Nakjoong Kim

Nonlinear optical polymers with novel benzoxazole chromophores: IV. Synthesis of maleimide–styrene and maleimide–methacrylate copolymers

Four nonlinear optical maleimide copolymers were synthesized by radical copolymerization of N-phenylmaleimide and methacrylate-based or styrene-based monomer with benzoxazole chromophores, respectively. The copolymers had high glass transition temperatures of 158°C and exhibited good thermal stability. The most transparent film was prepared from a alternating copolymer (PMIBz 2) derived from N-phenylmaleimide and styrene-based NLO monomer. The second harmonic generation coefficient and electro-optical coefficient (r33) of a poled PMIBz 2 film was 45 pm/V (at 1.064 μm) and 6.1 pm/V (at 1.3 μm), respectively. The temporal stability of r33 of PMIBz 2 was superior to that of only methacrylate-based copolymer.

Nonlinear optical polymers with novel benzoxazole chromophores: V. Linear and crosslinked polyurethanes using nitrothiophene and nitrophenol as electron acceptors

Abstract We synthesized two new diol monomers with benzoxazole-based nonlinear optical (NLO) chromophores, one of which has an additional hydroxyl group as a crosslinkable moiety and the other has a nitrothiophene group as an electron withdrawing unit. The diol monomers were polymerized with 4,4′-methylenebis(phenyl isocyanate) to give NLO polyurethanes, respectively. Linear polyurethane with hydroxyl groups could be crosslinked between side chain chromophores themselves after poling using an additional crosslinking agent such as teramethyl-1,3-xylylene diisocyanate. Temporal stability of electro-optic coefficient of a crosslinked polyurethane was improved compared with that of a linear polyurethane. The second harmonic generation coefficient of linear polyurethane with benzoxazole–thiophene chromophores was 94 pmxa0V −1 (1.064 μm) and nonresonant d 33 value was 17.1 pmxa0V −1 calculated by two-level model equation.

N-phenylmaleimide polymers for second-order nonlinear optics

Abstract Second-order nonlinear optical properties of the polymers of N -phenylmaleimides coupled with nonlinear optical (NLO) chromophores through urethane linkages were investigated. N -[4-(Azidocarbonyl)phenyl]-maleimide, the precursor of the isocyanato N -phenylmaleimide, was prepared and reacted with NLO chromophores, N -(4-nitrophenyl)- l -prolinol (NPP) or 4′-[(2-hydroxyethyl)methylamino]-4-nitrostilbene (ANS) to give monomer 5 or monomer 6 . The monomers were polymerized and copolymerized with methyl methacrylate (MMA) and styrene (ST). The nonresonant linear electro-optic (EO) coefficients, r 33 values of the copolymers of 5 with MMA or ST corona-poled under 0.6 MV cm −1 were found to be about 10–15 pm V −1 when measured at 632.8 nm, and those measured at 830 nm were lower by 15–20%. The r 33 values of the copolymers of 6 with MMA measured at 632.8 nm and 830 nm were 25–35 pm V −1 and 8–10 pm V −1 , respectively. The homopolymer of 5 showed the excellent thermal stability of the EO coefficient, which retained 85% of its original value when aged at 80°C for 48 h. The EO coefficients of the copolymers were 45–70% of their original values after 48 h at 80°C. At room temperature, no decay of r 33 values of all polymers was observed over a period of 1 month.

Optimal synthetic design of second-order nonlinear optical material with good temporal stability

Abstract Second-order nonlinear optical copolymers containing p-hydroxyphenyl maleimide or 4-cinnamoyloxy-phenylmaleimide as a comonomer were newly synthesized. For improving the temporal stability, we adopted the crosslink reaction thermally and photochemically. Second-order nonlinear optical properties of the poled/cured films were investigated in terms of the second harmonic generation (SHG) and linear electro-optic (EO) coefficient measurement. SHG coefficient, d33 was found to be 14 pm/V at the fundamental wavelength of 1064 nm and EO coefficient, r33 was found to be 25–30 pm/V at 633 nm wavelength in two different crosslinked structures. To prevent the orientational relaxation of poled polymer, thermal crosslink reaction was induced using diisocyanate as a crosslinker between the side chains themselves. Another photo-crosslink was induced exposing the film at 257 nm wavelength during poling. Temporal stabilities of second-order NLO coefficients of crosslinked polymer systems were proved much better ...

Nonlinear optical polymers with novel benzoxazole chromophores: III. Synthesis and characterization of self-crosslinkable glycidyl methacrylate copolymers

Self-crosslinkable nonlinear optical copolymers (PGBz) were synthesized by radical copolymerization of vinyl monomer containing benzoxazole chromophore and glycidyl methacrylate as a comonomer. The thermal properties of these copolymers were compared to the corresponding copolymers (PGSt) containing stilbene chromophores. It was found that both the PGBz and PGSt copolymers were amorphous and fairly soluble in chlorinated solvents such as trichloroethane and tetrachloroethane. The glass transition temperatures of the copolymers were in the range of 117–134°C depending on the contents of benzoxazole chromophores. From the results of thermogravimetric analysis before and after heat treatment, the thermal stability of PGBz copolymers was improved after heat treatment due to crosslinked polymer networks. The crosslinked PGBz had a better thermal stability than crosslinked PGSt. The nonlinear optical coefficient (d33) and electro–optical coefficient (r33) of PGBz was 63.4 pm/V (at 1064 nm) and 7.8 pm/V (1.3 μm), respectively.

