Quasi-living Polymerization Research Articles

Synthesis of All-Conjugated Diblock Copolymers by Quasi-Living Polymerization and Observation of Their Microphase Separation

We designed and synthesized the all-conjugated diblock copolymers poly(3-hexylthiophene-block-3-(2-ethylhexyl)thiophene)s (P(3HT-b-3EHT)s) via a modified Grignard metathesis (GRIM), a type of quasi-living polymerization, and studied their microphase-separated structures. The P(3HT-b-3EHT)s synthesized had well-controlled molecular weights and very narrow polydispersity indices (PDIs), which demonstrates the usefulness of GRIM polymerization for the synthesis of semiconducting block copolymers. P(3HT-b-3EHT)s self-organized to form clear microphase-separated patterns upon thermal treatment, as observed by AFM. Interestingly, the enhancement of the interchain interaction of the P3HT segments compared with the P3HT homopolymer was clearly observed from the UV-vis spectra, despite the fact that the amount of crystalline P3HT fraction was reduced to 83% of the total polymer amount in P(3HT-b-3EHT). It is suggested that the relatively unconstrained, amorphous segments of P3EHT can enhance the crystallization of P3HT segments to form an ordered self-organized nanostructure.

Kinetic and mechanistic study of the quasiliving cationic polymerization of styrene with the 2-phenyl-2-propanol/AlCl 3 · OBu 2 initiating system

The cationic polymerization of styrene with the 2-phenyl-2-propanol (CumOH)/AlCl 3 · OBu 2 initiating system at various dibutyl ether concentrations in a mixture of 1,2-dichloroethane and n-hexane (55:45 v/v) at −15 °C was investigated. The experimental results showed that an increase in dibutyl ether concentration leads to a noticeable decrease in the polymerization rate as well as to the more controlled polymerization in terms of molecular weight ( M n) and molecular weight distribution (MWD) evolutions. The kinetic investigation revealed that the polymerization proceeds in two stages. The first stage is characterized by high polymerization rate and slow initiation relative to propagation. During this stage molecular weight decreases or does not change and MWD increases with conversion. In the second stage considerably slower quasiliving polymerization of styrene occurs. The quasiliving nature of the styrene polymerization by the CumOH/AlCl 3 · OBu 2 system is proved and mechanistic scheme of the polymerization is proposed.

Quasiliving Cationic Polymerization of Styrene and Isobutylene: Run Number and Apparent Rate Constant of Ionization by TiCl4 and Energies of Activation of Elementary Reactions

The quantity kp/k-i was measured from first-order kinetic data for cationic quasiliving polymerization of styrene and isobutylene initiated with 5-tert-butyl-1,3-bis(2-chloro-2-propyl)benzene (bDCC)/TiCl4 in 60/40 MCHex/MeCl, via analysis of an initiation event termed rapid monomer consumption (RMC). RMC is characterized by an initial period of high polymerization rate followed by slower first-order decay in monomer concentration and is due to a larger ionization rate for the initiator compared to the polymer chain end. The value of kp/k-i was used in conjunction with the apparent rate constant for propagation, kapp, to calculate apparent rate constants of chain-end ionization, ki, for both monomers at −60, −70, −80, and −90 °C, independently of kp. Rate constants of ion-pair collapse and ionization equilibrium were calculated assuming published values of kp. Apparent energies of activation for kp/k-i of −2.4 and −4.6 kcal/mol were determined for styrene and IB, respectively. Apparent energies of activati...

