Living carbocationic polymerization of isobutyl vinyl ether and the synthesis of poly[isobutylene-b-(isobutyl vinyl ether)]

The MeCH(O-i-Bu)Cl/TiCl₄/MeCONMe₂ initiating system was found to induce the rapid living carbocationic polymerization (LC^⊕Pzn) of isobutyl vinyl ether (IBuVE) at ?100°C. Degradation by dealcoholation which usually accompanies the polymerization of alkyl vinyl ethers by strong Lewis acids is “frozen out” at this low temperature and poly(isobutyl vinyl ether)s (PIBuVEs) with theoretical molecular weights up to ca. 40,000 g/mol (calculated from the initiator/monomer input) and narrow molecular weight distributions (M?_w/M?_n ≤ 1.2) are readily obtained. According to ¹³C-NMR spectroscopy, PIBuVEs prepared by living polymerization at ?100°C are not stereoregular. The MeCH(O-i-Bu)Cl/TiCl₄ combination induces the rapid LC^⊕Pzn of IBuVE even in the absence of N,N-dimethylacetamide (DMA). The addition of the common ion salt, n-Bu₄NCl to the latter system retards the polymerization and meaningful kinetic information can be obtained. The kinetic findings have been explained in terms of TiCl₄. IBuVE and TiCl₄ · IBuVE and TiCl₄ · PIBuVE complexes. The HCl (formal initiator)/TiCl₄/DMA combination is the first initiating system that can be regarded to induce the LC^⊕Pzn of both isobutylene (IB) and IBuVE. Polyisobutylene (PIB)–PIBuVE diblocks were prepared by sequential monomer addition in “one pot” by the 2-chloro-2,4,4-trimethylpentane (TMP-Cl)/TiCl₄/DMA initiating system. Crossover efficiencies are, however, below 35% because the PIB^⊕ + IBuVE → PIB-b-PIBuVE^⊕ crossover is slow. © 1993 John Wiley & Sons, Inc.     

Novel star‐block polymers: Three polyisobutylene‐b‐poly(methyl methacrylate) arms radiating from an aromatic core

A series of novel three‐arm star blocks consisting of three polyisobutylene‐b‐poly(methyl methacrylate) (PIB‐b‐PMMA) diblocks radiating from a tricumyl core were synthesized, characterized, and tested. The synthetic strategy involved three steps: the synthesis of Cl^t ‐tritelechelic PIB by living cationic isobutylene (IB) polymerization, the conversion of the Cl^t termini to isobutyryl bromide groups, and the initiation of living radical methyl methacrylate (MMA) polymerization by the latter groups. The PIB and PMMA segment lengths (M_n 's) could be controlled by controlling the conditions of the living cationic and radical polymerizations of IB and MMA, respectively. Core destruction analysis directly proved the postulated three‐arm microarchitecture. The structures of the products were analyzed by ¹H NMR and Fourier transform infrared spectroscopies, and their thermal properties were analyzed by differential scanning calorimetry and thermogravimetric analysis. The presence of a low‐ and a high‐temperature glass transition (T_g,PIB ∼ −63°C, T_g,PMMA ∼ 120°C) indicated a phase‐separated micromorphology. Stress/strain analysis showed a tensile strength of up to ∼ 22.9 MPa and an elongation of ∼ 200%. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 706–714, 2000     

Living Carbocationic Polymerization. LIX. The Synthesis of Novel Asymmetric Telechelic Polyisobutylenes

Abstract

The synthesis of novel asymmetric telechelic polyisobutylenes (PIB) carrying a CH₃OCO— headgroup and a —CH₂C(CH₃)₂C1 tailgroup by the use of novel initiators mediating the living carbocationic polymerization (LC⁺Pzn) of isobutylene (IB) is described. Subsequently, the parent headgroup has been quantitatively converted into a HOCO— group, and the parent tailgroup into a —pC₆H₄OH group. Scheme 1 summarizes the synthesis routes to the initiators, as well as the polymerizations and functionalizations leading to various asymmetric telechelic PIBs. The CH₃OCO— headgroup of the initiator most likely functions as an internal electron donor during the LC⁺Pzn of IB.     

Construction of PIB‐b‐PDEAEMA well‐defined amphiphilic diblock copolymers via sequential living carbocationic and RAFT polymerization

A series of well‐defined amphiphilic diblock copolymers consisting of hydrophobic polyisobutylene (PIB) and hydrophilic poly(2‐(diethylamino)ethyl methacrylate) (PDEAEMA) segments was synthesized via the combination of living carbocationic polymerization and reversible addition fragmentation chain transfer (RAFT) polymerization. Living carbocationic polymerization of isobutylene followed by end‐capping with 1,3‐butadiene was first performed at ?70 °C to give a well‐defined allyl‐Cl‐terminated PIB with a low polydispersity (M_w/M_n =1.29). This end‐functionalized PIB was further converted to a macromolecular chain transfer agent for mediating RAFT block copolymerization of 2‐(diethylamino)ethyl methacrylate at 60 °C in tetrahydrofuran to afford the target well‐defined PIB‐b‐PDEAEMA diblock copolymers with narrow molecular weight distributions (M_w/M_n ≤1.22). The self‐assembly behavior of these amphiphilic diblock copolymers in aqueous media was investigated by fluorescence spectroscopy and transmission electron microscope, and furthermore, their pH‐responsive behavior was studied by UV‐vis and dynamic light scattering. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1478–1486     

Synthesis and characterization of thermoplastic elastomers with polyisobutylene and polyalloocimene blocks

This article presents the synthesis and characterization of diblock, triblock, and tetrablock copolymers of alloocimene (Allo), a terpene from renewable resources, and isobutylene (IB) using the recently reported two‐phase living carbocationic system. The addition of a second Allo increment to diblocks of Allo and IB yielded triblock and tetrablock structures. The block copolymers showed thermoplastic elastomeric (TPE) properties. It is demonstrated that the unusual behavior of diblocks exhibiting TPE properties is due to the strain‐induced crystallization of the polyisobutylene block. The polyalloocimene blocks can be cured, making this material a potential replacement of halobutyl rubber without halogen content. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1567–1574     

Living carbocationic polymerization of p-halostyrenes. III. Syntheses and characterization of novel thermoplastic elastomers of isobutylene and p-chlorostyrene

Novel linear and three-arm star radial thermoplastic elastomers (TPE) comprising rubbery polyisobutylene (PIB) center blocks connected to glassy poly(p-chlorostyrene) (PpClSt) outer blocks have been synthesized by sequential monomer addition. For triblock polymer synthesis isobutylene (IB) was added continuously to a bifunctional initiating system (dicumylmethyl ether/TiCl₄) dissolved in CH₃Cl/methylcyclohexane solvent mixture at –80°C. After the living PIB sequence has reached the desired molecular weight p-chlorostyrene (pClSt) was added to produce the PpClSt end blocks. The synthesis conditions for the TPEs were developed with the help of model experiments using the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ initiating system and subsequent PIB-PpClSt diblock syntheses. The triblock and radiol block polymers after solvent extraction exhibited excellent TPE characteristics. Copolymer compositions were determined by ¹H-NMR and UV spectroscopy and further characterization was carried out by GPC, DSC, DMTA, and selective solvent extraction techniques. The TPEs exhibit two T_g's characteristic of glassy PpClSt (129°C) and rubbery PIB (?70°C) segments. Cast TPE films were clear and gave tensile strengths of 1.2-21 MPa with elongations of 460–1500%. Transmission electron microscopy (TEM) of a triblock polymer containing ca. 38 wt % PpClSt suggests cylindrical PpClSt domains of 40–70 nm length and 25–35 nm diam embedded in a PIB matrix.     

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

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.     

Living Carbocationic Polymerization. LII. Living Carbocationic Copolymerization of Indene and p-Methylstyrene. 2. Synthesis,Characterization, and Physical Properties of Poly((Indene-co-p-Methylstyrene)-b-Isobutylene-b-(Indene-co-p-Methylstyrene)) Thermoplastic Elastomers

