Cationic Polymerization Of Alkenes Research Articles

Low‐cost bifunctional initiators for bidirectional living cationic polymerization of olefins. III. centrally functionalized polyisobutylenes

ABSTRACTAllyl‐telechelic polyisobutylene (A‐PIB‐A) produced by the bis‐benzocyclobutane dichloride (bBCB‐diCl) initiator contains the bis‐benzocyclobutane (bBCB) fragment at the center of the macromolecule (A‐PIB‐bBCB‐PIB‐A). Thermolysis of A‐PIB‐bBCB‐PIB‐A quantitatively converts the central bBCB fragment to a substituted conjugated tetraene (A‐PIB‐tetraene‐PIB‐A). The structure of A‐PIB‐tetraene‐PIB‐A was anticipated from small molecule models and identified/quantitated by 1H NMR spectroscopy. This is the first time a reactive functional group was introduced at the statistical center of a (telechelic) PIB. Subsequently, the A‐PIB‐tetraene‐PIB‐A was peroxidized to an epoxy derivative. Reaction of the A‐PIB‐tetraene‐PIB‐A with HSCH2CH2OH produced HOCH2‐telechelic PIB containing a central CH2OH function, and hydrosilation with HSi(Me2)‐O‐Si(Me2)H produced SiH‐telechelic PIB with a central SiH function. Reactions with maleic anhydride, tetracyanoethylene, butyl lithium, and potassium permanganate have also been examined. In sum, A‐PIB‐bBCB‐PIB‐A and A‐PIB‐tetraene‐PIB‐A are useful intermediates for the synthesis of novel PIB‐based materials for various end uses under investigation. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1140–1145

Low cost bifunctional initiators for bidirectional living cationic polymerization of olefins. II. hyperbranched styrene–isobutylene–styrene triblocks with superior combination of properties

ABSTRACTBoth bifunctional initiators, the new low cost bBCB‐diCl [4,9‐dichloro,2,4,7,9‐tetramethyl‐tricyclo[6.2.0.036]deca‐1(8),2,6‐triene] and the universally used “hindered” HDCCl [1‐(tert‐butyl)‐3,5‐bis(2‐chloropropan‐2‐yl)benzene] induce the living bidirectional block copolymerization of isobutylene (IB) followed by styrene (St), and produce PSt‐b‐PIB‐b‐PSt (SIBS) triblocks. We discovered that the molecular weights of triblocks kept significantly increasing long after St conversion reached completion during syntheses. Results were explained by the formation of blends consisting of the expected linear SIBS plus hyperbranched SIBS, HB(SIBS)n. The structure of high molecular weight (>106 g/mol) HB(SIBS)n was characterized by various techniques, and key properties of SIBS/HB(SIBS)n blends were investigated. The mechanism of HB(SIBS)n formation and the synthesis of SIBS/HB(SIBS)n blends was elucidated. The properties of SIBS/HB(SIBS)n blends are superior to those of SIBS. Thus, whereas SIBS exhibits ∼25 MPa tensile strength and ∼450% elongation, SIBS/HB(SIBS)n blends exhibit 25–27 MPa tensile strength and >400% elongation; deformation under constant load of SIBS is ∼12%, whereas that of SIBS/HB(SIBS)n is <1%; permanent set of SIBS is 1.3% whereas that of SIBS/HB(SIBS)n is <0.5%. SIBS/HB(SIBS)n blends also exhibit higher yield, yield strength, and toughness than SIBS. The microstructure/property relationship of HB(SIBS)n is discussed and the reasons for enhanced properties of SIBS/HB(SIBS)n blends are analyzed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 705–713

ChemInform Abstract: Taming Living Carbocations in Catalytic Direct Conjugate Addition of Simple Alkenes to α,β‐Enones.

AbstractThe use of a BINOL derived phosphonic acid ester salt as the catalyst facilitates the selective β‐proton elimination by suppressing cationic olefin polymerization in direct alkene addition to enones to afford vinyl‐type adducts in high yields.

Aluminium coordination complexes in copolymerization reactions of carbon dioxide and epoxides

Al complexes are widely used in a range of polymerization reactions (ROP of cyclic esters and cationic polymerization of alkenes). Since the discovery in 1978 that an Al porphyrin complex could copolymerize propylene oxide with carbon dioxide, Al coordination compounds have been studied extensively as catalysts for epoxide-carbon dioxide copolymerizations. The most widely studied catalysts are Al porphyrin and Al salen derivatives. This is partially due to their ability to act as mechanistic models for more reactive, paramagnetic Cr catalysts. However, this in depth mechanistic understanding could be employed to design more active Al catalysts themselves, which would be beneficial given the wide availability of this metal. Polymerization data (% CO3 linkages, M(n), M(w)/M(n) and TON) for these complexes are presented and mechanisms discussed. In most cases, especially those employing square-based pyramidal Al complexes, co-catalysts are required to obtain high levels of carbon dioxide incorporation. However, in some cases, the use of co-catalysts inhibits the copolymerization reaction. Lewis acidic Al phenolate complexes have been used as activators in CHO-carbon dioxide copolymerizations to increase TOF and this has recently led to the development of asymmetric copolymerization reactions. Given the ready availability of Al, the robustness of many complexes (e.g. use in immortal polymerizations) and opportunity to prepare block copolymers and other designer materials, Al complexes for copolymerization of carbon dioxide are surely worth a second look.

Solvation as a Main Factor That Determines the Strength of Liquid Superacids and the Selectivity of the Acid‐Catalyzed Reactions of Olefins

AbstractFor Abstract see ChemInform Abstract in Full Text.

Solvation as a main factor that determines the strength of liquid superacids and the selectivity of the acid-catalyzed reactions of olefins

Analysis of literature and ab initio quantum chemical calculations indicates that the solvation of protons in anhydrous H 2SO 4 or HF is considerably weaker than in aqueous solutions. This results in very low constants of autoprotolysis of anhydrous superacids. In contrast, hydration of protons in moderately concentrated acids is much stronger, resulting in higher dissociation constants. Therefore, the strength of superacids is connected to the high chemical activity of the weakly solvated protons, rather than to the amount of protons. In a similar way, solvation of protonated active intermediates of the acid-catalyzed transformations of olefins in anhydrous superacids is also weaker than in aqueous solutions. This results in the real carbenium ion mechanisms of the isoparaffin–olefin alkylation or “conjunct oligomerization” of olefins. In contrast, solvation with water in moderately concentrated or dilute sulfuric acid transforms alkyl carbenium ions into oxonium ions. Therefore, cationic polymerization of olefins in moderately concentrated sulfuric acid is not a real carbenium ion reaction. Similar to the acid-catalyzed transformations of olefins on zeolites, it involves oxonium ions as the stable active intermediates and alkyl carbenium ions as transition states.

Is the cationic polymerization of iso-olefins in a moderately concentrated sulfuric acid a real carbenium-ion reaction?

The different reaction products resulting from 2-methyl-2-butene transformations in 95 and 65% sulfuric acid at 0°C clearly indicate the different mechanisms of the acid catalyzed ‘conjunct olygomerization’ and cationic polymerization of olefins in the concentrated and more dilute acid. The formation of paraffinic oligomers with even and odd numbers of carbon atoms in the 95% acid indicates the predominant role of hydride transfer and cracking. This should be considered as an evidence of the real carbenium-ion mechanism of ‘conjunct olygomerization’, although the steady state concentration of alkyl carbenium ions is below the limit of 13 C NMR detection. The absence of these reactions in a moderately dilute acid indicates a different mechanism of cationic polymerization. The latter represents an oxonium ion reaction where similar to transformations of olefins on zeolites the carbenium ions are formed only as transition states.

Living cationic polymerization of olefins. How did the discovery come about?

The tortuous road to living carbocationic polymerizations is chronicled. The impetus for this project was my conviction that, just as living anionic polymerizations have started with a critical insight, a similar breakthrough will also be possible with cations. Upon retrospect, the facts show a three-step progression to the objective: Discovery of 1) controlled initiation, 2) reversible termination (quasiliving systems), and 3) controlled chain transfer. But what good is the discovery of a process without demonstrating its usefulness in terms of desirable products? Thus, a section concerns unique microarchitectures obtainable only by this technique: functional liquids, telechelics, thermoplastic elastomers, etc. The marketing of some of these products has already started, and the fundamental exploration of the promises of this technique is in progress worldwide. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2285–2293, 1999

Theoretical Estimation of Acid Strength of Boron Fluoride-Alcohol Complexes During Cationic Polymerization of Olefins

Complexes of alcohols (CH3OH, C2H5-OH, iso-C3H7, t-C4H9) and boron fluoride, BRnF3−n , (here n = 0, 1, 2, 3; R = CH3, C2H5, iso-C3H7, t-C4H9) are the traditional acidic catalysts of polymerization of olefins [1–3]. Change of the nature of proton donors-alcohols and of ligand environment of B provides the formation of initiating systems with a wide range of activity.

Organo-Lewis Acids As Cocatalysts in Cationic Metallocene Polymerization Catalysis. Unusual Characteristics of Sterically Encumbered Tris(perfluorobiphenyl)borane

Organo-Lewis acids such as methylalumoxane (MAO) and B(C{sub 6}F{sub 5} ){sub 3} (I) play pivotal roles as alkide/hydride abstractors/ cocatalysts in generating highly active, cationic olefin polymerization catalysts (II; L,L` = anionic ancillary ligands; X{sup -} = weakly coordinating anion). We communicate here the unusual cocatalytic characteristics of the new, sterically encumbered fluoroarylborane, tris(2,2`,2``-perfluorobiphenyl)-borane (PBB, III). Characteristics include substantially different abstractive and ion pair structure/reactivity relationships vis-a-vis I. PPB was synthesized as colorless microcrystals in 76% yield from C{sub 6}F{sub 5}Br. Reaction with group 4 and Th methyls proceeds cleanly to yield cationic complexes, which were characterized by standard {sup 1}H/{sup 13}C/{sup 19}F NMR spectroscopic and analytical techniques. The results illustrate the substantial and surprising differences in cationic complex ion pair structure and reactivity that can be brought about by modifications in fluoroarylborane catalyst architecture. 10 refs., 1 fig., 1 tab.

Theoretical Estimation of Acid Strength of Boron-Fluoride-Alcohol Complexes during Cationic Polymerization of Olefins

Abstract The quantum-chemical investigations of ROH BRnF3-n-complexes were carried out and their acidic strength determine as function of alcohols and ligand characteristics and the environment of the heteroatom B.

Improved synthesis and cationic polymerization of N‐vinylmaleimide

The cationic polymerization of olefins in the presence of strong protonic acids or Lewis acids has attracted considerable attention over a long period of time. As an example of significant industrial importance one can point to the production of butyl rubber obtained by the polymerization of isobutylene and isoprene in the presence of AICl, I). In the early 1980s this area became even more promising, as it was discovered that vinyl ethers undergo a living cationic polymerization in the presence of HI/IZ2). This process offers the possibility to prepare well-defined polymers with respect to structure, molecular weight and end-group functionality. In the last decennium a number of research groups showed that also isobutylene (cumyl acetate/BCl,), styrene derivatives (HI/12) and N-vinylcarbazole (HI) can be polymerized in a living way'). During our search for new monomers we became interested in N-vinylmaleimide (l), which can be characterized as a dual monomer. It should be possible to polymerize the monomer by two different mechanisms, e. g., via cationic (vinyl group) and radical (maleimide group) species. This paper describes an improved method for the preparation of 1 and preliminary results of the polymerization of 1 in the presence of BF, . Et,O and HCVZnCI, .

Developments in the cationic polymerization of alkenes - A personal view

In this paper the author presents some of his contributions to the theory and practice of the cationic polymerization (C.P.) of alkenes since 1944. The first phase of his work at the University of Manchester comprises the discovery of co-catalysis by water with TiCl4, the invention of the pseudo-Dewar reaction vessel, the use of trichloroacetic acid as co-catalyst, and the disproof of the alleged cationic isomerization of cis-stilbene.

Carbenium ions, onium ions, and covalent species in the cationic polymerization of alkenes

AbstractThe importance of exchange reactions between various types of active species present in the cationic polymerization of alkenes is addressed. Reactivities of carbocations, corresponding ion pairs, onium ions, and covalent species are discussed for model systems and in real polymerization. The influence of various parameters on the equilibria between carbenium ions, onium ions, and covalent species is described. Rate constants of the isomerization of active sites are estimated and correlated with polydispersities. General ways to improve control of cationic polymerization of alkenes are discussed.

Cationic polymerization of alkenes and heterocyclics. More similarities than differences

AbstractThe cationic polymerization of alkenes and heterocyclics is compared in a critical way. After a brief introduction to the polymerizability of various monomers and efficiency of initiators, various active sites involved in propagation are discussed. They include covalent species, onium ions and carbenium ions of different degrees of association. Proportions and reactivities of these active sites are discussed for different monomers. Structure‐reactivity correlations for both systems are described. The construction of a general unifying theory of cationic polymerization is attempted, with peculiarities typical for each system pointed out.

Mechanism of Chain Initiation and Propagation Stages in the Cationic Polymerization of Olefins

Abstract A discussion is presented of the mechanism of chain initiation and propagation stages in the cationic polymerization of olefins based on the example of catalytic systems of the type “aluminum chlorides-weak proton donor” (water, alcohols).

Initiators of cationic polymerization of olefins arising from interaction between two lewis acids

AbstractBy an interaction between two relatively weak Lewis acids, highly effective initiators of the cationic polymerization of olefins are obtained. Under conditions where the polymerization of isobutylene with BCl3, TiCl4 or VOCl3 does not proceed in methylene chloride or heptane solution, it can be initiated with a small or even trace quantity of FeCl3. The formation of complex compounds was investigated by UV spectroscopy and by the conductometric titration in methylene chloride. Hydrogen chloride, which has no co‐initiation effect on polymerization in heptane solution initiated with metal halides alone, is an effective co‐initiator in a mixture of Lewis acids containing a small quantity of FeCl3. The results support a hypothesis regarding the initiation of polymerization of olefins by cations of metal halides arising by the ionization of a weaker acid with a stronger one.

Complexes of Lewis acids in the cationic polymerization of olefins

AbstractFindings concerning the origin of electron donor‐acceptor complexes between olefinic hydrocarbons and chosen Lewis acids supplemented by new results are summarized. The important characteristics reported here are stoichiometric ratios of complex formation determined by the variation and titration methods, equilibrium constants and the thermodynamic parameters AG, AH and AS derived from them. Attention has been devoted to the characterization of frontier orbitals of olefins and Lewis acids using ionization potentials, half‐wave polarographic oxidation potentials, electron affinities and half‐wave polarographic reduction potentials. The aim consists in a quantitative characterization of redox processes which occur in elemental initiation reactions. The final evaluation of the data obtained has confirmed that the complexes involved in this case are weak and behave in accordance with the Mulliken theory.

“The projects that never were”. A lecture given to the polymer discussion group

In reviewing his life's work on the cationic polymerization of alkenes and oxacyclic compounds and the many branch-lines which sprang therefrom, the author emphasizes some of the research projects which did not come to fruition, and speculates on the reasons for the lack of success. A failure in 1946 to initiate a cationic polymerization by high-energy radiation is contrasted with an initially unsuccessful and a subsequent successful attempt in 1955 to use liquid carbon dioxide as a solvent for polymerizing isobutene; it was the much better understanding of the processes involved after the lapse of 9 yr which made the difference. That this, the first-ever use of carbon dioxide as a reaction medium, raised no interest amongst industrialists, despite the cheapness and harmlessness of this solvent, is attributed to the lack of economic incentive.

A correlation of anodic peak potentials with HOMO energies of various monomers

AbstractElectroinitiated cationic polymerization of olefins can be initiated by direct electron transfer from the highest occupied molecular orbital (HOMO) of monomers, by constant potential electrolysis. Potentials, at which some monomers lose electrons, were measured by cyclic voltammetry. Measurements were made on a Pt electrode versus Ag0/Ag+, in acetonitrile. The measured anodic peak potentials (Ep,a) were correlated to HOMO energies (ϵm), calculated by Hückel molecular orbital (HMO) considerations for coplanar molecules. For methyl‐substituted monomers the ω‐technique was also applied. A linear equation has been developed for Ep,a as a function of ϵm, for styrene derivatives having +I and +E substituents.