Bifunctional Initiator Research Articles

Thermosensitive poly(N-isopropyl acrylamide-co-N,N-dimethyl acryl amide)-block-poly(d,l-lactide) amphiphilic block copolymer micelles for prednisone drug release

Novel amphiphilic block copolymers consisting of hydrophobic poly(D,L-lactide) segments and hydrophilic poly( N-isopropylacrylamide- co- N, N-dimethylacrylamide) blocks were designed and synthesized through a simple free radical copolymerization route based on a bifunctional initiator, followed by the ring-opening polymerization of D,L-lactide. The copolymers self-assembled into thermosensitive spherical-nanosized core–shell micelles in aqueous solution in the presence or the absence of the model drug prednisone. The chemical and physical characterizations of drug-loaded and unloaded micelles revealed a lower critical solution temperature of 40°C–47°C, and a critical micelle concentration less than 7.20 mg L−1, a transmission electron microscope mean particle size from 50 to 75 nm, and a narrow dynamic light scattering diameter below 180 nm. The prepared blank and drug-loaded micellar nanoparticles were thermodynamically stabile and employed in targeted drug delivery by responding to the higher temperature of the local microenvironment. Based on prednisone release kinetic studies, structural changes of the self-assembled micelles as well as temperature- or environment-induced diffusion controlled drug release and improved bioavailability. The copolymer micelles exhibited good biocompatibility as established by the MTT cytotoxicity assay. Therefore, an effective target therapy against lesion tissues is feasible using these polymeric micelles.

Synthesis of end-functionalized phosphate and phosphonate-polypeptides by ring-opening polymerization of their corresponding N-carboxyanhydride

Phosphopolypeptides provide an interesting biomimetic analog for phosphorylated proteins that are involved in biomineralization. We have developed a high yielding synthesis of cysteine-based phosphate and phosphonate N-carboxyanhydride (NCA) by using the thiol–ene coupling reaction. These phosphate and phosphonate NCA monomers underwent polymerization using simple primary amine initiators to form well defined homophosphopolypeptides. Using a bifunctional initiator we were able to install a “clickable” alkyne or azide group at the end of the polypeptide chain. We were also able to successfully synthesize fully water-soluble phosphonate based polypeptides by hydrolysis of the corresponding phosphonate ester groups in the polypeptide. These water-soluble phosphopolypeptides adopt a random coil conformation at physiological pH.

One-pot synthesis of poly(norbornene)-block-poly(lactide) copolymers using a bifunctional initiator

Block copolymers of poly(norbornene) and poly(lactide) were synthesized in one-pot using a bifunctional initiator bearing a ruthenium complex for the Ring-Opening Metathesis Polymerization (ROMP) of norbornenes and an alcohol to initiate the 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) catalyzed Ring-Opening Polymerization (ROP) of L-lactide.

Synthesis and photoresponsive behavior of azobenzene‐containing side‐chain liquid crystalline diblock polymers with polypeptide block

AbstractWell‐defined azobenzene‐containing side‐chain liquid crystalline diblock copolymers composed of poly[6‐(4‐methoxy‐azobenzene‐4′‐oxy) hexyl methacrylate] (PMMAZO) and poly(γ‐benzyl‐L‐glutamate) (PBLG) were synthesized by click reaction from alkyne‐ and azide‐functionalized homopolymers. The alkyne‐terminated PMMAZO homopolymers were synthesized by copper‐mediated atom transfer radical polymerization with a bromine‐containing alkyne bifunctional initiator, and the azido‐terminated PBLG homopolymers were synthesized by ring‐opening polymerization of γ‐benzyl‐L‐glutamate‐N‐carboxyanhydride in DMF at room temperature using an amine‐containing azide initiator. The thermotropic phase behavior of PMMAZO‐b‐PBLG diblock copolymers in bulk were investigated using differential scanning calorimetry and polarized light microscopy. The PMMAZO‐b‐PBLG diblock copolymers exhibited a smectic phase and a nematic phase when the weight fraction of PMMAZO block was more than 50%. Photoisomerization behavior of PMMAZO‐b‐PBLG diblock copolymers and the corresponding PMMAZO homopolymers in solid film and in solution were investigated using UV–vis. In solution, trans–cis isomerization of diblock copolymers was slower than that of the corresponding PMMAZO homopolymers. These results may provide guidelines for the design of effective photoresponsive anisotropic materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Production and Application Properties of Dispersive Viscosity Index Improvers

