Kinetic study on the radical polymerization of 2‐methacryloyloxyethyl phosphorylcholine

Polymerization of 2‐methacryloyloxyethyl phosphorylcholine (MPC) was kinetically investigated in ethanol using dimethyl 2,2′‐azobisisobutyrate (MAIB) as initiator. The overall activation energy of the homogeneous polymerization was calculated to be 71 kJ/mol. The polymerization rate (R_p) was expressed by R_p = k[MAIB]^0.54±0.05 [MPC]^1.8±0.1. The higher dependence of R_p on the monomer concentration comes from acceleration of propagation due to monomer aggregation and also from retardation of termination due to viscosity effect of the MPC monomer. Rate constants of propagation (k_p) and termination (k_t) of MPC were estimated by means of ESR to be k_p = 180 L/mol · s and k_t = 2.8 × 10⁴ L/mol · s at 60 °C, respectively. Because of much slower termination, R_p of MPC in ethanol was found at 60 °C to be 8 times that of methyl methacrylate (MMA) in benzene, though the different solvents were used for MPC and MMA. Polymerization of MPC with MAIB in ethanol was accelerated by the presence of water and retarded by the presence of benzene or acetonitrile. Poly(MPC) showed a peculiar solubility behavior; although poly(MPC) was highly soluble in ethanol and in water, it was insoluble in aqueous ethanol of water content of 7.4–39.8 vol %. The radical copolymerization of MPC (M₁) and styrene (St) (M₂) in ethanol at 50 °C gave the following copolymerization parameters similar to those of the copolymerization of MMA and St; r₁ = 0.39, r₂ = 0.46, Q₁ = 0.76, and e₁ = +0.51. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 509–515, 2000     

Synthesis and characterization of fluorinated benzoxazole polymers with high Tg and low dielectric constant

Next generation microelectronic packaging requirements are driving the need to produce increasingly lower dielectric constant materials while maintaining high thermal stability and ease of processing. Efforts have focused on the synthesis and analysis of new polymers with the goals of high thermal stability [degradation temperature (T_d) > 400 °C, low glass‐transition temperature (T_g) > 350 °C], low water uptake (<1%), solubility in selected organic solvents, dielectric constant less than 2.5, and low thermal expansion coefficient. These stringent combined goals have been largely achieved with flexible aromatic benzoxazole polymers. Intramolecular hydrogen bonding between pendant hydroxyl groups and the double‐bond nitrogen of the benzoxazole has been exploited to increase the polymer T_g, whereas the incorporation of perfluoroisopropyl units effectively decreases the dielectric constant. Out‐of‐plane impedance measurements on films of materials in this family (38–134 μm thick) have resulted in typical dielectric values of 2.1–2.5 at 1 MHz, depending on copolymer ratios and functionalizations. Results have been correlated with optical waveguide measurements of films 4‐μm thick to determine film anisotropy and the high‐frequency dielectric constant, and have been corroborated by in‐plane interdigitated electrode dielectric measurements on samples 0.75 μm thick. Candidate materials exhibited extremely low water uptake (0.2%) even after submersion in boiling water for several days. Dynamic mechanical analysis of the polymers enabled the determination of the influence of intermolecular hydrogen bonding on the T_g and loss tangent magnitude. Finally, the coefficient of thermal expansion has been examined and correlated with copolymer constitution. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1991–2003, 2000     

Effect of LiClO4 on the radical polymerization of Di-2-[2-(2-methoxyethoxy)ethoxy]ethyl itaconate

