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.     

Elaboration of corona functionalized regular unimolecular hyperbranched polystyrene nanoparticles

Functional arborescent graft polystyrenes prepared by the “graft-on-graft” technique, involving the iterative grafting of end functional polymer chains onto reactive polymer backbones were synthesized. The zero-generation comb polymers and then the first generation hyperbranched structures were obtained by the coupling reaction of living α-acetal polystyryllithium onto linear or comb chains of poly(chloroethyl vinyl ether) (PCEVE) of controlled D̄P̄_n and structure. Both the PS grafts and the PCEVE reactive backbones were synthesized individually by living polymerization techniques. Initiation of styrene polymerization from acetal functionalized lithium derivatives yield the ω-functionalization of all external polystyrene branches. Derivatization of these acetal branch termini allowed the generation of aldehyde, hydroxyl and carboxyl groups as well as the introduction of functional organic molecules at the periphery of the nanoparticles.     

Cationic RAFT Polymerization Using ppm Concentrations of Organic Acid

A metal‐free, cationic, reversible addition–fragmentation chain‐transfer (RAFT) polymerization was proposed and realized. A series of thiocarbonylthio compounds were used in the presence of a small amount of triflic acid for isobutyl vinyl ether to give polymers with controlled molecular weight of up to 1×10⁵ and narrow molecular‐weight distributions (M_w/M_n<1.1). This “living” or controlled cationic polymerization is applicable to various electron‐rich monomers including vinyl ethers, p‐methoxystyrene, and even p‐hydroxystyrene that possesses an unprotected phenol group. A transformation from cationic to radical RAFT polymerization enables the synthesis of block copolymers between cationically and radically polymerizable monomers, such as vinyl ether and vinyl acetate or methyl acrylate.     

Tailor-made polymers and copolymers from aziridines and 1,3-oxacyclanes

Telechelic poly(tert-butylaziridine)s (polyTBA) and poly(1,3,6-trioxocane)s (polyTOC) and macromonomers were synthesized mainly by living cationic polymerization. Both, molecular weight and end-functionality distributions of polyTOC oligomers and polymers were studied using a combination of HPLC under “critical conditions”, gradient HPLC and SEC with double detection following a preparative HPLC fractionation. Monofunctional and bifunctional polyTBA with various end-groups were synthesized by the end-capping method. Several modification reactions were examined for terminal transformation of polyTBA and polyTOC hydroxy-telechelics into mono- and bifunctional vinyl ether macromonomers. Various tailor-made polymers based on uniform size telechelics and macromonomers were prepared using: 1. polymer-polymer coupling to produce block copolymers; 2. polyaddition of amino-functionalized telechelics to bisacrylamides; 3. addition of amino-polyTBA to polydienes; 4. synthesis of graft copolymers with well-defined graft component and networks.     

From linear side-chain functionalized poly(vinyl ether)s to functional macrocycles

This paper deals with the synthesis of functional polymers of controlled chain dimensions and architecture from poly(chloroalky1 vinyl ether)s. The living polymerization of chloroalkyl vinyl ethers initiated by HX/ZnX₂ systems, and the chemical substitution of the pendant chlorines by various organic functions and groups, in order to generate specific polymer properties are first discussed. Also based on the living character of the polymerizations, the preparation of poly(chloroethyl vinyl ether) with monomacrocyclic and plurimacrocyclic architectures as well as their characterization are then reported. Some evidence for specific host–guest interactions between large organic molecules and polymacrocycles is also presented.     

Synthesis of block and graft copolymers of tetrahydrofuran and cyclic acetals

The polymerization of tetrahydrofuran under a living form allows quantitative functionalisation as well as the formation of copolymers. Cyclic acetal polymerization is more complex but through the “Activated-Monomer Mechanism” approach, it is possible to prepare telechelic polymers as well as block and graft copolymers with particular emphasis concerning amphiphilic ones.     

Design of Well‐Defined Monofunctionalized Poly(3‐hexylthiophene)s: Toward the Synthesis of Semiconducting Graft Copolymers

The post‐functionalization of poly(3‐hexylthiophene) (P3HT) via various synthetic routes is reported. Well‐defined and monofunctionalized ω‐thiol‐terminated P3HT, ω‐carboxylic acid‐terminated P3HT, ω‐acrylate‐terminated P3HT, and ω‐methacrylate‐terminated P3HT are obtained in high yields through a straightforward procedure. From those, different novel P3HT‐based graft copolymers are synthesized following two routes: “grafting onto” and “grafting through” (macromonomer polymerization) methods. The synthesis of three types of graft copolymers is described. Each one has “rod” P3HT‐grafted side chains on a “coil” main chain, which can be polyisoprene, poly(vinyl alcohol), or poly(butyl acrylate). Each copolymer is characterized by size‐exclusion chromatography and NMR.     

Synthesis of new,functionalized poly(butyl vinyl ether) oligomers and novel copolymers containing these materials

This paper reports the synthesis and characterization of new, functionalized poly(alkyl vinyl ether) oligomers, and block copolymers containing poly(alkyl vinyl ether) and poly(methyl methacrylate). Using the HI/ZnI₂ initiating system in nonpolar solvents (hexane, toluene) at −20°C, both monofunctional and difunctional poly(alkyl vinyl ether) oligomers of predicted molecular weights precisely terminated with aldehyde, primary hydroxyl and ester endgroups have been prepared. Novel diblock copolymers comprised of poly(methyl methacrylate) and poly(butyl vinyl ether) have also been synthesized using a combination of living cationic and living group transfer polymerization.     

Conducting Block Copolymer Nanowires Containing Regioregular Poly(3‐Hexylthiophene) and Polystyrene

Grignard Metathesis polymerization (GRIM) for the synthesis of regioregular poly(3‐alkylthiophenes) proceeds via a “living” chain growth mechanism. Due to the “living” nature of this polymerization regioregular poly(3‐alkylthiophenes) with predetermined molecular weight, narrow molecular weight distributions and desired chain end functionality are now readily available. Allyl terminated poly(3‐hexylthiophene) was successfully used as a precursor for the synthesis of di‐block copolymers containing polystyrene. The addition of “living” poly(styryl)lithium to the allyl terminated regioregular poly(3‐hexylthiophene) generated the di‐block copolymer. Poly(3‐hexylthiophene)‐b‐polystyrene was also synthesized by atom transfer radical polymerization. Integration of poly(3‐hexylthiophene) in di‐block copolymers with polystyrene leads to the formation of nanowire morphology and self‐ordered conducting nanostructured materials.     

Preparation and properties of poly(alkyl vinyl ether-2-ethyl-2-oxazoline) diblock copolymers

A method for the synthesis of well-defined poly(alkyl vinyl ether–2-ethyl-2-oxazoline) diblock copolymers with hydrolytically stable block linkages has been developed. Monofunctional poly(alkyl vinyl ether) oligomers with nearly Poisson molecular weight distributions were prepared via a living cationic polymerization method using chloroethyl vinyl ether together with HI/ZnI₂ as the initiating system and lithium borohydride as the termination reagent. Using the resultant chloroethyl ether functional oligomers in combination with sodium iodide as macroinitiators, 2-ethyl-2-oxazoline was polymerized in chlorobenzene/NMP to afford diblock copolymers. A series of poly(methyl vinyl ether–2-ethyl-2-oxazoline) diblock materials were found to have polydispersities of ≈ 1.3–1.4 and are microphase separated as indicated by two T_g's in their DSC thermograms. These copolymers are presently being used as model materials to study fundamental parameters important for steric stabilization of dispersions in polar media. © 1993 John Wiley & Sons, Inc.     

Thermoresponsive NIPAM block copolymers containing densely grafted poly(vinyl ether) brushes synthesized by a combination of living cationic polymerization and RAFT polymerization

Diblock copolymers consisting of a multibranched polymethacrylate segment with densely grafted poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] pendants and a poly(N‐isopropylacrylamide) segment were synthesized by a combination of living cationic polymerization and RAFT polymerization. A macromonomer having both a poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] backbone and a terminal methacryloyl group was synthesized by living cationic polymerization. The sequential RAFT copolymerizations of the macromonomer and N‐isopropylacrylamide in this order were performed in aqueous media employing 4‐cyanopentanoic acid dithiobenzoate as a chain transfer agent and 4,4′‐azobis(4‐cyanopentanoic acid) as an initiator. The obtained diblock copolymers possessed relatively narrow molecular weight distributions and controlled molecular weights. The thermoresponsive properties of these polymers were investigated. Upon heating, the aqueous solutions of the diblock copolymers exhibited two‐stage thermoresponsive properties denoted by the appearance of two cloud points, indicating that the densely grafted poly[2‐(2‐methoxyethoxy)ethyl vinyl ether] pendants and the poly(N‐isopropylacrylamide) segments independently responded to temperature. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Atomic force microscopy imaging and dilute solution properties of cyclic and linear polystyrene combs

Large macrocyclic poly(chloroethyl vinyl ether)s (PCEVE)s of controlled ring size and narrow distribution were synthesized by a ring-closure process involving the intramolecular formation of acetal linkages between the two external blocks of linear ABC triblock precursors prepared by living cationic polymerization. The corresponding shape-persistent ring P(CEVE-g-PS) combs having macrocyclic poly(chloroethyl vinyl ether) backbones and polystyrene side chains were then synthesized by a "grafting onto" technique and characterized by size exclusion chromatography (SEC) analysis and atomic force microscopy (AFM) imaging of isolated molecules. Quantitative hydrolysis of the acetal linkages of the macrocyclic PCEVE backbone in acidic conditions yields the linear poly(chloroethyl vinyl ether)-g-polystyrene) homologue and allows a direct comparison of the characteristics and dimensions of cyclic and linear comb architecture. The influence of the chain architecture and PS graft dimensions on the dilute tetrahydrofuran (THF) solution properties, radius of gyration, and hydrodynamic radius of the comb copolymers is also studied and compared to data reported for linear and cyclic polystyrene chains.     

Synthesis of poly(vinyl ether)‐based,ABA triblock‐type thermoplastic elastomers with functionalized soft segments and their gas permeability

The ABA‐type triblock copolymers consisting of poly(2‐adamantyl vinyl ether) [poly(2‐AdVE)] as outer hard segments and poly(6‐acetoxyhexyl vinyl ether) [poly(AcHVE)], poly(6‐hydroxyhexyl vinyl ether) [poly(HHVE)], or poly(2‐(2‐methoxyethoxy)ethyl vinyl ether) [poly(MOEOVE)] as inner soft segments were synthesized by sequential living cationic polymerization. Despite the presence of polar functional groups such as ester, hydroxyl, and oxyethylene units in their soft segments, the block copolymers formed elastomeric films. The thermal and mechanical properties and morphology of the block copolymers showed that the two polymer segments of these triblock copolymers were segregated into microphase‐separated structure. Effect of the functional groups in the soft segments on gas permeability was investigated as one of the characteristics of the new functional thermoplastic elastomers composed solely of poly(vinyl ether) backbones. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1114–1124     

Poly(vinyl ethers) as building blocks for new materials

The living cationic polymerization of vinyl ethers has been used to prepare a number of new polymers with special properties. Sequential polymerization of the hydrophilic methyl vinyl ether (MVE) and the hydrophobic octadecyl vinyl ether (ODVE) has lead to amphiphilic block-copolymers with emulsifying properties for water/decane mixtures. Poly(vinyl-ether) macromonomers were obtained by end-capping of living polymers with hydroxyethyl acrylate. Copolymerization of polyODVE-macromonomer with usual acrylates lead to highly branched hydrophobic polymers. When the end-capping was performed with bifunctionally living polymers, the corresponding “bis-macromonomers” were obtained. Copolymerization of such bis-macromonomers with styrene or butyl acrylate, leads to the formation of segmented polymer networks. In the case of polyODVE-poly(butyl acrylate), these networks showed a pronounced phase separation. Due to the crystallinity of the polyODVE domains, these materials showed shape memory properties.     

Synthesis and properties of amphiphilic vinyl acetate triblock copolymers prepared by copper mediated living radical polymerisation

Polymerisation of vinyl acetate by conventional free radical polymerisation using a diazo initiator followed by copper mediated living radical polymerisation with a range of monomers was studied. This method led to the synthesis of triblock copolymers. We have thus successfully prepared several new ABA triblock copolymers where B is poly(vinyl acetate) and A is (dimethylamino)ethyl methacrylate (DMAEMA), (polyethylene glycol) methyl ether methacrylate (MeO(PEG)MA) or solketal methacrylate (SMA). The sequential conventional/living radical polymerisation approach provided an efficient route to synthesis of new block copolymers. The properties of these amphiphilic polymers have been subsequently investigated by ¹H NMR, fluorescence spectroscopy, tensiometry and dynamic light scattering to investigate their behaviour as potential surfactants.     

Investigation of the influence of the architectures of poly(vinyl pyrrolidone) polymers made via the reversible addition–fragmentation chain transfer/macromolecular design via the interchange of xanthates mechanism on the stabilization of suspension polymerizations

Linear, star, and block copolymers based on poly(vinyl pyrrolidone) (PVP) were synthesized with the macromolecular design via the interchange of xanthates (MADIX) process for use as potential stabilizers in suspension polymerization. The design of the leaving group of the dithioxanthate‐based transfer agent was shown to be key to the successful preparation of well‐defined PVP architectures. A linear correlation of the monomer conversion and molecular weight was found in the synthesis of star polymers, whereas the molecular weight distribution remained narrow (polydispersity index < 1.3). Significant side reactions, which typically broaden the molecular weight distribution when R‐designed MADIX agents are used, were absent. The living behavior of the PVP polymerization was furthermore confirmed via chain extension with vinyl acetate, which resulted in the formation of PVP–PVAc block copolymers [where PVAc is poly(vinyl acetate)]. The prepared polymers were used as stabilizers in suspension polymerization to prepare crosslinked poly(vinyl neodecanoate)/ethylene glycol dimethacrylate microspheres. The ratio of the interfacial tension of the aqueous and monomer phases and the overall viscosity were found to have an effect on the diameter of the particles, with PVP star polymers as stabilizers resulting in smaller particles. A smaller interfacial tension, measured when star polymers and block copolymers were used, resulted in the appearance of smaller particles, probably because of more breakup events of the monomer droplets and the enhanced stabilization of the particle surface area. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4372–4383, 2006     

Novel synthesis of photocrosslinkable polymers

A new preparative route to photocrosslinkable polymers in which the polymers are produced directly from the polymerization of vinyl monomers having photocrosslinkable groups has been investigated. The photosensitive resins thus produced have higher sensitivity and resolution than conventional photosensitive resins. The monomers were synthesized from the esterification of vinylphenols or vinyl β-chloroethyl ether with cinnamic acid, β-styrylacrylic acid, and their homologs, and from the etherification of vinyl β-chloroethyl ether with hydroxychalcones. Homopolymerizations of these monomers and their copolymerizations with other comonomers were investigated with the use of both radical and ionic initiators. It is shown that radical polymerization of the monomers gave soluble polymers only at low conversion. Anionic initiators did not initiate polymerization. Cationic polymerization imparted soluble polymers in high yield, except for the monomers bearing cyano groups, which generally gave insoluble polymers. Infrared and NMR spectroscopic investigation of the cationically obtained soluble polymers and comparative investigation by cationic polymerization of model compounds indicated that polymerization of the monomers proceeds through the vinyl double bond without affecting the photosensitive unsaturated bond. Thus, linear photocrosslinkable polymers with an intact photoreactive group may be produced by cationic polymerization. In general, these polymers have uniform structure and modifiable physical properties depending on the monomer used. The polymer thus obtained from β-vinyloxyethyl cinnamate has been shown to have excellent properties for use as a photo-resist.     

