Alla N. Klyamkina

Homo-and copolymerization of vinylcyclohexane with α-olefins in the presence of heterogeneous and homogeneous catalytic systems

The polymerization and copolymerization of vinylcyclohexane with α-olefins in the presence of several heterogeneous and homogeneous catalytic systems were studied. It was shown that, with respect to activity in the polymerization of vinylcyclohexane, the tested catalysts can be arranged in the following order: α-TiCl3 < titanium-magnesium catalyst < metallocene catalyst. Poly(vinylcyclohexane) prepared with heterogeneous catalytic systems is a solid semicrystalline polymer. The properties of polymers synthesized with homogeneous systems differ substantially depending on the type of the metallocene used. In the presence of metallocenes with a C2 symmetry, crystalline powderlike products arise, while in the case of metallocenes with C1 and C s symmetries, polymerization yields amorphous viscous products. Molecular-mass distributions of poly(vinylcyclohexane) samples prepared using both heterogeneous titanium-magnesium catalysts and homogeneous metallocene complexes show a bimodal pattern, indicating the heterogeneity of active centers of these catalysts. Upon introduction of a comonomer (ethylene, propylene, and 1-hexene) into the reaction mixture, the activity of all studied catalytic systems increases. When Me2C(3-Me-Cp)(Flu)ZrCl2 and rac-Me2SiInd2ZrCl2 are used as catalysts, the degree of crystallinity of the copolymers grows owing to the presence of ethylene or propylene units in poly(vinylcyclohexane) chains.

Using Raman spectroscopy to determine the structure of copolymers and polymer blends

We present Raman structural study of two grades of random propylene/1-octene copolymers with low and high molecular weights and the 1-octene content up to 4.5 mole %. The copolymer spectra are compared with the spectra of the α, γ, and smectic modifications of isotactic polypropylene. Raman investigation has showed that the degree of crystallinity and conformational order of the copolymer macromolecules slightly decrease with the growth of the 1-octene content. The degree of crystallinity is slightly higher for the samples of the high-molecular-weight grade compared to the low-molecular-weight one. Furthermore, we present Raman spectra of polyethylene/polypropylene (90/10) blends, mixed in the polyethylene melt at three different temperatures, corresponding to three different states of polypropylene macromolecules. It was concluded that the degree of crystallinity and conformational order of the polyethylene macromolecules in the blends are the highest for the temperature, at which polypropylene macromolecules have lost their packing and conformational order.

Biodegradation of Poly-ε-caprolactones and Poly-l-lactides by Fungi

This work assessed biodegradation, by Aspergillus, Fusarium, Penicillium and Parengyodontium fungi, of four samples of poly-ε-caprolactone (PCL), three samples of poly-l-lactide (PLA) and one sample of poly-d,l-lactide (DL-PLA) produced by ring-opening polymerization initiated by aluminium complexes of corresponding lactones. Mesophilic fungal strains actively biodegrading PCL (F. solani) and PLA (Parengyodontium album and A. calidoustus) were selected. The rate of degradation by the selected fungi was found to depend on the physicochemical and mechanical properties of the polymers (molecular weight, polydispersity, crystallinity). The most degradable poly-ε-caprolactone sample was shown to have the lowest molecular weight; the most biodegradable polylactide DL-PLA had the lowest crystallinity. Mass spectral analysis of biodegraded polymer residues showed PCL to be degraded more intensively than PLA. It is established that in the case of Parengyodontium album the colonization of the films of polypropylene composites with DL-PLA is observed, which will undoubtedly contribute to their further destruction under the influence of abiotic factors in the environment.

New insights into the structure of polypropylene polymorphs and propylene copolymers probed by low-frequency Raman spectroscopy

We present a low-frequency (or low-wavenumber) Raman spectroscopy study of isotactic polypropylene, namely the different modifications - α, γ, and smectic, with a degree of crystallinity ranging from 0 to 70 %, as well as of random propylene/1-butene and propylene/1-octene copolymers with the incorporated monomer contents of 5.3 and 19.5 mol % for 1-butene and 4.5 and 24.0 mol % for 1-octene. In the Raman spectra of the propylene/1-octene copolymers and the neat isotactic polypropylene, we have found that the band at 105 cm−1, which is connected to the torsion vibrations of CH2-CHCH3 groups in the polymer backbone, can be assigned to the vibrations of helical macromolecules in the α and γ crystallites and the smectic phase. If the smectic phase is absent in the corresponding polymer system, then the intensity of the 105 cm−1 band is related to the molecular vibrations in the crystallites. We have also observed a broadening of the band at 398 cm−1 accompanied by the appearance of a high-wavenumber shoulder in the Raman spectra of the copolymers with the increase in the incorporated monomer content. This experimental finding can be explained by the reduction of the degree of crystallinity, conformational disordering or by the increase in the dimensions of the crystal unit cell.