The effect of LiClO₄ on the polymerization of di-2-[2-(2-methoxyethoxy)ethoxy]ethyl itaconate (DMEI) with dimethyl 2,2′-azobisisobutyrate (MAIB) was investigated in methyl ethyl ketone (MEK) kinetically and by ESR. The polymerization rate (R_p) at 50°C, where the concentrations of DMEI and MAIB were 1.00 and 5.00 × 10⁻² mol/L, increased with increasing [LiClO₄]. Marked acceleration was observed at higher [LiClO₄]s than 1.0 mol/L. The molecular weight of resulting polymer (ca. 10,000) was relatively insensitive to [LiClO₄], indicating occurrence of chain transfer. IR analysis of mixtures of LiClO₄/DMEI and LiClO₄/poly(DMEI) indicated complexation of LiClO₄ with DMEI and its polymer. The rate constants of propagation (k_p) and termination (k_t) were determined by ESR. k_p (1.7–10.5 L/mol s at 50°C) increased with [LiClO₄]. k_t (5.2–1.0 × 10⁴ L/mol s at 50°C) showed remarkable decrease at higher [LiClO₄]s than 1.0 mol/L. R_p of polymerization of equimolar complex of LiClO₄/DMEI with MAIB at 50°C in MEK was expressed by R_p = k[MAIB]^0.5[DMEI]^2.4. k_p increased and k_t decreased with [DMEI]. The activation energies of overall polymerization, propagation and termination were estimated to be 34.5, 8.0, and 59.4 kJ/mol. Copolymerization of DMEI with styrene was also profoundly affected by the presence of LiClO₄. Such large effects of LiClO₄ on the homo- and copolymerization of DMEI are explicable in term of association of LiClO₄-complexed DMEI monomers. © 1997 John Wiley & Sons, Inc.     

Propagation velocity of the reaction front in addition polymerization systems

Traveling polymerization fronts in unstirred solutions of methylmethacrylate, methacrylic acid, or acrylamide with some free radicals initiators (through thermal decomposition) have been observed experimentally. A local heating of the initial reactant mixture, under suitable conditions, leads to a reaction front that propagates along the space coordinate with a constant velocity. In this article, a physical interpretation of this phenomenon is provided through a mathematical model that accounts for the depolimerization reaction and is based on the constant pattern approach. Moreover, an approximate explicit analytic expression for the velocity of propagation of the polymerization front is proposed. The theoretical values are compared with those measured experimentally as a function of the initiator concentration for different addition polymerization systems. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35:1047–1059, 1997     

Ionic absorption of polypropylene functionalized by surface grafting and reactions

Plasma-induced surface graft copolymerization of acrylic acid on polypropylene fibers and the subsequent reactions of the grafted carboxylic groups are reported. The extents of grafting was controlled by the plasma conditions. Reactions of the carboxylic acid with selected amines resulted in ion-exchanging and chelating functionalities. In general, ion adsorption is enhanced by higher levels of grafting and by raising temperature during adsorption. The adsorption level and preferences among ions of these functionalized fibers depend on the structure of the functional groups, i.e., the structure of the spacer and terminal groups. The carboxylic acid groups of the PP-g-AA fibers which behave like weakly acidic ion-exchangers are attributed to the low metal ion adsorption and the lack of ion preference. The F1 fibers with flexible  CH₂CH₂ spacer and small terminal  OH in the functional group exhibits highest ion adsorption among all functionalized fibers studied here. With benzene spacers, metal adsorption can be enchanced by the electron-donating nature of the terminal group. With the same ester end group in the functional structure, F3 fibers which contain benzene ring spacers show higher ion adsorption than F4 and F5 which have CH₂ and NH spacers, respectively. The ion preference and adsorption ability of the functionalized fibers, i.e., equilibrium binding constants (K_b) and saturation constants (K_s) derived from adsorption isotherms, also depend on the functional group structures. K_b increases with increasing grafting yield, increasing the electron donor atom in either terminal bonds or spacer, and reducing the steric hindrance of spacer. The K_s values are affected by the accessibility of functional groups, the size of spacer, and the terminal group structure. © 1997 John Wiley & Sons, Inc.     

Evident solvent effect on propagation reactions during radical copolymerization of maleimide and alkene

The radical copolymerization of N-(2,6-dimethylphenyl)maleimide (DMPhMI) and 2,4,4-trimethylpentene (TP) was investigated in several solvents at 60°C. The copolymerization rate and the molecular weight of the resulting copolymers were dependent on the kind of solvent used. It was also revealed that the monomer reactivity ratios depended on the solvent; r₁ = 0.086 and r₂ = 0 in chloroform and r₁ = 0.25 and r₂ = 0 in benzene, where DMPhMI and TP are M₁ and M₂, respectively. The propagation rate constants were determined for the homopolymerization and copolymerization in chloroform and benzene using electron spin resonance spectroscopy. The homo- and crosspropagation rate constants (k₁₁ and k₁₂, respectively) were revealed to depend on the solvent: k₁₁ is 20 and 37 L/mol·s and k₁₂ is 230 and 150 L/mol·s in chloroform and in benzene, respectively. The interaction between the maleimide moiety and the solvent molecules was discussed based on the acceptivity of the solvents. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1515–1525, 1997     

A positive-working photosensitive alkaline-developable polyimide with a highly dimensional stability and low dielectric constant based on poly(amic acid) as a polyimide precursor and diazonaphthoquinone as a photosensitive compound

A positive-working photosensitive polyimide precursor based on fluorinated poly(amic acid) (FPAA) and 2,3,4-tris(1-oxo-2-diazonaphthoquinon-4-ylsulfonyloxy)benzophenone (D4SB) as a photosensitive compound has been developed. FPAA was prepared by ring-opening polyaddition of dianhydrides, pyromellitic dianhydride and biphenyltetracarboxylic dianhydride, with diamine, 2,2′-bis(trifluoromethyl)benzidine, in methanol. The FPAA film showed excellent transparency to UV light and good solubility in a wide range of organic solvents. The dissolution behavior of FPAA containing 30 wt % D4SB after exposure was studied, and it was found that the difference of dissolution rate between exposed and unexposed parts was enough to get high contrast due to the photochemical reaction of D4SB in the polymer film. The photosensitive fluorinated polyimide (FPI) precursor containing 30 wt % D4SB showed a sensitivity of 80 mJ cm⁻² and a contrast of 7.8 with 365 nm light when it was developed with 0.3% aqueous tetramethyl ammonium hydroxide solution at room temperature. The FPI film cured up to 360°C had a low coefficient of thermal expansion of 10.3 ppm °C⁻¹ and a low dielectric constant of 3.04. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2261–2267, 1998     

The effect of crosslinking on thermal and mechanical properties of perfluorocyclobutane aromatic ether polymers

As the minimum features in semiconductor devices decrease, it is a new trend to incorporate copper and polymers with dielectric constant less than 3.0 to enhance the performance of the devices. Two fluorinated polymers, poly(biphenyl perfluorocyclobutyl ether) (BPFCB) and poly(1,1,1-triphenyl ethane perfluorocyclobutyl ether) (PFCB), are newly developed polymers with dielectric constants below 3.0. These two polymers have a similar backbone structure, but PFCB has the capability of crosslinking. To know the implications of these two polymers in the semiconductor industry, properties that are important for the integral reliability of Integral Circuits (IC), such as thermal and mechanical properties, should be understood. This comparative study shows that the crosslinking in perfluorocyclobutane aromatic ether polymer can reduce vertical thermal expansion and increase glass transition temperature (T_g) while water absorption, crystalline-like phase, and dielectric constant are slightly increased. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1383–1392, 1998     

石墨烯纳米孔道内受限水介电常数影响因素的分子动力学模拟

受限水的介电特性对于石墨烯电容器的储能效率有着重大的影响.因此本文使用分子动力模方法,研究了不同石墨烯纳米孔道宽度(0.812～10 nm)下内受限水介电常数的分布及其影响因素.结果表明,在石墨烯纳米孔道内部受限水双电层结构可分为空隙层、界面层和体相层三个部分.其整体的介电常数随孔道大小的降低而线性减少.这是由内部体相层的宽度的降低而导致的.此外电极电压大小和石墨烯-水相互作用参数ε_CO的强弱也会显著改变电极表面的双电层(Electric Double Layers, EDLs)结构.其中电压的增大使得介电常数分布的震荡的程度也随之增加,最终导致了整体介电常数的减小.与之类似,亲水态的石墨烯表面(高ε_CO)下受限水分布的震荡程度也显著增加,这导致了整体介电常数的降低.     

一种改进的轨道动力学模型

航天器的矢径可以分解为矢径模和单位矢量的乘积,利用该性质将传统轨道动力学方程分解为矢径模和矢径方向的动力学方程组,实现了航天器位置信息的分离;针对两个方程分别采用常数变易法和四元数描述方法,将轨道动力学模型转化为线性无奇异的方程组,同时得到了7 个新轨道变量,且建立了新轨道变量与惯性系下航天器位置速度信息以及轨道六要素之间的相互转换关系. 该轨道模型适用于任意形式的推力和摄动,避免了奇异性,且在虚拟时间的意义下,航天器的旋转角速度只取决于法向力;在常值推力和变推力的情况下,对该模型进行了数值验证,验证了新模型的可适用性、数值稳定性以及计算精度高的优势.