Tae Oan Ahn

Direct polymer reaction of poly(styrene-co-maleic anhydride): Polymeric imidization

Using direct polymer reaction of poly(styrene-co-maleic anhydride) (SMA), a synthesis of copolymer of styrene and N-aryl succinimide (SMI) has been investigated. SMI copolymers were synthesized from SMA copolymers by a concerted two-step reaction, which consisted of the condensation reaction (step 1) of SMA with aromatic amine to prepare a precursor, succinamic acid, for imide formation and the cyclodehydration reaction (step 2) of succinamic acid. In this article, the application of Searles preparation method of N-aryl or N-alkyl maleimide to the direct polymer reaction for SMI was attempted. Compared with synthesis of monomeric imides, the imide formation in polymeric condition appeared to be a little more sensitive to the reaction condition. The optimum condition for maximum conversion was examined in terms of time, temperature, and the amount of reactants.

Control of molecular weight distribution in propylene polymerization with Ziegler–Natta/metallocene catalyst mixtures

Propylene polymerization was investigated with a sequential addition of Ziegler-Natta and metallocene catalysts. From the fact that the molecular weights of polypropylene (PP) produced with Ziegler-Natta and with metallocene catalysts differ, it was possible to control the molecular weight distribution ( MWD ) of PP with a sequential addition of methylaluminoxane and rac-ethylenebis (indenyl) zirconium dichloride followed by triethylaluminum and magnesium dichloride-supported titanium tetrachloride catalyst. The obtained PP exhibited a wide MWD curve with shoulder peak. The position and height of each peak was controlled with the variation of polymerization time for each catalyst as well as the amount of each catalyst. The MWD of PP prepared with sequential addition of catalysts was much wider than that of PP obtained from each catalyst.

Nylon 6-polyethersulfone-nylon 6 block copolymer : synthesis and application as compatibilizer for polyethersulfone/nylon 6 blend

Abstract Nylon 6-polyethersulfone (PES)-nylon 6 block copolymers were synthesized by anionic polymerization of ϵ-caprolactam using chlorine-terminated PES, a polymeric activator. The structure and properties of these block polymers were examined using infra-red, nuclear magnetic resonance, differential scanning calorimetry, transmission electron microscopy, and thermogravimetric analysis. The compatibilizing effects of this block copolymer on PES/nylon 6 blends were investigated by examining thermal properties, morphology and dynamic mechanical characteristics. When the block copolymer was added, the size of dispersed phase in the blend decreased dramatically, and the glass transition temperatures of the constituent polymers converge. The improvement of dynamic tensile modulus and thermal resistance due to the dispersed PES phase were enhanced by the added block copolymer.

Enhancement of interfacial adhesion between polystyrene and styrene maleic anhydride random copolymer via reactive reinforcement

Abstract The effects of amine-terminated polystyrene (ω-amino-PS) of various molecular weights on the interfacial adhesion strength between polystyrene and styrene maleic anhydride (SMA) random copolymer have been investigated. The adhesive joint is composed of SMA and a blend of PS and ω-amino-PS, in which the ω-amino-PS acts as a reactive compatibilizer. Here, the amine end-group of ω-amino-PS in the PS/ω-amino-PS blend is known to react with the anhydride group of SMA and form an end-grafted copolymer, which acts as an interlinking molecule across an interface and improves the interfacial adhesion strength. The fracture toughness of the interface was measured using a modified double-cantilever beam fracture test. The enhancement of fracture toughness of the interface was evaluated as a function of molecular weight and content of ω-amino-PS, i.e. interlinking chain length and area density of interlinking molecules. The fracture toughness was found to increase with the amount of ω-amino-PS and then decreased or saturated at a certain content depending on the molecular weight of ω-amino-PS. When the molecular weight of ω-amino-PS was 26 000 (26 k), which is just above the entanglement molecular weight, there was an optimum content in reinforcing the interfaces due to the weak mechanical strength of 26 k ω-amino-PS. However, when the molecular weight was far above the entanglement molecular weight, i.e. 67 k and 127 k, the fracture toughness levelled off as the content of ω-amino-PS increased. At the same concentration of amine groups, 127 k ω-amino-PS showed the highest fracture toughness.

Mechanical effects according to the type of poly(styrene-co-methyl methacrylate) copolymers at polystyrene/poly(methyl methacrylate) interfaces

Abstract The effects of incorporating a thin layer of various types of polystyrene-poly(methyl methacrylate) copolymers, i.e. block, random, and graft copolymer on the interfacial adhesion between PS and PMMA have been investigated. The fracture toughness of the interface was measured using an asymmetric double cantilever beam fracture test and the enhanced toughness effect of copolymers was compared. The fracture toughness of the interface increased with increasing layer thickness of the copolymer and each copolymer had the layer thickness of saturated fracture toughness. The fracture toughness increased in the order of block > graft > random copolymer.

