摘要:

Polyesters are currently synthesized by a step-growth mechanism from a mixture of a diol and a diacid (or a diacid derivative), or from a hydroxy-acid when available. Ring-opening polymerization (ROP) of lactones and related compounds is an alternative method for the synthesis of aliphatic polyesters. Comparison of these two mechanisms is clearly in favor of the polyaddition process. The drawbacks of polycondensation are well known:high temperatures and long reaction times are required to produce high-molecular-weight chains. Even though conversion of the hydroxyl and acid group is close to completion, any departure from the reaction stoichiometry has a very detrimental effect on the chain length.

ISSN:1532-1797    

DOI:10.1080/15321799508014594

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An increase in the operation temperature of polymeric materials that also possess high mechanical strength at that temperature is undoubtedly one of the most important problems of modern polymer science. This prob-lem can be solved only on the basis of a thorough investigation of the heat resistance of these polymers. Meanwhile, one must answer with clarity the question “What is the best criterion of heat resistance in polymers?” Also, the polymeric structure that leads to the ultimate in heat resistance has notbeen determined. For instance, the loss of weight (ΔM) of the diglycidyl ether of bis-phenol A (DGEBA) cured with iso-methyltetrahydrophthalic anhydride (iso-MTHPA) after thermal oxidative destruction in air at 533°K for 100 hours has been determined experimentally to equal 2.8% w. However, DGEBA cured with the complex of copper salicylate with triethylenetetramine [Cu(trien)(HOC6H4COO)2] has AM = 3.5% w after thermal oxidative destruction under the same conditions [1]. Comparison of these data seems to lead to the conclusion that the epoxy-anhydride polymer is more heat resistant than the epoxy-chelate polymer. However, a similar investigation of these polymers at 573°K showed that after thermal oxidative destruction for 10 hours, DGEBA cured with iso-MTHPA has ΔM = 5.0% w while the copper-containing polymer has AM one-half of this value [1]. Thus it is obvious that an answer to the question about the more heat-resistant polymer is dependent on the temperature of the poly-mer treatment.

ISSN:1532-1797    

DOI:10.1080/15321799508014595

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

World production of plastics has increased from 1 × lo6 tons to 1000 × lo6 tons over the last half-century. The current concern regarding the disposal of industrial and postconsumer waste in diminishing landfill sites and the general impact of waste on the environment have drawn attention to the need to develop effective reclamation and recycling policies. The high visibility of waste products arising from plastics packaging, which accounts for about 30% of total plastics consumption, has contributed to the percep-tion of plastics as a major environmental problem [1].

ISSN:1532-1797    

DOI:10.1080/15321799508014596

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Polymer-analogous reactions represent deliberate changes of functional groups that are carried in macromolecular chains with the general objective of maintaining the polymerization degree of the original macromolecules. In comparison with low-molecular-mass analogs, the reactivity of the func-tional groups in macromolecules depends on the diffusional mobility of the reactants, intermediates, and products in the reaction mixture and steric hindrance to the approach of reagents to functional groups. A lower or enhanced reaction rate in polymer systems is a consequence of the primary, secondary, and tertiary structure of the polymer chains. For chemical modi-fication of macromolecules, different types of reactions can be used. From the structure of the basic unit of poly(2,6-dimethyl-1, Cphenylene oxide)(PPO)

ISSN:1532-1797    

DOI:10.1080/15321799508014597

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Polyethyleneterephthalate (PET) is a versatile engineering plastic with excellent thermal and chemical resistance and mechanical performance. It is extensively used as fibers for apparel, films for packaging, in bottles for beverages, and also in engineering components. Because of the high melting point (ca. 255°C) and glass transition temperature (ca. 7O°C), PET retains its good mechanical properties at temperatures up to 175°C. It is a semi-crystalline polymer composed of crystalline and amorphous regions. A great variety of microstructures can be developed in PET by changing the crystallization conditions. The crystallite size and shape, volume fraction, orientation, and perfection can be varied through control of crystallization process. Study of the crystallization process and the microstructure devel-opment is intriguing and provides deeper insight into the effect of process parameters on the structure development and ultimately the properties of the end product.

ISSN:1532-1797    

DOI:10.1080/15321799508014598

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:1532-1797    

DOI:10.1080/15321799508014593

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor