Polymer networks via cationic ring-opening polymerization

Three methods for the formation of polymer networks from bifunctionally growing polymers obtained by cationic ring-opening polymerization are described. The first method is based on the irreversible inter-molecular termination reaction of thietane polymerizations. Starting from bifunctionally living poly(THF) a new kind of polymer structure consisting of ABA block copolymers with cross-linked A-segments is obtained. The second method is the direct coupling of active species with primary amines or ammonia. The third method consists in transformation of the living end groups of poly(THF) into triethoxysilane end groups, followed by cross-linking by addition of water and a trace of acid.     

Reversible redox controlled acids for cationic ring-opening polymerization

Advancements in externally controlled polymerization methodologies have enabled the synthesis of novel polymeric structures and architectures, and they have been pivotal to the development of new photocontrolled lithographic and 3D printing technologies. In particular, the development of externally controlled ring-opening polymerization (ROP) methodologies is of great interest, as these methods provide access to novel biocompatible and biodegradable block polymer structures. Although ROPs mediated by photoacid generators have made significant contributions to the fields of lithography and microelectronics development, these methodologies rely upon catalysts with poor stability and thus poor temporal control. Herein, we report a class of ferrocene-derived acid catalysts whose acidity can be altered through reversible oxidation and reduction of the ferrocenyl moiety to chemically and electrochemically control the ROP of cyclic esters.

A class of ferrocene-derived acid catalysts whose acidity can be altered through reversible oxidation and reduction of the ferrocenyl moiety to chemically and electrochemically control the ROP of cyclic esters is reported.     

Synthesis of optically inactive cellulose via cationic ring-opening polymerization

Cellulose, which comprises D-glucose and L-glucose (D,L-cellulose), was synthesized from D-glucose (1D) and L-glucose (1L) via cationic ring-opening polymerization. Specifically, the ring-opening copolymerization of 3-O-benzyl-2,6-di-O-pivaloyl-β-D-glucopyranoside (2D) and 3-O-benzyl-2,6-di-O-pivaloyl-β-D-glucopyranoside (2L), synthesized from compounds 1D and 1L, respectively, in a 1:1 ratio, afforded 3-O-benzyl-2,6-di-O-β-D,L-glucopyranan (3DL) with a degree of polymerization (DPn) of 28.5 (Mw/Mn?=?1.90) in quantitative yield. The deprotection of compound 3DL and subsequent acetylation proceeded smoothly to afford acetylated compound 4DL with a DPn of 18.6 (Mw/Mn?=?2.08). The specific rotation of acetylated compound 4DL was?+?0.01°, suggesting that acetylated compound 4DL was optically inactive cellulose triacetate. Furthermore, before acetylation, compound 4DL was an optically inactive cellulose comprising an almost racemic mixture of D-glucose and L-glucose. Compound 4DL was an amorphous polymer. This is the first reported synthesis of optically inactive D,L-cellulose.

     

Microstructure of polymers obtained by cationic polymerization of endo-dicyclopentadiene

endo-Dicyclopentadiene (DCPD) was polymerized by various cationic initiating systems in different solvents. IR and ¹H NMR results show that four types of structural units are formed due to the corresponding addition modes: the addition on the norbornenic (NB) double bond generates unit I and rearranged unit II, while the addition on the cyclopentenic (CP) double bond produces unit III and rearranged unit IV. The reaction medium has a stronger effect on the microstructure of the polymer (PDCPD) than initiating systems. The polymers prepared in toluene and n-hexane contain all four structural units, while the polymer produced in methylene chloride is composed of structural units II and IV. © 1996 John Wiley & Sons, Inc.     

Stereoregular functionalized polysaccharides via cationic ring-opening polymerization of biomass-derived levoglucosan

We report the facile synthesis and characterization of 1,6-α linked functional stereoregular polysaccharides from biomass-derived levoglucosan via cationic ring-opening polymerization (cROP). Levoglucosan is a bicyclic acetal with rich hydroxyl functionality, which can be synthetically modified to install a variety of pendant groups for tailored properties. We have employed biocompatible and recyclable metal triflate catalysts – scandium and bismuth triflate – for green cROP of levoglucosan derivatives, even at very low catalyst loadings of 0.5 mol%. Combined experimental and computational studies provided key kinetic, thermodynamic, and mechanistic insights into the cROP of these derivatives with metal triflates. Computational studies reveal that ring-opening of levoglucosan derivatives is preferred at the 1,6 anhydro linkage and cROP proceeds in a regio- and stereo-specific manner to form 1,6-α glycosidic linkages. DFT calculations also show that biocompatible metal triflates efficiently coordinate with levoglucosan derivatives as compared to the highly toxic PF₅ used previously. Post-polymerization modification of levoglucosan-based polysaccharides is readily performed via UV-initiated thiol–ene click reactions. The reported levoglucosan based polymers exhibit good thermal stability (T_d > 250 °C) and a wide glass transition temperature (T_g) window (<−150 °C to 32 °C) that is accessible with thioglycerol and lauryl mercaptan pendant groups. This work demonstrates the utility of levoglucosan as a renewably-derived scaffold, enabling facile access to tailored polysaccharides that could be important in many applications ranging from sustainable materials to biologically active polymers.

We demonstrate the facile synthesis and characterization of stereoregular polysaccharides from the biomass-derived platform molecule levoglucosan via metal-triflate mediated cationic-ring opening polymerization.     

Solid-phase synthesis of polymers using the ring-opening metathesis polymerization

We report a general method for the solid-phase synthesis of polymers via the ring-opening metathesis polymerization (ROMP). The method involves polymerization in solution to form a block copolymer, immobilization of the polymer via reaction of one block with a resin-bound functional group, modification of the other block, and liberation of the polymer from the resin. We demonstrated the utility of this approach by generating a block copolymer with an N-hydroxysuccinimidyl ester-substituted block (for on-resin functionalization) and a maleimide-substituted block (for conjugation to the resin). We showed that the Diels-Alder reaction can be employed to immobilize the polymers and that amines of diverse structure can be used to modify the resin-bound polymers. The reversibility of the furan-maleimide Diels-Alder adduct was exploited to liberate the polymer from the support. Specifically, treatment of the resin with cyclopentadiene resulted in complete polymer release. The resulting polymers are functional: they were as potent in assays with the lectin concanavalin A as polymers generated by traditional solution routes. We anticipate that this method can be used for the rapid synthesis of diverse polymers via ROMP.     

Synthesis of hyperbranched carbohydrate polymers by ring-opening multibranching polymerization of anhydro sugar

The synthesis of novel hyperbranched carbohydrate polymers, prepared by the ring-opening multibranching polymerizations of anhydro and dianhydro sugars, is described. The hyperbranched carbohydrate polymers were formed by the cationic polymerization of 1,6-anhydro-beta-D-hexopyranose, 1,4-anhydrotetritol, 2,3-anhydrotetritol, and 1,2:5,6-dianhydro-D-mannitol. These polymerizations proceeded without gelation to produce water-soluble hyperbranched carbohydrate polymers with controlled molecular weights and narrow polydispersities. The values for the degree of branching of the polymers were in the range of 0.28-0.50. The polymerization method, which proceeds through a ring-opening reaction by a proton-transfer reaction mechanism, is a facile method leading to a spherical carbohydrate polymer with a high degree of branching.     

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.     

End capping ring-opening olefin metathesis polymerization polymers with vinyl lactones

The selective placement of a functional group at the chain end of a ring-opening metathesis polymer using ruthenium carbene initiators has been a significant limitation. Here we demonstrate a highly effective and facile end-capping technique for ROMP with living ruthenium carbene chain ends using single-turnover olefin metathesis substrates. Vinylene carbonate and 3H-furanone are introduced as functionalization and termination agents for the ruthenium-initiated ring-opening metathesis polymerization. This leads directly to the formation of functional polymer end groups without further chemical transformation steps. Aldehyde and carboxylic acid end groups can be introduced by this new method which involves the decomposition of acyl carbenes to ruthenium carbides. The high degrees of chain-end functionality obtained are supported by (1)H NMR spectroscopy, MALDI-ToF mass spectrometry, and end-group derivatization.     

Sterically controlled propagation in the cationic ring-opening polymerization of bicyclic acetals

This paper deals with sterically controlled propagation in the cationic ring-opening polymerization of bicyclic acetals in relation to the chemical synthesis of structurally regulated polysaccharides, particularly focusing on the following two topics: 1) Chemical synthesis of (1→6)-β-linked polysaccharides by the ring-opening polymerization of 1,6-anhydrosugar derivatives. 2) Asymmetric selective copolymerization of racemic bicyclic acetal with optically active monomer.     

