摘要:

AbstractFurfuryl alcohol was polymerized by trifluoroacetic acid in methylene chloride to give a colored polymer. This polymer possesses two main sequences in which the furan rings are connected by methylene groups (sequence1) or by dimethylene ether groups (sequence2). The polymer is not linear but highly branched, as detected by1H and13C NMR spectroscopy. Variations of the experimental conditions, such as the presence of air, the trifluoroacetic acid concentration, the reaction temperature and the solvent, do not allow a significant increase in the linear structure of the polymer. However, an increase in the acid concentration or an increase in temperature produce a decrease in the ether‐bridged structure (sequences2

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930101

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractA series of rigid‐rod polyesters with flexible alkoxy side chains of different length has been studied in order to determine the structure and properties of the polymers in various states (solid state, mesophase, melt). Various supermolecular structures can be obtained depending on the length of the side chains and on the preparation conditions of the samples. The relaxation behavior of the polymers has been investigated by dynamic mechanical measurements. Complex relaxation spectra have been observed, and types of molecular motions and structural rearrangements have been assigned to the observed mechanical relaxation transitions. The rheological behavior was studied in the mesophase and in the melt. In some polymers typical liquid‐crystalline properties have been observed, as for example the flow‐thinning effect. Large deformation of polymer films as well as the structure and mechanical strength of oriented samples have also been st

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930102

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractBenzoxazole‐2‐thiol (1)/dibenzoyl peroxide (Bz2O2) was used as photoinitiator for the polymerization of methyl methacrylate (MMA) in bulk and in solution. The study of initiator decomposition was conducted spectrophotometrically. Kinetic studies of the photopolymerization indicated the formation of a complex between1and Bz2O2in the stoichiometric ratio 2:1. The initiation is believed to occur via in situ formation of bis(benzoxazol‐2‐yl) disulfide in the presence o

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930103

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractCopolymerization of propene with 1‐hexene was performed at 40°C under atmospheric pressure using both aspecific and isospecific catalysts composed of TiCl3/MgCl2and Al(C2H5)3, and of Solvay type TiCl3and Cp2Ti(CH3)2(Cp: cyclopentadienyl), respectively. The isospecific catalyst gave two kinds of copolymers with different content of 1‐hexene, whereas the aspecific catalyst gave a uniform copolymer abundant in 1‐hexene. Both copolymers produced with the isospecific catalyst were found to show isotactic stereoregulation in the propylene units. From these results, it was concluded that the catalyst composed of Solvay type TiCl3and Cp2Ti(CH3)2has two kinds of isospecifically active species which differ in the monomer reactivity ratio for propene‐1‐hexene copoly

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930104

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effects of crystallinity and spherulite size on the enzymatic degradation of microbial poly(3‐hydroxybutyrate) (PHB) films have been studied at 37°C and pH 7,4 in aqueous solutions of an extracellular PHB depolymerase fromAlcaligenes faecalisT1. The rate of enzymatic degradation of PHB films decreases with an increase in crystallinity, but it is little influenced by the size of PHB spherulites. It was suggested that the PHB depolymerase firstly hydrolyzes the PHB chains in the amorphous state on the surface of the films and subsequently erodes the PHB chains in the crystalline sta

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930105

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractCu(II) complexes of polyorganosiloxanes with pyridyl group in the side chains (1–6) were investigated as catalysts for hydroquinone oxidation. The catalytic oxidations followed Michaelis‐Menten‐like kinetics. The kinetic parameters were evaluated, and the greatest value ofk2/Kmis 119 dm3· mol−1· s−1due to the large value ofk2(0,262 s−1) in methanol/water (vol. ratio 2/1) at 25°C. It has been shown that the main factors which influence the substrate‐binding process are hydrophobicity, hydrogen bonding between functional groups in the side chains, conjugation and basicity of pyridine, and adsorption of substrate by amido groups. Largek2values were obtained in the present system due to flexibility and hydrophobicity of the siloxane backbone. Additionally, in the activation process, hydrogen bonding between amido groups, which is easily formed due to the flexibility of the polymer chains, should contribute to decrease both activation enthalpy and ac

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930106

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe melt viscosity of polycarbonate from bisphenol‐ASystem name: 4,4′‐isopropylidenediphenol.was measured in a wide range of temperatures, fromTg+ 55°C up to aboutTg+ 185°C. The experimental results are discussed in terms of the classical WLF (Williams‐Landel‐Ferry) and Arrhenius models. There are clear indications that the WLF approach holds over the entire temperature range investigated. This is rather unusual as the Arrhenius behaviour is reported to be the correct one for temperatures above approximatelyTg+ 100°C. The most critical factor in our case seems to be the restricted number of bonds with rotational degree of freedom in the polycarbonate unit. The reduced number of virtual bonds with respect to real ones is discussed to be a possible reason for the large temperature range in which the free volume is the rate‐limiting factor for th

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930107

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe energy gaps of poly(p‐arylenevinylene)s with phenylene, naphthylene and anthrylene subunits are determined by extrapolating the UV/VIS spectroscopic data of the oligomers. The band structure of the three polymers was theoretically investigated. The topology‐, geometry‐ and correlation‐factors were determined upon which the energy spectra of this class of one‐dimensional π‐electron sy

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930108

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractRing‐opening metathesis copolymerization of 5‐norbornen‐2‐ylSystem. name: bicyclo[2.2.1]hept‐5‐en‐2‐yl.acetate (NBEAc; 80%endo) with cyclooctene (COE) and norborneneSystem. name: bicyclo[2.2.1]hept‐2‐ene.(NBE) was studied using WCl6/(CH3)4Sn as catalytic system. The copolymerization parameters (r1=r2= 1 for the NBEAc/NBE system andr1= 1/r2= 132 for the NBEAc/COE system) show that the reactivity of the monomers is not affected by the presence of an ester substituent but that it depends on the structure of the hydrocarbon cycle. Thus the well known inhibition effect of the ester group may be concluded not to lie in the propagation step of

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930109

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY

摘要:

AbstractThe kinetics and the molecular weight distributions (MWD) in the anionic polymerization oftert‐butyl acrylate (tBuA) in tetrahydrofuran at 23 ± 3°C were investigated.Tert‐butyl α‐lithioisobutyrate (tBiB‐Li) was used as the initiator in the absence and presence of the additives lithium chloride and lithiumtert‐butoxide (tBuOLi). A flow tube reactor was used which allowed very rapid mixing of reagents, within milliseconds. The polymerization is extremely fast, half‐lives being 0,01 s for the system without additive, 0,05 s for LiCl and 3 s for tBuOLi as an additive. The rate of termination was estimated from the strong UV absorption of the enolized β‐oxoester end group formed. The number‐average degree of polymerization is a linear function of conversion, the absolute values, however, demonstrate initiator efficiencies of only ca. 30%. The MWD's of the polymers formed are narrow (Mw/Mn= 1,35 without additive,M/Mn= 1,08 in the presence of LiCl andMw/Mn= 1,77 in the presence of tBuOLi). After precipitation these values are reduced to 1,17; 1,06 and 1,32, respectively. Experiments in a stirred tank reactor and in ampoules lead to much broader MWD's. This shows that the rate of mixing has a strong effect on the MWD and is of substantial importance in these ra

ISSN:0025-116X    

DOI:10.1002/macp.1992.021930110

出版商:Hüthig&Wepf Verlag    

年代:1992

数据来源: WILEY