Living carbocationic polymerization

A new family of initiating systems has been discovered that efficiently induces the truly living polymerization of isobutylene (IB). The initiating systems are complexes of organic tertiary esters e.g., cumyl acetate, 2,4,4-trimethylpentane-2-acetate, with BCl₃. Living polymerizations proceed very rapidly in a variety of solvents, i.e., CH₃Cl, CH₂Cl₂, C₂H₅Cl, and mixtures of chlorinated solvents plus n-hexane, in the range from –10° to –50°C. The living nature of the polymerizations was demonstrated by linear ¯M_n versus W_PIB (g of polymer formed) plots starting at the origin and horizontal N (number of PIB chains) versus W_PIB plots. The DP_n of the products obeys [M_o]/[I_o] where [M_o] and [I_o] are initial monomer and initiator concentrations, respectively. Conversions and initiator efficiencies are 100%. In carefully controlled experiments narrow molecular weight distribution polyisobutylenes (PIB) have been obtained, i.e., M_w/M_n=1.17 – 1.3. A mechanism is outlined that helps rationalize the findings. It is postulated that the living polymerization of IB initiated by organic tertiary ester·BCl₃ complexes most likely proceeds by a two-component group transfer polymerization process.     

Thermal polymerization of methyl (meth)acrylate via reversible addition-fragmentation chain transfer (RAFT) process

Thermal polymerization of methyl (meth)acrylate (MMA) was carried out using 2-cyanoprop-2-yl-1-dithionaphthalate (CPDN) and cumyl dithionaphthalenoate (CDN) as chain transfer agents. The kinetic study showed the existence of induction period and rate retardation, especially in the CDN mediated systems. The molecular weights of the polymers increased linearly with the monomer conversion, and the molecular weight distributions (M_w/M_ns) of the polymers were relatively narrow up to high conversions. The maximum number-average molecular weights (M_ns) reached to 351?900 g/mol (M_w/M_n = 1.47) and 442?400 g/mol (M_w/M_n = 1.29) in the systems mediated by CPDN and CDN, respectively. Chain-extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA-block-polystyrene (PMMA-b-PSt) copolymer with controlled structure and narrow M_w/M_n. Thermal polymerization of methyl acrylate (MA) in the presence of CPDN, or benzyl (2-phenyl)-1-imidazolecarbodithioate (BPIC) also demonstrated “living”/controlled features with the experimented maximum molecular weight 312?500 g/mol (M_w/M_n = 1.57). The possible initiation mechanism of the thermal polymerization was discussed.     

Living cationic random copolymerization of β-pinene and isobutylene with 1-phenylethyl chloride/TiCl4/Ti(OiPr)4/nBu4NCl

The first example of living cationic random copolymerization of β-pinene and isobutylene was achieved with 1-phenylethyl chloride/TiCl₄/Ti(OiPr)₄/nBu₄NCl (TiCl₄/Ti(OiPr)₄ mole ratio: 3/1) initiating system in CH₂Cl₂ at −40 °C. β-Pinene and isobutylene was consumed at almost the same rate, suggesting that the two monomers exhibit almost equal reactivity. At any monomer feed ratio, the number-average molecular weight (M_n) of the copolymers increased in direct proportion to the total monomer conversion, and the molecular weight distribution was relatively narrow (M_w/M_n=1.1-1.2) throughout the reaction. The reactivity ratios determined by the Kelen-Tüdõs method were rβ-pinene=1.1 and r_isobutylene=0.89, which indicated that the composition of copolymer is approximately identical to the monomer feed ratio. The analysis of the structure and sequence distribution of the copolymers by ¹H NMR spectroscopy further confirmed that perfectly random copolymers were obtained by this living cationic polymerization system. The glass transition temperatures of the copolymers obtained with varying monomer compositions were also determined by DSC method.     

