Yanzhi Ren

Two-dimensional Fourier-transform Raman and near-infrared correlation spectroscopy studies of poly(methyl methacrylate) blends: 1. Immiscible blends of poly(methyl methacrylate) and atactic polystyrene

Abstract Fourier-transform (FT) Raman and near infrared (NIR) spectra have been measured for poly(methyl methacrylate) (PMMA) and its immiscible blends with atactic polystyrene (PS) of small PS contents from 1 to 10 wt.%. Generalized two-dimensional (2D) correlation spectroscopy has been applied to analyze the composition-dependent FT-Raman and NIR spectral variations of the immiscible blends. The synchronous 2D FT-Raman correlation analysis separates the Raman bans of the minority PS from those due to the majority PMMA. It detects the bands due to PS at 2900, 2856, 1562, 1494, 1201, 1184, 1156, 1130, 1097, 1069, 964, 904, 796, and 759 cm −1 , which are too weak to be observable from the one-dimensional blend spectra. The synchronous 2D Raman-NIR hetero-correlation analysis further separates NIR bands of PS from those of PMMA. It detects the bands at 6082, 5972, 5937, 5920, 4834, and 4663 cm −1 due to PS, which are virtually unidentifiable from the one-dimensional blend spectra. These results are further proved by the synchronous 2D NIR correlation analysis.

Two-Dimensional Near-Infrared Correlation Spectroscopy Studies on Composition-Dependent Spectral Variations in Ethylene/Vinyl Acetate Copolymers: Assignments of Bands Due to Ethylene Units in Amorphous, Disordered, and Orthorhombic Crystalline Phases

Generalized two-dimensional (2D) correlation spectroscopy has been applied to the study of the composition-dependent near-infrared (NIR) spectral changes in 11 different ethylene/vinyl acetate (EVA) copolymers with vinyl acetate (VA) content from 6 to 42 wt %. The 2D synchronous correlation analysis of the 11 NIR spectra has separated the bands due to ethylene units from those due to the VA units. The obtained results are consistent with those reached by the calculation of the second derivative and by chemometrics analysis reported in our previous paper. However, the 2D correlation analysis has given clearer evidence for the band separation. Two-dimensional asynchronous correlation analysis has revealed out-of-phase variations between some bands due to ethylene and some bands due to VA and has determined the order of intensity change between them. On the basis of the order of intensity change, the bands of ethylene in the orthorhombic crystalline phase have been discriminated from those in the amorphous and disordered phases. This paper discusses the potentials of three powerful techniques, 2D correlation analysis, the calculation of the second derivatives, and that of regression coefficients in chemometrics, in unraveling rather complicated NIR spectra.

Two-dimensional Fourier-transform-Raman and near-infrared correlation spectroscopy studies of poly(methyl methacrylate) blends: 2. Partially miscible blends of poly(methyl methacrylate) and poly(4-vinylphenol)

Abstract Fourier-transform (FT)-Raman and near-infrared (NIR) spectra have been measured for poly(methyl methacrylate) (PMMA) and its partially miscible blends with poly(4-vinylphenol) (PVPh) of small content from 1 to 10 wt.%. Generalized two-dimensional (2D) correlation spectroscopy has been applied to analyze the composition-dependent FT-Raman and NIR spectral variations of the blends. The 2D FT-Raman correlation analysis is effective in analyzing the hydrogen-bonding interaction between PMMA and PVPh, which is responsible for the partial miscibility of the blends. It detects a band at 1706 cm −1 for the hydrogen-bonded CO of PMMA, and two bands at 599 and 549 cm −1 for the ester group whose Raman intensities are very sensitive to the intermolecular hydrogen bonding effect. The Raman-NIR hetero-correlation analysis detects two bands at 6764 and 4637 cm −1 for the hydrogen-bonded hydroxyl group of PVPh, and one band at 5052 cm −1 for the hydrogen-bonded carbonyl group of PMMA. All these bands are not readily identifiable from the one-dimensional (1D) spectra.

Infrared Study on the Crystallization Behavior and Prestructural Change of Syndiotactic Polystyrene in Its Blends with Small Amounts of Poly(2,6-dimethyl-1,4-phenylene ether)

Fourier transform infrared spectra were measured for syndiotactic polystyrene (SPS) and its miscible blends with poly(2,6-dimethyl-1,4-phenylene ether) (PPE) of 3, 7, and 10 wt % over a temperature range of 303–493 K at an increment of 10 K. Crystallization of SPS from the glass state to the planar all-trans form occurred in the temperature range of 423–453 K and was delayed by about 10 K in the SPS/PPE blends, as evidenced by the temperature-dependent absorbance changes in bands at 2846.7, 1374.0, 1333.5, 1222.7, 1091.3, 964.1, 939.2, and 839.8 cm−1. A downward shift of the CH2 symmetric stretching band during the heat-induced crystallization was observed. A kind of “prestructural change” from 383 to 423 K was identified for pure SPS by the temperature-dependent changes in the combination modes of aryl CH out-of-plane deformation vibrations. It was diminished in the SPS/PPE blends with the increase in the PPE content, and disappeared in the blends of 10 wt % PPE. This phenomenon was explained by the favorable dispersive interaction between the phenyl rings of SPS and PPE, which was responsible for the blend compatibility.

Two-dimensional Raman-near infrared heterospectral correlation spectroscopy studies of the specific interactions in partially miscible blends of poly(methyl methacrylate) and poly(4-vinylphenol)

Fourier-transform (FT) Raman and near infrared (NIR) spectra have been measured for poly(methyl methacrylate) (PMMA) and its partially miscible blends with poly(4-vinylphenol) (PVPh) of contents from 1 to 10 wt%. Generalized two-dimensional (2D) correlation spectroscopy has been applied to analyze the composition-dependent FT-Raman and NIR spectral variations of the blends. The Raman-NIR hetero-correlation analysis detects a band at 1706 cm−1 for the hydrogen-bonded C=O of PMMA and a band at 6764 cm−1 for the hydrogen-bonded O–H of PVPh. The two bands are involved in the specific interaction between PMMA and PVPh that is responsible for the partial miscibility of the blends.