Free radical ring-opening polymerization and its use to make biodegradable polymers and functionally terminated oligomers

Since a carbon-oxygen double bond is considerably more stable than a carbon-carbon double bond, it has been possible to use this driving force to promote free radical ring-opening polymerization of unsaturated heterocyclic compounds. This process, for the first time, has permitted the introduction of functional groups, such as esters, amides and carbonates, into the backbone of addition polymers. Hydrolysis of the copolymers with common monomers produced oligomers capped with hydroxyl, amino or carboxylic acid groups. The presence of an ester group in a copolymer, such as in a copolymer of ethylene, render the copolymer biodegradable.     

Molecular mechanisms contributing to the strength and toughness of glassy polymers

In this short summary reference will be made to some recent molecular level studies of strength. Especially the role of chains and of their entanglements in stress transfer and energy dissipation and the influence of rate of loading will be referenced.     

Rational design of amphiphilic polymers to make carbon nanotubes water-dispersible, anti-biofouling, and functionalizable

We report rational design of amphiphilic polymers capable of making carbon nanotubes (CNTs) highly water dispersible and resistant to biofouling; such CNTs can be conjugated with bioactive molecules so as to be potential drug delivery vehicles.     

Deformation and fracture mechanisms in filled polymers

As fillers are traditionally designated those finely divided solids which are added to a polymer matrix in relativly large amounts to modify its properties and/or to reduce the price of the resulting compound. Generally a filler material is stiffer than the matrix and depending on their origin, shape and treatment fillers are reinforcing or not. In this presentation the authors will briefly review the characteristic mechanical effects on small strain behaviour, structure and time‐dependent properties of filled polymers stemming from the addition of more or less “spherical” fillers such as calcium carbonate, quartz flour, silica or glass spheres. The effect of such fillers on yield deformation, the nature of possible damage proceeding fracture and their effect on the toughness of particulate filled thermoplastics and thermosets will be discussed in more detail.     

Chain and photochain mechanisms of photooxidation of polymers

The mechanisms of photooxidation of the popular commercial polymers polystyrene (PS), polyethylene (PE), and an ethylene-carbon monoxide copolymer (polyketone, PK) differing in the polymer chain structure and the nature and concentration of chromophore groups are considered. In the case of the formation of photosensitive intermediates in polystyrene, taken as an example, the photochain oxidation mechanism was revealed and thoroughly studied, according to which the polymer “burns” into complete oxidation products (CO₂, H₂O) with a degree of conversion of ≥50% and a kinetic-chain length of l = 10³–10⁴ units. The hydroperoxide mechanism plays a minor role in the photooxidation of PS, it is a short-chain process (as in the case of thermal oxidation, l ∼ 10) and does not exceed 1.5% of the total amount of absorbed oxygen. Carbonyl groups, as weak photoinitiators, induce in PE and PK the conventional radical chain mechanism of photooxidation with degenerate branching of kinetic chains on hydroperoxide groups and other oxidations products.     

Photostabilisation mechanisms in polymers: A review

Key degradative processes for various polymers are itemised, together with photostabilisation mechanisms which can minimise these processes. Polymers can be conveniently classified as inherent absorbers, which absorb large amounts of solar uv, and as ‘non-absorbers’, that is polymers transparent in the near uv. The former group which includes aramids, polycarbonates and polyesters is predominantly photodegraded by primary processes causing direct bond scission and stabilisation is best effected by the use of uv absorbing additives or opaque pigments. The ‘non-absorbers’ include polyolefins and poly(vinylchloride) which are degraded as the result of oxidative chain processes initiated by chromophoric impurities. For polypropylene the dominant photooxidation product is hydroperoxide which photocleaves to initiate further oxidation. Various uv. stabilisers for polyolefins appear to owe their effectiveness to their ability to decompose hydroperoxide groups and/or to their ability to scavenge free radical intermediates in the oxidative process.     

