摘要:

AbstractThis paper deals with the non‐steady‐state kinetics of direct thermal initiated polymerization. The initiation is assumed to be a bimolecular reaction of the monomer. The relationship between the radical concentration and the monomer conversion is rigorously derived. In further treatment a few very close approximations are introduced based on the fact that the number of monomer molecules reacting in the initiation step is much less than that consumed in the propagation step for a process producing high polymer, and the value of the rate constant for propagation or chain transfer is much lower than that for chain termination. Expressions for various molecular parameters, such as molecular weight distribution, number‐average and weight‐average degrees of polymerization, and dispersity, are given. Several numerical examples are p

ISSN:0959-8103    

DOI:10.1002/pi.4990280302

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe curing behavior of bis(methacryloxy) derivatives of diglycidyl ether of bisphenol A (vinyl ester resin) containing acrylates (methyl, ethyl and butyl acrylate) as the reactive diluents (40% w/w) were studied by DSC analysis. Data found in this study indicated that an appreciable curing rate is obtained at lower temperature with increased concentrations of initiator. The acid value, activation energy, Arrhenius factor and specific heat are discussed.

ISSN:0959-8103    

DOI:10.1002/pi.4990280303

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractOn heating films of long‐chain alkylamino‐1,3,5‐triazine‐2,4‐dithiols, substituted with unsaturated groups in the 6‐position, on copper plates in air, the films become partially insoluble in benzene. The polymerization rate and monomer conversion increased with temperature above 80°C and with time. At low temperatures, an induction period was observed. The detailed behavior was dependent upon the number and length of the alkyl chains. Films with high packing density polymerized more slowly. In the presence of azobis(isobutyro)nitrile (AIBN) and benzoyl peroxide (BPO), the rate and conversion increased and the induction period disappeared. The optimum concentration of initiators was approximately 0.0025 mol% of monomer. The polymerization of the films was initiated by oxygen activated with copper, or by radicals derived from AIBN and BPO. It is proposed that the growth of polymer proceeded mainly by the addition of thiyl radicals to unsaturated groups, the insoluble polymers being formed by the coupling of th

ISSN:0959-8103    

DOI:10.1002/pi.4990280304

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe complexation behaviour of dithiocarbamate functions supported on polyacrylamides with varying extents (2‐20 mol%) ofN,N′‐methylene‐bis‐acrylamide (NNMBA) crosslinks was investigated. The crosslinked polyacrylamides were prepared by the free radical solution polymerization of the monomers in water at 80°C using potassium persulphate as initiator. The dithiocarbamate ligands were introduced by polymer‐analogous reaction involving transamidation with ethylenediamine and dithiocarbamylation with carbon disulphide and alkali. The complexation behaviour of these dithiocarbamate resins with the ligand functions in different macromolecular environments were investigated towards Co(II), Ni(II), Cu(II), Zn(II) and Hg(II) ions by a batch equilibration technique. The metal ion intake varied with the extent of the NNMBA‐crosslinking. Thus the 8% crosslinked system has the highest complexation capacity. The values for metal ion intake followed the order Hg(II)>Cu(II)>Zn(II)>Ni(II)>Co(II). The time‐course of complexation, the possibility of recycling and the swelling characteristics of the uncomplexed and complexed resins were considered, and IR characterization and thermal studies were undertaken. The swelling values of the complexed resins are lower than those of the uncomplexed resins. The thermal stability of dithiocarbamates varied with the extent of NNMBA‐crosslinks and

ISSN:0959-8103    

DOI:10.1002/pi.4990280305

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractSynthesis and lithographic characterization of a series of negative acting electron sensitive resists based on poly(4‐methylstyrene‐co‐chloromethylstyrene) are reported. The sensitivity and contrast of these resists were found to depend on the chloromethylstyrene (CMS) content and an optimum value of 5 wt% was determined from consideration of parameters associated with the reproducibility of the synthetic method and also the lithographic performance. Both the sensitivity and resolution were found to depend on the molecular weight and CMS content of the copolymer. Several methods ofscale upfor the synthesis were explored, the route having a very significant influence on the film formation characteristics of the resists. The reactivity ratios of the monomers were measured in order that the compositional drift, which occurs during the synthesis, could be quantified. The effect of solvent composition and molecular weight of the copolymer were explored in relation to the quality of the resulting lithography. These studies have indicated that the copolymer has the potential of being used as a VLSI sub‐micron resist with good plasma etch res

