Progress in controlled polymerization and design of novel polymer architectures

Recent developments of new synthetic methods are stimulating the design of new polymers. Modern generations of highly active and selective transition metal catalysts give excellent control on molecular weight, regio- and stereoregularities, long- and short-chain-branching, polymer crystallization, and morphology of olefin, diene, cyclolefin, and styrene polymers. Ethene is copolymerized with polar comonomers such as carbon monoxide and acrylates in new low pressure processes. Catalytic coupling reactions of aromatic halogen compounds and bisphenols afford rigid polyarylenes. „Living” radical polymerization (“TEMPO” and “ATRP”) produce a wide range of telechelics, block copolymers and cascade macromolecules. In reactive processing oxazoline-mediated coupling reactions are the key to melt diversification of well-known polymers. Supramolecular concepts are being applied to tailor hybrid polymers and nanocomposites. Precision in polymer synthesis is the key to new materials with wide application range.     

Anionic ring-opening polymerization of a strained phosphirene: a route to polyvinylenephosphines

A strained 1-phenyl-2,3-dimethylphosphirene undergoes anionic ring-opening polymerization upon initiation with n-butyl lithium at ambient temperature to yield polyvinylenephosphine, an unsaturated organophosphorus polymer.     

Metal-catalyzed radical polyaddition as a novel polymer synthetic route

A new class of polymerizations was developed via metal-catalyzed C-C bond forming radical polyaddition; the monomers were designed to have a reactive C-Cl bond, which can be activated by the metal catalysts to generate a carbon radical species, along with a C=C double bond, to which the carbon radical generated from another molecule adds to form a C-C backbone polymer with an inactive C-Cl pendant.     

A synthetic approach to a fullerene-rich dendron and its linear polymer via ring-opening metathesis polymerization

Through the esterification of an acyl chloride functionalized fullerene precursor with dendritic alcohol, a fullerene-rich dendron containing a norbornene unit at the focal point is prepared for ring-opening metathesis polymerization to obtain its linear polymer with a unimodal and narrow molar mass distribution (PDI = 1.08) by a progressive addition of catalysts.     

Shape-tunable polymer nodules grown from liposomes via ring-opening metathesis polymerization

A new inisurf (acting as surfactant and initiator) molecule for ring-opening metathesis polymerization (ROMP) was synthesized and used in aqueous solution in order to control the size and shape of polymer nodules grown from liposomes. Nodules were observed to grow in size with conversion of monomer, and depending on the monomer used, they adopted either a spherical or comet-like shape. Here, we investigate polymer production from a liposome surface. We use a hydrophobic derivative of the Grubbs catalyst positioned at the liposome surface to allow for ROMP of monomers dissolved in the aqueous outer phase. We obtain nodules of polymer that can grow up to tens of micrometers, unveiling new efficient possibilities of polymerization from a membrane in an aqueous solution.     

Transmetalation as a route to novel styryllithium reagents

[structure: see text] Transmetalation of beta-tributyl(styryl)stannanes with n-BuLi gives the functional equivalents of the corresponding styryllithium intermediates. Reaction of the intermediates with chlorotrimethylsilane, iodomethane, or dimethyl sulfate gives the substituted styryl products in moderate to good yields. In all cases, the configuration about the double bond was retained in the products.     

Ring-opening polymerization of 1,4,8-trioxaspiro-[4.6]-9-undecanone: A route to novel molecular architectures for biodegradable aliphatic polyesters

The ring-opening polymerization of 1,4,8-trioxaspiro-[4.6]-9-undecanone (TOSUO) initiated by aluminum isopropoxide, Al(OⁱPr)₃, is typically “living” and allows random and block copolyesters of predictable molecular weight and composition to be prepared. Deacetalization of the polyester chains is complete, and reduction of the accordingly formed ketone groups into hydroxyl groups as well. No chain scission is observed when these two derivatization reactions are carried out. The potential of these novel functional aliphatic polyesters has been discussed as drug colloidal vectors and macroinitiators for the synthesis of biodegradable and biocompatible comb, graft and even hyperbranched polymers.     

