Ring‐Opening Metathesis Polymerization in Aqueous Media Using a Macroinitiator Approach

Water‐soluble and amphiphilic polymers are of great interest to industry and academia, as they can be used in applications such as biomaterials and drug delivery. Whilst ring‐opening metathesis polymerization (ROMP) is a fast and functional group tolerant methodology for the synthesis of a wide range of polymers, its full potential for the synthesis of water‐soluble polymers has yet to be realized. To address this, we report a general strategy for the synthesis of block copolymers in aqueous milieu using a commercially available ROMP catalyst and a macroinitiator approach. This allows for excellent control in the preparation of block copolymers in water. If the second monomer is chosen such that it forms a water‐insoluble polymer, polymerization‐induced self‐assembly (PISA) occurs and a variety of self‐assembled nano‐object morphologies can be accessed.     

End group transformations of RAFT‐generated polymers with bismaleimides: Functional telechelics and modular block copolymers

End group activation of polymers prepared by reversible addition‐fragmentation chain transfer (RAFT) polymerization was accomplished by conversion of thiocarbonylthio end groups to thiols and subsequent reaction with excess of a bismaleimide. Poly(N‐isopropylacrylamide) (PNIPAM) was prepared by RAFT, and subsequent aminolysis led to sulfhydryl‐terminated polymers that reacted with an excess of 1,8‐bismaleimidodiethyleneglycol to yield maleimido‐terminated macromolecules. The maleimido end groups allowed near‐quantitative coupling with model low molecular weight thiols or dienes by Michael addition or Diels‐Alder reactions, respectively. Reaction of maleimide‐activated PNIPAM with another thiol‐terminated polymer proved an efficient means of preparing block copolymers by a modular coupling approach. Successful end group functionalization of the well‐defined polymers was confirmed by combination of UV–vis, FTIR, and NMR spectroscopy and gel permeation chromatography. The general strategy proved to be versatile for the preparation of functional telechelics and modular block copolymers from RAFT‐generated (co)polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5093–5100, 2008     

A versatile approach for the preparation of end‐functional polymers and block copolymers by stable radical exchange reactions

A versatile strategy for the preparation of end‐functional polymers and block copolymers by radical exchange reactions is described. For this purpose, first polystyrene with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl end group (PS‐TEMPO) is prepared by nitroxide‐mediated radical polymerization (NMRP). In the subsequent step, these polymers are heated to 130 °C in the presence of independently prepared TEMPO derivatives bearing hydroxyl, azide and carboxylic acid functionalities, and polymers such as poly(ethylene glycol) (TEMPO‐PEG) and poly(ε‐caprolactone) (TEMPO‐PCL). Due to the simultaneous radical generation and reversible termination of the polymer radical, TEMPO moiety on polystyrene is replaced to form the corresponding end‐functional polymers and block copolymers. The intermediates and final polymers are characterized by ¹H NMR, UV, IR, and GPC measurements. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2387–2395     

Morphology control in polymeric multiphase systems with block copolymers and structured latexes

Some application possibilities of block copolymers for the morphology control in polymeric multiphase systems are reviewed. The microdomain formation of block copolymers in the solid state is illustrated in the case of functionalized block copolymers and for interpolymer complexes. The preparation of “hairy latex” by emulsion polymerization in the presence of hydrophilic-hydrophobic block copolymers is shown in connection with their applications in the controlled agglomeration process of latexes and for the preparation of polymer particles having microvoids. The surface activity of block copolymers in polymeric oil-in-oil systems is illustrated for silicone oil filled polymers. These materials have a low kinetic friction coefficient and act as reservoir systems with the lubricant incorporated in the polymer matrix.     

Facilitating polymer conjugation via combination of RAFT polymerization and activated ester chemistry

The synthesis of block copolymers via polymer conjugation of well‐defined building blocks offers excellent control over the structures obtained, but often several coupling strategies need to be explored to find an efficient one depending on the building blocks. To facilitate the synthesis of polymers with adjustable functional end‐groups for polymer conjugation, we report on the combination of activated ester chemistry with RAFT polymerization using a chain transfer agent (CTA) with a pentafluorophenyl ester (PFP‐CTA), which allows for flexible functionalization of either the CTA prior to polymerization or the obtained polymer after polymerization. Different polymethacrylates, namely PMMA, P(t‐BuMA) and PDEGMEMA, were synthesized with an alkyne‐CTA obtained from the aminolysis of the PFP‐CTA with propargylamine, and the successful incorporation of the alkyne moiety could be shown via ¹H and ¹³C NMR spectroscopy and MALDI TOF MS. Further, the reactive α‐end‐groups of polymers synthesized using the unmodified PFP‐CTA could be converted into azide and alkyne end‐groups after polymerization, and the high functionalization efficiencies could be demonstrated via successful coupling of the resulting polymers via CuAAC. Thus, the PFP‐CTA allows for high combinatory flexibility in polymer synthesis facilitating polymer conjugation as useful method for the synthesis of block copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A “click” approach to ROMP block copolymers

Amphiphilic block copolymers can be conveniently prepared via convergent syntheses, allowing each individual polymer block to be prepared via the polymerization technique that gives the best architectural control. The convergent “click‐chemistry” route presented here, gives access to amphiphilic diblock copolymers prepared from a ring opening metathesis polymer and polyethylene glycol. Because of the high functional group tolerance of ruthenium carbene initiators, highly functional ring opening metathesis polymerization (ROMP) polymer blocks can be prepared. The described synthetic route allows the conjugation of these polymer blocks with other end‐functional polymers to give well‐defined and highly functional amphiphilic diblock copolymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2913–2921, 2008     

Synthesis of Boc protected block copolymers based on para-hydroxystyrene via NMRP

Nitroxide mediated free radical polymerization (NMRP) was used for the preparation of orthogonally protected block copolymers based on para-hydroxystyrene. The polymers have a low polydispersity and an active chain end. By a series of polymer analogous reactions, a partly deprotected block copolymer was synthesized consisting of a block with unprotected phenolic OH groups and a further block which is protected by the thermolabile Boc group.     

Facile Fabrication of Concentrated Polymer Brushes with Complex Patterning by Photocontrolled Organocatalyzed Living Radical Polymerization

Photocontrolled surface‐initiated reversible complexation mediated polymerization (photo‐SI‐RCMP) was successfully applied to fabricate concentrated polymer brushes with complex patterning structures. Positive‐type patterned polymer brushes were obtained by photo‐SI‐RCMP under visible light (550(±50) nm) using photomasks. A particularly interesting finding was that negative‐type patterned polymer brushes were also obtainable in a facile manner. A nonspecial UV light (250–385 nm) enabled the preparation of pre‐patterned initiator surfaces in a remarkably short time (1 min), leading to negative‐type patterned polymer brushes. Based on this unique selectivity between visible and UV light, the combination of two patterning techniques enabled the preparation of complex patterned brushes, including diblock copolymers, binary polymers, and functional binary polymers, without multistep immobilization of one or more initiators on the surfaces.     

“Clickable” polymers via a combination of RAFT polymerization and isocyanate chemistry

We describe a facile, one‐pot, two‐step polymerization towards synthesizing block co‐polymers bearing reactive isocyanate functional groups. Reversible addition fragmentation chain transfer (RAFT) polymerization is used to mediate the co‐polymerization of isocyanate‐bearing monomers dimethyl meta‐isopropenyl benzyl isocyanate (TMI) and 2‐isocyanatoethyl methacrylate (ICEMA) with styrene and methyl methacrylate (MMA), respectively. ICEMA was incorporated into the polymer at a faster rate than TMI and its unhindered isocyanate group was found to be more reactive than the hindered isocyanate group of TMI. Both the TMI/styrene and the MMA/ICEMA systems maintain the reactivity of the isocyanate functionality, which was exploited by attaching representative hydroxyl‐bearing small and large molecules as well as solid substrates to the block co‐polymers. Thus, we demonstrate the versatility of the block co‐polymer system as a basis for forming branched polymers or as grafts for a solid substrate. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Photoresponsive polymers and block copolymers by molecular recognition based on multiple hydrogen bonds

A new methacrylate containing a 2,6‐diacylaminopyridine (DAP) group was synthesized and polymerized via RAFT polymerization to prepare homopolymethacrylates (PDAP) and diblock copolymers combined with a poly(methyl methacrylate) block (PMMA‐b‐PDAP). These polymers can be easily complexed with azobenzene chromophores having thymine (tAZO) or carboxylic groups with a dendritic structure (dAZO), which can form either three or two hydrogen bonds with the DAP groups, respectively. The supramolecular polymers were characterized by spectroscopic techniques, optical microscopy, TGA, and DSC. The supramolecular polymers and block copolymers with dAZO exhibited mesomorphic properties meanwhile with tAZO are amorphous materials. The response of the supramolecular polymers to irradiation with linearly polarized light was also investigated founding that stable optical anisotropy can be photoinduced in all the materials although higher values of birefringence and dichroism were obtained in polymers containing the dendrimeric chromophore dAZO. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3173–3184     

Design and synthesis of fluorescent shell functionalized polymer micelles for biomedical application

pH‐sensitive polymers can be defined as polyelectrolytes that include in their structure weak acidic or basic groups that either accept or release protons in response to a change in the environmental pH. This work summarizes the design, synthesis, and potential applications of pH‐responsive fluorescent copolymers in the biomedical field. This was achieved using atom transfer radical polymerization (ATRP) of tert‐butyl acrylate using a CuBr/N,N,N′,N″N″‐pentamethyldiethylenetriamine catalyst system in conjunction with an alkyl bromide as the initiator. Well‐defined macroinitiators based on poly(tert‐butyl acrylate) with narrow molecular weight distributions were obtained by the addition of an appropriate solvent system in order to create a homogeneous catalytic system. The addition of n‐butyl acrylate as a second building block in order to create well‐defined poly(tert‐butyl acrylate)‐b‐poly(n‐butyl acrylate) block copolymers (PtBA‐b‐PnBA) followed by chemical modification of the block copolymers and functionalization with an appropriate fluorescent compound are the basis for the preparation of well‐defined fluorescent pH‐sensitive micelles. Thus, prepared water soluble nanosized pH‐sensitive micelles consisting of hydrophobic poly(n‐butyl acrylate) core and hydrophilic polyacrylic acid shell decorated with an appropriate fluorescent compound determined their potential applications of these systems in the field of biomedicine as biosensors, controlled drug delivery systems, and so on. In this respect, the cell viability and internalization of the polymer micelles were studied.     

Synthesis of dual pH/temperature‐responsive polymers with amino groups by living cationic polymerization

For the precision synthesis of primary amino functional polymers, cationic polymerization of a phthalimide‐containing vinyl ether monomer precursor, 2‐vinyloxyethyl phthalimide (PIVE), was examined using a base‐assisting initiating system. Living polymerization of PIVE in CH₂Cl₂ in the presence of 1,4‐dioxane as an added base yielded nearly monodispersed polymers (M_w/M_n < 1.1) and higher molecular weight polymers, which have never been obtained using other initiating systems. Furthermore, block copolymers with hydrophobic or hydrophilic groups could be prepared. The deprotection of the pendant phthalimide groups gave well‐defined pH‐responsive polymers with pendant primary amino groups. Dual‐stimuli–responsive block copolymers having a pH‐responsive polyamine segment and a thermosensitive segment self‐assembled in water in response to both pH and temperature. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1207–1213, 2010     

Some linear and branched macromolecules by ring-opening polymerization

In the first part the ring-opening polymerization of some macrocyclic ether-acetals is briefly described. Of special interest are acetal polymers with functional groups, for instance C=C-double bonds. Appropriate unsaturated monomers and their polymerizability are discussed. The second part deals with the polymerization of oxazolines, substituted in 2- and/or 4-position. Branched polymers are obtained by copolymerization of 2-ethyl-2-oxazoline with 2-hexyl-2-oxazoline or 2-undecyl-2-oxazoline. The properties of the random copolymers and corresponding block copolymers are compared. By a “mixed mechanism technique” a block copolymer composed of a poly(tert -butyl methacrylate) block and a poly(phenyloxazoline) block was prepared. A new initiator system for the polymerization of oxazolines using alkyl chloroformates is introduced. The chloroformate of a trifunctional alcohol led to a three-arm star polymer. Telechelics with two chloroformate endgroups form ABA type block copolymers. Finally four chiral oxazolines are described and the influence of substitution in dioxolanes and oxazolines on the polymerizability is discussed.     

Polysiloxane‐Backbone Block Copolymers in a One‐Pot Synthesis: A Silicone Platform for Facile Functionalization

Block copolymers consisting exclusively of a silicon–oxygen backbone are synthesized by sequential anionic ring‐opening polymerization of different cyclic siloxane monomers. After formation of a poly(dimethylsiloxane) (PDMS) block by butyllithium‐initiated polymerization of D3, a functional second block is generated by subsequent addition of tetramethyl tetravinyl cyclotetrasiloxane (D4^V), resulting in diblock copolymers comprised a simple PDMS block and a functional poly(methylvinylsiloxane) (PMVS) block. Polymers of varying block length ratios were obtained and characterized. The vinyl groups of the second block can be easily modified with a variety of side chains using hydrosilylation chemistry to attach compounds with Si—H bond. Conversion of the hydrosilylation used for polymer modification was investigated.     

Synthesis of bipolar charge transporting block copolymers and characterization for organic light‐emitting diode

A series of hole and electron transporting random and block copolymers consisting of triphenylamine moiety as a hole transporting unit and oxadiazole moiety as an electron transporting unit have been prepared via a nitroxide mediated radical polymerization. Oxadiazole monomers with t‐butyl or trifluoromethyl groups, 2 and 7, respectively, were used for copolymerization. Photoluminescent measurements of polymers revealed that the formation of the exciplex between triphenylamine and oxadiazole units tends to occur in the order of random copolymers, block copolymers, and polymer blends, implying phase‐separated morphologies in block or blend systems. The polymers were applied for OLED devices, and we found that the morphology in the polymer layer critically affected device performance. The block copolymer comprising hole and electron transporting units with the composition of 14/86 showed the highest external quantum efficiency over 10%. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1461–1468, 2010     

Living Cationic Polymerization of Vinyl Ethers through a Photoinduced Radical Oxidation/Addition/Deactivation Sequence

A new photoinitiating system for living cationic polymerization of vinyl ethers is reported. In the current approach, visible‐light irradiation of dimanganese decacarbonyl (Mn₂(CO)₁₀) in the presence of an alkyl bromide results in the formation of carbon‐centered radicals. The photochemically generated radicals were then oxidized by diphenyliodonium ions to the corresponding cations. These cations can add vinyl ether monomers, which are then rapidly deactivated by the bromide anions to give α‐halide functional end groups. Poly(vinyl ether) chains are then grown through successive photoinduced radical oxidation/addition/deactivation (PROAD) in a controlled manner. The living nature of the system is evaluated through kinetics studies and block copolymer formation.     

