Poly corona

Figure 5 Corona discharge behavior of polystyrene added with polystyrene-b-poly(sodium acrylate) [57].

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). 

Films of polyolefins, polyamides and poly(vinylidene dichloride) are made using this technique. As most of the films are used for flexible packaging, further down-stream surface treatments are usually applied to improve performance. For example, aqueous polymer emulsions, e.g., poly(vinylidene dichloride), or delaminated clay particles improve the barrier properties as will metallising with aluminium vapour. Corona discharge, causing slight surface oxidation, improves printability. 

Following these early solid-state investigations, 1,907 nm EFISHG studies by Tam and co-workers on several complexes [W(CO)5L] (L = py or a 4-substituted py) quote (3 values similar to that of 4-nitroaniline (ca. 10 x 10-30 esu) and sensitive to the nature of the pyridyl substituent.67-69 These results were quickly followed by ZINDO/SCI-SOS calculations on the same series of complexes by Kanis et al.70 the first time that MO theory had been used to describe the quadratic NLO responses of metal complexes. The results of these calculations agree reasonably well with the EFISHG data, and indicate that the modest (3 responses can be traced to relatively small Ap12 values.70 Lacroix et al. obtained low 1,064 nm SHG activities by corona poling films of poly (4-vinylpyridine) and of two other related polymers functionalized with W(CO)5 centers.71... 

Burlde A (2005) Poly(ADP-ribose). The most elaborate metabolite of NAD. Febs J 272 4576-4589 Burlde A, Brabeck C, Diefenbach J, Beneke S (2005) The emerging role of poly(ADP-ribose) polymerase-1 in longevity. Int J Biochem Cell Biol 37 1043—1053 Cardenas-Corona M, Jacobson E, Jacobson M (1987) Endogenous polymers of ADP-ribose are associated with the nuclear matrix. J Biol Chem 262 14863—14866 Chang P, Jacobson MK, Mitchison TJ (2004) Poly(ADP-ribose) is required for spindle assembly and structure. Nature 432 645-649... 

The non-aqueous system of spherical micelles of poly(styrene)(PS)-poly-(isoprene)(PI) in decane has been investigated by Farago et al. and Kanaya et al. [298,299]. The data were interpreted in terms of corona brush fluctuations that are described by a differential equation formulated by de Gennes for the breathing mode of tethered polymer chains on a surface [300]. A fair description of S(Q,t) with a minimum number of parameters could be achieved. Kanaya et al. [299] extended the investigation to a concentrated (30%, PI volume fraction) PS-PI micelle system and found a significant slowing down of the relaxation. The latter is explained by a reduction of osmotic compressibihty in the corona due to chain overlap. 

Note 2 Poly(vinylidene fluoride) after being subjected to a corona discharge is an example of a ferroelectric polymer. 

Sugita, K., S. Nagao and Y. Toriyama The corona resisting property of poly-tetraflnoroethylene. Brit. J. Appl. Phys. 7, 38 (1956). 

Table II. Second-Harmonic Coefficients ( 33) and Temporal Decay Parameters for Corona-Poled, NPP-Functionalized Poly(p-hydroxystyrene) Films as a Function of Thermal Cross-Linking a...

Dopant orientation during and following electric field-induced poling can be studied continuously and in real time in order to examine the microenvironment surrounding the dopants in terms of the polymer relaxations and the applied corona field. In the results presented below, the SHG of 4-dimethylamino-4 -nitrostilbene (DANS) dispersed in polystyrene (PS) or poly(methyl methacrylate) (PMMA) matrices has been examined in corona poled films as a function of temperature in order to understand the effect of thermal conditions on the temporal stability of the dopant orientation. 

Figure 6.1 Cylindrical micelles of a poly(ferrocenyldimethylsilane)/poly(dimethylsiloxane) or polyisoprene block copolymer showing the central core of the ferrocenylsilane units and the corona of the organic polymer blocks. Reproduced by permission of Prof. I. Manners.

Figure 9.4 Core-shell polyplex structures (A) cationic particles with a core from neutralized DNA and polycation and a corona from polycation chains adsorbed on the core (B) electroneutral particles ( polyion complex micelles or block ionomer complex ) with a core from neutralized DNA and poly cation and a corona from nonionic water soluble polymer.

The adsorption of block copolymers can be controlled by different stimuli, in particular by the pH since most of the brushes formed by block copolymers adsorption are polyelectrolyte brushes [129, 130], The group of Armes, for instance, studied the pH-controlled adsorption of a series of block copolymers [131, 132], In the case of copolymers bearing hydrophobic 2-(diethylamino)ethyl methacrylate groups (DEA) and a water-soluble zwiterionic poly(2-methacryloyl phosphoryl-choline) (MPC) block, they showed that at low pH the cationic DEA flatted to the anionic silicon surface while the MPC was in contact with the solution [132], At around neutral pH, micelles were formed in solution and adsorbed onto the surface because the DEA core was still weakly cationic. The MPC block formed the micelle coronas. Nevertheless, at higher pH the micelles became less cationic and the adsorption rate decreased. 