Mechanochemical ring-opening metathesis polymerization: development,scope, and mechano-exclusive polymer synthesis

Ruthenium-alkylidene initiated ring-opening metathesis polymerization has been realized under solid-state conditions by employing a mechanochemical ball milling method. This method promotes greenness and broadens the scope to include mechano-exclusive products. The carbene- and pyridine-based Grubbs 3^rd-generation complex outperformed other catalysts and maintained similar mechanistic features of solution-phase reactions. High-speed ball milling provides sufficient mixing and energy to the solid reaction mixture, which is composed of an initiator and monomers, to minimize or eliminate the use of solvents. Therefore, the solubility and miscibility of monomers and Ru-initiators are not limiting factors in solid-state ball milling. A wide variety of solid monomers, including ionomers, fluorous monomers, and macromonomers, were successfully polymerized under ball milling conditions. Importantly, direct copolymerization of immiscible (ionic/hydrophobic) monomers exemplifies the synthesis of mechano-exclusive polymers that are difficult to make using traditional solution procedures. Finally, the addition of a small amount of a liquid additive (i.e., liquid-assisted grinding) minimized chain-degradation, enabling high-molecular-weight polymer synthesis.

Mechanochemical ball-milling ring-opening metathesis polymerization minimized solvent use and produced previously inaccessible polymers in solution.     

Redox control of a ring-opening polymerization catalyst

The activity of an yttrium alkoxide complex supported by a ferrocene-based ligand was controlled using redox reagents during the ring-opening polymerization of L-lactide. The oxidized complex was characterized by X-ray crystallography and (1)H NMR, XANES, and M?ssbauer spectroscopy. Switching in situ between the oxidized and reduced yttrium complexes resulted in a change in the rate of polymerization of L-lactide. Synthesized polymers were analyzed by gel permeation chromatography. Polymerization of trimethylene carbonate was also performed with the reduced and oxidized forms of an indium alkoxide complex. The indium system showed the opposite behavior to that of yttrium, revealing a metal-based dependency on the rate of polymerization.     

Synthesis and anionic ring-opening polymerization of crown-ether-like macrocyclic dilactones: An alternative route to PEG-containing polyesters and related networks

Linear aliphatic polyesters whose structure is made of short polyethylene glycol (PEG) segments connected along the chain by malonate units were synthesized from two PEG-containing macrolactones: 15,15-dimethyl-1,4,7,10,13-pentaoxacyclohexadecane-14,16-dione (1) and 5,8,11,14,17-pentaoxaspiro[2,15]octadecane-4,18-dione (2). Anionic ring-opening polymerization conditions using either thiophenolates or a p-nitrophenolate as initiators yielded poly(ether-ester)s of low to moderate molecular weights, with broad molecular weight distributions. When the monomer also contains an activated cyclopropane unit of the cyclopropane-1,1-dicarboxylate type (such as in 2) and harsher polymerization conditions are used (higher temperatures and bulkier counterions), opening of the cyclopropyl ring can compete with the dilactone polymerization, providing access to crosslinked materials.     

A novel metal alkyl-free catalyst for the ring-opening polymerization of cycloolefins

A new catalytic system based on tungstic acid (H₂WO₄) and aluminum trichloride (AlCl₃) polymerizes cyclopentene and 1,5-cyclooctadiene through a ring-opening mechanism in high yields and high molecular weight.     

Design of new polymer architectures by combination of anionic and cationic living polymerization techniques

The grafting of polystyryl lithium onto poly(chloroethyl vinyl ether) chains has been investigated. The reaction proceeds cleanly and quantitatively thus allowing the synthesis of comblike polymers. Since the dimensions of the polystyrene branches and of the poly(chloroethyl vinyl ether) backbone can be controlled by living polymerizations, both the length and the number of branches of the graft copolymers can be tuned. The latter behave as star polymers. The possibility to initiate a new cationic polymerization of chloroethyl vinyl ether from polystyrene branches bearing acetal termini in order to prepare the corresponding stars with poly(chloroethyl vinyl ether-b- styrene) branches is also examined. Finally access to hyperbranched polymers of controlled architecture and dimensions by deactivation of a second amount of polystyryl lithium onto the last blocks of poly(chloroethyl vinyl ether) is also reported.     

Synthesis of novel hydrophobically modified water soluble polymers by ring-opening metathesis polymerization

Ring-opening metathesis polymerization has been used to prepare a series of water soluble polymers based on the Diels-Alder adducts of furan and cyclopentadiene. Hydrophobically modified forms of these polymers were obtained either by copolymerization with 5-decylbicyclo[2.2.1]hept-2-ene, post-polymerization modification of the acid forms of the polymers with 1-decylamine or chain transfer to 1-hexadecene. Polymers were characterized by NMR specroscopy and viscometry.     