Polymerization of propylene with [ t-BuNSiMe 2Ind]TiMe 2–MAO catalyst systems

ansa-Indenylamidodimethyltitanium complex ([ t-BuNSiMe 2Ind]TiMe 2: 1) was synthesized by one-pot reactions starting from the ligand, MeLi and TiCl 4. The structure of 1 was determined by X-ray crystallography and the results obtained revealed that the indenyl ligand coordinate to titanium in an η 4-tendency. Propylene polymerization was conducted with 1 in toluene or heptane as solvent at 0 °C in the presence of dried methylaluminoxane (MAO) or dried modified MAO (MMAO), which was prepared from the toluene solutions of MAO or MMAO by removing free trialkylaluminium contained. Polymerization behavior was investigated from the consumption rate of propylene in a semi-batch system. The dried MAO/toluene system showed the highest activity without any deactivation. The produced polymer in the dried MAO/toluene system had the highest molecular weight and narrowest molecular weight distribution. The number-average molecular weight of the polymer increased almost linearly with increasing polymerization time accompanied by narrowing molecular weight distribution from 1.42 to 1.37 and the number of polymer chains was almost constant. Thus, it was found that quasi-living polymerization of propylene proceeded. The 13C NMR measurement indicated that 1-dried MAO/toluene produced poly(propylene) with isotactic triad of 40%.

Controlled free-radical polymerization of vinyl chloride

Owing to the importance of poly(vinyl chloride) (PVC) as the second-largest plastic in volume after the polyolefins and above styrene polymers, the control of the free-radical polymerization of vinyl chloride (VC) is of high industrial and academic interest. But still the term “controlled” polymerization is not yet clearly defined. Often it is used for quasi-living polymerizations with equilibrium reactions in the initiation and/or termination step or for the control of the molecular weight distribution (MWD), but it can also be applied to several structural aspects such as stereochemistry, branching, or special technical properties. In the present article, the control of chain growth and chain transfer is discussed. It has been well known for many years that the propagation step in the VC polymerization is terminated to a large degree by the rather frequent and temperature-dependent chain transfer of the growing macromolecules to the monomer. Therefore, the degree of polymerization is strongly governed by the polymerization temperature. However, this transfer step does not result in a controlled or a narrow MWD. By means of free-radical nitroxide-mediated polymerization of VC in suspension, PVC with a narrower MWD can be obtained also at higher polymerization temperatures. The resulting PVC with nitroxide end groups can act as a macro-initiator for various monomers, resulting in two-block copolymers, which are, e.g., interesting compatibilizers in blends with PVC. J. VINYL ADDIT. TECHNOL., 11:86–90, 2005. © 2005 Society of Plastics Engineers

<b>Polymerization of propene with <sup>t</sup>BuNSiMe<sub>2</sub>C<sub>5</sub>Me<sub>4</sub>TiMe<sub>2</sub>: Effects of trialkylaluminiums as additives</b>

Propene was polymerized at 0 o C with t BuNSiMe 2 C 5 Me 4 TiMe 2 /MAO. Kinetic features and other parameters indicated quasi-living polymerization. Effects of various trialkylaluminiums as additives have been investigated; it was found that compounds with more bulky groups like i Bu 3 Al, Oct 3 Al increased the activities significantly whereas Me 3 Al and Et 3 Al reduced the activities of the catalyst system. The triad sequence in the 13 C NMR spectrum confirmed a syndiotactic-enriched atactic polypropene. KEY WORDS: P olymerization of propene, t BuNSiMe 2 C 5 Me 4 TiMe 2 , Trialkylaluminiums, Syndiotactic-enriched atactic polypropene Bull. Chem. Soc. Ethiop. 2004 , 18(2), 131-141.

New Titanium Complexes with Two β-Enaminoketonato Chelate Ligands: Syntheses, Structures, and Olefin Polymerization Activities

New titanium complexes with two nonsymmetric bidentate beta-enaminoketonato (N,O) ligands (4a-e), [(Ph)NC(R-2)C(H)C(R-1)O](2)TiCl2, have been synthesized. X-ray crystal structure reveals that complex 4a has a C-2-symmetric conformation with a distorted octahedral geometry around the titanium center. With modified methylaluminoxane (MMAO) as a cocatalyst, complexes 4a-e are active catalysts for ethylene polymerization at room temperature, producing high molecular weight polyethylenes bearing linear structures. The 4a,b/MMAO catalyst systems exhibit the characteristics of a quasi-living polymerization of ethylene, producing polyethylenes with narrow molecular weight distributions. Moreover, the 4a-d/MMAO catalyst systems are also capable of promoting the quasi-living copolymerization of ethylene with norbornene at room temperature, yielding high molecular weight alternating copolymers with narrow molecular weight distributions. The quasi-living nature of the catalysts allows the synthesis of new A-B polyethylene-block-poly(ethylene-conorbornene) diblock copolymer.

