Sequential Monomer Research Articles

Synthesis and fractionation of syndiotactic-polystyrene/polyethylene copolymers with C 5H 5TiCl 3 catalysts

Highly stereoregulated syndiotactic-polystyrene/polyethylene (s-PS/PE) block copolymers with variable ethylene block lengths are synthesized using the sequential monomer feed scheme with C 5H 5TiCl 3 catalyst. The copolymer, after removing the atactic portion, is separated into two fractions by tetrahydrofuran (THF). The insoluble fraction contains a highly stereoregulated s-PS block linked with PE blocks, while the soluble fraction also contains a highly stereoregulated s-PS block but separated randomly by a shorter or isolated ethylene unit. For the I-fraction, r E=25±5 and r S=1.9±0.3, and for the S-fraction r E=0.4±0.1 and r S=0.34±0.15. These results are compared with prior studies, where mainly random type PS/PE copolymers with low styrene stereoregularity and rigio-irregular styrene and polyethylene are produced. Apparently, both the sequential feed scheme coupled with the use of a lower reactivity metallocene catalyst facilitated the switching of catalytical sites with the majority product being of block nature.

Direct Living Cationic Polymerization of p-Hydroxystyrene with Boron Trifluoride Etherate in the Presence of Water

Direct living cationic polymerization of p-hydroxystyrene (pHS) has been developed in the presence of a fairly large amount of water using BF3OEt2 as a Lewis acid catalyst and the adducts (1−4) of p-methoxystyrene (pMOS) and a series of protonic compounds as initiators. In contrast to most living cationic polymerizations, the water and the alcohol adducts (3 and 4, respectively) produced polymers with number-average molecular weights (Mn) close to the calculated values from the monomer/initiator mole ratios. With 4/BF3OEt2, the Mn increased with monomer conversion, and the living nature of the chains was confirmed by sequential monomer addition experiments. The polymerization proceeded even in the presence of a large amount water to afford polymers whose Mn increased in direct proportion to monomer conversion with fairly narrow MWDs (Mw/Mn < 1.4). This initiating system was also effective at or above ambient temperature (from −15 to +60 °C). The success of this controlled cationic polymerization of unprotected pHS is due to the stability of BF3OEt2 and to its tolerance of the hydroxy groups in the monomer and water and the proper selection of the initiator. This initiator contains a covalent C−O bond that is preferentially dissociated by an oxophilic Lewis acid, BF3. This is the first example of a direct living polymerization of pHS, by any mechanism, without protecting the hydroxy groups.

Controlled polymerization of methylmethacrylate and ethylacrylate using tris(4,4'-dimethyl-2,2'-bipyridine) copper(II) hexafluorophosphate complexes and aluminium isopropoxide

The radical polymerization of methylmethacrylate and ethylacrylate was carried out in the presence of tris(4,4'-dimethyl-2,2'-bipyridine) copper(II) hexafluorophosphate complexes and aluminium isopropoxide. The molecular weight of the synthesized polyethylacrylates increased proportionally with conversion, whereas the polymerization of methylmethacrylate revealed a nonlinear behavior. The polydispersities of the molecular weight distributions observed were between 1.09 and 1.34. Poly(styrene-block-polymethylmethacrylate) was synthesized by sequential monomer addition.

Synthesis of Poly(α-methylstyrene-b-isobutylene) Copolymers by Living Cationic Sequential Block Copolymerization: Investigation on the Crossover from Living Poly(α-methylstyrene) Chain End to Isobutylene

The synthesis of poly(α-methylstyrene-b-isobutylene) (P(αMeSt-b-IB)) copolymers via sequential monomer addition was studied using the adduct of the olefinic αMeSt dimer and HCl (DiαMeSt·HCl) as ini...

Living cationic polymerization ofp-alkoxystyrenes by free ionic species

In contrast to the common view, living cationic polymerization of p-methoxy- and p-t-butoxystyrenes proceeded in polar solvents such as EtNO2/CH2Cl2 mixtures, and involvement of free ionic growing species therein was examined. For example, the two alkoxystyrenes were polymerized with the isobutyl vinyl ether-HCl adduct/ZnCl2 initiating system at −15°C in such polar solvents as CH2Cl2 or EtNO2/CH2Cl2 [1/1 (v/v)], as well as toluene. The number average molecular weight (M̄n) of the polymers increased in direct proportion to the monomer conversion, even after sequential monomer addition, and the molecular weight distribution (MWD) stayed very narrow throughout the reaction. In addition, the M̄n agreed with the calculated values, assuming that one adduct molecule generates one living polymer chain. In these polar media the addition of a common ion salt retarded the polymerization, indicating that dissociated ionic species are involved in the propagating reaction. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3694–3701, 1999

Cationic Macromolecular Design and Synthesis Using Furan Derivatives

General methodologies for the synthesis of block copolymers and functional polymers using furan derivatives are reported on the basis of a study of addition reactions of 2-substituted furans to living polyisobutylene (PIB+). Rapid and quantitative monoaddition of 2-methylfuran (2-MeFu) and 2-tert-butylfuran (2-tBuFu) to PIB+ has been observed in conjunction with TiCl4 as Lewis acid in hexanes (Hex)/CH2Cl2 or CH3Cl 60/40 v/v at −80 °C and with BCl3 in CH3Cl at −40 °C, in the presence of proton trap. Upon monoaddition, the formation of the stable allylic cation was confirmed by trapping the resulting cation with tributyltin hydride, which yielded PIB with dihydrofuran functionality. Quenching with methanol resulted in the quantitative formation of 2-alkyl-5-PIB-furan. The stable allylic cation was found to be an efficient initiating species for the polymerization of methyl vinyl ether (MeVE), yielding P(IB-b-MeVE) block copolymers by sequential monomer addition with up to 75% crossover efficiency. 2-PIB-Fu, a polymeric capping agent, was obtained in quantitative yields in a reaction of PIB+ with 2-Bu3SnFu in Hex/CH3Cl 60/40 v/v in the presence of TiCl4 at −80 °C. In a subsequent reaction of 2-PIB-Fu with living PIB+, under conditions similar to capping PIB+ with 2-tBuFu, close to quantitative coupling of the two PIB chains was achieved. The concept of coupling a living cationic polymer with an ω-furan functional polymer to obtain AB-type linear block copolymers and for the synthesis of ABC- and AA‘B-type three-arm star-block copolymers is presented.

Block copolymers from isobutyl vinyl ether and 2-chloroethyl vinyl ether

Scope and limitation of the vinyl ether block copolymerization of isobutyl vinyl ether (IBVE) and 2-chloroethyl vinyl ether (CEVE) initiated by CH3CHIOR/ZnI2 were studied. These polymerizations exhibit the characteristics of a living polymerization. Di- and triblock copolymers were synthesized by sequential monomer addition (IBVE, CEVE). The poly(2-chloroethyl vinyl ether) (PCEVE) segment in those block copolymers is of particular interest because of the possibility to modify this segment by nucleophilic substitution of the chlorine. This strategy allows the synthesis of tailor made amphiphilic block copolymers.

Synthesis and bulk properties of poly(tetrahydrofuran)-poly(2-methyl-2-oxazoline) ABA triblock copolymers

A series of linear triblock-copolymers of the ABA type in which the central B-block is poly(tetrahydrofuran) (polyTHF) and the A-segments are poly(2-methyl-2-oxazoline) (polyMeOX) were synthesized by a one-pot sequential monomer addition copolymerization, utilizing the living nature of the cationic ring-opening polymerization of both monomers.

Synthesis of Poly(Styrene)-block-poly(methacrylate)-block-poly(styrene) via Site Transformation Reaction

Triblock copolymers with polystyrene outer blocks and an inner polymethacrylate block were synthesized by a site transformation reaction using anionic and cationic polymerization techniques. In order to obtain such ABA block copolymers, two synthetic routes have been applied. In the first case, different methacrylates (methyl methacrylate, 2-ethylhexyl methacrylate) were polymerized anionically with a bifunctional initiator to get poly(methacrylate) dianions later forming the inner block whereas in the second case poly(styrene)-block-poly(methacrylate) anions were synthesized by monofunctional initiation via sequential monomer addition. In a subsequent step, the living chain ends of the methacrylate dianions on one side, and the diblock copolymer anions on the other side, were functionalized with 1,4-bis(l-bromoethyl)benzene in order to obtain a potential bifunctional or monofunctional macroinitiator for the cationic polymerization of styrene. Then, styrene was polymerized cationically with the macroinitiator in the presence of SnCl4 as coinitiator and n Bu4NBr as a common ion salt in CH2Cl2 at -15°C. Block formation was proven by SEC measurements, preparative SEC and NMR characterization.

Copolymerization of methyl methacrylate with lauryl methacrylate using group transfer polymerization

The syntheses of random and block copolymers (using sequential monomer addition) of methyl methacrylate (MMA) and lauryl methacrylate (LMA) have been investigated by group transfer polymerization (GTP) over a wide composition range using tetrabutylammonium bibenzoate (TBABB) as catalyst and 1-methoxy-1-(trimethylsiloxy)-2-methyl-1-propene (MTS) as initiator in tetrahydrofuran (THF) at room temperature. The absolute molecular weight of the copolymers were determined by SEC-MALLS. The observed molecular weights were generally higher than the calculated molecular weights. However, the molecular weight distributions were very narrow (1.02–1.1). Use of trimethylsilyl benzoate as a “livingness enhancer” improved the livingness of the first block (PLMA) and block copolymers with no detectable contamination of homopolymer. Statistical copolymers of MMA and LMA were prepared, and the reactivity ratios of the two monomers under the defined conditions were determined. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1999–2007, 1997

Chemical heterogeneity in poly [styrene-co-(butyl methacrylate)] copolymer latexes prepared using different monomer addition modes. A study by isopycnic centrifugation in density gradient

Three different styrene-butyl methacrylate copolymer latexes were prepared by a uniform procedure but introducing styrene (S), butyl methacrylate (BMA), and minor amounts of acrylic acid (AA), in three different orders: i) simultaneous monomers addition, which yielded P(SBMA); ii) addition of S (and half of the AA) followed by BMA (and the remaining AA), yielding PS/PBMA and iii) the inverse order, PBMA/PS. Product characterization was done by centrifugation in density gradients coupled to scattered light scanning photometry of the centrifugation tubes. IR and NMR spectra were obtained from bulk polymer as well as from isopycnic centrifugation fractions. In agreement with findings of other authors, the particles produced by simultaneous monomer addition P(SBMA) are made out of the statistical copolymer, whereas sequential monomer addition leads to the formation of latex with homopolymer domains. IR and NMR spectra of PS/PBMA and PBMA/PS are identical but isopycnic density band profiles of all three samples are distinct. Acrylic acid residues are not detected in the dialyzed latex, using both IR and NMR. Spectra of latex isopycnic fractions do also show significant differences arising from their monomer chemical compositions, but isopycnic centrifugation and spectral data do not reveal any correlation between particle density and monomer composition. Isopycnic centrifugation can thus solve two problems on latex characterization: first, it is a high-resolution preparative technique, unmatched by any other separation method. Second, it yields latex particle fingerprints, which are dependent on particle chemical characteristics, rather than on particle diameters.

Synthesis and characterization of new triblock copolymers of isobutylene and 1,3-pentadiene

New linear triblock copolymers consisting of a rubbery polyisobutylene (PIB) midsegment bonded both sides by glassy cyclized poly(1,3-pentadiene) (cy-PPD) blocks were synthesized by carbocationic polymerization using sequential monomer addition. First, the living polymerization of isobutylene (IB) was induced by bifunctional dicumylmethylether (DiCumOMe)/TiCl 4 as initiating system in n-hexane/CH 2Cl 2 (1/1 v/v) as solvent mixture at −60°C in the presence of DMSO as electron donor (ED). After the living PIB sequences had reached the desired number average molar weight ( M n) in the range of 5000 to 25 000 g mol −1, 1,3-pentadiene (PD) was added to produce the hard cy-PPD outer blocks with M n close to 6000 g mol −1. The crude copolymers were purified by CH 2Cl 2 extraction at −60°C and characterized by size exclusion chromatography (s.e.c.) and nuclear magnetic resonance (n.m.r.) spectroscopy.

