EFFECT OF STRESSES ON POLYMER OXIDATION. QUANTITATIVE ASPECTS. II. PLASTICS

Abstract

In the previous paper of this series we considered corrosive degradation of polydiene elastomers subjected to tensile stresses. In this paper other polymer materials will be considered, in particular, semicrystalline polymers in a highly elastic state, viz., high-density polyethylene (HDPE), low-density polyethylene (LDPE), isotactic polypropylene (PP), polyamides of different chemical structure, PE/PP mixtures, and a few others. Besides, data for polymers in the glassy state will also be presented, although they are of lesser interest in regard of the effect of structural strains on reactivity because of the long relaxation times involved.     

PERFORMANCE AND MECHANISMS OF HINDERED AMINE LIGHT STABILIZERS IN POLYMER PHOTOSTABILIZATION

Abstract

Hindered amine light stabilizers (HALS) have probably been the most studied compounds in the field of polymer stabilization overthe past 15 years [1–16]. Their excellent performance in polyolefins [1–8], poly(vinyl chloride) [9], polystyrene [10], rubbers [11], polyamides [12], and other polymers such as acrylic resins 113–161 has made them an attractive item for research. There have been many advances regarding the understanding of the nature of the stabilization mechanism of these compounds, and there is still a great amount of controversy particularly with regard to the relative importance of some reactive intermediates [1–16]. This continuing research has led to the development of some novel compounds which are more efficient and have better compatibility with the polymer [1–16]. This article reviews the current understanding of the mechanism of action of HALS, its relationship with their performance in polymers, and their interaction with other additives used in a given stabilization system. The excellent performance of HALS in polyolefins has given rise to a great number of publications on their action in these polymers, and therefore most of the discussion will be related to this.     

Novel Methods for Obtaining High Modulus Aliphatic Polyamide Fibers

Super high modulus polyethylene fibers can be created by converting high molecular weight flexible PE chains into highly oriented and extended chain conformations. However, unlike polyethylene, aliphatic polyamides have very high cohesive energy and therefore cannot be easily drawn and highly oriented. This review addresses this fundamental problem by analyzing various novel approaches that can be used to suppress hydrogen bonding in these types of polyamides. Plasticization of such polymers with ammonia, iodine, salts, and Lewis acids, as well as dry spinning, wet spinning, and gel spinning, are discussed. Specialized techniques that involve vibrational zone drawing and annealing as well as laser heating zone drawing and annealing are also reviewed. Some of these methods definitely lead to remarkable improvements in initial modulus and other mechanical properties. The development of recombinant spider silk proteins as well progress in spinning these materials is also reported. The advantages and disadvantages of all of these processes are then summarized.     

Synthesis of polyamides from diols and diamines with liberation of H2

The amidation reaction based on catalytic coupling of alcohols with amines previously reported by us, using the pincer complexes 1 and 2 as catalysts, was applied to the generation of polyamides from nonactivated diols and diamines. A range of polymers was prepared, with M_n up to 26.9 kDa. Unlike the traditional syntheses of polyamides based on carboxylic acid derivatives, which require the use of toxic reagents and generate stoichiometric amounts of waste, this process generates only molecular hydrogen as byproduct. Both aromatic and aliphatic diols and diamines were used. Gel permeation chromatography measurements of the dimethylformamide‐soluble polymers and thermal studies of the polyamides were performed. Matrix assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) spectra are also reported. Thermogravimetric analyses studies indicate that the aromatic polyamides (with the exception of the pyridine‐based polyamide) are more thermally stable than the aliphatic ones. This general, environmentally benign method for the synthesis of polyamides is homogeneously catalyzed under neutral conditions by dearomatized ruthenium‐pincer complexes 1 and 2 and proceeds in 1,4‐dioxane under an inert atmosphere. Conditions for polyamidation in the absence of solvent are also reported, using the pincer complex 2 as catalyst. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Modification of Nylons via Graft Copolymerization

Abstract

Polyamides or nylons are linear thermoplastic polymers with recurring amide groups as integral parts of the polymer chain. Polyamides or nylon fibers have been defined by the U.S. Federal Trade Commission as “a manufactured fiber in which the fiber forming substances are any long chain synthetic polyamides having amide groups (— CONH —) as an integral part of the polymer chain.”     

Polycondensation design of tailored high performance polymers

The ways of the preparing of high performance polymers (HPP) having tailored properties are considered. Common two and one step methods of such polymers synthesis are compared. Some peculiarities of one step polycyclization including the catalytic processes are discussed. Matrix polycondensation leading to the formation of HPP and their blends is analysed. The synthesis of some functional polymers (polyamides and polyamides) having quinuclidine moieties is described.     

Nachhaltige Bausteine für die Kunststoff‐Herstellung

Plant oils are currently the principle resource for the production of bio‐based, high performance polymers, such as polyamides. This process is facilitated by giant strides in chemical catalysis and biotechnology, which allows conversion of vegetable oils in “drop‐in” chemical building blocks. These bio‐based polymer building blocks have equivalent chemical and physical properties as well as similar cost structures compared to conventional petrochemical synthesis feedstock. This allows integration of bio‐based resources into industrial production processes without significant adaptations in logistics or process configuration. However, only use of synergies between chemical and biotechnological unit operations will in future provide for sustainable and eco‐efficient process designs. To allow sustainable supply of bio‐oils to a growing chemical industry without a significant impact on food production demands development of alternative bio‐oil sourcing strategies. In this respect the development of processes for the production of microbial oils, which have equivalent chemical properties to their plant counterparts is imperative. One leading option is the biotechnological conversion of agricultural and food waste streams into microbial oils by combining enzymatic hydrolysis and fermentative production using oleaginous organisms, such as yeasts.     

ABSORBABLE SURGICAL SUTURES

Abstract

Sutures are sterile’ filaments used to close wounds and are made of either absorbable or nonabsorbable materials. The choice of suture materials for surgery is made mainly on the basis of biocompatibility and mechanical properties. The biological interaction with the tissues is considered from the point of view of the inflammatory reaction caused. An ideal suture is one that does not merely avoid negative reactions but also keeps a sterile environment and stimulates the process of healing. An absorbable suture is one which is degraded in body tissues to soluble products and disappears from the implant site, usually within 2 to 6 months. A nonabsorbable suture is resistant to biodegradation, becomes encapsulated in a fibrous sheath, and remains in the tissue as a foreign body unless it is surgically removed (e.g., skin sutures) or extruded. Sutures may be fabricated as monofilaments or multifilaments. The latter are generally braided but sometimes twisted or spun and may be coated with wax, silicone, or other polymers to decrease capillarity and improve handling properties. Hoffman [1] presented a survey on the medical applications of synthetic and natural fibrous materials made from such polymers as poly-(fluorocarbons), polyamides, polyolefins, polypeptides, and polysaccharides which are both nonbiodegradable or slowly biodegrad-ing and biodegradable fibers. Frazza [2] prepared a review on mechanical properties and sterilization of natural and synthetic absorbable and nonabsorbable suture materials. The present paper is a review on materials that have been in recent times as absorbable sutures     

Polyamides based on diamines and N,N′-dimethyldiamines derived from biphenol

Aromatic-aliphatic polyamides containing a biphenyl mesogen were prepared by both interfacial and solution polymerization reactions. Substitution of the amide nitrogen with methyl groups yielded polymers with significantly different properties than the unsubstituted polyamides. The methyl-substituted polyamides had improved thermal stability, significantly lower meltin temperatures, and greater solubility in common solvents. Copolyamides were also synthesized which contained different flexible spacer units that varied in the number of methylene groups. No evidence for the presence of liquid crystalline phases could be obtained in either the unsubstituted polyamides or polyamides containing N-methylated amide units. © 1994 John Wiley & Sons, Inc.     

