Parylene C at subambient temperatures

Dependence of Parylene C deposition rate on dimer sublimation temperature, inert gas pressure, substrate temperature, and mass of dimer has been investigated. It was found that Parylene C deposition proceeds best at ambient temperature and produces film of optimum performance. Opacity in the film results from its rough morphology and not from the incorporation of the dimer in the film as is normally thought. This was evidenced from scanning electron microscopy and from an estimation of the volatile contents of the Parylene C films. Deposition of Parylene C at liquid nitrogen temperature proceeds via trapping of active monomer species followed by spontaneous polymerization. A quantitative study of the monomer to polymer transition by ESR spectroscopy is presented.     

Estimation of the electron-collision initiation rate constant for the plasma polymerization and deposition of ethane using a transport-based model

The plasma polymerization and deposition of ethane in a parallel-plate electrode system was predicted using gas-phase transport equations and published gas-phase kinetic rate constants, with the assumption that the deposition rate was limited by the production of monomer free radicals and their diffusion to the deposition surface. The kinetic rate constant for radical initiation by electron collision with ethane was adjusted to bring the modelpredictionsfor mass deposition into line with experimental measurements reported in the literature for 12 combinations of power, gas fowrate, and pressure. Furthermore, the shapes of the predicted deposition profiles were made to closely match the experimental profiles by introducing an adjustable parameter to account for plasma boundary effects and two coefficients to account for nonradical polymerization (constant for all conditions). The best-fit electron-collision initiation constant was compared with theoretical predictions for oxygen and hydrogen in a manner explainable by bond strengths and vibrational degrees of freedom.     

Critical evaluation of conditions of plasma polymerization

Under conditions of plasma polymerization, we are dealing with the “reactive” or “self-exhausting” rather than the “nonreactive” or “non-self-exhausting” gas phase (plasma). Therefore, many parameters that define the gas phase, such as system pressure and monomer flow rate, which are measured in the nonplasma state (before glow discharge is initiated), do not apply to a steady state of plasma, the conditions under which most of the studies on plasma polymerization are carried out. Consequently, information based on: (1) the polymer deposition rate measured at a fixed flow rate and discharge power, (2) the dependence of deposition rate on flow rate at fixed discharge power, or (3) the dependence of deposition rate on discharge power at fixed flow rate, does not provide meaningful data that can be used to compare the characteristic nature of various organic compounds in plasma polymerization. The significance and true meaning of experimental parameters applicable to conditions of plasma polymerization are discussed. The most important feature is that plasma polymerizations of various organic compounds should be compared at comparable levels of composite discharge power parameter W/FM, where W is discharge power, F is the monomer flow rate (given in moles), and M is the molecular weight of a monomer.     

Kinetics of DC Discharge Plasma Polymerization of Hexamethyldisiloxane and Pyrrole

This paper investigates DC plasma polymerization kinetics by combining plasma parameters with film deposition rate in different conditions. The monomers hexamethyldisiloxane (HMDSO) and pyrrole were used. Both single and double Langmuir probes were used to measure the plasma parameters in pulsed power and continuous discharges. In order to avoid probe tip contamination, the probe was heated. Plasma density and electron temperature are reported. The electron current wave form is obtained in pulse power conditions. From the data, a plasma polymerization model is proposed. The conclusion is that the monomer molecules and free radicals adsorbed on the substrate surface react with activated sites produced by high energy ions bombarding the film, resulting in polymerization at the film surface.     

Studies on the thermal polymerization of substituted benzoxazine monomers: Electronic effects

To evaluate the influence of the electronic effects on the polymerization temperature, we looked at several 3‐phenyl‐3,4‐dihydro‐2‐H‐1,3‐benzoxazine monomers with electron‐withdrawing or electron‐donating groups in the 6 and 4′ positions. The monomers were synthesized and characterized using different synthetic methods to achieve the best possible results. The thermal polymerization of these benzoxazine monomers was analyzed by differential scanning calorimetry, and the polymerization behavior and the polymer characteristics were related to the electronic character of the substituent and the polymerization mechanism. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3353–3366, 2008     

Polymerization of para-xylylene derivatives (parylene polymerization). IV. Effects of the sublimation rate of di-p-xylylene on the morphology and crystallinity of parylene N deposited at different temperatures

The effect of the sublimation rate of di-p-xylylene on the crystallinity and morphology of Parylene N deposited on stainless steel was studied as a function of substrate temperature. For a given rate of dimer sublimation, the deposition rate increases with decreasing substrate temperature. Increasing the sublimation rate of the dimer increases the deposition rate 10-fold, decreases the crystallinity, and shifts the appearance of the hexagonal β structure towards higher substrate temperature for samples synthesized from room temperature (RT) to ?60°C. Solution annealing resulting from solvent extraction, and isothermal annealing, increase the crystallinity of the polymers and result in structures containing both α and β polymorphs. The surface topology, as revealed by scanning electron microscopy (SEM), for polymers synthesized from RT to ?40°C shows a globular structure, whereas low temperature samples exhibit a rod-type morphology. For higher sublimation rates of the dimer, SEM micrographs show that oligomeric species start appearing on the polymer films after a period of 4–5 days. Solvent extraction removes the oligomeric crystals, and GPC analysis of the resulting extract indicates that most of the oligomers range in molecular weight from 100 to 900. The cross-sectional morphology for fractured low temperature samples, however, reveals different morphologies as polymerization proceeds. It is postulated that in the temperature range ?50 to ?78°C, both surface condensation and surface adsorption of monomer occurs, leading to different morphologies and lower crystallinity. The polymer synthesized at liquid nitrogen temperature shows the presence of voids along with different morphologies. X-ray diffractograms of polymers synthesized at liquid nitrogen reveal a considerable amount of amorphous phase in the films. Hence, it is inferred that, although the liquid nitrogen polymerization is a solid state polymerization of the crystalline monomer, it does not lead to 100% crystalline material, and the reasons for this are discussed.     

Semi-continuous emulsion polymerization of styrene in the presence of poly(methyl methacrylate) seed particles. Polymerization conditions giving core-shell particles

This work reports the morphology of two-phase latex particles prepared by semi-continuous seed emulsion polymerization of styrene in the presence of polar poly(methyl methacrylate), PMMA, seed particles, using different conditions of non-polar styrene feed rate, rate of initiation, seed particle concentration and temperature of polymerization.The expected latex particle morphology at thermodynamic equilibrium is an inverted core-shell structure where the non-polar polystyrene would form the core. However, depending on the set of process conditions used the morphology of the resulting two-phase particles varied from that of a pure core-shell structure, over intermediate structures in which a shell of PS surrounded a PMMA core containing an increasing number of PS phase domains, to a structure in which the entire PS phase was present as discrete PS phase domain, more or less evenly distributed in a matrix of PMMA.By the use of a caloirimetric reactor system the monomer concentration in the particles during the different polymerization experiments could be calculated by comparing the integral of the polymerization rate curve with the integral of the monomer feed rate. A comparison between particle morphology and the calculated concentration of plasticizing monomer in the polymerizing particles strongly suggested that the diffusivity of the entering oligo radicals determined by the difference between polymerization temperature and the glass transition temperature of the monomer-swollen core polymer is a key factor determining the morphology of two-phase particles prepared by semi-continuous seed emulsion polymerization.Two-phase particles with a true core-shell structure were obtained in experiments where the estimated glass transition temperature of the PMMA phase was only a few degrees below the polymerization temperature. The results show that such particles can be obtained under conditions of high as well as low styrene feed rates, provided that the rate of initiation is properly adjusted.     

Distribution of polymer deposition in plasma polymerization. I. Acetylene,ethylene, and the effect of carrier gas

Factors which influence the distribution of polymer deposition in an electrodeless glow-discharge system were investigated for acetylene and ethylene. Under the conditions in which “full glow” is maintained, the distribution of polymer deposition from pure monomer flow systems is nearly independent of flow rate of monomer or of the system pressure in discharge, but is largely determined by the characteristic (absolute) polymerization rates (not deposition rate) of the monomers. Acetylene has a high tendency to deposit polymer near the monomer inlet, whereas ethylene deposits polymer more uniformly in wider areas in the reactor. The addition of carrier gas such as argon or partially copolymerizing gas such as N₂, H₂, and CCl₂F₂ was found to narrow the distribution of polymer deposition. The distribution of polymer deposition is also influenced by a glow characteristic which is dependent on flow rate and discharge power.     

Polymerization of vinylpyridinium salts. III. Further studies on the interfacial and isotropic polymerization of 4-vinyl-N-methylpyridinium methylsulfate

In the present study the polymerization of 4-vinyl-N-methylpyridinium methylsulfate at liquid–liquid interfaces is investigated. Various experimental procedures that may favor the interfacial mode of polymerization over the isotropic one are discussed. The effectiveness of the methods was evaluated by physical characterization studies and particularly polymer tacticity. This last property is directly associated with the achieved organization of the monomers at interfaces. ¹³C-NMR technique was used for tacticity determination. According to tacticity, random polymers are primarily obtained that result from an isotropic polymerization in the aqueous phase, where the monomer is extremely soluble. The small predominance of the syndiotactic triad over the isotactic one is explained by the occurrence of an interfacial polymerization induced by the orientation of the monomers. A polymerization model is proposed that justifies the stereospecificity modification of polymerization.     

