摘要:

AbstractIsobaric variations of the characteristic temperaturesTgandTmax, obtained on uniform cooling and heating of glasses, are investigated in terms of their dependence on the relevant experimental variables, using a single retardation time model. The corresponding partial derivatives ofTgandTmaxare derived as functions of the partition parameterx(ranging between zero and unity), which determines the relative contributions of temperature and structure to the retardation time. It is shown that the variation ofTgwith the cooling rate is independent ofx. In contrast,Tmaxcritically depends onx, and its value as well as those of its three partial derivatives are linear functions ofx−1. The variations ofTmaxare analyzed in terms of a set of reduced variables, leading to simple reduction rules between any two of the experimental variables when the third is kept invariant. The reduction rules are further substantiated by investigating the behavior of glasses in two‐step thermal cycles, which result in a unique set of inter‐relationships between any pair of the partial derivatives ofTmax, whatever the value ofx. The results are discussed in terms of their relevance to the behavior of real gl

ISSN:0098-1273    

DOI:10.1002/pol.1979.180171201

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe kinetics of the photoinitiated polymerization of lauryl acrylate (LA), 1,6‐hexanedioldiacrylate (HDDA) and pentaerythritol tetraacrylate (PET4A) have been investigated using differential scanning calorimetry (DSC). An autoacceleration phenomenon is observed with the multifunctional acrylates, but not with lauryl acrylate. The empirical dependences of reaction rate on such parameters as incident light intensity, initiator concentration, and temperature have been established and are in general found to vary with monomer conversion. Apparent activation energies for the photopolymerizations have been determined from rate versus temperature data. The multifunctional acrylates show an increasing activation energy with monomer conversion, whereas the apparent activation energy for lauryl acrylate not only decreases with conversion, but becomes negative at conversions greater than about 30%. The ratiokp/k t1/2is calculated from rate versus conversion data under constant illumination and the (independently determined) initiation rate. Analysis of rate versus time data under nonsteady‐state conditions (light turned off) yields the ratiokt/kp. With these two ratios the rate constants for propagation (kp) and termination (kt) may be separated and their respective values calculated. Bothkpandktare found to decrease substantially with monomer conversion, indicating a significant change in the rates of both the propagation and termination steps as the polymerization advances. These observations are explained in terms of a radical isolation phenomenon and diffusion control of the propagation

ISSN:0098-1273    

DOI:10.1002/pol.1979.180171202

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe effect of intermolecular correlations on the angular dependence of the intensity of Rayleigh scattering from a dilute solution of a flexible‐chain polymer in a good solvent is studied for an approximate model that retains the random‐flight intramolecular segment‐pair correlation while probabilities of multiple intermolecular contacts are simplified as products of probabilities of single contacts, all conditional on a common “initial” contact. This model, unlike one in which a polymer chain is represented as a spherically symmetrical cloud of segments, gives very little deviation from Zimm's “single‐contact” approximation in light scattering: i.e., the initial concentration dependence of the concentration/intensity ratio is almost the same at all scattering angles. This behavior, which appears to underestimate the intermolecular correlations, can be accounted for by the symmetry of the bimolecular cluster as represent

ISSN:0098-1273    

DOI:10.1002/pol.1979.180171203

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe aromatic Polyamide‐hydrazide, Monsanto X‐500, has been studied by light scattering in dimethyl sulfoxide, a thermodynamically good solvent. The unperturbed dimensions, (〈r 02〉av/M)1/2= 1.93 × 10−8at 25°C., indicate a rather highly extended chain. The persistence length falls in the range 35–63 Å, which corresponds to a length of between two and four formula units. This is considerably smaller than the values which have been reported for the aromatic polyamides, poly(p‐benzamide) and poly(p‐phenylene terephthalamide). X‐500 appears to approximate coil‐like behavior at a molecular weight of 45,000. Theoretical predictions, based upon the 〈r 02〉av/bLratio, are compared with the observation that no evidence for an anisotropic phase has been found in X‐500 solutions in dimethyl sulfoxide at polymer volume ranging from 0.12 to 0.19 (depending upon

ISSN:0098-1273    

DOI:10.1002/pol.1979.180171204

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractZero‐shear‐rate intrinsic viscosities [η]0in benzene at 25°C and in cyclohexane at 34.5°C were measured for two series of polystyrene samples: six fractions ranging inMw(weight‐average molecular weight) from 8.8 × 106to 5.7 × 107and 11 “monodisperse” samples ranging inMwfrom 4 × 103to 4.8 × 106. The results, combined with typical literature data, yielded\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {[\eta ]_0 = 7.8 \times 10^{ - 5} \bar M_w^{0.75 \pm 0.01} } & {(4 \times 10^5 < \bar M_w < 6 \times 10^7 ,{\rm benzene at }25^\circ {\rm C})} \\ {[\eta ]_0 = 8.8 \times 10^{ - 4} \bar M_w^{0.50} } & {(10^3 < \bar M_w < 6 \times 10^7 ,{\rm cyclohexane at }34.5^\circ {\rm C})} \\ \end{array} $$\end{document}These relations cover the broadest range of molecular weights reported so far in the literature on synthetic polymers. In contrast to Slagowski et al., we observe no “anomaly” in the molecular weight dependence of [η]0for benzene solutions of very high molecular

