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.     

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.     

Preparation of polymer colloids by chemical reactions in aerosols. I. Poly(p-tertiarybutylstyrene)

A procedure was developed by which polymer colloids can be prepared by polymerizing aerosol droplets of monomers with an initiator in the vapor state. This work describes the formation of poly(p-tertiarybutylstyrene) particles by exposing the corresponding monomer droplets to trifluoromethanesulfonic acid. It was found that the monomer-to-initiator mass ratio is the critical factor in determining the uniformity and morphology of the particles. Under ideal conditions spheres of narrow size distribution are obtained. Otherwise porous particles or soft particles with whiskers may develop. The aerosol was prepared in a falling film generator, but other procedures for producing monomer droplets may be used.     

Selective surface modification of polymers by means of hydrogen and oxygen plasmas

An ESCA investigation has been made of the changes in surface functionalization for a series of polymers effected by means of low-powered inductively coupled rf plasmas excited in hydrogen and oxygen. Reactions in each case are confined to the outermost surfaces of the polymer films and the use of oxygen plasmas leads to extensive oxidative functionalization. Bisphenol-A polycarbonate and polyethylene terephthalate exhibit similar overall reactivities to both oxygen and hydrogen plasmas, while polystyrene is shown to be substantially more reactive than high-density polyethylene to the plasma treatments of interest in this work. Comparison has been made of the effects of straight hydrogen and oxygen plasmas and of sequential hydrogen/oxygen and oxygen/hydrogen plasma treatments.     

Versatile wettability gradients prepared by chemical modification of polymer brushes on polymer foils

A method to create a wettability gradient by variation of the chemical functionality in a polymer brush is presented. A poly(N-methyl-vinylpyridinium) (QP4VP) brush was created on a poly(ethylene-alt-tetrafluoroethylene) (ETFE) foil by the grafting of 4-vinylpyridine and subsequent quaternization. The instability of QP4VP, a strong polyelectrolyte, in alkaline media was exploited to transform it to the neutral poly(vinyl(N-methyl-2-pyridone)) (PVMP), as confirmed with ATR-IR spectroscopy. The slow transformation resulted in a substantial, time-dependent decrease in wettability. A nearly linear gradient in water contact angle (CA) was created by immersion of a QP4VP brush modified sample into a sodium hydroxide solution, resulting in CAs ranging from 10° to 60°. The concurrent decrease in the number of charged functional groups along the gradient was characterized by loading an anionic dye into the polymer brush and measuring the UV transmittance of the sample. The versatility of the wettability gradient was demonstrated by exchanging the counterions of the N-methyl-vinylpyridinium groups, whereby a reversal of gradient direction was reproducibly achieved.     

Electrochemical and chemical modification of poly-o-phenylenediamine redox polymer

Various methods for modification of poly-o-phenylenediamine (PPD) redox polymer with polyaniline (PANI) electron-conducting polymer, ReO ₄ ⁻ and [SiMo₁₂O₄₀]⁴⁻ anions, and palladium clusters are compared. Participation of anions is proven in the processes of PPD synthesis and redox transformations. Formation mechanisms and properties of composites consisting of a redox polymer and electron-conducting polymer and those of two different electron-conducting polymers are compared for example of PPD-PANI and ethylene-dioxythiophene-polybithiophene. A comparison of these systems shows the main change in the potential drop to take place at the metal/polymer interface for a redox polymer and at the polymer/solution interface, for an electron-conducting polymer. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 12, pp. 1409–1416. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22, 2005, Moscow. The article was translated by the authors.     

Synthesis of heterocycles by means of intramolecular radical-addition reactions (Review)

Methods for the synthesis of heterocyclic compounds based on intramolecular reactions with the formation of free radicals with an unpaired electron on the heteroatom as intermediate particles — photochemical cyclization of unsaturated nitrites, mercaptans, and sulfides and the photochemical and catalytic cyclization of unsaturated N-chloroamines — are examined.Paper presented at the conference on the chemistry of heterocyclic compounds in La Grande Motte, France, May, 1973.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 579–593, May, 1975.     

Colour formation in poly(ethylene terephthalate) during melt processing

The discolouration, that occurs in virgin poly(ethylene terephthalate) - PET during melt processing, was studied using various bulk and surface analytical techniques. Proton nuclear magnetic resonance (¹H NMR) was used to study the bulk chemical changes occurring in the polymer during thermo-oxidative degradation. Chemical derivatisation with trifluoroacetic anhydride (TFAA) was used to label the hydroxyl groups introduced on the polymer surface by thermal oxidation.From the surface analysis studies using photoacoustic Fourier transform infrared spectroscopy (PA/FT-IR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and X-ray photoelectron spectroscopy (XPS) it was evident that colour formation starts initially with the hydroxylation of the terephthalic ring. Further, the formation of additional carbonyl functionalities and conjugated chromophoric systems complete the colour formation process.     

Pu(IV) polymer formation

Nearest-neighbor coagulation is proposed as a mechanism for Pu(IV) polymer formation. The distribution of colloids generated by this process is intuitive and easy to understand.     

