Synthetic polymers have a molecular weight distribution and, in addition, copolymers composed of multiple monomers have a compositional distribution. Differences in molecular weight and compositional distributions among materials affect the performance of the materials, so it is important to characterize these molecular structures in detail. Gradient polymer elution chromatography (GPEC), one of the solvent gradient HPLC methods, is an effective way to evaluate compositional distribution. In addition, two-dimensional liquid chromatography (2D-HPLC), which combines GPEC with size exclusion chromatography, is a very good analytical method because it allows simultaneous evaluation of composition and molecular weight. In this study, the author examined compositional separation of an acrylic polymer blend and molecular weight analysis of each polymer that makes up the blend. And, the author analyzed the compositional distribution of ethylene vinyl acetate copolymer (EVA), styrene-methyl methacrylate copolymer, and styrene-butadiene rubber (SBR). As these results, it was confirmed that the molecular weights of the polymers constituting the blend samples could be determined separately. It was also found that the compositional distribution of the copolymers could be analyzed in detail, confirming the effectiveness of two-dimensional liquid chromatography.
Light produced by synchrotron radiation (SR) is much brighter than that produced by conventional laboratory X-ray sources. The photon energy of SR X-ray ranges from soft and tender X-rays to hard X-rays. Moreover, X-ray becomes element sensitive with decreasing photon energy. By using a wide energy range and high-quality light of SR, different scattering and spectroscopic methods were applied to various soft matters. We present four of our recent studies performed using specific light properties of a synchrotron facility, which are as follows: 1) in situ ultra-small angle X-ray scattering (USAXS) study to understand the deformation behavior of colloidal crystals during uniaxial stretching, 2) structure characterization of semiconducting polymer thin films along the film thickness direction by grazing-incidence wide-angle X-ray diffraction using tender X-rays, 3) X-ray absorption fine structure (XAFS) analysis of the formation mechanism of poly(3-hexylthiophene) (P3HT), 4) soft X-ray absorption and emission spectroscopic analysis of water structure in polyelectrolyte brushes.
Multivariate analysis was applied to nuclear magnetic resonance (NMR) spectra of methacrylate copolymers. Principal component analysis (PCA) of 13C NMR spectra of linear copolymers of methyl methacrylate (MMA) and tert-butyl methacrylate (TBMA) successfully extracted information on chemical compositions and monomer sequences. Quantitative analysis of the chemical composition and monomer sequence was achieved by partial least-squares (PLS) regression using NMR spectra of the corresponding homopolymers and their blends as a training dataset. PCA was also useful for the extraction of information on chemical composition in branched copolymers prepared by initiator-fragment incorporation radical copolymerization of TBMA and ethylene glycol dimethacrylate with dimethyl 2,2’-azobis(isobutyrate). The chemical compositions and degree of branching were predicted by PLS regression using NMR spectra of the corresponding homopolymers, their blends and branched copolymers as a training dataset. In addition, PCA was found to be a good measure to evaluate the monomer sequence distribution in linear copolymers of MMA and benzyl methacrylate (BnMA) prepared by various polymer reactions. Furthermore, PCA of 1H NMR spectra of linear copolymers of MMA and BnMA was applied to extract information on chemical compositions and monomer sequences. Monomer reactivity ratios were reasonably estimated from a single sample using the diad sequence distributions predicted by PLS regression.
High-resolution mass spectrometry is a powerful method for the characterization of polymer materials, but the resulting complex mass spectra bring with it the difficulty of data analysis. Kendrick mass defect (KMD) analysis, which converts complex but informative mass spectra into a two-dimensional plot, can visualize the distribution of multiple components, and has recently attracted attention as a practical polymer characterization technique. Conventional KMD analysis is still insufficient for analysis of industrial polymer materials with complex compositions, so we have proposed several advanced KMD analysis techniques, such as resolution-enhanced KMD (RE-KMD) and remainder of KM (RKM). Sample pretreatment methods have been further developed to observe high quality matrix-assisted laser desorption ionization (MALDI) mass spectra suitable for the KMD analysis. The KMD analyses have been further expanded to other mass spectrometric techniques such as electrospray ionization (ESI)-MS, direct analysis in real time (DART)-MS, and pyrolysis-GC-MS. These achievements are expected to accelerate polymer characterization using high-resolution mass spectrometry.