ISSN:0098-1273    

DOI:10.1002/pol.1979.180171205

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractIfMminandMmaxare lower and upper bounds, respectively, to the molecular weights of different molecular weight species contained in a polymer, the weight‐average to number‐average molecular weight ratioMw/Mncannot exceed (1 +Mmax/Mmin)2/(4Mmax/Mmin). The ratio attains this maximum possible value if the masses of the two species with molecular weightsMminandMmaxare equal and the masses of all the other species are negligibly small, corresponding to maximum spread in the molecular weight distribution within the specified bounds. Also for a given value ofMw/Mn= α, theMmaxcannot be smaller than [2α − 1 + 2α1/2(α − 1)1/2]Mmin. The minimum possible value ofMmax/Mminconsistent with α given is obtained in the case of maximum spread described above. If only one species is predominant, then bothMw/MnandMmax/Mminapproach unity, as is well known. Similar relations hold for the ratios of higher‐order average molecular weights for which the role of the mass fractions is replaced by higher‐order distri

ISSN:0098-1273    

DOI:10.1002/pol.1979.180171206

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractA new method is introduced to determine the degree of partitioning of noncrystallizable comonomer units (Bunits) between the two phases of a semicrystalline random copolymer. The method is based on the comparison of the intensities of small‐angle neutron and x‐ray scattering (SANS and SAXS, respectively). By this technique two quantities can be evaluated: the difference Δρ of the mass densities between the crystalline and the disordered regions, and the concentration fluctuations of theBunits in the two phases. It is found that SANS is very sensitive to the presence of small amounts ofBunits if their scattering length is sufficiently different from that of theAunits. This will be the case for copolymers withBunits, in which a hydrogen is substituted by another atom. But in addition it can also be achieved generally by deuteration of the comonomer units. So a wide range of copolymer systems can be studied by this method. The capability of the method was proved by measurements on chlorinated polyethylene and on 1,3,5‐trioxane–1,3‐dioxolane copolymers. Both copolymers are distinguished by a random distribution of the co‐units. The results show that even at relatively low concentrationsxBof the comonomer units a remarkable fraction of theBunits is incorporated into the crystallineAphase and that this fraction rises ifx

ISSN:0098-1273    

DOI:10.1002/pol.1979.180171207

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractAn analytical theory of block copolymer conformations is developed for systematically studying the effects of the chain length, chain architecture, and segment interactions. The main results obtained forABdiblock andABAtriblock chains are as follows: (i) In the absence ofAAandBBinteractions, both diblock and triblock chains collapse to a dense form if theABinteraction is attractive. In the collapsed coil form, the mean‐square end‐to‐end distance 〈R2〉 is proportional to the square root of the number of segmentsn1/2. (ii) The diblock chain has a dumbbell form ifAAandBBinteractions are attractive andABinteraction repulsive, but the triblock chain collapses. In the dumbbell form, 〈R2〉 is pro

ISSN:0098-1273    

DOI:10.1002/pol.1979.180171208

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractRaman spectra of a series of styrene‐sodium methacrylate copolymers of varying sodium methacrylate contents have been investigated in the 425–100 cm−1region. The bands appearing at 254 and 166 cm−1have been attributed to ion multiplets and clusters, respectively. From an analysis of the intensities of these bands and a comparison of these intensities with those obtained from an analysis of dielectric data, it seems that Raman spectroscopy is a useful method for determining the concentrations of ions in the two different kinds o

ISSN:0098-1273    

DOI:10.1002/pol.1979.180171209

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractLithium polyphosphate crystals produced by crystallization during polymerization and crystallization from the polymer melt were analyzed by thermal analysis. The glass‐transition and melting temperature, heat of fusion, and entropy of fusion were found to be 336°C, 651.5°C, 21 kJ/mole, and 23 J/deg mole, respectively. Crystallization from the macromolecular melt was followed by thermal analysis, x‐ray diffraction, and electron and optical microscopy. It could be shown that chain folding may be the first step to crystallization from the macromolecular melt. Oligomers could not effectively nucleate crystallization. Lithium polyphosphate is shown to present a prime example of the processes involved in crystallization during polymerization and macromolecular melt crystalliz

ISSN:0098-1273    

DOI:10.1002/pol.1979.180171210

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY