Search

The Smoluchowski coagulation equation derived back in 1916 is usually linked with the diffusivity and size of aggregating particles. It can also be used as a versatile tool for mean-field kinetic analyses. In this paper it is shown to be an efficient tool for studying the relationships between the reactivity of functional groups in monomers and the size distribution of polymer species in step and chain growth polymerizations. The Smoluchowski coagulation equation and its modifications are applied as models of kinetically controlled growth reactions (with irreversible elementary reaction steps). Advantages and limitations of this method of modeling polymerization processes are discussed. [ABSTRACT FROM AUTHOR]

This review summerizes the recent advances in characterization of some special intractable macromolecules in solution by laser light scattering. Since both static and dynamic laser light scattering (LLS) are theoretically well established, we focus the discussion on experimental details, such as the design of a high-temperature LLS spectrometer, the sample clarification, a novel differential refractometer, and some newly developed methods for data analysis which include a combination of static and dynamic LLS leading to molar mass distribution determination and LLS calibration of gel permeation chromatography. [ABSTRACT FROM AUTHOR]

Crystalline polymers generally comprise a variety of phase structures, including the crystalline and noncrystalline components. The noncrystalline component is thought to be in a supercooled state of the molten state of polymers, either in the rubbery or glassy state. The question is whether a somewhat ordered noncrystalline component exists or not, due to the coexistence with the crystalline component. Flory reported in 1949 that the boundary between the crystalline and amorphous regions of most long-chain molecules will not be well-defined as is typical of monomeric systems [1]. Subsequent theoretical analyses, involving several methods, have quantitatively established the existence of an interfacial region that comprises a transition phase from the crystalline to the amorphous phase [2 11]. Over the past few years, a variety of experimental methods have confirmed the expectation of such an interphase [12]. These methods involve broad-line 1H NMR [13 16] high-resolution solid-state 13C NMR [17 31] Raman spectroscopy [32 35], and small-angle X-ray and neutron scattering, among others [36 42]. [ABSTRACT FROM AUTHOR]

Recently a variety of technologies have been proposed for improving surface properties of polymers. Among them is surface grafting of polymers. Although this is a rather new technology, polymer surface grafting offers versatile means for providing existing polymers with new functionalities such as hydrophilicity, adhesion, biocompatibility, conductivity, anti-fogging, anti-fouling, and lubrication. This review article describes various methods of grafting and grafted surface characterizations. Medical and non-medical applications connected with this polymer surface grafting are also presented referring to recent publications. [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]

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]

The performance of standard poly-ethylene terephthalate filaments is in many cases seriously prejudiced by some negative properties of these fibers, such as their nearly complete water repellency, difficult dyeability, tendency to pilling, formation of static, etc. The present paper aimes to recall the methods proposed and realized in order to overcome these shortcomings by modification of the macromolecule. The subject is divided in two groups regarding respectively the modifications for obtaining changes of mechanical properties and shape of the fiber (shrinkage, elasticity, pilling performance, impact resistance, crimping) and of specific properties (dyeing behavior, static load, flame resistance, soiling and soil removal). [ABSTRACT FROM AUTHOR]

Molecular sieves have potential uses as catalysts for vinyl polymerization reactions. They have been widely used as cationic catalysts, and in a limited number of instances in anionic polymerization reactions. Molecular sieves also find uses as polymer modifiers bringing in definite improvements in their properties. [ABSTRACT FROM AUTHOR]

A large number of methacrylates containing various ester groups have been polymerized and copolymerized with radical and anionic initiators, such as organoalkali metal, magnesium and aluminum compounds. These polymerization and copolymerization are reviewed with special reference on their stereospecificity. The polymerizations of α-phenyl, α-alkyl and α-chloroacrylates are also included. [ABSTRACT FROM AUTHOR]

The synthesis of block copolymers, cooligomers or cotelomers performed from radical polymerization and radical telomerization is discussed. In the first part, the two main methods proposed for obtaining block copolymers by radical polymerization are reviewed. The first method concerns the use of multifunctional micro- or macroinitiators that decompose according to two processes or at two different temperatures, allowing the stepwise insertion of different base units. The second method, more recently proposed, tends to control the reactivity of the growing radicals by the use of either additional stable free radicals or organometallic compounds acting as counter radical, allowing reversible termination steps. These methods still in full development and often referred to as "living" processes, allow well defined block copolymers with narrow molecular weight distributions to be produced. The second part of the review deals with methods of preparation by radical telomerization. Besides the traditional process involving the coupling of ω-functional oligomers or telomers and the bistelomerization, the dormant or living telomerization methods are also described. In this last case, the "living" character is achieved by the use of well-chosen transfer agents with specific cleavable bonds leading to reversibility of the termination step. [ABSTRACT FROM AUTHOR]

Metallocenes are very versatile catalysts for the production of polyolefins, polystyrene and copolymers. Some polymers such as syndiotactic polypropene, syndiotactic polystyrene, cycloolefin copolymers, optically active oligomers, and polymethylenecycloalkenes can be produced only by metallocene catalysts. It is possible to tailor the microstructure of polymers by changing the ligand structure of the metallocene. The effect and influence of the ligands can more and more be predicted and understood by molecular modeling and other calculations. It is estimated that by the year 2000 nearly every second new polyolefin plant will run with metallocene systems. A lot of polymer-producing companies try to use mainly supported metallocene catalysts in their running plants, the so-called Dddrop in DD technology; others build plants specially equipped for these new types of catalysts. The copolymerization of olefins together with polar monomers is just beginning and has a great potential. A big step is also being made by metallocene research to understand the mechanism and the nature of the Ziegler-Natta catalysis. [ABSTRACT FROM AUTHOR]

Cationic polymerizations induced by thermally and photochemically latent N-benzyl and N-alkoxy pyridinium salts, respectively, are reviewed. N-Benzyl pyridinium salts with a wide range of substituents of phenyl, benzylic carbon and pyridine moiety act as thermally latent catalysts to initiate the cationic polymerization of various monomers. Their initiation activities were evaluated with the emphasis on the structure-activity relationship. The mechanisms of photoinitiation by direct and indirect sensitization of N-alkoxy pyridinium salts are presented. The indirect action can be based on electron transfer reactions between pyridinium salt and (a) photochemically generated free radicals, (b) photoexcited sensitizer, and (c) electron rich compounds in the photoexcited charge transfer complexes. N-Alkoxy pyridinium salts also participate in ascorbate assisted redox reactions to generate reactive species capable of initiating cationic polymerization. The application of pyridinium salts to the synthesis of block copolymers of monomers polymerizable with different mechanisms are described. [ABSTRACT FROM AUTHOR]

The present review summarizes results obtained in the last few years in this laboratory regarding the concentrated emulsion polymerization method. In this method, concentrated emulsions have been used as precursors for latexes of homopolymers, copolymers and tough polymers. They have also been employed to prepare conductive polymers, composites, composite membranes, microsponge molecular reservoirs and polymer supported quaternary onium salts, polymer supported palladium complexes and quaternary onium salts, polymer supported enzymes or cells. In contrast to the conventional emulsions, concentrated emulsions have a large volume fraction of dispersed phase, greater than 0.74 and as large as 0.99. When the volume fraction of the dispersed phase is sufficiently large, polyhedral cells of the dispersed phase are separated by thin films of continuous phase. Latexes have been prepared by dispersing a hydrophobic monomer(s) in a small amount of water containing a surfactant, or by dispersing a hydrophilic monomer(s) in a small amount of hydrocarbon (decane) containing a surfactant, and polymerizing the system. Composites have been prepared by dispersing an aqueous solution of a hydrophilic monomer(s) in a small amount of a solution of a hydrophobic monomer in a hydrocarbon, or by dispersing a solution of a hydrophobic monomer(s) in a hydrocarbon in a small amount of a solution of a hydrophilic monomer in water; this was followed by polymerization. Conventional emulsions, microemulsions or colloidal dispersions have been sometimes employed. It is important to emphasize that the polymerized system almost maintains the structure of the emulsion precursor employed. [ABSTRACT FROM AUTHOR]

The principle of the novel ultrasonic spectroscopy utilizing a wide-band polymeric transducer and the FFT (fast Fourier transformation) analysis of a single pulse is introduced and its application to various polymeric materials is reviewed. Ultrasonic analysis of mechanical relaxation processes and phase transitions in solid polymers as well as practical non-destructive inspection of defects in composite materials are described. [ABSTRACT FROM AUTHOR]

In this paper, general principles of physical kinetics are used for the description of creep, relaxation of stress and Young's modulus, and fracture of a special group of polymers. The rates of change of the mechanical properties as a function of temperature and time, for stressed or strained highly oriented polymers, is described by Arrhenius type equations. The kinetics of the above-mentioned processes is found to be determined by the probability of formation of excited chemical bonds in macromolecules. The statistics of certain modes of the fundamental vibrations of macromolecules influence the kinetics of their formation decisively. If the quantum statistics of fundamental vibrations is taken into account, an Arrhenius type equation adequately describes the changes in the kinetics of deformation and fracture over a wide temperature range. Relaxation transitions in the polymers studied are explained by the substitution of classical statistics by quantum statistics of the fundamental vibrations. [ABSTRACT FROM AUTHOR]

A summary is given of the kinetic theory of flexible macromolecules, represented by bead-spring models of arbitrary connectivity. The formal theory is applicable to polydisperse systems, multicomponent mixtures, dilute or concentrated solutions, and fluids with concentration, temperature, and/or velocity gradients. Formal expressions are given for the momentum-flux (stress) tensor, the mass-flux vector, and the heat-flux vector; these can be combined with stochastic simulations to solve problems in rheology, diffusion, and heat conduction. Care is taken to point out where empiricisms are introduced, so that these can be modified or eliminated in the future. Other topics included are: the equation of change for angular momentum, the elastic terms in the equation of change for energy, the effect of velocity gradients on thermal conduction, the uniqueness of the molecular expression for the stress tensor, the relation between the mass flux and the stress tensor, thermal diffusion, and the Onsager receiprocal relations. [ABSTRACT FROM AUTHOR]