Thermal Decomposition of Polyisoprene,Poly(p-isopropyl α-Methylstyrene), and Poly(isoprene/p-isopropyl α-Methylstyrene)

Thermal decompositions of polyisoprene, poly(p-isopropyl α-methylstyrene) (PPIPαMS), and poly(isoprene/p-isopropyl α-methylstyrene) (sample M-32) were carried out at various temperatures in the range 200–340° C in a differential thermo-gravimetric apparatus. The undecomposed polymers as well as their decomposed residues were analyzed by gel-permeation chromatography (GPC), infrared spectroscopy (IR), and nuclear magnetic resonance (NMR). Based on the changes observed in the distribution of molecular weights, depolymerization is the predominant step in the decomposition of PPIPAMS and polymer M-32, whereas random scissions predominate in the case of polyisoprene. The combined data of GPC, IR, and NMR indicate that only interchain reactions leading to the formation of cyclized products are present in the decomposition of polyisoprene while interchain as well as intrachain reactions are operative in the case of polymer M-32.     

Dynamic light scattering of polyethylene. I. Introduction and experimental procedures

An apparatus and procedures are described for the observation of the light-scattering changes during the periodic vibration of a polymer film sample. The relationship between static and dynamic scattering experiments is discussed as are the means for interpreting such experiments in terms of spherulite deformation and statistical theories. The performance of the apparatus is illustrated with some experiments on a medium-density polyethylene sample.     

New apparatus for studies on supermolecular structures of thin polymer films by small-angle light scattering

The construction and principle of operation of small-angle light scattering apparatus for studies of supermolecular structure in thin polymer films is described. The apparatus can be used to study changes in spherulite structure during crystallization and changes in films subjected to steady or sinusoidal strain. Typical results with polyethylene films are given.     

PHOTOTHERMAL DEFLECTION SPECTROSCOPY OF PHOTOSYNTHETIC PIGMENTS in vivo and in vitro

Abstract— This Technical Note describes the design of a photothermal beam deflection apparatus which allows the easy and rapid measurement of thermal dissipation of absorbed light energy in various photosynthetic materials including whole plant leaves. This system is based on the "mirage effect" in which the refractive index gradient induced in a fluid in contact with the sample, irradiated with an intensity-modulated light, causes the periodic deflection of a laser beam parallel to the sample surface. The deflection of the probe laser beam is detected by a position sensor, the output of which is processed by a lock-in amplifier. Photothermal deflection signals can be monitored in vivo in intact leaves placed in various (liquid or gaseous) environments with a satisfactory signal-to-noise ratio between 100 (in water) and 50 (in air) at low modulation frequencies (ca 30 Hz). It is shown that this new and simple photothermal technique is a very sensitive tool for the measurement of absorption spectra of photosynthetic pigments both in vivo (leaves, algae or chloroplasts) and in model systems (Langmuir-Blodgett and solid films of chlorophyll).     

Photostabilization of recycled pigmented polypropylene crate material

The photostabilizing efficiencies of various light stabilizer systems in recycled pigmented polypropylene crate materials, previously in use for 6–7 years, have been examined using the standard carbonyl index and time to embrittlement methods. Thirty-two polymer film samples with and without additional stabilizer have been prepared and exposed in both a Xenotest-150 and Microscal apparatus. The performance of the various light stabilizer systems in both exposure units are compared and discussed.     

Pressure-dependent Fourier transform infrared spectroscopy of a poly (ester urethane)

The effects of hydrostatic pressure upon (1) a segmented poly (ester urethane), (2) a hydrolytically degraded sample of the same polymer, and (3) models for the polyurethane and polyester segments in this polymer have been studied by Fourier transform infrared spectroscopy using high-pressure diamond anvil cells (DACs). The pressure responses of the vibrational frequencies of specific functional groups of the poly (ester urethane) in the 0-100-kbar range are compared with data for individual segment models and the partially degraded sample. The results indicated that the polymer is highly stable in this pressure regime, with no measurable degradation or phase changes. Differences in the pressure dependency of specific infrared bands between the poly (ester urethane) sample and the partially degraded sample are slight and consistent with changes in hydrogen-bonding interactions and shorter chain lengths in the degraded sample.     

Apparatus for instantaneously measuring ultraviolet,visible, or infrared dichroism from thin polymer during high-speed stretching

An apparatus has been constructed for following changes in the dichroism of a polymer film undergoing rapid elongation. By means of a rapidly rotating mirror with evenly spaced open sectors, a beam of radiation is passed through the sample and then alternately polarized in the horizontal and vertical direction so that the horizontal and vertical absorbances may be rapidly compared in time as compared with the time of sample elongation (a few milliseconds). The apparatus utilizes reflection optics and a grating monochromator so that measurements may be made by using ultraviolet, visible, or infrared radiation. The transmitted intensity is detected by a photomultiplier or semiconductor infrared device, the output of which is amplified and displayed on an oscilloscope. A temperature-controlled sample chamber is provided. The operation of the apparatus is illustrated by following the change in dichroism of a sample of dehydrohalogenated poly(vinyl chloride) with visible radiation during rapid extension.     

FTIR-PAS-spectroscopic study of transparent double-layer polymer films

Depth profiling measurements are carried out on aluminum-foil coated with a tie-resin and a polyethylene (P.E.) film. Since the total thickness is constant, an increase of the thickness of the tie-resin brings about a thinner P.E.-film. For a series of different combinations, the photoacoustic signal is investigated for different modulation frequencies. Gradual changes in the intensity of the tie-resin vibrations are observed. Mostly, these peaks are inverted but, in some cases, they can be turned into normal vibration bands. This is caused by phase errors due to a time delay of heat detected at different depths in the sample. The purpose of this study is to determine the thickness of polymer layers on aluminum-foil using photoacoustic measurements at different modulation frequencies.     

Synthesis and characterization of variable-architecture thermosensitive polymers for complexation with DNA

Copolymers of N-isopropylacrylamide with a fluorescent probe monomer were grafted to branched poly(ethyleneimine) to generate polycations that exhibited lower critical solution temperature (LCST) behavior. The structures of these polymers were confirmed by spectroscopy, and their phase transitions before and after complexation with DNA were followed using ultraviolet and fluorescence spectroscopy and light scattering. Interactions with DNA were investigated by ethidium bromide displacement assays, while temperature-induced changes in structure of both polymers and polymer-DNA complexes were evaluated by fluorescence spectroscopy, dynamic light scattering, laser Doppler anemometry, and atomic force microscopy (AFM) in water and buffer solutions. The results showed that changes in polymer architecture were mirrored by variations in the architectures of the complexes and that the overall effect of the temperature-mediated changes was dependent on the graft polymer architecture and content, as well as the solvent medium, concentrations, and stoichiometries of the complexes. Furthermore, AFM indicated subtle changes in polymer-DNA complexes at the microstructural level that could not be detected by light scattering techniques. Uniquely, variable-temperature aqueous-phase AFM was able to show that changes in the structures of these complexes were not uniform across a population of polymer-DNA condensates, with isolated complexes compacting above LCST even though the sample as a whole showed a tendency for aggregation of complexes above LCST over time. These results indicate that sample heterogeneities can be accentuated in responsive polymer--DNA complexes through LCST-mediated changes--a factor that is likely to be important in cellular uptake and nucleic acid transport.     

An apparatus for continuous separation of macromolecules by combined electrophoresis and gel filtration

Summary An apparatus for continuous separation of soluble and particulate macromolecules, and of other electrically charged particles by combined electrophoresis and gel filtration, is described. The two principles, electrophoresis and gel filtration, which operate simultaneously at right angles, enable separation between the various macromelecules, depending upon differences in electric charge and molecular wight. The sample to be fractionated is fed continuously into the apparatus while the separated macromolecules reaching the distal end of the instrument are collected at the outlet ports. Data for a continuous fractionation of human plasma proteins using the instrument are given.     

