Reactive Chain Ends Research Articles

Star and Hyperbranched Polyisobutylenes via Terminally Reactive Polyisobutylene‐Polystyrene Block Copolymers

AbstractUnique, highly branched polyisobutylenes (PIB) were prepared via quasiliving carbocationic copolymerization of isobutylene and styrene (St) monomers. The junction points were formed by Friedel‐Crafts self alkylation of PSt segments by the carbocationic chain ends. First, linear PIB was prepared with reactive chain ends. This was reacted with St monomer to form PIB‐b‐PSt AB, and PSt‐b‐PIB‐b‐PSt ABA type triblock copolymers with reactive carbocationic chain ends. The terminal carbonations react with the phenyl group of the polystyrene end‐segments of the block copolymers leading to chain coupling, and thus PIB star polymers in the case of AB and hyperbranched PIB from ABA block copolymers. The resulting branched polymers were characterized and the branch formation was confirmed by gel permeation chromatography (GPC) and proton nuclear magnetic resonance spectroscopy (1H NMR).

On a novel method to synthesize POSS-based hybrids: An example of the preparation of TPU based system

A novel method to prepare polymer/polyhedral oligomeric silsesquioxanes (POSS) hybrids by melt reactive blending is proposed in this paper, by the controlled polymer chain scission and reaction of chain ends with functional silsesquioxanes. Application to thermoplastic polyurethanes (TPU) is addressed, taking advantage of the polyurethane chain scission equilibrium reaction, leading to the formation of highly reactive isocyanate and hydroxyl chain ends. Despite the isocyanate chemistry has been widely studied for the preparation of polymer/POSS hybrids by in situ copolymerisation, the exploitation of similar chemical processes in an industrially viable and environmental friendly melt blending process is currently an open research field. In this work, the reaction in the molten state of dihydroxyl-functionalised POSS with the polyurethane chain is demonstrated to produce a TPU/POSS hybrids. The effect of POSS concentration on nanomorphol- ogy, thermal properties and surface properties is studied, showing significant changes compared to pristine TPU. In partic- ular, an increase of glass transition temperature is observed in the presence of reactive POSS (!T up to about 10°C in the presence of 10 wt% loading). Furthermore, an increase of surface water wettability, evidenced by the decrease of water contact angle from 95° for pristine TPU to 70° in TPU containing 10wt% of reactive POSS, is found.

Well‐defined poly(oxazoline)‐b‐poly(acrylate) amphiphilic copolymers: From synthesis by polymer–polymer coupling to self‐organization in water

AbstractIn this contribution, we report on the self‐assembly in water of original amphiphilic poly(2‐methyl‐2‐oxazoline)‐b‐poly(tert‐butyl acrylate) copolymers, synthesized by copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction. For such purpose, (poly(2‐methyl‐2‐oxazoline)) and (poly(tert‐butyl acrylate)) are first prepared by cationic ring‐opening polymerization and atom transfer radical polymerization, respectively. Well‐defined polymeric building blocks, ω‐N3‐P(t‐BA) and α‐alkyne‐P(MOx), bearing reactive chain end groups, are accurately characterized by matrix‐assisted laser desorption ionization time‐of‐flight spectroscopy. Then, P(MOx)n‐b‐P(t‐BA)m are achieved by polymer–polymer coupling and are fully characterized by diffusion‐ordered NMR spectroscopy and size exclusion chromatography, demonstrating the obtaining of pure amphiphilic copolymers. Consequently, the latter lead to the formation in water of well‐defined monodisperse spherical micelles (RH = 40–60 nm), which are studied by fluorescence spectroscopy, static light scattering, atomic force microscope, and transmission electronic microscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Macromol. React. Eng. 11/2012

Cover: Living anionic polymerization of tert-butyl acrylate in the presence of LiCl using a flow microreactor system can be conducted at −20 °C. The subsequent reaction of a reactive polymer chain end with an alkyl methacrylate in an integrated flow microreactor system leads to the formation of a block copolymer. Further details can be found in the article by A. Nagaki, Y. Takahashi, K. Akahori, and J. Yoshida* on page 467.

