Chul Joo Lee

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.

Preparation of high molecular weight polyvinylalcohol by low temperature azoinitiator

Abstract Vinylacetate was bulk-polymerized at 30, 40, and 50 °C using a low temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN), and effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of polyvinylacetate (PVAc) and the corresponding polyvinylalcohol (PVA) obtained by saponifying with sodium hydroxide. Low polymerization temperature and low conversion by adopting ADMVN proved to be successful in obtaining PVA of high molecular weight. At conversion of below 20%, PVAc having a number-average degree of polymerization (Pn) of 6800-10,100 was obtained, whose degree of branching for acetyl group was calculated to be 0.60-0.70,0.75-0.90, and 1.05-1.45 at 30,40, and 50 °C, respectively. Saponifying this PVAc yielded PVA having a Pn of 3100–6100.

Preparation and characterization of syndiotacticity-rich ultra-high molecular weight poly(vinyl alcohol)/imogolite blend film

To enhance the physical properties of syndiotacticity-rich (syndiotactic diad content 63·4%) ultra-high molecular weight (UHMW) (number-average degree of polymerization 12300) poly(vinyl alcohol) (PVA) film, it was solution blended with rigid-rod imogolite in dimethyl sulphoxide. In addition, the blend film prepared was stretched using a high-temperature zone drawing technique for effective orientation of the film. Through a series of experiments, it was found that imogolite caused significant changes in the structure and properties of syndiotacticity-rich UHMW PVA film, i.e. imogolite acted as an important agent which increased crystal orientation of syndiotacticity-rich UHMW PVA, resulting in enhanced tensile strength of the film. However, imogolite played a hindering role in raising the amorphous orientation of syndiotacticity-rich UHMW PVA. The maximum tensile modulus of 19·8GPa and maximum tensile strength of 1·8GPa could be obtained at the maximum draw ratio of 7·45 for PVA/imogolite blend film. In the case of PVA homo film, the highest tensile modulus and strength were 25·2GPa and 1·4GPa, respectively.

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.

Preparation and characterization of iodinated poly(vinyl alcohol) microfibril

Iodination of poly(vinyl alcohol) (PVA) microfibril, which was obtained from saponification of poly(vinyl pivalate), was conducted before and after zone drawing at various conditions. The resulting PVA microfibrils were characterized by differential scanning calorimeter and scanning electron microscopy. Surface morphologies of these PVA microfibrils showed some differences between PVA microfibril iodinated after and before drawing. Crude shapes of PVA microfibrils iodinated after drawing indicated that iodine decreased the structural regularity severely. On the other hand, PVA microfibrils iodinated before drawing showed relatively ordered surfaces. This was ascribed to the enhanced molecular ordering of PVA microfibrils due on zone drawing. Iodinated PVA microfibrils showed a decrease in crystal melting temperature of about 100 °C compared to the untreated sample. PVA microfibrils drawn after iodination showed relatively higher crystal melting temperature than those of microfibrils iodinated after drawing. These results were considered as the proofs of the changes in crystalline lattice of the PVA microfibrils. Effects of drawing temperature on sublimation of iodine were also evaluated.

Preparation and Molecular Structure of Poly(Vinyl Alcohol) by Low Temperature Bulk Polymerization of Vinyl Acetate and Saponification

Abstract Vinyl acetate (VAc) was bulk-polymerized at 30, 40 and 50°C using a low temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN), and effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl acetate) (PVAc) and corresponding poly(vinyl alcohol) (PVA) obtained by saponifying it with sodium hydroxide. Low polymerization temperature and low conversion by adopting ADMVN proved to be successful in obtaining PVA of high molecular weight. PVAc having number-average degree of polymerization (Pn ) of 6,800–10,100 was obtained, whose degree of branching for acetyl group of 0.6–0.7 at 30°C, 0.8–1.1 at 40°C, and 1.0–1.9 at 50°C at conversion of below 40%. Saponifying so prepared PVAc yielded PVA having Pn of 3,100–6,200, and syndiotactic diad (S-diad) content of 51–53%. The whiteness, S-diad content, and crystal melting temperature were higher with PVA prepared from PVAc polymerized at lower temperatures.