Graft polymerization of polysilsesquioxane containing chloromethylphenyl groups by atom transfer radical polymerization

Polysilsesquioxane with phenyl and chloromethylphenyl groups (PCPSQ) was prepared readily from phenyltrimethoxysilane and [2‐(chloromethylphenyl)ethyl]trimethoxysilane under acidic conditions. Polymerization with chloromethylphenyl groups on PCPSQ with methyl methacrylate (MMA) was conducted in the presence of a catalytic amount of copper(I) bromide and (−)‐sparteine. Atom transfer radical polymerization yielded a graft polymer (PCPSQ‐g‐MMA) efficiently, and no gelation was observed. The process was also applied to the preparation of graft block copolymers on PCPSQ with several methacrylate monomers. An advantage of the graft hybrid polymers was shown in improved thermal behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4212–4221, 2004     

Coordination polymerization of ω-alkenoates and ω-epoxyalkanoates

As functional polymers have become more and more used, the need for a general synthesis of addition polymers with functional groups became greatly important. We have achieved the polymerization of ω-alkenoates with coordination initiators of the Ziegler-Natta initiation type using titanium trichloride-based transition metal initiators modified with dialkylaluminum chloride. To accomplish this polymerization required that the ω-alkenoates be precomplexed with dialkylaluminum chloride. High molecular weight homopolymers and copolymers with olefins have been obtained. The polymerization of ω-epoxyalkanoates with coordinative anionic polymerization systems based on triethylaluminum/water/acetylacetone (1.0/0.5/1.0) has also been accomplished. Homo- and copolymers of high molecular weight and of relatively narrow molecular weight distribution have been prepared. All polymers and copolymers of functional olefins and epoxides have been characterized and the study of the reactivity of the functional groups attached via a flexible spacer to the polymer main chain has been started. Special attention was given to the classical cationic copolymerization of trioxane with derivatives of ω-epoxyundecanoate to prepare novel functional polyoxymethylenes of potential commercial interest.     

Thermal‐initiating potentialities of poly(methyl methacrylate) peroxide: Metamorphosis of block‐into‐block copolymer and comparative studies on surface texture and morphology

This is the first report concerning the use of vinyl polyperoxide, namely, poly(methyl methacrylate) peroxide (PMMAP), as a thermal initiator for the synthesis of active polymer PMMAP‐PS‐PMMAP by free‐radical polymerization with styrene. The polymerizations have been carried out at different concentrations of macroinitiator PMMAP. The active polymers have been characterized by ¹H NMR, DSC, thermogravimetric analysis, and gel permeation chromatography. PMMAP‐PS‐PMMAP is further used as the thermal macroinitiator for the preparation of another block copolymer, PMMA‐b‐PS‐b‐PMMA, by reacting the active polymers with methyl methacrylate. The block copolymers have been synthesized by varying the concentrations of the active polymers. The mechanism of block copolymers has been discussed, which is also supported by thermochemical calculations. Studies on the surface texture and morphology of the block copolymer of polystyrene (PS) and PMMA material have been carried out using scanning electron microscopy. Furthermore, in this article, a blend of the same constituent materials (PS and PMMA) in proportions (v/v) similar to that contained in block copolymers has been formulated, and the morphology and surface textures of these materials were also investigated. A comparative microscopical evaluation between two processing methods was done for a better understanding of the processing route dependence of the microstructures. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 546–554, 2001     

Synthesis of Block Copolymers by Combination of Atom Transfer Radical Polymerization and Visible Light‐Induced Free Radical Promoted Cationic Polymerization

A new synthetic approach for the preparation of block copolymers by mechanistic transformation from atom transfer radical polymerization (ATRP) to visible light‐induced free radical promoted cationic polymerization is described. A series of halide end‐functionalized polystyrenes with different molecular weights synthesized by ATRP were utilized as macro‐coinitiators in dimanganese decacarbonyl [Mn₂(CO)₁₀] mediated free radical promoted cationic photopolymerization of cyclohexene oxide or isobutyl vinyl ether. Precursor polymers and corresponding block copolymers were characterized by spectral, chromatographic, and thermal analyses.