摘要:

AbstractInterchain transesterification reactions (ITR) play an important role in high temperature synthesis of most linear polyesters. For example, polyethylene terephthalate (PET) is prepared commercially by heating and distillation of ethylene glycol from a glycol capped oligomer of PET. In this paper, the potential importance of ITR to effect a much wider range of reactions and process is examined. For example, the ability to control the sequence distribution in linear copolyesters is described. In particular, it is shown that one can induce a random sequence distribution in copolyesters by ITR or, conversely, develop an ordered sequence from a random copolyester again by ITR. In one family of liquid crystalline copolyesters an unusual competition between ordering and a thermal Fries rearrangement is described. A whole new family of crosslinked copolyesters has been developed based on this knowledge of ITR. Solid state processing of cured copolyesters into finished articles by ITR has also been demonstrated. These crosslinked copolyesters can be depolymerized back to the starting oligomers by a reverse ITR, providing for the first time a recyclable thermosetting resin.

ISSN:1022-1360    

DOI:10.1002/masy.19981280103

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractSome hyperbranched aromatic polyamides have been synthesized by direct polycondensation using the modified Higashi's method. Structures of the above polymers have been realized taking in proper account the analogies with amide group sequences of poly(p‐phenyleneterephthalamide) (PPDT) and poly(p‐benzamide) (PBA). Therefore, AB2‐ type monomers as well as suitable combinations of different bi‐ and trifunctional reactants (AA + B3) (e.g.,p‐phenylenediamine + trimesic acid or other trifunctional acids) have been considered. For the latter systems, network formation has been minimized. In the present paper, our results on their direct polyamidation together with some preliminary characterization data on the resultant hyperbranched aramids

ISSN:1022-1360    

DOI:10.1002/masy.19981280104

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThis paper concerns the synthesis of two different structures of styrene‐butadiene block copolymers that were respectively obtainedviasequential and statistical ring‐opening metathesis copolymerization of norbornene‐terminated polystyrene (PS) and polybutadiene (PB) macromonomers. The stimulus for preparing such styrene‐butadiene copolymers originates from the observation that phase‐separated morphologies in block copolymers not only depend on the respective size of the blocks and the interaction parameter (χ), but also on the topological constraints introduced in the copolymer structure. From the differential scanning calorimetry study that was carried, it can be inferred that the two types of copolymers ‐prepared by sequential and statistical copolymerization of PS and PB macromonomers respectively‐ exhibit quite different phase separation behaviors, indicating that they develop distinct equilibrium domai

ISSN:1022-1360    

DOI:10.1002/masy.19981280105

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThe stereochemical aspects of controlled polymerization of lactide and β‐butyrolactone are discussed. The physicochemical and thermal properties of these polymers are shown to be depending on the stereochemical structure of the macromolecular chain. Different types of processes involving change of enantiomeric composition in the course of the polymerization reaction are examined in function of different initiators used. The formation of stereocomplexes from stereocopolymers of various enantiomeric compositions is report

ISSN:1022-1360    

DOI:10.1002/masy.19981280106

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractNeodymium catalysts are typical for the cis polymerization of 1,3‐dienes. The systems prepared from a neodymium‐carboxylate, a chlorine donor and A1(i‐C4H9)3are characterized by a low efficiency, only ca. 6% of the neodymium being active in the catalysis. Much more active systems are obtained using allyl derivatives of neodymium in combination with aluminoxanes, in particular with methylaluminoxane (MAO). These systems have the characteristics of a single site catalyst. Evidence suggesting an ionic structure for the catalytic species is reported. Terminally substituted butadienes give polymers with a cis‐1,4 isotactic structure, with the exception of (E, E)‐2,4‐hexadiene, which gives trans‐1,4 polymers. An interpretatio

ISSN:1022-1360    

DOI:10.1002/masy.19981280107

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractThis paper summarizes our recent efforts to offer block copolymers through the transformation reactions of a cationic growing center into an anionic one by the utilization of divalent samarium complexes. Four types of transformation reactions are described, and their scope and limitations are discussed. Several applications of these transformation reactions are also presented.

