Polypropylene (PP)/maleic anhydride grafted poly(styrene-b-ethylene-co-butylene-b-styrene) triblock copolymer (SEBS-g-MA)/halloysite nanotube (HNT) ternary nanocomposites were prepared by two methods: onestep simultaneous melt mixing (SM) of all components; and masterbatch-based melt mixing (MB) involving revolution/rotation-type high shear mixing of a concentrated solution of HNT and SEBS-g-MA, followed by melt blending with PP. Organically modified HNTs (Org-HNTs) with cetyltrimethyl ammonium bromide were prepared via a special cryoscopic expansion/modification technique (C-XP/M). The morphological structures and mechanical properties of the composites, as well as the amount of reinforcer/toughener-compatibilizer (HNT/SEBS-g-MA) at a ratio of 1/3, were discussed as a function of SM and MB techniques. Morphological studies showed that the SM technique revealed microcomposite structures with large aggregates of Org-HNTs in the matrix. In contrast, the MB technique, with the help of elastomeric phase encapsulation, resulted in the best HNT dispersion in the PP matrix, leading to improved mechanical properties. In particular, the PP-based ternary nanocomposite with 3 wt % Org-HNT and 9 wt % SEBS-g-MA prepared by the MB method exhibited 200% higher impact strength compared with PP, attributed to well dispersed, encapsulated, and compatibilized HNTs in the matrix, which created a good balance between stiffness and toughness. POLYM. COMPOS., 00:000-000,
A strategy for the synthesis of new cross-linkable bimodal amphiphilic grafts (bAPGs) was developed. These grafts are of hydrophilic PDMAAm backbones carrying low (M n ∼ 17 200 g/mol) and high (M n ∼ 117 000 g/mol) molecular weight hydrophobic PDMS branches, each branch carrying a vinylsilyl end-group. The bAPGs were cross-linked by Karstedt catalyst to bimodal amphiphilic conetworks (bAPCNs) by the use of polyhydrosiloxane-co-PDMS as the cross-linker. Membranes prepared from bAPCNs exhibit mechanical properties surprisingly superior to earlier APCNs prepared with APGs with monomodal low molecular weight branches. Membrane bimodality controls surface morphology and topography by means of elastic wrinkling instability during film formation. Semipermeable bAPCN membranes with precisely controlled nanochannel dimensions were prepared so as to allow rapid insulin diffusion and prevent passage of IgG. bAPCN membranes were designed for immunoprotection of live pancreatic islets and are thus key components for a bioartificial pancreas.
Micelle formation in tetrahydrofuran-methanol, 1,2-dichloroethane-methanol, tetrahydrofuranwater, and water solutions by PS-PEO diblock copolymers was studied by the fluorescence spectroscopy. For this purpose, a series of PS-PEO copolymers was labeled by the phenanthrene or anthracene groups at the block junctions. The chromophore contents in copolymers were determined by the absorbance spectroscopy using suitable model compounds. When micelles were present, intramicellar nonradiative energy transfer could be observed. For the PS-PEO copolymer (M" = 114 000,93 weight % PEO) we find the onset of micelle formation in water in the range of 10 X 10-3 g/L (9 X -8 M).
Polypropylene (PP)/maleic anhydride grafted polystyrene-b-poly (ethylene/butylene)-b-polystyrene (SEBS-g-MA)/organophilic halloysite nanotube clay ternary nanocomposites were produced by using HNT/SEBS-g-MA masterbatches at different nanotube loadings (1 wt%, 3 wt%, and 5 wt%). The masterbatches with different ratios of HNT/SEBS-g-MA (1/1, 1/2, and 1/3) were prepared via a revolution/rotation type mixing-assisted masterbatch process. All nanocomposites showed higher storage moduli and damping at low temperatures as compared to neat polypropylene. The nanocomposites having HNT/SEBS-g-MA ratio of 1/3 were found to act as effective dampers with their relatively higher damping values. In terms of short-term creep performance, 1 wt% and 3 wt% organophilic halloysite nanotube loaded systems with low amount of SEBS-g-MA (<9 wt%) enhanced dimensional stability of polypropylene with their lower creep strain and permanent deformation values. More specifically, among the nanocomposites, 3 wt% organophilic halloysite nanotube loaded nanocomposite with HNT/SEBS-g-MA ratio of 1/3 and co-continuous like morphology not only exhibited an effective damping over a wide range of temperature (from −70℃ to 50℃) but also showed relatively higher storage moduli at low temperature region together with lower permanent creep deformation as compared to neat polypropylene. As a result, the HNT/SEBS-g-MA masterbatch in 1/3 ratio was found to be the most suitable in polypropylene blend nanocomposites. It may be advantageous for polypropylene nanocomposite based applications where high damping/toughness at low temperature conditions and high dimensional stability under load are desired.
