerization of propylene oxide (PO) using several xanthate salts was studied. Low molecular weight oily polymers with variable sulphur content were obtained by using either potassium ethyl xanthate or potassium benzyl xanthate. The highest attainable conversion of PO was limited to ca 10%. The polymerization was accompanied by formation and precipitation of a by-product salt. In the presence of CS 2 , an oily copolymer with about 40% sulphur was obtained from the above mixtures. In reaction systems with CS 2 /PO mole ratio larger than unity, all the PO in the feed could be copolymerized without precipitation of salt. Zinc isopropyl xanthate (ZnXt 2 ) polymerized PO into a partially stereoregular high polymer. Addition of CS 2 to PO and ZnXt 2 solution yielded high copolymers with monomeric unit ratios (CS 2 /PO) of 0.06–0.15.

Polymethylaluminium oxide and stereoregular polymerization of propylene oxide

Abstract Polymethylaluminium oxide (PMAO) was prepared by reacting trimethylaluminium (AlMe3) with water in dilute dioxane solution. Several PMAO samples with different degrees of polymerizations (DP) were prepared (1 ⩽ DP ⩽ 7) either by changing reaction conditions or by fractionating the products. PMAO with DP about unity was found to be trimeric in dilute dioxane solutions but, in higher dielectric solvents, it partially dissociated into free ions. Electrical conductance measurements showed that the initially present ion-pairs were converted into another type of ion-pairs (solvent-bound ion-pairs) with a lower dissociation constant as the solution was aged. Catalytic activities of several PMAO samples in the stereoregular polymerization of propylene oxide were studied. Only a slight improvement of the stereoregular yield was observed by increasing the DP of the used catalyst. It was concluded that the methylaluminium oxide repeating units are the active species in the stereoregular polymerization and catalytic activity cannot be ascribed either to the presence of an “undetected impurity” or an “unidentified unique structure of PMAO”.

A mechanistic study on the polymerization of n-butyl isocyanate by pruitt-baggett adduct

Abstract The mechanism of the polymerization of n-butyl isocyanate by the Pruitt-Baggett adduct (PBA) was studied; on the basis of the experimental evidences, a coordinated mechanism was proposed and verified. This mechanism considers a monatomic active site, which is the Fe atom of PBA with Lewis acid character. The N atom of the isocyanate monomer is coordinated by the Fe atom and the resultant positive charge is transmitted to another N atom which covalently binds the growing chain to the active centre. Thus the formed ammonium ion is added to the incoming monomer yielding Nylon-1 structure and the active site is regenerated.

Dipole moments of isotactic and atactic poly(propylene oxide) samples

Abstract Dipole moments of poly(propylene oxide) (PPO) samples with different tacticities were determined from dielectric constant and refractive index increment measurements, which were performed on dilute toluene and isooctane solutions. In contrast to previous reports, both refractive index increments and the dipole moment ratios showed a marked dependence on the tacticities of the samples. The dipole moment ratios of isotactic samples were greater than unity and decreased with increasing sequence concentrations of structural irregularities. The temperature coefficients in toluene were negative for both isotactic and atactic samples. No effect of excluded volume was observed.

Investigation of Chlorinated Poly(Propylene Oxide) and Polyepichlorohydrin by Direct Pyrolysis Mass Spectrometry

The thermal degradation of chlorinated poly(propylene oxide) and polyepichlorohydrin samples were studied with the use of direct pyrolysis mass spectrometry. The data indicated that chlorine atoms were gathered on some repeating units leaving the rest intact in case of chlorinated poly(propylene oxide). On the other hand, a more homogenous structure with a uniform thermal behavior was detected for chlorinated polyepichlorohydrin.