Three different ways have been developed to produce nanoparticle of PE-surfs. The most simple one is the mixing of polyelectrolytes and surfactants in non-stoichiometric quantities. An example for this is the complexation of poly(ethylene imine) with dodecanoic acid (PEI-C12). It forms a solid-state complex that is water-insoluble when the number of complexable amino functions is equal to the number of carboxylic acid groups [128]. Its structure is smectic A-like. The same complex forms nanoparticles when the polymer is used in an excess of 50% [129]. The particles exhibit hydrodynamic diameters in the range of 80-150 nm, which depend on the preparation conditions, i.e., the particle formation is kinetically controlled. Each particle consists of a relatively compact core surrounded by a diffuse corona. PEI-C12 forms the core, while non-complexed PEI acts as a cationic-active dispersing agent. It was found that the nanoparticles show high zeta potentials (approximate to +40 mV) and are stable in NaCl solutions at concentrations of up to 0.3 mol l-1. The stabilization of the nanoparticles results from a combination of ionic and steric contributions. A variation of the pH value was used to activate the dissolution of the particles. 

In conclusion, it was found that complexes of poly(ethylene oxide)-h-poly(L-lysine) with retinoic acid with short poly(L-lysine) segments of 18 and 30 monomers form core shell micelles. The cores of the micelles contain a lamellar smectic A-like structure, formed by a poly(L-lysine) retinoate complex, which is surrounded by a corona of poly(ethylene oxide). Although the poly(L-lysine) chains are relatively short, they adopt an a-helical conformation to a pH as low as 9. This effective stabilization of the a-helix structure seems to be due to the formation of a protective surrounding coat of retinoate and a shell of poly(ethylene oxide). 

Systematic studies on micellar size and structure have been published for poly(styrene-h-acrylic acid) (PS-PAAc) [7, 8], poly(styrene-fr-sodium acrylate) (PS-PAAcNa) [9], or quaternized poly(styrene-h-4-vinyl-pyridine) (PS-P4VPMeI) [10, 11]. It was concluded that the polyelectrolyte chains in the micellar corona are almost fully stretched [8]. The effect of salt concentration was investigated by Guenoun et al. on poly(f-butylstyrene-fr-sodium styrene sulfonate) (PtBS-PSSNa) who observed a weak decrease of micellar size and aggregation number when the salt concentration was increased beyond 0.01 mol/1 [12]. Using small-angle neutron scattering (SANS), the authors could provide additional support for the rod-like conformation of the polyelectrolyte chains in the micellar corona [13]. 

For quite some time, there have been indications for a phase-separation in the shell of polyelectrolyte block copolymer micelles. Electrophoretic mobility measurements on PS-PMAc [50] indicated that a part of the shell exhibits a considerable higher ionic strength than the surrounding medium. This had been corroborated by fluorescence studies on PS-PMAc [51-53] and PS-P2VP-heteroarm star polymers [54]. According to the steady-state fluorescence and anisotropy decays of fluorophores attached to the ends of the PMAc-blocks, a certain fraction of the fluorophores (probably those on the blocks that were folded back to the core/shell interface) monitored a lower polarity of the environment. Their mobility was substantially restricted. It thus seemed as if the polyelectrolyte corona was phase separated into a dense interior part and a dilute outer part. Further experimental evidence for the existence of a dense interior corona domain has been found in an NMR/SANS-study on poly(methylmethacrylate-fr-acrylic acid) (PMMA-PAAc) micelles [55]. 

Giebeler et al. [73] investigated the polyelectrolyte complex formation of triblock copolyampholytes, polystyrene-frZock-poly( 2 or 4)-vinylpyridine)-b/oc/c-poly(methacrylic acid). By potentiometric, conductometric and turbi-dimetric titrations of acidic THF/water solutions the formation of an interpolymer complex at the isoelectric point was found, in which most likely the hydrophobic polystyrene cores are embedded in a mixed corona of the two polyelectrolyte blocks. 

Gohy et al. studied the solution properties of micelles formed by two polystyrene-frZock-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-b-P2VP- -PEO) copolymers in water by dynamic light scattering and transmission electron microscopy [92]. Spherical micelles were observed that consist of a PS core, a P2VP shell and a PEO corona. The characteristic sizes of core, shell and corona were found to depend on the copolymer composition. The micellar size increased at pH<5 due to P2VP block protonation (Fig. 19). 

Janus micelles are non-centrosymmetric, surface-compartmentalized nanoparticles, in which a cross-linked core is surrounded by two different corona hemispheres. Their intrinsic amphiphilicity leads to the collapse of one hemisphere in a selective solvent, followed by self-assembly into higher ordered superstructures. Recently, the synthesis of such structures was achieved by crosslinking of the center block of ABC triblock copolymers in the bulk state, using a morphology where the B block forms spheres between lamellae of the A and C blocks [95, 96]. In solution, Janus micelles with polystyrene (PS) and poly(methyl methacrylate) (PMMA) half-coronas around a crosslinked polybutadiene (PB) core aggregate to larger entities with a sharp size distribution, which can be considered as supermicelles (Fig. 20). They coexist with single Janus micelles (unimers) both in THF solution and on silicon and water surfaces [95, 97]. 

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