Loss of additives from polymers: A theoretical model

The rate at which an additive is lost from the surface of its solution in a polymer is considered to depend upon three factors—the solubility of the additive, the rate at which it volatilizes from the polymer surface, and its diffusion coefficient within the bulk of the polymer. By adapting the mathematics of heat flow in a solid, the loss of additive from a polymer is mathematically modeled in terms of these three variables for bulk polymer and for film and fiber samples. Two cases are considered—loss of additive by volatilization or dissolution from the polymer surface and loss by precipitation on the surface from a supersaturated solution of the additive. The results are applied to a discussion of the relative importance of the three parameters under various conditions occurring or expected in practical application of additives as oxidation stabilizers for polyethylene and polypropylene.     

Einfluß von Additiven und Verunreinigungen auf Kristallisationsprozesse

Influence of additives and contaminants on crystallisation processes. The presence of additives and contaminants in a crystallising solution can have a considerable influence on the crystallisation properties of the products, such as nucleation and growth kinetics, agglomeration or dispersion of the crystals, and the incorporation of foreign ions into the crystal lattice. These influences are caused by various mechanisms, depending upon the type of additive or contaminant. Tailor-made and multifunctional additives are distinguished. Trace amounts of metal ions can also modify the kinetics of crystallisation. The metal ions can be incorporated to a greater or lesser extent in the crystal, depending upon thermodynamic and kinetic factors.     

Diffusion and annealing in crystallizing polymers

Ultraviolet and fluorescent microscopy of additives in crystallizing polypropylene can be used to study the development of crystallinity within growing spherulites. As the spherulite forms, impurity species including fluorescent additives are initially rejected then subsequently diffuse back in. Simultaneously the interior of the spherulite is increasing in crystallinity and tending to push the impurities back towards the outside.The effect of these processes on the final distribution of impurities within the spherulite is calculated. These results suggest that non-uniformity in additive concentrations will have little impact on the stabilization of the polymer against photo-oxidation.     

The nucleation of microcellular thermoplastic foam with additives: Part I: Theoretical considerations

Microcellular foam is a polymeric foam with bubble sizes of 10 microns or less that is produced by saturating a polymer with gas and then utilizing the thermodynamic instabilities that result when the polymer is heated and the pressure is reduced to nucleate the cells. A model for the nucleation of microcellular foam in amorphous polymers with additives has been developed. The nucleation process depends on the solubility, concentration, and interfacial energy of any additives present. At very low levels, additives in solution act to increase the free volume of the polymer, resulting in homogeneous nucleation within the free volume Well above the solubility limit, heterogeneous nucleation dominates, as it lowers the activation energy for nucleation to levels below that for homogeneous nucleation. In the vicinity of the solubility limit of the additive, these two nucleation mechanisms compete. The polystyrene-zinc stearate system has been chosen for experimental evaluation.     

Nano-adsorbents control surface properties of polyurethane

Additives are minor but critical components that polymers need for processing and applications. However, these additives may also have adverse effects, e.g. for polymeric biomaterials, leaching additives can change surface properties, and may lead to poor biocompatibility. How to use additives yet keep them from detrimental behaviors is a challenging issue. Diffusion barriers may be used to slow down the additive migration but difficult to stop it. In this paper, we introduce the concept of “nano-adsorbents” in polymers. These nano-adsorbents confined the additives within the polymers by thermodynamically interacting with them. While the additives are still present in polymers to provide intended functions, they are thermodynamically constrained from free migration to the surface. Nano sized-fillers were selected due to their high surface to volume ratio. This new usage of nano-fillers for polymers was demonstrated with a biomedical polyurethane and a surface coated nanoclay that thermodynamically attracts the additive in the polyurethane.     