Living Anionic Polymerization of tert‐Butyl Acrylate in a Flow Microreactor System and Its Applications to the Synthesis of Block Copolymers

AbstractLiving anionic polymerization of tert‐butyl acrylate initiated by 1,1‐diphenylhexyllithium is conducted in a flow microreactor system in the presence of lithium chloride. A high degree of control over the molecular weight distribution is achieved under easily accessible conditions, for example at −20 °C. The subsequent reaction of a reactive polymer chain end with an alkyl methacrylate in an integrated flow micoreactor system leads to the formation of a block copolymer with a narrow molecular weight distribution. magnified image

Tracing a Moving Thin-Film Reaction Front with Nanometer Resolution

X-ray standing waves at grazing incidence are used to trace the position of the reactive chain ends of a surface-initiated (via protons in the underlying PEDOT:PSS layer) polymerization in a bulk polymer film, a procedure recently used to realize insoluble functional films for mutlilayer organic light-emitting diodes. The reactive chain ends as well as their respective counterions are found within a few nanometers thin layer, which moves away from the surface as the reaction proceeds. This reactive front remains narrow for polymerized films that are significantly thicker than the front width. This result can be rationalized by assuming that all oxetane units in contact with the PEDOT:PSS are initiated before the reaction proceeds at elevated temperature.

Selective Chain-End Postpolymerization Reactions and Property Tuning of a Highly Conjugated and All-Thiophene Polyazomethine

A highly conjugated polyazomethine (3) consisting uniquely of thiophenes was investigated for sustaining postpolymerization property tuning. This was courtesy of the ever-present and reactive amino and aldehyde chain ends. Subjecting the polymer to polymerization conditions in the absence of monomers resulted in a DPn increase from 15 to 70. The aldehyde chain end was selectively reacted with an aliphatic amine by undergoing reductive amination with sodium triacetoxyborohydride (NaBH(OAc)3) while the imines along the conjugated polymer framework remained intact. This illustrates the robustness of the azomethine bond. Reductive amination of 3 with a monofunctional amine resulted in selective chain-end capping and prevented repolymerization. 3 was resistant to dynamic component exchange and monomer shuffling as a result of its high degree of conjugation. Conversely, chain extension was possible both by reductive amination with an α−ω-diamine and by reheating the polymer. Covalent attachment of two separate segments of 3 was possible by reductive amination with a 2:1 polymer/α−ω-diamine stoichiometry. This resulted in molecular weight doubling and serves to illustrate the possibility of multiblock tethering via the ever-active chain ends. Meanwhile, a 1:1 polymer/α−ω-diamine stoichiometry gave rise to a polymer with an aliphatic and aromatic amine functionalized at either chain end. As a result of the noncomplementary of the two chain ends, the polymer could not be repolymerized. However, it exhibited consistent molecular weight under various repolymerization reaction conditions indicating the robustness of the heteroconjugated bonds and their tolerance toward dynamic component exchange. The color of 3 was also changed from its inherent blue color to green via the covalent attachment of a yellow dansyl derivative by reductive amination at the aldehyde chain end. The collective property modification including repolymerization, coblock tethering, color modification, and increased degree of polymerization presenting unequivocal evidence that polyazomethines are capable of undergoing postpolymerization property tailoring.

Anionic polymerization of alkyl methacrylates using flow microreactor systems

Living anionic polymerization of alkyl methacrylates initiated by 1,1-diphenylhexyllithium was conducted in a flow microreactor system. A high level of molecular-weight distribution control was achieved under easily accessible conditions, such as at −28°C (MMA: Mw/Mn=1.16), 0°C (BuMA: Mw/Mn=1.24) and 24°C (ButMA: Mw/Mn=1.12). The molecular weight (Mn) increased with an increase in the monomer/initiator ratio. The subsequent reaction of a reactive polymer chain end with a second alkyl methacrylate in integrated flow micoreactor systems led to the formation of a block copolymer having narrow molecular-weight distribution.

Structural, mechanical and osmotic properties of injectable hyaluronan-based composite hydrogels

The osmotic and scattering properties of hyaluronan-based composite hydrogels composed of stiff biopolymer chains (carboxymethylated thiolated hyaluronan (CMHA-S)) crosslinked by a flexible polymer (polyethylene glycol diacrylate (PEGDA)) are investigated and analyzed in terms of the scaling theory. The total pre-gel polymer weight concentration is varied between 0.5wt.% and 3.2wt.%, while the mole ratio between the reactive PEG chain ends and the thiolated HA moieties is changed between 0.15 and 1.0. The shear modulus G of the fully-swollen gels exhibits a stronger dependence on pre-gel concentration than on the crosslink density. Osmotic deswelling measurements reveal that the osmotic mixing pressure depends on the weight ratio CMHA-S/PEGDA, and is practically unaffected by the pre-gel concentration. Small-angle neutron scattering observations indicate that the thermodynamic properties of these composite gels are governed by total polymer concentration, i.e., specific interactions between the two polymeric components do not play a significant role.

PEGylated Chromatography: Efficient Bioseparation on Silica Monoliths Grafted with Smart Biocompatible Polymers

Novel oligo(ethylene glycol)-based thermoresponsive stationary phases have been studied for the separation of bioanalytes. Well-defined copolymers of (2-methoxyethoxy)ethyl methacrylate and oligo(ethylene glycol) methacrylate were synthesized by atom-transfer radical polymerization in the presence of an N-succinimidyl-functionalized initiator. The reactive chain ends of these copolymers were then reacted with amino-functionalized silica monoliths. The formed composites were studied as chromatography materials. For instance, it was demonstrated that thermoresponsive oligo(ethylene glycol)-based stationary phases allow rapid, efficient separation of steroid and protein mixtures in pure water under isocratic high-performance liquid chromatographic elution.

Reactions Occurring during the Melt Mixing of Nylon 6 and Oxazoline−Cyclophosphazene Units

Specific reactions of amino and carboxyl end groups of Nylon 6 with the reactive oxazoline groups belonging to a cyclophosphazene compound (referred as CP2OXA) were carried out at 240 °C for different times, under inert atmosphere. Ny6 polymers terminated with one specific reactive chain end (−COOH or NH2) were reacted with different amounts of CP2OXA to study the kinetic order of the reactions. All Ny6−CP2OXA reacted products soluble in trifluoroethanol (TFE) were well characterized by MALDI−TOF MS, FT-IR and (1H and 13C) NMR techniques. The MALDI−TOF results show that the oxazoline rings react with the carboxyl chain ends of Ny6 following second-order kinetics. The reactions with amino chain ends are very fast and high amounts of gels are produced in just 5 min heating, whereas traces of gel are formed when Ny6COOH and CP-2OXA are reacted for 60 min. The gels were characterized by FTIR analyses, and also by MALDI−TOF MS after partial acid hydrolysis. MALDI−TOF mass spectra reveal also that oxazoline rings can react with −NH amide groups along the Ny6 chains, and with secondary amino groups formed by a condensation reaction involving the elimination of ammonia from two amino chain ends. These side reactions could be responsible of the formation of the gels. The polymerization of CP2OXA was also observed, and the oligomers formed could also react with Ny6 samples during the melt mixing.

A General Methodology Toward Drug/Dye Incorporated Living Copolymer−Protein Hybrids: (NIRF Dye-Glucose) Copolymer−Avidin/BSA Conjugates as Prototypes

Azide-terminated poly(tert-butyl acrylate) was synthesized via atom transfer radical polymerization (ATRP). Subsequent deprotection was performed to yield poly(acrylic acid) (PAA) possessing a reactive chain-end. A one-pot sequential amidation of the PAA with the amine derivatives of a near-infrared fluorescent dye (ADS832WS) and glucose produced NIRF dye-incorporated water-soluble copolymers. End-group modifications were performed to produce alkyne/biotin-terminated copolymers which were further employed to generate dye-incorporated polymer-protein hybrids via the biotin-avidin interaction with avidin or "click" bioconjugation with azide-modified BSA. We have overcome two fundamental limitations in the synthesis of bioconjugates: (a) the basic restriction in the diversity of copolymers which can be synthesized for producing bioconjugates, (b) the limitation in the number of dyes/drug molecules that can be attached per protein molecule. The copolymers possessed enhanced optical properties compared to the dye due to increased solubility in water. Potential utility of these copolymers and conjugates in multiwell plate based assays, cell surface imaging and in vivo animal imaging were explored.

Efficient synthesis of dendrimers via a thiol–yne and esterification process and their potential application in the delivery of platinum anti-cancer drugs

A combination of thiol-yne chemistry and esterification reactions were successfully applied for the preparation of dendrimers with an array of terminal functionalities via the divergent growth strategy; maximizing the number of reactive chain ends whilst minimizing the number of reaction steps required in the process.

Transition in Domain Morphology of Block Copolymers Undergoing Polymerization

We have studied the dynamics of a morphology transition of domains in a reactive system composed of A−B block copolymer and B monomer, where polymerization occurs at the end of the B subchain of the block copolymer. We propose a new dynamical model for reactive phase separation, where the chain architecture, the chain conformation, and the spatial distribution of the reaction points (reactive chain ends) are taken into account by the use of random phase approximation. Our model is essentially equivalent to the dynamical self-consistent field theory if the system is close to the critical point, but it has an enormous improvement in the computational efficiency. Simulation results show that our modeling is quite useful partially because the inhomogeneity of the spatial distribution of the reactants affects the polymerization and partially because we can perform large-scale and long time simulations because of the high efficiency of our model. We found that as a result of the competition between the phase separation and the polymerization the system shows complex nonequilibrium domain structures that depend on the kinetic pathway of the phase separation and the polymerization.

Synthesis and characterization of hyperbranched polymers with increased chemical versatility for imprint lithographic resists

AbstractHyperbranched polymers were prepared from a variety of mono‐ and difunctional monomers and used in the development of novel UV‐imprint lithography (UV‐IL) resists. The unique physical and chemical properties of these hyperbranched materials significantly increase the range of molecular systems that could be imprinted. Traditional challenges, such as the use of monomers that have low boiling points or the use of insoluble/highly crystalline momomers, are overcome by the preparation of hyperbranched polymers that incorporate these repeat units. In addition, the low viscosity of the hyperbranched macromolecules and the large number of reactive chain ends overcome many difficulties that are traditionally associated with the use of polymeric materials as imprint resists. Hyperbranched polymers containing up to 12 mol % pendant vinyl groups, needed for secondary crosslinking during imprinting, were prepared with a wide range of repeat unit structures and successfully imprinted with features from tens of microns to ∼ 100 nm. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6238–6254, 2008

Cure reaction and phase separation behavior of cyanate ester‐cured epoxy/polyphenylene oxide blends

AbstractThe cure reaction and phase separation mechanism of a cyanate ester‐cured epoxy and its blends with polyphenylene oxide (PPO) were studied. An autocatalytic mechanism was observed for the epoxy and its blends. The reaction rate of the blends was higher than that of the neat epoxy at initial stage; however, the reached conversion decreased with PPO content. FTIR analysis revealed that the cyanate functional group reactions were accelerated by adding PPO and indicated that several coreactions have occurred. This was caused by the reaction of cyanate ester with the PPO reactive chain ends. But at a later stage of cure, the reaction could not progress further due to diffusional limitation of PPO. To understand the relationship between the cure kinetics and phase separation of the blends, the morphology of the blends during cure was examined. When the homogeneous epoxy/PPO blends with low PPO content (10 phr) were cured isothermally, the blends were separated by nucleation and growth (NG) mechanism to form the PPO particle structure. But at high PPO content (30 phr), the phase separation took place via spinodal decomposition (SD). SD is favored near critical concentration and high cure rate system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1139–1145, 2006

Design and Synthesis of N-Maleimido-Functionalized Hydrophilic Polymers via Copper-Mediated Living Radical Polymerization: A Suitable Alternative to PEGylation Chemistry

A series of alpha-functional maleimide polymethacrylates (M(n) = 4.1-35.4 kDa, PDi = 1.06-1.27) have been prepared via copper-catalyzed living radical polymerization (LRP). Two independent synthetic protocols have been successfully developed and the polymers obtained in multigram scale, with an 80-100% content of maleimide reactive chain ends, depending on the method employed. A method for the synthesis of amino-terminated polymers, starting from Boc-protected amino initiators, has also been developed, as these derivatives are key intermediates in one of the two processes studied in the present work. The alternative synthetic pathway involves an initiator containing a maleimide unit "protected" as a Diels-Alder adduct. After the polymerization step, the maleimide functionality has been reintroduced by retro-Diels-Alder reaction, by simply refluxing those polymers in toluene for 7 h. These maleimido-terminated materials, poly(methoxyPEG((475))) methacrylates and poly(glycerol) methacrylates, differ for both the nature and size of the polymer side branches and showed an excellent solubility in water, a property that made them an ideal candidate for the synthesis of new polymer-(poly)peptide biomaterials. These functional polymers have been successfully employed in conjugation reactions in the presence of thiol-containing model substrates, namely, reduced glutathione (gamma-Glu-Cys-Gly) and the carrier protein, bovine serum albumin (BSA), in 100 mM phosphate buffer (pH 6.8-7.4) and ambient temperature.

Room-Temperature Free-Radical-Induced Polymerization of 1,1‘-(Methylenedi-1,4-phenylene)bismaleimide via a Novel Diphenylquinoxaline-Containing Hyperbranched Aromatic Polyamide

Two new diphenylquinoxaline-containing AB2 monomers, 2,3-bis(4-aminophenyl)quinoxaline-6-carboxylic acid, 5, and 2,3-bis[4-(4-aminophenoxy)phenyl]quinoxaline-6-carboxylic acid, 9, were prepared and polymerized via the Yamazaki reaction to form the hyperbranched aromatic polyamides (designated as II and III, respectively) with −NH2 as the reactive chain-end groups. Although these AB2 monomers and their respective hyperbranched polymers are structurally similar except for the presence of a p-phenyloxy spacer between the quinoxaline and p-aminophenyl segments in 9 and III, the physical and chemical properties of both monomers and hyperbranched polymers are distinctly different. It is believed that the tautomerism in 5 and II is likely the basis for these differences. Since III was only marginally soluble in polar aprotic solvents in which II readily dissolved, a known, soluble hyperbranched polyamide (I) was prepared from 3,5-bis(4-aminophenyloxy)benzoic acid for comparison purposes in a subsequent blends study. The curing behaviors and thermal properties of the hyperbranched polyamides I and II blended in 0.75−3.75 wt % with a common bismaleimide [1,1‘-(methylenedi-4,1-phenylene)bismaleimide, BMI] resin were studied with differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy. Whereas the DSC results indicated that I reacted normally with BMI in a Michael-addition fashion, followed by homopolymerization of the excess BMI, II appeared to be able to initiate free radical polymerization of BMI at room temperature after co-dissolution with BMI in N-methyl-2-pyrrolidinone. The DSC results of the BMI/II blends indicated that, at ≥1.5 wt % of II, no exotherm attributable to the thermal curing of BMI was detected. Electron spin resonance (ESR) experiments confirmed that the parmagnetic species present in II were more reactive toward BMI in solution at room temperature than the radical detected in I. This unique property of II to initiate room-temperature radical polymerization of BMI makes it important as a prototype for the development of low-temperature, thermally curable thermosetting resin systems for high-temperature applications.

Synthesis and Properties of Poly[N-(2-Hydroxypropyl) Methacrylamide] Conjugates of Superoxide Dismutase

The synthesis of N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers and semi-telechelic polymers (PHPMA) conjugates superoxide dismutase (SOD) is described. The polymer was conjugated with SOD by means ofnondegradable or degradable oligopeptide spacers randomly distributed along the polymer backbone. A second type ofconjugation, to a semi-telechelic polymer, poly(HPMA), (PHPMA) containing reactive chain end groups, with the SOD amino groups formed star structures. Physicochemical properties of the conjugates, such as temperature stability and stability to oxidation with hydrogen peroxide, were studied and compared to native SOD; an increase in temperature stability by the conjugates and an increase in stability towards oxidation with hydrogen peroxide was observed. The in vivo biological evaluation of PHPMA–SOD conjugates showed a significant decrease in immunogenicity compared to free SOD. A preliminary in vivo study of ischemic/reperfusion injury, revealed significantly more pronounced protective effects by PHPMA–SOD conjugates in comparison with the free SOD.

Poly(ether sulphone) copolymers with novel reactive chain-ends

This paper describes the synthesis of new model compounds and copolyether sulphones with different reactive chain-ends from the OH and NH 2 ends which are well documented for this type of polymer. These materials were characterised by 1H NMR, Fourier transformed infrared (FTIR) spectroscopy and elemental analysis. They are seen to have potential applications both in the chain-extension of low molecular weight thermoplastics and in the preparation of well-defined block copolymers.