Abstract

Novel thermoplastic elastomers (TPEs) consisting of a central rubbery polyisobutylene (PIB) segment flanked by two glassy outer segments comprising indene (Ind)-co-p-methylstyrene (pMeSt) random copolymers have been prepared. The synthesis was effected by sequential monomer addition in one reactor: The process starts by the biliving homopolymerization of isobutylene (IB) and yields the living dication ⁺PIB⁺; the latter, upon the introduction of Ind/pMeSt mixtures, induces the living copolymerization of these monomers and yields the target TPE P(Ind-co-pMeSt)-b-PIB-b-P(Ind-co-pMeSt) triblock. The length of the rubbery midblock and the composition of the Ind-co-pMeSt random copolymer outer blocks (i.e., the overall composition of the triblocks) can be readily controlled. The glass transition temperature (T_g ) of the outer blocks can be fine-tuned by controlling the relative Ind/ pMeSt composition. The triblocks are excellent TPEs; for example, a P(Ind-co-pMeSt)-b-PIB-b-P(Ind-co-pMeSt) of M _n ≈ 115,000 g/mol containing a PIB midblock of M _n ≈ 70,200 g/mol and glassy copolymer outer blocks of P(Ind-co-pMeSt) [Ind/pMeSt = 41/59 (w/w)] exhibited 23.4 MPa tensile strength and 460% elongation. Tensile strengths and 300% moduli increase with the relative amount of the glassy segment present. Hardness increases with increasing Ind content.     

Amphiphilic conetworks. III. Poly(2,3‐dihydroxypropyl methacrylate)–polyisobutylene and poly(ethylene glycol) methacrylate–polyisobutylene based hydrogels prepared by two‐step polymer procedure

This article describes the synthesis and characterization of new amphiphilic polymer conetworks containing hydrophilic poly(2,3‐dihydroxypropyl methacrylate) or poly(ethylene glycol) methacrylate (PEGMA) and hydrophobic polyisobutylene chains. This conetworks were prepared by a two‐step polymer synthesis. In the first step, a cationic copolymer of isobutylene and 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (IDI) was prepared. The isocyanate groups of the IB‐IDI random copolymer were subsequently transformed in situ to methacrylate (MA) groups in reaction with 2‐hydroxyethyl methacrylate (HEMA). In the second step, the resulting MA‐multifunctional PIB‐based crosslinker, PIB(MA)_n, with an average functionality of approximately four per chain, was copolymerized with 2,3‐dihydroxypropyl methacrylate or poly(ethylene glycol) methacrylate by radical mechanism in tetrahydrofuran giving rise to amphiphilic conetworks containing 11–60 mol % of DHPMA or 10–12 mol % of PEGMA. The synthesized conetworks were characterized with solid‐state ¹³C‐NMR spectroscopy and differential scanning calorimetry. The amphiphilic nature of the conetworks was proved by swelling in both water and n‐heptane. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4074–4081, 2007     

Polyisobutylene‐b‐Poly(N,N‐diethylacrylamide) well‐defined amphiphilic diblock copolymer: Synthesis and thermo‐responsive phase behavior

Polyisobutylene‐b‐poly(N,N‐diethylacrylamide) (PIB‐b‐PDEAAm) well‐defined amphiphilic diblock copolymers were synthesized by sequential living carbocationic polymerization and reversible addition‐fragmentation chain transfer (RAFT) polymerization. The hydrophobic polyisobutylene segment was first built by living carbocationic polymerization of isobutylene at ?70 ° C followed by multistep transformations to give a well‐defined (M_w/M_n = 1.22) macromolecular chain transfer agent, PIB‐CTA. The hydrophilic poly(N,N‐diethylacrylamide) block was constructed by PIB‐CTA mediated RAFT polymerization of N,N‐diethylacrylamide at 60 ° C to afford the desired well‐defined PIB‐b‐PDEAAm diblock copolymers with narrow molecular weight distributions (M_w/M_n ≤1.26). Fluorescence spectroscopy, transmission electron microscope, and dynamic light scattering (DLS) were employed to investigate the self‐assembly behavior of PIB‐b‐PDEAAm amphiphilic diblock copolymers in aqueous media. These diblock copolymers also exhibited thermo‐responsive phase behavior, which was confirmed by UV‐Vis and DLS measurements. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1143–1150     

Amphiphilic conetworks. IV. Poly(methacrylic acid)‐l‐polyisobutylene and poly(acrylic acid)‐l‐polyisobutylene based hydrogels prepared by two‐step polymer procedure. New pH responsive conetworks

This article describes the synthesis and characterization of new amphiphilic polymer conetworks containing hydrophilic poly(methacrylic acid) (PMAA) or poly(acrylic acid) (PAA) and hydrophobic polyisobutylene (PIB) chains. These conetworks were prepared by a two‐step polymer synthesis. In the first step, a cationic copolymer of isobutylene (IB) and 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (IDI) was prepared. The isocyanate groups of the IB–IDI random copolymer were subsequently transformed in situ to methacrylate (MA) groups in reaction with 2‐hydroxyethyl methacrylate (HEMA). In the second step, the resulting MA‐multifunctional PIB‐based crosslinker, PIB(MA)_n, with an average functionality of approximately four methacrylic groups per chain, was copolymerized with methacrylic acid (MAA) or acrylic acid (AA) by radical mechanism in tetrahydrofuran giving rise to amphiphilic conetworks containing 31–79 mol % of MAA or 26–36 mol % of AA. The synthesized conetworks were characterized with solid‐state ¹³C‐NMR spectroscopy and differential scanning calorimetry. The amphiphilic nature of the conetworks was proven by swelling in both aqueous media with low and high pH and n‐heptane. The effect of varying pH on the swelling behavior of the synthesized conetworks is presented. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1284–1291, 2009     

Living Carbocationic Polymerization of p-Methylstyrene and Sequential Block Copolymerization of Isobutylene with p-Methylstyrene

Abstract

A novel scheme was developed for the synthesis of pure polyisobutylene-poly(p-methylstyrene) block copolymers by sequential monomer addition. The synthesis involves the living polymerization of isobutylene by the TiCl₄/methyl chloride:methylcyclohexane or hexanes 40:60 v:v/ -80°C system in the presence of di-tert-butylpyridine. When the polymerization of isobutylene is complete, the living polyisobutylene chain end is transformed to the corresponding diphenyl alkyl end by capping with 1,1-diphenylethylene. Subsequently, titanium(IV) isopropoxide or titanium(IV) butoxide is added to decrease the Lewis acidity followed by the addition of p-methylstyrene. The success of the method was demonstrated by p-methylstyrene homopolymerization experiments initiated by 2-chloro-2,4,4-trimethylpentane that resulted in ～ 100% initiator efficiencies when the TiCl₄/titanium(IV) isopropoxide or -butoxide ratio was less than 25/7, as well as by the clean synthesis of polyisobutylenepoly(p-methylstyrene) diblock copolymers.     

Sulfonation of tert-alkyl chlorides: Application to the tert-chloride-terminated polyisobutylene system

The direct sulfonation of tert-chloride-terminated polyisobutylene was carried out using acetyl sulfate in methylene chloride/hexanes diluent to produce low molecular weight model ionomer systems with narrow molecular weight distribution. The room temperature sulfonation of 2-chloro-2,4,4-trimethylpentane, which serves as a model for the polyisobutylene chain end obtained in the controlled cationic polymerization of isobutylene, was found to be quantitative after 3 h reaction. The two major products, isomeric β,γ-unsaturated sulfonic acids differing only in the location of the double bond, were the same products obtained from the sulfonation of 2,4,4-trimethyl-1-pentene, which serves as a model for the polyisobutylene chain end after quantitative dehydrochlorination. Near-monodisperse, tert-chloride-terminated, three-arm star polyisobutylene was synthesized under living cationic polymerization conditions using the tricumychloride/TiCl₄/pyridine initiation system in hexanes/methyl chloride consolvents. Sulfonation was carried out directly upon the obtained polymer, and the sulfonated product was purified using ion-exchange chromatography. Structural elucidation was performed using NMR. Titration and molecular weight characterization revealed that sulfonation produced exactly one sulfonic acid group per polyisobutylene chain end.     

Living carbocationic polymerization. IV. Living polymerization of isobutylene

Truly living polymerization of isobutylene (IB) has been achieved for the first time by the use of new initiating systems comprising organic acetate-BCl³ complexes under conventional laboratory conditions in various solvents from −10 to −50°C. The overall rates of polymerization are very high, which necessitated the development of the incremental monomer addition (IMA) technique to demonstrate living systems. The living nature of the polymerizations was demonstrated by linear versus grams polyisobutylene (PIB) formed plots starting at the origin and horizontal number of polymer molecules formed versus amount of polymer formed plots. obeys [IB]/[CH₃COOR^t · BCl₃]. Molecular weight distributions (MWD) are very narrow in homogeneous systems whereas somewhat broader values are obtained when the polymer precipitates out of solution . The MWDs tend to narrow with increasing molecular weights, i.e., with the accumulation of precipitated polymer in the reactor. Traces of moisture do not affect the outcome of living polymerizations. In the presence of monomer both first and second order chain transfer to monomer are avoided even at −10°C. The diagnosis of first and second order chain transfer has been accomplished, and the first order process seems to dominate. Forced termination can be effected either by thermally decomposing the propagating complexes or by nucleophiles. In either case the end groups will be tertiary chlorides. The living polymerization of isobutylene initiated by ester · BCl₃ complexes most likely proceeds by a two-component group transfer polymerization.     

