Molecular Weight Diblock Copolymers Research Articles

Self-assembly behavior of ultra-high molecular weight in-situ anionically synthesized polymer matrix composite materials “grafted from” single- or multi-wall CNTs

A pioneering synthetic approach for the design of novel composite materials is reported. The final products are consisting of high number average molecular weight diblock copolymers which are surface initiated (“grafting from” approach) from either single or multi-wall carbon nanotubes (SWCNTs or MWCNTs respectively). In-situ anionic polymerization results in nanocomposites, exhibiting narrow dispersity indices which are in accordance with anionic polymerization standards, able to self-assemble when studied in bulk. The polymer matrices are diblock copolymers of the PS-b-PI type [PS: polystyrene and PI: poly(isoprene)]. The successful “grafting from” the corresponding CNTs is verified by Raman and Χ-Ray Photoelectron spectroscopy, while the structure/properties relationship of the composites is determined employing High Resolution Transmission Electron Microscopy (HR-TEM). HR-TEM characterization is very important for the successful identification of the MWCNTs as well as for the justified conformation of the polymeric chains grafted from the CNTs.

A15, σ, and a Quasicrystal: Access to Complex Particle Packings via Bidisperse Diblock Copolymer Blends.

A renewed focus on the phase behavior of nominally single-component, compositionally asymmetric diblock copolymers has revealed a host of previously unanticipated Frank-Kasper (FK) and quasicrystalline phases. However, these periodic and aperiodic particle packings have thus far only been reported in low molecular weight, highly conformationally asymmetric diblock copolymers, leaving researchers with a relatively small library of polymers in which these phases can be studied. In this work, we report on a simple approach to access these morphologies: blending two diblock copolymers with the same corona block length and varied core block lengths. Compositionally symmetric and asymmetric polystyrene-b-1,4-polybutadiene (SB) diblock copolymers with constant corona block lengths were blended together and shown via small-angle X-ray scattering and transmission electron microscopy to order into the FK A15 and σ phases, as well as a dodecagonal quasicrystal, providing a route to various particle packings in high molecular weight diblock copolymer melts.

Self-Assembly in ultrahigh molecular weight sphere-forming diblock copolymer thin films under strong confinement

Ultrahigh molecular weight (UHMW) diblock copolymers (DBCs) have emerged as a promising template for fabricating large-sized nanostructures. Therefore, it is of high significance to systematically study the influence of film thickness and solvent vapor annealing (SVA) on the structure evolution of UHMW DBC thin films. In this work, spin coating of an asymmetric linear UHMW polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) DBC is used to fabricate thin films, which are spherically structured with an inter-domain distance larger than 150 nm. To enhance the polymer chain mobility and facilitate approaching equilibrium nanostructures, SVA is utilized as a post-treatment of the spin coated films. With increasing film thickness, a local hexagonal packing of PMMA half-spheres on the surface can be obtained, and the order is improved at larger thickness, as determined by grazing incidence small angle X-ray scattering (GISAXS). Additionally, the films with locally hexagonal packed half-spherical morphology show a poor order-order-poor order transition upon SVA, indicating the realization of ordered structure using suitable SVA parameters.

Tertiary Amine Methacrylate based Polymers as Corrosion Inhibitors in HCl Solution. Part II

In this study, the inhibitive performance of novel synthesised water-soluble of different molecular weight diblock copolymers of derivative methyl methacrylate (VB84, VB206, VB207, VB361, VB371,VB406) on the corrosion behavior of AISI 304 stainless steel in 10–3 M HCl containing various concentrations of polymers was investigated using potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS), scanning electron microscopy(SEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM) and inductively coupled plasma optical emmision spectrometry (ICP-OES) methods. Polarisation curves indicated that all studied polymers were acting as mixed type inhibitors. All electrochemical measurements showed that inhibition efficiencies increased with increasing polymer concentration. It was determined that the increase of inhibitor efficiency by concentration resulted from the adsorption of polymers to metal surface, and the adsorption fitted to the Langmuir adsorption equation. The variation in inhibitive efficiency mainly depends on the type and the nature of the substituents present in the polymer molecule and also depends on the molecular weight of the polymer. The best inhibition in 10-3 M HCl shows VB84 homopolymer. Surface images obtained with SEM, EDX, and AFM methods determined by verifying these results that inhibitors decrease the dissolution of metal, prevented the corrosion.

