Lee Soon Park

Thermal behaviour of poly (phenylene sulfide) and its derivatives

Abstract Poly(phenylene sulfide) (PPS) and its derivatives, poly(phenylene sulfide-co-phenylene ketone) (PPSK), poly(phenylene sulfide-co-phenylene ether) (PPSE), poly (biphenylene sulfide) (PBPS) and poly(phenylene sulfide-co-phenylene sulfone) (PPSS), were synthesized and their thermal properties were investigated by differential scanning calorimetry and thermogravimetric analysis. PPSK, PBPS and PPS show high crystallinity, in that descending order, while PPSS is totally amorphous. Semi- and non-crystalline PPS/PPSS polymers were melt blended. The blends showed relatively high miscibility and thermal stability. The Tg of PPS/PPSS blends shows 10 and 45°C inward shift; the melt crystallization temperature (Tmc) of PPS decreased to 227°C in the PPS/PPSS blend compared to 244°C for the PPS homopolymer, as determined by differential scanning calorimetry in a cooling scan.

Synthesis of conjugated polymers containing anthracene moiety and their electro‐optical properties

Both fully conjugated polymer poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene vinylene-alt-9,10-anthrylene vinylene] [poly(MEHPV-AV)] and conjugated/nonconjugated block copolymers poly(alkanedioxy-2-methoxy-1,4-phenylene-1,2-ethenylene-9,10-anthrylene-1,2-ehthenylene-3-methoxy-1,4-phenylene)[poly(BFMPx-AV), (x = 4, 8, and 12)] were synthesized by Horner–Emmons reaction utilizing potassium tert-butoxide. Of these synthesized polymers poly(BFMP4-AV) and poly(BFMP8-AV), which has four and six methylene groups as solubility spacer in the main chain exhibited liquid crystalline to isotropic transition in addition to the two first order transitions. Light-emitting diode (LED)s made from the organic solvent soluble poly(BFMP12-AV) as emitting layer showed blue shift in the emission spectrum compared to the one made from fully conjugated poly(MEHPV-AV). Although poly(BFMP12-AV) had higher barrier to the electron injection from cathode than poly(MEHPV-AV), the luminance efficiency of LED made from poly(BFMP12-AV) was about 25 times higher than the one made from poly(MEHPV-AV), which had fully conjugated structure. LEDs fabricated by both poly(BFMP12-AV) and poly(MEHPV-AV) exhibited Stokes shift in the range of 155 to 168 nm from the absorption maximum due to the excimer formation between the ground and excited state anthracene groups.

Synthesis of nonlinear optical maleimide copolymer by polymer reaction and their electro‐optic properties

Thermally stable poly(α-methyl styrene-co-maleimide) (MSMI) and poly(α-methyl styrene-co-4-carboxyphenyl maleimide) (MSCM) substrate polymers were obtained readily by free radical polymerization of comonomers. Introduction of a DR1 chromophore to the maleimide units of MSMI substrate polymer by the Mitsunobu reaction was dependent on the reaction solvent. The degree of substitution of DR1 into the MSMI polymer was bound to be 91.1 mol % and 0.4 mol % by UV spectrometers in the THF and DMF solvent, respectively. DR1 chromophore was, however, substituted in the MSCM polymer at 33.0 mol % by Mitsunobu reaction in the THF solvent. Both substrate and NLO polymer exhibited high thermal stability due to the incorporation of maleimide units in the polymer chain. The glass transition temperature (T g ) and initial decomposition temperature (T i ) of the NLO polymer were in the range of T g = 185°C and T i = 310-345°C. The electro-optic coefficient (r 33 ) of NLO polymer was determined with an experimental setup capable of the real-time measurement while varying both the poling field and temperature. The NLO polymer MSMI-THF had a higher r 33 value than MSCM-DR due to an increased degree of substitution of DR1 chromophore. MSMI-THF had a maximum r 33 value of 16 pm/V at 135 MV/m poling field with a 632.8 nm light source.