Synthesis and nonlinear optical properties of PMMA copolymers having novel benzoxazole chromophores attached with various electron-withdrawing groups

Abstract For improvements of thermal stability and nonlinear optical (NLO) activity of chromophores, we newly synthesized a series of NLO chromophores incorporating aromatic benzoxazole unit as a π -conjugated bridge with various electron-withdrawing groups, such as nitrophenyl, nitrothiophene, nitrofuran, dicyanovinylphenyl, and nitrophenylethenyl group. Polymethylmethacrylate copolymers (PMBz) containing these benzoxazole chromophores were synthesized and their properties were investigated by thermogravimetry and ultraviolet-visible spectroscopy. The PMBz copolymers exhibited better thermal and ultraviolet stabilities than the corresponding copolymer with general stilbene chromophores (PMSt). Moreover, temporal stability of nonlinear optical coefficient ( d 33 ) of PMBz copolymer increased in comparison with that of PMSt. The copolymer with benzoxazole–nitrothiophene chromophores had the largest d 33 value of 153xa0pm/V (at 1.064xa0mm) and nonresonant d 33 calculated by the two-level model was 21.3xa0pm/V.

Third-Order Optical Nonlinearity of Poly(1,6-Heptadiyne) Derivatives Containing Mesogenic Moiety

Abstract Poly (1,6-heptadiyne) derivatives with side group liquid crystalline mesogens were prepared by the metathesis polymerization with transition metal catalyst. It was found that the MoCl5-based catalyst systems were very effective for the polymerization of 1,6-heptadiyne monomers with various mesogenic groups. Polymerization of these monomers gave to the conjugated polyenes that contain cyclic recurring unit in the polymer backbone. Resulting polymers with electron donating mesogenic groups exhibited good solubility in common organic solvents and were easily spin coatable on fused silica substrate. Copolymerization of the mesogen-containing monomers with diethyl dipropargyl malonate (DEDPM) was also attempted to improve their physical properties. The third-order nonlinear optical susceptibility, x (3), was evaluated by the optical third-harmonic generation measurement. The near-resonant x (3) value was found to be in the range of 1.75 ∼ 8.22 × 10−11 esu at the fundamental wavelength of 1.907 μm.

Solution polymerization behavior of N-vinylcarbazole by low-temperature azoinitiator

N-Vinylcarbazole (VCZ) was solution polymerized in 1,1,2,2,-tetrachloroethane (TCE) at 30, 40, and 50°C using a low-temperature initiator, 2,2-azobis(2,4-dimethylvaleronitrile) (ADMVN); the effects of polymerization temperature and concentrations of initiator and solvent were investigated. On the whole, the experimental results corresponded to predicted ones. Low-polymerization temperature using ADMVN proved to be successful in obtaining poly(N-vinylcarbazole) (PVCZ) of high molecular weight with smaller temperature rise during polymerization, nevertheless of free radical polymerization by azoinitiator. The polymerization rate of VCZ in TCE was proportional to the 0.46 power of ADMVN concentration. The molecular weight was higher and the molecular weight distribution was narrower with PVCZ polymerized at lower temperatures. For PVCZ produced in TCE at 30°C using ADMVN concentration of 0.00005 mol/mol of VCZ, weight-average molecular weight of 271 000 was obtained, with polydispersity index of 1.66.

Thermally stable maleimide copolymer for second-order nonlinear optics

Second-order nonlinear optical copolymer containing p-hydroxyphenyl maleimide as a comonomer was newly synthesized. Second-order nonlinear optical properties of the poled films were investigated in terms of the second harmonic generation (SHG) and linear electrooptic (EO) coefficient measurement. SHG coefficient, d33 was found to be 14 pm/V at the fundamental wavelength of 1064 nm and EO coefficient, r33 was found to be 25-30 pm/V at 633 nm wavelength. To prevent the orientational relaxation of poled polymer, the thermal crosslink reaction was induced using diisocyanate as a crosslinker between the side chains themselves. Temporal stabilities of second-order NLO coefficients of crosslinked polymer systems were proved much better than that of guest-host system or other side chain polymers.

Nonlinear Optical Polymers with Novel Benzoxazole Chromophores. 1. PMMA Copolymers with Good Thermal and Temporal Stability

Abstract New copolymers (PMBz) from the benzoxazole-based vinyl monomer and methylmethacrylate as a comonomer, were synthesized for an improvement of thermal stability of second-order nonlinear optical activity. The thermal stability of the chromophores in PMBz copolymers monitored by IR and UV-visible spectroscopy was much better than in PMSt copolymer bearing general pendant stilbene units. The electro-optic coefficient r33 of the poled PMBz film exhibited as large as 45 pm/V at 632 nm of He-Ne laser. Thermal relaxation behavior of the poled PMBz films at 100[ddot]C showed that the PMBz having more rigid benzoxazole structure had better temporal stability of r33 compared to the general stilbene structure.