摘要:

AbstractThe chemistry and properties of the ionomer cements are reviewed. These cements are defined by the acid‐base interaction between metal oxides or silicates with aqueous solutions of organic polymeric acids. the cements formed both from ion‐leachable aluminosilicates and from zinc oxide are of practical importance and characterised by their ability to bond to active substrates under moist conditions. The polymer solutions used in these formulations tend to gel slowly over a period of several months. This phenomenon can be avoided by partial methylation of the polymer or by the use of a suitable copolymer. The role of the anoins present in the system and those, such as tartrate, added to improve rheological properties, is discussed. The nature of the bonding in these cement gels is considered in terms of ion‐binding of polyanions of polyvalent cations. The function of water in the cement and hydrolysis of cations is discused. In the final section the long‐term development of surface hardness and compressive strenght is reported. The modulus of elasticity and stress relaxation properties of these cements are compared to those of the brittle dental silicate

ISSN:0007-1641    

DOI:10.1002/pi.4980070502

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractA comparison is made of the mechanical properties of ionic polymer cements, prepared by reacting an aqueous poly(acrylic acid) solution with ion‐leachable inorganic powders. Out of the wide range of powders investigated, specially formulated aluminosilicate glasses gave the most promising results, and the properties of cements made from them are discussed in greater detail. In particular, the dependence of compressive strength on cement age is described, and the loss of water from the material when exposed to atmospheres of low relative humidity is shown to be related to property changes which occur under these conditions. An interpretation of these detrimental effects is presented in terms of variation in the cement microstructure, and methods of minimising the effects by various modifications to the basic system are reviewe

ISSN:0007-1641    

DOI:10.1002/pi.4980070503

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractOxide glasses can be regarded as network polymers consisting of oxygen atoms linked through multivalent atoms such as boron, silicon and phosphorus, and many of their properties can be related to two simple parameters of the network; the crosslink density and the packing density of oxygen atoms. The effects of changes in composition on the transformation temperatures of phosphate, borate, and borophosphate glasses can be rationalised in terms of these two network parameters.

ISSN:0007-1641    

DOI:10.1002/pi.4980070504

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractThe temperature dependence of d.c. conductivity of poly(ethylene oxide) complexes with sodium iodide and the thiocyanates of sodium, potassium and ammonium has been investigated. In each case a transition to a lower activation energy at higher temperatures was observed. For the sodium complexes this transition occurs atca55°C which is well below the crystalline melting points at 200°C. For the potassium and ammonium complexes however, the transitions coincide with the melting points atca100 and 70°C respectively. It is proposed that at the transitions, thermal disintegration of complexes in the amorphous regions occurs. The complexes involve coordination of the cations to the ether oxygen atoms in the polymer backbo

ISSN:0007-1641    

DOI:10.1002/pi.4980070505

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractBlock copolyetheresters of poly(hexamethylene terephthalate) (6GT) with poly(oxyethylene) terephthalate (POET) units have been prepared by polycondensation and certain of their thermal, morphological and mechanical properties have been determined. The copolymers rich in 6GT or POET units show the crystalline characteristics of the single respective homopolymers, whereas in the middle of the composition range crystalline phases of both types coexist. Increase in the proportion of POET units causes a decrease in the melting and glass transition temperatures and in the crystallisation rates whilst concomitantly the mechanical properties change from fibrous to elastomer in type. The results are interpreted in terms of a polycrystallite model in which the compostion‐dependent nature of the crystallites and tie bars determines the overall mechanical properties of the copolymer

ISSN:0007-1641    

DOI:10.1002/pi.4980070506

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractA study has been made on skin formation of melt spun polyethylene monfilaments, which were solidified in air or in cold solvents and non‐solvents. Application of air or non‐solvents, such as water and acetone, as cooling media induced spherulitic crystallisation of the polymer, as was revealed in the scanning electron microscope. When the flowing polyethylene melt was quenched in good solvents, a 0.5 mm thick layer of lamellar or shish kebab structures developed on the polymeric fibres. It was established that shish kebabs were formed when the solvents, in which the polymer filament was quenched, were boiling during this solidification proc

ISSN:0007-1641    

DOI:10.1002/pi.4980070507

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

摘要:

AbstractThe use of anhydrosulphite and anhydrocarboxylate derivatives of α‐pentafluorophenyl‐α‐hydroxypropanoic acid as precursors in the formation of fluorine‐containing poly α‐esters is described. Kinetic studies have enabled the nature of the competing mechanisms to be determined and compared with those occurring in the hydrocarbon analogues. The pentafluorophenyl group markedly enhances the susceptibility of both ring systems to hydroxyl‐initiated polymerisation and in the case of the anhydrocarboxylate this is the only viable polymerisation mechanism under the conditions described here. Although polymerisation of the anhydrosulphites is possible, purification of both the phenyl, and especially the pentafluorophenyl substituted monomer, is more difficult than in the case of either alkyl substituted anhydrosulphites or phenyl and pentafluorophenyl substituted anhydrocarboxylates. For this reason anhydrocarboxylate polymerisation represents the preferred route to pentafluorophenyl substituted poly α‐esters. The characterisation of the polymers prod

ISSN:0007-1641    

DOI:10.1002/pi.4980070508

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980070509

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980070510

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980070501

出版商:John Wiley&Sons, Ltd    

年代:1975

数据来源: WILEY