Rapid Production of Internally Structured Colloids by Flash Nanoprecipitation of Block Copolymer Blends.

Colloids with internally structured geometries have shown great promise in applications ranging from biosensors to optics to drug delivery, where the internal particle structure is paramount to performance. The growing demand for such nanomaterials necessitates the development of a scalable processing platform for their production. Flash nanoprecipitation (FNP), a rapid and inherently scalable colloid precipitation technology, is used to prepare internally structured colloids from blends of block copolymers and homopolymers. As revealed by a combination of experiments and simulations, colloids prepared from different molecular weight diblock copolymers adopt either an ordered lamellar morphology consisting of concentric shells or a disordered lamellar morphology when chain dynamics are sufficiently slow to prevent defect annealing during solvent exchange. Blends of homopolymer and block copolymer in the feed stream generate more complex internally structured colloids, such as those with hierarchically structured Janus and patchy morphologies, due to additional phase separation and kinetic trapping effects. The ability of the FNP process to generate such a wide range of morphologies using a simple and scalable setup provides a pathway to manufacturing internally structured colloids on an industrial scale.

Abstract P3-10-04: A open-label, randomized, parallel, phase III trial to evaluate the efficacy and safety of Genexol®-PM compared to Genexol®(conventional paclitaxel with cremorphor EL) in recurrent or metastatic breast cancer patients

Abstract Background: The rationale for developing an alternative paclitaxel formulation concerns Cremophor EL-related side effects, and a novel paclitaxel delivery system might augment its therapeutic efficacy. Genexol-PM is a novel polymeric micelle formulated paclitaxel free of Cremophor. The polymeric micelle formulation is composed of hundreds of low molecular weight, non-toxic, and biodegradable amphiphilic diblock copolymers which include monomethoxy poly (ethylene glycol)-block-poly (D,L-lactide). This multicenter phase III study was designed to evaluate the non-inferiority of efficacy of Genexol-PM compared to conventional CrEL-based paclitaxel. Methods: In this phase III study, 213 patients were enrolled onto the study and randomly assigned (1:1) to treatment group according to prior recurrent or metastatic breast cancer chemotherapy. The study evaluated the objective response rate for the primary objective, and others including overall survival (OS), progression free survival (PFS), time to tumor progression (TTP), duration of overall response and adverse events. Eligible patients were randomly assigned to receive either Genexol-PM or standard paclitaxel. Genexol-PM or standard paclitaxel was administered on the first day of every 3 weeks. Measurable disease was assessed by imaging using the RECIST 1.0 criteria. Results: The objective response rate (ORR) was higher by the administration of the study drug (39.05% v 24.30% in ITT, 56.92% v 39.29% in PP). One-sided 95% upper confidence limit was -4.36%, which is lower than the non-inferiority threshold (7%), indicating that the study group is not inferior to the control group. OS, PFS, TTP and duration of overall response were analyzed in the ITT population. The analysis of OS showed no significant difference (p=0.5878) (859 days, 95% CI : 732.00∼1,025.00 v 726 days, 95% CI : 553.00∼ -). Median PFS periods were 232 days (95% CI: 164.00∼274.00) vs. 191 days (95% CI: 159.00∼237.00). Median TTPs were 233 days (95% CI: 165.00∼286.00) vs. 191 days (95% CI: 159.00∼241.00) between the groups. Difference in PFSs and TTPs between the groups were not statistically significant. (p=0.2407, 0.2076, respectively) Genexol-PM was not significantly different from the comparator in terms of safety. Conclusion: Genexol-PM demonstrated non-inferior efficacy and comparable safety profile compared with standard paclitaxel in this patient population. Of note, Genexol-PM permits the delivery of a higher paclitaxel dose without additional toxicity achieved with CrEL-based formulation. In the absence of CrEL, no filter or special tubing is required that conventional PVC infusion sets can be used. Citation Format: Jung Sil Ro, Joo Hyuk Sohn, Sung Bae Kim, Keun Seok Lee, Joo Seop Chung, Jae Hoo Park, Soo Hyeon Lee, Tae You Kim, Kyung Hae Jung, Eun Kyung Cho, Yang Soo Kim, Hong Suk Song, Jae Hong Seo, Hun Mo Ryoo, Sun Ah Lee, So Young Yoon, Chul Soo Kim, Yong Tai Kim, Hwa Jung Sung, Si Young Kim, Yong Jin Lee. A open-label, randomized, parallel, phase III trial to evaluate the efficacy and safety of Genexol®-PM compared to Genexol®(conventional paclitaxel with cremorphor EL) in recurrent or metastatic breast cancer patients [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-10-04.