Dynamic small-angle x-ray scattering from crystalline polymers

The variation in small-angle x-ray scattering (SAXS) for samples of crystalline polymers subjected to oscillatory strains has been observed employing the 10-m SAXS apparatus with a two-dimensional position-sensitive detector at the National Center for Small-Angle Scattering Research at Oak Ridge National Laboratory. Signal averaging has been carried out in accordance with the π/2-sector technique by gating the detection of scattered intensity in synchronism with the sample strain. In-phase and out-of-phase intensity changes have been observed for a high-density polyethylene at various frequencies (0.05–3.2 Hz) and temperatures (0–70°C). Changes are greatest at small scattering angles. Frequency dependence is greatest at lower temperatures, indicating a time-dependent response of the structural changes leading to scattering at these temperatures. The behavior is not pronounced at elevated temperatures. The similarity of the scattering at both azimuthal angles of 0° and 90° suggests the existence of an additional mechanism, perhaps microvoid formation. To evaluate void contribution, the dynamic invariant function is determined as a function of frequency and temperature. It appears that the microvoid formation lags behind the applied strain. The static and swelling SAXS studies present further evidence of void generation during elongation.     

Infrared technique for the measurement of structural changes during the orientation process in polymers

Polarized infrared measurements were made on polymer samples to obtain the structural changes occurring during the orientation process. The absorbances of the infrared bands were measured by determining the three components of the absorbance. Two components were obtained directly with plane-polarized light while the third is obtained by tilting the sample and extrapolating. Corrections were made for machine optics polarization, sample birefringence, polarizer inefficiency, anisotropy of the index of refraction, and scattering from the film surface. Data are reported for polyethylene obtained from cold-drawn specimens as a function of draw temperature. Polyethylene exhibits no strain-induced crystallization as a result of the chain-alignment process. Annealing of the drawn samples reperfects the distorted crystals.     

Rheo-optical properties of polyethylene films in the nonlinear viscoelastic region

A new apparatus was designed to investigate the dynamic viscoelastic properties of solid polymer materials in the nonlinear viscoelastic region. The apparatus was combined with a birefringence apparatus in such a way that birefringence could be measured simultaneously with stress under oscillatory deformation. The nonlinear viscoelastic behavior of bulk-crystallized high-density polyethylene films was examined. Nonlinearity of mechanical properties became evident around 30°C, while optical properties became markedly nonlinear around 50°C. The nonlinearity of viscoelastic properties changes very little when the films are swollen with tetrachloroethane. It is proposed that disruption of lamellae to crystallites in the drawing process is one of the most important causes of the nonlinear behavior of high-density polyethylene films.     

Interactions of inorganic salts with poly(ethylene oxide)

Evidence is presented for the interaction of metal salts such as potassium iodide with polyethers such as poly(ethylene oxide). This interaction is sufficiently marked that the incorporation of 10–30% of the salt in the bulk polymer markedly reduces crystallinity while retaining compatibility. Examination of electroviscous effects in methanol demonstrates that the salt–polymer adduct behaves as a typical polyelectrolyte at low salt concentrations, while the polymer in absence of salt is essentially insoluble in methanol at room temperature. Measurements of the equilibrium between salt and polymer along with a study of various molecular weight polymers strongly suggest that one salt molecule associates with about nine ethylene oxide units. It is proposed that the association is due to an ion–dipole interaction, and the anion is tentatively postulated as the species directly associating with the polymer. The association of other metal salts and other polymers are interpreted in this light. The significance of these results in interpreting salting-in phenomena is also discussed.     

The dynamic birefringence of high polymers

The simultaneous measurement of the birefringence and strain of a sample subjected to sinusoidal strain is proposed as a means for elucidating the molecular mechanism of the response to high polymers to mechanical deformation. A linear phenomenologicical theory is proposed in which strain-optical coefficient distribution functions are assigned to the elastic and viscous members of a distribution of Maxwell elements. An apparatus has been constructed to determine the dynamic strain-optical coefficient at frequencies between 0 and 600 cycles/sec. By means of mechanical excitation of vibration at low frequencies and electromagnetic at high frequencies. The dynamic birefringences of polyethylene has been studied at room temperature over this frequency range.     

