摘要:

AbstractTo carry out dispersion polymerization of methyl methacrylate (MMA) in petrol, we have used a poly(MMA) grafted‐poly(12‐hydroxystearic acid) copolymer as the stabilizer. This special copolymer was prepared as a solution in a mixture of ethyl acetate and butyl acetate solvents. We investigated the effect of graft chain length of the stabilizer on the dispersion polymerization in petrol. We synthesized the stabilizer copolymer withn= 1–4 and determined the rate and the molecular weight of the PMMA formed. There is no dispersion polymerization forn= 1. However, for any othern, for a given stabilizer concentration, as the chain length of the graft is increased, the molecular weight as well as the rate of PMMA formation increases. As opposed to this for a given graft length as the concentration of the stabilizer increases, the molecular weight of PMMA first rises, but for a larger concentration, it begins to fall after undergoing a maximum. In this work, we modeled the heterogeneity of the reaction mass and proposed a mathematical model for dispersion polymerization of MMA in petrol. The computer results are found to conform to the experimentally observed molecular weight of the PMMA. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070490801

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe use of semiempirical and empirical relationships have been developed to estimate the mechanical properties of polymeric materials. Based on these relationships, properties can be calculated from only five basic molecular properties. They are the molecular weight, van der Waals volume, the length and number of rotational bonds in the repeat unit, as well as theTgof the polymer. Since these are fundamental molecular properties, they can be obtained from either purely theoretical calculations or from group contributions. The use of these techniques by polymer chemists can provide a screening technique that will significantly diminish their bench time so that they may pursue more creatively the design of new polymeric materials. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070490802

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractA stepwise scheme has been devised for the calculation of molecular weight distribution in condensation polymers prepared under the condition of unequal reactivity. In the scheme, a condensation polymerization is arbitrarily subdivided into a number of steps. The polymer obtained in one step is treated as the monomer for the next step. In each of the steps, Flory's distribution for the condensation polymer under equal reactivity is used as the molecular weight distribution for that step. Reactivity variances are incorporated into the calculation through the application of weighing factors on the concentrations of the reacting molecules in each of the steps. The distributions of polymers prepared under other unusual conditions, such as monomers with only limited solubility or endcapping at late stages of the condensation reaction, can also be conveniently calculated by this scheme. The treatment presented in this paper is devoted only to polymers prepared by monomolecular condensation. Extension to bimolecular condensation will not be trivial and will be the subject of another paper. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070490803

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractA systematic evaluation of two types of light‐scattering detectors for size exclusion chromatography (SEC) was completed. The two detectors were the low‐angle laser light scattering photometer (LALLS) and the multiangle laser light‐scattering photometer (MALLS). Instrument evaluations were performed at both room (30–40°C) and high (135–145°C) temperatures using the polystyrene standard, NBS 706, at room temperature and the polyethylene standard, SRM 1476, at high temperature. Results of the evaluation showed that when experimental uncertainties were taken into account LALLS and MALLS demonstrated equivalent precision and accuracy for molecular weight determination. The main source of inaccuracy found (particularly for SRM 1476) was the sensitivity difference between the light‐scattering and the concentration (DRI) detectors; i.e., the DRI detector was unable to measure very low concentrations of very high molecular weight material present in SRM 1476, whereas the light‐scattering detectors respond strongly. It was shown that for LALLS the overall weight‐average molecular weight (M̄w) for the whole polymer calculated using an equation that did not require the DRI detector output circumvented this sensitivity problem while assuming that the low angle used was sufficiently close to zero. Use of this equation for MALLS is possible by extrapolating data from all angles used to obtain a light‐scattering chromatogram at zero angle. However, this possibility was not examined here. A particular advantage of MALLS over LALLS is that MALLS can provide thez‐average root mean square radius (commonly referred to here and in other light‐scattering literature as the “radius of gyration”) values from the same data as those used to obtain molecular weight values. Although the radius of gyration values at each retention volume were not as precise as the corresponding weight‐average molecular weights, at room temperature, precision was better than 2% for a significant portion of the chromatogra

