摘要:

The thermostimulated creep of two amorphous polyolefins having the repeating unit ─(CH2)mC(CH3)2─, where m = 2 and 3, was investigated from 77° to 350°. Two relaxation processes are distinguished: a secondary relaxation is observed at 138 and 113°, respectively, for m = 2 and m = 3; a primary relaxation is found around the glass transition. These relaxations have been resolved in their elementary components. From the data acquired, the mechanical losses have been calculated and compared with data from an inverted torsional pendulum. The activation energy found for the secondary relaxation—0.26 eV at 138° K for the amorphous polyolefin with m = 2 and 0.19 eV at 113° K for the polyolefin with m = 3—confirms that this relaxation mode is associated with restricted backbone motion.

ISSN:0022-2348    

DOI:10.1080/00222347808212270

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The thermostimulated creep of three amorphous polyolefins having the repeating unit ─(CH2)mC(CH3)(C2H5)─, where m = 1, 2, and 3, was investigated from 77° K to 350° K. A broad relaxation process is observed around the glass transition temperature in each polyolefin. The corresponding TSC peaks have been resolved into elementary components with a relaxation time τ obeying a compensation law τ = τcexp {(ΔH/k)[1/T) —(1/Tc)], where Tcand Tcare characteristic of the polyolefin. From the TSC data, we have calculated, the mechanical loss peaks associated with the glass transition and we have compared them with the dielectric loss peaks.

ISSN:0022-2348    

DOI:10.1080/00222347808212271

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A combination of dielectric and thermomechanical techniques is used for studying relaxation transitions in plasticized poly(vinyl chloride) compounds at different stages of the calendering process. An unplasticized aggregate phase is discovered to be present at a fairly high concentration, even in completely processed samples. By analysing the dielectric depolarization spectra in comparison with thermomechanical creep-shrinkage curves it is concluded that a relatively large part of the PVC aggregates remains untouched by the plasticizer in each phase of the calendering process, the compound being thus a heterogeneous mixture of the aggregate and plasticized phases. This conclusion is supported by computer simulations of the Maxwell-Wagner-Sillars type polarization in this heterogeneous mixture. The dielectric depolarization method was found useful for characterizing the efficiency of processing.

ISSN:0022-2348    

DOI:10.1080/00222347808212272

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Two thermally stimulated techniques were used to perform a detailed study of the retardation mode found in amorphous poly(ethylene terephthalate) below the glass-rubber transition. The complex retardation process observed has been resolved in its elementary components. From the data acquired, the dielectric and mechanical losses have been calculated and compared with data from conventional mechanical and dielectric techniques.

ISSN:0022-2348    

DOI:10.1080/00222347808212273

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Kinetic theories of crystallization of polymers do not apply to high supercooling. The thickness of the crystalline lamellae becomes independent of the crystallization temperature and is a characteristic parameter of the polymer. We relate this limiting thickness to the flexibility of the polymer chain in the pure liquid or in solution before crystallization. The folded chain in the crystalline state is analogous to the coiled chain before crystallization. Flexibility and limiting thickness depend in a similar way on the solvent, defect concentration in the polymer chains, pressure, pH, and salt concentration in case of crystallization of polyelectrolytes. Folded chains appear also in oligomer crystals when the oligomers have a coiled shape in the liquid state. The limiting fold period of crystalline polymers and oligomers is found to be an order of magnitude greater than the persistence length of the Gaussian chain in the liquid state.

ISSN:0022-2348    

DOI:10.1080/00222347808212274

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The effects of the degrees of rotational freedom, as defined by the Hayes factor n, on the physical properties of polymers were studied. The applicability of the Hayes relationship was extended to include polymers with aromatic entities in the backbone chain and also the various units within a polymer repeat unit that are capable of independent motion. A rule of constant specific heat at Tg, ΔCp, dependent upon rotational motion was established. This rule was subsequently used to derive an inverse relationship between n and the characteristic ratio o. A strict linear dependence was found to exist between these two variables within a specific polymer grouping, but, in turn, is dependent upon structural complexity and the free volume present. The rule was employed to interpret the type of rotational motion present at and below Tg, the result being that torsional oscillation or hindered rotation around single bonds is the best description. An interpretation of Wunderlich's rule of constant ΔCp is presented within this framework.

ISSN:0022-2348    

DOI:10.1080/00222347808212275

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

The molecular mechanism of the α→β phase transformation of poly-p-xylylene was studied by transmission electron microscopy using solution-grown single crystals. The observations suggest that the phase transformation from the α to β-phase occurs by a coordinated lateral movement of the molecules from the lattice sites of the α-phase to the sites of the β-phase.

ISSN:0022-2348    

DOI:10.1080/00222347808212276

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

Quantum-mechanically derived potential energy surfaces, employing reasonable monomeric models, are used to explore both the phenylene/carboxylate and ethylenic linkage conformations in poly(ethylene terephthalate). The predictions are consistent with what is found experimentally and help in understanding the conformational changes which occur on commercial orientation.

ISSN:0022-2348    

DOI:10.1080/00222347808212277

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor

摘要:

A technique is described, leading to dispersions of individual molecules and their aggregates of OsO4-tagged polyisoprene in an untagged matrix of poly-isobutylene.

ISSN:0022-2348    

DOI:10.1080/00222347808212278

出版商:Taylor & Francis Group    

年代:1978

数据来源: Taylor