摘要:

AbstractThe commonly used spectroscopic analyses of polymers include infrared (IR), nuclear magnetic resonance (NMR), mass(MS), x‐ray(XR), and the rapidly growing near infrared(NIR). The uncommon methods that are not frequently used include nuclear quadrupole resonance(NQR), electron spin resonance, and combination techniques such as gas chromatography‐infrared, thermal‐infrared, gas chromatography‐mass spectroscopy, and even thermal‐gas chromatography‐infrared or mass spectroscopy. The use of two of these methods (thermal‐infrared(TGA‐IR) and NQR is described. Appropriate examples are shown to point out how use

ISSN:0258-0322    

DOI:10.1002/masy.19930720103

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractBiodegradable polyesters obtained by fermentation ofAlcaligenes eutrophusare characterized with the aid of H, D, C NMR spectroscopy. Copolymers of 3‐hydroxybutyrate and 3‐hydroxyvalerate are Bernoullian or mixture of two Bernoullian copolymers depending on fermentation conditions. The reverse reaction was found in the reaction catalyzed by beta‐ketothiolase during biosynthetic pathway. The fractional population ofgaucheandtransconformers around the skeletal CH‐CH2bond is 0.6:0.4 for both poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) in chloroform. This result suggests the possibility of formation of isomorphic crystals between copolymers with different c

ISSN:0258-0322    

DOI:10.1002/masy.19930720104

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe deuterium NMR (2H‐NMR) is used for probing the chain segment orientation in polymer networks under uniaxial stress. The method is based on the observation of an incomplete time averaging of quadrupolar interactions affixed to deuterated segments. The samples are end‐linked polydimethylsiloxane networks. The2H‐NMR experiments are performed either on labelled network chains or an labelled probe polymer chains dissolved in the network. The basic results are the following:— The induced uniaxial order is related to a uniaxial dynamics of chain segments around the direction of the applied constraint.— A permanent orientation is observed on free polymer chains dissolved in the deformed networks.— The mean degrees of orientational order induced along short and long chains in bimodal networks are the same.These experimental facts appear as evidences for cooperative orientational couplings between chain segments in the deform

ISSN:0258-0322    

DOI:10.1002/masy.19930720105

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractCapability of NMR technique to study fracture and elementary destruction acts in polymers is discussed. Tensile stress influences macromolecular mobility As a rule mobility of macromolecules decreases under deformation. So far deformation remains reversible, this effect is reversible, too. As a result of chain micro‐Brownian motion hindering under stress the amorphous layers can pass from high‐elastic to solid state even at temperatures rather higher than Tgmeasured under initial conditions. It is mechanical vitrification (not structure changes) that is regarded as the general causes of draw process interruption (destruction of polymer).Deformation‐induced electron emission was detected. It is caused by ionization of stressed chains and tunnel transitions of electrons into deep traps. Influence of molecular mobility on the traps and their destroying under stress are consi

ISSN:0258-0322    

DOI:10.1002/masy.19930720106

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA series of thermotropic main chain polymers with extended dimethylsiloxane segments was investigated. The study of dielectric properties of polymers revealed the relationship between their ability to form a mesophase and their molecular mobility. The peculiar behaviour of dielectric α‐relaxation parameters during the transition from mesomorphic to isotropic members of this polymeric series was shown. The theoretical approaches were developed for understanding macrochain dynamics of liquid crystalline polymers. The theoretical and experimental results are in good agreeme

ISSN:0258-0322    

DOI:10.1002/masy.19930720107

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractDuring thermal decomposition, most of the thermo‐resistant polymers leave a considerable fraction of the original mass behind, consisting mainly of a carbonaceous material. The gases evolved are, to the largest part, low‐molecular (H2O, CO2, CO, NH3, HCN, hydrocarbons); they are formed during polycondensation processes. The rate of heating strongly influences the degradation mechanism and thus the composition of the gaseous pyrolyzate. Rapid heatingi.v.to the maximum temperature chosen frequently favors the formation of heavy fragments. These can be identified by field‐ionization or low‐voltage mass spectrometry; they usually allow conclusions on the composition of the original polymer.Slow, temperature‐controlled heating allows rearrangement and polycondensation reactions in the polymer. A study of the processes going on in the residue during temperature‐controlled heating is important with regard to the behavior of thermoresistant polymers under real conditions.An elegant method of continuous residue analysis is FTIR spectrometry. A heatable IR cell designed in our institute allows the study of both gaseous pyrolyzate and solid residue in separate experiments. The time needed for the measurement of one spectrum (from 20 scans) was 36 s. This, with a heating rate of 5 K/min, corresponds to a temperature resolution of 3 K/spectrum.Results are given for aromatic polyethers and polye

ISSN:0258-0322    

DOI:10.1002/masy.19930720108

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThermotropic main‐chain LC polyesters have been studied with the aid of IR and NMR spectroscopy. Rigid mesogens and mesogens with a possibility of conformational isomerism were examined. The dependence of the order parameters of the mesogens and spacers on the chemical structure of the polymer has been determined. The IR spectroscopy data and the data of the calculation of the possible conformations of the mesogen and the spacer confirm the theoretical predictions about the straightening of macromolecules in the anisotropic melt. Solid‐state2H NMR spectra show that p‐oxybenzoic rings adjacent to a flexible spacer are more mobile than inner terphthalic rings. In decamethylene spacer the contrary holds true: the mobility of inner methylene groups is more marked than that of the α‐methylene groups bound to the

ISSN:0258-0322    

DOI:10.1002/masy.19930720109

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractTwo‐dimensional infrared (2D IR) spectroscopy was used to probe the submolecular dynamics of atactic polystyrene. 2D IR is a powerful analytical technique especially suited for the elucidation of localized motions of polymer segments. In 2D IR, a polymer sample is excited by a small‐amplitude oscillatory strain at a frequency in the acoustic range. The fluctuation of IR dichroism signals resulting from the strain‐induced reorientation of electric dipole‐transition moments is monitored with a time‐resolved spectrometer. Spectra defined by two independent wavenumber axes are constructed by applying a correlation analysis to such signals. The 2D spectra provide detailed information about the local dynamics of submolecular constituents of the system. From the sign of cross peaks in the synchronous 2D IR spectrum of glassy polystyrene, it is shown that the main‐chain backbone of polystyrene reorients in the direction of applied strain. Cross peaks in an asynchronous 2D IR spectrum reveal highly localized reorientational motions of phenyl side groups occurring more or less independently of the main‐chain realignment. In the glassy state, the phenyl ring tends to fold back along the main‐chain, indicating that there exists a highly constrained local distortion of side groups dur

ISSN:0258-0322    

DOI:10.1002/masy.19930720110

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe transition front of the neck between the isotropic and oriented region in uniaxially stretched polyvinylidene fluoride (PVDF) and polypropylene (PP) is analyzed with a high spatial resolution by micro‐Raman spectroscopy. The variation of the microstructure, i.e. change in the degree of crystalline modification in the case of PVDF and in the orientation of the PP chains in function of the strain rate, is correlated with other parameters associated with the drawing response of these polymers and the temperature rise during deformation. The results here described can be understood through the clear increase of temperature that was detected in the neck due to the heat generated by the deformation work of the drawing proces

ISSN:0258-0322    

DOI:10.1002/masy.19930720111

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractMeasurements on insulating and conducting polymers from the polyaniline (PANI) family and investigations on semiconducting poly(tetrathiafulvalenes) (PTTF) have been used for illustration and discussion of some methodical questions of electron spin resonance (ESR). This concerns especially the new possibilities of the recently developed high‐resolution ESR in the 2 mm wave band. It was applied for the study of the nature and dynamics of paramagnetic centres (PC) and charge carriers in PANI and PTTF. The rate of the quasi‐one‐dimensional (1D) intrachain electron motion and of the three‐dimensional (3D) interchain electron hopping has been estimated separately. In iodine ‐ doped PTTF the maximum electrical conductivity is 10−4S ·cm−1. It is almost identical with the 3D‐conductivity estimated by ESR and shows the typical temperature dependence of a semiconductor. The quasi‐1D‐conductivity is several orders of magnitude higher and shows in its dependence on temperature similarities with a metal. The PANI samples show in the highly doped form a maximum conductivity of about 10 S ·cm−1and relativly small differences between the 1D‐ and 3D‐conductivity, supporting th

ISSN:0258-0322    

DOI:10.1002/masy.19930720112

出版商:Hüthig&Wepf Verlag    

年代:1993

数据来源: WILEY