Chemical modification of polymers. XII. Control of triboelectric charging properties of polymers by chemical modification

Chemical modification of polymers leads to changes in triboelectric charging properties which are proportional to the degree of conversion. This contrasts to physical mixtures in which the surface energy causes one component to dominate the surface, hence the charging properties. Relationships between molecular structure and triboelectric charging have been deduced from the results. Thus the direction of change of triboelectric charging on chemical modification is governed by the nature of the reaction and the magnitude of the change is governed by the extent of reaction.     

Modification of epoxy-anhydride polymers with aluminum oxide

The effect of the heat treatment of aluminum hydroxide on the heat resistance and mechanical strength of composite materials based on ED-20 epoxy oligomer cured with isomethyltetrahydrophthalic anhydride was studied.     

Chromatography of functional polymers: A new approach to the characterization of reactive polymers obtained by chemical modification

High-performance liquid chromatography (HPLC) has been used to complement size-exclusion (gel permeation) chromatography (SEC) for the characterization of functional polymers. Whereas SEC is unable to detect compositional changes, HPLC in an appropriate interacting medium can provide detailed information on compositional changes occurring during chemical modification of a polymer. The method has been demonstrated using a normal-phase column consisting of porous monodisperse 10 μm poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate) beads that have a homogeneous coverage of aliphatic hydroxyl groups for the analysis of brominated poly(isobutylene-co-4-methylstyrene). Differences of well below 1 mol % of bromomethylstyrene units are easily detected and quantified. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1173–1180, 1997     

Confined crystallization of polymers within anodic aluminum oxide templates

In this article, a review of recent literature on confined crystallization within nanoporous anodic aluminum oxide (AAO) templates is presented. For almost all infiltrated polymeric materials, crystal orientation within the nanopores is a function of pore diameter. T_c and T_m usually decrease and are a function of pore size. When no pore interconnection remains, the crystallization occur at large supercoolings in heterogeneity free environments. Hence, the nucleation mechanism changes from heterogeneous to surface or homogeneous nucleation. The crystallization kinetics of infiltrated polymers should be close to first order, since in confined environments nucleation is the determining step of the overall crystallization and Avrami indexes (n) of ～1 (or lower in some cases) should be obtained. Examples are provided where these conditions have been met and first order kinetics (n = 1) were measured as opposed to higher orders (n = 3?4) for the same polymer in the bulk. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1179–1194     

Phase transfer catalysis in the chemical modification of polymers. Part II

A soluble partly chloromethylated polystyrene has been successfully modified by compounds containing labile hydrogen and by NaCN or NaSCN, under PTC conditions.     

Liquid-crystalline side chain polymers by chemical modification of poly(chloroalkylvinylether)s

The synthesis of polyalkylvinylethers with pendant 4-cyano-4'-oxybiphenyl groups gives thermotropic liquid-crystalline polymers. The new method developed here consists of the living cationic polymerization of chloroalkylvinylethers and the subsequent modification of the polymer by the mesogenic groups. The liquid-crystalline polymers have a controlled degree of polymerisation and narrow molecular weight distributions. The influence on the mesomorphic properties of various parameters such as the degree of polymerization, the spacer length and the proportion of the mesogenic side chain content has been investigated. Binary phase diagrams with low molar mass analogues are also reported and the properties of both neat materials and binary mixtures are compared.     

Lactic acid-based functionalized polymers via copolymerization and chemical modification

Poly(lactic acid) polymers (PLA) are presently the most attractive compounds in the field of artificial degradable and biodegradable polymers. In order to enlarge the family, and thus the range of accessible properties, stereocopolymers and copolymers with various co-monomers have been synthesized. However, very few are functionalized, i.e. include functional groups attached to the main chains or as part of the side chains. In the search for degradable PLA-type polymers bearing functional groups to serve as intermediates for further chemical modifications, we are exploring two different routes. The first one is copolymerization with a protected hydroxyl-bearing lactide-type monomer, namely 3-(1,2,3,4-tetraoxobutyldiisopropylidene)dioxane-2,5-dione. The second route consists of the formation of a carbanionic site in the alpha-position to intrachain carbonyl functions by using lithium N,N-diisopropylamide followed by the coupling of electrophiles. Recent advances in this search are presented using several examples. In particular, it is shown that OH-functionalized PLA-type macromolecules can be made fluorescent by chemical coupling. It is also shown that substituents can be attached to PLA-type macromolecules in solution or to the surface of PLA-based devices selectively.     

Control of the anodic aluminum oxide barrier layer opening process by wet chemical etching

In this work, it has been shown that, through a highly controlled process, the chemical etching of the anodic aluminum oxide membrane barrier layer can be performed in such a way as to achieve nanometer-scale control of the pore opening. As the barrier layer is etched away, subtle differences revealed through AFM phase imaging in the alumina composition in the barrier layer give rise to a unique pattern of hexagonal walls surrounding each of the barrier layer domes. These nanostructures observed in both topography and phase images can be understood as differences in the oxalate anion contaminated alumina versus pure alumina. This information bears significant implication for catalysis, template synthesis, and chemical sensing applications. From the pore opening etching studies, the etching rate of the barrier layer (1.3 nm/min) is higher than that of the inner cell wall (0.93 nm/min), both of which are higher than the etching rate of pure alumina layer (0.5-0.17 nm/min). The established etching rates together with the etching temperature allow one to control the pore diameter systematically from 10 to 95 nm.     

Macromolecule-metal complex interactions as precursors for the catalytic chemical modification of polymers

Chemical modification of polymers via catalysis has recently emerged as an area of increasing importance in macromolecular chemistry. It provides an efficient synthetic route for the production of novel polymers with desirable physical properties and functional groups which are often inaccessible by conventional polymerization techniques. Diene-based polymers and copolymers are ideal for chemical modification because of the technological importance associated with the parent materials and the reactivities of the double bonds in the polymer chain. In employing organometallic catalysts for such modifications, it has been found that the ligand environment of the catalyst as well as the functionality of the polymer has a profound effect on the nature of the macromolecule-metal complex interaction and the resulting polymer modification. The importance of the macromolecule metal complex interactions and the design of appropriate catalyst systems is illustrated for the hydrogenation, hydroformylation/hydroxymethylation and hydrosilylation of a number of polymers.     

Study on chemical speciation in aluminum chloride solution by ESI-Q-MS

AlCl(3) solution was analyzed at concentrations from 0.02 to 100 mM using an electrospray ionization quadrupole mass spectrometer (ESI-Q-MS), and the dissolution state of aluminum ions is discussed. Results obtained using ESI-Q-MS were consistent with those obtained using (27)Al nuclear magnetic resonance ((27)Al NMR). Aluminum species existed mainly as positively charged monomeric aluminum hydroxide coordinated with several water molecules in solution. The complexation of chloride ions by aluminum ions differed between the positive and negative ion modes. Chemical reactions that partially modified chemical forms of species through ESI-Q-MS measurement were also observed. In the same aluminum chloride solution, using ESI-TOF-MS and ESI-Q-MS/MS studies, the disagreement of the reports is discussed. It is concluded that ESI-TOF-MS might show also the gas-phase reaction in the mass spectrometer but the dissolution state of aluminum species can be shown by ESI-Q-MS.     

Improvement of quality of epoxide materials by modification with ethylsilicates

The influence of ethylsilicate additive on the properties of epoxide compositions and cured films on their basis was investigated. It was shown that the introduction of ES-32 ethylsilicate to epoxide composition formulation reduces their viscosity and favors the significant improvement of the physicomechanical properties of cured polymers.     

Challenges in polypropylene by chemical modification

Radical reactions of i-PP are a well known technical process for the chemical degradation to increase the flowability of the i-PP melt. By decreasing the temperature and increasing the life time of the PP-radicals, a process to synthesize long chain branched i-PP, was developed. The long chain branched-i-PP allows to introduce the i-PP in processing technologies as blow moulding film technology or foaming technology. The mechanism will be discussed. The radical grafting of Polypropylene (PP) becomes more important for the developing of PP-alloys with extended properties. Methylmethacrylate and styrene were polymerized and grafted in PP at low temperatures in solid state. Grafting and polymerizing in solid state means solving the monomers in the PP-powder directly from the reactor without contacting with oxygen (air). The reaction is started by the thermal decomposition of a peroxide. The reactivity of the primary radicals from the peroxide and the transfer reactions of the polymer radical of the PMMA or PS influences the amount of the grafted polymer. The solubility of the monomers and the peroxide in the amorphous i-PP-phase was measured. The grafting yield and the dispersity of the second polymer depends on the solubility and dispersity of peroxide and monomers in the PP-powder particles.     

Physical and chemical properties of nano-sized aluminum hydroxide and oxide particles obtained by the electrochemical method

The structure and properties of nanoparticles of aluminum hydroxides and oxides obtained by electrochemical, chemical, and combined methods were studied by transmission electron microscopy, X-ray diffraction, thermal analysis, and atomic emission spectroscopy. The influence of synthesis conditions on the structure and morphology of nanoparticles was studied. It was shown that the effect of an electrochemical field allows monophasic systems to be obtained with a narrower range of particle sizes than in the case of chemical deposition.     

Study of annihilation processes of positrons in polystyrene-related polymers

The positrons injected into a polymer annihilate with electrons through several kinds of processes influenced by environmental conditions. The AMOC is an appropriate method to investigate the influences of functional groups in polymer on positron and positronium annihilation process. The experiments were performed for polystyrene-related materials. The results showed that the S-parameters relating to ortho-positronium were higher than those relating to free annihilation in all samples and the annihilation process was affected by functional group.     

Tailored polymers by free radical processes

This paper describes a versatile and effective method for the control of free radical polymerization and its use in the preparation of narrow polydispersity polymers of various architectures. Living character is conferred to conventional free radical polymerization by the addition of a thiocarbonylthio compound of general structure S=C(Z)SR, for example, S=C(Ph)SC(CH₃)₂Ph. The mechanism involves Reversible Addition-Fragmentation chain Transfer and, for convenience of referral, we have designated it the RAFT polymerization. The process is compatible with a very wide range of monomers including functional monomers such as acrylic acid, hydroxyethyl methacrylate, and dimethylaminoethyl methacrylate. Examples of narrow polydispersity (≤1.2) homopolymers, copolymers, gradient copolymers, end-functional polymers, star polymers, A-B diblock and A-B-A triblock copolymers are presented.     

Thermosets obtained by chemical modification of epichlorohydrin-ethylene oxide copolymer and their crosslinking through double bonds

The epichlorohydrin-ethyleneoxide copolymer is modified with 10-undecenoate and 4-pentenoate moieties in order to obtain thermosets by cross-linking through their double bonds. These polymers are then characterized using NMR, IR, chlorine elemental analyses, X-ray powder diffraction, DSC, TGA, and viscosimetric measurements. Because the thermal crosslinking reaction overlaps in all cases with degradation processes, a free radical source (dicumyl peroxide) is necessary. The Arrhenius kinetic parameters are determined by DSC, using Ozawa and Kissinger expressions. Finally, the quality of cured materials is tested by TGA. © 1995 John Wiley & Sons, Inc.     

Surface modification of polymers by photoinitiated graft polymerization

Two methods for modification of polymer surfaces by photoinitiated grafting have been developed and applied to films and fibers of synthetic polymers, e.g. polyethylene and polypropylene with acrylic monomers. In the batch process the substrate is enclosed in a cell containing initiator and monomer vapor. UV light through a quartz window initiates the grafting reaction by exciting the initiator (e.g. benzophenone). The grafting reaction is slow (1 to 3 min) due to the inefficient transfer of initiator and monomer through vapor phase. In the continuous process the substrate is presoaked in a solution of initiator and monomer and then drawn into a reactor “on line” where the substrate is irradiated by UV light through a quartz window. The grafting takes place in the very thin surface layer of solution on the substrate. The grafting efficiency is high (70–80% of the polymer formed is grafted) and the process is rapid (5–15 s due to the efficient transfer of initiator and monomer through the liquid phase. The continuous surface grafting process is promising for industrial applications.     

Surface modification of polymers: Physical,chemical, mechanical and biological methods

The principal objectives and methods of surface modification of polymers are reviewed in this paper. The techniques covered include physical, chemical, mechanical and biological methods.     

Study on modification of polymers with the aid of the Schmidt reaction

A study of the Schmidt reaction on several polymers with pendant carboxylic and ketone moieties was carried out. Four polymers were used as starting materials: (1) poly(methyl vinyl ketone), (2) poly(acrylic acid), (3) a copolymer of methyl vinyl ketone and acrylic acid, and (4) a copolymer of styrene and acrylic acid. Most reactions were conducted in an acetic acid medium with the exception of one reaction on poly(acrylic acid) which was done in dioxane and another on copolymer of styrene and acrylic acid done in chloroform. It was found that a Schmidt reaction on poly(acrylic acid) in acetic acid solution will lead to intermolecular reactions of the intermediate with the solvent in preference to reactions with neighboring carboxyl groups on the polymer backbone. A tendency of poly(acrylic acid) to form cyclic anhydrides under these reaction conditions interferes with the yield of acetamide units.