Cagelike polymer microspheres with hollow core/porous shell structures

Submicron‐scaled cagelike polymer microspheres with hollow core/porous shell were synthesized by self‐assembling of sulfonated polystyrene (PS) latex particles at monomer droplets interface. The swelling of the PS latex particles by the oil phase provided a driving force to develop the hollow core. The latex particles also served as porogen that would disengage automatically during polymerization. Influential factors that control the morphology of the microspheres, including the reserving time of emulsions, polymerization rate, and the Hildebrand solubility parameter and polarity of the oil phase, were studied. A variety of monomers were polymerized into microspheres with hollow core/porous shell structure and microspheres with different diameters and pore sizes were obtained. The polymer microspheres were characterized by scanning electron microscopy, transmission electron microscopy, optical microscopy, and Fourier transform infrared spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 933–941, 2007     

An overall mechanism for the deposition of plasma polymers from methane in a low-pressure argon plasma jet

An overall mechanism for plasma polymer deposition from a methane-seeded argon plasma jet was established from experimental measurements and a simplified model of reaction kinetics within the plasma jet. Total mass deposition rates were obtained at various substrate positions and methane flow rates. Methane consumption was estimated from residual gas analysis. The influence of substrate coolant temperature on deposition rate was evaluated. The model was based on particle densities, jet temperature, and jet velocity data published previously, and reaction rate constants from the literature were used. No adjustable parameters were employed in this model. Experimental results for total deposition rate and methane consumption were in good agreement with model predictions. The overall deposition mechanism consists of three steps: Penning ionization of methane by excited argon neutrals, followed by dissociative recombination of CN _x ⁺ to yield CH, followed by incorporation of CH into the growing film upon impact. Contributions of species other than CH to the total deposition rate are minor, and adsorption is not a prerequisite for incorporation into the growing film.     

Kinetics of vinyl fluoride polymerization

Vinyl fluoride was polymerized, at low temperatures and pressures, by photo- and γ-ray initiation. The kinetics of this heterogeneous polymerization reaction was studied and a general scheme was proposed to explain the experimental results. The scheme is based on the assumption that the main site of the polymerization is in the “polymer phase.” The solvent used determines the rate of the reaction by its effect on the swelling of the polymer. The degree of polymerization is determined mainly by transfer reactions.     

Ammonia gas sensor based on electrosynthesized polypyrrole films

In this work, design and fabrication of micro-gas-sensors, polymerization and deposition of poly(pyrrole) thin films as sensitive layer for the micro-gas-sensors by electrochemical processing, and characterization of the polymer films by FTIR, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), are reported. The change in conductance of thin polymer layers is used as a sensor signal. The behaviours, including sensitivity, reproducibility and reversibility, to various ammonia gas concentrations ranging from 8 ppm to 1000 ppm are investigated. The influence of the temperature on the electrical response of the sensors is also studied. The experimental results show that these ammonia gas sensors are efficient since they are sensitive to ammonia, reversible and reproducible at room temperature.     

Initiated chemical vapor deposition of poly(1H,1H,2H,2H-perfluorodecyl acrylate) thin films

A solvent-free initiated chemical vapor deposition (iCVD) process was used to create low surface energy poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA) thin films at deposition rates as high as 375 nm/min. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy showed full retention of the fluorine moieties, and no measurable cross-linking was detected. Additionally, the FTIR studies support the hypothesis that film deposition results from vinyl polymerization. For all iCVD PPFDA films, the static contact angle was found to be 120.8 +/- 1.2 degrees. The roughness of the films was found to be between 14.9 and 19.8 nm RMS, and the refractive index of the films was found to be between 1.36 and 1.37. The deposition rate was studied as a function of the substrate temperature and the partial pressure of the monomer. It was found that the deposition rate increases with decreasing substrate temperature and increasing monomer partial pressure. It was also found that the molecular weight increases with decreasing substrate temperature and increases with increasing monomer partial pressure. The highest molecular weight measured was 177 300 with a polydispersity of 2.27. Quartz crystal microbalance (QCM) measurements showed that these effects correlated with an increased monomer concentration at the surface. The deposition rate data and the QCM data were quantitatively analyzed to find the rate constants of the process using a previously published model for the iCVD process involving nonfluorinated monomers. The determined values of the rate constants of the surface polymerization were found to be similar to the rate constants measured in liquid-phase free radical polymerization. The kinetic data found in this paper can now be used to study iCVD deposition onto substrates with more complex geometries.     

An Unexpected Molecular Imprinting Effect for a Polyaromatic Hydrocarbon,Anthracene, Using Uniform Size Ethylene Dimethacrylate Particles

A non-covalent type of molecular imprinting effect toward a polyaromatic hydrocarbon (PAH), viz. anthracene, was studied utilizing uniformly sized ethylene dimethacrylate (EDMA) polymer particles without functional host monomers. Although polymerization at 0°C initiated by a redox initiation system was expected to afford larger molecular imprinting effect due to stronger and more effective intermolecular interaction between the template and surface functional groups of the polymer, almost no imprinting effect was observed, while a much higher polymerization temperature of 70°C unexpectedly afforded a larger molecular imprinting effect for the template anthracene. In order to determine the unexpected imprinting effects observed, uniformly sized, macroporous un-imprinting EDMA polymer particles (base particles) were prepared by various polymerization techniques at different polymerization temperature as well as with different initiation systems. The careful studies proved that each kind of base polymer particle showed different molecular recognition ability, especially toward anthracene, which is depends upon the physical properties of each kind of base polymer particle. On the basis of these facts, we would propose that the potential molecular recognition ability of the un-imprinted base polymer particles is another important factor for realization of effective molecular imprinting alongside the factors reported previously.     

Broadband reflection in polymer stabilized cholesteric liquid crystal cells with chiral monomers derived from cholesterol

In this study, a series of achiral monomers and chiral monomers of different flexible spacer chains based on cholesteryl moiety were synthesized. Polymer stabilized cholesteric liquid crystal (PSCLC) cells were then created by incorporation of the polymer networks. The influence of the nature of the monomers and the spacer length of chiral monomers on the reflectance properties of PSCLC was investigated as well as the polymerization condition. The results strongly suggest that the chirality of the polymer networks plays an integral role in the observed reflection spectra, and the chiral polymer networks with chiral centers separated well from the polymer backbone induce a greater change in the bulk helix pitch, and produce the broader reflection band in these LC composites. In addition, the temperature dependence of the pitch of the composites before and after polymerization was investigated. To broaden the reflection band further, the experimental processes of thermally induced pitch variation simultaneously with a UV crosslinking reaction of the composites were presented. The morphology of the polymer network in the composites was studied by scanning electron microscopy (SEM). Copyright © 2008 John Wiley & Sons, Ltd.     

极性介质中醋酸乙烯酯的辐照引发分散聚合

用钴 60γ射线引发醋酸乙烯酯的分散聚合 ,通过选择各种极性溶剂体系 ,确立了醋酸乙烯酯在极性介质中稳定的分散聚合体系 .对异丙醇 水体系 ,聚合物分子量随剂量率的降低、稳定剂含量的增加、单体浓度的增大、反应温度的升高以及醇水比的降低而增加 .运用XPS、元素分析等表征聚合物粒子 ,及通过辐射接枝理论的分析 ,可以判断稳定剂所起的稳定作用主要是以物理吸附为主     

二过碘酸合银(II)氧化还原引发丙烯酸甲酯在尼龙1010上接枝共聚合反应的研究

二过碘酸合银（ＩＩ）氧化还原引发丙烯酸甲酯在尼龙１０１０上接枝共聚合反应的研究刘盈海刘卫宏赵敏孟劲功（河北大学化学系保定０７１００２）关键词二过碘酸合银（ＩＩ）钾，尼龙１０１０，氧化还原引发，丙烯酸甲酯，接枝共聚目前Ｃｅ（ＩＶ）被认为是一种十分...     

超声辐照原位乳液聚合制备P(BA-MMA-AA)/TiO_2纳米复合乳液的研究

通过超声辐照原位乳液聚合制备了稳定的丙烯酸丁酯-甲基丙烯酸甲酯-丙烯酸共聚物[P(BA-MMA-AA)/TiO2]纳米复合乳液.系统研究了乳化剂浓度,单体及TiO2用量对超声辐照原位乳液聚合反应的影响.结果表明,随乳化剂浓度增加、单体及TiO2用量的减少,聚合反应速率增高.TEM、SEM和FTIR证实了P(BA-MMA-AA)包覆在纳米TiO2表面,并与TiO2粒子有较强相互作用.用DSC、GPC和1H-NMR表征共聚产物,发现随TiO2加入,共聚物分子量降低,共聚链段中BA单元比例增加,导致聚合物玻璃化转变温度降低.     

Spinodal phase separation in semi-interpenetrating polymer networks—polystyrene-cross-polymethacrylate

Morphology control in semi-interpenetrating polymer networks has been achieved by means of a two-step process, separating morphology formation and polymerization/crosslinking. Phase textures formed during spinodal liquid/liquid demixing of a solution of atactic polystyrene in methacrylate monomers were arrested by thermoreversible gelation of the polymer-rich phase as this phase passed its glass transition temperature. The phase separated structure was permanently stabilized by low-temperature crosslinking ultraviolet (UV) polymerization of the methacrylate monomer, and studied by transmission electron microscopy. Thus, it was directly observed how the initial demixing process depended on the initial viscosity of the polymer solution and the mode of quenching. Arrest of the earliest stage of spinodal demixing resulted in separated domains of 0.05–0.08 μm thickness, which were separated by a distance of the spinodal wavelength λ. A cocontinuous network only developed in a relatively late stage of demixing. ©1995 John Wiley & Sons, Inc.