Polymeric dispersive viscosity index improvers of lubricating mineral oils based on styrene, dodecyl-methacrylate, octadecyl methacrylate, and N,N-dimethylaminoethyl methacrylate (d-PSAMA) were produced by performing copolymerizations isothermally up to the high conversion in mineral base oil solution, using monofunctional or bifunctional peroxide initiator. The obtained kinetics results reveal the benefits of the usage of a bifunctional peroxide initiator over a monofunctional, because complete conversion of monomers was accomplished in the shorter reaction time, performing the process in a full batchwise mode. When the bifunctional initiator was applied, the required polymerization temperature was slightly higher (105 °C), and copolymers of higher average molecular weight values (Mw = 60–120 kg mol–1) were obtained, while in case of the monofunctional peroxide initiator, the reaction temperature was 100 °C, and average molecular weight values of copolymers were Mw = 30–100 kg/mol. Investigated applicati...

Bifunctional initiators on the polymerization of vinyl acetate

AbstractInitiators with functionality bigger than one can be used in free radical polymerization (FRP) to increase the polymerization rate without decreasing the molecular weight of the polymer. The use of bifunctional initiators to produce linear polymers (like polystyrene and Poly(methyl methacrylate) (PMMA)) can be found in the literature; however, their application to produce branched polymers is rarer. This work reports the effect of the bifunctional initiator Luperox 531 (1.4‐bi(t‐butyl‐carboperoxide) cyclehexane) on the FRP of vinyl acetate, which produces branched polymers. The monofunctional initiator Luperox TBEC (tert‐butylperoxide‐2‐etyhexil carbonate) is also used as base of comparison. Polymerizations in ampoules have been performed in different temperatures and initiator concentrations. Results were compared to those obtained from the styrene polymerization, which produces linear chains. It can be concluded that the effect of bifunctional initiators on FRP depends strongly on the kinetic mechanism, kind of monomer, and operating conditions adopted. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Optimization of the property profile of poly‐L‐lactide by synthesis of PLLA‐polystyrene–block copolymers

AbstractDiblock and triblock copolymers of poly‐L‐lactide (PLLA) and polystyrene (PS) were synthesized and the mechanical properties of these copolymers studied. Free radical polymerization of styrene in the presence of 2‐mercaptoethanol as functional chain transfer agent produced mono‐functionalized PS‐blocks which were used as macroinitiators in the subsequent ring opening polymerization (ROP) of L‐lactide to produce the diblock copolymers. Furthermore a α‐ω‐bishydroxyl functionalized PS‐block was synthesized by RAFT, which was then engaged as bifunctional initiator for the ROP of L‐lactide to provide the triblock copolymers PLLA‐PS‐PLLA. Through the copolymerisation and high molar masses, it was possible to achieve an improved mechanical property profile, compared with pure PLLA, or the analogous blends of PLLA and PS. A weight fraction of PS of 10–30% was found to be the optimal range for improving the heat deflection temperature (HDT), as well as mechanical properties such as ultimate tensile strength or elongation at break. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Supramolecular X-Shaped Homopolymers and Block Polymers by Midsegment Complementary Hydrogen Bonds: Design of Bifunctional Initiators with Interactive Sites for Metal-Catalyzed Living Radical Polymerization

Two polymer chains, each carrying a complementary multiple hydrogen-bonding site at the center, led to supramolecular block copolymers where two segments are connected in an X-shaped configuration. For the precision synthesis of the pairing precursor polymers, a set of bifunctional initiators were designed, X-DAD-X and Y-ADA-Y, that consist of three hydrogen bond-forming sites in series (DAD or ADA; D = hydrogen donor; A = hydrogen acceptor) and two initiating sites (X or Y) for ruthenium-catalyzed living radical polymerization; thereby, DAD and ADA units are complementary to each other upon supramolecular association. Typically, DAD is of an −NH–C–N–C–NH– unit derived from 2,6-diaminopyridine, and ADA is of a −CO–NH–CO– unit from 2′-deoxyuridine. These functionalized initiators initiated living radical polymerizations of methyl methacrylate and styrene to give homopolymers (PMMA and PS, respectively) with a DAD or an ADA unit at the backbone center. Upon mixing in CDCl3, for example, a pair of “complemen...

Studies on Micellization Behavior of Thermosensitive PNIPAAm-b-PLA Amphiphilic Block Copolymers

Thermo-sensitive amphiphilic block copolymers, poly(N-isopropylacrylamide)-block- poly(D,L-lactide) (PNIPAAm-b-PLA), were synthesized through a simple free radical copolymerization route based on a bifunctional initiator, 2,2'-azobis(2-methylpropion amidine) dihydrochloride (AMAD), followed by the ring-opening polymerization of D,L-lactide in the presence of Sn(Oct)2 catalyst. The Chemical structure characterization were conducted by means of 1H NMR, FT-IR, GPC. The amphiphilic PNIPAAm-b-PLA block copolymers could self-assemble into micelles with regularly spherical shape in an aqueous solution, with a TEM diameter range of 46-56 nm, DLS hydrodynamic diameter of 158-199 nm. This behavior depends on the environmental temperature, the hydrophobic interactions among PNIPAAm molecular chains, intermolecular hydrogen bonding between the PNIPAAm chains and water molecules as well as intramolecular hydrogen bonding between -CONH2 groups. The copolymers held a CMC from 5.50 to 6.17 mg L(-1) and LCST from 31.41-32.03 degrees C, being more or less affected by their compositions, PLA or PNIPAAm block length. The as-prepared PNIPAAm-b-PLA block polymers are anticipated to be applied as a potential candidate of drug release carriers.

Near-Monodisperse Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-Based Macromonomers Prepared by Atom Transfer Radical Polymerization and Thiol–Ene Click Chemistry: Novel Reactive Steric Stabilizers for Aqueous Emulsion Polymerization

Poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC) macromonomers have been prepared by the atom transfer radical polymerization (ATRP) of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) using a bifunctional disulfide-based initiator. To attach a terminal polymerizable methacrylate group, the central disulfide bond was cleaved and the resulting thiols were conjugated to 3-(acryloyloxy)-2-hydroxypropyl methacrylate using tris(2-carboxyethyl)phosphine (TCEP) in water. Here TCEP serves as both the disulfide cleavage agent and also the catalyst for the subsequent Michael addition, which is highly selective for the acrylate group. The resulting methacrylate-terminated macromonomers were used as a reactive steric stabilizer for the aqueous emulsion polymerization of styrene, yielding near-monodisperse PMPC-stabilized polystyrene (PS) latexes of around 100-200 nm in diameter. As a comparison, the disulfide-containing PMPC homopolymer precursor and the intermediate thiol-functional PMPC homopolymer (PMPC-SH) were also evaluated as potential steric stabilizers. Interestingly, near-monodisperse latexes were also obtained in each case. These three sterically-stabilized latexes, prepared using either PMPC macromonomer, disulfide-based PMPC homopolymer, or PMPC-SH homopolymer as a reactive steric stabilizer, remained colloidally stable after both freeze-thaw experiments and the addition of an electrolyte, indicating that a coronal layer of PMPC chains prevented flocculation in each case. In contrast, both a charge-stabilized PS latex prepared in the absence of any steric stabilizer and a PS latex prepared in the presence of a nonfunctional PMPC homopolymer exhibited very poor colloidal stability when subjected to a freeze-thaw cycle or the addition of an electrolyte, as expected.

Thermoreversible high-temperature gelation of an ionic liquid with poly(benzyl methacrylate-b-methyl methacrylate-b-benzyl methacrylate) triblock copolymer

In this paper, we describe a novel thermosensitive triblock copolymer in an ionic liquid (IL) that shows a low-temperature-sol–high-temperature-gel transition. A well-defined ABA triblock copolymer consisting of poly(benzyl methacrylate) as the terminal A blocks and poly(methyl methacrylate) as the middle B block (P(BnMA-b-MMA-b-BnMA), BMB) was successfully synthesized using atom transfer radical polymerization (ATRP) from a bifunctional initiator. The number-average molecular weights of the PBnMA blocks and the PMMA block were estimated to be 25 kDa and 33 kDa, respectively. The temperature dependence of the hydrodynamic radius obtained from dynamic light scattering showed that in dilute solutions (0.1 wt%) the triblock copolymer exhibited lower critical micellization temperature (LCMT)-type aggregation behaviour around 135 °C in a common hydrophobic IL, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C2mim][NTf2]). Dynamic viscoelastic measurements for a 20 wt% BMB solution in [C2mim][NTf2] confirmed that a viscous liquid at low temperature (G′ (storage elastic modulus) G′′) upon heating above the aggregation temperature of the PBnMA terminal blocks. No gelation was observed when the triblock copolymer concentration was below 10 wt%. Furthermore, the thermoreversible ion gel exhibited excellent sol–gel transition reversibility for multiple heating/cooling cycles performed over several days.

Preparation of stimuli responsive polycaprolactone membranes of controllable porous morphology via combined atom transfer radical polymerization, ring-opening polymerization and thiol–yne click chemistry

Linear di-block copolymers of poly(N-isopropylacrylamide) (PNIPAM) with a center disulfide linkage were prepared by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM) using a bifunctional disulfide-based initiator. The center disulfide bond was cleaved by reduction with excess DL-1,4-dithiothreitol (DTT) to form thiols. The resulting thiol-terminated PNIPAM chains were conjugated to alkyne-terminated poly(e-caprolactone) (PCL) via UV-initiated thiol–yne click reaction to produce the PCL-click-PNIPAM AB2-type copolymers. The PCL-click-PNIPAM copolymers were cast by phase inversion in an aqueous medium into microporous membranes of well-defined and uniform pores. The PNIPAM content in the PCL-click-PNIPAM copolymers could be used to control the pore size and porosity of the resulting membranes. The PCL-click-PNIPAM-b-PNaSS membrane was prepared via surface-initiated ATRP of sodium 4-styrenesulfonate (NaSS) from the PCL-click-PNIPAM membrane and pore surfaces. The temperature and electrolyte responsive characteristics of the PCL-click-PNIPAM and PCL-click-PNIPAM-b-PNaSS membranes were illustrated in the swelling behavior and controlled glucose transport through the membranes. These stimuli responsive membranes with controllable morphology and low cytotoxicity have potential applications in biomedical engineering, drug delivery and tissue engineering.

Synthesis and micellization of thermosensitive PNIPAAm-b-PLA amphiphilic block copolymers based on a bifunctional initiator

The thermo-sensitive amphiphilic block copolymer poly(N-isopropylacrylamide)-block-poly(D,L-lactide) (PNIPAAm-b-PLA) was synthesized using a simple free radical copolymerization route based on a bifunctional initiator, 2,2-azobis(2-methylpropion amidine) dihydrochloride followed by the ring-opening polymerization of D,L-actide in the presence of a Sn(Oct)2 catalyst. The chemical structure of the PNIPAAm-b-PLA copolymers was verified using Fourier transform-infrared spectrophotometry and nuclear magnetic resonance, and the molecular weight and polydispersity index were examined using gel permeation chromatography. The amphiphilic PNIPAAm-b-PLA block copolymers could self-assemble into spherically shaped micelles in an aqueous solution with a transmission electron microscopy diameter range of 40–56 nm and a dynamic laser scattering hydrodynamic diameter of 90–200 nm. This behavior depends on the environmental temperature, the hydrophobic interactions among PNIPAAm molecular chains, the intermolecular hydrogen bonding between the PNIPAAm chains and water molecules, and the intramolecular hydrogen bonding between the -CONH2 groups. The copolymers held a critical micellization concentration of 4.93–7.21 mg·L−1 and a low critical solution temperature of 31.15–32.62 °C being more or less affected by their compositions, PLA or PNIPAAm block length, and polymerization temperature. The as-prepared PNIPAAm-b-PLA block polymers are anticipated to be applied as candidate drug release carriers.

Selective Enzymatic Degradation of Self-Assembled Particles from Amphiphilic Block Copolymers Obtained by the Combination of N-Carboxyanhydride and Nitroxide-Mediated Polymerization

Combining controlled radical polymerizations and a controlled polypeptide synthetic technique, such as N-carboxyanhydride (NCA) ring-opening polymerization, enables the generation of well-defined block copolymers to be easily accessible. Here we combine NCA polymerization with the nitroxide-mediated radical polymerization of poly(n-butyl acrylate) (PBA) and polystyrene (PS), using a TIPNO and SG1-based bifunctional initiator to create a hybrid block copolymer. The polypeptide block consists of (block) copolymers of poly(L-glutamic acid) embedded with various quantities of L-alanine. The formed superstructures (vesicles and micelles) of the block copolymers possessed varying degrees of enzyme responsiveness when exposed to elastase and thermolysin, resulting in controlled enzymatic degradation dictated by the polypeptide composition. The PBA containing block copolymers possessing 50% L-alanine in the polypeptide block showed a high degradation response compared to polymers containing lower L-alanine quantities. The particles stabilized by copolypeptides with L-alanine near the hydrophobic block showed full degradation within 4 days. Particles containing polystyrene blocks revealed no appreciable degradation under the same conditions, highlighting the specificity of the system and the importance of synthetic polymer selection. However, when the degradation temperature was increased to 70 °C, degradation could be achieved due to the higher block copolymer exchange between the particle and the solution. A number of novel biohybrid structures are disclosed that show promise as enzyme-responsive materials with potential use as payload release vehicles, following their controlled degradation by specific, target, enzymes.

TREN versus Me6‐TREN as ligands in SET‐LRP of methyl acrylate

AbstractThe commercially available tris(2‐aminoethyl)amine (TREN) was used as ligand to mediate the single‐electron transfer‐living radical polymerization (SET‐LRP) of methyl acrylate in dimethyl sulfoxide initiated with the bifunctional initiator bis(2‐bromopropionyl)ethane and catalyzed by both nonactivated and activated Cu(0) wire. A comparative study between TREN and tris(2‐dimethylaminoethyl)amine (Me6‐TREN) ligand, that is more commonly used in SET‐LRP, demonstrated that TREN provided a slower polymerization but the chain‐ends functionality of the resulting bifunctional poly(methyl acrylate) was near quantitative and comparable to that obtained when Me6‐TREN was used as a ligand. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.

SET‐LRP of methyl acrylate catalyzed with activated Cu(0) wire in methanol in the presence of air

AbstractSingle electron transfer‐living radical polymerization (SET‐LRP) of methyl acrylate (MA) in methanol, catalyzed with nonactivated and activated Cu(0) wires, was performed in the presence of nondeoxygenated reagents and was investigated under a simple blanket of nitrogen. The addition of a small amount of hydrazine hydrate mediates the deoxygenation of the reaction mixture by the consumption of oxygen through its use to oxidize Cu(0) to Cu2O, followed by the reduction of Cu2O with hydrazine back to the active Cu(0) catalyst. SET‐LRP of MA in methanol in the presence of air requires a smaller dimension of Cu(0) wire, compared to the nonactivated Cu(0) wire counterpart. Activation of Cu(0) wire allowed the polymerization in air to proceed with no induction period, linear first‐order kinetics, linear correlation between the molecular weight evolution with conversion, and narrow molecular weight distribution. The retention of chain‐end functionality of α,ω‐di(bromo) poly(methyl acrylate) (PMA) prepared by SET‐LRP was demonstrated by a combination of experiments including 1H NMR spectroscopy and matrix‐assisted laser desorption ionization–time of flight mass spectrometry after thioetherification of α,ω‐di(bromo) PMA with thiophenol. In SET‐LRP of MA in the presence of limited air, bimolecular termination is observed only above 85% conversion. However, for bifunctional initiators, the small amount of bimolecular termination observed at high conversion maintains a perfectly bifunctional polymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Acid dissolution of copper oxides as a method for the activation of Cu(0) wire catalyst for SET‐LRP

AbstractHere we reported the acid dissolution of copper oxides as a methodology for the activation of Cu(0) wire used as catalyst in single‐electron transfer living radical polymerization (SET‐LRP). In this method, the oxide layer on the surface of commercial Cu(0) wire was removed by dissolution in a concentrated acid such as nitric acid, glacial acetic acid and hydrochloric acid. SET‐LRP of methyl acrylate catalyzed with Cu(0) wire activated with acids showed comparable k value to that of the nonactivated Cu(0) wire‐catalyzed counterpart. However, the polymerizations catalyzed with activated Cu(0) wire proceeded with no initial induction period, predictable molecular weight evolution with conversion, and narrow molecular weight distribution. Regardless of the activation method, the chain end functionality of α,ω‐di(bromo) poly(methyl acrylate) (PMA) prepared from SET‐LRP initiated with a bifunctional initiator is extremely high, maintaining a 100% chain end functionality at ∼90% monomer conversion. The degree of bimolecular termination increased as the polymerization exceeds 92% conversion. However, for binfunctional initiators this small amount of bimolecular termination at high conversion maintains a perfectly bifunctional polymer. Structural analysis by MALDI‐TOF upon thioetherification of α,ω‐di(bromo) PMA with thiophenol and 4‐fluorothiophenol confirmed the high fidelity of bromide chain ends. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis of PCL-b-PVAc block copolymers by combination of click chemistry, ROP, and RAFT polymerizations

The synthesis of new poly(e-caprolactone)(PCL)-b-poly(vinyl acetate)(PVAc) block copolymers was investigated using different combinations of click chemistry, reversible addition-fragmentation transfer (RAFT), and ring opening polymerization (ROP) techniques. Two approaches, “coupling” and “macroinitiator” routes were studied. For the coupling approach, a chain transfer agent comprising an azide function was synthesized and used as initiator for the VAc polymerization. PCL containing an alkyne termination was obtained from a bifunctional initiator bearing an alkyne function and an hydroxyl group. These two functionalized precursors, PVAc and PCL, were coupled by a 1,3 cyclo addition reaction “click chemistry” in order to obtain the corresponding block copolymer. For the macroinitiator approach, PCL-b-PVAc block copolymers were synthesized using a two-step procedure: at first, a PCL macroinitiator with a xanthate end group was prepared by coordinated anionic polymerization of e-caprolactone; then, the RAFT polymerization of VAc was initiated from the PCL, for the preparation of PCL-b-PVAc block copolymers. Whatever the method used, no detectable quantities of unreacted PVAc or PCL were observed. 1H NMR and size exclusion chromatography analyses indicated successful synthesis of the block copolymers with well-defined structures.

Improving the initiation efficiency in the single electron transfer living radical polymerization of methyl acrylate with electronic chain‐end mimics

AbstractComputational studies on the heterolytic bond dissociation energies and electron affinities of methyl 2‐bromopropionate (MBP) and ethyl 2‐bromoisobutyrate (EBiB) in the dissociative electron transfer (DET) step of single electron transfer living radical polymerization (SET‐LRP) of methyl acrylate (MA) combined with kinetic experiments were performed in an effort to design the most efficient initiation system. This study suggests that EBiB is more effective than MBP in the SET‐LRP of acrylates catalyzed by Cu(0) wire, thus being a true electronic mimic of the dormant PMA species. EBiB allows for a more predictable dependence of the molecular weight evolution and distribution. This is exemplified by the absence of a deviation in the PMA molecular weight from theoretical values at low conversions, as a result of a faster SET activation with EBiB than with MBP. The enhanced control over molecular weight evolution was also observed in the SET‐LRP of MA initiated with bifunctional initiators similar in structure to MBP and EBiB, suggesting a higher reactivity than MBP in the SET activation, which matches closely that of the polymer dormant chains. The use of bifunctional initiators in conjunction with activated Cu(0) wire in SET‐LRP allows for dramatically accelerated polymerizations, although still providing for exceptional control of the molecular weight evolution and distribution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis of Thermo-Responsive Fluorinated Star-Shaped Polymers by Living Cationic Polymerization

ABSTRACTWell-controlled fluorinated star-shaped polymers with oxyethylene units were designed and synthesized by living cationic polymerization. These fluorinated star-shaped polymers were prepared using successive fluorinated initiators to generate fluorinated, end-functionalized and hydrophilic segments with oxyethylene. Poly(vinyl ether)s with oxyethylene units are known to be thermo-responsive polymers that exhibit a lower critical solution temperature (LCST) in aqueous solutions. These novel fluorine-containing star-shaped polymers with oxyethylene were also thermo-responsive, as expected. In addition, the hetero-fluorinated star-shaped polymers with oxyethylene segments and different fluorine compositions were synthesized with various bifunctional initiators by living cationic polymerization having narrow molecular weight distributions (Mw/Mn=1.23−1.29) and contained very little, if any, presence of the linear homopolymer precursor, as evidenced by GPC. The LCST of this polymer depended on the end group fluorine composition and significant changes in cloud points were observed in water, as confirmed by static light scattering (SLS) measurements. As an example, aqueous solutions the star-shaped polymers without fluorine terminal groups showed no cloud point below up to 60 ºC in aqueous solution. After the fluoro-functionality was incorporated into the terminal groups, the cloud point of the aqueous solutions decreased to almost 20 ºC.