G. Yu. Nikolaeva

Polarized Raman study of random copolymers of propylene with olefins

The polarized Raman spectroscopy is employed in the study of structural modifications in the films of isotactic polypropylene (PP) whose chain contains ethylene, 1-butene, 1-hexene, 1-octene, and 4-metyl-pentene-1, which represents an isomer of 1-hexene. It is demonstrated that the phase and conformational compositions of copolymer molecules depend on the comonomer content and the side-chain length of the second monomer. The content of the PP molecules in the helical conformation in the crystalline and amorphous phases of the copolymers monotonically decreases with increasing content of the second monomer. The decrease in the content of helical macromolecules in the crystalline phase is faster than the decrease in the amorphous phase. At a certain content of comonomers, the total content of the helical fragments decreases with increasing length of the side chain of the second monomer. The structures and Raman spectra of the copolymers of propylene with 1-hexene and 4-methyl-1-pentene are similar.

Raman study of ethylene-propylene copolymers and polyethylene-polypropylene reactor blends

The Raman spectra of the ethylene-propylene copolymers (EPC) synthesized using new metallocene catalytic systems and the polypropylene/polyethylene/diblockcopolymer of propylene and ethylene (PP/PE/DBC) blends obtained using the sequential polymerization are studied. The copolymer and reactor blend spectra are analyzed using the Raman spectra of a series of liquid n-alkanes. Significant monotonic changes are observed in the spectra of EPC and the PP/PE/DBC blends when the ethylene content increases. Substantial differences between the series of samples of blends and copolymers are revealed. In contrast to the EPC spectra, the spectra of the PP/PE/DBC reactor blends are represented as an exact superposition of the homopolymer spectra with the weight coefficients proportional to the contents of the blend components. A monotonic blue shift of the line that corresponds to the symmetric stretching mode of the CH2 groups is observed in the EPC Raman spectra when the ethylene content increases. It is demonstrated that, for this line, the peak position only depends on the relative content of comonomers and does not depend on the contents of the PP and PE crystalline phases. The intensity ratio of two fundamental vibrations of PE and PP with frequencies of 1295 and 1330 cm−1 can be used to determine the relative contents of the PE molecules in the trans-conformation and PP macromolecules in the helical conformation in the PP/PE blends. It is demonstrated that variations in the Raman spectra of n-alkanes, EPC, and PP/PE/DBC reactor blends related to variations in the relative contents of various chemical groups are reliably traced in the spectra of all of the materials under study.

Raman study of polyethylene-polypropylene blends

The Raman spectra of the blends that result from the melt mixing of polyethylene (PE) and isotactic polypropylene (PP) are studied. The contents of the blend components can be determined using the ratio of the integral intensities of the PE and PP fundamental vibrations.

Raman spectra of various polymorphs of isotactic polypropylene

The Raman spectra of the α, γ, and smectic modifications of isotactic polypropylene (PP) are studied. The most significant spectral differences are observed in the frequency range around 2960 cm−1 for the spectral doublet assigned to the asymmetric stretching vibrations of the CH3 groups and in the frequency range around 800 cm−1, which is used for analysis of the phase composition of isotactic PP. It is demonstrated that the peak positions and relative intensities of the doublet assigned to the asymmetric stretching vibrations of the CH3 groups can be used to identify the polymorph modifications of isotactic PP.

Quantitative characterization of the orientation of macromolecules in intercalated nanocomposites of polyolefins/layered silicates by Raman spectroscopy

Raman spectroscopy is used to study variations in the orientational order of macromolecules in the uniaxially drawn intercalated nanocomposites based on two polymer matrices (polyethylene (PE) and isotactic polypropylene (PP)) and a filler (modified clay (MC)). The orientation parameters of macromolecules measured using Raman spectroscopy are compared with the X-ray data. It is demonstrated that, for the uniaxially drawn PE-MC and PP-MC intercalated nanocomposites, the filler impedes the orientation along the draw direction for the macromolecules localized in the noncrystalline phase of the polymer matrix. The orientational ability of the PE and PP crystallites in nanocomposites is not affected by the filler.

Raman structural study of reactor blends of ultrahigh molecular weight polyethylene and random ethylene/1-hexene copolymers

For the first time we carried out a detailed Raman study of reactor blends of high-density ultrahigh molecular weight polyethylene (UHMW PE) with random ethylene/1-hexene copolymers (CEHs). The blends were produced by consecutive two-step polymerization in the presence of rac-Me2Si(Ind)2ZrCl2/methylaluminoxane catalyst. The blends differed significantly in the CEH content as well as in the 1-hexene content in the CEH. We revealed a strong dependence of the Raman spectra of the blends on their structure. We found out that an increase in both the CEH content in the blend and the 1-hexene content in the CEH causes a reduction of the blend crystallinity and the total content of trans-conformers, while an increase in the content of gauche-conformers is observed. To investigate the effect of molecular weight on the neat polyethylene (PE) structure and Raman spectrum, we analyzed three neat PE samples with molecular weights of 34 000, 750 000, and 1 000 000. In order to better understand general regularities in the spectra, Raman spectra of solid n-alkanes C18H38 and C36H74 were also studied.

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.

Raman study of uniaxial deformation of single-crystal mats of ultrahigh molecular weight linear polyethylene

We present for the first time a Raman spectroscopic study of the deformation process of solution-crystallized single-crystal mats of ultrahigh molecular weight linear polyethylene (UHMW PE). We study the deformed regions of the films, drawn only until the formation of the neck, and the films of much higher draw ratios, just before rupture starts. For comparison, we have also carried out Raman investigations of films produced by compression of UHMW PE powder. We have found that the uniaxial molecular orientation in the neck region of the single-crystal mat films develops more slowly as compared to the films, prepared by compression of the UHMW PE powder.

Raman structural study of random copolymers of propylene with 1-pentene

Nascent form of random propylene/1-pentene copolymers was studied for the first time by Raman spectroscopy. For the purpose of detailed interpretation of the copolymer spectra, we investigated Raman spectra of neat PP with low and high crystallinity. It was found that the copolymer Raman spectra depend on the 1-pentene content. We registered the most significant spectral alterations in two lines at 809 and 841 cm−1. The first line corresponds to vibrations of polypropylene (PP) isotactic chains in the crystalline phase, while the second one is associated with vibrations of PP isotactic chains having isomeric defects. We found out that increase in the 1-pentene content results in reduction of the copolymer crystallinity and in the content of isotactic chains in the copolymer amorphous phase.

New advances in Raman study of polyvinylchloride structure

Polyvinylchloride (PVC) is one of the most widely used commercial polymers, and the field of its application continues to expand rapidly. Effective development of state-of-art functional materials, such as PVC-based nanocomposites, copolymers, blends and fabrics, subjected to special kinds of treatment, requires elaboration of new, more informative approaches of PVC structure evaluation. Industrial PVC is characterized by variety of states of macromolecules and very low degree of crystallinity. Thus, the best way to evaluate PVC structure is to apply vibrational spectroscopy, the unique feature of which is high information capacity in the study of the different configurational and conformational states of macromolecules. Most of the Raman spectroscopic methods of PVC structure testing were developed more than 20 years ago. Therefore, improvement of the already recognized methods and development of modern computerbased processing of the spectra for the detailed quantitative analysis of PVC structure are important. In this work, we present an extensive study of polarized Raman spectra of a number of industrial grades of PVC powder and films, prepared from solutions of tetrahydrofuran and acetophenone. For PVC itself and residues of the solvents, remained in the films, we determined the number of Raman lines and their spectral characteristics. These data were used to assign accurately PVC Raman lines and to evaluate structure of different grades of PVC powder and films.In this work we investigated Raman spectra of a number of industrial grades of polyvinylchloride powder and films, prepared from solutions in tetrahydrofuran and acetophenone. The number and spectral characteristics of the Raman lines in the spectral regions of the C-Cl stretching vibrations and in the region of the C-H and CH2 stretching vibrations were evaluated.