Synthesis and applications of triblock and multiblock copolymers using telechelic oligopropylene

Isotactic polypropylene (iPP)-polystyrene (PS) and iPP-poly(methyl methacrylate) (PMMA) multiblock copolymers were synthesized by atom transfer radical coupling (ATRC) of PS-iPP-PS and PMMA-iPP-PMMA triblock copolymers obtained by atom transfer radical polymerization (ATRP) of styrene (St) and methyl methacrylate (MMA), respectively, using α,ω-dibromoisobutyrateoligopropylene (iPP-Br) as a bifunctional macroinitiator. The iPP-Br was prepared by hydroxylation and subsequent esterification of telechelic oligopropylene having terminal vinylidene double bonds at both ends obtained by controlled thermal degradation of iPP. ATRP of St and (meth) acrylic monomers using iPP-Br formed the corresponding triblock copolymers. It was confirmed that the PMMA-iPP-PMMA triblock copolymer was effective as the compatibilizer for the iPP/PMMA blend. An iPP-PS multiblock copolymer (M_n: 25?000 g/mol and M_w/M_n: 4.1) was prepared by ATRC of PS-iPP-PS triblock copolymer (M_n: 8900 g/mol and M_w/M_n: 1.3). ATRC with St of PMMA-iPP-PMMA triblock copolymer (M_n: 13?000 g/mol and M_w/M_n: 1.4) provided an iPP-PMMA multiblock copolymer containing St chains (M_n: 39?000 g/mol and M_w/M_n: 2.8).     

Electroreductive block copolymerization of dichlorosilanes in the presence of disilane additives

The electroreductive polymerization of dichloromethylphenylsilane in the presence of triphenylsilyl group‐containing disilanes such as hexaphenyldisilane followed by the electroreductive termination with chlorotriphenylsilane afforded triphenylsilyl group‐terminated polymethylphenylsilane in 15–32% yield. The isolated polymethylphenylsilane (M_n = 3350 g mol^?1, M_w/M_n = 1.4) was found to react as a macroinitiator to copolymerize with dibutyldichlorosilane under electroreductive conditions producing the corresponding block copolymer (M_n = 4730 g mol^?1, M_w/M_n = 1.2) in 38% yield. The ratio of monomer units (? MeSiPh? to? BuSiBu? ) of the copolymer was determined to be 75:25 using ¹H NMR analysis, which was in good agreement with the calculated ratio (74:26) on the assumption that molecular weight of the macroinitiator was not changed. The block structure of the resulting copolymer, poly(methylphenylsilane)‐block‐poly(dibutylsilane), was also confirmed by comparing its ¹H NMR and UV absorption spectra with those of polymethylphenylsilane, polydibutylsilane and a statistical copolymer prepared by electroreductive polymerization of dichloromethylphenylsilane with dibutyldichlorosilane. This method is applicable to the preparation of other types of macroinitiator such as triphenylsilyl group‐terminated polydibutylsilane, and polydibutylsilane‐block‐polymethylphenylsilane was also obtained using this macroinitiator. Copyright © 2011 Society of Chemical Industry     

Synthesis of an amphiphilic conjugated polymer through block copolymerization of phenylacetylene and (p-trityloxycarbonylphenyl)acetylene and the subsequent hydrolysis

Summary The polymerization of (p-trityloxycarbonylphenyl)acetylene (p-TrOCOPA) with [(nbd)RhCl]₂/Ph₂C=C(Ph)Li/Ph₃P ternary catalyst proceeded in a living fashion to provide polymer with low polydispersity index (M _w/M _n∼1.1) in good yield. Block copolymerizations of p-TrOCOPA with phenylacetylene (PA) selectively formed the corresponding block copolymers regardless of the order of monomer addition. The hydrolysis of the homo- and block copolymers of p-TrOCOPA catalyzed by hydrochloric acid gave carboxyl-containing hydrophilic homopolymer and amphiphilic block copolymers, respectively. The amphiphilic block copolymer formed micelles in solution and monomolecular membrane at the air-water interface. Received: 2 April 2001/Accepted: 17 April 2001     

Heterogeneity of active sites of Ziegler‐Natta catalysts: The effect of catalyst composition on the MWD of polyethylene

Experimental data on the molecular weight distribution (MWD) of polyethylene (PE) produced over a broad number of Ziegler‐Natta catalysts differing in composition and preparation procedure are presented. These catalysts include nonsupported TiCl₃ catalyst, four types of supported titanium‐magnesium catalysts (TMC) differing in the content of titanium and the presence of various modifiers in the composition of the support, and a supported catalyst containing VCl₄ as an active component instead of TiCl₄. The studied catalysts produce PE with different molecular weights within a broad range of polydispersity (M_w/M_n = 2.8–16) under the same polymerization conditions. The heterogeneity of active sites of these catalysts was studied by deconvolution of experimental MWD curves into Flory components assuming a correlation between the number of Flory components and the number of active site types. Five Flory components were found for PE produced over nonsupported TiCl₃ catalysts (M_w/M_n = 6.8), and three–four Flory components were found for PE produced over TMC of different composition. A minimal number of Flory components (three) was found for PE samples (M_w/M_n values from 2.8 to 3.3) produced over TMC with a very low titanium content (0.07 wt %) and TMC modified with dibutylphtalate. It was shown that five Flory components are sufficient to fit the experimental MWD curve for bimodal PE (M_w/M_n = 16) produced over VMC. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Controlled radical polymerization of styrene utilizing excellent radical capturing ability of diphenyl ditelluride

Summary The radical polymerization of styrene was investigated in the presence of diphenyl ditelluride (DPDTe) under varied conditions. In the polymerization without any radical initiator at higher temperature (125°C), the addition of DPDTe surely decreased the polymer molecular weight (M _n) while the polydispersity (M _w/M _n) was rather broad. The polymerization with benzoyl peroxide (BPO) as the initiator was also uncontrollable to afford polymers with broad M _w/M _n probably due to the redox side reaction of BPO with DPDTe. On the contrary, the precision control of M _n and the initiating end structure could be achieved by the polymerization with 2,2'-azobisisobutyronitrile (AIBN), that is, M _n increased in proportion to the molar ratio of monomer to initiator suggesting the suppression of bimolecular chain termination reactions by the excellent radical capturing ability of DPDTe. Received: 23 June 1999/Revised version: 11 August 1999/Accepted: 16 August 1999     

Copolymerization of phenylisocyanate and ϵ‐caprolactone with rare earth chloride systems

A copolymer of phenylisocyanate (PhNCO) and ε‐caprolactone (CL) was synthesized by the rare earth chloride systems lanthanide chloride isopropanol complex (LnCl₃·3iPrOH) and propylene epoxide (PO). Polymerization conditions were investigated, such as lanthanides, reaction temperature, monomer feed ratio, La/PO molar ratio, and aging time of catalyst. The optimum conditions were: LaCl₃ preferable, [PhNCO]/[CL] in feed = 1 : 1 (molar ratio), 30°C, [monomer]/[La] = 200, [PO]/[La] = 20, aging 15 min, polymerization in bulk for 6 h. Under such conditions the copolymer obtained had 39 mol % PhNCO with a 78.2% yield, M_n = 20.3 × 10³, and M_w/M_n = 1.60. The copolymers were characterized by GPC, TGA, ¹H‐NMR, and ¹³C‐NMR, and the results showed that the copolymer obtained had a blocky structure with long sequences of each monomer unit. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2135–2140, 2007     

Synthesis and antitumour activity of medium molecular weight phthalimide polymers of camptothecin

Attachment of anticancer agents to polymers has been demonstrated to improve their therapeutic profiles. A new monomer containing camptothecin, 5‐norbonene‐endo‐2,3‐dicarboxylimidoundecanoyl‐camptothecin (NDUCPT) and its homopolymer and copolymer with acrylic acid (AA) were synthesized and spectroscopically characterized. The NDUCPT content in poly(NDUCPT‐co‐AA) obtained by elemental analysis was 51%. The average molecular weights of the polymers determined by gel permeation chromatography were as follows: M_n = 12 100, M_w = 23 400 g mol^?1, M_w/M_n = 1.93 for poly(NDUCPT), M_n = 15 400, M_w = 28 300 g mol^?1, M_w/M_n = 1.83 for poly(NDUCPT‐co‐AA). The IC₅₀ value of NDUCPT and its polymers against U937 cancer cells was larger than that of CPT. The in vivo antitumour activity of all polymers in Balb/C mice bearing the sarcoma 180 tumour cell line was greater than that of CPT at a dose of 100 mg kg^?1. Copyright © 2003 Society of Chemical Industry     

Synthesis and characterization of perfluorocyclobutyl aryl ether-based amphiphilic diblock copolymer

Perfluorocyclobutyl aryl ether-based amphiphilic diblock copolymer containing hydrophilic poly(ethylene glycol) segment was synthesized by atom transfer radical polymerization (ATRP). Perfluorocyclobutyl-containing methacrylate-based monomer, 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate, was prepared firstly, which can be polymerized by ATRP in a controlled way to obtain well-defined homopolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.30). The molecular weights increased linearly with the conversions of monomer and the apparent polymerization rate exhibited first-order relation with respect to the concentration of monomer. ATRP of 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate was initiated by PEG-based macroinitiators with different molecular weights to obtain amphiphilic diblock copolymers with narrow molecular weight distributions (M_w/M_n < 1.35) and the number of perfluorocyclobutyl linkage can be tuned by the feed ratio and the conversion of the fluorine-containing methacrylate monomer. The critical micelle concentrations of these amphiphilic diblock copolymers in water and brine were determined by fluorescence probe technique. The morphologies of the micelles were found to be spheres by TEM.     

Slow initiation by tert-butoxybenzenes in living cationic polymerization of isobutylene

Summary tert-Butoxybenzenes including the 4-substituted derivatives of anisole, toluene and p-chlorobenzene have been synthesized and studied as initiators in combination with TiCl₄ for polymerization of isobutylene (IB) in CH₂Cl₂/methylcyclohexane (MeCHx) solvent mixtures at -78°C. Living polymerizations with slow initiation were observed by the allmonomer-in (AMI) and incremental monomer addition (IMA) techniques, and polymers with narrow molecular weight distribution (MWD) (M_w/M_n>1.1) were obtained under certain conditions. Aging of the initiating system prior to charging the monomer does not improve the initiating efficiency. It has been found that the initiating efficiency can be increased by increasing the solvent polarity, however, the relative volume of CH₂Cl₂ is limited in order to avoid polymer precipitation and bimodal MWD.     

Synthesis and Characterization of a novel star shaped Rod-Coil Block Copolymer

Summary A novel star shaped rod-coil block copolymer, tri-armed star poly (-caprolactone)-b-poly {2,5-bis[(4-methoxyphenyl) oxycabony] styrene} [S-(PCL-b-PMPCS)₃], was successfully synthesized via atom transfer radical polymerization in chlorobenzene solution using macro-initiator and CuBr/Sparteine complex as catalyst. The results showed that the number average molecular weigh M_n was increased versus monomer conversion, and that the polydispersities M_w/M_n was quite narrow (<1.35), which were the character of controlled polymerization. The structure of the star shaped blcok copolymers was experimentally confirmed by ¹H NMR. The liquid crystalline behavior of them was studied using DSC and POM. The star shaped block copolymer with low molar percentage of PMPCS block could show T_m of PCL. And only those copolymers with long rigid segment PMPCS could form liquid crystalline phase which was quite stable with a high clearing point.     

Synthesis and characterization of emulsion copolymer of N‐cyclohexylmaleimide and methyl methacrylate

Copolymers of N‐cyclohexylmaleimide (ChMI) and methyl methacrylate (MMA) were synthesized by the emulsion semibatch copolymerization method. The effects of the monomer mixture composition on the average molecular weight (M_n and M_w ), glass transition temperature (T_g), degradation temperature, mechanical properties, and rheological behavior of the copolymers were investigated. The results show that M_n and M_w have maximum values when the ChMI feed content was about 20% (by wt). The degradation temperature and T_g of the copolymers increase with increasing ChMI moieties in the copolymer. The mechanical properties (tensile strength and impact strength) decrease with an increasing ChMI feed content. All copolymers in the melt show pseudoplastic behavior. The flow index n increases with an increasing ChMI feed content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1070–1075, 2002; DOI 10.1002/app.10394     

Carbocationic polymerization in supercritical carbon dioxide

Polymerization of isobutylene (IB) in supercritical carbon dioxide (SC·CO₂) at 32.5°C and 140 bar by the use of 2-chloro-2,4,4-trimethyl-pentane (TMPCl) initiator in conjunction with a mixture of TiCl₄/BCl₃ leads to well-defined polyisobutylenes (PIB) capped by a t-Bu head group and a t-Cl tail group (tBu-PIB-Cl^t) of M_n1800 g/mole and M_w/M_n=1.3. The TiCl₄/BCl₃ mixture may be viewed a new Friedel-Crafts Acid that effects rapid initiation, essentially chaintransferless propagation and reversible termination. The mechanism of IB polymerization of TiCl₄/BCl₃ mixtures is discussed.     

Synthesis and biological activity of medium range molecular weight polymers containing exo‐3,6‐epoxy‐1,2,3,6‐tetrahydrophthalimidocaproic acid

A new monomer, exo‐3,6‐epoxy‐1,2,3,6‐tetrahydrophthalimidocaproic acid (ETCA), was prepared by reaction of maleimidocaproic acid and furan. The homopolymer of ETCA and its copolymers with acrylic acid (AA) or with vinyl acetate (VAc) were obtained by photopolymerizations using 2,2‐dimethoxy‐2‐phenylacetophenone as an initiator at 25 °C. The synthesized ETCA and its polymers were identified by FTIR, ¹H NMR and ¹³C NMR spectroscopies. The apparent average molecular weights and polydispersity indices determined by gel permeation chromatography (GPC) were as follows: M_n = 9600 g mol^?1, M_w = 9800 g mol^?1, M_w/M_n = 1.1 for poly(ETCA); M_n = 14 300 g mol^?1, M_w = 16 200 g mol^?1, M_w/M_n = 1.2 for poly(ETCA‐co‐AA); M_n = 17 900 g mol^?1, M_w = 18 300 g mol^?1, M_w/M_n = 1.1 for poly(ETCA‐co‐VAc). The in vitro cytotoxicity of the synthesized compounds against mouse mammary carcinoma and human histiocytic lymphoma cancer cell lines decreased in the following order: 5‐fluorouracil (5‐FU) ≥ ETCA > polymers. The in vivo antitumour activity of the polymers against Balb/C mice bearing sarcoma 180 tumour cells was greater than that of 5‐FU at all doses tested. © 2001 Society of Chemical Industry     

Fabrication of poly(methyl methacrylate)‐block‐poly(N‐isopropylacrylamide) amphiphilic diblock copolymer on silicon substrates via surface‐initiated reverse iodine transfer polymerization

Amphiphilic diblock copolymer on silicon substrates were synthesized via surface‐initiated reverse iodine transfer polymerization (RITP) technique. The silicon substrates (Si (111) surface) were modified with the azo groups, which were introduced by the treatment of Si (111) surface with 4,4′‐azobis (4‐cyanopentanoic acid). The poly(methyl methacrylate) (PMMA) were then prepared under RITP conditions from the Si (111) wafer. The synthesis of amphiphilic diblock copolymer was carried out on Si‐g‐PMMA substrate by sequential addition of monomer N‐isopropylacrylamide (NIPAM). The observed narrow molecular weight distributions (M_w/M_n), linear kinetic plots, and linear plots of molecular weight (M_n) versus monomer conversion indicate that the chain growth from the silicon substrates is a controlled process with a “living” characteristic. The ellipsometry and contact angle results indicated that the MMA had grafted from the surface of the silicon substrates successfully and the graft layer was well defined. The structure of the polymer and the ability to extend the chains were characterized and confirmed with the surface sensitive techniques such as X‐ray photoelectron spectroscopy and atomic force microscope. POLYM. ENG. SCI., 54:925–931, 2014. © 2013 Society of Plastics Engineers     

Preparation of photoresist polymer by a photoreactive monomer containing N,N-diethyldithiocarbamate group

A novel photosensitive monomer with a pendant photoreactive diethyldithiocarbamoyl group, VBDC, was synthesized and copolymerized with some vinyl monomers by AIBN. The copolymers obtained have efficient photocrosslinking abilities, and are thermally stable. Therefore, there was no loss of dithiocarbamoyl group during radical polymerization, and the polymerization proceeded through vinyl group. The degree of photocrosslinking was proportional to the concentration of the photosensitive group, but photosensitivity of the polymer was not. Water-soluble photoreactive copolymers, VBDC with AAm or MA, were also prepared. AAm copolymer has a good photosensitivity by only 3 mol % VBDC incorporation. Photocrosslinking yields of these polymers depend on the viscosity of original polymers except in the case of low concentration of VBDC. The relation between copolymer composition and glass transition temperature was also investigated. From the investigation of T_g, it was concluded that the copolymer structure largely affected on ΔT_g. The mechanism of photocrosslinking was studied by photodecomposition of benzyl N, N-diethyldithiocarbamate, and the result that the decreases of sulfur content clearly related to photocrosslinking points was also obtained.     

In-chain functionalization by alternating anionic copolymerization of styrene and 1-(4-dimethylaminophenyl)-1-phenylethylene

Anionic copolymerizations of styrene (M₁) with excess 1-(4-dimethyl-aminophenyl)-1-phenylethylene (M₂) were conducted in benzene at 25°C for 24h, using sec-butyllithium as initiator. Narrow molecular weight distribution copolymers with M?;_n = 16.1 × 10³ g/mol (M?_w/M?_n = 1.04) and 38.2 × 10³g/mol (M?_w/M?_n = 1.05), and 24 and 38 moles of M₂ per macromolecule, respectively, were characterized by size exclusion chromatography, ¹H NMR spectroscopy and DSC. The monomer reactivity ratio, r₁ = 5.6, was obtained from the copolymer composition at complete consumption of M₁, assuming that the rate constant k₂₂ =0,i.e. r₂ =0. The polymers exhibited T_g values of 128 and 119°C, respectively, which correspond to an estimated T_g = 217°C for the hypothetical homopolymer of M₂.     

Cationic polymerization of 1,3‐pentadiene coinitiated by zinc halides

Technology of industrial production of liquid rubber under trademark “SKOP” is based on the cationic polymerization of 1,3‐penadiene (piperylene) in the presence of TiCl₄ or AlCl₃‐based catalytic systems. The disadvantage of these catalytic systems is the high probability of formation of branched and insoluble fractions due to the chain transfer to polymer. This deteriorates the useful qualities of SKOP. Here we propose the new initiating systems for the cationic polymerization of 1,3‐pentadiene based on the homogeneous (dissolved in a minimal amount of diethyl ether) zinc halides (ZnCl₂ and ZnBr₂) as coinitiators and hydrochloric acid, tert‐butyl chloride or trichloroacetic acid as initiators. These initiating systems allow to synthesize fully soluble low molecular weight (M_n = 1000–3000 g mol^?1) poly(1,3‐pentadiene)s with relatively narrow molecular weight distribution (M_w/M_n < 2.0), which do not contain any high molecular weight and insoluble fractions in the whole range of monomer conversion. The polymers synthesized in the presence of zinc halides possess the same microstructure that those prepared with TiCl₄ as coinitiator. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013