ISSN:0007-1641    

DOI:10.1002/pi.4980120402

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractSeveral different series of rigid and flexible polyesters with main chain liquid crystalline units were prepared and their properties were examined in relation to their structures. The first group of polymers were rigid aromatic copolyesters with mesogenic groups based on either chloro or methyl hydroquinone terephthalate units combined with varying amounts of different types of bisphenol terephthalate units The bisphenol comonomers used contained the structure:in which X was none, C(CH3)2, CH2, O, S, and So2. It was observed that the bisphenols with the bulkier X group were more efficient in destroying thermotropic liquid crystallinity of the resulting copolymers. The second group of polymers studied were flexible polyesters consisting of various types of mesogenic units which were connected together by different lengths of polymethylene flexible spacers. The liquid crystalline behaviours of these polymers, particularly their transition temperatures, were correlated with their structures. A brief review of previous studies on the synthesis of thermotropic liquid crystalline pol

ISSN:0007-1641    

DOI:10.1002/pi.4980120403

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractThe use of different linking units to promote liquid crystal behaviour in rigid rod like polyarylates is reviewed. By systematically varying the proportion of non linear,meta, ortho, or bent bisphenol units in one particular series based on chloro‐ 1,4 phenylene: 4,4′ oxydibenzoate/terephthalate, complete series of compositions, extending from liquid crystal through to isotropic behaviour, have been prepared, characterised and compared. Using this data, parallels between thermotropic and lyotropic behaviour are illustrated and used to postulate physical models for the structure of liquid crystalline melts and sol

ISSN:0007-1641    

DOI:10.1002/pi.4980120404

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractMelt‐spun and injection‐moulded liquid crystalline polyesters have very high strength and stiffness and a very low coefficient of linear thermal expansion. The exceptional properties that characterise these polyesters are due to the presence of stiff, rod‐like polymeric chains, which become highly oriented during melt‐spinning or injection‐moulding, and long relaxation times, which permit the chains to retain their orientation while the polymer is cooling. The introduction of either flexible aliphatic groups or kinks in the rod‐like polymer chains reduces the polyester melting points and thereby permits easier melt processing but also adversely affects the strength and stiffness properties which are obtained. The effects of composition on the melting point and properties of plastics and fibres of liquid crystalline aromatic polyesters i

ISSN:0007-1641    

DOI:10.1002/pi.4980120405

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractRheological measurements were made on a variety of substantially aromatic copolyesters. All of them differ from flexible chain polymers in having unusually long relaxation times, estimated from shear rate dependence of viscosity and from melt elasticity. This behaviour is not accounted for by an unusual molecular weight distribution (MWD); limited measurements indicate that the MWD is somewhat narrower than that of conventional condensation polymers.Numerous anomalous flow phenomena have been observed, though not necessarily with all samples. These include the occurrence of a yield stress, large secondary shear stress maximum after start‐up of steady shear, transient negative normal stress, and shear‐thickening of melt viscosity. Although the melts are highly elastic, they do not exhibit swelling after extrusion from a capillary.The melt rheology is often very sensitive to temperature and dependent upon thermal history. In one material this dependence has been linked to the destruction and/or growth of crystallites formed from blocks of one comono

ISSN:0007-1641    

DOI:10.1002/pi.4980120406

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractFor a polymer to be capable of forming a nematic, liquid crystalline state the molecules must be nearly rigid and rod‐like. There are two main classifications of such liquid crystalline states: lyotropic ‐ generally applied to polymer solutions and implying the formation of a low viscosity state in a critical concentration range. and thermotropic ‐ usually applied to melts where the low viscosity mesophase appears over a limited temperature range.Lytropic —generally applied to polymer solutions and implying the formation of a low viscosity state in a critical concentration range. and thermotropic — usually applied to melts where the low viscosity mesophase appears over a limited temperature range.For polymers we further find that attaining this low viscosity state depends critically on the previous thermomechanical history of the mesophase and that, by appropriate thermo‐mechanical history, it is possible to induce a low viscosity state under conditions where such is not spontaneously formed. This extension of the liquid crystal state may also include polymers whose molecular flexibility is such that they do not naturally form liqu

ISSN:0007-1641    

DOI:10.1002/pi.4980120407

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractSolutions of cellulose were prepared with liquid crystal phases by mixing cellulose, water and N‐methylmorpholine N‐oxide under appropriate conditions of concentration and temperature. Their rheological behaviour was studied using capillary rheometry. For each solution, flow curves were plotted over a temperature range of 70‐‐120°C, and a shear rate range of 1‐‐500 sec−1.Considerable agreement was found between the rheological and optical characterisations of the anisotropic‐isotropic transition temperatureT*. The variations of the strain rate sensitivity parametermwere studied over a large temperature range and particularly aroundT*. These results, new for cellulose solutions, provide some valuable information about the rheology of anisotropi

ISSN:0007-1641    

DOI:10.1002/pi.4980120408

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractTwo types of crystalline morphology seem to be present in commercial PVC powder, both related to syndiotactic sequences in Natta orthorhombic cell: (1) ribbon‐like crystats formed during the second stage of the mass‐process and in suspension or by annealing PVC samples aboveTg. (2) high melting fringed‐micelles are the main crystalline feature of emulsion type powder and of low‐conversion mass PVC.A second less ordered phase, which does not fit the Natta cell is found also in emulsion powder and in highly strained samples (like fibres).Ribbon‐like crystals and fringed‐micelles influence the i.r. absorption at 604 and 638 cm−1respectively. 685cm−1might be related to the low‐order phase, the X‐ray spacing of which is 3.8‐

ISSN:0007-1641    

DOI:10.1002/pi.4980120409

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980120410

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY

摘要:

AbstractSome observations on the formation and growth of PVC granules during polymerisation are described, particularly with reference to granule morphology. The physical structure of the final granule is very dependent on polymerisation variables and of these, the influence of reactor agitation, temperature of polymerisation and protective colloid are briefly discussed.

ISSN:0007-1641    

DOI:10.1002/pi.4980120411

出版商:John Wiley&Sons, Ltd    

年代:1980

数据来源: WILEY