Living Polymerization Process Research Articles

Phase Diagrams of Polymerization-Induced Self-Assembly Are Largely Determined by Polymer Recombination.

In the current work, atom transfer radical polymerization-induced self-assembly (ATRP PISA) phase diagrams were obtained by the means of dissipative particle dynamics simulations. A fast algorithm for determining the equilibrium morphology of block copolymer aggregates was developed. Our goal was to assess how the chemical nature of ATRP affects the self-assembly of diblock copolymers in the course of PISA. We discovered that the chain growth termination via recombination played a key role in determining the ATRP PISA phase diagrams. In particular, ATRP with turned off recombination yielded a PISA phase diagram very similar to that obtained for a simple ideal living polymerization process. However, an increase in the recombination probability led to a significant change of the phase diagram: the transition between cylindrical micelles and vesicles was strongly shifted, and a dependence of the aggregate morphology on the concentration was observed. We speculate that this effect occurred due to the simultaneous action of two factors: the triblock copolymer architecture of the terminated chains and the dispersity of the solvophobic blocks. We showed that these two factors affected the phase diagram weakly if they acted separately; however, their combination, which naturally occurs during ATRP, affected the ATRP PISA phase diagram strongly. We suggest that the recombination reaction is a key factor leading to the complexity of experimental PISA phase diagrams.

Living polymerization in nano-scale volumes. Impact of process conditions on polymerization kinetics and product characteristics

Living polymerization processes, irreversible and reversible, proceeding in a large number of isolated (no mass exchange) nano-scale reactors (droplets) were modeled using stochastic (Monte Carlo) and deterministic simulations and analytical solutions of derived mathematical equations. Monomer and living unimer used as initiator were redistributed in droplets uniformly or accordingly to the Poisson distribution, resulting in nanoreactors containing a small number of growing chains. Stochasticity of reactions involving low number of molecules affects the concentration of monomer and chain length distributions in individual droplets, both differing from ones accounted in macroscopic system. The developed mathematical description, based on values of rate constants of propagation (kp) and depropagation (kd) reactions and on initial monomer and living unimer concentrations, as well as numerical simulations, allow predicting kinetics of the process and of several characteristics of the products resulting therefrom, e.g. chain length distribution. Moreover, they allow also following evolution of droplet subpopulations that differ in composition. Moreover, for the reversible process the equilibrium monomer concentration in a droplets system [M]eq can be calculated. As living ionic and coordination polymerization and the controlled radical polymerization in nano-scale dispersions are rather little explored the theoretical predictions shown in this work could facilitate their further development.

A photoswitchable catalyst system for remote-controlled (co)polymerization in situ

The fundamental properties of a polymeric material are ultimately governed by its structure, which mainly relies on monomer composition and connection, topology, chain length, and polydispersity. Thus far, these structural characteristics are typically set ex situ by the specific polymerization procedure, eventually limiting the future design space for the creation of more sophisticated polymers. Herein, we report on a single photoswitchable catalyst system, which enables in situ remote control over the ring-opening polymerization of l-lactide and further allows regulation of the incorporation of trimethylene carbonate and δ-valerolactone monomers in copolymerizations. By implementing a phenol moiety into a diarylethene-type structure, we exploit light-induced keto–enol tautomerism to switch the hydrogen-bonding-mediated monomer activation reversibly ON and OFF. This general and versatile principle allows for exquisite external modulation of ground-state catalysis of a living polymerization process in a closed system by ultraviolet and visible light and should thereby facilitate the generation of new polymer structures.

Synthesis and polymerization kinetics of ε-caprolactone and ʟ-lactide to low molecular weight polyesters catalyzed by Zn(II) and Cu(II) N-hydroxy-N,N′-diarylformamidine complexes

Discrete Zn(II) and Cu(II) complexes have been synthesized by using N-hydroxy-N,N′-diarylformamidine ligands: N-hydroxy-N,N′-bis(2,6-diisopropylphenyl)formamidine (L1), N-hydroxy-N,N′-bis(2,6-dimethyl)formamidine (L2), N-hydroxy-N-(2-methoxyphenyl)-N′-(2,6-diisopropylphenyl)formamidine (L3), and N-hydroxy-N-(2-methoxyphenyl)-N′-(2,6-dimethylphenyl)formamidine (L4). Reaction of ligands L1–L4 with either ZnOAc2·2H2O or CuOAc2·2H2O in aqueous ethanol gave mononuclear Zn(II) or Cu(II) complexes [Zn-(L1)2] (1), [Zn-(L2)2] (2), [Zn-(L3)2] (3) and [Zn-(L4)2] (4), or [Cu-(L1)2] (5), [Cu-(L2)2] (6), [Cu-(L3)2] (7) and [Cu-(L4)2] (8), respectively, with high yields of up to 84%. All the complexes were characterized by elemental analysis, IR, NMR and mass spectroscopy. The molecular structures of complexes 3 and 7 were determined by single crystal X-ray diffraction analyses. The Zn(II) center in complex 3 exhibited a distorted tetrahedral geometry while in complex 7, the Cu(II) center had a square planar geometry with near C2 symmetry. In both structures, the coordination sites are occupied by imino N- and hydroxyl O-donor atoms from the chelating ligands. All complexes showed catalytic activity and exhibited well-controlled living polymerization process in ring-opening polymerization of ε-caprolactone and l-lactide in the presence of benzyl alcohol co-initiator. The molecular weights were found to be low ranging from 1855 to 3999 Da for polycaprolactone (PCL) and up to 1720 Da for polylactic acid (PLA). The Zn(II) catalysts were found to be more active than Cu(II) catalysts with complex 2 (kapp = 0.1751 h−1) being the most active.

Exploration of tertiary aminosquaramide bifunctional organocatalyst in controlled/living ring-opening polymerization of l-lactide

A series of tertiary aminosquaramides as bifunctional organocatalysts in the ring-opening polymerization (ROP) of l-lactide (l-LA) were developed, allowing the activation of both the l-LA monomer and the alcohol group of the initiator/propagating species. Further, the impact of tertiary nitrogen substituents on catalytic activity in ROP of l-LA was explored. The tertiary aminosquaramide— an air-stable and moisture-stable catalyst—exhibited superior activity in contest with thiourea counterpart when both were equipped with a similar tertiary amine group. Kinetic and chain-extension experiments indicated that the formed poly(l-LA) is featured with narrow polydispersity and high end-group fidelity, hallmarks of a living polymerization process. The initiator efficiency was further executed at ease by preparation of an ABA triblock copolymer poly (l-LA)-b-poly (ethylene glycol)-b-poly (l-LA) in the presence of a dual-headed PEG macroinitiator. 1H NMR titration experiments suggested a bifunctional catalytic mechanism, wherein both the l-LA monomer and the propagating hydroxyl group were activated en route to polymerization. The 1H NMR, SEC, and MALDI-TOF MS measurements validated the quantitative incorporation of the initiator in the polymeric chains and enchainment over competitive trans-esterification reaction. Overall, the structure-activity relationships were surveyed to uncover aminosquaramide as a new bifunctional dual hydrogen-bond donor catalyst for living ROP of l-LA. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

Z-type and R-type macro-RAFT agents in RAFT dispersion polymerization – another mechanism perspective on PISA

The location of RAFT groups plays a key role for the living polymerization process and the formation of nano-objects in RAFT dispersion polymerization.

Grafting olefin polymers for stretchiness

Materials Science Thermoplastic elastomers (TPEs) are stretchy rubberlike polymers that can be melt-processed, do not require cross-linking, and, unlike rubbers, can be recycled. Ohtaki et al. set out to create TPEs based solely on olefin polymers that would not require or be limited by the need for living polymerization processes. They grafted either isotactic or syndiotactic polypropylene segments to a backbone made from ethylene and α-olefins. The polypropylene is crystalline and imparts stiffness and a physical networks structure to the polymer, whereas the noncrystallizing backbone lets the polymer stretch. Samples showed up to 85% elastic recovery when stretched up to 1000%, rivaling the best linear block polyolefin TPEs. Macromolecules 10.1021/acs.macromol.5b01975 (2015).

Catalytic living ring-opening metathesis polymerization.

In living ring-opening metathesis polymerization (ROMP), a transition-metal-carbene complex polymerizes ring-strained olefins with very good control of the molecular weight of the resulting polymers. Because one molecule of the initiator is required for each polymer chain, however, this type of polymerization is expensive for widespread use. We have now designed a chain-transfer agent (CTA) capable of reducing the required amount of metal complex while still maintaining full control over the living polymerization process. This new method introduces a degenerative transfer process to ROMP. We demonstrate that substituted cyclohexene rings are good CTAs, and thereby preserve the 'living' character of the polymerization using catalytic quantities of the metal complex. The resulting polymers show characteristics of a living polymerization, namely narrow molecular-weight distribution, controlled molecular weights and block copolymer formation. This new technique provides access to well-defined polymers for industrial, biomedical and academic use at a fraction of the current costs and significantly reduced levels of residual ruthenium catalyst.

The influence of reagent concentration on the kinetics of carbon dioxide-propylene oxide copolymerization in the presence of a cobalt complex

The effect of the concentrations of propylene oxide and the catalyst (salen)CoDNP/[PPN]Cl ((salen)CoDNP: [PPN]Cl = 1: 1, mol/mol) on the kinetics of the copolymerization of CO2 and propylene oxide at 0.5 MPa and 20°C has been studied. The reaction proceeds at a constant rate after an induction period, and the value of this period varies with the reagent concentrations. The steady-state reaction rate increases linearly with the propylene oxide concentration in the range 5.0–14.3 mol/L. At high catalyst concentrations, such as (5.2–7.3) × 10−3 mol/L, the reaction rate is first order in the catalyst; at concentrations below 5 × 10−3 mol/L, the reaction rate is second order in the catalyst. Molecular mass increases in proportion to the propylene oxide conversion, that is consistent with a living polymerization process. A regioregular copolymer with 96% head-to-tail (HT) connectivity of propylene oxide has been obtained.

Synthesis of star polymers by “core-first” one–pot method via ATRP: Monte Carlo simulations

Results of the simulation of star polymers synthesis by one–pot, core–first method are presented. The simulated ideal living polymerization process consists of two steps. In the first one (core growth) an atom transfer radical polymerization (ATRP) of a crosslinker is performed. When the crosslinker conversion is close to completion, a bifunctional monomer is added and the ATRP polymerization of the monomer takes place from the obtained cores to form linear arms of the stars. The simulation method is based on dynamic lattice liquid (DLL) algorithm, which takes into account changes of local dynamics resulting from polymerization and formation of complex polymer molecules. In the first stage of the synthesis (core formation), in addition to the effect of concentrations of initiator and crosslinker, the rate of intramolecular crosslinking is also very important. This process “consumes” the reactive crosslinker in the cores, limiting the core size and preventing further star–star coupling. The effect of various parameters on star size and internal structure was studied. These parameters involve the rate of intramolecular crosslinking, initial concentrations of the components and the moment of monomer addition. The results can be used as guidelines for the experimental work on star synthesis.

Rhodium-Catalyzed Polymerization of Phenylacetylene and its Derivatives

The present report overviews relevant aspects of rhodium-catalyzed polymerization of phenylacetylenes and substituted acetylene monomers. The π-conjugated polymers obtained through this catalytic homogeneous process are very interesting because of their outstanding electronic, optical and structural properties. The employed rhodium-based catalysts span from simple and well-defined mononuclear complexes to complex binary or even ternary catalytic systems. Extensive fine-tuning of the electronic and steric properties of the catalysts has allowed tailoring the synthesis of conjugated polymers using living polymerization processes. Additionally, recent detailed studies concerning the mechanism of phenylacetylene polymerization are enlightened.

In-situ synthesized hollow nickel-silica spheres for hydrolytic dehydrogenation of ammonia borane

) is able to hydrolyze at room temperature to generate hydrogen with high purity. For this feature, ammonia borane is expected as a hydrogen storage material for polymer membrane fuel cells for mobile use. It is reported that nickel-based catalyst is one of the highly active catalysts for this reaction [1-7]. Studies of catalysts for hydrogen generation from aqueous ammonia borane solution show that dispersion of active metals and/or amorphousness of active phase play important roles in the catalytic performances [1-7]. The morphological effect of nickel-silica catalyst was reported by comparing the activity between composite catalyst and supported catalyst [4]. In recent years, the fabrication and study of core-shell solid and hollow microspheres with well-defined structures have attracted substantial interest because of their potential applications in controlled drug delivery system, lightweight fillers, catalysis, chromatography, vessels for confined reactions, and photonic band gap material [8-13 ]. Sever al strategies have been developed, such as heterophase polymerization/combined with a sol-gel process [14, 15], emulsion/interfacial polymerization approach [1], spray-drying method [16 ], self 7assembly technique [18], surface living polymerization process [19], and the template -based route [20-23 ] to prepare hollow spheres comprising polymeric or ceramic materials. In this study, we firstly fabricat ion reported method of the highly active in-situ synthesized hollow nickel-silica composite spheres . By the method, the hollow nickel-silica composite spheres can be obtained in the simple way, and can be synthesized by sol-gel based method using L(+)-arginine as a promoter for the reaction to

MWD design in a series of CSTRs with living polymerisation reactions

In previous papers of this work methodologies have been established i) to predict the molecular weight distribution (MWD) of living polymerisation processes in various reactor configurations, ii) and - in a reversed calculation process - to design reactor parameters and feed profiles for a single CSTR or a tubular reactor to meet a target MWD. In this paper a model of a series of continuous stirred tank reactors (CSTRs) with various initiator and monomer feed strategies have been used to establish i) the possible MWD shapes with constant feed, ii) the MWD with the lowest possible polydispersity index, and iii) a methodology to design multimodal MWDs with a continuous steady state process. Both the MWD prediction and the design methodologies use a simplified, very fast, direct algorithm, well suited for control purposes.

π共役系高分子アーキテクチャー

π-Conjugated polymers are an attractive class of materials due to their potential applications in electronic devices, but the molecular weight and polymer end groups have not been preciously controlled because most of the polymers have been synthesized by typical step-growth condensation polymerization. However, living polymerization process in the synthesis of π-conjugated polymers has been recently attained by catalyst transfer condensation polymerization, in which the metal catalyst is transferred intramoleculary to the polymer end group of the elongated molecule. This highlight review provides the discovery and development of this polymerization method and its application to the synthesis of π-conjugated polymer architectures such as polymer brush and block copolymers.

SUNLIGHT CONTROLS POLYMER GROWTH

A NOVEL LIVING POLYMERization process that is governed by light could lead to the generation of functional and complex metal-rich polymer architectures. The growth of polymer chains by the repeated addition of monomers normally involves three steps: initiation of the process, propagation of the polymer chain, and chain termination. If there is no termination step, the process is known as a living polymerization, because the chains continue to grow as long as the chains are fed with monomers. Chemists in England and Canada now show that, in the presence of bright sunlight or light from a mercury lamp, ferrocene derivatives with a silicon atom bridging the two cyclopentadienyl ligands can be polymerized by using a cyclopentadienyl anion as a nucleophilic initiator ( Nature Mat. , published online May 14, dx.doi.org/10.1038/nmatl649). To the best of our knowledge, this is the first example of a living polymerization of any monomer—organic or metal-containing—where the monomer needs to be ...

Living/controlled copolymerization of acrylates with nonactivated alkenes

AbstractThe living/controlled copolymerization of methyl acrylate with 1‐alkenes and norbornene derivatives through several radical polymerization techniques has been achieved. These techniques include atom transfer radical polymerization, reversible addition–fragmentation transfer polymerization, nitroxide‐mediated polymerization, and degenerative transfer polymerization. These systems display many of the characteristics of a living polymerization process: the molecular weight increases linearly with the overall conversion, but the polydispersity remains low. Novel block copolymers have been synthesized through the sequential addition of monomers or chain extension. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6175–6192, 2004

Dendrimers as scaffolds for multifunctional reversible addition–fragmentation chain transfer agents: Syntheses and polymerization

AbstractThe synthesis and characterization of novel first‐ and second‐generation true dendritic reversible addition–fragmentation chain transfer (RAFT) agents carrying 6 or 12 pendant 3‐benzylsulfanylthiocarbonylsulfanylpropionic acid RAFT end groups with Z‐group architecture based on 1,1,1‐hydroxyphenyl ethane and trimethylolpropane cores are described in detail. The multifunctional dendritic RAFT agents have been used to prepare star polymers of poly(butyl acrylate) (PBA) and polystyrene (PS) of narrow polydispersities (1.4 < polydispersity index < 1.1 for PBA and 1.5 < polydispersity index < 1.3 for PS) via bulk free‐radical polymerization at 60 °C. The novel dendrimer‐based multifunctional RAFT agents effect an efficient living polymerization process, as evidenced by the linear evolution of the number‐average molecular weight (Mn) with the monomer–polymer conversion, yielding star polymers with molecular weights of up to Mn = 160,000 g mol−1 for PBA (based on a linear PBA calibration) and up to Mn = 70,000 g mol−1 for PS (based on a linear PS calibration). A structural change in the chemical nature of the dendritic core (i.e., 1,1,1‐hydroxyphenyl ethane vs trimethylolpropane) has no influence on the observed molecular weight distributions. The star‐shaped structure of the generated polymers has been confirmed through the cleavage of the pendant arms off the core of the star‐shaped polymeric materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5877–5890, 2004

Molecular Weight Distribution Design with Living Polymerization Reactions

It has been previously shown that it is feasible to control the molecular weight distribution (MWD) of polymers produced from living polymerization processes in flow reactors through the control of reactant feeds. Here, attention is given to the problem of establishing an inverse process model as a step toward a fully automatic control strategy for the synthesis of polymers with predefined MWD. Particular attention is given to the prediction of instantaneous reactor feed conditions for a specified product MWD. The reactor is modeled as an ideal continuous stirred tank reactor with constant monomer concentration in the reactor. The way in which a real laboratory-scale polymerization system can be developed from this approach is outlined.

LIVING POLYMERISATION REACTORS: MOLECULAR WEIGHT DISTRIBUTION CONTROL USING INVERSE NEURAL NETWORK MODELS

In principle, it is possible to exercise control over the molecular weight distribution (MWD) of the polymers produced from living polymerisation processes in flow reactors through the control of reactant feeds in a predetermined fashion. Some of the factors that influence the extent to which control can be achieved with feed perturbations to a single stage continuous flow stirred tank (CSTR) reactor have been reported previously. Here, attention is given to the problem of establishing inverse process models as a first step towards a fully automatic control strategy for the synthesis of polymers with pre-ordained MWD in a real process. Particular attention is given to the development of a neural network model for predicting the instantaneous reactor feed conditions for a specified product MWD and characterising the MWD for the purpose of dimension reduction using principal component analysis. Data collected from a simulated ideal reactor process are used in the study. The way in which this approach will u...

Catalytic Polymerization of Methyl Methacrylate in Different Media Using Supported Metal Phthalocyanines, 1. Bulk Polymerization in Relation to the Microcrystalline Structure of Supported Metal Phthalocyanines

Different catalyst samples of nickel(II) and copper(II) phthalocyanines supported over bentonite clay (Indian type) were prepared with complex loadings ranging between 0.2 and 2.2 wt.-%. Catalyst activities were investigated in the bulk polymerization of methyl methacrylate (MMA) at 80°C in the absence and in the presence of sodium bisulfite as a cocatalyst. In all cases, the catalyst efficiency was evaluated in terms of conversion yield (%), polydispersity index (M w /M n ) was determined via GPC analysis in toluene. The stereotacticity was determined from 1 H NMR spectra. Optimum polymerization conditions were determined for both catalyst systems. Samples with metal phthalocyanines loadings of 1.8% were the most active ones. The polymers produced have controlled molecular weights, which are nearly proportional to conversion, show narrow molecular weight distributions and syndiotactic-rich steric structures. Nickel phthalocyanine seemed to have more stereoregulating effect while copper phthalocyanine had a more enhancing effect for the living polymerization process. The microstructure of solid catalysts was investigated by means of scanning electron microscopy and were correlated with activity data.