Deposition behavior in a low‐temperature cascade arc torch (CAT) polymerization process

Two kinds of hydrocarbon type monomers and three kinds of organosilicons were polymerized by a low‐temperature cascade arc argon plasma torch. Their deposition behaviors were studied as a function of experimental parameters and monomer elemental compositions. It was found that the normalized deposition rate (DR), expressed as deposition yield of DR/(FM)_m, was determined by a composite operational parameter, W*(FM)_c/(FM)_m, where W is the power input, and (FM)_c and (FM)_m are the mass flow rates of carrier gases and monomers, respectively. Experimental results indicated that the deposition yield is highly dependent on the elementary compositions of monomers. Optical emission spectroscopy study on the argon plasma torch showed that the emission intensity of excited argon neutrals was proportional to the value of the parameter W*(FM)_c. These results further certified that excited argon neutrals are the main energy carriers from the cascade arc column to activate monomers in the argon plasma torch. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 967–982, 1999     

Comparisons of glow-discharge polymerizations among tetramethylsilane,dimethyldimethoxysilane, and tetramethoxysilane

Glow-discharge polymerizations among tetramethylsilane, dimethyldimethoxysilane, and tetramethoxysilane were compared by elemental analyses and infrared spectroscopy. The elemental composition of the polymers prepared from the three monomers depended strongly on the operational conditions necessary to sustain a glow discharge, i.e., the W/FM parameter, where W is the rf power, F is the flow rate of the monomer, and M is the molecular weight of the monomer. Methoxy groups were more susceptible to glow discharge than methyl groups. Differences in chemical structure among these monomers appeared in the polymer structures formed when the glow-discharge polymerization was carried out at a low value of the W/FM parameter, while the differences disappeared at high values of the W/FM parameter, for analogous polymers. Substitution with methoxy groups was favorable for the formation of polymers of low carbon content only when the glow-discharge polymerization was performed at low values of W/FM.     

Glow discharge polymerization of tetramethylsilane investigated by infrared spectroscopy and ESCA

The influence of operating conditions (W/FM parameter: W input energy of rf power; F flow rate of monomer; M molecular weight of monomer) on glow discharge polymerization of tetramethylsilane (TMS) was investigated by infrared spectroscopy and ESCA. Elemental analyses showed that the compositions of the polymers formed strongly depended on the level of the W/FM parameter, i.e., whether the W/FM value was more or less than 190 MJ/kg. The infrared spectra indicated that these polymers were composed of Si? H, Si? O, Si? C, Si? CH₃, and Si? CH₂ groups, and that there was no significant difference in structural features between polymers prepared at W/FM parameters of more or less than 190 MJ/kg. ESCA spectra (C_1s and Si_2p core-level spectra) showed that the polymers included carbonized carbon, aliphatic carbon Si? C, C? O, Si? O, and SiO₂ species, and that the sum of carbonized and aliphatic carbons reached more than 50%. Raising the W/FM value increased the formation of the carbonized carbon but did not influence the formation of Si units such as Si? C and Si? O groups. From this evidence the rupture of Si? CH₃ bonds in the polymer forming process is emphasized. The magnitude of the W/FM parameter may be related to the detachment of hydrogen from the aliphatic carbon units.     

Glassy poly(methacrylate) terpolymers with covalently attached emitters and sensitizers for low‐power light upconversion

Low‐power light upconversion by triplet–triplet annihilation (TTA‐UC) was only recently demonstrated in glassy polymers and the upconversion efficiency in these materials is typically much lower than in solution. As aggregation of the chromophores was thought to be the culprit, we here report the covalent tethering of a suitable chromophore pair to a polymeric backbone. The new materials were based on the sensitizer‐bearing monomer palladium meso‐phenoxy‐tris(heptyl)porphyrin‐ethylmethacrylate (PdmPH3PMA), which was copolymerized with a diphenylanthrancene methacrylate (DPAMA), as the emitter‐bearing monomer, and methyl methacrylate (MMA) as an optically inert comonomer. The DPA content was kept within a narrow range of 30–37 wt %, while the PdmPH3PMA content was varied between 0.73 and 0.012 wt %. To explore additional compositions, blends of a high‐porphyrin‐content terpolymer with a DPAMA‐MMA copolymer were also prepared. All of the materials studied were processed into thin films by solution‐casting and displayed blue TTA‐UC emission. The UC emission intensity was found to strongly depend on the composition and the underlying effects were investigated through a systematic study. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1629–1639     

