Pavel Schmidt

Stretching and deformation vibrations of CH2, C(CH3) and O(CH3) groups of poly(methyl methacrylate)

Abstract Infrared and Raman spectra of atactic PMMA and infrared spectra of stereoregular PMMA and of its four deuterated derivatives , were measured. They were used to assign the bands of stretching and deformation vibrations of CH 2 , CCH 3 and OCH 3 groups in the infrared and Raman spectra and to discuss the effect of stereoregularity on these bands in the infrared spectra.

Conformational structure of bisphenol A polycarbonate studied by infra-red spectroscopy

Abstract Infra-red spectra of amorphous and partly crystalline bisphenol A polycarbonate were measured. Based on the temperature dependences of the infra-red spectra of the polycarbonate and its model compound, diphenyl carbonate, infra-red bands sensitive to transitions between the trans-trans and trans-cis conformations of the carbonate group were determined. Using the spectral data obtained for the polycarbonate solution in chloroform, the enthalpy change ΔH for the trans-cis to trans-trans transition was estimated to be ∼0.5 kcal mol −1 . Infra-red spectra of solid polycarbonate suggest that the interchain forces in the crystalline state stabilize the less favoured conformation of the carbonate group, most probably the trans-cis structure.

Conformational study of poly(α,β-L-aspartic acid)

The conformation of poly(α‐L‐aspartic acid) was investigated on a sample in which β‐bonds were not detected. CD and ir spectroscopy showed that poly(α‐L‐aspartic acid) passes through a conformational change induced by changes of the degree of ionization that is accompanied by precipitation; the precipitate is probably highly helical. The change was also detected by potentiometric titration.

Structural modifications of hexagonal crystalline polyoxymethylene. Infra-red and X-ray study

Abstract Infra-red spectra and X-ray diagrams of polyoxymethylene samples prepared in various ways, of trioxanedioxolane copolymers and of a polyoxymethylene-polydioxolane blend were obtained. With hexagonal crystalline polyoxymethylene (HCPOM), it is possible to prepare two forms, A and B, differing in their infrared spectra; with copolymers, the maximum attainable content of form A rapidly decreases with increasing content of oxyethylene units in the chain. Form A could not be prepared in the polyoxymethylene-polydioxolane blend. Infra-red spectra of the two forms, A and B, of HCPOM differ in the vibrational interactions of neighbouring chains; these interactions are large in form A and small in form B. The possible structures of the A and B forms of HCPOM are discussed.

Vibrational spectra of hexagonal crystalline polyoxymethylene

Abstract Infrared and Raman spectra of two hexagonal crystalline forms of polyoxymethylene were measured, and the characteristic infrared bands have been determined. The Raman spectra of these two forms do not differ. The vibrational spectra of both forms can be explained by the occurrence of defects in the helical structure of one of them.

Temperature changes of infra-red bands of poly(methyl methacrylate)

Abstract Studies were made of the changes with temperature of infra-red bands of poly(methyl methacrylate). of its deuterated analogues and of methyl acetate. It was found that the large changes of the maximum intensities of bands of antisymmetric vibrations of the ester methyl group are caused by rotation about the oxygen-methyl bond.

Role of hydration and water coordination in micellization of Pluronic block copolymers

Raman, attenuated total reflectance FTIR, near-infrared spectroscopy, and DFT calculations have been used in a study of aqueous solutions of three tri-block copolymers poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) or PEO-PPO-PEO with commercial names Pluronic PE6200, PE6400 and F68. It is shown that the process of micellization as a response to increased temperature is reflected in the hydroxyl stretching region of infrared and Raman spectra, which contains information both about restructuring of water and changes of polymer chains in polymer/water aggregates. Raman spectra exhibit differences between individual Pluronics even at temperatures below the critical micellization temperature (CMT). According to the attenuated total reflection (ATR) FTIR spectra, the same five water coordination types defined by the number of donated/accepted hydrogen bonds are present in interacting water as in bulk water. It indicates that models considering mixed states of water with different hydrogen bonding environments provide appropriate descriptions of bound water both below and above the CMT. Above the CMT, aggregate hydration increases in the order PE6400 < PE6200 < F68, although that does not fully correspond to the EO/PO ratio, and points to the differences in microstructure of aggregates formed by each copolymer. This study relates nanoscale phenomena (hydrophobic and hydrophilic hydration) with the mesoscale phenomenon of micellization.

Conformation of poly(glutamic acid) and of poly(aspartic acid) in the solid state. X-ray diffraction, infra-red and 13C cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopic study

Abstract In order to assess the manifestation of possible conformations of poly(amino acids) in 13C cross-polarization/magic angle spinning nuclear magnetic resonance (CP/MAS n.m.r.) spectra, the conformational structures of poly(α- l -glutamic acid) (poly(Glu)), of poly(α-L-aspartic acid) (poly(Asp)) and of irregular poly(α,β,- dl -aspartic acid) in the solid state were studied by X-ray diffraction and infra-red spectroscopy and compared with the results of 13C CP/MAS n.m.r. spectroscopy. None of the methods alone can fully characterize the conformation; by a combination of the results it could be determined that poly(Glu) and poly(Asp) in the free acid form exhibit both α-helical and β-structure, whereas the random-coil structure predominates in their sodium salts. Both the free acid and the sodium salt of poly(α,β- dl -Asp) exist predominantly in the random-coil form. It turns out that the sodium salts are especially suitable for determining the n.m.r. characteristics of the random-coil conformation in the solid state. The dynamic behaviour studied by the spin-lock cross-polarization experiment indicates that the studied poly(amino acids) in the free acid form are much more rigid than, for example, the poly(alkyl methacrylates).

Structure and vibrational spectra of the sodium and potassium tert-butoxides

Abstract By analysis of vibrational spectra of the sodium and potassium tert -butoxides and of their perdeuterated analogues it was found that potassium tert -butoxide forms cubic tetramers in solution. Sodium tert -butoxide forms similar aggregates only in strongly solvating solvents, whereas in non-polar solvents and in the solid state more complicated aggregates of symmetry lower than T d are formed.

i.r. and 13C-CP-MAS-NMR spectra of pyromellitide and of its precursor based on 4,4′-diaminodiphenylmethane

i.r. and 13C-CP-MAS-NMR spectra were recorded for polyamidocarboxylic acid, polyimide and polyisoimide based on pyromellitic acid dianhydride (PMDA) and 4,4′-diaminodiphenylmethane (MDA), and of polyimide based on PMDA and 4,4′-diaminodiphenylether. The 13C-NMR spectra were interpreted and bands in solid state 13C-NMR spectra suitable for characterizing the structure of the PMDA/MDA polyimide were found. By measurement of i.r. spectra, the applicability of i.r. spectroscopy for monitoring the imidization of polyamidocarboxylic acid in PMDA/MDA was verified. Bands indicating the occurrence of precursor side reactions have not been observed in any of the studied spectra.