摘要:

AbstractPoly(N‐ethyl laurolactam) and poly(N‐benzyl laurolactam) were prepared from the corresponding monomers by hydrolyic polymerization. Unlike the partially crystalline poly(N‐methyl laurolactam), these two homopolymers were completely amorphous by x‐ray diffraction. Diffraction patterns of copolymers ofN‐ethyl laurolactam orN‐benzyl laurolactam with laurolactam were shown to be composition‐dependent. ForN‐ethyl laurolactam copolymers, crystallinity developed with 20% laurolactam as a comonomer and increased steadily with a subsequent change in the x‐ray pattern, up to 50% laurolactam. Higher laurolactam percentages resulted in copolymers having a nylon 12 x‐ray pattern.N‐Benzyl laurolactam copolymers with 30% laurolactam showed only 6% crystallinity. The x‐ray patterns ofN‐benzylated nylon 12 made with more than 50% laurolactam showed patterns similar to that of nylon 12. Differential scanning calorimetry data of all these polymers substantiate the x‐ray findings. The effect of type and concentration of theN‐substituent on the glass transition, melting, and crystallization temperatures

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110511

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractA surface zone composed of at least three distinct layers has been detected in injection‐molded polypropylene. The morphology of these layers as determined by optical and scanning electron microscopy forms a continuous picture from the “as‐molded” surface to the core. With the exception of the first layer which is always featureless, the observed morphology is mostly spherulitic. Starting in the second layer, the spherulites decrease steadily in size until they reach a minimum somewhere near the middle of the third layer. After passing this point, they increase in size—rather rapidly—as the boundary between layer 3 and the core is approached. In samples prepared at the shorter fill times, the spherulites continue to decrease in size until they are replaced by the mixed matted straw–flat plate texture. The overall morphological features of this surface zone are explained by using an extension of a model for the crystallization of a quiescent polymer melt. In this model, growth originates from heterogeneous nuclei whose density varies throughout the sample as a function of both a temperature gradient and the induction time. Interpretation of anomalies in the fine structure of the individual layers indicates that shear is influencing the crystalline mo

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110512

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractInjection‐molded specimens of polypropylene were examined by x‐ray diffraction for texture and orientation patterns as a function of the distance from the surface and of molding conditions. At least three distinct layers in the surface region whose texture patterns differ and an isotropic core of the moldings have been identified. These layers show preferred orientations; the axes of symmetry of the oriented textures lie in a plane passing through the direction of flow and perpendicular to the mold surface, but are inclined to the mold surface at a small angle. Some of these layers may be missing in conditions of either very high or very low shear during the injection‐molding flow. A tentative explanation of the formation of the texture patterns is pro

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110513

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractDetermination of important thermodynamic and physical properties of polymers has often been frustrated by the tendency of these materials to reorganize when heated. A novel technique has been developed which permits a more careful examination of the relationships existing between melting and morphology of single crystals. This has lead to the observation that high molecular weight polymers possess much narrower melting ranges than had been previously reported. By using this technique it has been possible to identify distinct transition temperatures for {100} and {110} fold sectors. DTA and DSC data have been previously reported for dried down single crystals. The applicability of this data to single crystals as they exist in suspension is questioned.

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110514

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractWe have outlined a theory which considers the durability of adhesive joints in the presence of a hostile environment. The approach is basically the Griffith theory modified for the presence of liquids. Two main conditions for spontaneous delamination of a composite appear to be immiscibility of the liquid in the environment with the members of the composite and complete interaction of the liquid (in a surface‐chemical sense) with one or more members of the composite. In the absence of chemisorption and interdiffusion in an A‐B composite, we find that (σfL/σf)2=WABL/WAB, where σfis the critical stress to failure,WABis the work of adhesion, and the superscript L refers to the presence of a liquid phase. When the liquid (L) interacts, in a surface‐chemical sense, with the composite, we haveWAB>WABL, and σfL<σf. To illustrate the main features of the theory, composites are prepared whose interfacial tensions have been modified by the presence of an adsorbed monolayer of a fatty acid. In this instance, the interfacial tensions are changed so thatWAB≈WABLand σfL≈ σf. The composite then becomes more stable under an applied stress in the presence of an environment of high r

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110515

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY

摘要:

AbstractModification of the Griffith theory for the presence of liquids has been shown to explain some facets of the environmental stress cracking of polyethylene. In the absence of intercrystalline links and tie molecules, we find that one important factor is the interfacial tension generated between the spherulite boundary and the liquid environment. Judicious incorporation of silanes into polyethylene appear to reduce the tendency to stress cracking by modifying the interfacial tensions between the environment and the polymer.

ISSN:0098-1273    

DOI:10.1002/pol.1973.180110516

出版商:John Wiley&Sons, Inc.    

年代:1973

数据来源: WILEY