Reversible addition–fragmentation transfer (RAFT) copolymerization of methyl methacrylate and styrene in miniemulsion

In the reversible addition–fragmentation transfer (RAFT) copolymerization of two monomers, even with the simple terminal model, there are two kinds of macroradical and two kinds of polymeric RAFT agent with different R groups. Because the structure of the R group could exert a significant influence on the RAFT process, RAFT copolymerization may behave differently from RAFT homopolymerization. The RAFT copolymerization of methyl methacrylate (MMA) and styrene (St) in miniemulsion was investigated. The performance of the RAFT copolymerization of MMA/St in miniemulsion was found to be dependent on the feed monomer compositions. When St is dominant in the feed monomer composition, RAFT copolymerization is well controlled in the whole range of monomer conversion. However, when MMA is dominant, RAFT copolymerization may be, in some cases, out of control in the late stage of copolymerization, and characterized by a fast increase in the polydispersity index (PDI). The RAFT process was found to have little influence on composition evolution during copolymerization. The synthesis of the well‐defined gradient copolymers and poly[St‐b‐(St‐co‐MMA)] block copolymer by RAFT miniemulsion copolymerization was also demonstrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6248–6258, 2004     

Comparisons of glow discharge polymerization between hexamethyldisilazane and trimethylsilyldimethylamine

Glow discharge polymerization between hexamethyldisilazane (HMDSZ) and trimethylsilyldimethylamine (TMSDMA) was compared by means of infrared spectroscopy and ESCA analysis. Infrared spectra pointed out differences in chemical structure between the polymers prepared from the two monomers, although the two polymers were mainly composed of resembling units such as Si? CH₃, Si? CH₂, Si? H, Si? O? Si, and Si? O? C groups: (i) The polymers prepared from TMSDMA contained N → O group, but the polymers from HMDSZ did not contain this group. (ii) Influences of the W/FM parameter (W is the input energy of rf power, F the flow rate of the monomer, and M the molecular weight of the monomer) appeared on decreasing the C? N group and increasing the C?O group in the TMSDMA system, but little influence appeared in the HMDSZ system. ESCA spectra (C_1s, Si_2p, and N_1s core levels) supported the differences between the two polymers elucidated by infrared spectroscopy, and pointed out differences in susceptibility of the Si? N bond to plasma: The N? Si sequence of TMSDMA was completely ruptured in discharge to yield polymers, and the Si? NH? Si sequence of HMDSZ remained in considerable amount.     

Plasma homo- and copolymerizations of tetrafluoroethylene and chlorotrifluoroethylene

The plasma homo- and copolymerizations of tetrafluoroethylene (TFE) and chlorotrifluoroethylene (CTFE) in a capacitively coupled tubular reactor (TR) with external electrodes were studied by means of microgravimetry and FT-IR and XPS analyses. The deposition rates for CTFE/TFE plasma copolymers, as well as the ratios of IR absorbances at 1180 and 1225 cm⁻¹, and the XPS-derived Cl/C and F/C ratios, varied regularly with mol % CTFE in the feed, all of which results were dependent upon the rf power at which the plasma copolymerizations were conducted. The deposition rates for the plasma homopolymers of TFE (PPTFE) and CTFE (PPTCFE) depended markedly on rf power (W) and monomer molar flow rate (F). The F/C ratio for PPTFE was nearly independent of the composite parameter,W/FM (whereM is the monomer molecular weight), while for PPCTFE, the F/C ratio decreased significantly and the Cl/C ratio increased slightly with increase inW/FM. The percentage of carbon as CF₃ was 20–24% in PPTFE and 7–14% in PPCTFE. Plots of deposition rate versusW/FM for PPTFE and PPCTFE obtained in a TR differed considerably from corresponding plots in the literature for the same homopolymers prepared in a glass-cross or bell-jar reactor.     