Synthesis of Photocrosslinkable Non-Linear Optic Polyimides and Electro-Optic Properties

Abstract Photocrosslinkable polyimide-type non-linear optical (NLO) polymers were obtained by multi-step reactions. Polyimide substrate polymer (P05) made from 3,3′-diamino-4,4′-dihydroxybiphenyl (HAB) and aromatic dianhydride (6FDA) had higher molecular weight than other polyimides due to the high nucleophilicity of the amine group in HAB compared to the one in 2,2′-bis(3-amino-4-hydroxyphenyl)hexafluoropropane(Bis-AP-AF) with the electron-withdrawing group. The introduction of DR-1 chromophore into the polyimide substrate polymers depended on the steric factor between the bulky DR-1 chromophore and the substrate polyimide in the polymer reaction via the Mitsunobu reaction. In the DR-i substituted NLO polyimides, Tg decreased with the increasing amount of DR-1 chromophore. Photocrosslinkable NLO polyimide (P05-DR-cin) was obtained by the introduction of the photoreactive cinnamoyl group into the DR-1 substituted polyimides. The electro-optic coefficient (r33) of the NLO polymer was determined with an experimental set-up capable of real-time measurement by varying both the poling field and temperature. The electro-optic coefficient (r33) of the linear NLO polymer (P05-DR) started to show a decrease of the r33 value from about 80°C. The photocrosslinked NLO polymer (P05-DR-cin), however, maintained a high r33 value up to 150°C due to chromophores locked in the polymer matrix with a network structure.

Synthesis of Polyazomethine Type Conjugated Polymers as Light Emitting Materials

Abstract Aromatic dialdehyde based on phenothiazine and aromatic diamine were used to synthesize polyazomethine type conjugated polymer, poly(PZ-PI) which had good solubility in common organic solvents. The UV absorption maximum(λmax,UV) and edge(λedg,UV) of poly(PZ-PI) were observed at 415 and 510 nm, respectively. The threshold voltage of ITO/polymer/Mg and ITO/polymer/Alq3(100 Å)/Mg device was at 10 V and 7 V, respectively. Besides double layer LED with Alq3 exhibited both enhanced emission intensity and efficiency compared to the single layer LED.

Synthesis and thermal properties of randomcopoly(p-phenylene/biphenylene sulfide)s

Abstract Copoly(p-phenylene/biphenylene sulfide)s (PPBS) were synthesized from sodium sulfide and p-dichlorobenzene (DCB)/4,4′-dibromobiphenyl (DBB) comonomers in N-methyl-2-pyrrolidinone (NMP) solvent under high temperature (270°C) and pressure. The copolymer composition and molecular weight of PPBS were determined by elemental (C,H,S) analysis and high temperature (210°C) g.p.c. with 1-chloronaphthalene as eluent, respectively. The reactivity of DBB monomer was found to be higher than that of DCB toward the thiolate anion from the copolymer composition analysis. The molecular weight of PPBS copolymer showed maximum value (Mw = 23.9−24.1 × 103) at DCB/DBB feed ratio of 70 30 − 60 40 mol%. The Tgs of copolymer were in good agreement with Foxs equation. The PPBS samples exhibited Tms over all copolymer compositions by d.s.c. measurement. The eutectic point appeared to be at about 30 mol% of DBB repeat unit in the copolymer.

Miscibility of partially imidized styrene-maleic anhydride copolymers with styrene-acrylonitrile copolymers

Abstract The miscibility of blends of poly(styrene-co-acrylonitrile) (SAN) and partially imidized poly(styrene-co-maleic anhydride) (SMI) was investigated using differential scanning calorimetry. SMIs with various contents and chemical structures of the imide unit were used in this study. The SANs whose acrylonitrile content is 20–32 wt% were miscible with these SMI s. It was observed that the type of substituent on the imide in SMI also affects the miscibility of the blend.