Controlled Molar Mass Research Articles

Synthesis of Macrocyclic Copolymer Brushes and Their Self-Assembly into Supramolecular Tubes

We report on an efficient route to design large macrocyclic polymers of controlled molar mass and narrow dispersity. The strategy is based on the synthesis of a triblock copolymer ABC, in which the long central block B is extended by two short A and C sequences bearing reactive antagonist functions. When reacted under highly dilute conditions, this precursor produces the corresponding macrocycle by intramolecular coupling of the A and C blocks. Chloroethyl vinyl ether was selected as the monomer for the central block B, because it can be readily derivatized into brushlike polymers by a grafting process. The corresponding macrocyclic brushes were decorated with polystyrene or randomly distributed polystyrene and polyisoprene branches. In a selective solvent for the polyisoprene branches, the macrocyclic brushes self-assemble into cylindrical tubes of up to 700 nanometers.

Controlled High-Speed Anionic Polymerization of Propylene Oxide Initiated by Onium Salts in the Presence of Triisobutylaluminum

The conventional anionic polymerization of propylene oxide (POx) proceeds at a very slow rate in low polar media and is characterized by an important transfer reaction to monomer. This only allows the formation of poly(propylene oxide) oligomers. A new polymerization strategy allowing the fast and controlled anionic polymerization of POx has been developed. It is based on the formation of complexes with both the anionic initiator and the monomer. The influences of alkali metal alkoxides (i-PrONa), ammonium salts (NBu4Cl and NOct4Br), and phosphonium salts (PBu4Cl) as initiators, in combination with triisobutylaluminum, have been investigated in terms of reactivity, molar mass control, livingness, and polymerization mechanism. PPOx with narrow polydispersities and controlled molar masses, up to 150 000 g/mol, have been obtained in hydrocarbon media, at low temperature, and in short reaction times.

NMR and MALDI-TOF MS study of side reactions in hyperbranched polyesters based on 2,2-bis(hydroxymethyl)propanoic acid

Hyperbranched polyesters of 2,2-bis(hydroxymethyl)propanoic acid (BMPA) with various molar ratios of tetra(hydroxymethyl)methane (PE) core molecule were characterized by NMR spectroscopy and MALDI-TOF mass spectrometry. In all polyesters, the formation of ether groups was observed. The extent of etherification increased with increasing PE content. This was assigned to a higher reactivity of PE towards etherification than BMPA. Intra- and intermolecular etherifications and intramolecular esterifications were detected by MALDI-TOF MS on the core molecule-containing polyesters, resulting in the formation of cycle-containing hyperbranched molecules. The ratio of cycle-containing molecules reached 50% at high reaction time for the polyester without core molecule, but was much lower for the polyesters containing a core molecule. As a consequence of these side reactions, the control of hyperbranched polyester molar mass by varying the core molecule (chain limiter) molar ratio is much more difficult than for linear polyesters.

Controlled/Living Cationic Polymerization of p-Methoxystyrene in Solution and Aqueous Dispersion Using Tris(pentafluorophenyl)borane as a Lewis Acid: Acetonitrile Does the Job

The living cationic polymerization of p-methoxystyrene using the 1-(4-methoxyphenyl)ethanol/B(C6F5)3 initiating system in solution and in aqueous dispersion is reported. Solution experiments first showed that the molar mass of the obtained polymers increases in direct proportion to the monomer conversion and the molar mass distribution stays narrow in the course of the polymerization (Mw/Mn ∼ 1.2). The living nature of the growing chains was confirmed by sequential monomer addition experiments, although matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF-MS) revealed some hydroxyl elimination under monomer-starved conditions. Aqueous suspension polymerization of p-methoxystyrene using the same initiating system did not show a good control of molar masses, since after polymerization has proceeded at the interface up to critical DP, oligomers terminated by water penetrate inside the particles where they stop propagating. This limitation was leveled off for the first time by polymerizing p-methoxystyrene in an aqueous dispersion, i.e., in a mixture of H2O:CH3CN 3:2 (v/v). Under these conditions, the hydroxyl-terminated poly(p-methoxystyrene)s can be reactivated by B(C6F5)3 located inside the particles to reinitiate the polymerization; molar masses thus increase with conversion, up to 3000 g mol-1, and exhibit a narrow molar mass distribution (Mw/Mn ∼ 1.3) and an almost pure hydroxylated functionality.

Association of Star-Shaped Poly(d,l-lactide)s Containing Nucleobase Multiple Hydrogen Bonding

A new family of associating polymers based on four-arm, star-shaped poly(D,L-lactide) (PDLLA) containing peripheral complementary hydrogen-bonding sites is described. Hydroxy-terminated, four-arm, star-shaped PDLLAs of controlled molar mass were functionalized with complementary DNA base pairs, adenine (A) and thymine (T), to obtain PDLLA-A and PDLLA-T, respectively. 1H NMR spectroscopy confirmed quantitative functionalization and the subsequent formation of PDLLA-A and PDLLA-T hydrogen-bonded complexes. Job's analysis revealed a 1:1 optimal stoichiometry for the hydrogen-bonded complexes, and the association constant (Ka) that was determined using the 1H NMR-based Benesi-Hildebrand treatment was 84 M(-1) for the low molar mass complementary polymers. Furthermore, the PDLLA-based hydrogen-bonded complexes exhibited higher solution viscosities compared to the corresponding non-hydrogen-bonded precursors, which further confirmed strong complementary multiple-hydrogen-bonding associations between the star-shaped polymers with terminal adenine and thymine groups. Moreover, variable-temperature 1H NMR studies demonstrated the thermoreversibility of the hydrogen-bonded PDLLA-based complexes in solution.

Elaboration of well‐defined Rasta resins and their use as supported catalytic systems for atom transfer radical polymerization

AbstractNew supported catalytic systems based on the immobilization of a ligand onto supported (co)polymers were prepared, allowing copper immobilization onto a solid support during the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). These supported catalysts were elaborated by the ATRP of 2‐vinyl‐4,4‐dimethyl‐5‐oxazolone and/or styrene onto a Wang resin initiator. Two different approaches were used, involving well‐defined architectures synthesized by ATRP. First, a supported electrophilic homopolymer [Wang‐g‐poly(2‐vinyl‐4,4‐dimethyl‐5‐oxazolone)] was synthesized to obtain an azlactone ring at each repetitive unit, and a supported statistical copolymer [Wang‐g‐poly(2‐vinyl‐4,4‐dimethyl‐5‐oxazolone‐stat‐styrene)] was synthesized to introduce a distance between the azlactone rings. The azlactone‐based (co)polymers were then modified by a reaction with N,N,N′,N′‐tetraethyldiethylenetriamine (TEDETA) to create supported complexing sites for copper bromide. The ATRP of MMA was studied with these supported ligands, and a first‐order kinetic plot was obtained, but high polydispersity indices of the obtained poly(methyl methacrylate) were observed (polydispersity index > 2). On the other hand, the supported ATRP of styrene was performed, followed by the nucleophilic substitution of bromine by TEDETA (Wang‐g‐polystyrene–N,N,N′,N′‐tetraethyldiethylenetriamine) at the chain end of the grafted polystyrene chains. This strategy led the ligand away from the core bead, depending on the length of the polystyrene block (number‐average molecular weight determined by size exclusion chromatography = 1100–2250 g/mol). These supported complexes mediated a controlled polymerization of MMA, yielding polymers with controlled molar masses and low polydispersity indices. Moreover, after the polymerization, 96% of the initial copper was kept in the beads. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5316–5328, 2006

Online control of molar mass and particle‐size distributions in emulsion polymerization

AbstractProduct quality control is a complex issue in polymerization than in conventional chemical processes. The key polymer properties are related to the polymer particle‐size distribution (PSD), and molecular‐weight distribution (MWD), which are in turn sensitive to the thermo‐kinetic and operating history of the process. Disturbances in operating conditions may cause irreversible changes in the quality of the polymer formed. Therefore, adjustments must be made during the reaction through effective online control schemes. For this purpose, model predictive control (MPC) algorithm for on‐line control of polymer PSD and MWD was developed and implemented. An intelligent control hierarchy was formulated for the distributed parameter system at three levels: off‐line optimization, on‐line MPC and regulatory control successively. The novelty of our approach includes the incorporation of a validated high‐order dynamic model as a soft‐sensor for on‐line feedback of PSD and MWD. The MPC was implemented successfully on a reactor facility, where off‐line sample analysis, using CHDF and GPC instruments, were used to update the on‐line model predictions. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Molar Mass Control by Diethyl Zinc in the Polymerization of Butadiene Initiated by the Ternary Catalyst System Neodymium Versatate/Diisobutylaluminum Hydride/Ethylaluminum Sesquichloride

The polymerization of 1,3‐butadiene (BD) catalyzed by the ternary Ziegler/Natta catalyst system neodymium versatate (NdV)/diisobutylaluminum hydride (DIBAH)/ethylaluminum sesquichloride (EASC) is investigated in regard to molar mass control by diethyl zinc (ZnEt2). Within the investigated range of ratios of ZnEt2 to NdV, the features of a living polymerization with a reversible exchange of the living polybutadienyl chains between neodymium and zinc are observed. In summary, ZnEt2 can be considered as an efficient molar mass control agent, which has a negligible impact on polymerization rates. In addition to the reduction of molar masses, ZnEt2 also reduces the polydispersity (PDI) and leads to a decrease of the cis‐1,4‐content.

Independent control of sol molar mass and gel content in acrylate polymer/latexes

Poly n-butylacrylate latexes are commonly used as the base ingredient in the formulation of pressure sensitive adhesives, PSA. In the typical starved semi-batch process carried out to produce this latex and due to the non-linear nature of the kinetics, chain transfer to polymer plus bimolecular termination by combination, polymer networks are produced. The molar mass distribution of these polymer latexes is characterized by a soluble and an insoluble fraction, so-called gel. Both fractions strongly affect the adhesion properties, but unfortunately the independent control of these properties is a difficult task, that has not been solved yet. In this work, the concentrations of chain transfer agent and cross-linker were used in an attempt to exercise control over the molar mass of the soluble part and the amount of gel polymer. It was found that by simultaneously manipulating both variables it was possible to modify the gel content of the polymer without completely sacrificing the sol molar mass. The adhesion properties, tack and resistance to shear, measured on films cast from the latex demonstrated that a good PSA can be obtained by properly balancing the amount of CTA and cross-linker in the formulation.

Influence of Peripheral Hydrogen Bonding on the Mechanical Properties of Photo-Cross-Linked Star-Shaped Poly(d,l-lactide) Networks

Four-arm, star-shaped poly(D,L-lactide) (PDLLA) oligomers of controlled molar mass and narrow molar mass distribution were successfully synthesized by use of an ethoxylated pentaerythritol initiator. Derivatization of the terminal hydroxyl groups with either methacrylic anhydride (MAAH) or 2-isocyanatoethyl methacrylate (IEM) to yield PDLLA-M (M = methacrylate end group) and PDLLA-UM (UM = urethane methacrylate end group), respectively, was monitored by in situ Fourier transform infrared (FTIR) spectroscopy. Photo-cross-linking of the functional oligomers yielded networks with high gel contents (>95%). The glass transition temperature (T(g)) of these networks was strongly dependent on prepolymer molar mass, and networks based on low molar mass precursors were more rigid than the networks obtained from higher molar mass oligomers. The tensile strength (TS) and Young's modulus of the PDLLA-M samples, approximately 7 and 17 MPa, respectively, were significantly lower than the values of 19 MPa (TS) and 113-354 MPa (Young's modulus) for the PDLLA-UM samples. The introduction of terminal hydrogen-bonding sites that were adjacent to the photo-cross-linking site resulted in higher performance poly(lactide)-based bioadhesives.

Cobalt(II) octanoate and cobalt(II) perfluorooctanoate catalyzed atom transfer radical polymerization of styrene in toluene and fluorous media—A versatile route to catalyst recycling and oligomer formation

AbstractCobalt(II) perfluorooctanoate‐catalyzed atom transfer radical polymerization (ATRP) and reverse ATRP were developed to prepare oligostyrenes (Mn < 2500) with low polydispersities Mw/Mn < 1.5. Fluorous biphase catalysis was applied for effective recycling of catalyst and fluorous solvent. The homogeneous polymerization reaction was performed at 90 °C in toluene/cyclohexane/perfluorodecalin mixture (1:1:1) and fluorine‐free solvents. Temperature‐induced phase separation of this fluorous solvent mixture occurred at room temperature and proved to be the key for the very effective separation of the cobalt(II) perfluorooctanoate from the oligostyrene and fluorine‐free solvents. Both the fluorine‐tagged cobalt catalysts and the fluorous media were recycled and reused up to three times without encountering catalyst activity losses. The roles of cobalt catalysts, fluorous media, and monomer/initiator ratio were examined with respect to the polymerization kinetics. Fluorine‐containing and fluorine‐free cobalt(II) octanoate catalyzed controlled styrene oligomerization according to the ATRP mechanism. The molar mass control range was limited in fluorous biphase catalysis most likely because of precipitation of high molar mass polystyrenes in the fluorous reaction medium. To the best of our knowledge, this is the first time temperature‐induced phase separation of fluorous and fluorine‐free solvents has been successfully applied to polymerization processing. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3804–3813, 2005

On-line multi-variable predictive control of molar mass and particle size distributions in free-radical emulsion copolymerization

A multi-variable model predictive control (MPC) was formulated to solve control problems associated with a combination of regulation and targeting desired set-points. We investigated the simultaneous control of key polymer properties: the particle size (PSD) and molecular weight distribution (MWD) by manipulating the flow rates of the monomers (styrene, MMA), surfactant, initiator and the temperature of the reactor. A multi-input–multi-output (MIMO) formulation was constructed for the constrained optimal control problem to maximize the width of the PSD (with M n at a constant set-point), and to maximize the average molar mass. The strategy developed within a gPROMS-API-DCS environment allowed real-time implementation of model-based control of the process. The optimal control problem was implemented via an interface to a dynamic optimization code. Major improvements in process operation and polymer property control resulted on the implementation of our multi-variable MPC algorithm. The manipulation of the four flow rates and the temperature increased the degree of freedom in the system and achieved tighter PSD and MWD control. The on-line performance of MPC for MWD and PSD control was found to be satisfactory.

Synthetic and characterization aspects of dimethylaminoethyl methacrylate reversible addition fragmentation chain transfer (RAFT) polymerization

Abstract2‐cyanoprop‐2‐yl dithiobenzoate (CPDB) mediated RAFT polymerization of dimethylaminoethyl methacrylate (DMAEMA) was carried out in dioxane at 90 °C. The influence of several parameters, such as the monomer to CPDB molar ratio (100 to 500), the monomer concentration (2 mol·L−1 to 5.9 mol·L−1), and CPDB to initiator molar ratio (1 to 10), was evaluated with regards to conversion and polymerization duration, as well as control of molar mass and molar mass distributions. Number average molar masses from 10,000 to 70,000 g·mol−1 can be targeted. The determination of the molar masses has been carried out by size exclusion chromatography (SEC) with a refractometer detector with poly(methyl methacrylate) (PMMA) standards. The experimental values were lower than the expected ones. Then, SEC in aqueous medium with an online laser light scattering detector was used both to get absolute molar masses and to recalibrate the SEC column in THF. Characterization of well‐controlled PDMAEMA samples has been performed by proton NMR spectroscopy and matrix assisted laser desorption ionization time of flight mass spectrometry. Finally, a chain extension experiment was evaluated with regard to living features. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3551–3565, 2005

Stereoselective Cyclopolymerization of Polar 1,6‐Heptadiynes by Novel, Tailor‐Made Ruthenium‐Based Metathesis Catalysts

AbstractSummary: The cyclopolymerization of 4,4‐bis(hydroxymethyl)‐1,6‐heptadiyne (M1), 4‐(carboxyethyl)‐1,6‐heptadiyne (M2), 4‐(hydroxymethyl)‐1,6‐heptadiyne (M3), and 4‐carboxy‐1,6‐heptadiyne (M4) using five different well‐defined metathesis initiators was investigated. Control of molar mass was achieved with catalysts bearing trifluoroacetate ligands. 13C NMR experiments showed that poly‐M2, prepared by the action of any catalyst consisted solely of five‐membered ring structures, i.e., 1,2‐(cyclopent‐1‐enylene)vinylene units. Effective conjugation lengths of all polymers were calculated from the corresponding UV‐Vis absorption maxima, which varied reversibly with temperature. magnified image

Activation Mechanisms of Trialkylaluminum in Alkali Metal Alkoxides or Tetraalkylammonium Salts / Propylene Oxide Controlled Anionic Polymerization

AbstractThe anionic polymerization of propylene oxide (PO) initiated by alkali metal alkoxides is in non polar solvents a very slow and non controlled reaction process. Transfer reaction to monomer is predominant, allowing only the preparation of low molar masses PPO. The influence of the addition of trialkylaluminium to either an alkali metal alkoxide or a tetraalkylammonium salt used as initiator for PO polymerization in hydrocarbon media was investigated. A strong enhancement of the polymerization rate accompanied by a drastic decrease of the transfer reactions is observed, allowing the synthesis of PPO with well controlled molar masses. At constant monomer and alkali metal alkoxide concentrations, the polymerization rate increases with increasing trialkylaluminium concentration. Results indicate that the trialkylaluminium derivative is involved in the formation of two distinct complexes, one with the alkali metal alkoxide or the tetraalkylammonium salt and another one with the PO monomer which is strongly activated towards nucleophilic active species. Significant differences between the alkali metal and tetraalkylammonium based initiators are observed. In particular much less trialkylaluminum activator is needed with the ammonium salt to get the same rate of propagation and controlled polymerization.

Polymerization of 1,3‐Butadiene Initiated by Neodymium Versatate/Triisobutylaluminum/Ethylaluminum Sesquichloride: Impact of the Alkylaluminum Cocatalyst Component

The polymerization of 1,3‐butadiene (BD) by the ternary Ziegler/Natta (Z/N) catalyst system neodymium versatate (NdV)/ethylaluminum sesquichloride (EASC)/aluminum alkyl is investigated. Special attention is paid to the impact of the aluminum alkyl on the polymerization kinetics and on the control of molar masses. In this respect diisobutyl aluminumhydride (DIBAH) and triisobutylaluminum (TIBA) are compared. Within a broad range of n Al‐Alkyl/n NdV‐ratios for both aluminum compounds the features of a living polymerization with a reversible exchange of the living polybutadienyl chains between neodymium (Nd) and aluminum are observed. The equilibrium position of this reaction is different for TIBA and DIBAH. At the same molar loadings DIBAH results in polybutadienes with molar masses which are 1/8 of those obtained in the presence of the cocatalyst TIBA. This difference is explained by a significantly more facile substitution of a hydride moiety from DIBAH than an isobutyl group from either DIBAH or TIBA by a living polybutadienyl chain.

Síntese de copolímeros em bloco de p-acetoxiestireno com isopreno através de polimerização "viva" via radical livre

Neste trabalho, é mostrada a síntese de homopolímeros de p-acetoxiestireno e copolímeros diblocos de p-acetoxiestireno com isopreno, utilizando um iniciador TEMPO-modificado, por um processo de polimerização "viva" via radical livre. As análises de GPC indicaram a formação de copolímeros em bloco com massas molares e polidispersão mais altas quando comparadas aos dos homopolímeros correspondentes. Os copolímeros em bloco poli(p-acetoxiestireno-b-isopreno) foram preparados com controle de composição e massa molar até 94500 u.m.a. As análises de DSC mostraram que a transição vítrea do bloco de p-acetoxiestireno foi de 5 a 18 °C mais baixa que aquelas obtidas para os homopolímeros correspondentes. A transição vítrea do bloco de isopreno apresentou valores similares àqueles dos homopolímeros de poliisopreno (-67 a -55 °C).

Resorcinarene‐based ATRP initiators for star polymers

AbstractTwo novel multifunctional initiators for atom transfer radical polymerization (ATRP) were synthesized by derivatization of tetraethylresorcinarene. The derivatization induced a change in the conformation of the resorcinarene ring, which was confirmed by NMR spectroscopy. The initiators were used in ATRP of tert‐butyl acrylate and methyl methacrylate, producing star polymers with controlled molar masses and low polydispersities. Instead of the expected star polymers with eight arms, polymers with four arms were obtained. Conformational studies on the initiators by rotating‐frame nuclear Overhauser and exchange spectroscopy NMR and molecular modeling suggested that of eight initiator functional groups on tetraethylresorcinarene, four are too close to each other to be able to initiate the chain growth. Starlike poly(tert‐butyl acrylate) macroinitiators were used further in the block copolymerization of methyl methacrylate. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4189–4201, 2004

Synthesis of di‐ and tetra‐adducts by addition of polystyrene macroradicals onto fullerene C60

AbstractBr‐terminated polystyrenes of controlled molar masses and low polydispersities prepared by atom transfer radical polymerization (ATRP) can be converted to macroradicals using an appropriate catalytic complex (CuBr/bipyridine/100 °C). The addition of this macroradicals PS° to 6–6 bonds of C60 follows a specific atom transfer radical addition mechanism that favors the grafting of even number of chains onto the fullerene core. This peculiar mechanism, resulting from the properties of C60, offers an easy synthetic route toward well‐defined di‐ and tetra‐adducts. In these adducts the disturbance of the electronic structure of the fullerene is kept at its minimum, as only one double bond needs to be opened on the C60 to add two PS chains and only two double bonds are converted to single bonds in the tetra‐adduct. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3456–3463, 2004

Synthesis of Block, Statistical, and Gradient Copolymers from Octadecyl (Meth)acrylates Using Atom Transfer Radical Polymerization

The synthesis of well-defined homopolymers and random, block, and gradient copolymers from octadecyl acrylate (OA) and octadecyl methacrylate (OMA) using atom transfer radical polymerization (ATRP) is reported. Random copolymers were synthesized by the one-pot copolymerization of either tert-butyl acrylate/octadecyl acrylate (Mn,p(tBA-r-OA) = 13 680; Mw/Mn = 1.13) or tert-butyl methacrylate/octadecyl methacrylate (Mn,p(tBMA-r-OMA) = 24 250; Mw/Mn = 1.14) monomer pairs. Additionally, gradient copolymers were prepared by the simultaneous copolymerization of either tert-butyl acrylate/octadecyl methacrylate (Mn,p(tBA-co-OMA) = 21 790; Mw/Mn = 1.25) or tert-butyl methacrylate/octadecyl acrylate (Mn,p(tBMA-co-OA) = 21 900; Mw/Mn = 1.20) monomer pairs. AB and ABA triblock copolymers containing octadecyl groups were also prepared with controlled molar mass and composition. The sequence of blocking was varied starting from either poly(tert-butyl (meth)acrylate) or poly(octadecyl (meth)acrylate) macroinitiators. The halogen-exchange technique allowed preparation of various well-defined polyacrylate−polymethacrylate block copolymers. Furthermore, uniform phase-separated structures were formed in ultrathin films cast from AB diblock copolymers of ptBMA-b-pOMA (Mn = 52 000; Mw/Mn = 1.12) and ptBA-b-pOMA (Mn = 28 750; Mw/Mn = 1.20) as determined from AFM. ABA triblock copolymers of pOMA-b-ptBA-b-pOMA (Mn = 75 900; Mw/Mn = 1.14) and poly(octadecyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(octadecyl methacrylate) (Mn = 74 400; Mw/Mn = 1.16) were also analyzed using AFM.