Fate of excited probes in micellar systems

This article presents studies on the photophysical and photochemical behavior of probes within micellar systems: organized emulsifier/polymer aggregates; the intra- and interpolymer association of amphiphilic polymers; monomer-swollen micelles (microdroplets); and the interfacial layer. Pyrene (Py) as a probe is particularly attractive because of its ability to measure the polarity of its microenvironment. Dipyme yields information on the microviscosity of micellar systems. Probes such as laurdan and prodan can be used to explore the surface characteristics of micelles or microdroplets. The dansyl group has a special photophysical property that gives information about the local polarity and mobility (viscosity) of the microenvironment. The organized association of amphiphilic polymer and emulsifier introduces a heterogeneity in the local concentration of the reactants. This heterogeneity also results from the attractive interaction between hydrophilic monomer and emulsifier in the case when the monomer carries a positive charge and the counterpart a negative one, and vice versa. Some emulsifiers can bind to the amphiphilic copolymers by simple partitioning between the aqueous phase and the polymer--non-cooperative association. The interaction between micelles (microdroplets) and charged polymers leads to the formation of mixed micelles. Binding emulsifiers to these polymers was detected at emulsifier concentrations much below the critical micellar concentration (CMC). Emulsifiers often interact cooperatively with polymers at the critical aggregation concentration (CAC) below the CMC, forming micelle-like aggregates within the polymer. The CAC can be taken as a measure of interaction between the emulsifier and polymer. A decrease in the monomer fluorescence intensity of probe-labeled polymer results from increased excimer formation, or higher aggregates within the unimolecular polymeric micelles. An increase in the monomer fluorescence intensity of probe-labeled polymer within the micellar system can be ascribed to shielding of the probe chromophores by emulsifier micelles. The quenching of probe emission by (un)charged hydrophilic monomer depends on partitioning of the monomer between the aqueous phase and the micelles. Penetration of reactants into the interfacial layer determines the quenching of the hydrophobic probe by hydrophilic quencher, or vice versa. Quenching depends on the thickness, density and charge of the interfacial layer. Compartmentalization prevents the carbonyl compound and unsaturated monomer from coming into sufficiently close contact to allow singlet or triplet-monomer interaction. All negatively charged carbonyl probe molecules are quenched with significantly lower rates than the parent neutral hydrophobic benzophenone molecules, which were located further inside the aggregates. This results from the different conformation and allocation of reactants within the micellar system. In the reverse micelles, quenching depends on the amount of water in the interfacial layer and the total area of the water/oil interface.     

Partitioning of unsaturated hydrophilic monomer in microemulsion media monitored by pyrene fluorescence method

The extent of intra‐ and interchain associations of (un)charged water‐soluble monomers in the homogeneous and micellar solutions was studied with steady‐state fluorescence spectroscopy. Fluorescence spectroscopic experiments were performed on uncharged (acryl amide) and charged hydrophilic monomers [zwitterionic 3‐dimethyl(methacryloyloxyethyl)ammonium propane sulfonate (DMAPS), etc.] with pyrene as a probe. In both the homogeneous and micellar solutions, linear Stern–Volmer plots were obtained that implied that the quenching process can be considered as totally dynamic. The Stern–Volmer constant (K_SV) for DMAPS decreased with an increasing dielectric constant of solvent and the concentration of simple electrolyte. An abrupt decrease in K_SV was observed in the presence of a small amount of anionic emulsifier [below the critical micelle concentration (cmc)]. The dependence of K_SV on pH for DMAPS was described by a curve with a maximum at about pH = 7. This was interpreted in terms of segregation of DMAPS and the variation of a optimal microenvironment for the probe and quencher with pH. The quenching rate in the micellar solutions strongly increased above the cmc but was lower than that in the homogeneous solutions. In the micellar solutions (above the cmc), the microenvironment for an interaction between the probe and quencher was suggested to be the whole microdroplet. The dependence of K_SV on pH for DMAPS is described by a curve with a maximum at about pH = 9.3. The synergistic effect arises from the segregation of charged quencher molecules within the microdroplets. The complex (or strong interaction) between quencher and additive(s) is supposed to increase the dynamic nature of microdroplets that provides an optimal microenvironment for probe and quencher. A good coemulsifier, however, removes quencher from the interface and creates a barrier for entering monomer (quencher) into the core of micelles; therefore, quenching is depressed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 571–581, 2003     

Effects of Charge and Structure of Hyaluronic Acid on the Luminescence Quenching in Aqueous Solution

The quenching of electronically excited Ru(bpy)₃²⁺ (bpy = Tris-2,2′-bipyridine) by methylviologen (MV) and ferricyanide (FC) in aqueous solutions of hyaluronic acid (HA) was studied. The structural and viscosity changes occuring with increasing HA concentration were found to influence the photophysical and photochemical properties of the sensitizer. Different kinetic models had to be used for the quenchers studied. The kinetics of the quenching of *Ru(bpy)₃²⁺ by MV can be described by the pseudophase model, which indicates that the rate for the exchange of the quencher between the microdroplets is higher than that for the excited state decay of the Ruthenium complex. In contrast, the quenching by the negatively charged quencher, FC, can be described by the Infelta-Tachiya equation, which indicates that the distribution of this quencher on the aqueous microdroplets is of the Poisson type and there is no exchange of quencher molecules during the lifetime of the sensitizer. The lifetimes of the excited Ruthenium complex, the unimolecular constants for its quenching by FC and the average concentration of the aqueous microdroplets increase with increasing HA concentration, reflecting the change in the solution structure during the transition from semidilute to concentrated regions. For MV no significant dependence of the quenching constant on the HA content of the solution was found. The reaction behavior of charged reactants in HA solution depends strongly on the sign of the charge.     

Reversible addition–fragmentation chain transfer polymerization of 2‐naphthyl acrylate with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate as a chain‐transfer agent

The reversible addition–fragmentation chain transfer (RAFT) polymerizations of 2‐naphthyl acrylate (2NA) initiated by 2,2′‐azobisisobutyronitrile were investigated with 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN) as a RAFT agent at various temperatures in a benzene solution. The results of the polymerizations showed that 2NA could be polymerized in a controlled way by RAFT polymerization with CPDN as a RAFT agent; the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with the monomer conversion. The polydispersities of the polymer were relatively low up to high conversions in all cases. The chain‐extension reactions of poly(2‐naphthyl acrylate) (P2NA) with methyl methacrylate and styrene successfully yielded poly(2‐naphthyl acrylate)‐b‐poly(methyl methacrylate) and poly(2‐naphthyl acrylate)‐b‐polystyrene block polymers, respectively, with narrow polydispersities. The P2NA obtained by RAFT polymerization had a strong ultraviolet absorption at 270 nm, and the molecular weights had no apparent effect on the ultraviolet absorption intensities; however, the fluorescence intensity of P2NA increased as the molecular weight increased and was higher than that of 2NA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2632–2642, 2005     

Preparation of Tube‐Like ZrO2/NaCl by Microemulsion Method

On the basis of w/o microemulsion and surfactant template‐assembly technology, tube‐like ZrO₂/NaCl was prepared using sodium bicarbonate as precipitant. The w/o microemulsion consisted of a nonionic surfactant OP emulsifier, cosurfactant pentanol and oil hexamethylene alkyl. The morphology, structure, and optical properties of the tube‐like ZrO₂/NaCl have been studied by SEM, XRD, FTIR, UV‐vis, and PL techniques.     

An Unprecedented Blueshifted Naphthalimide AIEEgen for Ultrasensitive Detection of 4‐Nitroaniline in Water via “Receptor‐Free” IFE Mechanism

The development of a new naphthalene appended naphthalimide derivative ( NMI ) with aggregation‐induced enhanced emission (AIEE) property for the sensitive detection of 4‐nitroaniline (4‐NA) in aqueous media is presented here. The newly designed naphthalimide AIEEgen has an exceptional blue‐shifted condensed state emission that is devoid of any receptor site, accomplished ultrasensitive detection of 4‐NA, which is one of the broad‐spectrum pesticides that belong to the class III toxic chemical, at parts per billion level (LOD/36 ppb, K_sv=4.1×10⁴ m ^?1) in water with excellent selectivity even in the presence of potentially competing aliphatic and aromatic amines. The reported probe is the first of its kind, demonstrating major advantages of receptor‐free inner filter effect (IFE) mechanism for the sensitive detection of 4‐NA using an AIEEgenic probe. Excellent sensitivity for 4‐NA is also achieved on paper‐based test‐strip for low‐cost on‐site detection.     

Microemulsion polymerization of styrene in the presence of a cationic emulsifier

The principal subject discussed in the current paper is the radical polymerization of styrene in the three- and four component microemulsions stabilized by a cationic emulsifier. Polymerization in the o/w microemulsion is a new polymerization technique which allows to prepare the polymer latexes with the very high particle interface area and narrow particle size distribution. Polymers formed are very large with a very broad molecular weight distribution. In emulsion and microemulsion polymerizations, the reaction takes place in a large number of isolated loci dispersed in the continuous aqueous phase. However, in spite of the similarities between emulsion and microemulsion polymerization, there are large differences caused by the much larger amount of emulsifier in the latter process. In the emulsion polymerization there are three rate intervals. In the microemulsion polymerization only two reaction rate intervals are commonly detected: first, the polymerization rate increases rapidly with the reaction time and then decreases steadily. Essential features of microemulsion polymerization are as follows: (1) polymerization proceeds under non-stationary state conditions; (2) size and particle concentration increases throughout the course of polymerization; (3) chain-transfer to monomer/exit of transferred monomeric radical/radical re-entry events are operative; and (4) molecular weight is independent of conversion and distribution of resulting polymer is very broad. The number of microdroplets or monomer-starved micelles at higher conversion is high and they persist throughout the reaction. The high emulsifier/water ratio ensures that the emulsifier is undissociated and can penetrate into the microdroplets. The presence of a large amount of emulsifier strongly influences the reaction kinetics and the particle nucleation. The mixed mode particle nucleation is assumed to govern the polymerization process. At low emulsifier concentration the micellar nucleation is dominant while at a high emulsifier concentration the interaction-like homogeneous nucleation is operative. Furthermore, the paper is focused on the initiation and nucleation mechanisms, location of initiation locus, and growth and deactivation of latex particles. Furthermore, the relationship between kinetic and molecular weight parameters of the microemulsion polymerization process and colloidal (water/particle interface) parameters is discussed. In particular, we follow the effect of initiator and emulsifier type and concentration on the polymerization process. Besides, the effects of monomer concentration and additives are also evaluated.     

N-丁基马来酰亚胺/苯乙烯微乳液共聚合研究

研究了氘代氯仿中Ｎ－丁基马来酰亚胺（ＮＢＭＩ）和苯乙烯（Ｓｔ）的络合性能。以十二烷基硫酸钠（ＳＤＳ）和正戊醇（ＰＴＬ）为复合乳化剂,配制了含有ＮＢＭＩ（Ｍ１）和Ｓｔ（Ｍ２）的Ｏ／Ｗ微乳液。用过硫酸钾引发该体系进行微乳液共聚合。固定乳化剂的浓度为〔ＳＤＳ〕＝０．２１ｍｏｌ／Ｌ,〔ＰＴＬ〕＝０．２８ｍｏｌ／Ｌ,详细研究了聚合温度、单体配比和引发剂用量对共聚合动力学的影响。用元素分析法确定共聚物的组成,     

Synthesis of polynorbornene‐poly(tert‐butyl acrylate) nanoparticles with original morphologies by tandem ROMP and ATRP in microemulsion

Composite latex particles based on homopolymers and graft‐copolymers composed of polynorbornene (PNB) and poly(tert‐butyl acrylate) (PtBA) were synthesized in microemulsion conditions by simultaneous combination of two distinct methods of polymerization: Ring‐opening metathesis polymerization (ROMP) and atom transfer radical polymerization (ATRP). Only one commercial compound (first generation Grubbs catalyst) was used to initiate the ROMP of norbornene (NB) and activate the ATRP of tert‐butyl acrylate (tBA). Well‐defined nanoparticles with hydrodynamic diameters smaller than 50 nm were prepared with original morphologies depending on the monomer compositions, the type of combination (polymer blend or graft‐copolymer), and the conditions of microemulsion polymerizations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and Characterization of a Water‐Soluble Carboxylated Polyfluorene and Its Fluorescence Quenching by Cationic Quenchers and Proteins

We have developed a new intermediate monomer, 2,7‐[bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐9,9‐bis(3‐(tert‐butyl propanoate))]fluorene, that allows the easy synthesis of water‐soluble carboxylated polyfluorenes. As an example, poly[9,9′‐bis(3′′‐propanoate)fluoren‐2,7‐yl] sodium salt was synthesized by the Suzuki coupling reaction, and the properties of the polymer were studied in aqueous solutions of different pH. Fluorescence quenching of the polymer by different cationic quenchers (MV²⁺, MV⁴⁺, and NO₂MV²⁺; MV=methyl viologen) was studied, and the quenching constants were found to be dependent on the charge and electron affinity of the quencher molecule and the pH of the medium. The largest quenching constant was observed to be 1.39×10⁸ M ^?1 for NO₂MV²⁺ at pH 7. The change in polymer fluorescence upon interaction with different proteins was also studied. Strong fluorescence quenching of the polymer was observed in the presence of cytochrome c, whereas weak quenching was observed in the presence of myoglobin and bovine serum albumin. Lysozyme quenched the polymer emission at low protein concentrations, and the quenching became saturated at high protein concentrations. Under similar experimental conditions, the polymer showed improved quenching efficiencies toward cationic quenchers and a more selective response to proteins relative to other carboxylated conjugated polymers.     

Double Naphthalene‐Tagged Cyclodextrin‐Peptide Capable of Exhibiting Guest‐Induced Naphthalene Excimer Fluorescence

A cyclodextrin‐peptide hybrid (17NNβ) bearing two naphthalene units in the peptide side chain has been designed and synthesized as a novel chemosensor molecule. Circular dichroism study of the compound revealed that the peptide has α‐helix structure with a helix content of 41%. The peptide revealed both monomer and excimer emission and the intensity of the excimer emission increased while that of the monomer emission decreased upon addition of the guest compound. This behavior was observed for various guest molecules, suggesting that the system can be used for detecting molecules in aqueous solution.     

Synthesis and characterization of color‐stable electroluminescent polymers: Poly(dinaphtho[1,2‐a:1′,2′‐g]‐s‐indacene)s

Two new stepladder conjugated polymers, that is, poly(7,7,15,15‐tetraoctyldinaphtho[1,2‐a:1′,2′‐g]‐s‐indacene) (PONSI) and poly(7,7,15,15‐tetra(4‐octylphenyl)dinaphtho[1,2‐a:1′,2′‐g]‐s‐indacene) (PANSI) with alkyl and aryl substituents, respectively, have been synthesized and characterized. In comparison with poly(indenofluorene)s, both polymers have extended conjugation at the direction perpendicular to the polymer backbone because of the introduction of naphthalene moieties. The emission color of the polymers in film state is strongly dependent on the substituents. While PONSI emits at a maximum of 463 nm, PANSI with the same backbone but aryl substituents displays dramatically redshifted emission with a maximum at 494 nm. Both polymers show stable photoluminescence spectra while annealing at 200 °C in inert atmosphere. The PONSI‐based devices with the configuration of ITO/PEDOT:PSS/polymer/Ca/Al turn on at 3.7 V, and emit at a maximum of 461 nm with the CIE coordinates of (0.19, 0.26), a maximum luminance efficiency of 1.40 cd/A, and a maximum brightness of 2036 cd/m² at 13 V. Meanwhile, the emission color of the devices is independent of driving voltage and keeps unchanged during the continuous operation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4866–4878, 2008     

Poly(thieno[3,4‐b]‐1,4‐oxathiane) and poly(3,4‐ethylenedioxythiophene‐co‐thieno[3,4‐b]‐1,4‐oxathiane)/poly(styrene sulfonic sodium): Preparation,characterization, and optoelectronic performance

In this work, the asymmetrical analog of 3,4‐ethylenedioxythiophene (EDOT), thieno[3,4‐b]‐1,4‐oxathiane (EOTT), was synthesized and chemically polymerized first in aqueous solution using poly(styrene sulfonic sodium) (PSS) as the polyelectrolyte to yield poly(thieno[3,4‐b]‐1,4‐oxathiane) (PEOTT)/PSS. As‐formed film exhibited low electrical conductivity (～10^?4 S/cm). Alternatively, EOTT together with EDOT (in different molar ratio of 1:1 and 1:5) was copolymerized and the polymer poly(EOTT‐co‐EDOT)/PSS had electrical conductivity of 10^?1 S/cm. After dimethyl sulfoxide (DMSO) treatment, the electrical conductivity was enhanced to 10⁰ S/cm; however, the conductivity of the above homopolymer was reduced (～10^?5 S/cm). Raman spectroscopy was used to interpret conductivity enhancement or reduction after DMSO treatment. The conductivity decrease of PEOTT/PSS compared to poly(EOTT‐co‐EDOT)/PSS may arise from the conformational change of PEOTT backbone from the quasi‐planar to the distorted planar mode induced by PSS^–/PSSH through ionic interaction. Kinetic studies revealed that the copolymer had high coloration efficiencies (375 cm²/C), low switching voltages (?0.8 to +0.6 V), decent contrast ratios (45%), moderate response time (1.0 s), excellent stability, and color persistence. An electrochromic device employing poly(3‐methylthiophene) and poly(EOTT‐co‐EDOT)/PSS as the anode and cathode materials was also studied. From these results, poly(EOTT‐co‐EDOT)/PSS would be a promising candidate material for organic electronics. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2285–2297     

Synthesis of a norbornene monomer having cyclic carbonate moiety based on CO2 fixation and its transition metal‐catalyzed polymerizations

A norbornene monomer bearing cyclic carbonate moiety ( NB‐CC ) was successfully synthesized from the corresponding precursor having epoxy moiety by its reaction with carbon dioxide under atmospheric pressure, which was efficiently catalyzed by lithium bromide. NB‐CC underwent the ring‐opening metathesis polymerization (ROMP) catalyzed by a ruthenium carbene complex to give the corresponding poly(norbornene), of which side chain inherited the cyclic carbonate moiety from the monomer without any deterioration. The same ROMP system was applicable to the copolymerization of NB‐CC and 5‐butyl‐2‐norbornene ( BNB ), which afforded the corresponding copolymer with a composition ratio same as a feed ratio. In addition, by using a catalytic system consisted of palladium (II) acetate/tricyclohexylphosphine/triphenylcarbenium tetrakis(pentafluorophenyl)borate, the copolymerization of NB‐CC and BNC proceeded successfully in a vinyl addition polymerization mode to give the corresponding poly(norbornene) having CC moiety in the side chain. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3896–3902, 2010     

Preparation of Polar Ethylene–Norbornene Copolymers by Metallocene Terpolymerization with Triisobutylaluminium‐Protected But‐3‐en‐1‐ol

But‐3‐en‐1‐ol has been pre‐protected by triisobutylaluminium and terpolymerized with ethylene and norbornene by rac‐[Et(Ind)₂]ZrCl₂/MAO catalysts. The strong polarity of diisobutyl(but‐3‐en‐1‐oxy)aluminum causes a slight reduction in the catalyst activity and yields a small fraction of crystallinity. The but‐3‐en‐1‐ol content in the terpolymer is as high as 3.2% and can be readily adjusted by varying the reaction conditions. When the norbornene/ethylene ratio is over 10, the norbornene incorporation efficiency is not affected by the polar monomer and is close to that of the copolymerization. Similar to the ethylene/norbornene copolymers, the thermal properties of the obtained terpolymers are mainly determined by their norbornene contents.

     

Pure white‐light‐emitting diodes from phosphorescent single polymer systems

New white polymeric light‐emitting diodes from phosphorescent single polymer systems have been developed using a blue‐light‐emitting fluorene monomer copolymerized with a red‐light‐emitting phosphorescent dye, and end‐capped with a green‐light‐emission dye. All of the copolymers have good thermal stability with 5% weight loss temperatures at 380–413 °C and glass transition temperatures at 75–137 °C. We obtained white‐light‐emission devices by adjusting the molar ratio of the comonomers with a structure of indium tin oxide/poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonic acid)/polyvinylcarbazole (PVK)/emission layer/Ca/Ag. The highest brightness in such a device configuration is 300 cd/m² at a current density of 2900 A/m² with high white color quality (Commission Internationale de l'Eclairage (CIE) coordinates of (0.33, 0.34)). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 464–472, 2008     

Synthesis and characterization of novel photoactive polymer poly(vinyl alcohol)‐graft‐poly(vinyl naphthalene)

A copolymer of poly(vinyl naphthalene) grafted onto poly(vinyl alcohol) has been synthesized with nitroxide‐mediated controlled radical polymerization. By separating the processes of the generation of grafting sites and polymerization, we can avoid the formation of the homopolymer. Because of its architecture, the polymer is soluble in water, despite the high content of hydrophobic groups. The naphthalene chromophores tend to aggregate, forming hydrophobic microdomains in an aqueous solution. Those aggregates exist in a very constrained environment that leads to extraordinarily large redshifts of both the absorption and emission of the polymer. The polymer acts as an efficient photosensitizer in photoinduced electron transfer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2675–2683, 2006     

Ethylene‐Norbornene Terpolymerization with 5‐Vinyl‐2‐norbornene Using Single‐Site Catalysts

The incorporation of 5‐vinyl‐2‐norbornene (VNB) into ethylene‐norbornene copolymer was investigated with catalysts [Ph₂C(Fluo)(Cp)]ZrCl₂ ( 1 ), rac‐[Et(Ind)₂]ZrCl₂ ( 2 ), and [Me₂Si(Me₄Cp)^tBuN]TiCl₂ ( 3 ) in the presence of MAO by terpolymerizing different amounts of 5‐vinyl‐2‐norbornene with constant amounts of ethylene and norbornene at 60°C. The highest cycloolefin incorporations and highest activity in terpolymerizations were achieved with 1 . The distribution of the monomers in the terpolymer chain was determined by NMR spectroscopy. As confirmed by XRD and DSC analysis, catalysts 1 and 3 produced amorphous terpolymer, whereas 2 yielded terpolymer with crystalline fragments of long ethylene sequences. When compared with poly‐(ethylene‐co‐norbornene), VNB increased both the glass transition temperatures and molar masses of terpolymers produced with the constrained geometry catalyst whereas decreased those for the metallocenes.     

Synthesis of reactive poly(norbornene): Ring‐opening metathesis polymerization of norbornene monomer bearing cyclic dithiocarbonate moiety

A norbornene monomer bearing cyclic dithiocarbonate moiety (NB‐DTC) was successfully synthesized from the corresponding precursor having epoxy moiety by its reaction with carbon disulfide. NB‐DTC underwent the ring‐opening metathesis polymerization (ROMP) catalyzed by a ruthenium carbene complex to give the corresponding poly(norbornene). The dithiocarbonate moiety incorporated into the side chain of the obtained poly(norbornene) reacted with amine to afford the corresponding thiourethane moiety with thiol group, which underwent oxidative S‐S coupling and/or addition reaction to the C‐C double bond in the main chain, leading to formation of a cross‐linked polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Synthesis and characterization of materials prepared via the copolymerization of ethylene with 1‐octadecene and norbornene using a [(π‐cyano‐nacnac)Cp] zirconium complex

[3‐Cyano‐2‐(2,6‐diisopropylphenyl)aminopent‐2‐en‐4‐(phenylimine)tris (pentafluorophenyl)borate](η⁵‐C₅H₅)ZrCl₂, [(B(C₆F₅)₃‐ NC‐nacnac)CpZrCl₂], precatalyst ( 2 ) can be treated with low concentrations of methylaluminoxane (MAO) to generate active sites capable of copolymerizing ethylene with 1‐octadecene or norbornene under mild conditions. A series of poly(ethylene‐co‐octadecene) and poly(ethylene‐co‐norbornene) copolymers were prepared, and their properties were characterized by NMR, differential scanning calorimetry, and mechanical analysis. The results show that this system produced poly(ethylene‐co‐octadecene) copolymers with a branching content of about 8 mol %. However, upon increasing the comonomer concentration, a drastic reduction in the M_n of the product is observed concomitant with an increase in comonomer incorporation. This leads to a gradual decrease in Young's modulus and stress at break, indicating an increase in the “softness” of the copolymer. In the case of copolymerizations of ethylene and norbornene, the catalytic system ( 2 /MAO) shows a substantial decrease in reactivity in the presence of norbornene and generates copolymer chains in which 5–10 mol % norbornene is in blocks. We also observe that ethylene norbornene copolymers exhibit a high degree of alternating insertions (close to 50%), as determined by NMR spectroscopy. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011