Novel dexamethasone-loaded nanomicelles for the intermediate and posterior segment uveitis.

Development and characterization of dexamethasone (DEX)-encapsulated polymeric nanomicelles have been reported. A low molecular weight di-block copolymer was synthesized and characterized for its structure, molecular weights, critical micelle concentration (CMC), and cytotoxicity in ocular cells. In order to delineate the effects of drug-polymer interactions on drug solubilization in micelle core, a response surface methodology was generated with the help of SAS 9.02 (exploratory model). The method for preparing micelle was modified based on the results obtained from exploratory model. The formulation was optimized by response surface methodology (optimization model) to achieve DEX solubility of above 1mg/mL. The optimized formulation was characterized for DEX solubility, nanomicelle size, polydispersity index, surface morphology, in vitro transport across conjunctival cell line, and ex vivo transport across excised rabbit sclera. Nanomicelles exhibited average sizes in range of 25-30nm with unimodel size distribution and low polydispersity of 0.125. Nanomicelles increased DEX permeability by 2 times across conjunctival cell line and by 2.5 times across the excised rabbit sclera as compared to DEX suspension. A design of experiment (DOE) strategy was successfully applied to understand the effects of drug-polymer interaction on drug solubility. DOE was also employed to achieve optimal formulation with high DEX solubility. Nanomicellar formulation significantly enhanced DEX permeability across the excised rabbit sclera. Therefore, nanomicellar formulation may provide therapeutic levels in the back of the eye following topical administration.

Aqueous reversible addition‐fragmentation chain transfer dispersion polymerization of thermoresponsive diblock copolymer assemblies: Temperature directed morphology transformations

AbstractIn this work, we demonstrate the formation of various 3D structures formed by a structural reorganization; a process not governed by self‐assembly. First, we packaged well‐defined diblocks, thermoresponsive poly(N‐isopropylacrylamide‐b‐styrene) or P(NIPAM‐b‐STY), into spherical particles made in situ using a reversible addition‐fragmentation chain transfer (RAFT) nanoreactor technique in water to obtain high polymer solids. The resultant spheres reorganized through a temperature stimulus to form equilibrium and kinetically trapped structures; we denote this process as temperature directed morphology transformation (TDMT). Cylinder and vesicle structures, other more unusual loop, buckled sphere and cauliflower (via ultrasound) structures were observed below the lower critical solution temperature (LCST) of PNIPAM. These structures were produced efficiently, rapidly, reproducibly at high polymer solids and can be stored for years in solution or be freeze‐dried and rehydrated without a change in structure, which becomes important in biological applications. We generated the first phase diagram for the TDMT changes of thermoresponsive diblock micelles in concentrated solutions (> 7% polymer solids) produced from narrow molecular weight diblock copolymers (PDI ∼ 1.1). The sphere/cylinder and cylinder/vesicle transition in the phase diagram were surprisingly found to be predominantly dictated by the length of the hydrophilic block, poly(N‐isopropylacrylamide). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Investigation on design of stable etoposide-loaded PEG-PCL micelles: effect of molecular weight of PEG-PCL diblock copolymer on the in vitro and in vivo performance of micelles

In the present study, six different molecular weight diblock copolymer of methoxy poly (ethylene glycol)-b-poly (ϵ-caprolactone) (MPEG-PCL) were synthesized and characterized and was used for fabrication of etoposide-loaded micelles by nanoprecipitation technique. The particle size and percentage drug entrapment of prepared micelles were found to be dependent on the molecular weight of PCL block and drug to polymer ratio. The maximum drug loading of 5.32% was found in micellar formulation MPEG5000-PCL10000, while MPEG2000-PCL2000 exhibited 2.73% of maximum drug loading. A variation in the fixed aqueous layer thickness and PEG surface density of micellar formulations was attributed to difference in MPEG molecular weight and interaction of PEG and PCL block of copolymer. The MPEG2000-PCL2000 micelles demonstrated poor in vitro stability among other micellar formulations, due to its interaction with bovine serum albumin and immediate release of drug from micelles. Furthermore, plain etoposide and MPEG2000-PCL2000 micelles exhibited greater extent of hemolysis, due to presence of surfactants and faster release of drug from micelles, respectively. The biodistribution studies carried out on Ehrlich ascites tumor-bearing Balb/C mice confirmed higher accumulation of etoposide-loaded micellar formulation at tumor site compared to plain etoposide due to enhanced permeability and retention effect.