ISSN:1022-1360    

DOI:10.1002/masy.19981280108

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractReactions induced by Sml2, such as reduction, coupling and cyclization are occurring in high yield upon mild conditions. It is due to the high redox potential of divalent samarium. Now reactions with Sml2are used in the polymer synthesis as well. By the coupling reaction of various diacid chlorides poly‐α‐diketones having molecular weight up to 20000 have been obtained at room temperature in quantitative yield. Isomeric difluorobenzils prepared by the one‐step reaction of Sml2and relevant fluorobenzoyl chlorides have been used in the nucleophylic substitution reaction with bisphenols. Film‐forming high molecular weight copolyetherketone‐α‐diketones have been synthesized when such difluorobenzils have been used as the comonomers in the polycondensation of 4,4'‐difluorobenzophenone and bisphenols. All these polymers bearing α‐diketogroups have been transformed into linear and network polyquinoxalines by their reaction with aromatic (bis)o‐diamines. Aromatic polypinacols have been synthesized by the reaction of dialdehydes and Sml2in THF under mild conditions. The availability of the reactive α‐hydroxy groups made it possible to carry out polymer chain reactions. It was stated that the imide cycle is reduced by Sml2at room temperature. The treatment of polyimides by Sml2leads to the change of polymer properties, mainly heat resistance and solubility. The possibility of formation of Si‐Si bonds by reductive coupling of organochlorosilanes with the use of Sml2instead of Na has been shown. It was found that the reaction of diorganodichlorosilanes with Sml2easily proceeds in THF solution at room temperature to yield

ISSN:1022-1360    

DOI:10.1002/masy.19981280109

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractPhoto‐ (PL) and electroluminescence (EL) properties of three different PPV derivatives carrying the 9,10‐diphenylanthracene units are compared. One (polymer1) of the polymers contains the 9,10‐diphenylanthracene structure as an integral part of the main chain, but the other two have it as the pendent group attached to the main chain through either oxyethyleneoxy (polymer2) or oxyhexamethyleneoxy (polymer3) spacer. Polymers1and2exhibit very similar PL and EL spectra that are more or less of superimposed feature of the spectra from the backbones and the anthracene pendents. In contrast, polymer3shows an EL spectrum that is completely different from its PL spectrum. Whereas the PL spectrum of polymer3appears to be a combination of the spectra from the main chain and the pendents, as for polymer1and2, the EL spectrum of polymer3, however, looks as if the lights were emitted only from the backbone. This difference is explained in terms of excited state electronic interactions between the main chain and the pen

ISSN:1022-1360    

DOI:10.1002/masy.19981280110

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractRecent results from our laboratory have shown that the formation of polyester and Polyurethane rotaxanes by polymerization in the presence of crown ethers is driven by hydrogen bonding of the OH groups with the oxygen atoms of the macrocycles. Here we summarize these findings. Then we describe the application of this type of self assembly for the production of polyrotaxanes by threading preformed macromolecules and for the controlled synthesis of branched and crosslinked systems. These latter protocols comprise a new and novel way to prepare mechanically linked, elastomeric materials. Rheological properties of main chain polyrotaxanes are compared to simple linear backbones; the rotaxanes display higher intrinsic viscosities and lower melt viscosities, reflecting larger hydrodynamic volumes and less entanglement, respectively; these are potentially useful aspects in terms of processability of this new class of polymeric materials.

ISSN:1022-1360    

DOI:10.1002/masy.19981280111

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY

摘要:

AbstractAlthough ortho‐diphenols had not been extensively used in the synthesis of LC esters, a great variety of molecular structures of low and high molecular weight LC esters containing high proportions of these units can be synthesized. In this paper we describe the synthesis and characterization of new series of low and high molecular weight cyclic and linear LC esters with mesogenic “U”‐shaped rigid units with terminal groups which are alkyl chains. Cyclic oligoesters and linear polyesters were formed by the polycondensation of 4,4'‐[1,10‐decamethylenebis(oxy)]bis(cinnamic acid) with monosubstituted catechols which are the alkyl esters of 3,4‐dihydroxybenzoic acid. Although the great importance that concomitant cyclization reactions have in polyesterifications involving high proportions of ortho‐diphenols does not seem to have been considered until now, we have found mat these polyesterifications produced linear polyesters along with high proportions of cyclic oligoesters even when reaction conditions disfavored cyclization. Copolymerization with p‐hydroxybenzoic acid decreased the amount of cyclic oligomers, however it was necessary to copolymerize with proportions of PB higher than 50 mol‐% to get copolyesters with low proportions of cyclic oligomers. As far as we know we describe the first examples of cyclic LC oligoesters and cyclic LC unimers and dimers which display enantiotropic LC mesophases stable over broad ranges of temperature. Cyclic dimers display mesophases whose isotropization temperatures (>300°C) are much higher than that of their linear high molecular mass homologues. Cyclic LC unimers and dimers, linear LC polyesters and model compounds were characterized by FAB‐MS, GPC,1H NMR, DSC and hot‐stage polarized microscopy. All these compounds contain reactive C=C double bonds and can be crosslinked thermally and photochemically. Cyclic unimers and dimers can be polymerized termally to produce high

ISSN:1022-1360    

DOI:10.1002/masy.19981280112

出版商:Hüthig&Wepf Verlag    

年代:1998

数据来源: WILEY