Self‐polyaddition of hydroxyalkyl vinyl ethers

With tetrahydrofuran as a solvent and pyridium p‐toluenesulfonate as a catalyst, the hydroxyalkyl vinyl ethers 2‐hydroxyethyl vinyl ether (2E), 4‐hydroxybutyl vinyl ether (4B), and 6‐hydroxyhexyl vinyl ether (6H) underwent step‐growth self‐polyaddition, generating polymers with an acetal main‐chain structure. The molecular weight of the resulting polymers increased gradually during the initial polymerization period at room temperature. However, decomposition occurred after about 22–24 h, and the presence of a large amount of catalyst accelerated the latter process. The three monomers exhibited different polymerization capabilities. In contrast to the smooth polymerization of 6H, cyclization side reactions usually took place during the polymerizations of 4B and 2E, which resulted in low polymer yields and low molecular weights because of the formation of unreactive small cyclic acetals. In the self‐polyaddition of 4B, this side reaction was greatly restricted at high concentrations of the monomer. Higher temperatures (60–70 °C) remarkably accelerated the self‐polyaddition process to produce polymers with high molecular weights. However, the polymerizations at high temperatures had to be terminated within about 2 h to avoid the severe decomposition of the polymers. Copolymers were also obtained via the copolyaddition of any two of the monomers. The easiness of the incorporation of the monomers into the copolymers was in the sequence 6H > 4B > 2E. Poly(6H), poly(4B), poly(2E), and the copolymers possessed different hydrophilicities and were stable in basic, neutral, and even weak acidic media but exhibited degradation in the presence of a strong acid. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3751–3760, 2000     

Recent developments in living cationic polymerization

Scope and limitation of the vinyl ether polymerization initiated by NR₄ClO₄(KClO₄;LiClO₄)/CH₃CHI-OR was discussed. Besides isobutyl vinyl ether (IBVE), N-vinylcarbazole (NVC) and 2-chloroethyl vinyl ether (CEVE) were initiated by NR₄ClO₄/CH₃CHI-OR. These polymerizations exhibited the characteristics of a living polymerization. However, in order to observe narrow molar mass distribution NVC was initiated with CH₃CHI-OR, without salts. Block copolymers were synthesized by the method of sequential monomer addition (NVC, IBVE, CEVE). The PCEVE segment was modified by nucleophilic substitution, which allowed the synthesis of amphiphilic block copolymers.     

New polymer structures based on vinyl ether polymerization

Sequential living cationic polymerization of octadecyl vinyl ether (ODVE) and methyl vinyl ether (MVE) was used for the preparation of amphiphilic ABA‐type block copolymers. The polymerization of ODVE was initiated with the trimethyl silyl iodide/1,1,3,3‐tetramethoxy propane/ZnI₂ system at 0°C in toluene. The living bifunctional polyODVE thus obtained was used as initiator for the polymerization of MVE. Below the LCST of polyMVE (37°C), the copolymers are amphiphiles. Above the LCST of polyMVE, the polyMVE‐blocks become hydrophobic and the amphiphilic nature of the block copolymer is lost. This was demonstrated by using the block copolymers as emulsifiers for water/decane mixtures. The emulsions were stable for several hours at room temperature, while the emulsion stability decreased to about 30 seconds at 40°C. PolyMVE‐α,ω‐bis‐methacrylates were obtained by end‐capping of living bifunctional polyMVE with 2‐hydroxyethyl methacrylate (HEMA). Copolymerization of these bis‐macromers with HEMA leads to segmented networks. The networks showed a reversible swelling/deswelling behavior in water as a function of temperature. This is caused by a change of the hydrophilicity of the polyMVE segments in the networks. Hexa(chloromethyl)melamine, combined with zinc chloride was found to be an efficient hexafunctional initiator for the living cationic polymerization of vinyl ethers. This simple initiating system opens new ways for the synthesis of endgroup‐functionalized star‐shaped poly(vinyl ethers).