High Refractive Index Polymers

Rodlike polymers with repeat units composed of groups with high π-electron density directly on the backbone, such as linearly conjugated double bonds and aromatic heterocyclic rings, exhibit high isotropic refractive indexes and high birefringence values when oriented. Typical polyamide birefringence values for oriented films far exceed 0.5 and several are as high as 0.85; the corresponding parallel and perpendicular indexes for these polymers are in the 2.2-2.4 and 1.5-1.7 range, respectively, depending on the molecular structure and degree of orientation. The isotropic index values may be as high as 1.8-2.0.

In order to make optical devices utilizing these highly birefringent films, it is frequently necessary to bond them to films or glass, which necessitates the use of index-matching, optical-quality bonding agents. We devised two synthetic strategies to obtain polymers that exhibit these properties. In one approach, we synthesized a series of colorless, nonbirefringent, polyacrylates (and methacry-lates) containing halogenated carbazole rings; these results will be reported in a forthcoming paper that is currently being prepared. We have also modified rodlike polyamides by substituting index-enhancing groups directly on the amide nitrogen; the refractive index values of the resulting materials are in the 1.60-1.67 range. The most important finding of the latter research was the realization that rodlike polyamides not only exhibit unusually high birefringence, but also greatly enhanced isotropic refractive indexes, which is directly related to their rodlike conformation.     

Structure of crystals of nylon 6,3 and related polymers: Folding is stabilized by thermodynamic interactions

The n,3 polyamides have the structure: [-(CH₂)n NHCOCH₂ CONH-]×. Due to the stereochemistry of the malonamide unit, these polymers have a unique hydrogen bonding system with two different orientations at 120°: they do not form hydrogen bonded sheets as in conventional polyamides. We have obtained a very well oriented mat from crystals of this polymer which shows up to ten orders of the lamellar spacing. In this paper we analyze the structure of the fold in the crystal surface of nylon 6,3 and in related polyamides, including polyglycine. The thickness of these lamellar crystals is in agreement with the values determined for other polyamides. These results, taken together with some recent findings with other polymers, indicate that the thickness of polymer lamellar crystals may be thermodynamically controlled. An outline of this hypothesis is presented.     

A novel generation of photoactive comb‐shaped polyamides for the photoalignment of liquid crystals

A new approach to the synthesis of photoactive comb‐shaped homo‐ and copolyamides containing azobenzene, cinnamate, and coumarin side groups for photoalignment of liquid crystals was elaborated. Photooptical properties and photoorientational ability of these polymers with respect to liquid crystals were studied. It was shown that polarized UV irradiation of all spin‐coated polyamides leads to orientation of liquid crystalline molecules deposited on the polyamide thin films. The synthesized polymers containing cinnamate and coumarin side groups as well as azobenzene‐containing cyano‐ and nitro‐substituted polymers demonstrated good orientation ability in relation to liquid crystals displaying photoinduced planar orientation with high dichroism values within the range of 0.68–0.72. Contrary to the above‐mentioned polyamides, azobenzene‐containing fluorosubstituted polymers induced a homeotropic orientation of liquid crystals. It was shown that the synthesized photoactive polyamides can be considered as promising photoalignment materials for application in display technology, photonics, and other “smart” optical devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4031–4041     

新型可溶性聚芳酰胺及其共聚物的合成与性能研究

采用新型二胺 1,2 二氢 2 (4 氨基苯基 ) 4 [4 (4 氨基苯氧基 ) 苯基 ] 二氮杂萘 1 酮与对苯二甲酸、间苯二甲酸、萘二酸进行均聚或共聚 ,所得聚芳酰胺的Tg 均高于 30 0℃ ,且易溶于非质子极性溶剂中 ,聚合物的特性粘数为 1 2 6～ 1 5 1dL g(2 5℃ ,NMP) ,拉伸强度为 6 2～ 89MPa ,断裂伸长率为 5 %～ 9% ,拉伸模量为 2 2～ 2 9GPa ,电阻系数为 10 1 4 ～ 10 1 6     

Advances and approaches for chemical recycling of plastic waste

The global production and consumption of plastics has increased at an alarming rate over the last few decades. The accumulation of pervasive and persistent waste plastic has concomitantly increased in landfills and the environment. The societal, ecological, and economic problems of plastic waste/pollution demand immediate and decisive action. In 2015, only 9% of plastic waste was successfully recycled in the United States. The major current recycling processes focus on the mechanical recycling of plastic waste; however, even this process is limited by the sorting/pretreatment of plastic waste and degradation of plastics during the process. An alternative to mechanical processes is chemical recycling of plastic waste. Efficient chemical recycling would allow for the production of feedstocks for various uses including fuels and chemical feedstocks to replace petrochemicals. This review focuses on the most recent advances for the chemical recycling of three major polymers found in plastic waste: PET, PE, and PP. Commercial processes for recycling hydrolysable polymers like polyesters or polyamides, polyolefins, or mixed waste streams are also discussed.     

Preparation and Properties of Novel Aromatic Polyamides from Diamines Containing 4,5-Imidazolediyl Structure

Novel aromatic polyamides were prepared from aromatic diamine containing 4,5-imidazolediyl unit, either by low temperature solution polycondensation or by direct polycondensation. Used diamines were 4,5-bis(4-aminophenyl)-2-phenylimidazole 1, 4,5-bis[4-(4-aminophenyl)]-2-(4-methylphenyl)imidazole 2 and 4,5-bis[4-(4-aminophenoxy)phenyl]-2-phenylimidazole 3. The obtained aromatic polyamides were produced with moderate to high inherent viscosity and soluble in polar aprotic solvents such as N,N-dimethylacetamide (DMAc), 1-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Thermogravimetric analysis showed those polymers were stable up to 422°C in nitrogen atmosphere. The glass transition temperature (T _g)s of the polymers derived from diamine 3 were in the range between 243 and 275°C, and these values were approximately 120–160°C lower than those analogue polyamide I series containing no phenoxy units. The properties of polyamide I series are also compared with those of analogue polymers that order of aromatic nuclei and amide linkage is reversible.     

NEW DEVELOPMENTS IN THE DEGRADATION,STABILIZATION, AND SENSITIZATION OF POLY(METHYL METHACRYLATE)

Abstract

Physical and chemical processes, combined under the general term aging, begin immediately after formation of a polymer. Oxygen and other components of the environment -ozone, water, etc.-are involved. Aging is accelerated by a rise in temperature, light, strong ionizing radiations, and mechanical stresses, which are especially rapid under processing conditions for thermoplastic polymers. Poly(methy1 methacrylate) (PMMA) is of particular interest, since at least at temperatures where thermal degradation is important, photolysis occurs by end-group initiation and is accompanied by extensive depolymerization. This polymer has also been photodegraded in air at room temperature by radiation from a low-pressure mercury lamp, and a quantum yield for random chain scission has been determined. Owing to the importance of these points, it is believed that a review of studies of degradation, stabilization, and sensitization of PMMA up to the present date will supply information on the most general problems of behavior of polymeric items during their service lives.     

Phenoxasilin-containing polyamides and polyesters

Silicon-containing polyamides and polyesters of a new type have been synthesized. They contain phenoxasilin rings with double-stranded structure. The polymers were synthesized by the interfacial polycondensation of 2,8-dichloroformyl-10,10-diphenylphenoxasilin with diamines and bisphenols, and were obtained in nearly quantitative yields. Their reduced viscosities were in the range of 0.53–1.47 dl g^?1 m dimethylformamide (DMF), m-cresol or chloroform. Some of the polyamides were soluble in polar aprotic solvents such as DMF and N-methyl-2-pyrrolidone (NMP) and the polyesters had good solubility in chloroform, phenol-sym tetrachloroethane (60:40 by wt %) and acidic solvents (m-cresol and nitrobenzene). The polymers hardly dissolved in cone. H₂SO₄ and some of them coloured in it. Only the polyester having sulphide bonds was soluble in benzene in addition to the above organic solvents. These polymers hardly degraded below 400° except for the polyamides derived from aliphatic diamines. The polymers from aliphatic diamines melted at 290–325°; the other polyamides and the polyesters decomposed without melting.     

Quantification of E. coli adhesion to polyamides and polystyrene with atomic force microscopy

Atomic force microscopy (AFM) was used to measure adhesion forces between E. coli bacteria and surfaces consisting of a series of polyamides and polystyrene, materials that are prominent in carpeting, upholstery, and other indoor surfaces. Bioparticle adhesion to such surfaces in air is poorly understood, yet these interactions are thought to play a key role in their accumulation and release as indoor air pollutants. The polymers employed were polyamide 6 (PA6), polyamide 6,6 (PA66), polyamide 12 (PA12) and polystyrene (PS). We report the interaction forces between immobilized E. coli and AFM tips coated with each polymer. The adhesion forces for the tip-bacterial interactions were in the range between 2.9 and 6.7 nN, which is of the same magnitude as the polymer-polymer interactions for the same series of polymers. Polystyrene had stronger adhesion with E. coli than any of the three polyamides, by an average factor of 1.4. The work of adhesion and Hamaker constants of the probe-surface interactions were calculated using a square-pyramid flat-surface model developed previously. A drag-force analysis suggests that model spheres with the same adhesion force as E. coli-poly(amide) (F approximately 4 nN) will remain adherent under normal foot traffic (F approximately 0.2 nN), but will release during vacuum cleaning (F>or=30 nN).     

Synthesis and properties of new aromatic polyamides with redox‐active 2,4‐dimethoxytriphenylamine moieties

A new triphenylamine‐based diamine monomer, 4,4′‐diamino‐2″,4″‐dimethoxytriphenylamine ( 2 ), was synthesized from readily available reagents and was reacted with various aromatic dicarboxylic acids to produce a series of aromatic polyamides ( 4a–h ) containing the redox‐active 2,4‐dimethoxy‐substituted triphenylamine (dimethoxyTPA) unit. All the resulting polyamides were readily soluble in polar organic solvents and could be solution cast into tough and flexible films. These polymers exhibited good thermal stability with glass transition temperatures of 243–289 °C and softening temperatures of 238–280 °C, 10% weight loss temperatures in excess of 470 °C in nitrogen, and char yields higher than 60% at 800 °C in nitrogen. The redox behaviors of the polymers were examined using cyclic voltammetry (CV). All these polyamides showed two reversible oxidation processes in the first CV scan. The polymers also displayed low ionization potentials as a result of their dimethoxyTPA moieties. In addition, the polymers displayed excellent stability of electrochromic characteristics with coloration change from a colorless neutral state to green and blue‐purple oxidized states. These anodically coloring polyamides showed high green coloration efficiency (CE = 329 cm²/C), high contrast of optical transmittance change (ΔT% = 84% at 829 nm), and long‐term redox reversibility. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3392–3401, 2010     

Interfacial polycondensation. I.

Interfacial polycondensation is a rapid, irreversible polymerization at the interface between water containing one difunctional intermediate and an inert immiscible organic solvent containing a complementary difunctional reactant. It is based on the Schotten-Baumann reaction in which acid chlorides are reacted with compounds containing active hydrogen atoms (—OH, —NH and —SH). A large number of polymers (heat-sensitive and infusible as well as stable and meltable) can be prepared. The method has been applied to the preparation of polyurethanes, polyamides, polyureas, polysulfonamides, and polyphenyl esters. Interfacial polycondensations are run in simple, open laboratory equipment with or without stirring. With suitable agitation granular or powdered polymers with high molecular weight are prepared at room temperature and isolated within a few minutes. The intermediates need not be absolutely pure or in balance nor is a quantitative yield needed in order to obtain high polymer. The major variables in the interfacial polycondensation process are discussed and the laboratory techniques and principles are contrasted with melt polycondensation.