Distribution of polymer deposition in plasma polymerization. III. Effect of discharge power

Distribution of polymer deposition in an inductively coupled rf discharge system is studied as a function of level of discharge power with acetylene and styrene as monomers. When a fixed flow rate is used, the discharge power has a relatively small effect on the pattern of distribution of polymer deposition as long as values of W/FM, where W is discharge wattage, F is flow rate, and M is molecular weight of monomer, are maintained above a critical level to maintain full glow in the reaction tube. It has been shown that plasma polymerization of two monomers which have different molecular weights can be compared in a fair manner by selecting conditions to yield similar value of W/FM.     

Plasma polymerization of ethylene glycol monomethylether and water-vapor permeability

Plasma polymerization of ethylene glycol monomethylether (EGMME) was investigated by elemental analysis, infrared spectroscopy, and ESCA. The surface and permeation properties for the formed polymers were discussed. EGMME was plasma-polymerized to yield films. The films contained a large amount of oxygen-containing groups such as hydroxy, carbonyl, carboxylate ester, and ether groups. The formation of polymers having hydroxy groups was favorable in plasma polymerization at low W/FM values. Their surface energy was high (63.2–57 dyn/cm) and decreased with increasing the W/FM value. The plasma-polymers from EGMME had slightly high water-vapor permeability and low oxygen and nitrogen permeabilities. The plasma-polymers, conclusively, are characterized to have high selectivity in water-vapor permeation.     

Pulsed-plasma polymerization of 1-vinyl-2-pyrrolidone: Synthesis of a linear polymer

The RF plasma induced polymerization of 1-vinyl-2-pyrrolidone was examined under variable duty-cycle pulsed-plasma conditions. Large-scale progressive changes in the composition of the resultant polymeric films were observed with sequential changes in the plasma duty cycle employed during polymerization, all other plasma variables held constant. The film compositional changes obtained are in the direction of increased retention of the lactam ring of the monomer in the resultant polymers as the duty cycles employed (i.e., the ratio of plasma on to plasma off times) were decreased. Particularly significant are the relatively linear polymeric structures obtained under the exceptionally low-average power deposition conditions made accessible with the pulsed plasma technique. XPS and FTIR spectroscopic examination of these latter films reveal compositions that are similar to those obtained by conventional (i.e., nonplasma) synthesis of the linear polymer. The film chemistry controllability demonstrated in the present study is achieved while maintaining the many advantages of the plasma polymerization approach for surface modifications. This work provides additional support for use of the pulsed operational mode as an effective means of film chemistry control, in particular extending the plasma polymerization technique to include synthesis of linear polymers, in lieu of the more highly crosslinked structures typically produced in conventional continuous-wave plasma polymerization processes. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3121–3129, 1998     

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.     

Internal stress in plasma polymer films prepared by cascade arc torch polymerization

Thin plasma polymer films were deposited from several liquid monomers (mainly siloxane‐type monomers) in a low‐temperature cascade arc torch (CAT) reactor. The effects of monomer structures and plasma parameters on internal stress in the films were experimentally studied. By appropriately adjusting these factors, the internal stress in the film was reduced nearly two orders of magnitude from 10⁹ to 10⁷ dyn/cm². It was noted that the polymer films prepared from siloxane‐type monomers showed lower internal stress than their hydrocarbon counterpart. Fourier transform‐infrared spectroscopy (FTIR) studies indicated that a large amount of Si O Si structure from siloxane monomers, which are very flexible bonds, was preserved in the resultant plasma polymers. Ellipsometry results suggested that the internal stress can be qualitatively correlated with the refractive index of the plasma polymer film. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1577–1587, 1999     

Synthesis and thermal characterization of poly(dimethyl bicyclobutane‐1,3‐dicarboxylate) and its copolymers

Dimethyl bicyclobutane‐1,3‐dicarboxylate was synthesized. Its homopolymer (PDBD) containing exclusively cyclobutane rings in its backbone was prepared by free radical polymerization. The copolymers of this bicyclobutane monomer with methyl methacrylate were also prepared. The glass transition temperature of the homopolymer is 159°C, while those of its copolymers are 143 and 121°C with 75/25 and 50/50 of the P(DBD/MMA) composition ratio, respectively. The T_g of PDBD homopolymer is substantially higher than that of commercial PMMA homopolymer despite a lower molecular weight, and is also much higher than that of its monomethyl cyclobutanecarboxylate analogue. These DBD homopolymer and copolymers also show better thermostability than the PMMA homopolymer. The weight‐average molecular weight of homopolymer is 37,000. The polydispersities of these polymers are relatively narrow, with the range of 1.6–1.9. These polymers form clear colorless films resembling PMMA film. The DBD homopolymer film shows a very similar optical cutoff compared to PMMA. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1569–1575, 1999     

Plasma polymerization investigated by the substrate temperature dependence

Plasma polymerization of tetra fluoroethylene (TFE), perfluoro-2-butyl-tetrahydrofuran (PFBTHF), ethylene, and styrene were investigated in various combinations of monomer flow rates and discharge wattages for the substrate temperature range of ?50 to 80°C. The polymer deposition rates can be generally expressed by k₀ = Ae^?bt, where k₀ is the specific deposition rate given by k₀ = (deposition rate)/(mass flow rate of monomer), A is the preexponential factor representing the extrapolated value of k₀ at zero absolute temperature, and b is the temperature-dependence coefficient. It was found that the value of b is not dependent on the condensibility of monomer but depends largely on the group of monomer; that is, perfluorocarbons versus hydrocarbons. The values of A are dependent on domains of plasma polymerization. In the energy deficient region A is given by A = α(W/FM)ⁿ, where α is the proportionality constant, W is discharge wattage, FM is the mass flow rate, and n is close to unity. In the monomer deficient region A becomes a constant. The kinetic equation is discussed in view of the bicyclic rapid step-growth polymerization mechanisms.     

Synthesis of star‐shaped copolymers with methyl methacrylate and n‐butyl methacrylate by metal‐catalyzed living radical polymerization: Block and random copolymer arms and microgel cores

Various star‐shaped copolymers of methyl methacrylate (MMA) and n‐butyl methacrylate (nBMA) were synthesized in one pot with RuCl₂(PPh₃)₃‐catalyzed living radical polymerization and subsequent polymer linking reactions with divinyl compounds. Sequential living radical polymerization of nBMA and MMA in that order and vice versa, followed by linking reactions of the living block copolymers with appropriate divinyl compounds, afforded star block copolymers consisting of AB‐ or BA‐type block copolymer arms with controlled lengths and comonomer compositions in high yields (≥90%). The lengths and compositions of each unit varied with the amount of each monomer feed. Star copolymers with random copolymer arms were prepared by the living radical random copolymerization of MMA and nBMA followed by linking reactions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 633–641, 2002; DOI 10.1002/pola.10145     

Determination of chain transfer constant to dodecanethiol in styrene/methyl methacrylate and butyl acrylate/methyl methacrylate copolymerization and effect of chain length on composition and stereochemical configuration of copolymers

Free radical copolymerization of styrene/methyl methacrylate (S/MMA) and butyl acrylate/methyl methacrylate (BA/MMA) in the presence of n-dodecanthiol (DDT) has been studied at 60°C in a 3 mol/L benzene solution using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator. Overall chain transfer constant to DDT has been determined for both copolymerization systems, as a function of monomer feed composition using complete molecular weight distribution and the Mayo method. Overall transfer coefficients have values which are dependent on both monomer feed composition and individual comonomer transfer values. Composition, sequence distribution, and stereoregularity of copolymers obtained are, in our experimental conditions, independent of copolymer molecular weight. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2913–2925, 1998     

Molecular adsorption and the chemistry of plasma-deposited thin organic films: Deposition of oligomers of ethylene glycol

Weakly ionized, radio-frequency, glow-discharge plasmas formed from methyl ether or the vapors of a series of dimethyl oligo(ethylene glycol) precursors (general formula: H-(CH₂OCH₂)_n-H;n=1 to 4) were used to deposit organic thin films on polytetrafluoroethylene. X-ray photoelecton spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS) of the thin films were used to infer the importance of adsorption of molecular species from the plasma onto the surface of the growing, organic film during deposition. Films were prepared by plasma deposition of each precursor at similar deposition conditions (i.e., equal plasma power (W), precursor flow rate (F), and deposition duration), and at conditions such that the specific energy (energy/mass) of the discharge (assumed to be constrained byW/FM, whereM=molecular weight of the precursor) was constant. At constantW/FM conditions, two levels of plasma power (and, hence, twoFM levels) and three substrate temperatures were examined. By controlling the energy of the discharge (W/FM) and the substrate temperature, these experiments enabled the study of effects of the size and the vapor pressure of the precursor on the film chemistry. The atomic % of oxygen in the film surface, estimated by XPS, and the intensity of theC-O peak in the XPS C_ls spectra of the films, were used as indicators of the degree of incorporation of precursor moieties into the plasma-deposited films. Analysis of films by SIMS suggested that these two measures obtained from XPS were good indicators of the degree of retention in the deposited films of functional groups from the precursors. The XPS and SIMS data suggest that adsorption of intact precursor molecules or fragments of precursor molecules during deposition can have a significant effect on film chemistry. Plasma deposition of low vapor pressure precursors provides a convenient way of producing thin films with predictable chemistry and a high level of retention of functional groups from the precursor.     

