Jean M.J. Fréchet

Functionalization of crosslinked polystyrene resins: 2. Preparation of nucleophilic resins containing hydroxyl or thiol functionalities

Abstract Crosslinked polystyrene resins containing thiol or hydroxyl functionalities on a fraction of their aromatic rings were prepared by reaction of crosslinked polystyryllithium with elemental sulphur or oxygen followed by reduction of the resulting polymer. Similarly, resins containing hydroxymethyl or thiomethyl functional groups were prepared from chloromethylated polystyrene by displacement of chloride in procedures involving three phase systems and the use of a phase transfer catalyst. The degree of functionalization could be controlled easily and the sulphur containing polymers were free of disulphide bonds.

Polymeric Reagents.II. Synthesis and Applications of Crosslinked Poly(vinylpyridinium Hydrobromide Perbromide) Resins

Abstract Crosslinked bead polymers containing vinylpyridine units were prepared by pearl copolymerization of monomer mixtures containing various percentagesof 4-vinylpyridine, styrene, and di-vinylbenzene. The polymers were functionalized by reaction with hydrogen bromide and bromine, and the resulting poly-(vinylpyridinium hydrobromide perbromide) resins, which were stable for long periods of time, were used to brominate a number of alkenes and ketones. In most cases, the brominated products were obtained in excellent yields and could be separated from the polymeric by-product by a simple filtration. The polymeric reagent could be fully regenerated after use without loss of activity.

FUNCTIONALIZATION OF CROSSLINKED POLYSTYRENE RESINS BY CHEMICAL MODIFICATION: A REVIEW

Functionalized crosslinked polystyrene resins have received much attention recently due to their numerous possible applications in chemistry and biochemistry. Three types of insoluble polymers with various degrees of cross-linking and different physical properties are used frequently as starting materials in the functional!zation reactions; these are popcorn polymers, solvent swellable beads and macroreticular beads. The reactions used in the chemical modification of these polymers are reviewed with emphasis on those reactions which introduce versatile, easily transformed functional groups which may serve to anchor the more specific functionalities of many special use resins. The following reactions of crosslinked polystyrene resins are reviewed: halogenation, chloromethylation, metalation, formylation, acylation, carboxylation, phosphination, nitration, amination and the introduction of hydroxyl, anhydride and sulfur containing functional groups. Finally, the analytical problems encountered in the characterization of the functionalized resins are reviewed.

Mechanism of phase-transfer catalysis using glycidyl methacrylate-ethylene dimethacrylate copolymers modified with tributylammonium groups in nucleophilic displacement reactions

Abstract The kinetics of phase-transfer catalysis using glycidyl methacrylate-ethylene dimethacrylate resins modified with pendant quaternary butylammonium groups have been studied. In contrast to expectations based on currently proposed mechanisms, the activity of polymeric catalysts is not improved through modifications that balance the hydrophilic and hydrophobic properties of the material. It is believed that much of the activity of the polymeric catalysts derives from the swelling of the polymer in both aqueous and organic phases. This enhances not only the rate of diffusion of both reagents to the vicinity of the catalytically active groups but also the ability of reactive groups to oscillate between the two phases. Both swelling and diffusion are restricted severely as the percentage of crosslinking is increased. This restriction is of particular importance with macroporous resins. Comparison of kinetic data obtained with various polymers suggests that gel polymers with very small bead sizes and therefore high external surface areas provide much higher reactivities than their macroporous counterparts.

Chemical Modification of Halogenated Polymers Under Phase Transfer Conditions

Abstract The chemical modification of several polymers including poly (vinyl bromide), poly (chloromethyl styrene), poly (vinylidene bromide), and poly (epichlorohydrin) was studied using various nucleophiles in multiphase systems with the assistance of a phase transfer catalyst. Satisfactory results were obtained using o-dichlorobenzene as solvent and powerful nucleophiles. The use of dimethylformamide as solvent often resulted in large increases in both reaction rates and conversions but sometimes created other problems. With several polymers dehydrohalogenation or chain cleavage were observed and in general the more basic nucleophiles were more destructive. With poly (vinyl bromide) the reaction was used to produce efficiently polymers containing alkyl sulfide, methyl sulfone, vinyl sulfone, or thioethanol side chains with little apparent polymer degradation.

Synthesis of new dialkylaminopyridine acylation catalysts and their attachment to insoluble polymer supports

Abstract Dialkylaminopyridines whose N -substituents bear a hydroxyl or amino group can be made economically from 4-cyanopyridine. Simple but selective alkylation of these compounds with commercial (chloromethyl) or (3-bromopropyl) polystyrene gives several new solid-phase catalysts which are highly active in promoting the acylation of hindered alcohols. Comparison of syntheses and reactivities, among these and some other heterocyclic polymers, illustrates several useful general principles of reactive polymer chemistry such as local concentration and microenvironment effects.

Positive/Negative Mid Uv Resists With High Thermal Stability

New mid UV resist systems based on poly(p-vinylbenzoates) sensitized with diphenyl-4-thiophenoxyphenylsulfonium hexafluoroantimonate are described. t-Butyl, cyclohexenyl, a-methylbenzyl, and a-methylallyl esters are converted upon postbake to poly(p-vinylbenzoic acid) through thermolysis reaction catalyzed by the photochemically generated Bronsted acid, inducing a large change in the polarity of the repeating units. Thus, development in aqueous base such as MF312/water or alcohol provides a positive tone image of the mask, while the use of a nonpolar organic developer allows a negative tone imaging. Because the glass transition temperature of poly(p-vinylbenzoic acid) is ca. 250° C, the negative image is devoid of thermal flow to this temperature even without any hardening processes. Another interesting feature of the benzoate resists is their high opacity in the deep UV region. The optical density of a 1μ thick film of poly(p-vinylbenzoic acid) is 3.5 at 254 nm and the benzoate polymers are as absorbing as the acid polymer. This high deep UV absorption of the resin necessitates the imaging above 300 nm for good light penetration (or by e-beam or X-ray) and makes the use of this resist as an imaging layer in the PCM scheme very attractive. This imaging layer is especially useful when employed in conjunction with a planarizing layer absorbing above 240 nm (for example, PMGI) as addition of a dye is not required.

The role of chelation in the formylation of grignard reagents with N-formyl amines.

Abstract The formylation of Grignard reagents with N-alkyl-N-formyl amines is best carried out with reagents such as N-(N-formyl-N-methyl)aminopiperidine which contain an additional ligand.

Poly(vinyl-t-butyl carbonate) synthesis and thermolysis to poly(vinyl alcohol)

SummaryThe use of the t-BOC protecting group for the preparation of an organic soluble derivative of poly(vinyl alcohol) is reported. Poly(vinyl-t-butyl carbonate) can be obtained by free-radical polymerization of the monomer using peroxide or azo initiators at 90–120°C. The t-BOC polymer is thermolyzed cleanly to poly(vinyl alcohol) with evolution of carbon dioxide and 2-methyl-propene when heated to 210–220°C. The t-BOC polymer may be useful for imaging processes involving acid-catalyzed thermolysis.

Chemical modification of polymers via phase transfer catalysis

The preparation of functional polymers is an area of organic-polymer chemistry which continues to receive much attention in view of the numerous new and imaginative applications which are discovered for specialty polymers with reactive functionalities. The two main approaches which can be used in the preparation of functional polymers consist of the polymerization or copolymerization of suitably functionalized monomers or the chemical modification of pre-formed polymers. The first approach is often considered to be the most attractive due to its apparent simplicity, although it is often ill suited for the preparation of polymers with fairly complex functionalities. In some cases, even simple polymers such as poly(vinyl alcohol) are only accessible via a chemical modification route. In other cases it may be desirable to effect a simple chemical modification reaction to prepare a less common or more reactive polymer such as poly(iodomethyl styrene) from a more readily accessible but less reactive precursor such as poly(chloromethyl styrene).