摘要:

AbstractThermochromic phenomena in various regioregular and non‐regioregular polythiophene derivatives have been investigated both in the solid state and in solution. These studies have revealed the existence of two different types of thermochromic phenomena which are correlated to the substitution pattern of the polymers. Formation of delocalized conformational defects (twistons) has been observed in regioregular polythiophene derivatives but did not occur in non‐regioregular polythiophenes. For the latter polymers, only localized conformational defects can be created along the polymer backbone leading to a monotonic blue shift of the absorption maximum upon heating. It is suggested that all these optical features are driven by order‐disorder transitions of the side‐chains, side‐chain disordering increasing their steric hindrance and/or disrupting short‐range ordered assemblies, which then force the thiophene backbone to adopt a nonplanar conformation. It has been also found that non‐covalent interactions between alkali metal ions and regioregular ether‐substituted polythiophenes can modify the side‐chain organization and can lead to interesting ionochromic effects. It is believed that chromic phenomena can be induced via a large range of external stimuli which should lead to the development of novel affinitychromic and photo

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970701

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractTheN,N′‐methylenebis(acrylamide) (NNMBA)‐crosslinked polyacrylamide supported amino ligands undergo complexation with Cr(III), Mn(II), Fe(III), Pb(II) and Cd(II) ions. Complexation is maximum for Cr(III) ion. The metal intake decreases as the crosslinking increases. The NNMBA resin can be reused after complexation and desorption without appreciable reduction in amino capacity. The IR spectrum of the Cr(III) complex gives an additional peak for sulfate complexation and the amino peak undergoes a negative shift, which is a clear evidence of metal coordination through the amino nitrogen. EPR, electronic spectra and magnetic moment are indicative of a distorted geometry for Cu(II), Cr(III), Fe(III) and Mn(II) complexes. Cd(II), Pb(II) complexes are diamagnetic. Complexation brings about vivid changes in the surface morphology of polymeric ligand. The thermal stability of Cr(III) complex increases as the metal content incr

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970702

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractAn ethylene‐vinyl acetate copolymer (EVA) was chemically modified by the introduction of pendent thiol groups (EVA‐SH) suitable for chain transfer. The resulting copolymer was grafted with 4‐phenylazophenyl 4‐(4‐acryloyloxybutoxy)benzoate, a liquid crystalline monomer (LCM), initiated by AIBN. Grafting was performed at LCM/EVA‐SH mass ratios of 10, 5, 2 and 1 in the feed. The grafting degree, i.e., the fraction of LC polymer in the graft copolymer, ranged from ca. 5–30 wt.‐%. The thermal transitions were investigated by DSC, pointing at marked microphase separation between LC and polyethylene moieties. The anisotropic properties of the graft copolymers were confirmed by cross‐polarized light microscopy. All the samples showed birefringence at 140°C, some only o

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970703

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractPolystyrene‐block‐poly(4‐vinylpyridine) diblock copolymer micelles of various compositions and molecular weights were characterized in toluene. Static light scattering, quasielastic light scattering and viscosity measurements were used to determine the basic micellar characteristics (aggregation number, micellar size, geometry and polydispersity). Depending on the copolymer under investigation, two different geometries (spherical and non‐spherical geometry) were observed. The micelles which are spherical in shape have aggregation numbers in the range 200–600 while the non‐spherical micelles have a much larger aggregation number (ranging between 600–1000). The sizes of the micelles remain unchanged in our concentration range (10−3− 5 middot; 10−3g/mL) and no critical micelle concentration could be detected in the concentration range from 10−5to 10−3g/mL. A detailed analysis of the structural parameters of the micelles which are spherical in shape, reveals that the core‐shell interfacial area per copolymer chain as well as the volume fraction of the copolymer in the shell are relatively constant, and that the core is almost not swollen by the solvent. Mixed uniform micelles were observed after mixing equal amounts of two solutions containing micelles differing in size and molecular weight. The reequilibration rate

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970704

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractBy the use of pseudo‐high dilution techniques a 40‐membered cyclic arylene sulfone 4,n= 1 was produced in 67% yield by “1 + 1 cyclization” of 4,4′‐dichlorodiphenyl sulfone with 4,4′‐bis(p‐hydroxyphenylisopropylidene phenoxy)diphenyl sulfone, derived in turn from bisphenol‐A and the dihalosulfone. This is a significant improvement over our previously reported yield of 11%. However, the use of cesium carbonate did not result in a yield improvement, i.e., no “cesium effect” was observed. The purity of macrocycle4,n= 1 was established by high‐performance liquid chromatography (HPLC), NMR spectroscopy and fast atom bombardment mass spectrosccopy (FAB MS). Macrocycle4,n= 1 has poor solubility due to its crystallinity (Tm= ca. 500°C), but does have high thermal stability (5% weight loss at 507°C in air). HPLC and FAB MS demonstrated that other homologous macrocyclic products resulted from “2 + 2 cyclization” (4,n= 3), “3 + 3 cyclization” (4,n= 5) and backbiting ether exchange reactions (4,n= 2). The high melting point of4,n= 1 precludes its use as a monomer for melt ring opening polymerization, but this study provides a methodology for the synthesis of other cyclic monomers designed to have lower melting points and be useful i

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970705

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe thermoreversible gelation of solutions of poly(ethylene terephthalate) (PET) in liquid diglycidyl ether of bisphenol‐A epoxy resin has been investigated. The critical polymer concentration for gel formation is 10 wt.‐%. The solutions were found to solidify rapidly into gels on cooling. Polarized light microscopy (PLM) and small‐angle light scattering (SALS) studies showed that these gels contain many large, regular PET spherulites. The gels in this system may be formed according to two consecutive processes: first the liquid‐liquid phase separation, and second the crystallization of PET in polymer‐rich domains. Hence, gelation occurs by formation of a three‐dimensional PET network in the epoxy solvent, where the nodes of the network are PET

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970706

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractFour series of copolyesters, namely BB6‐DMT, BB5‐DMT, BB6‐DMI and BB5‐DMI series, were prepared by melt polycondensation of dimethyl 4,4′‐bibenzoate (BB) with a dimethyl phthalate (DMT: dimethyl terephthalate or DMI: dimethyl isophthalate) and an alkanediol (1,6‐hexanediol or 1,5‐pentanediol). The homopolyesters poly(hexamethylene 4,4′‐bibenzoate) (BB6) and poly(pentamethylene 4,4′‐bibenzoate) (BB5) exhibit a smectic phase. The thermotropic liquid crystalline and crystalline properties of the copolyesters are significantly influenced by the presence of the non‐mesogenic rigid phthalate unit. All BB6‐DMT copolyesters remain crystalline. Asx, the molar fraction of the phthalate units in the diacid units, ≧ 0.7 the mesophase of the BB6‐DMT copolyesters is destroyed completely. For BB5‐DMT copolyesters, the mesophase disappears asx≧ 0.4, and the copolyesters become amorphous as 0.5 ≦x≦ 0.8. The mesophase and the crystallinity of the BB6‐DMI copolyesters are destroyed completely asx>0.5. The BB5‐DMI copolyesters lose the mesophase asx≧ 0.3, and become amorphous asx≧ 0.4. The results indicate that the non‐linear isophthalate unit destroys mesophase and crystallinity of the copolyesters to a grea

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970707

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractTapping mode atomic force microscopy has been used to observe single‐chain polystyrene (SCPS) particles sprayed with an atomizer onto freshly cleaved mica surfaces from very dilute solutions of a polydisperse polystyrene sample in good solvents, methylene cloride and benzene, and in poor solvents, CH2Cl2/MeOH 3/1.2 v/v and CH2Cl2/MeOH 3/1.3 v/v. The SCPS particles possess a definite morphology irrespective of the molecular weight but depending on the solvent. The morphology was found to change with time during drying after spraying and to be very sensitive to solvent environment and external forces exerted by the tip of the scanning probe. The particles became oriented due to probe‐tip‐particle interaction during probe scanning. Only qualitative comparison were made for the sizes of the observed images owing to the polydispersity and irregular shape of the particles and uncertainties about the tip convolution effects on the lateral dimensions. Only in the case of spraying the solution in poor solvents particles close to the shape of spheres were observed. In other cases the heights of the particles sprayed were an order of magnitude smaller than the lateral dimensions. AFM imaging has been applied to observe changes in morphology of SCPS particles sprayed from solutions after freeze thaw cycling. The results do not support the idea of cryogenic degradation of PS but the morphology of PS in solution changed to a smaller coil size during cryogenic freezing which persisted after being brought back to room temperature. When the freeze thaw cycled solution was heated to 100°C and then cooled to room temperature the coil size increased with a resulting morphology similar to the morphology observed before freeze thaw c

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970708

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractThe conformational change of α‐keratose in the polyelectrolyte complex (PEC) formation with chitosan was investigated by means of differential scanning calorimetry and infrared spectroscopy. The change of the secondary structure of α‐keratose in the reaction mixture was estimated quantitatively with circular dichroic spectra by the curve fitting method. The α‐helix structure of 30% and above of α‐keratose was found to be destructed and transformed into random structures at a mixing ratio of maximum PE

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970709

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY

摘要:

AbstractTwo copolyethers were prepared by chemical modification of poly[3,3‐bis(chloromethyl)oxetane] with sodium 4‐cyano‐4′‐biphenyl oxide, employing the concept of having the cyanobiphenyl species serve concomitantly as both the nonlinear optical chromophore and the mesogenic moiety in the polymer. Their thermal behavior was established by means of DSC and optical microscopy. Some preliminary Corona poling experiments were performed, and the second harmonic generation coefficientsd31andd33were measured by Maker fringe analysis. The results showed that liquid crystallinity enhances field‐induced polar ordering. The ratiod33/d31was found to be much larger than 3, in agreement with the theoretical models for electric field poling of liquid crystalline polymers where hyperpolarizable chromophores are attached as side groups to a polym

ISSN:1022-1352    

DOI:10.1002/macp.1996.021970710

出版商:Hüthig&Wepf Verlag    

年代:1996

数据来源: WILEY