Anionic ring opening polymerization by alkali metal solutions

The alkali metal solutions were found to be active initiators in the ring-opening polymerization of β-lactones. The chemistry of those solutions and their activity as initiators were discussed.     

Anionic ring opening of norbornenes fused to heterocycles

The 2-hydroxy and 2-oxo derivatives of 1,2,3,4-tetrahydro-1,4-methanophenazine were prepared and found to evolve in basic media through the opening of their bicyclo[2.2.1]heptene moiety, affording 2,3-dihydro-1H-cyclopenta[b]quinoxaline derivatives with two-carbon 1-substituents that depend on the starting compound. In the case of 2-hydroxy starting compounds, ring-opening occurs regardless of the orientation of the hydroxyl group, and in methanolic solution is spontaneous, though slow, even in the absence of added base (at least in the case of the endo derivative). It is presumably favoured by the steric strain of the heteroaryl-fused bicyclo[2.2.1]heptene moiety, and is hypothesized to involve the base-promoted formation of anionic intermediates that are stabilized by the π-deficient nature of the quinoxaline system.     

Free‐radical polymerization of dioxolane and dioxane derivatives: Effect of fluorine substituents on the ring opening polymerization

Partially fluorinated and perfluorinated dioxolane and dioxane derivatives have been prepared to investigate the effect of fluorine substituents on their free‐radical polymerization products. The partially fluorinated monomer 2‐difluoromethylene‐1,3‐dioxolane (I) was readily polymerized with free‐radical initiators azobisisobutyronitrile or tri(n‐butyl)borane–air and yielded a vinyl addition product. However, the hydrocarbon analogue, 2‐methylene‐1,3‐dioxolane (II), produced as much as 50% ring opening product at 60 °C by free‐radical polymerization. 2‐Difluoromethylene‐4‐methyl‐1,3‐dioxolane (III) was synthesized and its free‐radical polymerization yielded ring opening products: 28% at 60 °C, decreasing to 7 and 4% at 0 °C and −78 °C, respectively. All the fluorine‐substituted, perfluoro‐2‐methylene‐4‐methyl‐1,3‐dioxolane (IV) produced only a vinyl addition product with perfluorobenzoylperoxide as an initiator. The six‐membered ring monomer, 2‐methylene‐1,3‐dioxane (V), caused more than 50% ring opening during free‐radical polymerization. However, the partially fluorinated analogue, 2‐difluoromethylene‐1,3‐dioxane (VI), produced only 22% ring opening product with free‐radical polymerization and the perfluorinated compound, perfluoro‐2‐methylene‐1,3‐dioxane (VII), yielded only the vinyl addition polymer. The ring opening reaction and the vinyl addition steps during the free‐radical polymerization of these monomers are competitive reactions. We discuss the reaction mechanism of the ring opening and vinyl addition polymerizations of these partially fluorinated and perfluorinated dioxolane and dioxane derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5180–5188, 2004     

Some new aspects of alkylene sulphides polymerization with ring opening

A new possibility has been demonstrated for opening of the three-membered sulphur-containing heterocycles and formation of linear polymers under the action of charge-transfer complexes.     

Block copolymers via macromercaptan initiated ring opening polymerization

Poly(styrene) macromercaptanes (M_n = 1900, 3600, and 6100 g mol^?1, PDI ≈ 1.2) derived from thiocarbonyl thio capped polymers prepared via reversible addition fragmentation chain transfer polymerization were employed to initiate the ring opening polymerization (ROP) of D ,L ‐lactide under conditions of organo‐catalyis employing 4,4‐dimethylaminopyridine. Poly(styrene)‐block‐poly(lactide) polymers of number average molecular weights up to 25,000 g mol^?1 (PDI ≈ 1.2 to 1.6) were obtained and characterized via multiple detection size exclusion chromatography (SEC) using refractive index as well as UV detection. In addition, diffusion ordered nuclear magnetic resonance and liquid chromatography at critical conditions (of both polystyrene as well as poly(lactide) were employed to assess the copolymers' structure. Furthermore, it was demonstrated that polyethylenes capped with a thiol moiety can also be readily chain extended in a ROP employing D ,L ‐lactide, evidenced via NMR and high temperature SEC. This study indicates that the direct use of macromercaptantes is indeed a methodology to switch from a radical to a ROP process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Selectivity of siloxane-siloxane copolymer synthesis by ring opening polymerization

Anionic ring-opening polymerization of 1,1-diphenyl-2,2,3,3-tetramethylcyclotetrasiloxane was studied as a model polymerization of cyclic siloxane with mixed siloxane units. Sequencing of siloxane units was investigated by ²⁹Si NMR. Various initiator-promoter-solvent systems were used. In most cases reaction was highly chemoselective, as sequencing were not affected by back biting, chain transfer and terminal unit exchange processes. Reactions showed, however, low regioselectivity in monomer ring opening. The coordination of the metal counter-ion to monomer plays a considerable role in propagation and affects sequencing of the polymer.     

Living ring opening metathesis polymerization of mesogenic norbornene derivatives

A new class of SCLCPs was prepared by polymerizing mesogenic norbornene derivatives using Mo(CHCMe₂R)(N-2,6-C₆H₃-i-Pr₂)(O-t-Bu)₂ (R = CH₃ or Ph). Monomers based on norbornene ring systems were chosen because the rings are highly strained and therefore yield irreversible polymerizations. The Mo-alkylidene initiators were chosen because they initiate norbornene derivatives relatively fast and quantitatively, and provide stable chain ends which have low reactivity to both the internal double bonds of the polymer backbone and the functional groups present in the monomers. The apparent absence of termination and transfer reactions in ROMP results in polymerizations which appear to be living, and the fast initiation and irreversible chain growth leads to polymers with narrow molecular weight distributions in which the degree of polymerization is controlled by the ratio of monomer to initiator used. The resulting well-defined polymers were used to determine the most basic structure-property relationships of this new class of SCLCPs. The thermotropic behavior of both terminally attached and laterally attached SCLCPs based on polynorbornene backbones becomes independent of molecular weight at approximately 25 repeat units. In addition, polydispersity was found to have no effect on the breadth of nematic phase transitions in the terminally attached polymers, with the transition temperature determined simply by the number average degree of polymerization.     

Novel ring opening polymerization induced by alkali metal anions

Novel homogeneous initiation systems consisting of organic alkali metal complexes: Me⁺/Ligand, Me⁻ enable synthesis of “living” tailor made polymers and copolymers promising materials for engineering and biomedical applications. The mechanism of this polymerization has been elucidated.     

Zinc anilido-oxazolinate complexes as initiators for ring opening polymerization

Three new anilido-oxazolines, ortho-C(6)H(4)(NHAr')(4,4-dimethyl-2-oxazoline) [Ar'=2,4,6-trimethylphenyl, HNPh(TriMe)Oxa (1); 2,6-diisopropylphenyl, HNPh(DiiPr)Oxa (2); 2-methoxyphenyl, HNPh(OMe)Oxa (3)], have been prepared. Reactions of 1 or 2 with one molar equivalent of ZnEt(2) in tetrahydrofuran or hexane solution give the zinc ethyl complexes (NPh(TriMe)Oxa)ZnEt (4) and (NPh(DiiPr)Oxa)ZnEt (5). The dinuclear zinc benzyloxide complexes, [(NAr'Oxa)Zn(mu-OBn)](2), [Ar'=2,4,6-trimethylphenyl, (6); 2-methoxyphenyl, (7)], were synthesized by the reaction of 4 with one molar equivalent of benzyl alcohol in tetrahydrofuran solution (for 6) or by treatment of with 3 one molar equivalent of ZnEt(2) in tetrahydrofuran solution followed by the addition of one molar equivalent of benzyl alcohol (for 7). The molecular structures are reported for compounds 6 and 7. Their catalytic activities toward the ring opening polymerization reactions are under investigation.     

Advances in the frontal ring opening metathesis polymerization of dicyclopentadiene

The frontal ring opening metathesis polymerization of dicyclopentadiene using first and second generation Grubbs' catalysts is reported. To have sufficiently long pot lives, dimethylaminopyridine is added as an inhibitor. By choosing the proper compositions, it is possible to determine the ranges in which pure frontal polymerization occurs. A thorough study on the effect of the above components on the maximum temperatures reached by the front and on its velocities is performed. Namely, temperatures range from 164 to 205 °C depending on the type of catalyst and the above component ratios. Besides, front velocities range from 1.0 to 15.0 cm/min, which are one of the lowest and one of the highest values reported so far in any frontal polymerization experiment reported in literature. This finding allows the complete control of the frontal ring opening polymerization of dicyclopentadiene also in practical applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2776–2780     

Stationary phases for chromatography prepared by ring opening metathesis polymerization

The chemistry of metathesis polymerization-derived stationary phases is summarized. Since both ring-opening metathesis and 1-alkyne polymerization triggered by well-defined transition metal alkylidenes are living polymerization methods, they allow for the controlled and highly reproducible synthesis of stationary phases in terms of both the nature and total content of the functional group(s) of interest. In addition, the high functionality tolerance of these polymerization techniques allows for creating chromatographic supports with an unprecedented diversity in terms of functional groups that may be introduced. Their applications in various areas of separation science such as SPE, ion-chromatography, RP chromatography, chiral chromatography, and the high-performance liquid chromatographic separation of biomolecules are summarized. Within the context of the latter topic, special attention will be given to metathesis polymerization-derived monolithic supports. Consideration will also be given to those aspects of polymer chemistry that are relevant to the separation performance of these supports.     

Double metal cyano catalyst for ring opening polymerization of propylene oxide

A double metal cyano (DMC) catalyst is very effective for ring opening polymerization of propylene oxide (PO). The characteristics of the DMC complex were studied by Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TG). DMC complex generally result in a significant reduction of monols in the polyol production process. DMC catalyst is characterized by an approximately 1000 times higher activity compared to the conventional KOH catalyst. Disadvantages of the conventional KOH process are long reaction times, costly work-up procedures to remove the base catalyst and the formation of undesired unsaturated by-products (so called “monols”) especially in the preparation of long chain polyether polyols.     