Photolysis of cellulose and related compounds by 253.7 nm light. I. Rates of gas production from hydrocellulose

The initial stages of the photolysis of cellulose under vacuum can be followed by the gas production. A photolysis cell is described which allows a rigorous temperature control and gives a reproducible photolysis surface of the solid carbohydrate sample. A mass spectrometer was used to analyze the gases. To measure accurately the small amounts produced in a small volume requires careful calibration of this instrument, together with a fixed routine for the experimental procedure. Using this apparatus, we have photolyzed hydrocellulose under vacuum with 253.7 nm light. Only H₂, CO, and CO₂ were evolved, the rate of H₂ production increasing to a constant value, that of CO increasing more slowly without becoming constant, and that of CO₂ decreasing rapidly to a constant value. No induction periods were observed. The gas evolution was not caused by residual O₂ or CO₂ adsorbed on the polymer, but the rates were altered by leaving the photolyzed sample under vacuum overnight or heating the unphotolyzed sample under vacuum at 100°C. The rates of gas production increased markedly when the light filter was changed to allow a combined photolysis by 253.7 and 184.9 nm light. The results illustrate that stringent precautions must be taken to filter off the latter line in polymer photolyses with Hg arc light if the results are to be meaningfully interpreted in terms of 253.7 nm light photolysis. On photolyzing hydrocellulose previously boiled in NaOH solution, a larger H₂ production rate and a smaller CO₂ rate (compared with untreated hydrocellulose) were observed. It is suggested that this standard alkali treatment is the reason for the differences between our results and the results of the photolysis of cellulose reported in the literature.     

A thermal evolution — differential trapping — mass spectrometric technique for polymer characterization

The ability of thermal evolution techniques for polymer characterization is greatly enhanced when spectroscopic methods are combined, thus allowing identification of the off-gases. This work describes a thermal evolution—differential trapping—mass spectrometric technique for analysis of polymer systems. The technique involves heating the sample under controlled temperature and pressure conditions, condensing the evolved gases in traps maintained at various temperatures, continuously monitoring the pressure changes at strategic locations, and analyzing the selectivity trapped volatiles by mass spectrometry. Both qualitative and quantitative aspects of the technique will be discussed.     

3D mapping of the output laser beam from a PDLC sample

Self-transparency due to thermal non-linearities is presented as a basic switching effect in a thick polymer dispersed liquid crystal sample. For the first time a detailed 3D mapping of the output laser beam as a function of the x-y coordinates is presented: changes of the transmitted beam profile are recorded vs. both incident power and time. It is discussed how light intensity and temperature can be used as control parameters for the non-linear part of the refractive index. The experimental results confirm the existence of a threshold value of the incident light intensity at which the device switches from the scattering state to the transmissive state.     

3D mapping of the output laser beam from a PDLC sample

Self-transparency due to thermal non-linearities is presented as a basic switching effect in a thick polymer dispersed liquid crystal sample. For the first time a detailed 3D mapping of the output laser beam as a function of the x-y coordinates is presented: changes of the transmitted beam profile are recorded vs. both incident power and time. It is discussed how light intensity and temperature can be used as control parameters for the non-linear part of the refractive index. The experimental results confirm the existence of a threshold value of the incident light intensity at which the device switches from the scattering state to the transmissive state.     

聚合物基粘土纳米复合材料的流变行为研究

聚合物基粘土纳米复合材料具有与常规颗粒填充体系类似的流变特性 :在整个频率范围内 ,储能模量和损耗模量均随粘土含量的增加而变高 ,其频率依赖性会表现出非未端行为 :且当粘土含量超过临界值以后 ,储能模量会在低频区表现出似固体的平台发展。但与之不同的是前者在低粘土含量的条件下 (<10 % (wt) )就会表现出似固体行为或非末端行为。这些流变特性还会受到粘土的径厚比、化学特性、聚合物基体的分子结构参数和粘土与基体间的相互作用强度等因素的影响。聚合物基粘土纳米复合材料的流变行为是与其微观结构的形成和演化以及聚合物分子链在特定环境下的粘弹松弛过程紧密联系在一起的。本文综述了插层型、剥离型和聚合物分子链一端受限剥离型聚合物基粘土纳米复合材料在力场作用下的流变特性和粘弹松弛机理方面的研究进展。