ISSN:0959-8103    

DOI:10.1002/pi.4990280306

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThis study examined both the effect of chemical composition and of storage (ageing), for periods up to 28 weeks, and at temperatures from ‐ 15 to 50°C on the mechanical properties.The presence of high contents of barium sulphate, zinc oxide and colouring agent in commercial dental gutta‐percha has the same effect on the mechanical properties of gutta‐percha as prolonged storage time, i.e. increase in brittleness. On the contrary, the presence of Thermoplast or Wax (75%) has an accentuated plasticising effect on gutta‐percha improving thus, to a certain extent, its clinical charact

ISSN:0959-8103    

DOI:10.1002/pi.4990280307

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe dielectric relaxation properties of poly[2,2‐propane‐bis‐(4‐phenyl thiocarbonate)] (PTC) have been studied. The existence of crystallinity, which can be eliminated by quenching, is detected. The degree of crystallinity of polymer samples was determined by differential scanning calorimetry in order to investigate the effect of this factor on the dielectric behaviour of this polymer. The thermal degradation of the samples was studied by thermogravimetry. The degradation of the polymer begins before the glass transition temperatureTg. The dielectric spectrum is complex showing several relaxation phenomena. With increasing temperature a γ relaxation can be observed at ‐ 100°C (5 kHz). The activation energy obtained from an Arrhenius plot (lnfvsT−1) is 6 kcal mol−1. At 160°C the α relaxation which is associated with the glass transition temperatureTgis detected. The dielectric behaviour of this poly(thiocarbonate) is compared with the correspondin

ISSN:0959-8103    

DOI:10.1002/pi.4990280308

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe variation in radiation resistance with composition of statistical terpolymers of (1) bisphenol‐A and biphenol, and (2) hydroquinone and biphenol, with diphenyl sulphone was studied by electron spin resonance spectroscopy after γ irradiation at 77 K and by analysing volatile products after irradiation at 423 K. Approximately linear relationships were obtained between the radiation chemical yields for both radicals,G(R), and sulphur dioxide,G(SO2), and the mole fraction of biphenol units in the terpolymers. Substantially higher radiation resistance was shown by biphenol units compared with either bisphenol‐A or hydroqui

ISSN:0959-8103    

DOI:10.1002/pi.4990280309

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractFinely divided inorganic solids can be used for drop stabilisation in suspension polymerisation. Usually solids are dispersed in water in the presence of electrolytes formed during their preparation. Experiments, using a wax model as described previously,1have been carried out by using two inorganic solids, magnesium phosphate and calcium phosphate, in either the presence or absence of electrolytes. The experiments showed that the effect of electrolytes depends on both the inorganic solid which is used and on the nature of the electrolyte which is present. Magnesium phosphate was a destabiliser in the absence of electrolytes but could act as a stabiliser in the presence of sodium sulphate. Calcium phosphate acted as a stabiliser both in the presence and in the absence of electrolytes.

ISSN:0959-8103    

DOI:10.1002/pi.4990280310

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTernary copolymerizations of tri‐n‐butyltin 4‐acryloyloxybenzoate (ABTB) with acrylonitrile (AN) and alkyl acrylates [methyl (MA), ethyl (EA) or butyl acrylate (BA)], methyl methacrylate (MMA) or styrene (ST) were carried out in solution at 70°C in the presence of free radical initiator. Experimental terpolymerization data agreed well with calculations based on the Alfrey‐Goldfinger equation. The determination of unitary, binary and ternary azeotropies of various systems studied was easily handled by a computer program. The results obtained show that there is no ternary azeotropic composition for any terpolymer, system studied. Selective unitary and binary azeotropic compositions were polymerized and the results obtained show good agreement between the theoretical and experimental terpolymer composition for e

ISSN:0959-8103    

DOI:10.1002/pi.4990280311

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY