Cationic polymerization of isobutylene with H2O/TiCl4 initiating system in the presence of electron pair donors

Cationic polymerization of isobutylene (IB) in a mixture of methylene dichloride (CH₂Cl₂) and n-hexane (n-Hex) was conducted by using H₂O as initiator, TiCl₄ as co-initiator in the presence of strong external electron pair donor (ED), such as pyridine (Py), dimethylacetamide (DMA) or triethylamine (TEA). The effects of ED concentration, TiCl₄ concentration, solvent polarity, polymerization temperature (T) and time on IB polymerization, molecular weight (MW) and molecular weight distribution (MWD, M_w/M_n) of polyisobutylene (PIB) products were investigated. The relative amount of polymer formed via uncontrolled initiation by conventional active species (I) decreased with increasing the solvent polarity, TiCl₄ concentration and ED concentration in the polymerization. The desirable polymerization of IB with apparent absence of chain transfer reactions could be obtained by H₂O/TiCl₄ initiating system in the presence of ED under the appropriate reaction conditions. The external electron pair donors and TiCl₄ did specially play important and effective roles on polymerization.     

Synthesis of polyisobutylene with arylamino terminal group by combination of cationic polymerization with alkylation

The controlled cationic polymerization of isobutylene (IB) initiated by H₂O as initiator and TiCl₄ as coinitiator was carried out in n‐Hexane/CH₂Cl₂ (60/40, v/v) mixture at −40 °C in the presence of N,N‐dimethylacetamide (DMA). Polyisobutylene (PIB) with nearly theoretical molecular weight (M_n = 1.0 × 10⁴ g/mol), polydispersity (M_w/M_n) of 1.5 and high content (87.3%) of reactive end groups (tert‐Chlorine and α‐double bond) was obtained. The Friedel‐Crafts alkylation of triphenylamine (TPA) with the above reactive PIB was further conducted at different reactions, such as [TPA]/[PIB], solvent polarity, alkylation temperature, and time. The resultant PIBs with arylamino terminal group were characterized by ¹H NMR, UV, and GPC with RI/UV dual detectors. The experimental results indicate that alkylation efficiency (A_eff) increased with increases in [TPA]/[PIB], reaction temperature, and reaction time and with a decrease in solvent polarity. The alkylation efficiency could reach 81.0% at 60/40(v/v) mixture of n‐Hex/CH₂Cl₂ with [TPA]/[PIB] of 4.49 at 50 °C for 54 h. Interestingly, the synthesis of PIB with arylamino terminal group could also be achieved in one pot by combination of the cationic polymerization of IB initiated by H₂O/TiCl₄/DMA system with the successive alkylation by further introduction of TPA. Mono‐, di‐ or tri‐alkylation occurred experimentally with different molar ratio of [TPA]/[PIB]. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 936–946, 2008     

Polyisobutylene-containing block polymers by sequential monomer addition. II. Polystyrene–polyisobutylene–polystyrene triblock polymers: Synthesis,characterization, and physical properties

New linear and three-arm star thermoplastic elastomers (TPEs) comprising a rubbery polysobutylene (PIB) midblock flanked by glass polystyrene (PSt) blocks have been synthesized by living carbocationic polymerization in the presence of select additives by sequential monomer addition. First, isobutylene (IB) was polymerized by bi- and trifunctional tert-ether (dicumyl- and tricumyl methoxy) initiators in conjunction with TiCl₄ conintiator in CH₃Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at ?80°C. After the living, narrow molecular weight, distribution PIB (M?_w/M?_n = 1.1-1.2) has reached the desired molecular weight, styrene (St) together with an electron pair donor (ED) and a proton trap (di-tert-butylpyridine, DtBP) were added to block PSt from the living chain ends. Uncontrolled initiation by protic impurities that produces PSt contamination is prevented by the use of DtBP. PSt-PIB-PSt blocks obtained in the absence of additives are contaminated by homopolymer and /or diblocks due to inefficient blocking and initiation by protic impurities, and exhibit poor physical properties. In contrast in the presence of the strong ED N,N-dimethylacetamide (DMA) and DtBP the blocking of St from living PIB chain occurs efficiently and block copolymers exhibiting good mechanical properties can be prepared. Virgin TPEs can be repeatedly compression molded without deterioration of physical properties. The products exhibit a low and a high temperature T_g characteristic of phase separated PIB and PSt domains. Transmission electron microscopy of linear triblocks containing ～ 34 wt % PSt also indicates microphase separation and suggests PSt rods dispersed in a PIB matrix.     

Poly(styrene‐b‐isobutylene) multiarm star‐block copolymers

Multiarm star‐branched polymers based on poly(styrene‐b‐isobutylene) (PS‐PIB) block copolymer arms were synthesized under controlled/living cationic polymerization conditions using the 2‐chloro‐2‐propylbenzene (CCl)/TiCl₄/pyridine (Py) initiating system and divinylbenzene (DVB) as gel‐core‐forming comonomer. To optimize the timing of isobutylene (IB) addition to living PS⊕, the kinetics of styrene (St) polymerization at −80°C were measured in both 60 : 40 (v : v) methyl cyclohexane (MCHx) : MeCl and 60 : 40 hexane : MeCl cosolvents. For either cosolvent system, it was found that the polymerizations followed first‐order kinetics with respect to the monomer and the number of actively growing chains remained invariant. The rate of polymerization was slower in MCHx : MeCl (k_app = 2.5 × 10⁻³ s⁻¹) compared with hexane : MeCl (k_app = 5.6 × 10⁻³ s⁻¹) ([CCl]_o = [TiCl₄]/15 = 3.64 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M). Intermolecular alkylation reactions were observed at [St]_o = 0.93M but could be suppressed by avoiding very high St conversion and by setting [St]_o ≤ 0.35M. For St polymerization, k_app = 1.1 × 10⁻³ s⁻¹ ([CCl]_o = [TiCl₄]/15 = 1.82 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M); this was significantly higher than that observed for IB polymerization (k_app = 3.0 × 10⁻⁴ s⁻¹; [CCl]_o = [Py] = [TiCl₄]/15 = 1.86 × 10⁻³M; [IB]_o = 1.0M). Blocking efficiencies were higher in hexane : MeCl compared with MCHx : MeCl cosolvent system. Star formation was faster with PS‐PIB arms compared with PIB homopolymer arms under similar conditions. Using [DVB] = 5.6 × 10⁻²M = 10 times chain end concentration, 92% of PS‐PIB arms (M_n,PS = 2600 and M_n,PIB = 13,400 g/mol) were linked within 1 h at −80°C with negligible star–star coupling. It was difficult to achieve complete linking of all the arms prior to the onset of star–star coupling. Apparently, the presence of the St block allows the PS‐PIB block copolymer arms to be incorporated into growing star polymers by an additional mechanism, namely, electrophilic aromatic substitution (EAS), which leads to increased rates of star formation and greater tendency toward star–star coupling. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1629–1641, 1999     

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     

Similarities and differences of epoxide, aldehyde and peroxide initiators for Cp2TiCl-catalyzed styrene living radical polymerizations

Cp₂TiCl is the first example of a single electron transfer (SET) agent that both provides initiating radicals from three different types of functionalities (i.e. radical ring opening of epoxides and reduction of aldehydes and peroxides) and doubles as mediator for the living radical polymerization of styrene (St) by reversibly endcapping the growing polymer chains. An initiator (I) comparison was performed using 1,4-butanediol diglycidyl ether (BDE), benzaldehyde (BA) and benzoyl peroxide (BPO) as models. The investigation of the effect of reaction variables was carried out over a wide range of experimental conditions ([Cp₂TiCl₂]/[I] = 0.5/1-4/1; [Zn]/[Cp₂TiCl₂] = 0.5/1-3/1, [St]/[I] = 50/1-400/1 and T = 60-130 °C) to reveal living polymerization features such as a linear dependence of molecular weight on conversion and narrow molecular weight distribution (M_w/M_n) for each initiator class. However, progressively lower polydispersities and larger initiator efficiencies are obtained with increasing the [Cp₂TiCl₂]/[I] and [Zn]/[Cp₂TiCl₂] ratios and with decreasing temperature. Accordingly, optimum conditions correspond to [St]/[I]/[Cp₂TiCl₂]/[Zn] = [50-200]/[1]/[2-3]/[4-6] at 70-90 °C. By contrast to peroxides, aldehydes and the more reactive epoxides provide alcohol end groups useful in block or graft copolymers synthesis.     

Living Cationic Sequential Block Copolymerization of Isobutylene with 4‐tert‐Butoxystyrene: Synthesis and Characterization of Poly(p‐hydroxystyrene‐b‐isobutylene‐b‐p‐hydroxystyrene) Triblock Copolymers

The living polymerization of p‐tert‐butoxystyrene (tBuOS) was studied in methylcyclohexane (MeChx)/methylchloride (MeCl) 60/40 v/v solvent mixture at –80°C. The model initiator 1,1,‐ditolylethylene (DTE) capped 2‐chloro‐2,4,4‐trimethylpentane (TMPCl) was formed in situ in conjunction with TiCl₄. Lowering the Lewis acidity by the addition of Ti(OIp)₄ was necessary to induce a rapid and controlled polymerization of tBuOS. Well‐defined polymers with controlled molecular weights, however, were only obtained at a narrow [Ti(OIp)₄]/[TiCl₄]=0.83–0.86 ratio. Above this ratio, the polymerization of tBuOS was slow and became absent at [Ti(OIp)₄]/[TiCl₄]≥1.18. At ratios lower than 0.83, the polymerization was too rapid and the initiator efficiency was lower than 100%. The living polymerization of tBuOS was also studied with SnBr₄ as Lewis acid. After capping TMPCl with DTE, Ti(OIp)₄ was added to reach [Ti(OIp)₄]/[TiCl₄]=1.2, followed by the addition of tBuOS and SnBr₄. SnBr₄ induced a well‐controlled living polymerization approximately first order in [SnBr₄], and the polymers exhibited close to theoretical M _ns and low polydispersity indices (PDI<1.2). The success of the method was also demonstrated by the clean synthesis of poly(isobutylene‐b‐p‐tert‐butoxystyrene) PIB‐b‐PtBuOS diblock copolymers. PtBuOS‐b‐PIB‐b‐PtBuOS triblock copolymer thermoplastic elastomers were prepared by employing 5‐tert‐butyl‐1,3‐bis(1‐methoxy‐1‐methylethyl)benzene (DCE) as a difunctional initiator for the living polymerization of IB followed by capping with DTE and substitution of TiCl₄ with SnBr₄ for the polymerization of tBuOS. Deprotection of the triblock copolymer in the presence of catalytic amount of HCl yielded poly(p‐hydroxystyrene‐b‐isobutylene‐b‐p‐hydroxystyrene) (PHOS‐b‐PIB‐b‐PHOS). PHOS‐b‐PIB‐b‐PHOS with 39.3 wt% p‐hydroxystyrene content exhibited typical characteristic of a thermoplastic elastomers (TPEs) with tensile strength of 18 MPa and ultimate elongation of 300%.     

Combination of “living” nitroxide-mediated and photoiniferter-induced “grafting from” free-radical polymerizations: From branched copolymers to unimolecular micelles and microgels

We report on solution properties of lightly grafted copolymers composed of polystyrene (PS) backbone (degree of polymerization of PS backbone, N_b=95) and variable length of poly(tert-butyl methacrylate) P(tBuMA) side chains (degree of polymerization of side chains, N_sc=14-222) at fixed number of grafting sites n = 11 and polydispersity index (M_w/M_n) ranging from 1.05 to 2.63. Synthesis of these graft copolymers is based on a novel synthetic route [Gromadzki D, Makuška R, Netopilík M, Holler P, Lokaj J, Janata M, et al. Eur Polym J 2008;44:59-71] involving two independent controlled/“living” polymerization mechanisms, namely nitroxide-mediated radical polymerization (NMP) for the synthesis of the backbone and photoinduced “grafting from” iniferter process for building of P(tBuMA) branches. The viscosity-related contraction factors g^′<1 confirmed high degree of branching of the studied graft copolymers. Dilute solutions of graft copolymers in non-selective solvent (THF), examined by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS) and viscometry, revealed a transition from comb-like conformation through wormlike-star to a microgel architecture under increasing number of monomeric units in side chains. These data were further supported by the structure factors R_η/R_h and R_g/R_h obtained by independent measurements and extrapolated to infinite dilution. Persistence lengths of the samples exhibiting comb-like topology were larger compared to linear polystyrene backbone and P(tBuMA) side chains in THF suggesting stiffening of the main chain with increasing size of the attached side chains. Unimolecular micelles were detected by DLS and SAXS in solvent selective for grafts, tert-amyl alcohol.     