Photoconductivity in polymers. Chemical structures and physical mechanisms

Synthesis and photoconductivity measurements are presented for two different types of photoconductors: i) polymers with pendant carbazolyl groups and ii) conjugated polymers. The temperature- and field dependence of the effective carrier mobility has been measured in a series of polymethacrylates with pendant carbazolyl groups and is discussed in relation to theoretical models. Time-of-flight measurements show that conjugated polymers like poly(methylphenylsilane) and poly(1,4-phenylenevinylene) exhibit extremely high carrier mobilities.     

Micropollutant sorption to membrane polymers: a review of mechanisms for estrogens

Organic micropollutants such as estrogens occur in water in increasing quantities from predominantly anthropogenic sources. In water such micropollutants partition not only to surfaces such as membrane polymers but also to any other natural or treatment related surfaces. Such interactions are often observed as sorption in treatment processes and this phenomenon is exploited in activated carbon filtration, for example. Sorption is important for polymeric materials and this is used for the concentration of such micropollutants for analytical purposes in solid phase extraction. In membrane filtration the mechanism of micropollutant sorption is a relatively new discovery that was facilitated through new analytical techniques. This sorption plays an important role in micropollutant retention by membranes although mechanisms of interaction are to date not understood. This review is focused on sorption of estrogens on polymeric surfaces, specifically membrane polymers. Such sorption has been observed to a large extent with values of up to 1.2 ng/cm(2) measured. Sorption is dependent on the type of polymer, micropollutant characteristics, solution chemistry, membrane operating conditions as well as membrane morphology. Likely contributors to sorption are the surface roughness as well as the microporosity of such polymers. While retention-and/or reflection coefficient as well as solute to effective pore size ratio-controls the access of such micropollutants to the inner surface, pore size, porosity and thickness as well as morphology or shape of inner voids determines the available area for sorption. The interaction mechanisms are governed, most likely, by hydrophobic as well as solvation effects and interplay of molecular and supramolecular interactions such as hydrogen bonding, π-cation/anion interactions, π-π stacking, ion-dipole and dipole-dipole interactions, the extent of which is naturally dependent on micropollutant and polymer characteristics. Systematic investigations are required to identify and quantify both relative contributions and strength of such interactions and develop suitable surface characterisation tools. This is a difficult endeavour given the complexity of systems, the possibility of several interactions taking place simultaneously and the generally weaker forces involved.     

The interface between immiscible polymers in composite latexes: a small-angle x-ray scattering study employing contrast variation

An investigation of the radial structure of composite latex particles by small-angle x-ray scattering (SAXS) is given. Measurements at different contrasts were done by addition of sucrose to the dispersion medium water. The latex particles investigated here consist of a poly(styrene) core and a shell of poly(methylmethacrylate) and were prepared by seeded emulsion polymerization. Since the electron density of both polymers can be easily matched by concentrated sucrose solution, a full analysis of the radial electron density by contrast variation can be given. Depending on the mode of monomer addition during the second polymerization step a very sharp or a diffuse interface between the two incompatible polymers may result.Respectfully dedicated to Prof. E. W. Fischer on the occasion of his 65th birthday     

Using polymers to control substrate,ligand, or catalyst solubility

The attributes and design of soluble polymer supports for catalysis and synthesis are discussed. By manipulating polymer structure, polymer supports can be prepared so that the solubility of an attached reagent, substrate, or ligand is affected by heating, cooling, pH, or solvent identity. Supports with such engineered solubility are useful both in organic synthesis and catalysis. They can be used as purification handles in organic synthesis as a way to recover catalysts, as a way to turn reactions on or off, and more generally, as a handle for separations. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2351–2363, 2001     

Spin-probe studies. I. Applications to latexes and micelle characterization

The interaction of sodium dodecyl sulfate (NaDS) with styrene—butadiene latexes was investigated by application of the recently developed spin-probe technique. It is possible by this method to detect the presence of micelles in a latex reasonably quantitatively. The effective surface area occupied per molecule of soap was calculated to be 53 Ų. Differences in purity can readily be detected for several NaDS samples. The less pure samples show a lower critical micelle concentration (CMC) and a significantly more ordered micelle structure. The addition of hexane to NaDS solutions above the CMC leads to a greater immobilization of the spin probe. This is interpreted as reflecting a tighter packing of the soap molecules. The addition of ethanol, acetic acid, and acrylic acid leads to a looser association of the probe with the micelles. The micelles catalyze the decomposition of the nitroxide probe in the presence of organic acids. The aggregation of sodium deoxycholate was also conveniently followed by the spin-probe method.     

Preparation and characterization of core-shell latexes

Polymeric dispersions with a concentric core-shell structure of the latex particles were obtained by a two-stage emulsion polymerization technique. Conditions for the formation of shells on polymeric seeds are discussed. SANS and SAXS investigations were carried out in order to verify the core-shell structure of the particles. DSC and IR measurements indicate the existence of an interfacial layer between core and shell polymers. The results are transferred to emulsion polymers containing inorganic filler particles.     

Using dendrimers and hyperbranched polymers in chromatography and electrophoresis

The use of a new class of high-molecular-weight substances, dendritic polymers (dendrimers and hyperbranched polymers), as components of chromatographic and electrophoretic systems is discussed; the effect of their introduction into a background electrolyte or an eluent on the separation efficiency and selectivity of organic compounds of different classes is considered.     

Supramolecular gold(I) thiobarbiturate chemistry: combining aurophilicity and hydrogen bonding to make polymers,sheets, and networks

The cooperative forces of aurophilic and hydrogen bonding have been used in the self-assembly of phosphine or diphosphine complexes of gold(I) with the thiolate ligands derived from 2-thiobarbituric acid, SC(4)H(4)N(2)O(2), by single or double deprotonation. The reaction of the corresponding gold(I) trifluoroacetate complex with SC(4)H(4)N(2)O(2) gave the complexes [Au(SC(4)H(3)N(2)O(2))(PPh(3))], 1, [(AuSC(4)H(3)N(2)O(2))(2)(micro-LL)], with LL = Ph(2)PCH(2)PPh(2), 2a, Ph(2)P(CH(2))(3)PPh(2), 2b, or Ph(2)PCH=CHPPh(2), 2c, or the cyclic complex [Au(2)(micro-SC(4)H(2)N(2)O(2))(micro-Ph(2)PCH(2)CH(2)PPh(2))], 3. In the case with LL = Ph(2)P(CH(2))(6)PPh(2), the reaction led to loss of the diphosphine ligand to give [Au(6)(SC(4)H(3)N(2)O(2))(6)], 4, a hexagold(I) cluster complex in which each gold(I) center has trigonal AuS(2)N coordination. Structure determinations show that 1 has no aurophilic bonding, 2b, 3, and 4 have intramolecular aurophilic bonding, and 2c has intermolecular aurophilic bonding that contributes to the supramolecular structure. All the complexes undergo supramolecular association through strong NH...O and/or OH...N hydrogen bonding, and complex 3 also takes part in CH...O hydrogen bonding. The supramolecular association leads to formation of interesting polymer, sheet, or network structures, and 4 has a highly porous and stable lattice structure.     

Quantitative characterization of toughening mechanisms of rubber modified polymers

The volume changes of rubber modified polymers under creep at room temperature were successfully used to characterize the toughening mechanisms of blends with brittle polymer matrices such as high impact polystyrene.This approach cannot be applied to pseudo-ductile polymers such as polypropylene and polyamide,because they are ductile when stretched at low speed at room temperature.Based on the time-temperature equivalence princi ple,the volume change at low temperature is proposed to characterize quantitatively the toughening mechanisms of polymer blends with ductile matrices,which is illustrated by applying this approach to rubber modified polypropylene     

Correlation of thermal degradation mechanisms: Polyacetylene and vinyl and vinylidene polymers

The thermal degradation of poly(vinyl bromide) (PVB), poly(vinyl chloride) (PVC), poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), poly(vinyl fluoride) (PVF), poly(vinylidene chloride) (PVC₂), and poly(vinylidene fluoride) (PVF₂) has been studied by direct pyrolysis–mass spectrometry (DP-MS) and flash pyrolysis–gas chromatography–mass spectrometry techniques. Vinyl and vinylidene polymers exhibit two competitive thermal degradation processes: (1) HX elimination with formation of polyene sequences which undergo further moleculaar rearrangements, and (2) main-chain cleavage with formation of halogenated or oxigenated compounds. The overall thermal degradation process depends on the prevailing decomposition reaction in each polymer; therefore, different behaviors are observed. The thermal degradation of polyacetylene (PA) has also been studied and found important for the elucidation of the thermal decomposition mechanism of the title polymers.     

Using soluble polymers in latent biphasic systems

A new strategy for carrying out reactions with a soluble polymer-bound reagent or catalyst is described. In this latent biphasic process, a solvent mixture at the cusp of immiscibility is prepared and used to carry out a reaction under homogeneous conditions. Then, after the reaction is complete, this mixture is perturbed by the addition of solvent or some other perturbing agent to produce a biphasic mixture. The product-containing phase is then separated under liquid/liquid conditions from the polymer-containing phase. The generality of this process is demonstrated using both dye-labeled polymers as surrogates for polymer-bound catalysts and with various polymer-bound organic and transition metal catalysts or reagents. In cases where a polymeric catalyst is used, the addition of fresh solvent and substrate reforms the original mixture allowing facile reuse of the catalyst.     

Synthesis and characterization of novel polyacid-stabilized latexes

A series of novel polyacid macromonomers based on 2-hydroxypropyl methacrylate (HPMA) were prepared by atom transfer radical polymerization (ATRP) via a two-step route. First, a range of well-defined PHPMA homopolymer precursors were synthesized by ATRP using a tertiary amine-functionalized initiator, 2-(dimethylamino)ethyl-2-bromoisobutyrylamide, and a CuCl/2, 2'-bipyridine (bpy) catalyst in alcoholic media at 50 °C. ATRP polymerizations were relatively slow and poorly controlled in pure isopropanol (IPA), especially when targeting higher degrees of polymerization (DP > 30). Improved control was achieved by addition of water: low polydispersity (M(w)/M(n) < 1.25) PHPMA homopolymers of DP = 30, 40, 50, 60, or 70 were successfully prepared using a 9:1 w/w % IPA/water mixture at 50 °C. These PHPMA homopolymer precursors were then derivatized to produce the corresponding poly(2-(succinyloxy)propyl methacrylate) (PSPMA) macromonomers by quaternizing the tertiary amine end-group with excess 4-vinylbenzyl chloride, followed by esterification of the pendent hydroxyl groups using excess succinic anhydride at 20 °C. These polyacid macromonomers were evaluated as reactive steric stabilizers for polystyrene latex synthesis under either aqueous emulsion polymerization or alcoholic dispersion polymerization conditions. Near-monodisperse polystyrene latexes were obtained via aqueous emulsion polymerization using 10 wt % PSPMA macromonomer (with respect to styrene monomer) with various initiators as evidenced by scanning electron microscopy, disk centrifuge photosedimentometry and light scattering studies. PSPMA macromomer concentrations as low as 1.0 wt % also produced near-monodisperse latexes, suggesting that these PSPMA macromonomers are highly effective stabilizers. Alcoholic dispersion polymerization of styrene conducted in various ethanol/water mixtures with 10 wt % PSPMA(50) macromonomer produced relatively large near-monodisperse latexes. Increasing the water content in such formulations led to smaller latexes, as expected. Control experiments conducted with 10 wt % PSPMA(50) homopolymer produced relatively large polydisperse latexes via emulsion polymerization and only macroscopic precipitates via alcoholic dispersion polymerization. Thus the terminal styrene group on the macromonomer chains is essential for the formation of well-defined latexes. FT-IR spectroscopy indicated that these latexes contained PSPMA macromonomer, whereas (1)H NMR spectroscopy studies of dissolved latexes allowed stabilizer contents to be determined. Aqueous electrophoresis and X-ray photoelectron spectroscopy studies confirmed that the PSPMA macromonomer chains were located at the latex surface, as expected. Finally, these polyacid-stabilized polystyrene latexes exhibited excellent freeze-thaw stability and remained colloidally stable in the presence of electrolyte.