Ethylene Homopolymerization and Copolymerization with Functionalized 5-Norbornen-2-yl Monomers by a Novel Nickel Catalyst System

The homopolymerization and the copolymerization of ethylene with functionalized 5-norbornen-2-yl derivatives by the nickel catalyst system L(iPr2)Ni(η1-CH2Ph)(PMe3) (1) [L = N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamide] and Ni(COD)2 (bis(1,5-cyclooctadiene)nickel) produces polymers with high molecular weights and narrow molecular weight distributions. A typical ethylene polymerization reaction proceeds under 100 psi of ethylene and at 20 °C, using 1 (0.34 mM) and Ni(COD)2 (0.83 mM). Likewise, under similar conditions, the copolymerization of ethylene with 5-norbornen-2-yl acetate (3) (0.15 M) for 90 min by 1 (0.67 mM) and Ni(COD)2 (1.67 mM) produced a high molecular weight functionalized polyethylene bearing ester functionalities. 5-Norbornen-2-ol (0.15 M) underwent a similar copolymerization with ethylene for 20 min to yield a hydroxy-functionalized polyethylene. Narrow molecular weight distributions, coupled with the increase of polymer molar mass with time, are consistent with a quasi-living polymerization process in the case of ethylene homopolymerization and ethylene copolymerization with 3.

Phosphorylcholine-endcapped oligomer and block co-oligomer and surface biological reactivity

Phosphorylcholine (PC)-endcapped oligomer and block co-oligomer were prepared by employing a photoiniferter-based quasi-living polymerization technique. The designed oligomer had a PC polar head group attached to an alkylene chain at one end of the molecule and an oligo(styrene) (oligoST) segment at the other end. In the co-oligomer, an oligo( N, N-dimethylacrylamide) (oligoDMAAm) segment was inserted between both ends of the oligomer mentioned above. Surface coating of these amphiphilic substances, using an appropriate coating procedure, resulted in a very hydrophilic characteristic, suggesting that the oligoST anchored on the substrate and the PC polar head group was exposed to or located on the outer coating layer. Non-cell adhesivity in serum-containing medium was observed, while slightly reduced protein adsorption was observed. Thus, PC-endcapped oligomer and block co-oligomer appear to function as a biocompatible coating.

Quasi-Living Cationic Polymerization of Styrene and Isobutylene: Measurement of Run Number and Calculation of Apparent Rate Constant of Ionization by TiCl4

The run number (RN), the average number of monomer units added per ionization−termination cycle, was measured at −70 °C from first-order kinetic data for cationic quasi-living polymerization of styrene and isobutylene initiated with 5-tert-butyl-1,3-bis(2-chloro-2-propyl)benzene (bDCC)/TiCl4 in 60/40 MCHex/MeCl, via analysis of an initiation event termed rapid monomer consumption (RMC). RMC is characterized by an initial period of high polymerization rate followed by slower first-order decay in monomer concentration and is due to a larger ionization rate for the initiator compared to that for the polymer chain end. Styrene RN was found to decrease with increasing initiator concentration while that for isobutylene remained relatively unchanged; the dependence of styrene RN on initiator concentration was attributed to chain transfer to initiator during RMC. RN in the limit of zero initiator concentration was determined to be 39 and 4.7 for 0.5 M styrene and isobutylene, respectively. Apparent rate constants...

Evidence of the Quasi-Living Character of theansa-Zirconocene/MAO-Catalyzed Copolymerization of Ethylene and Norbornene

The kinetics of the ethylene-norbornene copolymerization, catalyzed by rac-Et(Ind)2ZrCl2/MAO, 90%rac/10%meso-Et(4,7-Me2Ind)2ZrCl2/MAO and rac-H2C(3-tert-BuInd)2ZrCl2/MAO was followed by sampling from the reaction mixture at fixed time intervals. Catalyst activity, copolymer composition and molar mass were studied as a function of time. The polymers showed an unusually low polydispersity and a significant increase in their molar mass with time, suggesting a quasi-living polymerization.

Kinetic investigation of propene polymerization with stopped-flow method

The stopped-flow technique, by which a quasi-living polymerization process can be performed within an extremely short period (ca. 0.2s), is a powerful method for kinetic investigation in Ziegler catalysis. Significant understanding of many controversial problems was achieved, such as arguments concerning the nonuniformity of the active sites, the accurate kinetic parameters, the active sites formed in the different stages, the role of cocatalyst, the effects of hydrogen and electron donors, etc..

Stopped-Flow Techniques in Ziegler Catalysis

The stopped-flow method, by which a quasi-living polymerization process can be realized within an extremely short period (ca. 0.2 s), has been proven to be one of the most powerful techniques for studies on the nature of the active sites and elucidation of the olefin polymerization mechanism based on the information from the polymers obtained in the initial stage of polymerization. It has been demonstrated that a better and deeper understanding of many controversial problems in Ziegler catalysis has been achieved, such as arguments concerning the non-uniformity of the active sites, the intrinsic kinetic parameters, the effects of catalyst preparation conditions, the role of cocatalysts, hydrogen and electron donor, etc. The successive modifications to the basic stopped-flow system have led to extensive applications in investigating the catalyst pretreatment effects induced by various reagents, as well as developing a series of novel block copolymers.

Synthesis and characterization of a model carbon-chain polymer substituted by two esters on every third atom via anionic ring-opening polymerization of a cyclopropane-1,1-dicarboxylate

Ultrapure diethyl 1,1-cyclopropanedicarboxylate (1) undergoes ring-opening polymerization when placed in the presence of small amounts of sodium thiophenolate (2) at temperatures above 80°C, and leads to the synthesis of a carbon-chain polymer substituted on every third carbon atom by ethyl ester substituents. 1 polymerizes also in the presence of 2 generated in situ from thiophenol and metallic sodium, but does not polymerize in the presence of metallic sodium alone. Polymerizations are slow and require high concentrations in monomer and initiator to obtain reasonable polymerization times. In spite of the high temperatures used in some experiments (up to 130°C), no structural subunit resulting from side reactions was detected, presumably due to the high stability of the propagating malonate carbanion. Polymers of narrow molecular weight distribution were obtained at both 80 and 130°C (M̄w/M̄n < 1,14), and absolute degrees of polymerization increased with polymer yields. These results were rationalized on the basic of a quasi-living polymerization mechanism. Thermal properties of poly(1) were determined by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Poly(1) is stable up to 275°C and is a micro-crystalline polymer insoluble in most typical solvents, with the noticeable exception of chloroform and dichloromethane.

Facilitated permeation of myoglobin through porous membranes: Different permeation behavior through membranes of polyoxyethylene‐ and dextran‐conjugated polyamides prepared by quasi‐living polymerization of a bicyclic lactam

AbstractIn the ultrafiltration test of a myoglobin solution through porous membranes of the ABA‐type block copolymers composed of polyamide as outer segments and polyoxyethylene (Mn = 1.9–2.0 × 104) as an inner segment, in which the values of weight fraction of the polyamide segments (W) were 0.90, 0.84, 0.82, 0.81, and 0.73, the concentration of the permeate was found to be much higher than that in feed under the pressure difference of 1–2 kg/cm2. Such singularly facilitated permeation was observed also in the test through the dense membranes of the polyamide–polyoxyethylene block copolymer with W of 0.81 and 0.73. On the other hand, neither porous nor dense membranes of the graft copolymer (W = 0.83) having a dextran stock (Mn = 1.8 × 104) and 2.6 pieces of polyamide branches showed similar facilitated permeation, although dextran was soluble in water as well as polyoxyethylene. The apparent interaction of myoglobin with dextran may be stronger than that with polyoxyethylene. © 1994 John Wiley &amp; Sons, Inc.

A survey of kinetic and mechanistic similarities in living polymerization systems

AbstractIn the light of recent discoveries in the field of living polymerizations it seems inevitable to reconsider our views on these polymerization systems. This paper surveys the kinetic and mechanistic similarities in living polymerizations, and analyses and compares chain transfer dominated nonliving polymerizations and living systems to conclude on the nature of propagating species, shelflife and livingness. Some recently raised specific problems are also summarized and discussed. It has been found that most of the living polymerizations known to date, such as living anionic, cationic ring opening, group transfer, carbocationic, ring opening metathesis, Ziegler‐Natta, free radical and immortal polymerizations, exhibit the characteristics of quasiliving polymerization, i.e., an equilibrium exists between propagating (active) and inactive (dormant) species. On the basis of this finding and a comparison between mechanistic and kinetic models of quasiliving and ideal living polymerizations, it is suggested that the former is the general phenomenon, and ideal living polymerization is a subclass of quasiliving polymerizations.

Stopped flow polymerization of propene with typical MgCl 2-supported high-yield catalysts

A new method, viz. stopped flow polymerization, has been employed to observe the quasi-living polymerization state of propene. It was found that the molecular weight distribution was maintained constant from the very start of the polymerization process ( i.e. after 0.1 s) and that the concentration of Al(C 2H 5) 3 used as well as method of catalyst preparation influenced some of the kinetic parameters.

Electron-Pair Donors in Carbocationic Polymerization. III. Carbocation Stabilization by External Electron-Pair Donors in Isobutylene Polymerization

Abstract The polymerization of isobutylene (IB) initiated by a variety of tertiary chloride/TiCl4 or BC13 systems can be very beneficially influenced by deliberately added electron-pair donors (ED's). ED's whose Gutmann's donor number is larger than ∼26, e.g., dimethylsulfoxide (DMSO) and dimethylacetamide (DMA), are most suitable to mediate numerous most desirable effects. Thus, in the presence of DMSO or DMA: (1) quasi-living polymerizations initiated by cumyl chloride (CumCl)/TiCl4 or 2-chloro-2,4,4-trirnethylpentane (TMPCl)/TiCl4 give rise to very narrow molecular weight distribution (MWD) polyisobutylene (PIB) ( M w / M n = 1.1–1.2); (2) the CumCl/BCl3/IB inifer system becomes living and yields PIB with very narrow MWD; (3) the polymerization-inactive TMPCl/BCl3 system becomes active and induces living IB polymerization to narrow-MWD product; (4) indanyl end-group formation, which may occur in the CumCl/BCl3 or p-dicumyl chloride/BCl3, inifer systems, is eliminated. The effect of reaction conditions,...

Quasiliving Carbocationic Polymerization. XVII. Synthesis Of Poly (Styrene-β-Isobutylene-β-Styrene)

Abstract Poly(styrene-b-isobutylene-b-styrene) has been synthesized by sequential carbocationic polymerization under quasiliving conditions at -90°C. The quasiliving synthesis was effected by first continuously and slowly condensing gaseous isobutylene (IB) to a bifunctional initiating system (p-dicumyl chloride/TiCl4) dissolved in a hexane-methylene chloride (60:40 v/v) mixture. After the quasiliving polyisobutylene (PIB) sequence had reached a desired molecular weight, styrene (St) was continuously and slowly added to produce the polystyrene (PSt) sequence. The products consisted of the target triblock. However, due to initiation by impurities and possibly to chain transfer to both IB and St, it also contained diblocks and small amounts of homopolymers. While the latter could be removed by selective fractionation, the triblocks and diblocks could not be separated. The mechanism of quasiliving polymerization leading to PIB/PSt blocks is discussed.

Quasiliving Carbocationic Polymerization. XIII. Polymerization of 2,4,6-Trimethylstyrene

Abstract The polymerization of 2,4,6-trimethylstyrene (vinyl mesitylene) has been investigated, and quasiliving polymerizations have been achieved under a comfortably wide experimental condition range. This monomer is particularly suitable for quasiliving polymerizations because the methyl groups in the 2 and 6 positions prevent chain transfer to monomer involving indanyl-skeleton formation. Quasiliving polymerizations readily occurred by the use of cumyl chloride/TiCl4 or BCl3 initiating systems in various n-C6H14/CH2Cl2 mixtures at -50°C. Because indanyl-skeleton formation is impossible, the rate of monomer addition can be safely decreased to very low values without risking chain transfer by intramolecular alkylation.