摘要:

AbstractEight epoxy–diamine networks have been formed, diamines with 2 to 12 methylene groups being used as curing agents. Dynamic mechanical tests revealed four transition regions in the dynamic loss modulus/temperature relationship. Two possible explanations for the relaxation of the glycidyl portion of the structure are proposed. One of the relaxations could be due to the breakdown of hydrogen bonds through the hydroxyl and ether groups. The second could be ascribed to the relaxation of the unbonded glycidyl groups or a second relaxation of the glycidyl groups after the breakdown of the hydrogen bond

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070501

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractTriad tacticity data obtained by NMR analysis have previously been interpreted in terms of two basic statistical models in order to elucidate the stereospecific polymerization mechanism. In this paper the characteristics of these two basic models for stereospecific polymerization, the enantiomorphic‐sites (EMS) model, and the polymer‐end control (PEC) model, are examined and compared. The tacticity values accessible to the two‐parameter EMS model, which includes the influence of the chain end unit, are shown to be highly restricted. Only about 20% of the isotacticity versus syndiotacticity plot is accessible to this model. To this extent the consistency of a set of triad tacticity data with the model can be tested. No such tacticity limits are exhibited by the two‐parameter PEC model, which includes the influence of the penultimate unit. Any set of tacticity values which can be interpreted in terms of the two‐parameter EMS model can also be interpreted in terms of the two‐paramete

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070502

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractA statistical model for the stereospecific polymerization of vinly monomers on Ziegler‐Natta catalytic systems is presented. The basic assumptions of the model are: (a) the catalytic centers are asymmetric, so that at a given catalytic center the monomer CH2CHR is inserted into the chain with two different rates according to the two different configurations of the opening carbon atom having the R group; (b) the insertion of a monomeric unit in the growing chain is affected also by interactions with the previous monomeric unit. Isotactic, syndiotactic, atatic, or stereoblock polymers are obtained according to the relative values of the two energy parameters expressing these two effe

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070503

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractPrevious theoretical calculations of elastic constants for cellulose based on force constants for bond stretching and bending of valence angles have yielded axial stiffness values admittedly too low. The present analysis accounts for a hitherto unexamined geometrical effect associated with deformation of interchain hydrogen bonds. To do this, most primary bond deformations are neglected so the resulting calculation gives an upper bound for the axial stiffness. By using two different sets of hydrogen bond force constants, values of 24.6 and 31.9 × 1011dyne/cm2were obtained for Young's modulus in the chain direction. These values are very much larger than earlier calculations and experimental determinations from cellulosic fibers, indicating both the importance of the effect considered here and the likelihood of an exact analysis yielding an acceptable result

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070504

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractDynamic mechanical properties determined with a torsion pendulum were used to ascertain the glass transition temperatureTgof poly‐ε‐caprolactone. By measurements on compatible blends of poly‐ε‐caprolactone and poly(vinyl chloride), theTgof amorphous poly‐ε‐caprolactone was shown to be 202°K at about 1 cps. This is 16°K lower than theTgof annealed, crystalline polymer. The blend transition data were well fitted by both the Fox and the Gordon‐Taylor expressions. The Fox expression was also used to describe the decrease from 233°K of the secondary low‐temperature relaxation due to poly(vinyl chloride) by assuming the low temperature relaxation of poly‐ε‐caprolactone, 138°K, was responsible for the decrease in the blends. The 138°K relaxation due to poly‐ε‐caprolactone was decreased when more than 50%

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070505

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractA novel gas‐flow method of measuring the diffusion, solubility, and permeability of gases and vapors in polymer films is described. The specific advantages of this system over the time‐lag technique are discussed. Transport data, including activation energies and enthalpies of solutions, for hydrogen and deuterium in poly(vinyl fluoride) are presented, and the effects of the glass transition and of orientation on the observed transport rates are discus

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070506

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractA specimen of linear polyethylene was subjected to isothermal secondary crystallization at a series of temperatures below the primary isothermal crystallization temperature, the melting and primary crystallization stages being held constant throughout the investigation. Dilatometric measurements exhibit an S‐character at low values of undercoolingTp–Ts, whereTpandTsare, respectively, the primary and secondary crystallization temperatures, whereas at larger undercooling, an initial very rapid crystallization is followed by a very slow stage. When corrected for thermal contraction of the polymer, the net degree of secondary transformation is seen to peak at a temperature about 5°C belowTp. The S‐character of the isotherms and the peaked temperature variation of degree of transformation lead to the conclusion that a large portion of the secondary crystallization consists of the nucleation and growth of the new crystallites. Johnson‐Mehl‐Avrami analysis leads to a model of heterogeneous nucleation within the remaining amorphous zones, followed by one‐dimensional, diffusion‐con

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070507

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractPoly(vinyl chloride) sheet was oriented by hot drawing. The yield behavior of the oriented sheet was then investigated under uniaxial tension at room temperature as a function of the angle between the tensile axis and the molecular alignment direction. The onset of yield was localized in deformation bands. The variation of yield stress with direction and the direction in which the deformation bands formed were found to be satisfactorily accounted for in terms of a yield criterion based on that of von Mises, provided that a term representing internal compressive stress in the molecular alignment direction was included. The internal stress was found to increase from zero with increasing draw ratio of the prior hot drawing. It is pointed out that other workers have found polymers to obey the yield criterion of Coulomb rather than that of von Mises.

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070508

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractThe conformational energy contribution (ΔUconf) to the heat of solution in polymer‐solvent systems is presented and discussed in connection with chain conformational properties. In particular, ΔUconfhas been discussed in terms of various possible mechanisms of coil deformat

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070509

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY

摘要:

AbstractHeats of solution (ΔHexp) in solvents of increasing thermodynamic power have been measured for four polymers: polystyrene (PS), poly(vinyl acetate) (PVAc), polyisobutylene (PIB) and polydimethylsiloxane (PDMS). After subtraction from ΔHexpof an interaction term (calculated by the Hildebrand treatment based on solubility parameters) and the excess volume term, the quantity remaining is interpreted as the conformational energy contribution (ΔUconf) to the heat of solution. ΔUconfappears to correlate well with some basic conformational properties of the chain, such as the sign of the temperature coefficient of unperturbed dimensions derived from solution properties, and shows a monotonic behavior with α, the expansion coefficient of the polymer coil in the final solution. Numerical values of ΔUconf, at least for those cases in which polymer solubility parameters are known with some certainty, are much larger than those evaluated from rubber elasticity experiments (through the experimentally accessible value of the energy component of the force of retraction im simple elonga

ISSN:0449-2978    

DOI:10.1002/pol.1969.160070510

出版商:John Wiley&Sons, Inc.    

年代:1969

数据来源: WILEY