Crystallization behavior of oxyethylene/oxybutylene diblock and triblock copolymers

The crystallization behavior of poly(oxyethylene)-b-poly(oxybutylene) block copolymers with different compositions, morphologies and architectures (E_mB_n diblock copolymers and E_mB_nE_m, B_nE_mB_n triblock copolymers) were investigated and the effect of volume fraction and architecture on the crystallization temperature (T_c) in non-isothermal crystallization was determined. It is found that the E_mB_n diblock copolymers having long E blocks exhibit similar crystallization temperatures, irrespective of volume fraction and morphology, but for the block copolymers with shorter E blocks the crystallization temperature increases with both the volume fraction, φ_E, and the length, m, of the E block. Some block copolymers with extremely low T_c, which fall into the temperature range normally associated with homogenous nucleation, were chosen for time-resolved small-angle X-ray scattering (SAXS) and isothermal crystallization kinetics experiments. The results show that breakout crystallization occurs in all these block copolymers. Therefore, unlike E_mB_n/B_h blends, there is no obvious relationship between T_c and crystallization behavior in neat block copolymers and homogeneous nucleation does not definitely lead to confined crystallization. The values of χ_c/χ_ODT for all the block copolymers with hex and bcc morphology were also calculated. It is found that all the block copolymers have χ_c/χ_ODT<3, in agreement with the previously reported critical value and consistent with their breakout crystallization behavior.     

Conformational behaviour of (styrene-p-chlorostyrene) triblock copolymers in dilute solutions. 2. Temperature dependence of conformational behaviour in a selective solvent

Intrinsic viscosity, osmotic second virial coefficient and light scattering of the B_mA_nB_m and A_mB_nA_m copolymers (A, styrene monomeric unit; B, p-chlorostyrene monomeric unit, m and n denote the number of units) in cumene which is a good solvent for polystyrene but a θ solvent for poly(p-chlorostyrene) at 59.0°C, were studied over the temperature range 65° to 15°C. The results suggested that conformational transition from a random coil form to a segregated form occurs at a critical temperature which appears to be in the range 40° to 30°C, depending on the composition, molecular weight and structure of the block copolymers; the θ condition could not be attained by cooling the block copolymer solutions, and micelle formations due to intermolecular associations were found in some cases below the transition temperature.     

Morphology of semicrystalline oxyethylene/oxybutylene block copolymer thin films on mica

The morphology of as-cast and annealed thin films of four symmetric semicrystalline block copolymers on mica was investigated by tapping mode atomic force microscopy (AFM) and grazing incidence X-ray diffraction (XRD). It is found that the morphology of the thin films is dependent on chain length of oxyethylene/oxybutylene block copolymers. The as-cast thin films of the shorter E_mB_n block copolymers on mica exhibit a multi-layered lamellar structure parallel to the surface, in which the stems of the E crystals in the first half polymer layer contacting mica are parallel to the mica surface and perpendicular to the mica surface in the upper polymer layers. In contrast, the as-cast thin film of longer E₂₂₄B₁₁₄ exhibits a structure with mixed orientations of lamellar microdomains on a half polymer layer parallel to the surface. After annealing, the multi-layered structure on mica is transformed into a half-layered, densely branched structure, which is formed following a diffusion-limited aggregation mechanism, opposed to the featureless half-layered structure on silicon. Upon annealing, the upper polymer layers gradually retreat and the remaining area becomes thicker, but in contrast the first half polymer layer contacting mica becomes thinner due to wetting and the parallel orientation of the E crystal stems. The densely branched structure and the different chain orientations of the E crystal stems in the first half polymer layer contacting mica are attributed to the strong interaction between the E block and mica, as revealed by our previous work. The width of branches was employed to analyze the kinetics of secondary crystallization. It is also found that the width of the branches and the velocity of crystal front decrease as the chain length increases.     

Synthesis and properties of novel biodegradable triblock copolymers of poly(5-methyl-5-methoxycarbonyl-1,3-dioxan-2-one) and poly(ethylene glycol)

Novel biodegradable triblock copolymers of poly(5-methyl-5-methoxycarbonyl-1,3-dioxan-2-one) (PMMTC) with poly(ethylene glycol) (PEG), PMMTC-b-PEG-b-PMMTC, were synthesized by the ring-opening polymerization of MMTC in bulk, using the dihydroxyl PEG as initiator and Sn(Oct)₂ as catalyst. The triblock copolymers with different compositions were characterized by IR and ¹H NMR, their molecular weight was measured by gel permeation chromatography (GPC). The results showed that the molecular weight of triblock copolymers increased either with the increase of the molar ratio of MMTC in feed while the PEG chain length kept constant, or by lengthening the backbone chain of PEG block with the same ratio of MMTC in feed. The hydrophilicity of copolymers was greatly improved by incorporation of PEG block into polycarbonate. The in vitro hydrolytic/enzymatic degradation and controlled drug release properties of the triblock copolymers were also investigated.     

Crystallization and coalescence of block copolymer micelles in semicrystalline block copolymer/amorphous homopolymer blends

Crystallization of two oxyethylene/oxybutylene block copolymers (E₇₆B₃₈ and E₁₅₅B₇₆) from micelles in block copolymer/amorphous homopolymer blends was studied by differential scanning calorimetry (DSC) and time-resolved small angle X-ray scattering (SAXS). Unlike the simultaneous crystallization and formation of superstructure in crystallization from an ordered structure, crystallization of block copolymer from micelles can be divided into two steps. The core of the micelles firstly crystallizes individually, with first-order crystallization kinetics and homogeneous nucleation mechanism. The SAXS revealed that crystallization-induced deformation occurs for the micelles, which strongly depends on microstructure of the block copolymers. For the shorter block copolymer E₇₆B₃₈, larger deformation induced by crystallization was observed, leading to coalescence of the micelles after crystallization, while for the longer block copolymer E₁₅₅B₇₆ the micelles show little deformation and the morphology of micelle is retained after crystallization.     

The melt rheological behavior of AB,ABA, BAB,and (AB)n block copolymers with monodisperse aramide segments

The melt rheological behavior of segmented block copolymers with high melting diamide (A) hard segments (HS) and polyether (B) soft segments was studied. The block copolymers can be classified as B (monoblock), AB (diblock), ABA (triblock, diamide end segment), BAB (triblock, diamide mid‐segment) and ? (AB)_n? (multiblock) block copolymers. Varied were the number of HS in the chain, the HS concentration, the position of the HS (in the chain or at the end of the chain) and the molecular weight of the copolymers. The melt rheological behavior of the copolymers was studied with a plate–plate method. The materials B (monoblock), BAB (triblock, diamide mid‐segment), and ? (AB)_n? (multiblock) block copolymers had a rheological behavior of a linear polymer and the complex viscosity increased with molecular weight. Surprisingly, the diblock copolymers AB and the triblock copolymers ABA at low frequencies and near the melting temperature of the copolymers had the behavior of a gelled melt. The diamide segments at the chain end seemed to form aggregates, whereas the diamide mid‐segments did not. Also, time‐dependent rheology of diblock copolymer confirmed the network structure built up in the melt. The block copolymers with H‐bonding diamide end segments had a thixotropic behavior. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Synthesis and characterization of polycation block copolymer Poly(l-lysine)-b-poly[N-(N′,N′-diisopropyl-aminoethyl)aspartamide] as potential pH responsive gene delivery system

A series of Poly(l-lysine)_m-b-poly[N-(N′,N′-diisopropylaminoethyl) aspartamide]_n copolymers, abbreviated as PLL_m-b-P[Asp(DIP)]_n were designed and synthesized via ring-opening polymerization(ROP), click chemistry, aminolysis and hydrolysis. Using ¹H NMR, FT-IR and GPC, the structures and compositions of these copolymers have been verified. Through feed ratio control, block copolymer PLL_m-b-P[Asp(DIP)]_n with different PLL and PAsp(DIP) block lengths were obtained, which can be modified to adjust the pH responsiveness and the self-assembling behaviors of the PLL_m-b-P[Asp(DIP)]_n. From the results of DLS, TEM and ¹H NMR, these block copolymers can form stable micelles with a partially hydrated PAsp(DIP) core and a PLL corona at pH 7.4. While as demonstrated by ¹H NMR and TEM, these PLL_m-b-P[Asp(DIP)]_n micelle was disassembled due to further protonation of the tertiary amine in the PAsp(DIP) block at pH 5.4. These pH responsive character of the PLL_m-b-P[Asp(DIP)]_n micelles made them as potential pH responsive gene delivery system which may co-deliver drug and DNA simultaneously.     

Polydispersity control in ring opening metathesis polymerization of amphiphilic norbornene diblock copolymers

Ring opening metathesis polymerization (ROMP) with Grubbs's catalyst was used to synthesize narrow polydispersity (PDI)diblock copolymers of norbornene (NOR) and norbornenedicarboxylic acid (NORCOOH). Norbornene (NOR) and 5-norbornene-2,3,-dicarboxylic acid bis trimethylsilyl ester (NORCOOTMS) were used as precursor monomers for thepolymerization. [NORCOOTMS]_m/[NOR]_n was converted to [NORCOOH]_m/[NOR]_n by precipitating the polymer solution in a mixture of methanol, acetic acid, and water. The conversion to 5-norbornene-2,3-dicarboxylic acid was evidenced by ¹H NMR. By polymerizing the bulkier NORCOOTMS precursor monomer first, lower PDIs were observed for the completed [NORCOOH]_m/[NOR]_n block copolymers in comparison to copolymers where the NOR block was polymerized first. The PDI of the diblock copolymers of [NORCOOH]_m/[NOR]_n decreased with increase in block length ofthe precursor NORCOOTMS monomer. This study shows that the PDI can be controlled by selecting a monomer with appropriate functionality as the starting block of the block copolymer to control the rate of propagation, R_p, as an alternative of using additives to change the reactivity of the catalyst.     

Effects of macromolecular architecture on the micellization behavior of complex block copolymers

The effect of macromolecular architecture on the aggregative behavior of A–B block copolymers with different complex structures in selective solvents was studied by Dissipative Particle Dynamics. We focus on two types of diblock copolymers, (I) asymmetric linear diblocks B_yA_x and (II) miktoarm stars (B_y)_n(A_x)_m, where A block is solvophilic and B block solvophobic. Note that y and x are the block lengths of A and B blocks; n and m denote arm numbers of A and B blocks in the star. For type I linear copolymer with a given ratio of y/x, the aggregation number <p> varies with the total length (x + y) for y/x > 1 but is essentially independent of the total length for y/x ? 1. For type II star copolymer with m · x = 24 and n · y = 24, the aggregation number varies with the branch number m at a given number of solvophobic blocks n. There exists a minimum aggregation number at m ≈ 4 so that <p> declines first and then grows with increasing the branch number. Moreover, <p> increases as the polymer concentration is increased. Our simulation results indicate that at a given chemical composition, the micelle properties such as aggregation number and micellar morphology may vary with the macromolecular architecture.     

PTPFCBBMA-b-PEG-b-PTPFCBBMA amphiphilic triblock copolymer: Synthesis and self-assembly behavior

We present the synthesis and self-assembly behavior of a new semi-fluorinated amphiphilic triblock copolymer. A series of perfluorocyclobutyl aryl ether-based amphiphilic ABA triblock copolymer containing hydrophilic poly(ethylene glycol) segment as the middle block were synthesized by atom transfer radical polymerization (ATRP). ATRP of 4-(4′-p-tolyloxyperfluorocyclobutoxy)benzyl methacrylate was initiated by PEG-based bifunctional macroinitiators with different molecular weights to obtain the desired copolymers with narrow molecular weight distributions (M_w/M_n ≤ 1.30) and the number of perfluorocyclobutyl linkage can be tuned by the feed ratio and the conversion of the fluorine-containing methacrylic monomer. The critical micelle concentrations of these amphiphilic ABA triblock copolymers in aqueous media were determined by fluorescence probe technique. They could aggregate to form spherical and cylindrical micelles visualized by TEM with varying the content of hydrophobic segment.     

Synthesis of water-soluble ABC triblock copolymers containing polypeptide segments

This article describes a facile approach for the synthesis of water-soluble ABC triblock copolymers through a combination of atom transfer radical polymerization (ATRP) and click reactions. The bromine-terminated MPEO–PtBA–Br precursor was first prepared by ATRP, and converted into the azido-terminated precursor MPEO–PtBA–N₃ by a simple nucleophilic substitution. Then, MPEO–PtBA–PzLLys triblock copolymers were synthesized via the click reaction of MPEO–PtBA–N₃ and the propargyl-terminated poly(N^ε-carbobenzoxy-l-lysine)s (PzLLys). The water-soluble MPEO–PAA–PLLys ABC triblock copolymers were obtained from the hydrolysis process. The structures of these block copolymers were characterized by NMR, IR and GPC.     