ISSN:0021-8995    

DOI:10.1002/app.1993.070490804

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractA new multiangle laser light‐scattering (MALLS) detector for size exclusion chromatography promises simultaneous measurement of both weight‐average molecular weight (Mw) and radius of gyration (rg) at each retention volume across the chromatogram. However, there are a variety of ways of interpreting the raw data to provide these results. This study examines variations of three different rearrangements of the basic light‐scattering equation. Data from a room temperature analysis of polystyrene and a high‐temperature analysis of polyethylene were used. The degree of fit of each equation to the data and the precision of theMwandrgvalues are evaluated. To define precision, joint confidence regions (JCRs) were calculated and compared to simple confidence intervals based upon standard deviations in order to see the effect of interdependence ofMwandrg. Results showed that the Debye equation was superior to the inverse Debye equation (similar to the Zimm plot) for the interpretation of MALLS data. The effect of the quantity of data included in the regression model was also assessed. Use of only the most precise four detector angles was compared to use of a full set of 15 angles. Precision of weight‐average molecular weight values was found to be improved as the detector angle decreased because of the shortened extrapolation to zero angle. Precision at room temperature was much superior to that at high temperature. Use of simple confidence intervals was shown to provide only a fair approximation to the more accurate JCR. The “natural scatter” of data shown by the JCR generally shows the same trend as do plots in the literature ofMwvs.rg. Thus, it is concluded that JCRs should be more often calculated in light‐scattering studies in order to distinguish random scatter from meaningful correlations of these values. © 1993 John

ISSN:0021-8995    

DOI:10.1002/app.1993.070490805

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAlkyl 2‐cyano‐2,4‐pentadienoates and alkyl 2‐cyano‐2,4‐hexadienoates were synthesized and characterized by spectroscopic methods. These were then evaluated as cross‐linkers in 2‐cyanoacrylate adhesive compositions to improve the heat stability of their adhesive bonds between various metal surfaces. © 1993 John

ISSN:0021-8995    

DOI:10.1002/app.1993.070490806

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractAnalysis of isothermal crystallization data of PET and PPS was carried out using Avrami and Tobin models. The models gave fractional values of exponentnand the standard deviation varied between 1 and 4%. No improvement in the standard deviation could be obtained even after incorporating the nucleation rate in these models. The Hillier model gave a good fit only to the isothermal crystallization data of PET. A simple model considering primary and secondary crystallization has been proposed. The model is verified using isothermal crystallization data of PPS. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070490807

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractDispersion of polystyrene (PS) and the molecular orientation of the polypropylene–polystyrene (PP–PS) composites acquired by thein situpolymerization of styrene in the oriented PP matrices were characterized by microscopic observations, birefringence measurements, and differential scanning calorimetry. It has been shown that applied processing of the “envelope” polymerization leads to obtaining oriented composites with large contents and the specific dispersion of PS. Some composites exhibit a substantial gradient of PS concentration and a gradient of molecular orientation, both strongly dependent on the initial structure of the oriented PP matrix. The modification of the PP structure taking place during processing does not disturb the orientation of the matrices deformed to the higher draw ratios. The structural changes of the oriented PP induced by processing are reflected in the shrinkage behavior and mechanical properties discussed in the second part of this paper. © 1993 John Wiley&S

ISSN:0021-8995    

DOI:10.1002/app.1993.070490808

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractIn this paper, the agglomeration of polymer latex that was caused by another latex was studied. The basic pattern and the factors affecting the agglomeration have been ascertained. Two agglomerating peaks appeared as the amount of added agglomeration latex increased. The agglomerating mechanism corresponding these two peaks has been proposed. © 1993 John Wiley&Sons, Inc

ISSN:0021-8995    

DOI:10.1002/app.1993.070490809

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractStyrene was graft‐copolymerized onto cotton cellulose using photoinitiators uranyl nitrate (UN), ceric ammonium nitrate (CAN), and benzoin ethyl ether (BEE) under ultraviolet radiation. UN gave somewhat higher graft add‐on. Preswelling of the substrate or using divinyl benzene in the grafting bath gave an increased level of graft, the later technique being more efficient. The moisture regain and tenacity decreased, whereas thermal stability increased in proportion to the graft add‐on. © 1993 John Wiley&Son

ISSN:0021-8995    

DOI:10.1002/app.1993.070490810

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY