Poly blends spectroscopy

The ionic aggregates present in an ionomer act as physical crosslinks and drastically change the polymer properties. The blending of two ionomers enhances the compatibility via ion-ion interaction. The compatibilisation of polymer blends by specific ion-dipole and ion-ion interactions has recently received wide attention [93-96]. FT-IR spectroscopy is a powerful technique for investigating such specific interactions [97-99] in an ionic blend made from the acid form of sulfonated polystyrene and poly[(ethyl acrylate - CO (4, vinyl pyridine)]. Datta and co-workers [98] characterised blends of zinc oxide-neutralised maleated EPDM (m-EPDM) and zinc salt of an ethylene-methacrylic acid copolymer (Zn-EMA), wherein Zn-EMA content does not exceed 50% by weight. The blend behaves as an ionic thermoplastic elastomer (ITPE). Blends (Z0, Z5 and Z10) were prepared according to the following formulations [98] ... 

Mohanty S, Santra RN, Nando GB (1997) Reactive blending of ethylene-methyl acrylate copolymer and poly-dimethyl siloxane rubber kinetics studies from infrared spectroscopy. Adv Poly Technol 16(4) 323—329... 

Ozaki and co-workers (99) applied 2D-FT Raman correlation spectroscopy to examine conformational changes and specific interactions in blends of atactic polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene ether) (PPE). 

Another good example of using Raman spectroscopy in the polymer industry is to investigate polymer blends. Raman microimages have been used to investigate the spatial distributions of the components in a blend of brominated poly(isobutylene-co-para-methylstyrene (BIMS) and cis-1-4-polybutadiene (BR) containing silica, zinc stearate, thiate, and other additives (21). A Raman spectrum of a blend is shown in Fig. 7-33. Specific bands can be assigned to BIMS, BR, silica, and zinc stearate. A 10 x 10 xm contour... 

In this paper, we first present a model study on blending a a,co-3,5-dinitrobenzoate PDMS and free 9H-carbazole-9-ethanol, in order to check whether the recently proposed 1 1 stoechiometry between carbazole and dinitrobenzoate molecules indeed applies (Scheme 1). [26] Then, we describe the preparation of triblock copolymers, poly[2-(N-carbazolyl)ethyl methacrylate]-fc-PDMS-fc-poly[2-(N-carbazolyl)ethyl methacrylate] (P(CzEMA)-fe-PDMS-fc-P(CzEMA)), using Atom Transfer Radical Polymerization (ATRP), and their blending with the acceptor-functionalized PDMS. In both studies, the physical association and thermal reversibility of these were followed by different techniques, including UV-Vis spectroscopy, DSC or Rheology. 

Evidence from spectral studies for interactions other than the above hydrogen bonds is not very plentiful. Polystyrene/poly(2,6 dimethyl-l,4-phenylene oxide) blends have been studied by infra-red and ultraviolet spectroscopy . Interactions involving the aromatic rings of the two polymers were proposed. Studies of low molecular weight ethers with aromatic compounds have shown evidence for specific interactions and this has recently been extended to blends of polystyrene with poly(methyl vinyl ether)... 

The materials analyzed were blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) in various ratios. The two components are miscible in all proportions at ambient temperature. The photooxidation mechanisms of the homo-polymers PS and PVME have been studied previously [4,7,8]. PVME has been shown to be much more sensitive to oxidation than PS and the rate of photooxidation of PVME was found to be approximately 10 times higher than that of PS. The photoproducts formed were identified by spectroscopy combined with chemical and physical treatments. The rate of oxidation of each component in the blend has been compared with the oxidation rate of the homopolymers studied separately. Because photooxidative aging induces modifications of the surface aspect of the material, the spectroscopic analysis of the photochemical behavior of the blend has been completed by an analysis of the surface of the samples by atomic force microscopy (AFM). A tentative correlation between the evolution of the roughness measured by AFM and the chemical changes occurring in the PVME-PS samples throughout irradiation is presented. 

The effect of dissolved CO2 on the miscibility of polymer blends and on phase transitions of block copolymers has been measured with spectroscopy and scattering (40). The shifts in phase diagrams with CO2 pressure can be pronounced. Polymer blends may be trapped kinetically in metastable states before they have time to phase separate. Metastable polymer blends of polycarbonate (PC) and poly(styrene-cn-acrylonitiile) were formed with liquid and supercritical fluid CO2 in the PCA process, without the need for a surfactant. Because of the rapid mass transfer between the CO2 phase and the solution phase, the blends were trapped in a metastable state before they... 

In the above, we have seen that a certain interpolymer interaction is required for different polymers to be miscible. Here, we will see that high resolution NMR enables us to locate interacting regions in component polymers. One of the most useful methods is the nuclear Overhauser effect (NOE) between H— H and H—NOE can be observed between spins whose distances are less than about 0.5 nm. The one- (ID) and two-dimensional (2D) NOE experiments have been used to reveal the spatial structure of biomolecules in solutions. Of course, these can be applied to locate interacting regions in a blend in solution and in solids [3]. For example, Crowther et al. [22] and Mirau et al. [23] applied NOE experiments to polystyrene/poly(vinyl methyl ether) (PS/PVME) in a toluene solution, and show that the interpolymer NOE signals between the aromatic protons of PS and the methoxy protons of PVME can be observed at polymer concentrations higher than 25 wt%. In the solid state, Heffner and Mirau [24] measured 2D H— H NOESY (NOESY nuclear Overhauser effect spectroscopy) spectra of 1,2-polybutadi-ene and polyisoprene (1,2-PB/PI) and observed NOE cross-peaks between these component polymers. White and Mirau observed interpolymer NOE interactions between the H spins of PVME and the spins of deuterated... 

There is much interest in the formation of blends of poly(imide)s with other polymers, so as to improve properties such as toughness and processability [14-19, 58, 59]. The subject of measurement of interactions and miscibility of blends by NMR spectroscopy has been discussed by Takagoshi and Asano in Chapter 10 of this book, and will not be referred to in detail here. The use of NMR to study miscibility in blends containing poly(imide)s is somewhat restricted because most poly(imide)s contain a high proportion of aromatic groups, and consequently form blends with other highly aromatic polymers. The CPMAS spectra, which as discussed above are broad and... 

The most direct way of looking at the specific interactions is by using spectroscopic measurements. Infra-red spectroscopy is the technique which has been most commonly used to study mixtures involving polymers. Studies of blends of PVC with polycaprolactone showed shifts of 4-6 cm 1 in the carbonyl band of polycapro-lactone relative to the pure polymer 99 l00), but this Figure should be treated with caution as the peak probably consists of the sum of a shifted and an unshifted peak and it is difficult to say what the frequency of the shifted peak would be, or what fraction of the carbonyl groups are, or can be, involved in the interaction. Frequency shifts have also been shown to exist in blends of poly(methyl methacrylate) with poly(vinylidene fluoride)63). 

Effects of addition of a compatibilizing block copolymer, poly(styrene-b-methyl methacrylate), P(S-b-MMA) on the rheological behavior of an immiscible blend of PS with SAN were studied by dynamic mechanical spectroscopy [Gleisner et al., 1994]. Upon addition of the compatibilizer, the average diameter of PS particles decreased from d = 400 to 120 nm. The data were analyzed using weighted relaxation-time spectra. A modified emulsion model, originally proposed by Choi and Schowalter [1975], made it possible to correlate the particle size and the interfacial tension coefficient with the compatibilizer concentration. It was reported that the particle size reduction and the reduction of occur at different block-copolymer concentrations. 

Radioluminescence spectroscopy has been used to examine molecular motion, solubility, and morphology of heterogeneous polymer blends and block copolymers. The molecular processes involved in the origin of luminescence are described for simple blends and for complicated systems with interphases. A relatively miscible blend of polybutadiene (PBD) and poly(butadiene-co-styrene) and an immiscible blend of PBD and EPDM are examined. Selective tagging of one of the polymers with chromophores in combination with a spectral analysis of the light given off at the luminescence maxima gives quantitative information on the solubility of the blend components in each other. Finally, it is possible to substantiate the existence and to measure the volume contribution of an interphase in sty-rene-butadiene-styrene block copolymers. 

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