Synthesis and Characterization of Amphiphilic Poly(ethylene oxide)‐block‐poly(hexyl methacrylate) Copolymers

We describe the preparation of amphiphilic diblock copolymers made of poly(ethylene oxide) (PEO) and poly(hexyl methacrylate) (PHMA) synthesized by anionic polymerization of ethylene oxide and subsequent atom transfer radical polymerization (ATRP) of hexyl methacrylate (HMA). The first block, PEO, is prepared by anionic polymerization of ethylene oxide in tetrahydrofuran. End capping is achieved by treatment of living PEO chain ends with 2‐bromoisobutyryl bromide to yield a macroinitiator for ATRP. The second block is added by polymerization of HMA, using the PEO macroinitiator in the presence of dibromobis(triphenylphosphine) nickel(II), NiBr₂(PPh₃)₂, as the catalyst. Kinetics studies reveal absence of termination consistent with controlled polymerization of HMA. GPC data show low polydispersities of the corresponding diblock copolymers. The microdomain structure of selected PEO‐block‐PHMA block copolymers is investigated by small angle X‐ray scattering experiments, revealing behavior expected from known diblock copolymer phase diagrams.

SAXS diffractograms of PEO‐block‐PHMA diblock copolymers with 16, 44, 68 wt.‐% PEO showing spherical (A), cylindrical (B), and lamellae (C) morphologies, respectively.     

Controlled synthesis and solution behavior of macrocyclic poly[(styrene)‐b‐(ethylene oxide)] copolymers

A series of cyclic poly[(styrene)‐b‐(ethylene oxide)] diblock copolymers 4 (1.5 kg/mol < M_n < 1.1 kg/mol) with narrow molecular weight distributions (I ≤ 1.12) have been synthesized. They were obtained by intramolecular cyclization of linear α‐diethyl acetal‐ω‐styrenyl poly(styrene ethylene oxide) 3 , under high dilution conditions. The use of well‐defined linear precursors in association with a cyclization process based on an unimolecular end‐to‐end coupling reaction allows the formation of macrocyclic diblocks in high yield (more than 90%). The structural characterization and the solution behavior of both the linear and cyclic amphipathic diblock copolymers have been investigated by means of NMR, size exclusion chromatography, and viscosimetry.     

Thermotropic liquid-crystalline aromatic polyester-graft-poly(2,6-dimethyl-1,4-phenylene oxide) copolymers

Dicarboxy-terminated poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) macromonomers were prepared and subjected to the preparation of tailor-made aromatic thermotropic liquid-crystalline (LC) polyester-graft-PPO copolymers. The macromonomers were obtained by hydrolysis of dimethyl carboxylate-terminated PPO macromonomers without cleavage of the PPO chains, which were derived from PPO oligomers with a terminal phenolic OH-group and a bromo derivative of isophthalate. The tailor-made aromatic thermotropic LC graft copolymers were prepared by direct polycondensation from the dicarboxy-terminated macromonomers, p-hydroxybenzoic acid, aromatic dicarboxylic acids and diphenols at definite mole ratios in pyridine in the presence of diphenyl chlorophosphate as a condensation reagent. The polyester-graft-PPO copolymers are thermally stable up to 280–300°C and show a thermotropic LC nematic phase in spite of introduction of PPO grafts on the polyester backbones.     

Homo‐ and Copolymerization of ω‐Functional Polystyrene Macromonomers via Coordination Polymerization

Macromonomers have been extensively used, as well defined building blocks for various macromolecular architectures via anionic, ROMP and free radical homo‐ or copolymerization processes. The purpose of the present work was to examine the homopolymerization and copolymerization of ω‐allyl, ω‐undecenyl and ω‐vinylbenzyl polystyrene (PS) macromonomers, in the presence of early or late transition metal catalysts. The influence of several parameters (type of catalytic system, nature of polymerizable end‐group and molar mass of the macromonomer) on the homopolymerization was first investigated. Whereas ω‐allyl or ω‐undecenyl PS macromonomers were not very reactive in homopolymerization whatever the catalyst, ω‐vinylbenzyl PS macromonomers gave interesting results with CpTiCl₃/MAO and Cp*TiCl₃/MAO. The copolymerization of these macromonomers with ethylene was also studied in the presence of the following palladium catalyst: [(ArN?C(Me)? C(Me)?NAr)Pd(CH₂)₃(COOMe)]⁺BAr₄′^?(VERSIPOL?) (Ar = 2,6‐iPr₂–C₆H₃ and Ar′ = 3,5‐(CF₃)₂? C₆H₃). ω‐vinylbenzyl PS macromonomers could not be incorporated into poly(ethylene) chains. On the contrary, the incorporation of ω‐allyl PS macromonomers was achieved. Moreover, for macromonomers containing an alkyl spacer between the allylic unit and the PS chain, the incorporation rate, the copolymerization yield and the molar masses of the copolymers were increased, giving access to a new type of graft copolymer structure.

Synthesis of polystyrene macromonomers.     

Synthesis and structural studies of new copolyimides 2. Influence of pyromellitimide rings on copolymer structure

The reaction of pyromellitic dianhydride (1,2 : 4,5-benzenetetracarboxylic dianhydride) ( 1 ) with L - and D -alanine ( 2 L ) and ( 2 D ) leads to new monomers which were used to synthesize new copolymers. These copolymers were obtained as a product of the condensation of optical isomers of bis[N-(1-chloroformylethyl)]pyromellitimides (CFEP) with poly(ethylene glycol) PEG-2000 ( 5 ). The effect of monomer structure on the structure and thermal properties of the polymers was studied using X-ray diffraction, differential scanning calorimetry and thermogravimetry. The copolymers were compared with similar copolyimides obtained previously from bis(N-chloroformylmethyl)pyromellitimide and poly(ethylene glycol), PEG 2000. The dominating effect of poly(ethylene glycol) comonomer on the crystallinity, structure and thermal stability of these new copolymers is proven.     

Thermo‐Responsive Brush Copolymers by “Grafting Through” Strategy Implemented on the Surface of the Macromonomer Micelles and Their High Emulsifying Performance

In the present study, the synthesis of water‐soluble thermo‐responsive brush copolymers via “graft through” strategy that is conducted on the surfaces of macromonomer micelles and their application as emulsifiers for thermo‐responsive emulsions are reported. Water‐soluble poly(N ,N‐dimethylacrylmide)‐block‐poly(N‐isopropylacrylmide) (PDMA‐b‐PNIPAM) diblock copolymers carrying a hydrophobic polymerizable vinyl group at the end of the PDMA block are synthesized by reversible addition‐fragmentation chain transfer polymerization and click functionalization. Increasing the temperature to above the low critical solution temperature of the PNIPAM block, the macromonomers self‐assemble to core–shell structure micelles with the polymerizable vinyl terminals on the surface of the micelles. Instead of being directly and freely exposed in the bulk water as the hydrophilic group, the hydrophobic vinyl terminals are protected by the partially looped PDMA segments. PMA‐g‐(PDMA‐b‐PNIPAM) brush copolymers with a high molecular weight and a narrow distribution are obtained by radical polymerization of the macromonomers using the potassium peroxydisulfate as initiator. The radical polymerization only proceeds within the single micelle, and intermicellar propagation and/or termination reactions are totally excluded. These brush copolymers feature the thermo‐responsive conformation transition property and high emulsifying performances for the formation of thermo‐responsive emulsion.

     

Novel Polyesteramide‐Based Diblock Copolymers: Synthesis by Ring‐Opening Copolymerization and Characterization

Block copolymers based on a polyesteramide sequence and a polyether block were synthesized in bulk at 250 °C by ring‐opening copolymerization (ROP) of ε‐caprolactone (CLo) and ε‐caprolactam (CLa) as initiated by Jeffamine® M1000, i.e., ω‐NH₂ copoly[(ethylene oxide)‐co‐(propylene oxide)] copolymer [P(EO‐co‐PO)‐NH₂]. For an initial molar ratio of [CLa]₀/[CLo]₀ = 1, the copolymerization allowed for the formation of a diblock copolymer with a statistical polyesteramide sequence, as evidenced by ¹³C NMR. Investigation of the ROP mechanism highlighted that CLo was first polymerized, leading to the formation of a diblock copolymer P(EO‐co‐PO)‐b‐PCLo‐OH, followed by CLa hydrolysis to aminocaproic acid that inserted into the ester bonds of PCLo via aminolysis and subsequent condensation reactions. The outcome is the selective formation of P(EO‐co‐PO)‐b‐P(CLa‐co‐CLo)‐OH diblock copolymers where the composition and length of the polyesteramide sequence can be fine‐tuned by the [CLa]₀/[CLo]₀ and ([CLa]₀ + [CLo]₀)/[P(EO‐co‐PO)‐NH₂]₀ initial molar ratios.     

Thermal and Mechanical Properties of Diblock Copolymers Based on 2,2‐Dimethyltrimethylene Carbonate and ε‐Caprolactone

Tri(sec‐butoxyaluminium) [Al(Osec‐Bu)₃]‐initiated copolymerization of 2,2‐dimethyl trimethylene carbonate (DTC) with ε‐caprolactone (CL) by stepwise addition of the monomers leads to high‐molecular weight block copolymers of the AB diblock type. By changing the amount of initiator and the molar ratio of the monomers, several diblock copolymers were prepared having either the same composition with different overall molecular weight or the same PDTC block length with various compositions. The thermal and mechanical properties of the copolymers were studied with the aim of assessing their dependence on molecular characteristics. Ageing time at room temperature was found to have a remarkable effect on tensile modulus and on melting of the ordered PDTC phases. This behavior has been attributed to mutual hindrance of the blocks on their crystallization and to a solid‐solid polymorphic transformation taking place in the crystalline PDTC microphases.     

Poly(phenylene oxide) macromonomers for graft copolymer synthesis via ring-opening olefin metathesis polymerization

Poly(oxy-2,6-dimethyl-1,4-phenylene) samples with bicyclic olefin end groups were obtained by esterification of the hydroxyl end group of the poly(phenylene oxide) with bicyclo[2.2.1]hept-5-ene-2-carbonyl chloride. Mixtures of these macromonomers with bicyclo[2.2.1]hept-5-ene-2-carboxylic acid 2-(2-(2-methoxyethoxy)ethoxy)ethyl ester were copolymerized by ring-opening olefin metathesis polymerization (ROMP) to produce graft copolymers with poly(phenylene oxide) side chains. The catalyst used for the metathesis polymerization was RuCl₃(hydrate). Molecular weights of the graft copolymers were in the range of 130 000 to 250 000. Macromonomers containing exclusively exo-linked bicyclic end groups were found to be more reactive than macromonomers with 55% exo- and 45% endo-substituted end groups.     

Random and block 2-alkyl-2-oxazolines telechelic macromonomers

Ring-opening polymerization of 2-methyl-2-oxazoline initiated by 2-(p-nitrobenzenesulfonato)ethyl methacrylate follows the so-called “living mechanism”, i.e. fast initiation compared to slow propagation and no chain transfer. Accordingly, methacryl macromonomers having homopolymers, block or random copolymers of 2-methyl and 2-pentyl-2-oxazoline backbones with narrow molecular weight distribution were obtained. Termination of the propagating species by ion-exchange or aminolysis with triethylamine yielded hydroxyl and quaternary ammonium terminated macromonomers, respectively.     

The Aggregation Behavior of Poly(ethylene oxide)‐Poly(methyl methacrylate) Diblock Copolymers in Organic Solvents

Poly(ethylene oxide)‐poly(methyl methacrylate) and poly(ethylene oxide)‐poly(deuteromethyl methacrylate) block copolymers have been prepared by group transfer polymerization of methyl methacrylate (MMA) and deuteromethyl methacrylate (MMA‐d₈), respectively, using macroinitiators containing poly(ethylene oxide) (PEO). Static and dynamic light scattering and surface tension measurements were used to study the aggregation behavior of PEO‐PMMA diblock copolymers in the solvents tetrahydrofuran (THF), acetone, chloroform, N,N‐dimethylformamide (DMF), 1,4‐dioxane and 2,2,2‐trifluoroethanol. The polymer chains are monomolecularly dissolved in 1,4‐dioxane, but in the other solvents, they form large aggregates. Solutions of partially deuterated and undeuterated PEO‐PMMA block copolymers in THF have been studied by small‐angle neutron scattering (SANS). Generally, large structures were found, which cannot be considered as micelles, but rather fluctuating structures. However, ¹H NMR measurements have shown that the block copolymers form polymolecular micelles in THF solution, but only when large amounts of water are present. The micelles consist of a PMMA core and a PEO shell.     

13C NMR analysis of α-olefins copolymers with 1,3-butadiene obtained with zirconocenes/methylalumoxane catalysts

Ethylene copolymers with propene and/or 1,3-butadiene were obtained using bis(η⁵-cyclopentadienyl)zirconium dichloride ( 1 ) or ethylenebis[1-3a, 7a-η-(4,5,6,7-tetrahydro)-1-indenyl]zirconium dichloride ( 2 ) and methylalumoxane as catalytic systems. A detailed ¹³C NMR analysis of the copolymers was performed. The resonances in the olefinic region of the terpolymers were assigned to ethylene/butadiene/ethylene and propene/butadiene/ethylene sequences while the butadiene/propene sequence was ruled out. Analogously, no polymers were obtained from the polymerization of propene in the presence of 1,3-butadiene. It is thus shown that the conjugated diene is an inhibitor for the polymerization of α-olefins. The presence of trans-1,2-cyclopentane rings was detected both in the ethylene/butadiene copolymers and in the ethylene/propene/butadiene terpolymers. A different behaviour of the two catalysts was observed.     

Controlled Synthesis of Well Defined Poly(3‐hydroxyalkanoate)s‐based Amphiphilic Diblock Copolymers Using Click Chemistry

A modular synthesis of short chain length and medium chain length poly(3‐hydroxyalkanoate)s‐b‐poly(ethylene glycol) (PHAs‐b‐PEG) diblock copolymers is described. First, length‐controlled oligomers of hydrophobic poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBHV), poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) (PHBHHx), and poly(3‐hydroxyoctanoate‐co‐hydroxyhexanoate) (PHOHHx) containing a carboxylic acid end group were obtained by thermal treatment, with molar masses ranging from 3 800 to 15 000 g · mol^?1. After quantitative functionalization with propargylamine, ligation with azide‐terminated poly(ethylene glycol) of 5 000 g · mol^?1 was accomplished using the copper (I) catalyzed azide alkyne cycloaddition (CuAAC). Well‐defined diblock copolymers were obtained up to 93% yield, with molar masses ranging from 9 900 to 23 100 g · mol^?1. All products were fully characterized using ¹H NMR, COSY, SEC, TGA, and DSC.

     

Copolymerization of epoxides and five-membered cyclic carbonates in the presence of zinc coordination catalysts

Alkylene oxides like ethylene oxide (1a) and propylene oxide (1b) were reacted with alkylene carbonates like ethylene carbonate (2a) and propylene carbonate (2b) in the presence of catalysts based on diethylzine and polyphenols (pyrogallol, 4-tert-butylcatechin) and catalysts based on diethylzinc-phenol at temperatures in the range of 35–100°C. Reaction products were characterized by means of elemental analysis, IR, ¹H NMR and ¹³C NMR spectroscopy and molecular weight determinations. The products appeared to be the respective low-molecular-weight copolymers – poly[oxyalkylene-co-(alkylene carbonate)]s: poly[oxyethylene-co-(ethylene carbonate)] (3 aa) , poly[oxyethylene-co-(propylene carbonate)] (3 ab) , poly[oxypropylene-co-(ethylene carbonate)] (3 ba) and poly[oxypropylene-co-(propylene carbonate)] (3 bb). Copolymers obtained with diethylzinc-polyphenol catalysts were of higher molecular weight than those obtained with diethylzinc-phenol catalysts. They contained more than 50 mol-% of alkylene oxide units. Predominant head-to-tail arrangement of these units including those connected via carbonate linkages was observed by means of NMR spectroscopy in the case of 3 bb.     

Biocompatibility of filomicelles prepared from poly(ethylene glycol)-polylactide diblock copolymers as potential drug carrier

A series of poly(ethylene glycol)-polylactide (PEG-PLA) diblock copolymers were synthesized by ring-opening polymerization of l-lactide using monomethoxy PEG as macroinitiator and zinc lactate as catalyst. Filomicelles were prepared from the resulting copolymers by co-solvent evaporation method. The biocompatibility of the various filomicelles was evaluated with the aim of assessing their potential as drug carriers. Various aspects of biocompatibility were considered, including agar diffusion test, MTT assay, release of cytokines, hemolytic test, dynamic clotting time, protein adsorption in vitro, and zebrafish embryonic compatibility in vivo. The results revealed that the filomicelles present good cytocompatibility and hemocompatibility in vitro. Moreover, the cumulative effects of filomicelles throughout embryos deveploping stages have no toxicity in vivo. It is thus concluded that filomicelles prepared from PEG-PLA copolymers with outstanding biocompatibility are promising as potential drug carrier.     

Synthesis of poly(N-tert-butylaziridine) macromonomers and graft copolymers with uniform side chains

Poly(N-tert-butylaziridine) (polyTBA) macromonomers with allylamino-, allyloxy- and methacrylate end-groups were synthesized via deactivation of living polyTBA with appropriate nucleophiles. The macromonomers were copolymerized with N-vinyl-2-pyrrolidone (NVP), 2-hydroxyethyl methacrylate (HEMA) and isoprene (Is). Two types of graft copolymers were obtained: the first one is constituted of hydrophilic backbone (polyNVP or polyHEMA) and hydrophobic uniform polyTBA side chains. The second type is composed of a flexible hydrophobic polyIs backbone and hard hydrophobic polyTBA side chains which, however, become water swellable after quaternization.     

Synthesis and characterization of amphiphilic and microphase-separated graft copolymers, 1. Synthesis and bulk characterization of polystyrene-graft-ω-stearyl-poly(ethylene oxide)

Using the rigid and hydrophobic polystyrene (PS) chain as backbone, onto which flexible and hydrophilic stearyl-poly(ethylene oxide) (SPEO) chains are grafted, a new kind of amphiphilic, microphase-separated graft copolymer was synthesized using the macromonomer technique. Stearyl-poly(ethylene oxide) macromonomers with acryloyl end-group (SPEO-A) were prepared through an end-group exchange reaction of α-stearyl-ω-hydroxypoly(ethylene oxide) (SPEO-OH) and acryloyl chloride in the presence of triethylamine. The radical copolymerization of styrene with SPEO-A was carried out under various experimental conditions. Following a careful examination of their purity, the structure of the prepared copolymers was characterized by means of IR, ¹H NMR and GPC analyses. A new feasible method using first derivative UV spectrometry was developed for quantitative determination of the bulk composition of the graft copolymers. Copolymers with a wide range of bulk composition and satisfactory grafting degree were obtained.     

Controlled Synthesis and Characterization of Poly[ethylene‐block‐(L,L‐lactide)]s by Combining Catalytic Ethylene Oligomerization with “Coordination‐Insertion” Ring‐Opening Polymerization

Model poly[ethylene‐block‐(L ,L ‐lactide)] (PE‐block‐PLA) block copolymers were successfully synthesized by combining metallocene catalyzed ethylene oligomerization with ring‐opening polymerization (ROP) of L ,L ‐lactide (LA). Hydroxy‐terminated polyethylene (PE‐OH) macroinitiator was prepared by means of ethylene oligomerization on rac‐dimethyl‐silylen‐bis(2‐methyl‐benz[e]indenyl)‐zirconium(IV)‐dichloride/methylaluminoxane (rac‐MBI/MAO) in presence of diethyl zinc as a chain transfer agent, and subsequent in situ oxidation with synthetic air. Poly[ethylene‐block‐(L ,L ‐lactide)] block copolymers were obtained via ring‐opening polymerization of LA initiated by PE‐OH in toluene at 100 °C mediated by tin octoate. The formation of block copolymers was confirmed by ¹H NMR spectroscopy, fractionation experiments, thermal behavior, and morphological characterization using AFM and light microscopy techniques.

     

Synthesis of polystyrene-poly(tert-butyl acrylate) diblock copolymers bearing fluorescent groups at the junctions

AB-type diblock copolymers composed of polystyrene as the A block and poly(tert-butyl acrylate) as the B block were synthesized by sequential anionic polymerization. 1-(2-Anthryl)-1-phenylethylene, a new fluorescent monomer, and 1-(9-phenanthryl)-1-phenylethylene were used to introduce fluorescent moieties at the block junctions. Ultraviolet (UV) spectroscopy and gelpermeation chromatography (GPC) analyses were used to characterize the prepared copolymers.     

Synthesis and characterization of poly[(2,6-dimethyl-1,4-phenylene oxide)-block-isoprene] diblock copolymers

As a first stage in the synthesis of a new class of thermoplastic elastomers, a suitable synthetic route for elastomeric tailor-made diblock copolymers based on poly(2,6-dimethyl-1,4-phenylene oxide), PPE, as the thermoplastic block and on 1,4-polyisoprene, PIP, as the elastomeric block, is outlined. The 2,6-dimethyl-1,4-phenylene oxide-block-isoprene diblock copolymers were synthesized via an amidation coupling route between the ammonium salt of PPE and the monocarboxylic acid of PIP in the presence of dicyclohexylcarbodiimide, DCC. Preliminary studies were focused on the synthesis of a welldefined low molar mass diblock copolymer (M _n = 10000) in order to facilitate the quantitative characterization by proton NMR spectroscopy. The developed amidation coupling route was successively applied to the synthesis of a similar diblock copolymer with a number-average molar mass of 40000 in order to obtain optimum overall properties.