世界塑料添加剂现状和发展

介绍了国内外一些主要和新型塑料添加剂的现状及发展趋势。添加剂功能不仅可以改善聚合物的工艺性能、改善加工条件、提高加工效率,而且可以改进制品性能、提高制品的使用价值、延长制品的使用寿命。并指出塑料添加剂未来的发展趋势将是高效、专用母料、无毒、环境友好及多功能化。     

A novel chemically amplified positive deep UV photoresist with significantly reduced sensitivity to environmental contamination

t-Boc protected Deep-UV transparent polymers with photoacid generators have been widely investigated as potential positive deep-UV resist systems. However, utility of these systems is seriously handicapped by environmental contaminants leading to an insoluble “surface skin” formation. Only with a specially controlled environment or by use of an “overcoat” material is the performance of these systems acceptable. We have investigated a series of t-Boc protected poly(styrene-maleimide) copolymers and poly(hydroxy styrene) polymers with onium-salts. Upon incorporation of a special class of organic additive, the surface effects inherent to these positive deep-UV systems are significantly reduced thereby avoiding any extraneous precaution of protecting the resist surface from a typical manufacturing environment. We evaluated these t-Boc polymer/onium-salt systems with different additives under a varied set of processing conditions. In addition, plausible structure-activity relationship of these additives in controlling the surface effects is presented.     

Ultraviolet stabilizing monomers and polymers. II. Synthesis and polymerization of acrylate and methacrylate derivatives of 2,4-dihydroxybenzophenone

In the addition of stabilizing agents to plastic materials, problems such as incompatibility, migration, volatility, and/or solvent extraction of the additive frequently arise. With a view toward overcoming such problems in the use of ultraviolet absorbing stabilizers, acrylate and methacrylate derivatives containing the 2-hydroxy-4-alkoxybenzophenone moiety have been synthesized. The ultraviolet absorbing monomers were synthesized by reaction of 2, 4-dihydroxybenzophenone with glycidyl acrylate and glycidyl methacrylate. They were homopolymerized and blended with poly(vinyl chloride), poly(vinylidene chloride), polystyrene, and poly(methyl methacrylate). They were also copolymerized with the corresponding monomers. The polymer blends and copolymers were investigated for ultraviolet stability versus corresponding controls. Effective ultraviolet stabilization was observed. Differences in the stability of some blends as compared to corresponding copolymers is thought to be due to incompatibility.     

Modifying and managing the surface properties of polymers

An ongoing challenge in polymer science is the preparation of materials with bespoke surface properties which differ from that of the bulk, for example hydrophobicity, wettability, chemical resistance, adhesion or biocompatibility. We highlight here recent efforts in the design, development and application of (multi)end‐functionalized polymers as additives for the efficient modification of polymer surface properties. Aryl‐ether moieties bearing up to eight functional groups have been used as initiators for the controlled polymerization of both styrene and methyl methacrylate by atom transfer radical polymerization (ATRP) and of lactide by ring opening polymerization (ROP). The resulting polymers have been used as additives to modify the surfaces of the corresponding bulk polymers. Fluorinated polymer surfaces are particularly appealing in terms of their liquid repellence, chemical inertness and low coefficient of friction. When an additive consisting of a low molecular weight polystyrene chain, end‐capped with four C₈F₁₇ groups, is present in a matrix of polystyrene at levels as low as 0.1%, near polytetrafluoroethylene‐like surface properties result. Copyright © 2007 Society of Chemical Industry     

Preparation and photophysical properties of organic fluorescent polymers and their nanoparticles

New classes of stable organic florescent polymer nanoparticles were prepared from the corresponding tetrahydrofuran (THF) solutions, upon slow evaporation of solvent under a mild vacuum. Uniform spherical nanospheres having mean diameter of ? 500–700 nm, showed enhanced fluorescence emission in solution, but it diminished when it is destroyed using an organic base. These end‐capped fluorescent polymers are highly stabilized in the excited states at higher concentration in solution, leads no more intra‐ and intermolecular interactions among the excited molecules, because of the absence of free functional groups. The significant enhancement in fluorescence emission was attributed to the high level of molecular stacking in the fluorescent nanoparticles, when compared with micron‐sized isolated powder sample. In addition, these fluorescent polymers exhibited significant thermal properties, along with better solubility in most of common organic solvents for their future application. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5344–5350, 2006     

Strength and deformation of rigid polymers: structure and topology in amorphous polymers

Glassy polymer is formed because the irregular chain architecture prevents crystallisation. Computer simulations allow Voronoi tessellation of atomic groups (for example monomers) to be carried out and measured along the molecular chain, which reveals significant density fluctuations. A Voronoi polyhedron is constructed for each particle according to a unique mathematical procedure [J Reiner Angew Math 134 (1908) 198]. When measured in terms of Voronoi polyhedra, amorphous structures show wide variations in packing density on the atomic/monomer scale, with a characteristic skewed distribution. The Voronoi method can be applied to all polymers; however, in this paper only uncrosslinked amorphous polymers are considered. Constriction points around a chain segment are defined as a locally specific configuration and arrangement of adjacent chains such that the local density within a sphere of radius approximately equal to two monomer diameters comes close to or below the hypothetical crystalline density. The topological theory of molecular structure developed by Bader defines the concepts of atoms and bonds in terms of the topological properties of the observable charge distribution [Rep Prog Phys 44 (1981) 893]. In polymers the high density regions become an even stronger topological feature, and are referred to as the constriction points.     

Perspectives on additives for polymers. 1. Aspects of stabilization

Since the earliest discovery and subsequent developments in the world of polymers associated problems and increasing applications have resulted in the rapidly expanding field of “additives.” In this context, the term additive is very generalized in that it encompasses many facets associated with ever growing needs. Of the most important are antioxidants (primary and secondary), light stabilizers, processing aids, metal deactivators, flame retardants, biocides, nucleating agents, antistatic compounds, fillers, dyes, pigments (nano, micro, and macro) to name but only a few each serving a particular function and not necessarily all at the same time in the one package. This article presents a general perspective on the type, mode of action, properties, uses, and problems (and circumvention) based on some of the more important key additives. The properties and behavior of many additives in this regard relates very much to the initial incorporation and formulation and in turn is often a major controlling factor in end use performance from a physical, esthetic, structural, mechanical, and chemical point of view. Indeed, with many polymers like PVC, for example, one enters a highly complex world of interactions which can in many cases destroy or even enhance the activity of functional processing additives. Some of these will be highlighted and hopefully the aim being here to enthuse the polymer and additive manufacturers and technologists in the processing laboratories to become more aware of potential issues and problems.     

Studies of heterocyclic polymers: Part 1. The synthesis and structure of macrocyclic polymers

Pyromellitic tetranitrile and 4,4′-diaminodiphenyl ether have been reacted in solution and in the solid state, and the macrocyclic polymer produced by each method of reaction has been shown to be structurally identical. Other macrocyclic polymers have been prepared by the solid state reactions of a number of aromatic diamines and pyromellitic tetranitrile. The diamines were selected to provide variations in the size of the macrocycle and in the level of strain within the ring. Preliminary studies suggest that these variations have an observable effect upon the ease of macrocyclization, but no marked influence upon the thermal stability of the polymers.     

Thermal gelation properties of methyl and hydroxypropyl methylcellulose

Aqueous solutions of methyl and hydroxypropyl methylcellulose are known to gel upon heating. These gels are completely reversible in that they are formed upon heating yet will liquefy upon cooling. The precipitation temperature, gelation temperature, and gel strength of these methylcellulose solutions were determined as a function of molecular weight, degree of methyl and hydroxypropyl substitution, concentration, and presence of additives. The precipitation temperature of these polymer solutions decreases initially with increasing concentration until a critical concentration is reached above which the precipitation temperature is little affected by concentration changes. The incipient gelation temperature decreases linearly with concentration. The strength of these gels is time dependent, increases with increasing molecular weight, decreases with increasing hydroxypropyl substitution, and depends on the nature of additives. Hydrophobe–hydrophobe interaction or micellar interaction is postulated to be the cause of gelation. This thermal gelation property of the polymers is utilized in many end uses including food, pharmaceuticals, ceramics, tobacco, and other industrial applications.     

Crystallisation kinetics and melting studies

Methods for determining the crystallisation characteristics of polymer by differential scanning calorimetry are discussed, particularly in terms of their limitations. Isothermal and non-isothermal crystallisation thermogrphs are analysed to determine crystallisation mechanism and compared with other techniques. The inadequacies of current theories of crystallisation rates are developed. Melting studies on oligomers and polymers are developed in terms of recent theories of melting, and a method suggested for quantifying the quality of crystallinity in polymeric material in terms of the averages of the lamellae thickness.     

Reactive Processing and Polymer

Polymer additives are primarily responsible for the ultimate properties and performance of commodity polymers which are being used increasingly in demanding applications. the physical loss of additives from the polymer substrate is a major limitation to the traditional method of incorporating additives into polymers. the relatively low degree of permanence of additives is undermined further during in-service performance of polymers under aggressive environments. Loss and migration of additives is, therefore, a major concern to the manufacturing industry because of adverse effects on polymer performance and durability as well as the inherent lexicological consequences of migrating additives, especially in medical and food applications. This paper explores the use of reactive processing to achieve the desired degree of permanence and substantivity of polymer additives. This method has been exploited to chemically bind additives to the polymer backbone. By comparison with conventional procedures, reactively processed polymers are superior.     

Characteristics of antiplasticized thermosets: Effects of network architecture and additive chemistry on mechanical fortification

A new class of molecular additives is investigated for epoxy‐based crosslinked polymers. These additives are shown to increase modulus and yield stress in the cured networks. In order to elucidate the mechanisms for reinforcement of epoxy thermosets, the effects of additive chemistry and network architecture are considered. Both model and commercial epoxy networks are studied, thereby probing the effect of molecular weight between crosslinks, M_c, on reinforcement. Additionally, the family of phosphates being studied ranges in molecular weight, solubility parameter and density. These parameters are demonstrated to strongly influence the degree of reinforcement and correlate with the ability of the additive to reduce mobility of the polymer network. Mechanisms of reinforcement are discussed. Polym. Eng. Sci. 44:2125–2133, 2004. © 2004 Society of Plastics Engineers.     

Surface characteristics of polymer/small molecule blends

Inverse gas chromatographic data have been obtained for polystyrene, polycarbonate, and two substituted amines used as additives in the polymers. Surface energies have been determined and evaluations made of acid/base interaction parameters and Flory–Huggins χ values for the surface bounded interphase. It was shown that acid/base considerations are implicated in the miscibility of these polymer/additive systems. Surface energy analyses showed that surface and bulk compositions in blends differed whether or not the blend components were miscible. Composition differences were the result of thermodynamic drives to minimize surface free energy. © 1994 John Wiley & Sons, Inc.     

Fluorescent polyelectrolytes as protein sensors

This review discusses recent advances in protein sensing using fluorescent polyelectrolytes that are mainly water‐soluble conjugated polymers. A quencher‐labeled substrate or fluorophore‐labeled substrate is generally used as a probe. In the presence of an enzyme, the linker between substrate and quencher/fluorophore is cleaved and fluorescence of the polymer is either ‘turned on’ or ‘turned off’. Fluorescence behavior of these conjugated polymers is highly sensitive to conformation of the polymeric chains. Since upon binding with proteins the conformation is perturbed and fluorescence is affected, these polyelectrolytes have been used to study conformational changes in proteins. The conformation‐dependent fluorescence is also a limitation for these sensors in some cases and non‐conjugated polyelectrolytes have been shown to provide an alternative. Copyright © 2006 Society of Chemical Industry     

超吸水聚合物的组成及其制备

超吸水聚合物是一种具有广泛实际用途的功能性聚合物。介绍了其合成研究及应用，从吸水动力学数据研究了定量聚合物水的体积吸收率，并且评述了其在国内未来的发展。