摘要:

AbstractUV and IR spectroscopy were used to follow the photolysis of poly(syclohexylmethylsilane) (1) and poly(hexylmethylsilane) (2). Striking correspondences were found between wavelengths at maximum absorption and absorbance in UV region and particular IR bands which undergo bleaching in parallel. New IR band assignments are proposed. In addition, there is some evidence of a random scission of the chains with no significant contribution of an unzipping process.

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910111

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractA DSC study is reported on the dependence of thermal properties on molecular weight in two series of thermotropic liquid‐crystalline poly(ester‐β‐sulfide)s,9S4and9S5. The molecular weights range from approximately 1 600 to 14 000. All of the polymers exhibit a nematic phase preceded, at lower temperature, by a smectic A phase which is monotropic in the majority of the cases. The nematic‐isotropic transition temperatures and relevant entropy changes were found to be practically insensitive to molecular weight variations. In contrast, the smectic A‐nematic transition temperatures and entropy changes increase with increasing molecular weight and reach a plateau value at an average chain length of 6–7 repeating units. It is suggested that in the nematic phase of these polymers the flexible segment plays a role of diluent of the rigid groups, whereas at the nematic‐smectic A transition a cooperative increase in chain stiffne

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910112

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractSix dicarboxylic acids (1a–f) were prepared from trimellitic anhydride and 4,4′‐oxydianiline, 4,4′‐methylenedianiline, 4,4′‐sulfonyldianiline, benzidine, 1,6‐hexamethylenediamine, and 4,4′‐methylenedicyclohexylamine. These diacids were condensed directly with various aromatic diamines using triphenyl phosphite in 1‐methyl‐2‐pyrrolidone/pyridine solution in the presence of calcium chloride. The inherent viscosity of the polymers is affected by the nature of the diamine and the solubility of the resulting polymers in the reaction media. The highest ηinh‐value of a poly(amide‐imide) obtained was 1,41 dl/g (inN,N‐dimethylacetamide/5% LiCl at 30°C). Among the polymers, the wholly aromatic ones show better solubility, higher glass transition temperatures, and higher thermostability than the aliphatic‐aromatic ones. Well‐defined melting points (Tm) of most wholly aromatic poly(amide‐imide)s were not obtained by differential scanning calorimetry (DSC); however, some poly(amide‐imide)s containing aliphatic chains showed clearTmin the first DSC heating traces. Measurements of wide‐angle X‐ray diffraction revealed that those polymers containing biphenyl or linear hexamethylene groups are partially crystalline. Flexible films with excellent tensile properties were cast fromN,N‐dimethylacetamide solutions of

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910113

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractPoly(vinyllactams) form a class of non‐ionic water‐soluble polymers from which only poly‐(1‐vinyl‐2‐pyrrolidone) (PVP) is well known and has been investigated extensively. The homologues poly(1‐vinyl‐2‐piperidone) (1, poly[1‐(2‐oxo‐1‐piperidyl)ethylene]) and poly(N‐vinylcaprolactam) (2, poly[1‐(2‐oxoperhydroazepin‐1‐yl)ethylene]) which are still soluble in water at room temperature have not yet been studied in aqueous solution. In this work the synthesis of these two polymers by radical polymerization in solution and the investigation of the dilute aqueous solution properties of these polymers by static and dynamic light scattering measurements are presented. Special attention is paid to the influence of the increasing hydrophobicity of these polymers on coil dimensions

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910114

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractBlends of crystallizable poly(vinyl alcohol) (PVA) and poly‐(N‐vinyl‐2‐pyrrolidone) (PVP) of different molecular weights were prepared from aqueous solutions by evaporation and studied by Fourier‐transform IR spectroscopy. When the molecular weight of one of the polymer components increases, the PVP content at which crystallinity in PVA is no longer observed decreases. The wide band representing hydroxyl stretching splits into four components at welldefined frequencies which are assigned to (1) multiple hydroxyl‐hydroxyl bonding in organized PVA regions, (2) hydroxyls which are simply bonded to carboxyl, (3) hydroxyls doubly bonded to two carbonyls or to one carbonyl and one hydroxyl, and (4) simple hydrogen‐hydrogen bonding in amorphous PVA regions. When the PVP content increases, the relative intensity of the bond of di‐hydrogen‐bonded hydroxyls remains quasi‐invariant, while that of multiple hydrogen bonds in PVA decreases, and that of simple hydroxyl‐carbonyl bonds increases correspondingly. It appears that the higher the molecular weight, the more effective the hindrance of PVP crystallization. An explanation of the mechanism leading to the formation of different structures in the blends is proposed on the basis of these results. It stresses the importance of the role of chain dynamics in an entangled chain network, which greatly affects the kinetics of crystallization of PVA d

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910115

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe kinetics of the pyridine‐initiated polymerisation of simple 1,3‐oxathiolan‐2,5‐diones (3a–c) in nitrobenzene was studied at various temperatures. Results show that, although the substituents in 4‐position have a marked effect on rate of polymerisation, the polymerisation of the three monomers studied is linked by a common mechanism. Thus, the pyridine, nucleophile attacks the carbonyl in 5‐position and forms a charge transfer complex which decomposes to form a highly reactive α‐thiolactone intermediate8together with carbon dioxide and pyridine. Chain addition continues by the direct attack on the thiolactone by the terminal‐SH group of traces of parent acid. The reaction of each of the three monomers with pyridine was found to show first order kinetic dependence on both monomer and pyridine, although the initiator (i.e. pyridine) is not consumed. The resultant polymers (molecular weight typically around 20000) are highly crystalline and relatively insoluble in commo

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910116

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe reaction of methyl α‐(S)‐malate withN,N′‐dicyclohexylcarbodiimide in the presence of amines under mild conditions was studied. It was established that in solvents with weak donor properties,N‐acyl derivatives are preferentially formed instead of ester condensation products. An optically active polymer fraction was separated by precipitation in diethyl ether (yield up to 30%) withM̄n,GPC1 000 to 4 000 and of low polydispersityM̄w/M̄n= 1,1–1,4. The method permits the preparation of optically active biodegradable condensation products with controlled mole

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910117

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractAromatic polyesters5and6were synthesized fromtert‐butyl‐ and phenoxyhydroquinone (4aand4b) and terephthalic acids3a–e. The introduction of substituents reduces the phase transition temperature and increases the solubility of the corresponding polyesters in common solvents. As a result, soluble, amorphous and liquid‐crystalline aromatic polyesters were obtained. Unexpectedly, the phenoxyhydroquinone moiety suppresses the formation of a mesophase in some pol

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910118

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

Abstract13C NMR analysis of isotactic polystyrene prepared in the presence of different catalysts reveals that isotactic polyinsertion can arise from mechanisms involving different regiospecificity and possibly different steric control.

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910119

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY

摘要:

AbstractThe Miscibility in blends of poly(2,6‐dimethylphenylene oxide)Systematic IUPAC name: poly[oxy(2,6‐dimethyl‐1,4‐phenylene)].(PPO) with random or block copolymers of styrene and methyl methacrylate (MMA) was studied by light microscopy and glass transition temperature measurements. Blends of PPO and the random copolymers were found to be miscible up to a copolymer content of 18 wt.‐% MMA. The transition from miscibility to immiscibility in these blends in independent of temperature in the range 100 to 350°C. From these data, the segmental interaction parameter between units of the homopolymer and MMA, χPPO/PMMAis estimated to be about 0,5. Blends of PPO and the block copolymers of styrene and MMA used behave essentially as the corresponding homopolymers in terms of

ISSN:0025-116X    

DOI:10.1002/macp.1990.021910120

出版商:Hüthig&Wepf Verlag    

年代:1990

数据来源: WILEY