1999 рік

Copolymerization of tetraethoxysilane (TEOS) and dimethyl(diethoxy)silane (DMDEOS) was studied by means of the 29Si NMR spectroscopy and ab initio quantum chemical calculations. 29Si NMR spectra of reaction mixtures of TEOS and DMDEOS were effectively measured by a slightly modified DEPT experiment, in which the pulse sequence is divided into two parts and all pulses on protons are replaced by selective pulses. Quantum chemical ab initio calculation of structures and 29Si NMR chemical shifts of some reaction products were used in signal assignment. The assignment of the signals to corresponding structure units is not yet unambiguous; however, a semiquantitative analysis of relations in the reaction mixture of TEOS and DMDEOS could be done. Although the reactivity of the DMDEOS monomer is much higher in comparison with TEOS, the arising gel is not strictly phase separated and copolymerization of both monomers occurs. In the first stages of the process, resulting oligomers are composed of 70% of DMDEOS structure units. In the final stages of polycondensation, domains of the TEOS structure units are formed, which can act as linking units between cyclic oligomers.

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Composition dependence of phase behavior in the mixture system of polystyrene (PS) with poly(cyclohexthyl methacrylate) (PCHMA) was examined in details using differential scanning calorimetry, optical and scanning electron microscopy, and infrared spectroscopy. This study shows that the 'transparent’ blends of PS/PCHMA with an apparent single T g, having been thought to be miscible in earlier reports, actually displayed micro-heterogeneity domains of about 100–300 Å. It is thus not appropriate to assess miscibility to the optically clear blends of PS/PCHMA; however, partial miscibility does exist. The PCHMA-rich (PCHMA 70 wt%) compositions are indeed miscible but the PS-rich compositions are only partially miscible with sub-micron discrete phase domains beyond detection limit of optical microscopy. The proximity of the T gs also prevented that the thermal transition of the micro phase domains in the PS-rich blends being resolved. The criterion of single T g commonly employed in in assessing phase behavior should be used with extra precaution in cases where microheterogeneity exists, whose ambiguity is even compounded in cases where the T gs of the constituent polymers are close. The FT-ir result indicates that intermolecular interactions are weak or non-specific for the PCHMA-PS pair.

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An improved synthetic route to a previously prepared self-polymerizable poly(phenylquinoxaline) (PPQ) monomer mixture, i.e., 2-(4hydroxyphenyl)-3-phenyl-6-fluoroquinoxaline and 3-(4-hydroxyphenyl)-2-phenyl-6-fluoroquinoxaline, was developed. The monomer mixture was then polymerized in stages in N-methyl-2-pyrrolidinone/toluene and in N-cyclohexyl-2-pyrrolidinone at elevated temperatures in the presence of potassium carbonate. Polymer samples were obtained that had intrinsic viscosities as high as 1.64 dl/g in m-cresol at 30.0 ^ 0.1°C and glass transition temperatures (Tgs) of 250–252°C. Thin films of the PPQ had a room temperature (RT) tensile strength of 114 MPa, a RT Young’s modulus of 3.7 GPa, and a RT elongation at break of 93%. The neat resin had a flexural modulus of 3.12 GPa, a fracture energy (G1c) of 2170 J/m 2 and a titanium–titanium lap shear strength of 31.4 MPa at room temperature. The polymer melt underwent shear thinning at 320°C. The melt viscosity decreased from 10 5to 10 6 Pa s to less than 10 4 Pa s as the frequency was increased from 10 ⫺2 to 10 2 rad/s. Carbon-fiber(T650)(R)-reinforced composites of the PPQ were prepared and their mechanical properties determined.

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NMR studies on completely cyclized polymers derived from N-substituted-N-allyl-2-(methoxycarbonyl)allylamines (1) were undertaken to determine the repeat cyclic unit. NMR techniques employed are two-dimensional INADEQUATE (Incredible Natural Abundance DoublE QUAntum Transfer Experiment), DEPT (Distortion Enhancement by Polarization Transfer) measurements, and those under suppressed nuclear Overhauser effect. These studies along with the comparison of the spectra of poly(1) with those of related compounds revealed that the poly(1) consists of two sets of five-membered rings. The main chain methylene carbons attached to the ring has a trans configuration for one of them and a cis arrangement for the other. The former was found to be a main component. The value 4.5 kJ/mol as the difference of the activation energy for the formation of the respective configuration, Ecis 2 Etrans, was obtained by the investigation of temperature effect. Comparison of these results with those reported so far for polymers with similar structures led to the conclusion that five-membered ring formation could be interpreted by a kinetic mechanism as in the radical cyclization reactions in low molecular weight compounds.

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The compatibilizing effect and mechanism of poly(styrene-b-4-vinylpyridine) diblock copolymer, P(S-b-4VPy), on the immiscible blend of polystyrene (PS)/zinc salt of sulphonated polystyrene (Zn-SPS) were studied. SEM results show that the domains of the dispersed phase in the blend become finer. DSC experiments reveal that the difference between the two T g’s corresponding to the phases in the blends becomes larger on addition of P(S-b-4VPy), mainly resulting from dissolving of the poly(4-vinylpyridine (P4VPy) block in the Zn-SPS phase. FTIR analysis shows that compatibility of P4VPy and Zn-SPS arises from the stoichiometric coordination of the zinc ions of Zn-SPS and pyridine nitrogens of P4VPy. SAXS analysis indicates the effect of the P(S-b-4VPy) content on the structure of the compatibilized blends. When the content of the block copolymer is lower than 4.1 wt%, the number of ion pairs in an aggregate in the Zn-SPS becomes smaller, and aggregates in ionomer in the blend become less organized with increasing P(S-b-4VPy). When the P(S-b-4VPy) content in the blend is up to 7.4 wt%, a fraction of P(S-b-4VPy) form a separate domain in the blend.

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With certain cationic initiators benzoxazine rings can be opened and polymerized at room temperature. Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, size exclusion chromatography, differential scanning calorimetry, and thermogravimetric analysis have been used to monitor the polymerization process and to characterize the obtained polymers. High performance bisphenol-A/aniline based polybenzoxazine with glass transition (Tg) at 220°C and char yield of approximately 60% at 800°C under nitrogen is obtained.

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Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film via UV-induced double graft copolymerization were carried out to improve the adhesion with evaporated copper. The PTFE film surface was first modified by graft copolymerization with a monomer, such as hydroxylethylacrylate and acrylamide, which contained functional moities for curing the epoxide groups. The so-modified PTFE surface was subsequently re-exposed to Ar plasma and subjected to UV-induced graft copolymerization with glycidyl methacrylate. The surface compositions of the PTFE films from single and double graft copolymerization were studied by X-ray photoelectron spectroscopy. The adhesion strength of the evaporated copper on the double graft copolymerized PTFE film was affected by the type of monomer used during the first graft copolymerization, the concentration of the first and second graft, the extent of O2 plasma post-treatment after the second graft copolymerization, and the extent of heat treatment after metallization. The T-type peel strength of the Cu–PTFE laminate obtained under optimum conditions was about 19 N/cm, which represented a more than ten-fold increase over that obtained when the PTFE film was treated by plasma alone. The mechanism of the peel strength enhancement and the cohesive failure of the metal–polymer laminate were also investigated.

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Dendritic hyperbranched polymers (HBPs) show outstanding performance as tougheners in epoxy resins. The critical strain energy release rate, G Ic, of a DGEBF resin is increased by a factor of 6 from 120 J/m 2 to 720 J/m 2 using only a 5% modifier weight content. This does not lead to a decrease in resin stiffness or glass transition temperature and the favourable processability of epoxy resins is fully maintained without requiring the use of solvents. Toughness properties are induced by a finely-dispersed particulate structure which is obtained by a controlled phase separation process during resin curing. A strong mechanical phase interaction is ensured by chemical bonding through reactive epoxy groups grafted onto the HBP. By tailoring the HBP’s epoxy functionality and polarity to control reactivity, phase separation, final morphology and phase interactions, this toughening system is potentially applicable to a variety of thermoset resins. With this in view, the influence of the chemical architecture of the HBP modifiers on phase separation, processability, properties and toughening mechanisms is investigated.

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A series of twelve aromatic diamines, 4,4 0 -diamino-2,2 0 -disubstitutedbiphenyls, has been designed and synthesized. These diamines were reacted with 2,2 0 -bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) to form polyimides via a one-step polycondensation method. All of the resulting polyimides could be dissolved in common organic solvents and exhibited excellent film forming ability. At the same time, their inherent high thermal and thermo-oxidative stability of these polyimides was retained in the films. Because of the incorporation of disubstituted groups at the 2- and 2 0 -positions of these biphenyl diamines, their crystallinity was suppressed to the level that they were in complete amorphous state. Further, the conjugation of the phenylene and imide groups in these polyimide films was interrupted, leading to clear blue shifts during light transmission. As this series of polyimides possessed the same backbone, the chain rigidity and linearity changed very little throughout the series. However, the molecular packing was affected by the introduction of different disubstituted pendant groups. Each polyimide film exhibited an a relaxation process related to the glass transition. This relaxation changed significantly with the size and the shape of the disubstituted pendant groups. In addition to this process, each of these polyimide films displayed a sub-glass transition, the b relaxation process, which was initiated by motion of the 4,4 0 -diamino-2,2 0 -disubstituted biphenyls. This study provided an opportunity to investigate how disubstituted pendant groups affected the a and b relaxation behaviors of these polyimides. With an increase of the sizes and the shape anisotropy of the disubstituted pendant groups at the 2- and 2 0 -position, the nature of the motion regarding to the b relaxation was found to evolve from a non-cooperative process to a cooperative one, while the glass transition temperature (the a relaxation temperature) correspondingly decreased.

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By reactive blending of polyamide 6 (PA) with polysulfone (PSU) using a gram-scale mixer (Mini–Max Molder), we prepared a series of PA/PSU (80/20 wt. ratio) blends with various diameters of PSU particles; 70 nm by using phthalic anhydride-terminated PSU (PSU-PhAH), 0.4 mm by epoxy-terminated PSU, 0.45 mm by maleic anhydride-grafted PSU and 1.3 mm by non-reactive PSU. By light scattering (LS), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry, it was shown that there did not exist any difference in the crystalline morphology of PA matrix among the blends. Although difference in tensile strength among blends was small but on elongation it was large; the smaller PSU particles yielded larger elongation at break. The bulk-fracture toughness was shown to be higher for the blend with smaller PSU particles. Especially, PSU-PhAH blend showed a remarkably high toughness. In this blend, ductile fracture was shown by SEM observation. Transmission electron microscopic (TEM) observation confirmed the homogenous plastic deformation without interfacial debonding in the two-phase material. In contrast, other blends showed brittle fracture accompanied with interfacial debonding. The adhesive strength between PA and PSU-PhAH phases measured by asymmetric double cantilever beam method was shown to be much higher than in other systems. Thus, when the interfacial adhesive strength is high enough to provide adequate stress transfer, plastic deformation of brittle PSU particle can occur and hence the uniform plastic deformation of the whole material may render high toughness. The lower interfacial adhesion seems to yield in less massive plastic deformation to resulting in lower toughness.

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