Synthesis of amphiphilic block copolymers via ring opening polymerization and reversible addition-fragmentation chain transfer polymerization

Amphiphilic block copolymers were synthesized via a dual initiator chain transfer agent (inifer) that successfully initiated the ring opening polymerization (ROP) of l -lactide (LLA) and subsequently mediated the reversible addition-fragmentation chain transfer (RAFT) polymerization of poly(ethylene glycol) ethyl ether methacrylate (PEGEEMA). The formation of each polymer block was confirmed using ¹H nuclear magnetic resonance spectroscopy, as well as gel permeation chromatography, and comprehensive kinetics studies provide valuable insights into the factors influencing the synthesis of well-defined block copolymers. The effect of monomer concentration, reaction time, and molar ratios of inifer to catalyst on the ROP of LLA are discussed, as well as the ability to produce poly(lactide) blocks of different molecular weights. The synthesis of hydrophilic PPEGEEMA blocks was also monitored via kinetics to provide a better understanding of the role the chain transfer agent plays in facilitating the complex and sterically demanding RAFT polymerization of PEGEEMA.     

Glasses-shaped triblock copolymer prepared by combination of atom transfer radical polymerization and ring opening polymerization

A glasses-shaped triblock copolymer of poly(ε-caprolactone)-b-polystyrene-b-poly(ε-caprolactone) (PCL-b-PS-b-PCL) is prepared by combining atom transfer radical polymerization (ATRP) and ring opening polymerization (ROP). Polystyrene (PS) star polymers are prepared via ATRP using a tetra-functional initiator, followed by azidation to yield azide end-functionalized star polymers. An alkyne-functionalized coupling agent, 2,2-bis[(2-propyn-1-yloxy)methyl]-1-propanol is employed to produce hydroxy 8-shaped PS via copper(I)-catalyzed alkyne-azide cycloaddition. Herein, hydroxy 8-shaped PS with high purity is obtained through preparative size exclusion chromatography (Prep SEC) and high-performance liquid chromatography, followed by the characterizations using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), size exclusion chromatography (SEC), infrared, and proton nuclear magnetic resonance (¹H NMR) spectroscopy. The hydroxy groups of the 8-shaped PS are utilized as initiators for the ROP of ε-caprolactone to obtain linear chains attached to the 8-shaped architecture. After SEC fractionation, the glasses-shaped triblock copolymer is characterized using ¹H NMR and SEC. This unprecedented topology possesses two free chain-ends and two cycles; thus, both the properties of linear and cyclic polymers may be expected to be observed.     

Anionic polymerization with expansion in volume

New bicyclic and tricyclic compounds have been synthesized by the Lewis acid-catalyzed condensation of epoxides with cyclic acid anhydrides or cyclic bislactones. These materials take part in the anionic addition polymerization of amine-functional polyamides with diepoxides, and modify the shrinkage that is characteristic of the reaction. It is possible to control the extent of shrinkage by choosing an appropriate comonomer and by adjusting the concentration of this material in the reaction mixture.     

Catalytic activity of N-heterocyclic carbenes in ring opening polymerization of cyclic siloxanes

Taking advantage of the strong nucleophilic properties of N-heterocyclic carbene (NHC), the efficient catalytic ring opening polymerization (ROP) of cyclotetrasiloxane D₄ was achieved under mild conditions.     

Effect of limonene on the frontal ring opening metathesis polymerization of dicyclopentadiene

The frontal ring opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) in the presence of limonene, using second generation Grubbs’ catalysts, is reported. The effect of limonene on the amount of catalyst and the typical frontal polymerization parameters, as maximum temperature (T_max) and velocity of the front (V_f), is studied. In addition, the influence of limonene on the mechanical properties of the polymeric samples is reported. Finally, a deep study on the swelling properties of polymers is done. It has been demonstrated that limonene acts as both inhibitor and solvent of the catalyst. The T_max, V_f, T_g, and Young modulus values decrease as the amount of limonene increases, and the polymer samples swell in THF depending on the amount of limonene. All results indicate that the limonene addition on FROMP of results in advantages on the polymerization reaction and its parameters and on the final polymer properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 63–68     

Synthesis of spirocycles via ring closing metathesis of heterocycles carrying gem-diallyl substituents obtained via ring opening of (halomethyl)cyclopropanes with allyltributyltin

In the presence of allyl tri-n-butyltin--AIBN, cyclopropylmethyl bromides/xanthates undergo ring-opening reaction with concomitant formation of geminal diallyl derivatives in good yields. The ring closing metathesis reactions on geminal diallyl derivatives with Grubbs' catalyst provided spirocyclopentenyl products. Combination of these two methodologies has been applied to the synthesis of mono-, bis-cyclopentyl-carbohydrates as well as spirocyclopentylproline derivatives.