A novel approach to zero-order constant-rate drug delivery from contact lenses is presented. Quasi-Case II non-Fickian transport is achieved by nonuniform drug and diffusivity distributions within three-layer bimodal amphiphilic conetworks (β-APCNs). The center layer is a highly oxygen permeable β-APCN matrix, which contains the drug and exhibits a high drug diffusivity. The outer β-APCN layers contain no-drug and are loaded with vitamin E, which slows diffusion. In contrast to single-layer neat-polymer and vitamin E-loaded films that display first-order "burst" kinetics, it is demonstrated experimentally and by modeling that the combined effect of nonuniform distribution of drug loading and diffusion constants within the three-layer lens maintains low local drug concentration at the lens-fluid interface and yields zero-order drug delivery. The release rates of topical antibiotics provide constant-rate therapeutic-level delivery with appropriate oxygen permeability for at least 30 h, at which time ≈25% of the drug was released.
This paper reports on the polyion complex micelles (PIC micelles) formed between neutral-ionizable double hydrophilic block copolymers (DHBC), poly(ethylene oxide)-block-poly(acrylic acid) (PEO-b-PAA), and oligochitosan, a natural polyamine. The controlled synthesis of PEO-b-PAA polymers was achieved by atom transfer radical polymerization (ATRP) of tert-butyl acrylate with u-bromide-functionalized PEO macroinitiators (M w ¼ 2000 and 5000 g mol À1 ) and the subsequent deprotection reaction under acidic conditions. A series of copolymers with a narrow molecular weight distribution (M w /M n # 1.2) and varied PAA block lengths was synthesized. Capillary electrophoresis (CE) was shown to unambiguously prove the blocky structure of the copolymers. It also showed that about 60%of the sodium counter ions were condensed onto the polyacrylate block in the pure diblock copolymer solution, which is consistent with the formation of polyion complex micelles triggered by counter-ion release in the presence of oligochitosan. The formation of oligochitosan/PAA-PEO core-corona micelles has been investigated by dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). A minimum length of the PAA block is necessary to ensure micelle formation. The range of pH, where PIC micelles form, critically depends on the PAA block length, which also determines the size of the micelles. Micelles can be dissociated at ionic strength above 0.4 mol L À1 . Since these PIC micelles have been used as recyclable structuring agents for the formation of ordered mesoporous materials, the reversibilty of the assembling process was studied upon pH and ionic strength cyclic variations. A hysteresis of stability was observed at low pH, probably due to hydrogen bonding.
SYNOPSISSome primary acrylates, such as methyl, ethyl, n.-butyl, and n-nonyl acrylate (MA, EA, nBuA and nNonA, respectively) have been anionically polymerized by using diphenylmethyl lithium (DPMLi) as an initiator, in the presence of a chelating p-u dual ligand, i.e., a polydentate lithium alkoxide, at low temperature. It has been found that lithium 2-(2methoxyethoxy) ethoxide (LiOEEM) is a very efficient ligand in preventing the anionic polymerization of these monomers from being disturbed by significant secondary transfer and termination reactions. Even for the difficult cases of ethyl and methylacrylate, that approach provides high polymerization yields and low polydispersity,allowing the molecular weight to be predetermined. LiOEEM/initiator molar ratio, solvent polarity, temperature and monomer concentration have proved to be key parameters in the control of the polymerization process. The efficiency of that control is however dependent on the monomer structure and improves with the length of the n-alkyl substituent, i.e., MA < EA < nBuA < nNonA. C 1997 John Wiley & Sons, Inc. Keywords: anionic polymerization q primary acrylates q n-butyl acrylate q n-nonyl acrylate q polydendate lithium alkoxides
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