Well‐defined polyolefin/poly(ε‐caprolactone) diblock copolymers: New synthetic strategy and application

A new synthetic strategy, the combination of living polymerization of ylides and ring‐opening polymerization (ROP), was successfully used to obtain well‐defined polymethylene‐b‐poly(ε‐caprolactone) (PM‐b‐PCL) diblock copolymers. Two hydroxyl‐terminated polymethylenes (PM‐OH, M_n= 1800 g mol^?1 (PDI = 1.18) and M_n = 6400 g mol^?1 (PDI = 1.14)) were prepared using living polymerization of dimethylsulfoxonium methylides. Then, such polymers were successfully transformed to PM‐b‐PCL diblock copolymers by using stannous octoate as a catalyst for ROP of ε‐caprolactone. The GPC traces and ¹H NMR of PM‐b‐PCL diblock copolymers indicated the successful extension of PCL segment (M_n of PM‐b‐PCL = 5200–10,300 g mol^?1; PDI = 1.06–1.13). The thermal properties of the double crystalline diblock copolymers were investigated by differential scanning calorimetry (DSC). The results indicated that the incorporation of crystalline segments of PCL chain effectively influence the crystalline process of PM segments. The low‐density polyethylene (LDPE)/PCL and LDPE/polycarbonate (PC) blends were prepared using PM‐b‐PCL as compatibilizer, respectively. The scanning electron microscopy (SEM) observation on the cryofractured surface of such blend polymers indicates that the PM‐b‐PCL diblock copolymers are effective compatibilizers for LDPE/PCL and LDPE/PC blends. Porous films were fabricated via the breath‐figure method using different concentration of PM‐b‐PCL diblock copolymers in CH₂Cl₂ under a static humid condition. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of poly(dimethylsiloxane)‐containing diblock and triblock copolymers by the combination of anionic ring‐opening polymerization of hexamethylcyclotrisiloxane and nitroxide‐mediated radical polymerization of methyl acrylate,isoprene, and styrene

Poly(dimethylsiloxane)‐containing diblock and triblock copolymers were prepared by the combination of anionic ring‐opening polymerization (AROP) of hexamethylcyclotrisiloxane (D₃) and nitroxide‐mediated radical polymerization (NMRP) of methyl acrylate (MA), isoprene (IP), and styrene (St). The first step was the preparation of a TIPNO‐based alkoxyamine carrying a 4‐bromophenyl group. The alkoxyamine was then treated with Li powder in ether, and AROP of D₃ was carried out using the resulting lithiophenyl alkoxyamine at room temperature, giving functional poly(D₃) with M_w/M_n of 1.09–1.16. NMRPs of MA, St, and IP from the poly(D₃) at 120 °C gave poly(D₃‐b‐MA), poly(D₃‐b‐St), and poly(D₃‐b‐IP) diblock copolymers, and subsequent NMRPs of St from poly(D₃‐b‐MA) and poly(D₃‐b‐IP) at 120 °C gave poly(D₃‐b‐MA‐b‐St) and poly(D₃‐b‐IP‐b‐St) triblock copolymers. The poly(dimethylsiloxane)‐containing diblock and triblock copolymers were analyzed by ¹H NMR and size exclusion chromatography. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6153–6165, 2005     

Hydrogen bond mediated self-assembly of two diblock copolymers

Two chemically dissimilar diblock copolymers, polybutadiene-b-poly(acrylic acid), PBd-b-PAA (M_w = 5.8–4 kg mol⁻¹) and poly(styrene)-b-poly(ethylene oxide), PS-b-PEO (M_w = 9–5 kg mol⁻¹) were blended in an effort to achieve morphologies typical of triblock copolymers. Blend compatibility was achieved by the hydrogen bond driven association of the PAA block of one diblock with the PEO block of the other. Small angle X-ray scattering was used to determine the morphologies of the compositions, which were further investigated using transmission electron microscopy and selective staining techniques. The crystallinity of the PEO block was determined by differential scanning calorimetry. The hydrogen bond interactions between PEO and PAA yielded a complex triblock lamellar morphology of the form PS-b-(PEO/PAA)-b-PBd-b-(PEO/PAA). This morphology was stable when crystallization of PEO was suppressed by sufficient interaction with PAA.     

Diblock copolymers based on allyl methacrylate: Synthesis,characterization, and chemical modification

Different diblock copolymers constituted by one segment of a monomer supporting a reactive functional group, like allyl methacrylate (AMA), were synthesized by atom transfer radical polymerization (ATRP). Bromo‐terminated polymers, like polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(butyl acrylate) (PBA) were employed as macroinitiators to form the other blocks. Copolymerizations were carried out using copper chloride with N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as the catalyst system in benzonitrile solution at 70 °C. At the early stage, the ATRP copolymerizations yielded well‐defined linear block copolymers. However, with the polymerization progress a change in the macromolecular architecture takes place due to the secondary reactions caused by the allylic groups, passing to a branched and/or star‐shaped structure until finally yielding gel at monomer conversion around 40% or higher. The block copolymers were characterized by means of size exclusion chromatography (SEC), ¹H NMR spectroscopy, and differential scanning calorimetry (DSC). In addition, one of these copolymers, specifically P(BA‐b‐AMA), was satisfactorily modified through osmylation reaction to obtain the subsequent amphiphilic diblock copolymer of P(BA‐b‐DHPMA), where DHPMA is 2,3‐dihydroxypropyl methacrylate; demonstrating the feasibility of side‐chain modification of the functional obtained copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3538–3549, 2007     

Synthesis and characterization of poly[styrene‐b‐methyl(3,3,3‐trifluoropropyl)siloxane] diblock copolymers via anionic polymerization

A series of narrow molecular weight distribution (MWD) polystyrene‐b‐poly[methyl(3,3,3‐trifluoropropyl)siloxane] (PS‐b‐PMTFPS) diblock copolymers were synthesized by the sequential anionic polymerization of styrene and trans‐1,3,5‐trimethyl‐1,3,5‐tris(3′,3′,3′‐trifluoropropyl)cyclotrisiloxane in tetrahydrofuran (THF) with n‐butyllithium as the initiator. The diblock copolymers had narrow MWDs ranging from 1.06 to 1.20 and number‐average molecular weights ranging from 8.2 × 10³ to 37.1 × 10³. To investigate the properties of the copolymers, diblock copolymers with different weight fractions of poly[methyl(3,3,3‐trifluoropropyl)siloxane] (15.4–78.8 wt %) were prepared. The compositions of the diblock copolymers were calculated from the characteristic proton integrals of ¹H NMR spectra. For the anionic ring‐opening polymerization (ROP) of 1,3,5‐trimethyl‐1,3,5‐tris(3′,3′,3′‐trifluoropropyl)cyclotrisiloxane (F₃) initiated by polystyryllithium, high monomer concentrations could give high polymer yields and good control of MWDs when THF was used as the polymerization solvent. It was speculated that good control of the block copolymerization under the condition of high monomer concentrations was due to the slowdown of the anionic ROP rate of F₃ and the steric hindrance of the polystyrene precursors. There was enough time to terminate the ROP of F₃ when the polymer yield was high, and good control of block copolymerization could be achieved thereafter. The thermal properties (differential scanning calorimetry and thermogravimetric analysis) were also investigated for the PS‐b‐PMTFPS diblock copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4431–4438, 2005     

Synthesis and crystallization behaviors of poly(styrene-b-isoprene-b-ε-caprolactone) triblock copolymers

The triblock copolymers, poly(styrene-b-isoprene-b-ε-caprolactone)s (PS-b-PI-b-PCL) have been synthesized successfully by combination of anionic polymerization and ring-opening polymerization. Diblock copolymer capped with hydroxyl group, PS-b-PI-OH was synthesized by sequential anionic polymerization of styrene and isoprene and following end-capping reaction of EO, and then it was used as macro initiator in the ring-opening polymerization of CL. The results of DSC and WAXD show big effect of amorphous PS-b-PI on the thermal behaviors of PCL block in the triblock copolymers and the lower degree of crystalline in the triblock copolymer with higher molecular weight of PS-b-PI was observed. The real-time observation on the polarized optical microscopy shows the spherulite growth rates of PCL₂₇, PCL₃₂₈ and PS-b-PI-b-PCL₃₄₄ are 0.71, 0.46 and 0.07 μm s⁻¹, respectively. The atomic force microscopy (AFM) images of the PS₉₀-b-PI₆₆-b-PCL₂₈ show the columns morphology formed by it’s self-assembling.     

Polymethylene‐b‐polystyrene diblock copolymer: Synthesis,property, and application

The design and synthesis of well‐defined polymethylene‐b‐polystyrene (PM‐b‐PS, M_n = 1.3 × 10⁴–3.0 × 10⁴ g/mol; M_w/M_n (GPC) = 1.08–1.18) diblock copolymers by the combination of living polymerization of ylides and atom transfer radical polymerization (ATRP) was successfully achieved. The ¹H NMR spectrum and GPC traces of PM‐b‐PS indicated the successful extension of PS segment on the PM macroinitiator. The micellization behavior of such diblock copolymers in tetrahydrofuran were characterized by dynamic light scattering (DLS) and atomic force microscopy (AFM) techniques. The average aggregate sizes of PM‐b‐PS diblock copolymers with the same length of PM segment in tetrahydrofuran solution (1.0 mg mL^?1) increases from 104.2 nm to 167.7 nm when the molecular weight of PS segment increases. The spherical precipitated aggregates of PM‐b‐PS diblock copolymers with an average diameter of 600 nm were observed by AFM. Honeycomb porous films with the average diameter of 3.0 μm and 6.0 μm, respectively, were successfully fabricated using the solution of PM‐b‐PS diblock copolymers in carbon disulfide via the breath‐figure (BF) method under a static humid condition. The cross‐sections of low density polyethylene (LDPE)/polystyrene (PS)/PM‐b‐PS and LDPE/polycarbonate (PC)/PM‐b‐PS blends were observed by scanning electron microscope and reveal that the PM‐b‐PS diblock copolymers are effective compatilizers for LDPE/PS and LDPE/PC blends. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1894–1900, 2010     

Effects of polystyrene-b-poly(aminomethyl styrene)s as stabilizers on dispersion polymerization of styrene in alcoholic media

The effects of polystyrene-b-poly(aminomethyl styrene) (PS_n-b-PAMS_m) stabilizers on the particle size (D_n) and size distribution (PSD) in dispersion polymerization of styrene were investigated. The block copolymers, PS_n-b-PAMS_m, were prepared as follows: (i) atom transfer radical polymerization (ATRP) of styrene (PS-Br), (ii) ATRP of vinylbenzylphthalimide with the PS-Br (PS-b-PVBP), and (iii) treatment of the PS-b-PVBP with hydrazine. When the dispersion polymerization of styrene proceeded at 60 °C in ethanol with PS₁₉-b-PAMS₁₃₀ stabilizer, spherical polystyrene particles with D_n=0.91 μm (PSD = 1.01) were obtained. The particle size was strongly affected by the copolymer composition. With an increase in PAMS block length from m=54 to 100 in PS₁₇-b-PAMS_m, particle diameter became smaller from 1.55 to 0.91 μm. On the other hand, an increase in the length from m=20 to 82 in PS₃₄-b-PAMS_ms caused an increase in particle size from 0.35 to 0.70 μm. Titration of the particles suggests that 14–81% of stabilizers used in the polymerization system were attached on the polystyrene particle surfaces, depending on the composition of the block copolymers. Thus, for the dispersion polymerization of styrene, PS_n-b-PAMS_m block copolymers have both functions as a stabilizer during polymerization and surface-modification sites of polystyrene particles.     

Well‐defined poly[(dimethylamimo)ethyl methacrylate]‐b‐poly(fluoroalkyl methacrylate) diblock copolymers: Effects of different fluoroalkyl groups on the solution properties

A series of well‐defined, fluorinated diblock copolymers, poly[2‐(dimethylamino)ethyl methacrylate]‐b‐poly(2,2,2‐trifluoroethyl methacrylate) (PDMA‐b‐PTFMA), poly[2‐(dimethylamino)ethyl methacrylate]‐b‐poly(2,2,3,4,4,4‐hexafluorobutyl methacrylate) (PDMA‐b‐PHFMA), and poly[2‐(dimethylamino)ethyl methacrylate]‐b‐poly(2,2,3,3,4,4,5,5‐octafluoropentyl methacrylate) (PDMA‐b‐POFMA), have been synthesized successfully via oxyanion‐initiated polymerization. Potassium benzyl alcoholate (BzO^?K⁺) was used to initiate DMA monomer to yield the first block PDMA. If not quenched, the first living chain could be subsequently used to initiate a feed F‐monomer (such as TFMA, HFMA, or OFMA) to produce diblock copolymers containing different poly(fluoroalkyl methacrylate) moieties. The composition and chemical structure of these fluorinated copolymers were confirmed by ¹H NMR, ¹⁹F NMR spectroscopy, and gel permeation chromatography (GPC) techniques. The solution behaviors of these copolymers containing (tri‐, hexa‐, or octa‐ F‐atom)FMA were investigated by the measurements of surface tension, dynamic light scattering (DLS), and UV spectrophotometer. The results indicate that these fluorinated copolymers possess relatively high surface activity, especially at neutral media. Moreover, the DLS and UV measurements showed that these fluorinated diblock copolymers possess distinct pH/temperature‐responsive properties, depending not only on the PDMA segment but also on the fluoroalkyl structure of the FMA units. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2702–2712, 2009     

Controlled polymerization of α-methyl-β-pentyl-β-propiolactone by a discrete zinc alkoxide complex

We report the zinc(II) alkoxide-mediated ring opening polymerization of α-methyl-β-pentyl-β-propiolactone. The polymerization proceeds to high conversion and in the absence of significant transesterification to yield polymers with narrow molecular weight distributions. Poly(α-methyl-β-pentyl-β-propiolactone), PMPP, is an amorphous, low glass transition material that forms immiscible blends with polylactide (PLA). PMPP-b-PLA diblock copolymers, for use as potential blend compatibilizers, were synthesized in a controlled manner by sequential monomer addition.     

Synthesis and structure–conductivity relationship of polystyrene-block-poly(vinyl benzyl trimethylammonium) for alkaline anion exchange membrane fuel cells

Block copolymers of polystyrene-b-poly(vinyl benzyl trimethylammonium tetrafluoroborate) (PS-b-[PVBTMA][BF₄]) were synthesized by sequential monomer addition using atom transfer radical polymerization. Membranes of the block copolymers were prepared by drop casting from dimethylformamide. Initial evaluation of the microphase separation in these PS-b-[PVBTMA][BF₄] materials via SAXS revealed the formation of spherical, cylindrical, and lamellar morphologies. Block copolymers of polystyrene-b-poly(vinyl benzyl trimethylammonium hydroxide) (PS-b-[PVBTMA][OH]) were prepared as polymeric alkaline anion exchange membranes materials by ion exchange from PS-b-[PVBTMA][BF₄] with hydroxide in order to investigate the relationship between morphology and ionic conductivity. Studies of humidity [relative humidity (RH)]-dependent conductivity at 80 °C showed that the conductivity increases with increasing humidity. Moreover, the investigation of the temperature-dependent conductivity at RH = 50, 70, and 90% showed a significant effect of grain boundaries in the membranes against the formation of continuous conductive channels, which is an important requirement for achieving high ion conductivity. © 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1751–1760, 2013     

Micellization behavior of diblock and triblock copolymers of poly(t-butyl methacrylate) bearing associating short polystyrene end-blocks

Anionic polymerization high vacuum techniques were employed for the synthesis of a diblock (PS-b-PtBuMA) and two triblock (PS-b-PtBuMA-b-PS) copolymers of polystyrene (PS) and poly(t-butyl methacrylate) (PtBuMA) bearing similar low molecular weight PS end-block(s). Dilute solution viscometry, as well as static and dynamic light scattering, were employed to assess whether the short PS end-blocks were able to promote association in t-amyl alcohol, a selective solvent for PtBuMA. The effect of macromolecular architecture on the association behavior of the copolymers was also examined.     

Synthesis and characterization of model diblock copolymers of poly(dimethylsiloxane) with poly(1,4‐butadiene) or poly(ethylene)

Model diblock copolymers of poly(1,4‐butadiene) (PB) and poly(dimethylsiloxane) (PDMS), PB‐b‐PDMS, were synthesized by the sequential anionic polymerization (high vacuum techniques) of butadiene and hexamethylciclotrisiloxane (D₃) in the presence of sec‐BuLi. By homogeneous hydrogenation of PB‐b‐PDMS, the corresponding poly(ethylene) and poly(dimethylsiloxane) block copolymers, PE‐b‐PDMS, were obtained. The synthesized block copolymers were characterized by nuclear magnetic resonance (¹H and ¹³C NMR), size‐exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and rheology. SEC combined with ¹H NMR analysis indicates that the polydispersity index of the samples (M_w/M_n) is low, and that the chemical composition of the copolymers varies from low to medium PDMS content. According to DSC and TGA experiments, the thermal stability of these block copolymers depends on the PDMS content, whereas TEM analysis reveals ordered arrangements of the microphases. The morphologies observed vary from spherical and cylindrical to lamellar domains. This ordered state (even at high temperatures) was further confirmed by small‐amplitude oscillatory shear flow tests. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1579–1590, 2006     

Synthesis of anionic amphiphilic diblock copolymers of poly(styrene) and poly(acrylic acid) by reverse iodine transfer polymerization (RITP) in solution and emulsion

Reverse iodine transfer polymerization (RITP), offering the appealing potential of the in situ generation of transfer agents out of molecular iodine I₂, is employed in the synthesis of anionic amphiphilic diblock copolymers of poly(styrene) and poly(acrylic acid). Starting with well‐characterized poly(styrene) as macro‐transfer agents synthesized by RITP, diblock copolymers poly(styrene)‐b‐poly(tert‐butyl acrylate) of various lengths are successfully yielded in solution with a good architectural control. These blocks are then subjected to acid deprotection and subsequent pH control to give rise to anionic amphiphilic poly(styrene)‐b‐poly(acrylic acid). Besides, homopolymers of tert‐butyl acrylate are produced by RITP both in solution and in emulsion. Furthermore, a fruitful trial of the synthesis of diblock copolymers poly(tert‐butyl acrylate)‐b‐poly(styrene) is carried out through chain extension of the poly(tert‐butyl acrylate) latex as a macro‐transfer agent in seeded emulsion polymerization of styrene. Finally, the prepared block copolymer is deprotected to bring about its amphiphilic nature and a pH control caters for its anionic character. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4389–4398     

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

Well‐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     

Synthesis and Characterization of Triblock Terpolymers with three Potentially Crystallisable Blocks: Polyethylene-b-poly(ethylene oxide)-b-poly(ε-caprolactone)

A first attempt was made to produce novel ABC triblock terpolymers with three potentially crystallisable blocks: polyethylene (PE), poly(ethylene oxide) (PEO), and poly(ε-caprolactone) (PCL). Polybutadiene-b-poly(ethylene oxide) diblock copolymers were synthesized by living anionic polymerization. Then, a non-catalyzed thermal polymerization of ε-caprolactone from the hydroxyl end group of the PB-b-PEO diblock precursors was performed. Finally, hydrogenation by Wilkinson catalyst produced PE-b-PEO-b-PCL triblock terpolymers. Side reactions were detected that lead to the formation of undesired PCL-b-PEO diblock copolymers, however, these impurities were successfully removed by purification. A range of triblock terpolymers with PCL and PEO minor components were prepared. Topological restrictions on the PEO middle block prevented this block from crystallizing while the complex crystallization behavior of the PE and PCL blocks was documented by DSC and WAXS measurements.     

Living polymerization of D,L‐3‐methylglycolide initiated with bimetallic (Al/Zn) μ‐oxo alkoxide and copolymers thereof

D,L ‐3‐Methylglycolide (MG) was successfully polymerized with bimetallic (Al/Zn) μ‐oxo alkoxide as an initiator in toluene at 90 °C. The effect of the initiator concentration and monomer conversion on the molecular weight was studied. It is shown that the polymerization of MG follows a living process. A kinetic study indicated that the polymerization approximates the first order in the monomer, and no induction period was observed. ¹H NMR spectroscopy showed that the ring‐opening polymerization proceeds through a coordination–insertion mechanism with selective cleavage of the acyl–oxygen bond of the monomer. On the basis of ¹H NMR and ¹³C NMR analyses, the selective cleavage of the acyl–oxygen bond of the monomer mainly occurs at the least hindered carbonyl groups (P₁ = 0.84, P₂ = 0.16). Therefore, the main chain of poly(D,L ‐lactic acid‐co‐glycolic acid) (50/50 molar ratio) obtained from the homopolymerization of MG was primarily composed of alternating lactyl and glycolyl units. The diblock copolymers poly(ϵ‐caprolactone)‐b‐poly(D,L ‐lactic acid‐alt‐glycolic acid) and poly(L ‐lactide)‐b‐poly(D,L ‐lactic acid‐alt‐glycolic acid) were successfully synthesized by the sequential living polymerization of related lactones (ϵ‐caprolactone or L ‐lactide). ¹³C NMR spectra of diblock copolymers clearly show their pure diblock structures. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 357–367, 2001     

Control of pH- and temperature-responsive behavior of mPEG-b-PDMAEMA copolymers through polymer composition

A series of poly(ethylene glycol) monomethyl ether-block-poly(2-(dimethylamino)ethyl methacrylate) (mPEG-b-PDMAEMA) diblock copolymers were synthesized using atom transfer radical polymerization to achieve controlled polymer molecular weight and narrow molecular weight distribution. The thermoresponsive properties of the mPEG-b-PDMAEMA diblock copolymers in aqueous buffered solutions were determined using UV-Visible spectroscopy and dynamic light scattering. The cloud point, a soluble-to-insoluble transition, was observed for all mPEG-b-PDMAEMA diblock copolymer solutions. Increasing either the mPEG or PDMAEMA molecular weight resulted in a decrease in observed cloud points as a function of pH and polymer concentration. Changing the mPEG molecular weight determined whether a second, higher temperature, thermal transition was observed as a function of pH and polymer concentration. Controlling the thermoresponsive properties of mPEG-b-PDMAEMA diblock copolymers through polymer composition, concentration, and pH enables the tailoring of these copolymers for applications ranging from non-viral gene delivery to use as a strengthening agent in paper.     

Synthesis and characterization of well‐defined ABC 3‐Miktoarm star‐shaped terpolymers based on poly(styrene), poly(ethylene oxide), and poly(ϵ‐caprolactone) by combination of the “living” anionic polymerization with the ring‐opening polymerization

A series of well‐defined ABC 3‐Miktoarm star‐shaped terpolymers [Poly(styrene)‐Poly(ethylene oxide)‐Poly(ε‐caprolactone)](PS‐PEO‐PCL) with different molecular weight was synthesized by combination of the “living” anionic polymerization with the ring‐opening polymerization (ROP) using macro‐initiator strategy. Firstly, the “living” poly(styryl)lithium (PS^?Li⁺) species were capped by 1‐ethoxyethyl glycidyl ether(EEGE) quantitatively and the PS‐EEGE with an active and an ethoxyethyl‐protected hydroxyl group at the same end was obtained. Then, using PS‐EEGE and diphenylmethylpotassium (DPMK) as coinitiator, the diblock copolymers of (PS‐b‐PEO)_p with the ethoxyethyl‐protected hydroxyl group at the junction point were achieved by the ROP of EO and the subsequent termination with bromoethane. The diblock copolymers of (PS‐b‐PEO)_d with the active hydroxyl group at the junction point were recovered via the cleavage of ethoxyethyl group on (PS‐b‐PEO)_p by acidolysis and saponification successively. Finally, the copolymers (PS‐b‐PEO)_d served as the macro‐initiator for ROP of ε‐CL in the presence of tin(II)‐bis(2‐ethylhexanoate)(Sn(Oct)₂) and the star(PS‐PEO‐PCL) terpolymers were obtained. The target terpolymers and the intermediates were well characterized by ¹H‐NMR, MALDI‐TOF MS, FTIR, and SEC. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1136–1150, 2008     

The doubly thermo-responsive triblock copolymer nanoparticles prepared through seeded RAFT polymerization

The doubly thermo-responsive triblock copolymer nanoparticles of polystyrene-block-poly(N-isopropylacrylamide)-block-poly[N,N-(dimethylamino) ethyl methacrylate] (PS-b-PNIPAM-b-PDMAEMA) are successfully prepared through the seeded RAFT polymerization in situ by using the PS-b-PNIPAM-TTC diblock copolymer nanoparticles as the seed. The seeded RAFT polymerization undergoes a pseudo-first-order kinetics procedure, and the molecular weight increases with the monomer conversion linearly. The hydrodynamic diameter (D _h) of the triblock copolymer nanoparticles increases with the extension of the PDMAEMA block. In addition, the double thermo-response behavior of the PS-b-PNIPAM-b-PDMAEMA nanoparticles is detected by turbidity analysis, temperature-dependent 1H-NMR analysis, and DLS analysis. The seeded RAFT polymerization is believed as a valid method to prepare triblock copolymer nanoparticles containing two thermo-responsive blocks.