Determination of the optimum polymer concentration for ultrahigh molecular weight polyethylene gel films by zone drawing method

Abstract A new method using a simple zone drawing technique was suggested for determining optimum initial concentration of polymer solution which has suitable macromolecular entanglements. Ultra high molecular weight (UHMW) polyethylene (PE) gel films were prepared from decalin solutions with concentrations of 0.3, 0.5, 0.7, and 1.0 g/dL, and different gelation/crystallization temperatures. In order to investigate drawing behaviors of UHMW PE gel films with different solution concentrations, those prepared were drawn under various zone drawing conditions. Through a series of experiments, it turned out that the initial concentration of PE solution in decalin caused significant changes in the draw ratio of UHMW PE gel film. That is, the one-step zone draw ratio of the gel film for initial concentration of 0.5 g/dL was at its maximum and gradually decreased at higher or lower concentrations. Moreover, this tendency was similar to the maximum draw ratio data. Thus, it was shown that the initial concentration ...

Direct polymerization of aromatic diacid dimethyl esters with aromatic diamines: I. Analysis of reaction mechanism

Abstract The direct polymerization of aromatic diacid dimethyl esters with aromatic diamines using phosphorus activating agents and tertiary amines was conducted at room temperature. The reaction mechanism was investigated with model compounds. The diacid dimethyl ester of pyromellitic dianhydride was reacted with the activating agent, along with pyridine as a catalyst, or reacted with an N -methylpyrrolidone (NMP)-activating agent complex to form the activated anhydride intermediate. It was characterized with 31 P and 1 H nuclear magnetic resonance, and ultra-violet—visible spectroscopy. The polymerization proceeded via the nucleophilic substitution reaction between aromatic acid and amine. The amidation reaction proceeded further to afford N -phenylphthalmide with phosphorus oxychloride and phenyl phosphonyl dichloride in the model reactions, but not in the polymerization reaction. As for the degree of polymerization, phenyl phosphonic dichloride and pyridine were superior to any other pairs of activating agent and tertiary amine. The direct polymerization of various diacid dimethyl esters of aromatic dianhydrides with aromatic diamines was successfully performed.

Preparation of high molecular weight poly(N-vinylcarbazole) in high yield by low-temperature precipitation polymerization of N-vinylcarbazole

To produce high molecular weight poly(N-vinylcarbazole) (PVCZ) with high conversion, N-vinylcarbazole (VCZ) was heterogeneously polymerized in methanol at 30, 40 and 50 °C using a low temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN), and the effects of polymerization temperature and concentration of initiator and solvent on the polymerization behaviour and molecular parameters of PVCZ investigated. Globally, experimental results correspond to predicted ones. Low polymerization temperature using ADMVN and a heterogeneous system using methanol proved to be successful in obtaining poly(N-vinylcarbazole) (PVCZ) of high molecular weight and high conversion with small temperature rise during polymerization, although free radical polymerization by azoinitiator was used. The polymerization rate of VCZ in methanol at 30 °C is proportional to the 0.88th power of ADMVN concentration. The molecular weight is higher and the molecular weight distribution is narrower with PVCZ polymerized at lower temperatures. For PVCZ produced in methanol at 30 °C using an ADMVN concentration of 0.0001 mol/mol of VCZ, a weight average molecular weight of 1 750 000 g mol−1 is obtained, with a polydispersity index of 1.82 © 2000 Society of Chemical Industry

Analysis of chemical structure of fluoro-containing copolyamic acid methyl esters and its effect on the thermal imidization process

Abstract Copolyamic acid methyl esters were directly synthesized from 2,5-dicarbomethoxy terephthalic acid (p-PMDE) and 4,4′-oxydianiline (ODA) and fluoro-containing diamines using phenyl phosphonic dichloride. The average sequence lengths of the copolyamic acid methyl esters were controlled by stoichiometric unbalance and monitored by proton nuclear magnetic resonance spectroscopy (1H-NMR). The effect of chemical structure of copolyamic methyl esters on thermal cyclization to the corresponding copolyimides was studied by differential scanning calorimetry and on thermal properties and solubility by thermogravimetry and solubility testing. The maximum imidization temperatures of the copolyamic acid methyl esters were between those of the homopolymers. The short sequence length of the fluoro-containing moiety of the copolyamic methyl esters made the copolyimide more soluble in organic solvents. The average sequence length of the copolymer did not affect the thermal properties of the corresponding copolyimide in this system.