M. Shen

Structural Characterization of Plasma-Polymerized Hydrocarbons

Abstract Oils and films were produced by passage of ethylene, acetylene, and butadiene gases as well as benzene vapor through a radio-frequency electric discharge. The hydrocarbon oils produced in the plasma were dissolved in carbon tetrachloride and were analyzed by infrared and nuclear magnetic resonance spectroscopy. Based on these analyses, concentrations of characteristic functional groups were determined and used to propose molecular structures. The hydrocarbon oils are postulated to consist of irregular sequences of highly branched and incompletely crosslinked aliphatic backbone chains with pendant aromatic rings. Double bonds are interspersed along the chains. Hydrogen/carbon ratios in the proposed structures are consistent with the results from elemental analyses. Products from py-rolysis mass spectrometry can also be interpreted on the basis of the proposed structures. Similar techniques are used to analyze the structures of insoluble plasma polymerized films obtained from the same hydrocarbons....

Effects of Reaction Conditions on the Plasma Polymerization of Ethylene.

Abstract Ehylene can be polymerized at low pressures in a radio-frequency glow discharge. The form of the resulting polymer may be a powder at low pressure (1 to 2 Torr) and low monomer feed rate (10 to 40 cc/min), a colorless film at low pressure and high feed rate (70 to 90 cc/min), or an oil at high pressure (4 to 5 Torr) and high feed rate. The powder and film forms of plasma-polymerized ethylene are insoluble in common organic solvents, indicating a highly cross-linked structure. The oily products, however, are soluble in acetone and xylene. Chemical evidence indicates that the oil is most likely composed of highly branched oligomers of ethylene. Mass spectrometric analysis of the gaseous effluents show that under film-forming conditions the only hydrocarbon species observable are those derived from ethylene. The powder- and oil-forming conditions, on the other hand, yielded oligomeric species. On the basis of this evidence, a mechanism for the plasma-polymerization of ethylene is proposed.

The Role of Halogens in the Plasma Polymerization of Hydrocarbons

Abstract Vinyl chloride, vinyl fluoride, and tetrafluoroethylene were polymerized in a radio frequency electric glow discharge. It was found that when compared with the unhalogenated simple hydrocarbons, the rates of polymer deposition are in the order vinyl chloride, acetylene, tetrafluoroethylene, vinyl fluoride, ethylene. This observation can be rationalized by considering the ease with which free radical and unsaturated species can be formed in the plasma. IR spectra show that the structures of plasma-polymerized vinyl chloride and vinyl fluoride are in many respects similar to the plasma-polymerized hydrocarbon. The spectrum of plasma-polymerized tetrafluoroethylene, however, does not resemble that of conventional polytetrafluoroethylene. Addition of dichlorodifluoromethane to the monomer stream dramatically increased the polymer deposition rate; the effect is more subdued for chloromethane and is negligible for tetrafluoromethane. Elemental analysis indicates that little of the added halogens is pre...

Morphological, rheo‐optical, and dynamic mechanical studies of a semicrystalline block copolymer

The morphology, rheo‐optical behavior, and mechanical relaxation properties were investigated for a series of three segmented copolyesters containing blocks of crystalline poly(tetramethylene terephthalate) and amorphous poly(tetramethylene ether). Transmission and replica electron micrographs show that if cast from a hot solution of 1,1,2‐trichloroethane on a heated surface, all the samples show distinct spherulitic structures. Annealing appears to increase the lamellar thickness. On the other hand, casting from a solution of 1,1,2,2‐tetrachloroethane produced a film that showed no evidence of the presence of spherulites, although microphase separation persists and crystallites appear to be randomly oriented in the amorphous matrix. Small‐angle light‐scattering experiments for trichloroethane‐cast samples confirmed the existence of spherulites. Dynamic mechanical data of these copolyesters show three principal relaxation peaks. These are the melting peak of the poly(tetramethylene terephthalate) block, t...