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 Epoxide Initiators for the Carbocationic Polymerization of Isobutylene

Summary: We recently reported the synthesis of polyisobutylene (PIB) via direct initiation by epoxycyclohexyl isobutyl polyhedral oligomeric silsesquioxane (POSS®) (Figure 1 ) in conjunction with titanium tetrachloride (TiCl₄). This system successfully initiated the living carbocationic polymerization of isobutylene (IB) in hexane/methyl chloride (Hx/MeCl -60/40, v/v) at T = −80 °C, yielding an asymmetric telechelic PIB with one POSS® cage head group and one tert-Cl end group. 1 This paper will discuss IB polymerizations initiated by 1,2-epoxycyclohexane and bis[3,4-(epoxycyclohexyl)ethyl]-tetramethyl-disiloxane, in conjunction with TiCl₄.     

Well‐defined amphiphilic polymethylene‐b‐poly(acrylic acid) diblock copolymers: New synthetic strategy and their self‐assembly

Well‐defined amphiphilic polymethylene‐b‐poly (acrylicacid) diblock copolymers have been synthesized via a new strategy combining polyhomologation and atom transfer radical polymerization (ATRP). Hydroxyl‐terminated polymethylenes (PM‐OH) with different molecular weights and narrow molecular weight distribution are obtained through the polyhomologation of dimethylsulfoxonium methylides following quantitative oxidation via trimethylamine‐N‐oxide dihydrate. Subsequently, polymethylene‐based macroinitiators (PM‐MIs M_n = 1,300 g mol^?1 [M_w/M_n = 1.11] and M_n = 3,300 g mol^?1 [M_w/M_n = 1.04]) are synthesized by transformation of terminal hydroxyl group of PM‐OH to α‐haloester in ～100% conversion. ATRPs of tert‐butyl acrylate (t‐BuA) are then carried out using PM‐MIs as initiator to construct PM‐b‐P(t‐BuA) diblock copolymers with controllable molecular weight (M_n = 8,800–15,800 g mol^?1 M_w/M_n = 1.04–1.09) and different weight ratio of PM/P(t‐BuA) segment (1:1.7–1:11.2). The amphiphilic PM‐b‐PAA diblock copolymers are finally prepared by hydrolysis of PM‐b‐P(t‐BuA) copolymers and their self‐assembly behavior in water is preliminarily investigated via the determination of critical micelle concentrations, dynamic light scattering, and transmission electron microscope (TEM). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of Si—H Functional Poly(phenylsilane) and Organosilane Copolymers: Low-valent Titanium Induced Polymerization of Organodichlorosilanes

在低价钛促进下,苯基二氯硅烷进行还原聚合反应生成Si-H官能化的聚苯基硅烷。应用此方法,在温和、中性反应条件下制备出Si-H官能团化的有机聚硅烷共聚物。     

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     

Synthesis and characterization of two novel star blocks: tCum[poly(isobutylene‐b‐norbornadiene)]3 and tCum[poly(norbornadiene‐b‐isobutylene)]3

Two structurally closely related three‐arm star blocks were synthesized and characterized: tCum(PIB‐b‐PNBD)₃ and tCum(PNBD‐b‐PIB)₃ [where tCum (tricumyl) stands for the phenyl‐1,3,5‐tris(‐2‐propyl) fragment and PIB and PNBD are polyisobutylene and polynorbornadiene, respectively]. The syntheses were accomplished in two stages: (1) the preparation of the first (or inner) block fitted with appropriate chlorine termini capable of initiating the polymerization of the second (or outer) block with TiCl₄ and (2) the mediation of the polymerization of the second block. Therefore, the synthesis of tCum(PIB‐b‐PNBD)₃ was effected with tCum(PIB‐Cl^t)₃ [where Cl^t is tert‐chlorine and number‐average molecular weight (M_n) = 102,000 g/mol] by the use of TiCl₄ and 30/70 CH₃Cl/CHCl₃ solvent mixtures at ?35 °C. PNBD homopolymer contamination formed by chain transfer was removed by selective precipitation. According to gel permeation chromatography, the M_n's of the star blocks were 107,300–109,200 g/mol. NMR spectroscopy (750 MHz) was used to determine structures and molecular weights. Differential scanning calorimetry (DSC) indicated two glass‐transition temperatures (T_g's), one each for the PIB (?65 °C) and PNBD (232 °C) phases. Thermogravimetric analysis thermograms showed 5% weight losses at 293 °C in air and at 352 °C in N₂. The synthesis of tCum(PNBD‐b‐PIB)₃ was achieved by the initiation of isobutylene polymerization with tCum(PNBD‐Cl^sec)₃ (where Cl^sec is sec‐chlorine and M_n = 2900 g/mol) by the use of TiCl₄ in CH₃Cl at ?60 °C. DSC for this star block (M_n = 14,200 g/mol) also showed two T_g's, that is, at ?67 and 228 °C for the PIB and PNBD segments, respectively. It is of interest that the Cl^sec terminus of PNBD, , readily initiated isobutylene polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 740–751, 2003     

Effect of reaction conditions on synthesis and properties of multiarm star-branched polyisobutylenes

A series of multiarm star-branched polyisobutylenes was synthesized from narrow polydispersity arms with molecular weights ranging from 12,000 to 60,000 g/mol, via living carbocationic polymerization using the cumyl chloride/TiCl₄/pyridine initiating system and divinylbenzene (DVB) as core-forming comonomer. The effect on star development of arm molecular weight, temperature, solvent composition, and DVB concentration was studied. The rate of star formation and the weight-average number of arms per star polymer, N̄_w, were found to scale inversely with arm molecular weight; N̄_w = 60 was attained for 13,100 g/mol arms, but N̄_w = 2.5 for 60,000 g/mol arms. It was established that star formation was much faster at −80°C compared to 23°C, regardless of solvent composition. For hexane : methyl chloride (MeCl) solvent compositions containing from 40 to 60 vol % MeCl, star–star coupling was observed at −80°C, but not at 23°C, even after 312 h; for the most polar 40 : 60 hexane : MeCl composition, star–star coupling was so extensive at −80°C that gelation was observed after only 44 h. The rate of star formation was found to be substantially higher in 60 : 40 hexane : MeCl compared to 60 : 40 hexane : methylene chloride (MeCl₂). Some reactions containing MeCl were immediately warmed to 23°C after DVB addition, and the MeCl thus volatilized was replaced with either MeCl₂ or hexane for the duration of the star-forming reaction. Slightly higher rates were consistently observed when MeCl₂ was the replacement solvent. The strong influence of initial MeCl content on rate of star formation was found to persist throughout the star-forming reaction, even when the solvent was immediately converted to 100% hexane. The fraction of arms that remained unlinked into stars was found to be higher at the higher temperature and at lower solvent polarity. Regardless of solvent or temperature, the residual arm fraction was approximately the same at a given stage of star development as measured by the average number of arms per star. One star sample was produced with the UV-transparent 2-chloro-2,4,4-trimethylpentane initiator; analysis showed that the residual arm fraction had approximately the same UV absorbance as the star fraction, indicating efficient crossover to DVB and the potential for approximately quantitative arm incorporation given sufficient time. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36 : 471–483, 1998     

Systhesis of double-hydrophilic core-shell type multiarm star copolymer polyethylenimine-block-poly(2-hydroxyethyl methacrylate

Multiarm star block copolymers hyperbranched polyethylenimine-b-poly(2-hydroxyethyl methacrylate) (HPEI-b-PHEMA) with average 28 PHEMA arms have been prepared by atom transfer radical polymerization (ATRP) of HEMA in a mixed solvent of methanol and water using a core-first strategy. The hyperbranched macroinitiator employed was prepared on the basis of well-defined hyperbranched polyethylenimine with Mw/Mn of 1.04 by amidation with 2-bromo-isobutyryl bromide. The polymerization condition was optimized to prepare star copolymers with narrow dispersity, and the variables included the volume ratio of methanol to water, the molar ratio of initiating site to CuCl and the molar ratio of [CuCl]:[CuBr2]. Under the optimized polymerization condition, the lowest Mw/Mn value of the obtained star copolymers was around 1.3. Kinetic analysis showed that an induction period existed in the polymerization of HEMA. After this induction period, a linear dependence of ln([M]0/[M]t) on time was observed. The obtained HPEI-b-PHEMA could adsorb hydrophilic molecules. The comparison with the star copolymer with hydrophobic core and hydrophilic PHEMA shell verified that both the hydrophilic core and shell could host the hydrophilic guests, but the amidated HPEI core was more effective than the PHEMA shell.     

Polyisobutylene-containing block polymers by sequential monomer addition. IV. New triblock thermoplastic elastomers comprising high Tg styrenic glassy segments: Synthesis,characterization and physical properties

New linear triblock thermoplastic elastomers (TPEs) comprising a rubbery polyisobutylene (PIB) midblock flanked by two glassy endblocks of various styrenic polymers have been synthesized by living carbocationic polymerization by sequential monomer addition. First isobutylene (IB) was polymerized by a bifunctional tert-ether (dicumyl methyl ether) initiator in conjunction with TiCl₄ coinitiator in CH₃Cl/methylcyclohexane (MeCHx) (40/60 v/v) solvent mixtures at ?80°C. After the living narrow molecular weight distribution PIB midblock ( = 1.1–1.2) has reached the desired molecular weight, the styrenic monomers together with an electron pair donor (ED) and a proton trap (di-tert-butylpyridine, DtBP) were added to start the blocking of the glassy segments from the living ⊕PIB⊕ chain ends. While p-methylstyrene (pMeSt), p-t-butylstyrene (ptBuSt) and indene (In) gave essentially 100% blocking to the corresponding glassy endblocks, the blocking of 2,4,6-trimethylstyrene (TMeSt) and α-methylstyrene (αMeSt) were ineffective. Uncontrolled initiation by protic impurities was prevented by the use of DtBP. In the simultaneous presence of DtBP and the strong ED N,N-dimethylacetamide (DMA), TPEs with good mechanical properties (10–20 MPa tensile strength, 300–600% elongation) were prepared. The products exhibit a low and a high temperature T_g characteristic of phase separated rubbery and glassy domains. The service temperature of these new TPEs exceeds that of PSt–PIB–PSt triblock copolymers due to the higher T_gs (PpMeSt = 108, PptBuSt = 142 and PIn = 220–240°C) of the outer blocks. The T_g of the glassy blocks can be regulated by copolymerizing two styrene derivatives; a triblock copolymer with outer blocks of poly(pt-butylstyrene-co-indene) showed a single glassy transition T_g = +165°C, i.e., in between that of PptBuSt and PIn. Virgin TPEs have been repeatedly compression molded without deterioration of physical properties. The high melt flow index obtained with a TPE containing PptBuSt endblocks suggests superior processability relative to those with PSt end-blocks. The tensile strength retention at 60°C of the former TPE is far superior to that of a PSt–PIB–PSt triblock of similar composition.     

Bis(pyrrolide-imine) Ti complexes with MAO: A new family of high performance catalysts for olefin polymerization

