Poly plasma treatment

Mention has already been made of the effectiveness of corona or plasma treatment in increasing the influence of subsequent or concurrent polymer treatment. As examples of polymers used in this way, mention can be made of reactive cationic polysiloxane [294] and polymerisation on the fibre of tetrafluoroethylene or hexafluoropropylene [299]. Water repellency was also improved by the fluorinated polymers. Tetrafluoroethylene gave superior shrink resistance this polymer covered the scale edges of the wool, whereas this did not occur with poly(hexafluoropropylene). 

Apart from modifications in the bulk, also surface modification of PHAs has been reported. Poly(3HB-co-3HV) film surfaces have been subjected to plasma treatments, using various (mixtures of) gases, water or allyl alcohol [112-114]. Compared to the non-treated polymer samples, the wettability of the surface modified poly(3HB-co-3HV) was increased significantly [112-114]. This yielded a material with improved biocompatibility, which is imperative in the development of biomedical devices. 

Before fluorination, the dielectric constant ofpoly(bisbenzocyclobutene) was 2.8, and this value was reduced to 2.1 after plasma treatment. No data were reported in the paper on characterization of structure or properties, except for the dielectric constant of the modified poly(bisbenzocyclobutene). The authors did report that the thermal stability offluorinatedpoly(vinylidenefluoride) was inferior to the original poly(vinylidenefluoride) when treated in a similar way. One of the probable reasons for the low thermal stability is that the NF3 plasma degraded the polymer. According to their results, the thickness of fluorinated poly(bisbenzo-cyclobutene) was reduced by 30%. The same phenomenon was observed for other hydrocarbon polymers subjected to the NF3 plasma process. A remaining question is whether plasma treatment can modify more than a thin surface layer of the cured polymer Additionally, one of the side products generated was hydrogen fluoride, which is a serious drawback to this approach. 

An alternative photo-SIP approach was described by Kang and coworkers, where they used an argon plasma to oxidize alkylthiolate SAMs on planar gold [55]. The plasma treatment oxidized carboxy-terminated SAMs to peroxide moieties. UV irradiation in the presence of acryhc acid and allylpentafluorobenzene yielded ultra-thin graft layers of 6-7nm. The poly(acrylic acid) layers were found to adsorb Fe " ions from solution. This particular photoinitiation method yields low-density polymer brush films. 

The use of static SIMS for the characterization of surfaces of polypropylene (PP), PTFE and a PMDA-ODA type poly-imide is described. Interfaces between evaporated copper or chromium films onto PTFE and polyimide were also analyzed. Some of the polymer substrates were modified by ion beams, corona discharge in air or plasma treatments in air, At and H2. It is demonstrated that SIMS is highly complementary to XPS for the analysis of such modified surfaces, in that effects such as crosslinking, unsaturation and formation of low-molecular weight material at surfaces can be detected. 

Substrates used included fiber-reinforced epoxy base polymer [FRP], nylon 66, polytetrafluoroethylene [Teflon], poly(ethylene terephthalate) [PET], phenolic resin, and thermoplastic polyimide [ULTEM, GE]. FRPs were the primary substrates used. Initially, they were cleaned with detergent in an ultrasonic bath followed by rinsing with deionized water and alcohol. For further cleaning, they were treated with oxygen plasma (1.33 seem, 60 W, 5 min) followed by a hydrogen plasma treatment (3 seem, 60 W, 5 min). 

Olde Riekerink MB, Terlingen JGA, Engbers GHM, and Feijen J. Selective etching of semicrystalline polymers CF4 gas plasma treatment of poly(ethylene). Langmuir 1999 15 4847-4856. 

Wijdenes and Geomini (170) examined the effects of the phenolic resin composition, its molecular weight distribution, solvent composition, and prebake temperature on the interfacial layer formation. They found that combined use of poly(p-vinylphenol) (structure 3.10) as matrix resin and cyclohexanone as the casting solvent in the diazoquinone resist formulation minimizes mixing of the two layers and yields a capped PCM structure without any plasma treatment. 

Polyacrylic acid (PAA)—P2VP mixed brushes were prepared by a similar synthetic procedure, by grafting of carboxyl-terminated poly(ferf-butyl acrylate) (PtBuA) and P2VP. Afterwards, PtBuA was hydrolyzed in the presence of p-toluene sulfonic acid. The same strategy was employed to graft mixed PEL brushes on polymer surfaces. In this case plasma treatment was used to functionalize surface of polymer substrates. We introduced amino groups on the surface of PA-6 and PTFE by treatment of the polymer samples with NH3 plasma. Then the carboxyl terminated homopolymers were grafted step by step from the melt to the solid substrate via amide bonds. 

Monomers Not Polymerizable by Plasma Initiation. When styrene and a-methy1styrene were subjected to plasma treatment, the monomers became yellowish and only trace amounts of insoluble films were formed. The discoloration was intensified and extensive formation of dark films were observed if carbon tetrachloride was added as the solvent. No post-polymerization was detectable for these monomers. Generally styrene and a-methylstyrene readily undergo thermal polymerization. However, no thermal polymerization was possible for these monomers after having been subjected to plasma treatment for one minute or less. It has been demonstrated from the emission spectra of glow discharge plasma of benzene (6) and its derivatives (7 ) that most of the reaction intermediates are phenyl or benzyl radicals which subsequently form a variety of compounds such as acetylene, methylacetylene, allene, fulvene, biphenyl, poly(p-phenylenes) and so forth. It is possible that styrene and a-methylstyrene also behave similarly, so that species from the monomer plasma are poor initiators for polymerization. 

Fig. 2 Temperature-dependent swelling behaviour of PNIPAAm and poly(NiPAAm-co-DEG-MA) thin films immobilised by low-pressure argon plasma treatment (reproduced from (Nitschke et al. 2007a) with permission)...

Nitschke, M. Schmack, G. Janke, A. Simon, R Pleul, D. and Werner, C. Low pressure plasma treatment of poly(3-hydroxybutyrate) toward tailored polymer surfaces for tissue engineering scaffolds. J. Biomed. Mater. Res. 2002, 59(4), 632-638. 

Turmanova, S. Minchev, M. Vassilev, K. Danev, G. Surface grafting polymerization of vinyl monomers on poly(tetrafluoroethylene) films by plasma treatment. J. Polym. Res. 2008,15 (4), 309-318. 

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