Surfactant-free miniemulsion polymerization as a simple synthetic route to a successful encapsulation of magnetite nanoparticles

Due to the existing interest in new hybrid particles in the colloidal range based on both magnetic and polymeric materials for applications in biotechnological fields, this work is focused on the preparation of magnetic polymer nanoparticles (MPNPs) by a single-step miniemulsion process developed to achieve better control of the morphology of the magnetic nanocomposite particles. MPNPs are prepared by surfactant-free miniemulsion polymerization using styrene (St) as a monomer, hexadecane (HD) as a hydrophobe, and potassium persulfate (KPS) as an initiator in the presence of oleic acid (OA)-modified magnetite nanoparticles. The effect of the type of cross-linker used [divinylbenzene (DVB) and bis[2-(methacryloyloxy)ethyl] phosphate (BMEP)] together with the effect of the amount of an aid stabilizer (dextran) on size, particle size distribution (PSD), and morphology of the hybrid nanoparticles synthesized is analyzed in detail. The mixture of different surface modifiers produces hybrid nanocolloids with various morphologies: from a typical core-shell composed by a magnetite core surrounded by a polymer shell to a homogeneously distributed morphology where the magnetite is uniformly distributed throughout the entire nanocomposite.     

Molecularly asymmetric triblock copolymers as a single-molecule route to ordered bidisperse polymer brushes

The conditions signaling the formation of bidisperse brushes in ordered block copolymers are investigated as an A(2) block is progressively grown onto an A(1)B diblock copolymer to form a series of molecularly asymmetric, isomorphic A(1)BA(2) triblock copolymers. Small-angle scattering and self-consistent field theory confirm that the microphase-ordered period decreases when the A(2) block is short relative to the A(1) block, but then increases as A(1)+A(2) bidisperse brushes develop. The mechanical properties systematically follow the spatial distribution of the A(2) block.     

Controlled ring-opening polymerization of cyclic esters with phosphoric acid as catalysts

(R)-(?)-1,1′-Binaphthyl-2,2′-diyl hydrogen phosphate (BPA) has been demonstrated as an efficient organocatalyst for controlled ring-opening homopolymerization of ε-caprolactone (ε-CL) and copolymerization of ε-CL with glycolide and lactide. High molar mass PCL with narrow molar mass distribution has also been synthesized from the bulk ring-opening polymerization (ROP) of ε-CL with BPA as catalysts; the highest molar mass of PCL is 4.35?×?10⁴ g/mol with polydispersity index of 1.20. The successful synthesis of high molar mass PCL is attributed to the bifunctional activation mechanism for the ROP of ε-CL catalyzed by BPA. More interestingly, ppm level of BPA is sufficient to catalyze controlled ROP of ε-CL.     

Dithiadiazolium salts as initiators for the cationic ring-opening polymerization of tetrahydrofuran

Mono-, bis- and tris-(1,3,2,4-dithiadiazolium) salts [R-(CNSNS ⁺)_n]_n+[AsF^-₆]_n (R = aryl, n = 1, 2, 3) were found to initiate the cationic ring-opening polymerization of tetrahydrofuran (THF) at room temperature to give clear gels from which the pure polymer was precipitated. 1,3,2,4-Dithiadiazolium cations associated with the hard [AsF₆]^- anion thus constitute a new class of cationic polymerization initiators. The poly(THF) formed by initiation with 1,3,2,4-dithiadiazolium cation was characterized by gel permeation chromatography, infrared spectrophotometry, and ¹³C-NMR spectroscopy. Number-average molecular weights of 198 700 g mol^-1 (polydispersity 1.96) and 190 000 g mol^-1 (polydispersity 1.61) were obtained using [PhCNSNS ] [AsF₆] and [C₆H₃-1,3,5-(CNSNS )₃][AsF₆]₃, respectively, as initiators. The use of multifunctional dithiadiazolium salts as initiators suggests that they may be useful in the preparation of starburst and dendritic polymers. © 1992 John Wiley & Sons, Inc.     

A novel high efficiency benzophenone based polymeric photoinitiator from ring-opening polymerization of benzoxazine

A novel polymeric photoinitiator based on benzoxazine was synthesized by introducing 4-hydroxy benzophenone, diglycolamine and paraformaldehyde into the macromolecular chain. Its molecular structure was characterized by ¹H NMR, FTIR, and UV-Vis spectroscopy. Photopolymerization of tripropylene glycol diacrylate and trimethylolpropane triacrylate initiated by polybenzoxazine, benzoxazine, and benzophenone was studied by real time FTIR spectroscopy. The results obtained are discussed.