Compatibilizing effect of polyarylate-polyamide-6 block copolymers on polyarylate/polyamide-6 blends: 2

Abstract Ternary blends of polyarylate (PAr), polyamide-6 (PA-6) and PAr-PA-6 block copolymer were prepared by the dissolution/precipitation method or by melt blending. The compatibilizing effect of PAr-PA-6 block copolymer was observed with scanning electron microscopy and differential scanning calorimetry. The inward shift of the glass transition temperature (Tg) of PAr and PA-6 and the depression of the melting temperature (Tm) of PA-6 in ternary blends depended on the block length as well as on the amount of the block copolymer added. The shorter block length and the higher amount of block copolymer added caused greater shifts of Tg and Tm. The compatibilizing effect of the block copolymer was also confirmed from the enhanced mechanical properties.

Phase structure and properties of some thermoplastic polyesteramide elastomers

Abstract Thermoplastic polyesteramide elastomers with aromatic moieties were prepared and their structure-property relations were studied. The elastomers were synthesized by the polycondensation of 4,4′-methylenediphenyl diisocyanate, carboxylic acid-terminated poly(butylene adipate) oligomers and three different aliphatic dicarboxylic acids. Mixing between the hard and soft phases, examined by thermal and i.r. spectroscopic measurements, depended on the contents and the molecular weights of the poly(butylene adipate) oligomers and also on the types of the aliphatic dicarboxylic acids used. The dissolution of the hard polyamide segment into soft polyester domains increased with decreasing molecular weights of the constituent segments. The mixing was more effective when adipic acid, 1,10-decanedicarboxylic acid and azelaic acid (in increasing order of effectiveness) were used. A higher degree of phase mixing appeared to enhance the moduli of the elastomers but impair the tensile properties at high deformation.

Effects of reactive reinforced interface on the morphology and tensile properties of amorphous polyamide–SAN blends

The effects of reactive reinforced interface on the morphology and tensile properties of amorphous polyamide (a-PA) and styrene-acrylonitrile (SAN) copolymer blend have been investigated using styrene maleic anhydride (SMA) copolymer as a reactive compatibilizer. The anhydride groups of SMA copolymer can react with the amine groups of polyamide and form in situ graft copolymers at the a-PA–SAN interfaces during the blend preparation. The interfacial adhesion strength of the reactive reinforced interface was evaluated quantitatively using an asymmetric double cantilever beam fracture test as a function of SMA copolymer content using a model adhesive joint. The interfacial adhesion strength was found to increase with the content of SMA copolymer and then level off. The morphological observations of a-PA–SAN (80/20 w/w) blends showed that the finer dispersion of the SAN domains with rather narrow distribution was obtained by the addition of SMA copolymer into the blends. The trend of morphology change was not in accord with that of the interfacial adhesion strength with respect to the content of SMA copolymer. However, the results of tensile properties showed very similar behavior to the case of the interfacial adhesion strength with respect to SMA content; that is, there was an optimum level of the reactive compatibilizer beyond which the interfacial adhesion strength and tensile strength did not change significantly. These results clearly reveal that tensile properties of polymer blend are highly dependent on the interfacial adhesion strength. Furthermore, it is suggested that the asymmetric double cantilever beam fracture test using a model interface is a useful method to quantify the adhesion strength between the phases in real polymer blends.

Influence of interchange reactions on the miscibility of polyesterurethanes/polycarbonate binary blends

A series of thermoplastic polyurethane elastomers (TPUs) with various hard-segment contents was prepared using 4,4′-diphenylmethane diisocyanate and 1,4-butanediol as the hard segment and poly(ethylene adipate)diol or poly(butylene adipate)diol, whose number-average molecular weight is 2000, as the soft segment. The miscibility of TPU/polycarbonate (PC) blends observed by differential scanning calorimetry was enhanced by the interchange reaction at high temperature. Both hard and soft segments were suggested to be involved in the interchange reaction with PC.

Morphology and toughening behaviour of diallyl isophthalate resin/polyarylate alloy

The excessively brittle diallyl isophthalate (DAIP) resin was toughened using polyarylate (PAr). The cure kinetics and appropriate cure condition were investigated with differential scanning calorimetry. Fracture surfaces showed that phase separation occurred, resulting in a two-phase morphology. At 2 and 5 phr of PAr, spherical particles of PAr containing DAIP inclusions were obtained. Observation of tails at the rear of particles on the fracture surfaces provides some evidence for crack pinning, which resulted in a slight increase in fracture toughness. At 10 phr of PAr a co-continuous connected globular morphology was obtained, leading to a step increase in the fracture toughness by ductile drawing of the PAr. Co-continuous structure was also observed at 15 phr of PAr, and fracture toughness was increased by 1.5 times with little sacrifice in other mechanical properties. From optical and scanning electron microscopy studies on fracture surfaces, the toughening mechanism is considered to be crack path deflection and ductile drawing of PAr.