摘要:

AbstractResults are presented for the thermal, ultraviolet, and γ‐ray polymerization of 2,4‐hexadiyne‐1,6‐diolbis‐(p‐toluene sulfonate) (PTS). Monomer extraction is used to obtain polymer conversion‐vs.‐time curves at 30, 50, and 80°C. In agreement with previous work over a narrower temperature range, the curves all display a dramatic autocatalytic effect with an onset at about 10% conversion to polymer. Although the polymerization rate undergoes a 200‐fold change over this temperature range, the shape of the conversion curves does not change. These data yield an activation energy (E tha) of 22.2 ± 0.4 kcal/mole when interpreted in terms of the time required to reach 50% polymer. An annealing technique is used to provide a closer look at the autocatalytic region. In that case,E tha= 22.5 ± 0.8 kcal/mole is determined from measurements of the time required to go from 10 to 50% polymer at temperatures ranging from 23 to 80°C (a 500‐fold change in rate). Thermal polymerization rates measured in the low‐conversion limit using a spectroscopic method based on diffuse reflectance yieldE tha= 22.8 ± 0.6 kcal/mole. ThusE thais independent of polymer conversion and the autocatalytic effect can be best understood as arising from a large increase in the propagation length of the polymer chains. The autocatalytic effect is shown to be present in both UV and γ‐ray polymerization. In the case of γ‐ray polymerization, conversion‐vs.‐time and spectroscopic measurements are consistent with inhomogeneities in the polymer concentration caused by particle tracks. Activation energies for UV and γ‐ray polymerization are quite low (2‐3 kcal/mole) and confirm that the chain initiation event makes the major energetic contribution toE tha. The polymerization mechanism is discussed in detail. The photopolymerization experiments can be consistently interpreted with a model based on the triplet excited state of the

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160511

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractIn co[poly(ethylene terephthalate)‐p‐oxybenzoate] containing 30 mole % oxybenzoate units, the ethylene terephthate units crystallize. The copolymer melts in the temperature range 180–210°C to form a nematic phase which, at a higher temperature, transforms to an isotropic liquid. The latent heat of the first transition is 5 cal/g, and the thermodynamic melting temperature, 247°C, is essentially that expected for a random copolymer of this composition. The nematic → isotropic transition occurs at 244°C, with an enthalpy change of 3.2 cal/g (10% of the heat of fusion of poly(ethylene terephthalate)). We conclude that semiflexible polymers form a nematic phase which is rather highly disordered. The model of the nematic phase treated by Flory is modified to increase its entropy through incorporation of chain bends (which must be correlated in position and direction with those in neighboring molecules). This increases the chain extension, as measured by the fraction (1–f) of collinear chain bonds, required to form the nematic phase. For binary polymer‐solvent systems, an appropriate scaling offvalues leaves the phase diagram as predicted by Flory's treatment essenti

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160512

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractA series of low‐molecular‐weight linear polyesters were epitaxially crystallized from dilute solution and the melt on a variety of organic and inorganic substrates. The rod‐like polyester crystals which were formed assumed general orientations in alignment with substrate geometry. This yielded monodirectional orientation of these crystals on one of the organic substrates, and bidirectional orientation on the other surfaces. Heterogeneous nucleation on the organic substrates, trioxane and naphthalene, induced the growth of much larger epitaxial crystals than have previously been observed on inorganic substrates. Those polyesters, with a high percentage of methylene units per chain repeat, crystallized in an unusual polymorphic form when in contact with the organic substrates. Polymorphic transformation to the normal form was not possible under thermal treatment or with increased crystal thickness. The expected relationship between dipolar alignment in the polymer crystal and this polymorphism was establ

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160513

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractDielectric properties of vinyl acetate and methyl methacrylate oligomers having chemically different end groups were compared. Dielectric measurements were carried out over the frequency range between 23 and 3 MHz and the temperature range between +50 and −50°C. The static dielectric constants of these oligomers are between 10 and 20. The relaxations were analyzed with the Havriliak–Negami equation. The dielectric properties depend on the chain end groups on the oligomers. The distribution of relaxation times of the vinyl acetate oligomers was wider than that of poly(vinyl acetate). It was concluded that two cooperative motions, that of the principal chain and that of the chain and that of the chain end group, take part in the dielectric relaxation of these short chain molec

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160514

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractThe strain history of the combined test is formed by a constant strain rate during the period 0

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160515

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

摘要:

AbstractPrecise melting and crystallization temperatures of extended‐chain and folded‐chain crystals of form I and folded‐chain crystals of form II poly(vinylidene fluoride) under high pressure have been obtained by microdifferential thermal analysis (DTA). Upon heating at pressures above 4000 kg/cm2, the micro‐DTA thermogram of form II crystallized from the melt at atmospheric pressure shows melting of the form II structure and the melting of the folded‐chain and extended‐chain crystals of form I, formed through recrystallization processes. These features were clarified by supplemental methods. The bandwidth seen in electron micrographs of the extended‐chain crystal of form I obtained by crystallization under high pressure was in the range of 1500 to 2000 Å. At atmospheric pressure, the extended‐chain crystal of form I melted at 207°C, approximately 17°C higher than the folded‐chain crystal of form I and 31°C higher than the folded‐c

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160516

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160517

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160518

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY

ISSN:0098-1273    

DOI:10.1002/pol.1978.180160519

出版商:John Wiley&Sons, Inc.    

年代:1978

数据来源: WILEY