Study of chemical processes in the modification of epoxide polymers by aluminum oxide

The processes occurring during the modification of epoxy polymers by various polymorphic aluminum oxide modifications (γ-AlO(OH), γ-Al₂O₃, α-Al₂O₃) with epoxy groups were studied by the methods of IR Fourier spectroscopy, chemical analysis, and differential scanning calorimetry (DSC) by an example of a model compound (phenyl glycidyl ether). Two types of interactions were revealed: a direct chemical reaction of phenyl glycidyl ether with the surface hydroxy groups of alyminum oxide, and phenyl glycidyl ether homopolymerization. By processing by graphical method the data of chemical analysis on the diminishing in amount of epoxy groups in the course of the polycondensation reaction the value of activation energy 106–110 kJ mol⁻¹ of the process of phenyl glycidyl ether interaction with aluminum γ-oxide was determined.     

Collapse of a polymer gel induced by complex formation with linear polymers

The thermodynamic theory of swelling and collapse of networks in the solution of linear polymers capable to form complexes with the network chains has been developed. The interaction of components is taken into account in the framework of the Flory-Huggins approximation. It was shown that complex formation in most of the cases leads to the contraction of the network, which can be either continuous or discrete. The influence of the solvent quality for the network and for the complex on the behavior of the network has been studied. If the solvent is poor for complexes the network reswells at high concentration of linear chains in the outer solution. This reswelling is realized as a steep conformation transition.     

Surface modification of polyacrylonitrile-based membranes by chemical reactions to generate phospholipid moieties

A novel approach for the surface modification of poly(acrylonitrile-co-2-hydroxyethyl methacrylate) (PANCHEMA) membranes by introducing phospholipid moieties is presented, which involved the reaction of the hydroxyl groups on the membrane surface with 2-chloro-2-oxo-1,3,2-dioxaphospholane (COP) followed by the ring-opening reaction of COP with trimethylamine. The chemical changes of phospholipid-modified acrylonitrile-based copolymers (PMANCP) membranes were characterized by Fourier transfer infrared spectroscopy and X-ray photoelectron spectroscopy. The surface properties of PMANCP membranes were evaluated by pure water contact angle, protein adsorption, and platelet adhesion measurements. Pure water contact angles measured by the sessile drop method on PMANCP membranes were obviously lower than those measured on the PANCHEMA membranes and decreased with the increase of the content of phospholipid moieties on the membrane surface. It was found that the bovine serum albumin adsorption and platelet adhesion were suppressed significantly with the introduction of phospholipid moieties on the membranes surface. These results demonstrated that the described process was an efficient way to improve the surface biocompatibility for the acrylonitrile-based copolymer membrane.     

Monitoring of the formation of binuclear ruthenium carbonyl complexes during reactions by means of high performance liquid chromatography

Reversed-phase high performance liquid chromatography has been used to monitor the reactions of Ru₃(CO)₁₂ with 1,4-diazabutadiene (DAB) and of Ru₂(CO)₆ (DAB) with DAB. The kinetic data show that the formation of an intermediate in the former reaction is the rate determining step, which is first order in Ru₃(CO)₁₂ as well as in DAB. The reactivity depends strongly on the type of substituent on DAB. Exchange of free and coordinated ligands (isopropyl DAB and tert-butyl DAB) is demonstrated in the reaction of Ru₂(CO)₆ (DAB) with DAB. A reversible reaction is proposed to account for this exchange.     

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     

The formation of a liquid crystalline main chain polymer by means of photopolymerization

A nematic liquid crystal material containing a mercapto group and an olefinic group was synthesized. Photopolymerization of this compound in the liquid crystalline state resulted in a liquid crystalline main chain polymer which showed a relatively high birefringence. Due to scattering, the material had a low transmission at ambient temperatures.     

Mechanical selfsimilarity of polymers during chemical gelation

Network polymers near their gel point exhibit selfsimilar mechanical behavior, as expressed by power law relaxations. The range of selfsimilarity is defined by two limiting length scales. The upper limit is the correlation length, defined by the linear size of the typical cluster, and a lower limit, roughly given by the size of one preformed linear chain, i. e., the mean distance between crosslinks. The correlation length increases with the approach to the gel point, and diverges at the critical extent of reaction, i. e., the gel point where the infinite cluster is formed. Above the gel point, it decreases again with further crosslinking. Dynamic mechanical measurements of the complex modulus at the gel point show a power law in the frequency dependence over the entire frequency range, monitoring selfsimilarity. Swelling effects reduce the fractal dimension of the percolation cluster form 2.5 to 2. It is shown how the power law G() ^1/2, found by experiment, is connected to the structure of the polymeric cluster.Presented at the Physikertagung 1987 in Berlin.     

Effects of temperature and chemical modification on polymer Langmuir films

We previously reported on a rheological study of Langmuir films of poly(tert-butyl methacrylate) (PtBMA), and this work describes further studies on this system. Here, surface pressure-area (Pi-A) isotherms and interfacial shear rheology experiments are performed to better understand the effects of two modifications: varying the temperature between 5 and 40 degrees C and introducing small amounts of carboxylic acid groups by partially hydrolyzing the polymer. Increased temperature produced isotherms with lower plateau surface pressures, Pip, and Pi values shifted to lower areas above Pip. Film properties transition from being primarily viscous to being dominated by elasticity as Pip is crossed for all temperatures studied, even as the value of Pip changes. Increasing the hydrolysis fraction leads to isotherms shifted to lower areas throughout the curve and higher Pip values. Both temperature variation and chemical modification are believed to affect the relative importance of polymer-polymer and polymer-subphase interactions.