A gradient polymer elution chromatography (GPEC) method was developed that can separate cellulose acetate (CA) with respect to a wide range of degrees of substitution (DS). A series of cellulose acetate propionate and cellulose acetate benzoate samples were synthesized by propionylation or benzoylation of CA samples with average degrees of substitution ranging from 0.6 to 2.9, and compositionally separated using the GPEC method. The reversed-phase gradient separation based on an adsorption/desorption mechanism, a linear gradient of acetonitrile : H2O = 6 : 1 and ethyl acetate was used with a phenyl group-modified silica column as stationary phase. Separation of samples with different DS values was achieved for both sample series. A slight molar mass effect was observed during elution for the sample with low DS. In addition, a sharp peak at low retention time was observed for the high DS sample. Although a search for further separation systems is necessary for the determination of quantitative substitution degree distribution, this method is applicable to the determination of DS distribution over a wide DS range.
Poly(styrene-co-methyl acrylate): SMA, poly(styrene-co-tert butyl acrylate): StBA and poly(styrene-co-methyl methacrylate): SMMA were synthesized by reversible addition-fragmentation chain transfer (RAFT) method. The relationship between the molecular weight and the styrene content was investigated by UV–RI dual detection size-exclusion chromatography. In the SMA and StBA of short polymerization time samples, the styrene content showed a tendency to decrease from the low molecular weight region toward the high molecular weight region. On the other hand, the styrene content tended to increase from the low molecular weight region toward the high molecular weight region in the long polymerization time copolymer samples. The SMMA samples showed no trend of similar changes as SMA and StBA. We have concluded that the phenomenon may be due to the difference in the chain length dependence of the equilibrium constants for the pre-equilibrium and main-equilibrium of the RAFT process.
Polyoxymethylene (POM) is a typical crystalline engineering plastic that is widely used in automotive fuel system components because of its excellent fuel resistance. It is known that direct contact between fuel and POM causes POM to absorb fuel and swell, thereby affecting its mechanical properties in such applications. It has also been found that the mechanical properties of POM are affected by an environmental temperature. From these situations, it is important for designing the products to investigate the effects of temperature and fuel swelling on the molecular mobility and higher-order structure of POM. In this study, the molecular mobility and higher-order structural changes of POM under heating and fuel swelling were analyzed using solid-state NMR, wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS). Solid-state NMR measurements showed that the molecular mobility of all regions including crystalline to amorphous phases was enhanced under heating, while selective enhancement of molecular mobility was observed only in the amorphous and intermediate phases under fuel swelling. The results of solid-state NMR, WAXD, and SAXS measurements also confirmed that higher-order structural changes, such as increased crystallinity and increased volume of amorphous portions which occurred simultaneously due to fuel swelling.
Acid anhydride monomer plays an important role such as functioning as a cross-linking point in polymer by copolymerizing with a monomer having an α-olefin. It is important to identify the acid anhydride structure in order to understand the mechanism of function expression by mixed products. Pyrolysis GC/MS is a useful technique for structural characterization of polymeric materials. It is an effective method for estimating types of monomer that consist of polymer materials, such as insoluble polymers and composite materials. However, structural characterization of acid anhydride monomer from polymeric material is not possible by pyrolysis GC/MS because an acid anhydride monomer is fragmented as CO2. In this study, we introduced a pretreatment method for derivatizing acid anhydride monomers with a primary amine and examined the method for characterizing the type of acid anhydride polymers by pyrolysis GC/MS. By combining imide derivatization using aniline and the pyrolysis GC/MS, we succeeded in obtaining the structural information of maleic anhydride monomer as a pyrolysis fragment of N-phenylmaleimide. Pyrolysis fragments containing copolymerization monomers were also detected. It is expected that the imide derivatization-pyrolysis GC/MS will enable discriminant analysis of acid anhydride polymers.
As a basic study of the degradation analysis of celluloid, TG measurement and FT-IR measurement by the ATR method were performed on a celluloid sheet irradiated with a xenon lamp and ultraviolet rays, and the results were compared with the cellulose acetate sheet. Celluloid showed a decrease in the thermal decomposition start temperature, and cellulose acetate showed an increase. Information on the deterioration of the sample surface was obtained from the pyrolysis start temperature and the IR spectrum of the surface, and information on the deterioration inside the sample was obtained from the peak temperature of DTG. The results were applied to the actual sample saved. Each celluloid sample was degraded by light, and the degree of degradation was considered to be similar to the change when a 0.2 mm thick sheet was irradiated with a xenon lamp for 8 hours. By devising the measurement conditions, it was confirmed that TG/DTA measurement and celluloid sample are effective measurement methods.