Grüneisen parameters of crystalline polyethylene

Values of the Gruneisen parameter γ reported in the literature for polyethylene (PE) vary over nearly four orders of magnitude. Part of the reason for this wide variation is the variety of definitions and experimental techniques used in obtaining γ. A simple unified derivation of these equations will be presented in an attempt to clarify the interrelations among them. Underlying assumptions used in arriving at these equations will be pointed out. Infrared spectra of a bulk polyethylene were taken at room temperature up to 40‐kbar pressures. Microscopic Gruneisen parameters were obtained from these data for rocking and bending modes of PE. It will be demonstrated that values of the Gruneisen parameters are dependent on lattice frequency, volume, wave vector, and degree of crystallinity for PE.

Synthesis and Properties of a New Class of Potential Biomedical Polymers

Abstract Both low molecular weight compounds and some polyelectrolytes containing quaternary nitrogen atoms in their structure have been known for some time to possess important biological activity. Aliphatic ammonium compounds are used as bacteriocides and muscle relaxants, and quinolinium compounds have recently been found to be excellent antileukemic agents. In addition, a considerable amount of evidence has been accumulated to show that organic ammonium salts combine with heparin, and the resulting complex may be used as a coating to render polymers blood-compatible. However, the introduction of ammonium groups into the backbone of a polymer exhibiting good mechanical properties offers certain advantages.

Dielectric Relaxations in Plasma-Polymerized Hydrocarbons and Fluorocarbons

Abstract The dielectric behavior of plasma-polymerized ethylene (PPE), ethylene/acetylene (PPEA), ethane/vinyl chloride (PPEVC) and tetrafluoroethylene (PPTFE) was studied over a frequency range of 102 to 105 Hz between -150 and 100°C. After exposure to the atmosphere, each of the polymers exhibited a pronounced loss peak. This relaxation process was designated as the γpprocess, and was attributed to the local mode motion of several molecular segments. The average activation energy for all four polymers was found to be 13.8 kcal/mole. It was proposed that oxidation introduces carbonyl groups into the nonpolar polymer chain. The added polar carbonyl groups then act as tracers to render the molecular motions observable by dielectric measurements. The presence of these carbonyl groups was confirmed by concomitant IR spectroscopic determinations. Comparison of the experimental data with the Kirkwood-Froelich theory was found to be satisfactory.

Dynamic mechanical and morphological studies of homopolymer/block copolymer blends

Abstract A triblock copolymer of styrene-butadiene-styrene (SBS) was blended with a high and a low molecular weight polybutadiene [designated as PB(H) and PB(L), respectively]. Electron micrographs of these blends show that PB(L) was solubilized into the butadiene domains of the SBS, while PB(H) was present in a separate phase. Dynamic mechanical data of the SBS&PB(L) blends indicate the presence of an intermediate loss peak between those of the glass transitions of the styrene and butadiene blocks in SBS, which can be attributed to the slippage of untrapped entanglements of PB(L) chains. Similar data for blends containing PB(H) also show an intermediate loss peak, which is, however, due to crystallization and melting of the polycisbutadiene chains. The peak due to the primary glass transition of the butadiene phase was shifted to lower temperatures upon incorporation of PB(L) as a result of plasticization effect of PB(L). The same transition for PB(H) blends is split into a doublet because of the presenc...

Effects of Monomer Flow Rate, Flow Configuration, and Reactor Geometry on the Rate of Plasma Polymerization

Abstract The effects of flow rate on the plasma polymerization of ethylene in an rf discharge were investigated using both a tubular and a bell-jar-type of reactor. Both reactors contained parallel plate internal electrodes. Experiments with the tubular reactor showed that both the total thickness of the deposit and its distribution in the axial direction were strong functions of the flow rate. At low flow rates the polymer thickness decreased in the flow direction, while at high flow rates the polymer thickness increased. Each of these observations is explained by a simple model of plasma polymerization. Using the bell-jar reactor, different monomer flow distribution configurations were tested to determine their effect on the distribution of polymer thickness. It was found that distribution or diffusion of the monomer inflow provided a more uniform film.

Contribution of Internal Energy to the Elasticity of Rubberlike Materials

Abstract Rubber is an interesting material possessing some remarkable properties, the most important of which is its high elastic extensibility. Ordinary solids, such as metals, nonmetallic crystals, and glasses, can be deformed or strained elastically only to a small extent, corresponding to an extension of the order of 1%. If an attempt is made to apply a greater extension, they either break, as in the case of glass, or deform plastically, like lead.