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This article reviews the various theories of polymer crystallization which have been proposed over the last thirty years. Their background in thermodynamics and crystal growth theories of simple substances is laid out in some detail. This provides the basis for a discussion of the application of surface nucleation and surface roughening concepts to polymer crystallization. The widely used nucleation model of Lauritzen and Hoffman is examined in depth with emphasis on its consistency with experimental evidence and including its recent modifications and extensions. Alternative approaches are also analyzed, in particular Point's ‘multipath’ model and the ‘roughness/pinning’ model by Sadler and Gilmer, but also ‘molecular nucleation’ and ‘chain sliding’. The aim of this article is to lead to a better understanding of the basic hypotheses of the various models and to give guidance to the theorist in improving the models as well as to the experimentalist in interpreting his/her data. It will hopefully make the subject more accessible and stimulate discussion and further research directed at resolving the controversial issues. [ABSTRACT FROM AUTHOR]

Some aspects of the polymorphic behavior of polymers, with particular reference to the structural organization at the molecular level are reviewed. After a temptative structure-based classification of different kinds of polymorphism, a description of possible crystallization and interconversion conditions is presented. The influence on the polymorphic behavior of comonomeric units and of a second polymeric component in miscible blends is described for some polymer systems. It is also shown that other characterization techniques, besides diffraction techniques, can be useful in the study of polymorphism in polymers. Finally, some effects of polymorphism on the properties of polymeric materials are discussed. [ABSTRACT FROM AUTHOR]

Polymer molecules respond to the application of stress by disentanglement, chain orientation and bond rupture. Being the last step in this series of events, the efficiency of flow-induced mechanochemical degradation depends markedly on the details of the pervading flow field. From the results of fluid mechanics, it is usual to distinguish degradation in simple shear flow from degradation in elongational flow. Polymer dynamics require a further subdivision between transient elongational flow, characterized by a short residence time (less than the chain relaxation time τ1) in the high strain rate region, from quasi-steady-state elongational flow which possesses a stagnation point and a long residence time . This chapter reviews the main factors which influence the degradation kinetics in transient elongational flow, exemplified by flow through a narrow contraction and ultrasonic irradiation. The experimental results reveal a fundamental difference in the kinetics of chain scission in transient and stagnant conditions. Differences in the characteristic residence time prevalent in each type of flow permits one to probe the different stages of the chain unravelling process up to the point of bond rupture. It is suggested that the intricate degradation behavior observed in transient elongational flow stems from the compact nature of the weakly deformed molecular coil. This favors intramolecular interactions during the dynamics of deformation. [ABSTRACT FROM AUTHOR]

Tethered polymer chains refers to macromolecular chains that are attached into microstructures by their ends. Highly branched polymers, polymer micelles and end-grafted chains on surfaces are a few examples. This review brings out the common features of these seemingly widely disparate microstructures. Tethering can be reversible or irreversible and is frequently sufficiently dense that the chains are crowded. Densely tethered chains stretch to alleviate the interactions caused by crowding. They thus exhibit deformed configurations at equilibrium. These effects of tethering on the structure of the polymer chains are reflected in distinctive behavior and properties of microstructures containing tethered chains. The topics we cover are: structure, in which the relationships of the free energy and characteristic dimensions of tethered chains to chain contour length, grafting density and geometry are developed; aggregation, by which we mean equilibrium microstructures formed by self-assembly such as micelles, adsorbed layers or ordered phases in block copolymers, where we can illustrate how the structural concepts come into play; phase behavior, which occurs, for example, in structures having more than one tethered component, such as mixed micelles; block copolymer melts, which are important systems which manifest the characteristics of tethered chains in both the aggregation and phase behavior, interactions, in which the behavior of two tethered layers in contact is explored, a subject of importance to applications involving colloidal stability; and kinetics and dynamics, where the chain deformation arising from tethering affects the kinetics of assembly and exchange processes and the entanglement behavior. [ABSTRACT FROM AUTHOR]

This article describes organic polymer hybrids with silica gels formed by means of the sol-gel method. The incorporation of organic polymers at the level of molecular dispersion into a metal oxide matrix was accomplished by the hydrolysis-condensation of tetraalkoxysilane (orthosilicate ester) in the presence of the appropriate organic polymer. Especially, organic polymers consisting of amide groups such as poly(2-methyl-2-oxazoline) were found to form molecular hybrids with silica gel through strong hydrogen bonding. The obtained organic-inorganic polymer hybrids were homogeneous and transparent glassy composite materials in a wide range of the contents of organic polymers. The homogeneity of the hybrid may be due to the molecular dispersion of organic polymer in the silica gel matrix, which is ascribed to the formation of hydrogen bonds between the polymer amide group and silanol group of the silica gel. The occurrence of this hydrogen bond was actually supported by FT-IR spectra of hybrids. Organic-inorganic polymer hybrids having chemical bonds at the ends of organic polymer segments were also prepared strating from polyoxazoline silane coupling agents. The water-adsorption properties of these hybrids showed the hydrophilic or amphiphilic modification of the silica gel. Another interesting material is porous silica gel with controlled-size pores which is prepared by the pyrolysis of the hybrid at a temperature far below the fusing point of silica gel. [ABSTRACT FROM AUTHOR]

In the course of attempts to develop conditions for the living polymerization of β-pinene (β-PIN) we discovered that the conventional “H2O”/EtAlCl2 system produces poly(β-PIN)s of heretofore unattained high molecular weights (at least up to ∼40,000) and that the molecular weight can be controlled by the polymerization temperature in the −23 to −100°C range. The log $$\bar M•n$$ versus 1/T plot is linear and yields ΔHDP=−0.83 kcal/mol. The repeat unit of the high molecular weight polymer is which reflects isomerization polymerization. The Tg of poly(β-PIN) is 65°C by DSC. Melt drawn fibers are amorphous by X-ray analysis. [ABSTRACT FROM AUTHOR]