Kwang Ung Kim

Study of the crystallization behaviors of polypropylene and maleic anhydride grafted polypropylene

Abstract The crystallization kinetics of isotactic polypropylene (iPP) and maleic anhydride grafted polypropylene (MA–PP) and their blends, crystallized both nonisothermally and isothermally, were investigated by differential scanning calorimetry. During isothermal crystallization, relative crystallinity developed with the time dependence described by the Avrami equation with exponents n ≈2.7 for neat iPP and n ≈3.8 for MA–PP. The half crystallization time for MA–PP was much smaller than that for iPP. The half crystallization time of iPP depended more strongly on the crystallization temperature than that of MA–PP did. A kinetic equation for nonisothermal crystallization was employed to analyze the crystallization characteristics of iPP and MA–PP. The nonisothermal crystallization kinetic analysis for MA–PP at different cooling rates was possible, assuming that the spherulitic growth was initiated by heterogeneous nucleation alone while that for iPP at high cooling rates was successfully done by assuming both homogeneous and heterogeneous nucleations. The diffusional activation energy was smaller for MA–PP than for iPP. The number of heterogeneous nuclei for MA–PP was larger than that for iPP. The presence of MA–PP in iPP affects the crystallization of iPP by acting as a nucleating agent.

Characterization and processing of blends of poly(ether imide) with thermotropic liquid crystalline polymer

Abstract We investigated thermal, rheological, morphological and mechanical properties of an in situ composite of poly(ether imide) (PEI) and thermotropic liquid crystalline polymer (TLCP). Ultem 1000 was used as a matrix and Vectra B950 was used as the in situ reinforcing TLCP. Fibre-spinning of the blends was performed on a capillary rheometer. Differential scanning calorimetry thermograms of extruded fibres indicated that the thermal properties of PEI did not change noticeably with the amount of TLCP but thermogravimetric analysis showed that thermal stability of the blend was decreased with the amount of TLCP. Immiscibility was checked with thermal data. The rheological properties of the blends changed remarkably with temperature and composition. The tensile strength and modulus of blend fibre increased with TLCP content and spin draw ratio. The increase of tensile strength was more striking for the fibre of the blend containing more TLCP. Wide angle X-ray patterns suggested that the increase in tensile strength was due to the enhanced molecular orientation and resultant fibrillation of TLCP. A modified Tsai-Halpin equation was used to predict the aspect ratio of microfibrils for these blends. Morphology of the blend showed that PEI/TLCP fibres contained fine fibrils of almost infinite aspect ratio and nearly perfect orientation in the flow direction. The draw ratio effect on the mechanical properties was remarkable at low draw ratio, but levelled off soon. The amount of TLCP influenced the fibril formation. Morphological observation showed the effect of thermal history of the blend and its effect on mechanical performance. The blend showed maximum aspect ratio and aspect ratio change when TLCP content was 25 wt%. TLCP orientation and its steric effect seem to induce the optimum TLCP amount for fibril formation.

Synthesis and curing of liquid crystalline epoxy resins based on 4,4′-biphenol

Abstract Two liquid crystalline epoxy (LCE) resins based on biphenol mesogen, BP1 and BP2, were synthesized to produce a highly heat-resistant liquid crystalline network, and the curing behaviour of them was investigated using diaminodiphenylsulfone (DDS) and diaminodipheylester (DDE) as curing agents. The curing rate and heat of curing of LCE resins were measured with dynamic and isothermal DSC. The curing reaction of BP2 based on aromatic ester was faster than that of BP1, and the degree of cure was vice versa. A densely cross-linked BP2 network showed a much higher glass transition temperature (≈280°C) and elastic modulus than other epoxy resins reported up to now. BP2 formed a liquid crystalline network on curing with DDS and DDE, while BP1 showed a liquid crystalline network on curing with DDE. The liquid crystalline phase of the resulting network was maintained up to decomposition temperature (

Compatibilizing effect of a poly(ester imide) on the properties of the blends of poly(ether imide) and a thermotropic liquid crystalline polymer: 2. Morphology and mechanical properties of the in situ composite system

Abstract Blends of a thermotropic liquid crystalline polymer (TLCP), [poly(ester amide), PEA, Vectra B950 from Hoechst Celanese] and poly(ether imide) (PEI, Ultem 1000 from G.E.) with the compatibilizer [poly(ester imide), PEsI] were extruded in a twin-screw extruder. The extruded strands were evaluated in terms of morphology and mechanical properties. The morphology of the compatibilized in situ composites was found to be significantly dependent on the concentration of the compatibilizer in the blend. For a TLCP phase content of 25 phr, a maximum reduction in phase size was observed when 1.5 phr by weight of compatibilizer was added to the blend. At high concentrations of the compatibilizer, flocculation of the TLCP phase was observed. Measurement of the tensile properties shows increased elongation as well as enhanced modulus and strength when properly compatibilized. This improvement is ascribed to better adhesion between the TLCP fibrils and the PEI matrix and better dispersion of the TLCP fibrils. Synthesized PEsI significantly improved the adhesion between the matrix phase (PEI) and fibril phase (PEA). However, maxima in tensile modulus, tensile strength and elongation were observed when excess compatibilizer was added. An emulsifying effect of the compatibilizer to coalesce the fibrils is believed to be the cause of the maxima in the tensile properties. Impact strength was seriously increased with the compatibilizer. A maximum in impact strength was also observed, but all compatibilized samples exhibited a higher impact strength than the non-compatibilized one. The reason is believed to be the failure mode difference between the tensile properties and the impact strength.

Compatibilizing effect of a poly(ester imide) on the properties of the blends of poly(ether imide) and a thermotropic liquid crystalline polymer: 1. Compatibilizer synthesis and thermal and rheological properties of the in situ composite system

Abstract This study investigates the compatibilizing effect of a poly(ester imide) (PEsI) on the blends of poly(ether imide)(PEI, Ultem 1000 from G.E.) and thermotropic liquid crystalline polymer (TLCP)(poly(ester amide), PEA, Vectra B950 from Hoechst Celanese). The compatibilizer, PEsI, was synthesized. Composite fibres were prepared by extrusion. Compatibility, thermal and theological properties of the compatibilized in situ composite have been analysed. PEI and PEA blends are known from previous studies to be immiscible. Differential scanning calorimetry (d.s.c.) and dynamic mechanical thermal analysis (d.m.t.a.) results, however, show that PEsI is miscible with both PEI and PEA. This means that synthesized PEsI can be used as a compatibilizer for the PEI/PEA in situ composite system. The viscosity of the compatibilized in situ composite was increased by the compatibilizer owing to the strong interaction. Significant changes in the dispersion of the TLCP were observed when the compatibilizing agent was added. The size of the dispersed phase appears to be controlled by interfacial phenomena rather than rheological effects. Explanations for the interaction of PEsI with PEI and TLCP related to the interfacial phenomena are presented.

Relationship between the structure of the bridging group and curing of liquid crystalline epoxy resins

The influence of the bridging group between the mesogenic group and the oxirane ring on the curing behavior and the liquid crystalline phase of liquid crystalline epoxy (LCE) resins was investigated. Two LCE resins containing ether and ester bridging groups were synthesized for this purpose. The ether linkage stabilized the liquid crystalline phase of the LCE and the LCE network more than the ester linkage. The retardation effect of curing was observed in LCE with the ester linkage. The LCE with the ether bridge showed higher mechanical and thermal properties than that with the ester bridge. The liquid crystalline phase of the LCE monomer remained after the crosslinking reaction and it was stable up to 300°C.

The effect of end-sulfonated polystyrene on the interfacial tension of nylon-6/polystyrene blends

Abstract The effect of reactive interfacial agents on the interfacial tension of nylon-6/polystyrene (PS) blends was studied. Two types of Li end-sulfonated polystyrene (e-SPS), namely (ω-SPS and α, ω-SPS) were used as the reactive interfacial agents. The interfacial tension in the melt state was measured by the breaking-thread method. As the e-SPS content was increased, the interfacial tension of the nylon-6/PS blend decreased and reached a saturation value, as observed in the case of block copolymers. An effect of the structure of e-SPS on the interfacial tension was observed: for ω-SPS, the saturation value of the sulfonate group concentration was very low (2 × 10 −5 mol 1 −1 ) and no molecular-weight effect was observed; however, for α,ω-SPS, the saturated interfacial tension was attained at a relatively higher sulfonate group concentration than that of ω-SPS, while the lower molecular weight of α,ω-SPS reduced the saturated interfacial tension to a lower value.

Synthesis of 4-tert-butyldimethylsilyloxystyrene and its copolymerization with styrene using (η5-indenyl)trichlorotitanium in the presence of methylaluminoxane

Poly(styrene-co-4-tert-butyldimethylsilyloxystyrene) as a precursor of hydroxyl-functionalized syndiotactic polystyrene was successfully synthesized via (η5-indenyl)trichlorotitanium (IndTiCl3)-catalyzed copolymerization of styrene with 4-tert-butyldimethylsilyloxystyrene in toluene at 25°C in the presence of methylaluminoxane (MAO) ([Al]/[Ti] = 2 000). The amount of styrene derivative incorporated into the polymeric chain for a 20,7 : 1 mole feed ratio of styrene to 4-tert-butyldimethylsilyloxystyrene was found to be 1,8 mol-% from a 1H NMR analysis. The styrene derivative was successfully prepared from 4-hydroxybenzaldehyde via first protecting the hydroxyl group using tert-butyldimethylchlorosilane followed by the ‘Wittig-type’ reaction with the ‘Tebbe’ reagent. The yield was about 82 wt.-% on the basis of the initial amount of 4-hydroxybenzaldehyde used.

Structure development during flow of ternary blends of a polyamide (nylon 66), a thermotropic liquid crystalline polymer (poly(ester amide)) and a functionalized polypropylene

It is shown that a fibril structure of a thermotropic liquid crystalline polymer (TLCP)(poly(ester amide)) can be developed in the shear flow field of a thermoplastic matrix (polyamide, nylon 66) when the viscosity of the latter is lower than that of the former. The addition of a third component, a functionalized polypropylene (maleic-anhydride-grafted polypropylene, MA-PP) that interacts with both the matrix polymer (nylon 66) and the thermotropic liquid crystalline polymer facilitates the structural development of the TLCP by acting as a compatibilizer at the interface. Morphological observations have demonstrated the significance of compatibilization in immiscible polymer blends. The compatibilizer brings about good adhesion at the interface, reduces the droplet size, and enables a finely dispersed liquid crystalline polymer to be deformed by shear flow without strong elongation, even when the viscosity of the matrix is much lower than that of the liquid crystalline polymer. The mechanical properties of the ternary blends are increased when a proper amount of MA-PP is added. This is attributed to fine strand generation induced by the addition of MA-PP. Enhanced adhesion at the interface invokes better elongation in the ternary blends.

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.