Small Amount Of Copolymer Research Articles

Preparation of monodisperse PMMA particles by dispersion polymerization of MMA using poly(styrene-co-methacrylic acid) copolymer as a steric stabilizer

Dispersion polymerization of MMA was conducted using poly(styrene-co-methacrylic acid) copolymer as a steric stabilizer in an aqueous methanol medium. Various composition copolymers were easily prepared with a conventional radical polymerization by changing the monomer ratios of styrene to methacrylic acid, and were employed as a steric stabilizer for dispersion polymerization. The copolymers prepared with monomer ratios of 1.25–1.50 were found to be suitable steric stabilizers for dispersion polymerization. A very small amount of copolymer (0.6 wt% based on MMA) could act as a steric stabilizer effectively to obtain monodisperse PMMA particles. The particle size decreased with increasing the solvent polarity from 4 to 0.14 μm.

Copolymer-Induced Stabilizing Effect of Highly Swollen Hexagonal Mesophases

We show that small amounts of copolymer that decorate an oil/water interface can greatly enhance the stability of swollen surfactant hexagonal phases, comprising oil tubes regularly arranged in a water matrix. Both the radius of the tubes and the thickness of the aqueous channel between the tubes can be controlled independently over large ranges. Such soft composite materials offer a potential interest for the synthesis of mesoporous materials.

Amphiphilic Block Copolymer as a Crystal Habit Modifier

The purpose of this study is to evaluate amphiphilic block copolymers, a new class of additives, for the habit modification of pharmaceuticals. The additive chosen is poly(ethylene glycol)-block-poly(lactic acid) (PEG-b-PLA). The model compound chosen is tolazamide, an oral hypoglycemic pharmaceutical agent. Crystallization was carried out in aqueous media by pH adjustment, with or without additives. PEG-b-PLA was found to be very effective in modifying the crystal habit of tolazamide. The habit changed from a needle shape to a plate shape at a concentration of 12.5 μg/mL. This change in habit required both blocks and could not be achieved in the presence of either block alone. A small amount of copolymer (0.55% weight) was found on/in tolazamide particles crystallized in the presence of 30 μg/mL of copolymer. Washing the crystals with toluene effectively removed the copolymer. It is thus concluded that the block copolymer is mainly adsorbed on the crystal surface(s) rather than being incorporated into the lattice of tolazamide crystals. The recrystallized tolazamide is of the same crystal form as that of the original solid, regardless of the concentration of the copolymer used.

Interfacial activity of natural rubber-g-poly(methyl methacrylate) in incompatible natural rubber/poly(methyl methacrylate) blends

Blend of natural rubber and poly(methyl methacrylate) (NR/PMMA) has been made compatible by the addition of graft copolymer of natural rubber and poly (methyl methacrylate) (NR-g-PMMA). The interfacial activity of the graft copolymer is studied as a function of concentration of the graft copolymer by following the morphology of the blend using optical and scanning electron microscopies. Domain size of the dispersed phase is decreased sharply by the addition of small amount of copolymer followed by a levelling off at higher concentration. Improvements in mechanical properties is noted with the addition of graft copolymer. Attempts have been made to correlate the morphology and properties.

Effect of diblock copolymers on dynamic mechanical properties of polyethylene/polystyrene blends

AbstractA systematic investigation of the dynamic mechanical properties of high‐density polyethylene (HDPE)/high‐impact polystyrene (HIPS)/copolymer blends was carried out. Blends of 80/20 weight percent of HDPE/HIPS were prepared in the melt state at 180°C in a batch mixer. Synthesized pure diblock (H77) and tapered diblock (H35) copolymers of hydrogenated polybutadiene (HPB) and polystyrene (PS) were added at different concentrations (1, 3, and 5 wt %), and the dynamic mechanical properties were investigated. The results show that: (1) both the tapered and the pure diblock copolymers enhance the phase dispersion and the interphase interactions; (2) structure and molecular weight are both important parameters in the molecular design of copolymers; (3) important effects occur when only small amounts of copolymer are added (up to the interface saturation concentration SC); (4) a micellar structure formation is possible when the copolymer is in excess in the blend; (5) the effect of the copolymer structure on the SC and the critical micellar concentration (CMC) is more pronounced than the effect of molecular weight. These concentrations are found to be lower for the tapered diblock copolymer. The analysis of the dynamic mechanical thermal analysis (DMTA) results obtained for the 20/80 HDPE/HIPS blend leads to the conclusion that the copolymers also enhance the interactions between heterogeneous phases. Similar conclusions based on electron microscopy were reported in the literature. DMTA shows great potential to relate macroscopic observations to the state of a copolymer in an immiscible blend.

The structure of poly(N‐vinylcarbazole) obtained with cationic initiators and electron acceptors as catalysts

AbstractPoly(N‐vinylcarbazole)s, [poly(l‐(N‐carbazolyl)ethylene)s], (PVCz's) were prepared under various polymerization conditions. The stereoregularities were estimated by means of 13C NMR spectroscopy. Although the stereoregularity of the polymers obtained by BF3O(C2H5)2 was hardly changed by the polymerization temperature, it changed with the solvent polarity from an isotactic‐rich configuration in toluene and CH2Cl2 to a syndiotactic‐rich configuration in nitrobenzene. The 13C NMR spectra of the polymers obtained by organic electron acceptors, support the conclusion that the polymerization by tetracyanoethylene, p‐bromanil, 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone, and tetrachlorophthalic anhydride proceed by a cationic mechanism. In the polymerization of N‐vinylcarbazole (VCz) with maleic anhydride as an electron acceptor, a small amount of copolymer was obtained together with the homopolymer of VCz. Although the structure of the homopolymers is the same as that of the radically obtained polymer, it is considered that the polymer is formed by a cationic mechanism. The polymerizations of VCz by inorganic compounds, such as ferric nitrate, cupric nitrate, cupric bromide, etc., as catalysts are cationic.

Dynamic mechanical properties of polystyrene/low density polyethylene blends

The dynamic mechanical properties of polystyrene/low density polyethylene blends and of polystyrene/polyethylene/di-block polystyrene-polyethylene copolymer blends have been investigated in the temperature range −160°C to +100°C. It is shown that anomalies in the low temperature shear modulus data of polystyrene-polyethylene blends are a consequence of non-adhesion between the components. From similar data of blends containing a partial di-block PS-PE copolymer it appears that only very small amounts of copolymer are needed to ensure adhesion between the polystyrene and polyethylene phase. Further it is shown that for modulus considerations of the blends, LDPE together with partial PS-PE copolymer can be treated as a single phase. In some cases the presence of copolymer causes formation of a continuous network throughout the polystyrene matrix, as reflected by a low value for the shear modulus of these blends. Phase reversal of polystyrene-polyethylene blends results in an increase of the loss modulus at 40°C which is ascribed to an increased friction caused by phase entanglements. This increase is more pronounced if an excess of polyethylene is present which is again a consequence of non-adhesion between the components.