Amphiphilic conetworks. II. Novel two‐step synthesis of poly[2‐(dimethylamino)ethyl methacrylate]–polyisobutylene,poly(N‐isopropylacrylamide)–polyisobutylene,and poly(N,N‐dimethylacrylamide)–polyisobutylene hydrogels

Amphiphilic polymer conetworks consisting of hydrophilic poly[2‐(dimethylamino)ethyl methacrylate], poly(N‐isopropylacrylamide), or poly(N,N‐dimethylacrylamide) and hydrophobic polyisobutylene chains were synthesized with a novel two‐step procedure. In the first step, a methacrylate‐multifunctional polyisobutylene crosslinker was prepared by the cationic copolymerization of isobutylene with 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate. In the second step, the methacrylate‐multifunctional polyisobutylene crosslinker, with a number‐average molecular weight of 8200 and an average functionality of approximately 4 per chain, was copolymerized radically with 2‐(dimethylamino)ethyl methacrylate, N‐isopropylacrylamide, or N,N‐dimethylacrylamide into transparent amphiphilic conetworks containing 42–47 mol % hydrophilic monomer. The synthesized conetworks were characterized with solid‐state ¹³C NMR spectroscopy and differential scanning calorimetry. The amphiphilic nature of the conetworks was proved by swelling in both water and n‐heptane. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6378–6384, 2006     

Synthesis of pH-responsive amphiphilic diblock copolymers containing polyisobutylene via oxyanion-initiated polymerization and their multiple self-assembly morphologies

 Two pH-responsive amphiphilic diblock copolymers, namely polyisobutylene-block-poly[2-(N,N-dimethylamino)ethyl methacrylate] (PIB-b-PDMAEMA) and polyisobutylene-block-poly(metharylic acid) (PIB-b-PMAA), were synthesized via oxyanion-initiated polymerization, and their multiple self-assembly behaviors have been studied. An exo-olefin-terminated highly reactive polyisobutylene (HRPIB) was first changed to hydroxyl-terminated PIB (PIB-OH) via hydroboration-oxidation of C＝C double bond in the chain end, and then reacted with KH to yield a potassium alcoholate of PIB (PIB-O^-K⁺). PIB-O^-K⁺ was immediately used as a macroinitiator to polymerize DMAEMA monomer, resulting in a cationic diblock copolymer PIB-b-PDMAEMA. With the similar synthesis procedure, the anionic diblock copolymer PIB-b-PMAA could be prepared via a combination of oxyanion-initiated polymerization of tert-butyl methacrylate (tBMA) and subsequent hydrolysis of tert-butyl ester groups in PtBMA block. The functional PIB and block copolymers have been fully characterized by ¹H-NMR, FT-IR spectroscopy, and gel permeation chromatography (GPC). These samples allowed us to systematically investigate the effects of block composition on the pH responsivity and various self-assembled morphologies of the copolymers in THF/water mixed solvent. Transmission electron microscopy (TEM) images revealed that these diblock copolymers containing small amount of original PIB without exo-olefin-terminated group are able to self-assemble into micelles, vesicles with different particle sizes and cylindrical aggregates, depending on various factors including block copolymer composition, solvent polarity and pH value.     

Synthesis of methyl methacrylate,styrene, and isobutylene multiblock copolymers using atom transfer and cationic polymerization

ABCBA‐type pentablock copolymers of methyl methacrylate, styrene, and isobutylene (IB) were prepared by the cationic polymerization of IB in the presence of the α,ω‐dichloro‐PS‐b‐PMMA‐b‐PS triblock copolymer [where PS is polystyrene and PMMA is poly(methyl methacrylate)] as a macroinitiator in conjunction with diethylaluminum chloride (Et₂AlCl) as a coinitiator. The macroinitiator was prepared by a two‐step copper‐based atom transfer radical polymerization (ATRP). The reaction temperature, ?78 or ?25 °C, significantly affected the IB content in the resulting copolymers; a higher content was obtained at ?78 °C. The formation of the PIB‐b‐PS‐b‐PMMA‐b‐PS‐b‐PIB copolymers (where PIB is polyisobutylene), prepared at ?25 (20.3 mol % IB) or ?78 °C (61.3 mol % IB; rubbery material), with relatively narrow molecular weight distributions provided direct evidence of the presence of labile chlorine atoms at both ends of the macroinitiator capable of initiation of cationic polymerization of IB. One glass‐transition temperature (T_g), 104.5 °C, was observed for the aforementioned triblock copolymer, and the pentablock copolymer containing 61.3 mol % IB showed two well‐defined T_g's: ?73.0 °C for PIB and 95.6 °C for the PS–PMMA blocks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3823–3830, 2005     

Living carbocationic polymerization. IV. Living polymerization of isobutylene

Truly living polymerization of isobutylene (IB) has been achieved for the first time by the use of new initiating systems comprising organic acetate-BCl₃ complexes under conventional laboratory conditions in various solvents from ?10 to ?50°C. The overall rates of polymerization are very high, which necessitated the development of the incremental monomer addition (IMA) technique to demonstrate living systems. The living nature of the polymerizations was demonstrated by linear M _n versus grams polyisobutylene (PIB) formed plots starting at the origin and horizontal number of polymer molecules formed versus amount of polymer formed plots. DP _n obeys [IB]/[CH₃COOR^t · BCl₃]. Molecular weight distributions (MWD) are very narrow in homogeneous systems (M _w/M _n = 1.2–1.3) whereas somewhat broader values are obtained when the polymer precipitates out of solution (M _w/M _n = 1.4–3.0). The MWDs tend to narrow with increasing molecular weights, i.e., with the accumulation of precipitated polymer in the reactor. Traces of moisture do not affect the outcome of living polymerizations. In the presence of monomer both first and second order chain transfer to monomer are avoided even at ?10°C. The diagnosis of first and second order chain transfer has been accomplished, and the first order process seems to dominate. Forced termination can be effected either by thermally decomposing the propagating complexes or by nucleophiles. In either case the end groups will be tertiary chlorides. The living polymerization of isobutylene initiated by ester. BCl₃ complexes most likely proceeds by a two-component group transfer polymerization.     

Living cationic polymerization of isobutylene coinitiated by FeCl3 in the presence of isopropanol

A simple but effective FeCl₃‐based initiating system has been developed to achieve living cationic polymerization of isobutylene (IB) using di(2‐chloro‐2‐propyl) benzene (DCC) or 1‐chlorine‐2,4,4‐trimethylpentane (TMPCl) as initiators in the presence of isopropanol (iPrOH) at ?80 °C for the first time. The polymerization with near 100% of initiation efficiency proceeded rapidly and completed quantitatively within 10 min. Polyisobutylenes (PIBs) with designed number‐average molecular weights (M_n) from 3500 to 21,000 g mol^?1, narrow molecular weight distributions (MWD, M_w/M_n ≤ 1.2) and near 100% of tert‐Cl terminal groups could be obtained at appropriate concentrations of iPrOH. Livingness of cationic polymerization of IB was further confirmed by all monomer in technique and incremental monomer addition technique. The kinetic investigation on living cationic polymerization was conducted by real‐time attenuated total reflectance Fourier transform infrared spectroscopy. The apparent constant of rate for propagation (k_p^A) increased with increasing polymerization temperature and the apparent activation energy (ΔE_a) for propagation was determined to be 14.4 kJ mol^?1. Furthermore, the triblock copolymers of PS‐b‐PIB‐b‐PS with different chain length of polystyrene (PS) segments could be successfully synthesized via living cationic polymerization with DCC/FeCl₃/iPrOH initiating system by sequential monomer addition of IB and styrene at ?80 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

An Attempt to Adapt Superacid Chemistry for “Living” Carbenium Ion Polymerizations

The discovery that carbocations can be stabilized in super acid media, e.g., SbF₅-SO₂, etc., raises the possibility of “living” carbenium ion polymerization. Polymerization experiments with isobutylene and styrene carried out at high acid concentrations and in the virtual absence of nucleophile, i.e., under conditions conducive for living polymerization, failed to indicate a linear conversion vs molecular weight relationship and/or block copolymer formation. Additional model experiments with 2,4,4-trimethyl-1-pentene substantiate our conclusions that “living” carbocation polymerizations are unlikely to be produced by superacid chemistry.