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.     

Energy-efficient manufacturing of polymers with tunable mechanical properties by frontal ring-opening metathesis polymerization

Frontal polymerization (FP) is a process in which the heat generated by the self-reaction transforms monomers to cured polymers. Here, in order to improve the flexibility of polydicyclopentadiene, comonomers (norbornene-terminated polyether, ND-230,400,2000) are designed and synthesized, which can copolymerize with dicyclopentadiene (DCPD) by FP. The polymers (ND) prepared by ND-2000 and DCPD have tunable mechanical properties, from thermosets to elastomers. Specifically, the breaking elongation of the polymers can be varied 69-fold, from 6.1% to 423.4% by controlling the proportion of ND-2000. Among them, ND polymer with 50 wt% ND-2000 has good elastic behavior without yield. And, the reaction mixture solutions of DCPD and ND-2000 have the characteristics of controllable gel time and shear thinning, which make it have the potential of application in additive manufacturing.     

Living cationic ring-opening polymerization by water-stable initiator: synthesis of a well-defined optically active polythiourethane

Living cationic ring-opening polymerization under air and water was achieved using a well-defined water-resistant cationic initiator in dichloromethane without purification at ambient temperature.     

Synthesis,structure and properties of chiral polymers from ring-opening polymerization

Different synthetic methods for the preparation of polymers by ring-opening polymerization with various distribution of enantiomeric units in the macromolecular chain are available. The structure of prepared polymers is determined by ¹H and ¹³C NMR, X-rays diffraction, ORD and CD. Physicochemical and mechanical properties may strongly depend upon the enantiomeric composition of the polymer chain. In several cases racemate mixtures of polyenantiomers form stereocomplexes with enhanced thermal properties.     

Living ring-opening polymerization of cyclic carbonate using cationic zirconocene complex as catalyst

Living ring-opening polymerization of the cyclic carbonate 1,3-dioxepan-2-one was achieved by using the cationic zirconocene complex [Cp₂ZrMe]⁺[B(C₆F₅)₄]⁻ as catalyst at room temperature. A linear relation between conversion and molecular weight of the obtained polymer was observed. Furthermore, block copolymerization of the cyclic carbonate and ε-caprolactone was successfully performed.     

Mechanism of formation of cyclic species in cationic ring-opening polymerization of cyclodimethylsiloxanes

A general feature of the cationic polymerization of all cyclodimethylsiloxanes is the formation of various cyclic products (cyclics) together with that of a linear high polymer. However, the types of cyclics as well as their rate of formation may vary considerably according to the number x of D units ((CH₃)₂SiO units) in the monomer. The case of initiation by trifluoromethanesulfonic (triflic) acid in methylene chloride solution at 20°C has been particularly studied. With D₄, D₅, D₆ and D₇, for which the polymerization rate increases with the size of the ring, all types of cycles D_x are formed in relative amount decreasing with their size ([D₇] < [D₆] < [D₅] < [D₄]). The high polymer final concentration and molecular weight are independent from triflic acid concentration. This may result from a polymerization-depolymerization reaction, involving all the cyclics formed by back-biting reactions occurring with silyl triflates activated by the acid, and leading finally to an equilibrium. The situation with D₃ is completely different. The high polymer (HP) and the cyclics (D_3x multiples of D₃ like D₆, D₉, …) are formed simultaneously under kinetic control. The yields of the various cyclics (formed in amount often larger than that of the HP) are proportional to that of the linear HP. The latter is formed from the beginning of the reaction with a molecular weight proportional to HP yield and inversely proportional to the acid concentration. The opposite role of added water on the polymerization is discussed: an activating effect for D₃, and a desactivating one for D₄, D₅ and D₆. “Copolymerization” experiments between D₃ (or D₄) and tetramethyldisiloxane diol confirmed the effect of water and gave new informations about the occurrence - or absence - of condensation reactions in the mechanism of the growth of the polymer chains. A discussion leads to the conclusion that while the cationic polymerization of D₄ by triflic acid is propagated by activated triflic esters, that of D₃ may also involve the monomer activated by the higher hydrates of the acid and linear oligomeric silanol esters. The latter, formed continuously, may also give the D_3x cyclics by intramolecular heterocondensation.