Sensing Membrane Stress with Near IR-Emissive Porphyrins

Internal-strain sensors, embedded within a membrane, can enhance our ability to monitor membrane dynamics and predict its failure. Development of these probes with model membrane systems may provide a tool to elucidate areas of membrane stress or stretching in cellular membranes. Molecular rotors are one such class of mechano-optical molecules that have potential as intrinsic stress sensors. Supermolecular porphyrin-based fluorophores demonstrate this capability since the twisting of various subunits of the dye can lead to significant shifts in the fluorophore emission wavelength. We encapsulated these hydrophobic porphyrin-based fluorophores into bilayer vesicle membranes made of diblock-copolymers (polymersomes) and characterized changes in the optical emission of these near-infrared (NIR) emissive probes in response to membrane stress. The conformation of entrapped fluorophore depends on the available space within the membrane. We systematically changed the available space for the fluorophore in the polymersome membrane by changing the amount of fluorophore loading as well as increasing the membrane volume by using a larger molecular weight diblock copolymer. In response to increased volume for the fluorophore, emission is blue shifted. Using this property, we studied how shifts in fluorescence correlate to membrane integrity, imparted by membrane stress produced through a range of physical and chemical perturbations, including surfactant-induced lysis, hydrolytic lysis, thermal degradation, and applied stress by micropipette aspiration. With the latter aspiration studies, we find that changes in the NIR probe's emission accompany measured changes in polymersome membrane tension. Studies conducted with this NIR probe and model membrane suggest that molecular rotors, such as these, can potentially be used in future studies to monitor intrinsic stress in a variety of membranes, ranging from synthetic membranes, to monitor the delivery of drugs or in vivo rheological changes, to cellular membranes, to monitor membrane stress during motility or transport processes.

Continuously tuneable optical filters from self-assembled block copolymer blends

We demonstrate that two symmetric high molecular weight diblock copolymers, of differing molecular weights, can be blended together and subsequently shear aligned to form one photonic structure without macrophase separation. The lameller period depends on the composition of the blend and gives a photonic structure that is easily tuneable in the wavelength range (λpeak = 400–850 nm).

Solution Behavior of Polystyrene−Polyisoprene Miktoarm Block Copolymers in a Selective Solvent for Polyisoprene

The dynamics and self-assembly of polystyrene− (PS−) polyisoprene (PI) miktoarm (mixed-arm) block copolymers in n-hexane, a selective solvent for PI, are investigated. The miktoarms present a branched arrangement in the soluble block in the fashion of PI−(PI)2, where two PI blocks are connected by a common end point to a linear PS−PI diblock. It is found that these copolymers self-assemble into spherical micelles having cores composed of the insoluble PS blocks and coronas of the well-solvated PI−(PI)2 blocks. Micelles formed from the branched polymer amphiphiles are more compact, having smaller sizes than the micelles formed from a linear PS−PI diblock copolymer of similar molecular weight and composition. As the concentration is decreased, the micelles with large aggregation numbers remain stable, only showing changes in the aggregation number. The hydrodynamic sizes and aggregation numbers determined from the micelles formed from miktoarm copolymers differ from theoretical predictions for spherical micelles made of the equivalent linear amphiphilic diblock copolymers. These differences may arise from the arrangements of the branched blocks inside the micellar corona.

Triblock copolymers composed of soft and semi-crystalline segments—synthesis and characterization of poly[(n-butyl acrylate)-block-(ε-caprolactone)-block-(L-lactide)

Poly(n-butyl acrylate) terminated with benzyl alcohol units (PnBA-MI) of varying molecular weights were synthesized by polymerizing n-butyl acrylate using substituted benzyl alcohol based initiators under atom transfer radical polymerization (ATRP) conditions. Between the ligands bipyridine and PMDETA, the latter ligand showed better control for the polymerization of n-BA. High molecular weight diblock copolymers of poly[(n-butyl acrylate)-block-(e-caprolactone)] were synthesized by ring opening polymerization (ROP) of e-caprolactone using PnBA-MI which formed thin, flexible and opaque films which are soft to touch. Triblock copolymers of poly[(n-butyl acrylate)-block-(e-caprolactone)-block-(L-lactide)] were synthesized in a one pot, two step reaction by the sequential addition of monomers. The molecular weights of PCL and PL segments in the triblock copolymers were comparable. Due to this, the triblock copolymer showed exothermic transition upon cooling well above the Tm of PCL block.

Strongly segregated cubic microdomain morphology consistent with the double gyroid phase in high molecular weight diblock copolymers of polystyrene and poly(dimethylsiloxane)

AbstractWe report the observation of a cubic phase consistent with the double gyroid structure in strongly segregated diblock copolymers of PS‐b‐PDMS over a volume fraction (φPDMS) range of ∼0.39 to 0.45. The samples have respective molecular weights of 127 kg/mol and 73 kg/mol and degree of segregation Nχ equal to 187 and 106, respectively, at annealing temperature of 130 °C. It is important to highlight that two out of the total four samples investigated, exhibited hexagonally close packed cylindrical domains of PDMS and alternating lamellae at φPDMS = 0.39 and 0.45, respectively, indicating the possible narrow range of the DG morphology for the specific diblock copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2419–2427, 2009

Diblock copolymers with an amorphous, high glass transition temperature, organometallic block: synthesis, characterisation and self-assembly of polystyrene-b-poly(ferrocenylisopropylmethylsilane) in the bulk state

Living anionic ring-opening polymerisation of isopropylmethylsila[1]ferrocenophane yields poly(ferrocenylisopropylmethylsilane) (PFiPMS) with controlled molecular weights and narrow polydispersities up to Mn=ca. 20,000Da. Polystyrene-b-poly(ferrocenylisopropylmethylsilane) (PS-b-PFiPMS) diblock copolymers have been prepared via sequential living anionic polymerisation. These materials are examples of diblock copolymers with an amorphous, organometallic block with a glass transition temperature (Tg) above room temperature (60°C). High molecular weight diblock copolymers (Mn=42,000–51,000Da) were targeted with low polydispersities (PDI=1.1). As both blocks are amorphous, these materials self-assemble into predictable morphologies in the bulk state with well-ordered nanodomains.

Phase Behavior of Binary Blends of High Molecular Weight Diblock Copolymers with a Low Molecular Weight Triblock

Binary blends of four different high molecular weight poly(styrene-b-isoprene) (SI) diblock copolymers with a lower molecular weight poly(styrene-b-isoprene-b-styrene) (SIS) triblock copolymer were prepared, and their morphology was characterized by transmission electron microscopy and ultra-small-angle X-ray scattering. All the neat block copolymers have nearly symmetric composition and exhibit the lamellar morphology. The SI diblock copolymers had number-average molecular weights, Mn, in the range 4.4 × 105−1.3 × 106 g/mol and volume fractions of poly(styrene), ΦPS, in the range 0.43−0.49, and the SIS triblock had a molecular weight of Mn ∼ 6.2 × 104 g/mol with ΦPS = 0.41. The high molecular weight diblock copolymers are very strongly segregating, with interaction parameter values, χN, in the range 470−1410. A morphological phase diagram in the parameter space of molecular weight ratio (R = Mndiblock/1/2Mntriblock) and blend composition was constructed, with R values in the range between 14 and 43, wh...

Computer Simulation of Architectural and Molecular Weight Effects on the Assembly of Amphiphilic Linear−Dendritic Block Copolymers in Solution

Langevin dynamics simulations are performed on linear-dendritic diblock copolymers containing bead-spring, freely jointed chains composed of hydrophobic linear monomers and hydrophilic dendritic monomers. The critical micelle concentration (CMC), micelle size distribution, and shape are examined as a function of dendron generation and architecture. For diblock copolymers with a linear block of fixed length, it is found that the CMC increases with increasing dendron generation. This trend qualitatively agrees with experiments on linear-dendritic diblock and triblock copolymers with hydrophilic dendritic blocks and hydrophobic linear blocks. The flexibility of the dendritic block is altered by varying the number of spacer monomers between branch points in the dendron. When comparing linear-dendritic diblock copolymers with similar molecular weights, it is shown that increasing the number of spacer monomers in the dendron lowers the CMC due to an increase in flexibility of the dendritic block. Analysis on the micellar structure shows that linear-dendritic diblock copolymers pack more densely than what would be expected for a linear-linear diblock copolymer of the same molecular weight.

The characterization of paclitaxel-loaded microspheres manufactured from blends of poly(lactic- co-glycolic acid) (PLGA) and low molecular weight diblock copolymers

Paclitaxel-loaded biodegradable drug delivery systems manufactured from poly(lactic- co-glycolic acid) (PLGA) are known to release the drug at extremely slow rates. The objective of this study was to characterize paclitaxel-loaded microspheres composed of blends of PLGA with low molecular weight ampipathic diblock copolymers. The encapsulation and release of a series of poly(ɛ-caprolactone) (PCL)- or poly( d, l-lactic acid) (PDLLA)- co-methoxypolyethylene glycol (MePEG) diblock copolymers was measured using quantitative gel permeation chromatography. Polymeric miscibility was determined by glass transition temperature measurements using differential scanning calorimetry and paclitaxel release was measured using HPLC methods. The PCL- and PDLLA-based diblock copolymers encapsulated at high efficiency and were miscible in PLGA microspheres (30–120 μm size range). The burst phase of paclitaxel release was increased up to 20-fold by the inclusion of diblock copolymers in PLGA microspheres. Approximately 10% of the more hydrophobic PCL-based copolymers released from the microspheres in a short burst over 3 days followed by very slow release over the following 10 weeks. Only the PDLLA-based copolymer released from the PLGA microspheres in a controlled manner over 10 weeks. All microspheres containing PEG were found to have more hydrophilic surfaces (as measured by contact angle) with improved biocompatibility (reduced neutrophil activation) compared to PLGA only microspheres. These results indicate that low molecular weight polyester-based diblock copolymers may be effectively encapsulated in PLGA microspheres to increase paclitaxel release (probably through a micellization process) and improve biocompatibility.

Peptide-Labeled Quantum Dots for Imaging GPCRs in Whole Cells and as Single Molecules

We report a robust and practical method for the preparation of water-soluble luminescent quantum dots (QDs) selectively coupled through an amine or thiol linkage to peptide ligands targeted to G-protein coupling receptors (GPCRs) and demonstrate their utility in whole-cell and single-molecule imaging. We utilized a low molecular weight ( approximately 1200 Da) diblock copolymer with acrylic acids as hydrophilic segments and amido-octyl side chains as hydrophobic segments for facile encapsulation of QDs (QD 595 and QD 514) in aqueous solutions. As proof of principle, these QDs were targeted to the human melanocortin receptor (hMCR) by chemoselectively coupling the polymer-coated QDs to either a hexapeptide analog of alpha-melanocyte stimulating hormone or to the highly potent MT-II ligand containing a unique amine. To label QDs with ligands lacking orthogonal amines, the diblock copolymers were readily modified with water-soluble trioxa-tridecanediamine to incorporate freely available amine functionalities. The amine-functionalized QDs underwent facile reaction with the bifunctional linker NHS-maleimide, allowing for covalent coupling to GPCR-targeted ligands modified with unique cysteines. We demonstrate the utility of these maleimide-functionalized QDs by covalent conjugation to a highly potent Deltorphin-II analog that allowed for selective cell-surface and single-molecule imaging of the human delta-opioid receptor (hDOR).

Living random and block copolymerization of ethene and propene on a tailor-made phenoxyimine catalyst and characterization of the resulting high molecular weight PE-block-P(E-co-P) block copolymers

The phenoxyimine catalyst (bis-(N-(3′,5′-diiodo-salicylidene)-2,6-difluoroaniline)-titanium(IV)-dichloride) was tailored to enable random and block copolymerisation of propylene and ethylene with compositions covering the entire feasible composition range. Well-defined high molecular weight diblock copolymers of the type PE-block-P(E-co-P), consisting of a semi-crystalline polyethylene and a soft P(E-co-P) block, were prepared and evaluated with respect to propylene content and the block lengths. The characterisation by means of AFM, CRYSTAF data and high temperature chromatographic elution provided the experimental evidence that no homo-polyethylene and less than 5% of the random copolymer are formed as by-products.