This contribution reports on the syntheses, structures and olefin polymerization behavior of Ti complexes having a pair of chelating pyrrolide-imine [N⁻,N] ligands. X-ray analyses as well as ¹H NMR studies demonstrate that bis(pyrrolide-imine) Ti complexes (named PI Catalysts) contain approximately octahedrally coordinated metal centers with mutually trans-pyrrolide-Ns, cis-imine-Ns and cis-Cls. DFT studies suggest that PI Catalysts, when activated, provide a metal alkyl in the cis position to a vacant coordination site for monomer binding. These theoretical studies also show that the active species derived from PI Catalysts normally possess higher electrophilicity and a sterically more open nature compared with those produced using bis(phenoxy-imine) Ti complexes (Ti-FI Catalysts) which are known as high performance olefin polymerization catalysts. These structural as well as electronic features suggest that PI Catalysts have high potential for the polymerization of olefinic monomers.Unlike high performance Ti-FI Catalysts, PI Catalysts do not require the presence of steric bulk in close proximity to the anionic donor. PI Catalysts combined with MAO display high ethylene polymerization activities (max. 33,200 kg-polymer/mol-cat/h, 25 °C, atmospheric pressure) comparable to those obtained with early group 4 metallocene catalysts (e.g., Cp₂TiCl₂ 16,700 kg-polymer/mol-cat/h) under identical conditions. As expected, PI Catalysts exhibit higher incorporation capability for propylene and 1-hexene relative to FI Catalysts though the incorporation levels are lower than those for Cp₂TiCl₂. To our surprise, PI Catalysts/MAO show remarkably high norbornene (NB) incorporation, superior to that seen with the [Me₂Si(Me₄Cp)N-tBu]TiCl₂ (CGC) catalyst system, and they readily form ethylene-NB copolymers with high NB contents. The highly electrophilic and sterically open nature is probably responsible for the high NB affinity. Additionally, PI Catalysts/MAO possess characteristics of living ethylene polymerization (though under limited conditions) and afford high molecular weight PEs with very narrow molecular weight distributions (M_n 225,000, M_w/M_n 1.15, 10-s polymerization, 25 °C). Moreover, these catalysts can copolymerize ethylene and NB in a highly controlled living manner to afford monodisperse alternating copolymers with very high molecular weights (M_n > 500,000, M_w/M_n < 1.2) at room temperature. This unique living nature allows the preparation of a number of ethylene- and NB-based block copolymers, including PE-b-poly(ethylene-co-NB) and poly(ethylene-co-NB)_a-b-poly(ethylene-co-NB)_b, in which each segment contains a different NB content. These are probably the first examples of the syntheses of block copolymers from ethylene and NB. Consequently, the discovery and application of PI Catalysts has exercised a significant influence on olefin polymerization catalysis and polymer synthesis.     

Study on cationic polymerization of isobutylene using electrochemical method

The cationic polymerization of isobutylene (IB) initiated by H₂O/TiCl₄ was carried out in a mixture of methylene dichloride and n-hexane at −60 °C in the presence of a variety of external electron pair donors (EDs), such as triethylamine (TEA), N,N-dimethyl acetamide (DMA) and pyridine (Py). The effects of ED concentration ([ED]), H₂O concentration ([H₂O]) on conductance and capacitance in H₂O/TiCl₄/ED/CH₂Cl₂ reaction system were investigated. The effects of [ED], [H₂O], solven polarity and polymerization time on monomer conversion, molecular weight (MW), molecular weight distribution (MWD, M_w/M_n) of polyisobutylene (PIB) were also investigated. Conductance decreased while capacitance increased with increases in both [ED] and electron donicity of ED. Conductance and capacitance increased with [H₂O] when [H₂O] was more than [Py]. Both unpaired and paired ions existed as propagating species or chain carriers in the presence of relatively low [ED] and polymers with bimodal molecular weight distribution (peak a and b) were obtained. The peak a with high molecular weight was induced by propagation via unpaired ions while peak b with low molecular weight was induced by propagation via paired ions. The propagation via paired ions could be achieved and polymers with unimodal molecular weight distribution could be produced when sufficient amounts of external ED was introduced to polymerization system.     

Synthesis of tertiary-butyl acrylate polymers and preparation of diblock copolymers using atom transfer radical polymerization

The synthesis of tert-butyl acrylate by atom transfer radical polymerization (ATRP) is reported. This polymer was prepared using FeCl₂ · 4H₂O(PPh₃)₂ catalyst system in conjunction with methyl 2-bromopropionate as initiator, in bulk and in solution using acetone as a solvent. The addition of solvent was necessary in order to decrease the polymerization rate and to afford low polydispersity polymers. The number-average molecular weights of the resulting polymers increased in direct proportion to the monomer conversion, and the polydispersities (M_w/M_n) were as low as 1.2. In addition, the preparation of an AB diblock copolymer of poly (n-butyl methacrylate)-block-poly (tert-butyl acrylate) by ATRP is reported. The resulting polymers and copolymers were characterized by means of size exclusion chromatography and ¹H-NMR Spectroscopy.