Surface Macromolecular Architectural Designs Using Photo-Graft Copolymerization Based on Photochemistry of Benzyl N,N-Diethyldithiocarbamate

Surface macromolecular architectures with regional dimensional precision, control of the thickness of a graft layer, and blocks of graft chains were attempted using the surface photo-graft copolymerization method pioneered by Otsu et al. This is based on the photochemistry of benzyl N,N-diethyldithiocarbamate, which can be photolyzed into a radical pair (one radical can initiate radical polymerization and the other tends to recombine with the former radical). Ultraviolet light (UV) irradiation of a benzyl N,N-diethyldithiocarbamyl group-immobilized polymer surface in the presence of a vinyl monomer such as N,N-dimethylacrylamide, N-[3-(dimethylamino)propyl]acrylamide, methacrylic acid, or styrene at room temperature allowed precise control of the macromolecular architectures of the grafted surfaces. X-ray photoelectron spectroscopy (XPS) analyses and water contact angle measurements before and after UV irradiation in a monomer solution provided evidence that the graft copolymerization proceeded only during photoirradiation and at photoirradiated portions. Atomic force microscopic (AFM) observations showed that the thickness of the graft-copolymerized layers increased almost linearly with UV irradiation time. Patterned grafted surfaces, which were prepared using the ionic or nonionic hydrophilic monomers listed above under irradiation through a projection mask, were clearly visualized by dye-staining or cell-culturing. The graft copolymerization under irradiation through a projection mask with sequential monomer charges yielded surfaces with regionally dimensionally controlled macromolecular architectures such as di- and triblock graft-copolymerized surfaces. A graft thickness-gradient surface was obtained by using a gradient filter.

Recent developments in living cationic polymerization

AbstractScope and limitation of the vinyl ether polymerization initiated by NR4ClO4(KClO4;LiClO4)/CH3CHI‐OR was discussed. Besides isobutyl vinyl ether (IBVE), N‐vinylcarbazole (NVC) and 2‐chloroethyl vinyl ether (CEVE) were initiated by NR4ClO4/CH3CHI‐OR. These polymerizations exhibited the characteristics of a living polymerization. However, in order to observe narrow molar mass distribution NVC was initiated with CH3CHI‐OR, without salts. Block copolymers were synthesized by the method of sequential monomer addition (NVC, IBVE, CEVE). The PCEVE segment was modified by nucleophilic substitution, which allowed the synthesis of amphiphilic block copolymers.

Polyisobutylene-Based Thermoplastic Elastomers. 3. Synthesis, Characterization, and Properties of Poly(.alpha.-methylstyrene-b-isobutylene-b-.alpha.-methylstyrene) Triblock Copolymers

The first efficient synthesis of poly(α-methylstyrene-b-isobutylene-b-α-methylstyrene) (PαMeSt-PIB-PαMeSt) triblock copolymer thermoplastic elastomers (TPEs) has been accomplished by living cationic polymerization using sequential monomer additions. Living PIB was prepared by the 5-tert-butyl-1,3-bis(1-chloro-1-methylethyl)benzene (tBuDicumcl)/TiclJHex :Mecl 60 :40 v :v/-80°C polymerization system. The living ends were capped by 1,1-diphenylethylene (DPE). TiCl 4 was replaced by SnBr 4 , followed by the addition of αMeSt. Triblock copolymers with close to theoretical molecular weights and narrow molecular weight distributions (M w /M n ∼1.1) were obtained. Homopolymer and diblock contamination have been found to be negligible. The thermal stability of the triblock copolymer was characterized by thermogravimetric analysis. Microphase separation was evidenced by the two glass transitions (at -65 and +180°C) observed by differential scanning calorimetry and in dynamic mechanical analysis. Triblock morphology was examined by transmission electron microscopy. Compression-molded samples with 16-45 wt % PαMeSt exhibited 12-24.5 MPa tensile strength, apparently directly related to the PαMeSt content and independent of the PIB molecular weight.

