Living Block Copolymers Research Articles

Understanding the Microstructure of Living Ethylene/1‐Octene Block Copolymers with Dynamic Monte Carlo Simulation

Living ethylene/1‐olefin copolymerization with multiple comonomer feeding stages allows the production of living block copolymers (LBCs) with well‐controlled microstructures. A dynamic Monte Carlo model is developed to simulate the production of LBCs in a semibatch reactor, and it is used to study how the polymer microstructure evolves during the polymerization. The model also describes how chain transfer reactions affect the microstructure of LBC blocks. These model predictions provide useful guidelines for producing LBCs with precisely designed microstructures. image

Cylindrical polymer brushes with dendritic side chains by iterative anionic reactions

We report in this paper an easy method for the synthesis of cylindrical polymer brushes with dendritic side chains through anionic reaction. The synthesis is accomplished by iteratively grafting a living block copolymer, polyisoprene-b-polystyrenyllithium (PI-b-PSLi), to the main chain and subsequently to the branches in a divergent way. PI segment is short and serves as a precursor for multifunctional branching unit. The grafting reaction involves two successive steps: i) epoxidation of internal double bonds of PI segments, either in main chain or side chains; ii) ring-opening addition to the resulting epoxy group by the living PI-b-PSLi. Repeating the two steps affords a series of cylindrical polymer brushes with up to 3rd generation and extremely high molecular weight. The branching multiplicity depends on the average number of oxirane groups per PI segment, usually ca. 8 in the present work. The high branching multiplicity leads to tremendous increase in molecular weights of the cylindrical products with generation growth. Several series of cylindrical polymer brushes with tunable aspect ratios are prepared using backbones and branches with controlled lengths. Shape anisotropy is investigated in dilute solution using light scattering technique. Worm-like single molecular morphology with large persistence length is observed on different substrates by atomic force microscopy.

Structure analysis of ethylene/1-octene copolymers synthesized from living coordination polymerization

A series of ethylene/1-octene random and block copolymer samples were synthesized via a living coordination polymerization catalyzed by bis[N-(3-methylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium(IV) dichloride/dMAO. The chain microstructures of the copolymers were elucidated by analytic TREF and DSC thermal fractionation techniques in this work. It was found that the living random copolymers possessed narrower intrachain composition distributions than those prepared from conventional metallocene catalysts. With the same short chain branching content, the melting temperature of living random copolymer was about 16°C lower than metallocene-catalyzed random copolymer. The living block copolymers were also studied in comparison with the olefin multiblock copolymer (OBC) produced from chain shuttling polymerization. The interchain composition distribution of OBC was found broader than living block copolymers. However, the crystal thickness distribution of OBC was narrower. The diblock copolymer had a bimodal distribution in the crystal thickness and the step triblock copolymer showed a trimodal distribution, in contrast to OBC’s single modal distribution.

Easy synthesis of dendrimer-like polymers through a divergent iterative “end-grafting” method

We report here an easy method for the synthesis of dendrimer-like polymers with high branching functionality (1 → 8). The synthetic process involves iterative grafting reactions in a divergent way. A multi-functional core containing short segments of polyisoprene (PI), either as a star-like block copolymer of isoprene and styrene or as a linear triblock copolymer of isoprene, styrene and isoprene (coded G1), is epoxidized on the double bonds and grafted with a living block copolymer, polyisoprene-b-polystyrenyllithium (PI-b-PSLi), again with a short PI segment, through the ring-opening reaction of oxirane by polymeric anions. The resulting graft polymer, G2, possesses a definite number of PI segments at the periphery. These PI segments are further epoxidized followed by the ring-opening addition of PI-b-PSLi, affording G3. Repeating the process leads to the synthesis of a dendrimer-like polystyrene up to 5th generation with a polydispersity lower than 1.21, as measured by SEC. A feature of the process is the easily accessible high chain density in the final product, although defects exist due to steric hindrance in the reactions of high generations. The solution properties of the dendritic products are investigated using viscometry and dynamic and static laser light scattering on the molecular conformation. The results support a compact globular conformation model for the dendrimer-like products. In addition, the chain density of the products from the star-like core is higher than that of products from a linear triblock core. AFM results show that the dendritic products adopt flattened conformations and tend to form lateral sphere-like aggregates on mica substrate.

Adding stimuli-responsive extensions to antifouling hairy particles

The use of living block copolymers as stabilisers in emulsion polymerisation allowed preparation of multilayer functional hairy particles via surface-initiated ATRP. Polymer films prepared from the obtained particles present antifouling properties along with stimuli-responsive behaviour.

Linear pentablock quintopolymers (l‐SIDMV) with five incompatible blocks: Polystyrene, polyisoprene‐1,4, poly(dimethylsiloxane), poly(tert‐butyl methacrylate), and poly(2‐vinylpyridine)

AbstractThree linear pentablock quintopolymers (l‐SIDMV), where S is polystyrene (PS), I polyisoprene‐1,4 (PI), D poly(dimethylsiloxane) (PDMS), M poly(tert‐butyl methacrylate) (PtBuM), and V poly(2‐vinylpyridine) (P2VP), were synthesized by anionic polymerization high vacuum techniques. The approach involves the following: (a) The synthesis of living triblock terpolymer PS‐b‐PI‐b‐PDMSLi and diblock copolymer P2VP‐b‐PtBuMK by sequential polymerizations of the corresponding monomers with sec‐BuLi and benzyl potassium, respectively; and (b) The selective linking of the living triblock terpolymer with the chlorosilane group of 2‐(chloromethylphenyl)ethyldimethylchlorosilane (CMPDMS), followed by linking of the living block copolymer with the remaining chloromethyl group of CMPDMS. Molecular characterization carried out by size exclusion chromatography, membrane osmometry, solution (in CDCl3 or d8‐toluene) and solid‐state 1H‐NMR spectroscopy indicated a high degree of molecular and compositional homogeneity. Differential scanning calorimetry results on the precursors and final polymers were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3938–3946, 2008

Synthesis of star‐shaped copolymers with methyl methacrylate and n‐butyl methacrylate by metal‐catalyzed living radical polymerization: Block and random copolymer arms and microgel cores

AbstractVarious star‐shaped copolymers of methyl methacrylate (MMA) and n‐butyl methacrylate (nBMA) were synthesized in one pot with RuCl2(PPh3)3‐catalyzed living radical polymerization and subsequent polymer linking reactions with divinyl compounds. Sequential living radical polymerization of nBMA and MMA in that order and vice versa, followed by linking reactions of the living block copolymers with appropriate divinyl compounds, afforded star block copolymers consisting of AB‐ or BA‐type block copolymer arms with controlled lengths and comonomer compositions in high yields (≥90%). The lengths and compositions of each unit varied with the amount of each monomer feed. Star copolymers with random copolymer arms were prepared by the living radical random copolymerization of MMA and nBMA followed by linking reactions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 633–641, 2002; DOI 10.1002/pola.10145

Synthesis and Characterization of Well-Defined Poly(α-methylstyrene)-b-poly(dimethylsiloxane) Block Copolymers

The anionic synthesis is reported for AB and ABA narrow distribution block copolymers of poly(α-methylstyrene) (PAMS, A) and poly(dimethylsiloxane) (PDMS, B) with molecular weights ranging between 8.2 × 103 and 1.9 × 105. In one approach living PAMS end-capped with a short polystyrene block (PAMS−PSLi) was obtained by the tert-butyllithium initiated polymerization of AMS in THF at −78 °C followed by the sequential addition of styrene, 2−3 equiv of 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (EDS) at −20 °C, and hexamethylcyclotrisiloxane (D3) at 25 °C. A more convenient synthesis without the use of styrene is the direct end-capping of living PAMSLi with EDS at −10 °C followed by the polymerization of D3 at 25 °C. The living block copolymers were then end-capped with Me3SiCl or coupled with Me2SiCl2 to give matching AB and ABA narrow distribution block copolymers. The glass transition temperatures of the PAMS blocks were at least 10 °C higher than that of the PAMS−PS blocks.

Polyisobutylene based thermoplastic elastomers: VI. Poly(α-methylstyrene-b-isobutylene-b-α-methylstyrene) triblock copolymers by coupling of living poly (α-methylstyrene-b-isobutylene) diblock copolymers

Poly(α-methylstyrene-b-isobutylene-b-α-methylstyrene) (PaMeSt-PIB-PaMePSt) triblock copolymers have been prepared via coupling of living diblock copolymers in a one pot procedure. The PaMeSt-PIB diblock copolymers were synthesized by living sequential cationic polymerization in methylcyclohexane (MeChx)/methylchloride (MeCl) solvent mixtures at -80 °C using BCl 3 for aMeSt polymerization and TiCl 4 for IB polymerization as coinitiators. The crossover efficiency, however, was only ∼57 %, due to intermolecular alkylation (indanyl ring formation) after the addition of TiCl 4 . By modifying the PaMeSt end with a short segment of p-chloro-a-methylstyrene before IB addition the crossover efficiency was increased to 90 %. Coupling of the living block copolymers with 2,2-bis[4-(1-phenylethenyl)phenyl]propane (BDPEP) was rapid and gave - 90 % efficiency.

Graft, Block-Graft and Star-Shaped Copolymers by an in Situ Coupling Reaction.

A tetrahydrofuran (THF) solution of the living poly(glycidyl methacrylate) (poly(GMA)) was prepared by the living anionic polymerization of GMA, using 1,1-diphenylhexyllithium (DPHL) as initiator, in the presence of LiCl ([LiCl]/[DPHL]0 = 3), at -45 degreesC. Upon introduction of a benzene solution of living polystyrene (poly(St)) into the above system at -30 degreesC, a very rapid coupling reaction between the epoxy groups of the living poly(GMA) and the propagating sites of the living poly(St) generated a graft copolymer containing a polar backbone and nonpolar side chains. When benzene solutions of living poly(St) and polyisoprene were sequentially transferred to the THF solution of living poly(GMA), a graft copolymer possessing two different nonpolar side chains was obtained. Further, a THF solution of the living block copolymer of methyl methacrylate (MMA) and GMA was prepared by the sequential anionic polymerization of the two monomers, at low temperatures. A block-graft copolymer having a poly(MMA-b-GMA) block backbone and poly(St) side chains was synthesized by reacting the living poly(St) with the epoxy groups of the above living block copolymer. In addition, when the poly(GMA) segment in poly(MMA-b-GMA) was short, a star-shaped copolymer containing a poly(MMA) arm and several poly(St) arms was obtained. GPC and 1H NMR measurements indicated that all the above copolymers possess high purity, designed molecular architectures, controlled molecular weights and narrow molecular weight distributions (Mw/Mn = 1.10-1.23).

Multifunctional Coupling Agents for Living Cationic Polymerization. 7. Synthesis of Amphiphilic Tetraarmed Star Block Polymers with α-Methylstyrene and 2-Hydroxyethyl Vinyl Ether Segments by Coupling Reactions with Tetrafunctional Silyl Enol Ether

By the polymer coupling reaction with a tetrafunctional silyl enol ether [1; C{CH2OC6H4C(OSiMe3)CH2}4], amphiphilic tetraarmed star polymers (6) with α-methylstyrene−2-hydroxyethyl vinyl ether (αMeSt−HOVE) block arm chains have been synthesized: C{CH2OC6H4COCH2−[CH(OCH2CH2OH)CH2]n−[C(CH3)(C6H5)CH2]m−}4. The synthesis consisted of the following steps: (i) the sequential living cationic polymerization of αMeSt and 2-[(tert-butyldimethylsilyl)oxy]ethyl vinyl ether (SiVE) into an αMeSt−SiVE living block copolymer (4); (ii) the coupling of four chains of 4 with the quencher 1 into a tetraarmed polymer (5); and (iii) the transformation of the poly(SiVE) segment into the poly(HOVE) chain by the fluoride-catalyzed deprotection. In step i the living polymerization was carried out at −78 °C in methylene chloride with a binary initiating system comprising tin tetrabromide and the hydrogen chloride adduct of 2-chloroethyl vinyl ether. After step iii, the tetraarmed amphiphile 6 (αMeSt/HOVE = 27/27 in n in each arm)...

Block copolymers polystyrene-polyacetylene grafted on C60

Abstract Living block copolymers polystyrene-poly(phenylvinylsulfoxide) have been grafted onto C 60 to form star shaped (PS-PPVS) x C 60 . These molecules could be converted to (PS-PA) x C 60 by thermal treatment. Some of them stay soluble depending on the length of the solubilizing PS sequence and of the PA(exPPVS) block. The number of branches varies from 1 to 3. Doping, up to high levels, could be achieved in solution.

Star‐shaped polymers by living cationic polymerization, 6. Amphiphilic star‐shaped block copolymers of vinyl ethers with carboxyl groups: synthesis and host‐guest interaction

AbstractAmphiphilic star‐shaped polymers (5 and 6) of vinyl ethers (VEs), the arms of which consist of apoly(carboxylic acid)/poly(alkyl VE) AB block copolymer, were prepared on the basis of living cationic polymerization. Thus, a sequential living polymerization of a VE with a pendant malonate group [CH2  CHOCH2CH2CH(COOCH2CH3)2] and and isobutyl VE with HI/ZnI2 at −15°C in toluene led to a living block copolymer (3a), which was subsequently allowed to react with a small amount of a bifunctional vinyl ether [1; CH2  CHOCH2CH2OC6H4C(CH3)2‐C6H4OCH2CH2OCH  CH2] to give a star‐shaped block copolymer (4a). Alkaline hydrolysis of the ester functions of 4a, followed by neutralization, gave the amphiphilic star copolymer (5a, diacid form; \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \{ H\rlap{--} [CH}_2 {\rm CH(OCH}_2 {\rm CH}_2 {\rm X)\rlap{---} ]}_m {\rm \rlap{--} [CH}_2 {\rm CH(O}i{\rm Bu)\rlap{--} ]}_n \} _f - {\rm (core)}, $\end{document} X = CH(COOH)2) with hydrophilic poly(carboxylic acid) segments in the outer region, and subsequent decarboxylation led to the monoacid form 6a (X = CH2COOH). Amphiphilic star copolymers (5b and 6b; \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \{ H\rlap{--} [CH}_2 {\rm CH(O}i{\rm Bu)\rlap{---} ]}_m {\rm \rlap{--} [CH}_2 {\rm CH(OCH}_2 {\rm CH}_2 {\rm X)\rlap{--} ]}_{n'} \} _f - {\rm (core)}, $\end{document} 5b: X = CH(COOH)2, 6b: X = CH2COOH) with an opposite segment sequence(inner polyacid chains) were also prepared. The star copolymer 5b (m′ = 30, n′ = 10) was insoluble in methanol, in which the polymer 5a (m = 10, n = 30) with the opposite segment sequence was soluble, and both 5a and 5b as well as both 6a and 6b differed in solubility from the corresponding linear polymer. The amphiphilic polymers 5 and 6 were also found to interact selectively with guests with polar functional groups such as benzoic acid and benzylamine.

Well-defined redox-active polymers and block copolymers prepared by living ring-opening metathesis polymerization

Mo(CH-t-Bu)(NAr)(O-t-Bu){sub 2} (1a) in Thf/0.1 M [n-Bu{sub 4}N]AsF{sub 6} is not oxidized at potentials up to 1.0 V and undergoes a reversible, one electron reduction at -2.16 V vs SCE at a Pt electrode. An analogous intiator containing a ferrocenylmethylidene ligand (1b) can be synthesized by treating 1a with vinylferrocene. Redox-active derivatives of norbornene, containing ferrocene (2) or phenothiazine (3), were prepared and polymerized by 1a or 1b to give living block copolymers containing the ring-opened norborene derivatives. The living polymer was cleaved from the metal in a Wittig-like reaction with pivaldehyde, trimethylsilylbenzaldehyde, or octamethylferrocenecarboxaldehyde. Polydispersities for the longer block copolymers containing up to {approximately}90 monomer units were found to be as low as 1.05 by GPC. In one case the polydispersity of a homopolymer made from the ferrocene-containing monomer was determined by FD-mass spectroscopy to be 1.06. DSC studies suggest that microphase studies of homo and block copolymers showed that the redox centers were electrochemically independent and that all centers exchanged electrons with the electrode. Neutral polymers became insoluble upon oxidation to a polycation, yielding an adsorbed polymer layer on the electrode that could then be cathodically stripped. This oxidative deposition process depended on the electrolyte and the polymermore » molecular weight but also could be controlled by the size of a nonelectroactive block in the block copolymers. Problems resulting from precipitation of the redox polymers could be circumvented by employing normal pulse voltammetry. Polymers containing redox centers in both end groups as well as in the polymer chain itself have been prepared and their nature confirmed in electrochemical studies.« less