摘要:

AbstractThe influence of residual styrene monomer and benzaldehyde on the surface properties of polystyrene latices has been considered. These materials are commonly found after emulsion polymerisation and their complete removal by dialysis is almost impossible. Steam stripping at reduced pressure (nitrogen atmosphere,<350K) can be used to remove the last traces of styrene and benzaldehyde from polystyrene, but this process results in some degree of hydrolysis of the surface sulphate groups.Latices are easily contaminated by microorganisms, especially those which are airborne. This can occur during cleaning and/or storage. Microorganisms can survive and multiply in suitable latex environments and can result in the destabilisation and subsequent flocculation of the latex. Controlled experiments with a latex dosed with various levels of a penicillium type fungus demonstrated the possibility that enzymes (classified as aryl sulphate sulphohydrolases ‐ E. C. 3.1.6.1.) were produced which resulted in the rapid hydrolysis of surface sulphate groups. Fungal growth was accompanied by the release of weak acids and metabolites which were titrated in the aqueous phase.Careful consideration should be given to the conditions of latex preparation, cleaning and storage, e.g. use of autoclaved water and γ‐irradiation techniques, which will reduce the possibility of microbial contamination. Routine tests for bacteria and fungi should be carried out by plating on microbiological media, since the usual tests for protein such as the Folin‐Ciocalteu are insensitive at the low levels of contamination which may be p

ISSN:0007-1641    

DOI:10.1002/pi.4980110102

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe Young's Modulus of PVC plasticised with various dialkylphthalates at concentrations from 40–120 phr that has been subject to a short heat treatment at 100°C, increases linearly with the logarithm of the time of storing at temperatures from 20–100°C. Both the Young's Modulus and its rats of increase with time is found to increase with increasing size of plasticiser to increase with decreasing concentration of plasticiser and to pass through a maximum with changing temperature of storage at a temperature of about 38°C. These effects can be explained if it is assumed that the elasticity results from a network linked by crystallites that can be melted on heating and reformed on storing at a lower temperature. The density of the plasticiser compositions is found to increase with time and this together with the development of endothermic DSC peaks support the hypothesis that changes in rigidity result from changes in crystallinity. The endothermic peak occurs at an almost constant temperature independent of plasticiser concentration or the size of the plasticiser molecule. It is suggested that the effect of these variables on the the melting point is nullified by the changes they also produce in crystallit

ISSN:0007-1641    

DOI:10.1002/pi.4980110103

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe electrical and physical properties of unstabilised and stabilised poly(vinyl chloride) (PVC) have been measured before and after ultraviolet irradiation. The results showed that the percentage changes in properties can be correlated with the structure of stabiliser added to the polymer.

ISSN:0007-1641    

DOI:10.1002/pi.4980110104

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe work arose from the need to explain the beneficial effect of post‐curing at an elevated temperature on the strengths of lap‐shear joints made with amine‐cured epoxy resins. Supermolecular structures were imaged by several electromicroscopy techniques, usually at 100,000 X. Three, if not four, stages of supermolecular structure were made visible. (i) A phase‐contrast image of 1.3 to 2.1 nm diameter which are probably stacked residues of bisphenol A. The d‐spacing seen in the diffracting mode of the microscope probably arises from within this structure. (ii) A nodular structure of ca. 5 nm. (iii) Aggregates of nodules of ca. 17 nm rising to 40 n m on post‐cure. These dimensions were obtained from cumulative distributions of sizes based on photodensitometer records from the electron‐micrograph negatives. Aggregate dimensions vary with curing agent and state of cure although minor variations occur with specime

ISSN:0007-1641    

DOI:10.1002/pi.4980110105

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractThe bulk polymerisation of pivalolactone (PVL) has been investigated using tertiary and quaternary phosphorus compounds as initiators. The quaternary P‐compounds were found to be essentially more active than the tertiary ones.The polymerisation mechanism with the two classes of initiators is as follows: Tertiary phosphines (and amines) form zwitterions and macro‐zwitterions with PVL, or: positive and negative charges are fixed on the same macromolecule. By chain transfer agents a separation of the charges onto two molecules takes place; the zwitterion character disappears.Using quaternary phosphonium (ammonium) compounds the anion starts the reaction; it is built into the polymeric chain. The gegenion retains its low molecular weight during the entire propagation reaction. During this stage an anion of high and a cation of low molecular weight are present side by side. The mechanism is not changed by any chain transfer reaction.The different reaction rates during propagation in the presence of these initiators are explained on one hand by a macrocation and on the other hand by a cation of low molecular weight. The degree of dissociation, which is higher in quaternary compounds than in tertiary ones, might also influence the reaction. The initiator molecule influences the start reaction as well as the total propagation react

ISSN:0007-1641    

DOI:10.1002/pi.4980110106

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractA new method is proposed for extrapolating light‐scattering data to the zero angle of scattering. Essentially the method consists of iterative extrapolations by use of the regression method as a subroutine, and it applies in general to the data obtained at low polymer concentrations and at low angles of scattering. Light‐scattering results on high molecular weight linear polystyrene in benzene were successfully analysed with the method. In comparison with other published methods, the strong points and limitations of the method are discus

ISSN:0007-1641    

DOI:10.1002/pi.4980110107

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

摘要:

AbstractFor light scattering analysis of an extremely high molecular weight polymer with large size in solution, use of mixtures of a given polymer with its low molecular weight homologue is described to have great advantages. With such bimodal mixtures as test samples, one can alter the unknown form of the angular variations of scattered lights to a form to be expected and widen the range of the linearity with sin2(ø/2), where ø is the scattering angle. According to the considerations, a sample of linear polystyrene was successfully analysed on a commercial apparatus, Fica 50 to have the weight‐average molecular weight of 27 mill

ISSN:0007-1641    

DOI:10.1002/pi.4980110108

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY

ISSN:0007-1641    

DOI:10.1002/pi.4980110101

出版商:John Wiley&Sons, Ltd    

年代:1979

数据来源: WILEY