Synthetic applications of non‐polymerizable monomers in living carbocationic polymerization

AbstractThe foundation and methodology of using highly reactive but non‐polymerizable monomers in living cationic polymerizations is introduced. The chemistry and kinetics of 1,1‐diphenylethylene (DPE) addition to living polyisobutylene (PIB) in methyl chloride/n‐hexanes 40/60 v/v at −80°C is reported. Monoaddition occurred even when large excess of 1,1‐diphenylethylene was used. The methanol quenched polymer of the DPE capped PIB carried ‐OCH3 functionality exclusively, suggesting that the diphenyl alkyl chain‐ends are completely ionized, which was confirmed by conductivity studies. By in‐situ functionalization using soft nucleophiles a variety of functional groups were obtained, most notably ester upon reaction with silyl ketene acetal. It was found that the diphenyl carbenium ion is an efficient initiating species for the polymerization of reactive monomers such as vinyl ethers and α‐methylstyrene. The synthesis of PIB based block copolymers was accomplished by sequential monomer addition, using para‐methylstyrene, α‐methylstyrene or isobutyl vinyl ether as the second monomer. It involved capping with DPE, followed by tailoring the Lewis acidity to the reactivity of the second monomer by the addition of titanium(IV) alkoxide, by replacing the Lewis acid with a weaker one or by the use of a common ion salt. PIB‐b‐PMMA was obtained by the combination of living cationic and group transfer (GTP) polymerizations.

Polyisobutylene-Based Thermoplastic Elastomers. II. Synthesis and Characterization of Poly(p-Methylstyrene-block-isobutylene-block-p-Methylstyrene) Triblock Copolymers

Abstract The synthesis of poly(p-methylstyrene)–polyisobutylene–poly(p-methylstyrene) triblock copolymer was accomplished by sequential monomer addition. The synthesis involves the living polymerization of isobutylene by the TiCl4/methylchloride:hexanes, 40:60 v:v/ −80°C system in the presence of di-tert-butylpyridine using di- or trifunctional initiator. When the polymerization of isobutylene is complete, the living polyisobutylene chain end is converted to the corresponding diphenyl alkyl end by capping with 1,1-diphenyl ethylene. Subsequently, titanium(IV)-isopropoxide is added to decrease the Lewis acidity and p-methylstyrene is introduced. The best triblocks exhibited ∼22 MPa tensile strength.

Synthesis of Poly(N-Vinylcarbazole-b-Isobutylvinylether)

Blockcopolymers consisting of N-vinylcarbazole (NVC) and isobutylvinylether (IBVE) were synthesized by sequential monomer addition. It is essential to start the synthesis with the NVC-segment and to initiate the polymerization by 1-iodo-1-(2-methylpropyloxy)ethane. The blockcopolymerization of IBVE proceeds only in the presence of an activator, such as (n-Bu)4NClO4. The blockcopolymers were characterized by GPC, 1H NMR, elemental analysis and DSC.

Living Carbocationic Polymerization ofp-Methylstyrene and Sequential Block Copolymerization of Isobutylene withp-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 cop...

Chain transfer and living functionalization of polymethacrylates by group transfer polymerization using ethyl 2‐Phenyl‐2‐butenoate

AbstractA living functionalization method has been investigated for group transfer polymerization (GTP) of poly(alkyl methacrylates) using ethyl 2‐phenyl‐2‐butenoate (EPB). The end‐capping reactions of EPB to living trimethylsilyl ketene acetal‐ended poly(methyl methacrylate) (PMMA) chain ends have been systematically studied and characterized by SEC, VPO, UV‐visible spectrosocopy, 1H and 13c NMR spectroscopy. The results of sequential monomer addition, varying stoichiometry and copolymerization indicate that EPB effects efficient chain end functionalization only at stoichiometric concentrations; chain transfer reactions (chain transfer constant = 0.4) occur with excess EPB and during copolymerization with MMA. Chain transfer reactions (chain transfer constant = 0.1) also occur when copolymerizing ethyl 2‐methyl‐2‐butenoate with MMA.