Nonlinear depression of the lower critical solution temperatures in aqueous solutions of thermo-sensitive random copolymers

We develop a theoretical model of cooperative hydration to clarify the molecular origin of the observed nonlinear depression of the lower critical solution temperature (LCST) in the aqueous solutions of thermosensitive random copolymers and find the monomer composition at which LCST shows a minimum. Phase diagrams of poly(N-isopropylacrylamide-co-N,N-diethylacrylamide) copolymer solutions are theoretically derived on the basis of the theory of cooperative hydration by introducing the microscopic structure parameter η which characterizes the distribution of the monomer sequences along the chains. We compared them with the experimental data of LCST of random copolymers with various monomer compositions and also of the diblock copolymers with equimolar monomer composition. The transition temperature shifts to lower than those of homopolymer counterparts when the monomer sequence of the chains has an alternative tendency. On the contrary, for the blocky polymers such as diblock copolymers, the transition temperature remains almost the same as those of the homopolymers. Thus, the nonlinear effect in phase separation appears when the average block length of the copolymers is shorter than the average sequence length of the cooperative hydration. The degree of hydration is calculated as a function of the temperature and polymer concentration for varied distribution of the copolymer compositions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1112–1123     

A comparative study of the stimuli‐responsive properties of DMAEA and DMAEMA containing polymers

Reversible addition‐fragmentation chain transfer copolymerization of dimethylaminoethyl acrylate (DMAEA) and methyl acrylate (MA) and their methacrylate counterparts (MMA) has been performed with good control over molecular weight and polydispersity. A screening in composition of copolymers has been performed from 0 to 75% of MA (or MMA). The behavior of these pH and temperature‐sensitive copolymers has been studied in aqueous solution by measuring the cloud point (CP) and the acid dissociation constants (pK_a). The higher incorporation of the hydrophobic monomer in the copolymer resulted in an increase in the pK_a values due to the larger distance between charges thus facilitating the protonation of adjacent nitrogens for both, the acrylate and methacrylate derivatives. The CP behavior of the copolymers has been studied in pure water and the CP values have been found to be irreproducible for the acrylate polymers, as a consequence of the self‐hydrolysis of DMAEA. Hence, kinetic studies have been performed to quantify the degree of self‐hydrolysis at different temperatures and polymer concentrations to explore the full potential and application of these versatile polymers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3333–3338     

DC plasma polymerization of hexamethyldisiloxane

Hexamethyldisiloxane (HMDS) was polymerized onto metallic and insulating substrates in a parallel-plate DC reactor. The limits of the DC reactor with respect to pressure and power were determined for deposition of PP-HMDS films. In all conditions ranging from 5 Pa/0.3 W to 100 Pa/50 W, solid films were deposited. No powders or oily films were obtained under any condition in this operating range. The films were polymeric in nature,i.e., they were neither carbon-like nor SiO _x -like films. The structures and crosslink densities of the plasma films dependend strongly on the deposition conditions. The highest deposition rates, up to 2 μm per minute (or0.3 mg/cm² min), were obtained at high power, pressure, and flow rate conditions. An efficiency ɛ is introduced, defined as the fraction of the monomer that is retained in the form of a polymer deposited on the substrate. Efficiencies as high as 25% could be obtained in certain conditions. Pulsing the discharge power increased the conversion efficiency markedly, but the effect depended strongly on the monomer used. In addition to HMDS, plasma polymers were also deposited from pyrrole in pulsed conditions for comparison. A method is described for depositing films on insulators from a DC glow discharge using two wire meshes held at a negative potential.