Functionalization of amphiphilic coil-rod-coil triblock copolymer poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine) with florescence moiety and C60

We recently achieved quantitative synthesis of an amphiphilic coil-rod-coil triblock copolymer, poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate)-b-poly(2-vinylpyridine), by coupling in situ living diblock copolymer poly(2-vinylpyridine)-b-poly(n-hexyl isocyanate) (P2VP-b-PHIC) using malonyl chloride in the presence of pyridine. This led to the introduction of an active methylene group that is a site for further functionalization in the rod block. The Michael addition reaction of the triblock copolymer with 7-(4-trifluoromethyl) coumarin acrylamide led to copolymer bearing a fluorescent pendent in the rod block. The fluorescent labeled copolymers were isolated in ∼94% yields. Similarly C₆₀ pendent was introduced to the rod block by the Bingel reaction. The yields of C₆₀ functionalized copolymers were ∼54%. The precursor and functionalized amphiphilic coil-rod-coil copolymer show diverse morphologies, such as micelles and vesicles by simply changing the solvent. For the C₆₀ functionalized block copolymer, structural constraints in micelles and vesicles prevented C₆₀ pendents to aggregate.     

Star-Block Copolymers: Organized Polymerization of Diblock Macromonomers

In the first part of this article, the method for preparation of heteroarm star (A _n B _n star-block) copolymers from diblock macromonomers possessing central functional groups is reviewed. These diblock macromonomers formed a microphase-separated structure in the solid state. The central functional groups at the position of the block junction were located regularly at the domain interface. The microgelation of diblock copolymer films formed A _n B _n star-block copolymers by organization effects. The second section reviews the methods for preparation of (AB) _n star-block copolymers from diblock macromonomers possessing a terminal vinylbenzyl group. The microgelation in micelles between diblock macromonomers and linking agent also formed (AB) _n star-block copolymers. Finally, the phase stability criteria of these star-block copolymers are reported briefly.     

Amphiphilic block copolymers bearing strong push-pull azo chromophores: Synthesis, micelle formation and photoinduced shape deformation

In this work, a series of amphiphilic diblock copolymers bearing strong push-pull type azo chromophores was synthesized through post-polymerization azo-coupling reaction scheme. The copolymers (P(CNAZO_m-b-MAA_n)), composed of 2-(N-ethyl-N-(4-(4′-cyanophenylazo)-phenyl)amino)ethyl methacrylate (CNAZO) and methacrylic acid (MAA) blocks, were obtained through four-step reactions. Firstly, precursor diblock copolymers (P(EMA_m-b-tBMA_n)) were obtained through sequential two-stage ATRP reactions of 2-(N-ethyl-N-phenylamino)ethyl methacrylate (EMA) and tert-butyl methacrylate (tBMA). Then, 4-amino-4′-cyanoazobenzene chromophores were introduced by azo-coupling reaction of P(EMA_m-b-tBMA_n) with diazonium salt of 4-aminobenzonitrile. Finally, P(CNAZO_m-b-MAA_n) was obtained through selective hydrolysis of the tert-butyl ester linkages in the tBMA blocks. Three block copolymers with the same CNAZO block length (m = 100) and different MAA block lengths (n = 5, 13, 23) were prepared by this method. The polymer and copolymers prepared in the process were characterized by GPC, ¹H NMR, UV-vis, DSC and TGA measurements. Results show that P(CNAZO_m-b-MAA_n) forms spherical micellar aggregates by gradually increasing the water content in THF/H₂O mixtures. The diameters of the spherical aggregates are related to the composition of the block copolymers and the water-adding rate. The block copolymer with larger molecular weight of the hydrophilic MAA block forms the aggregates with the smaller average size. The increase of the water-adding rate also shows an effect to reduce the diameters. Upon irradiation with a linearly polarized Ar⁺ laser beam, the spherical aggregates can be elongated in the light polarization direction. The deformation degree shows an almost linear dependence on the light irradiation time in the testing period. The deformed aggregates can recover the original spherical shape after thermal annealing at a temperature above T_g of the block copolymer.     

Synthesis and characterization of ABA‐type block copolymers of trimethylene carbonate and ϵ‐caprolactone

This paper describes the synthesis of a series of ABA‐type triblock copolymers of trimethylene carbonate and ?‐caprolactone with various molar ratios and analyses the thermal and mechanical properties of the resulting copolymers. The structures of the triblock copolymers were characterized by ¹H and ¹³C nuclear magnetic resonance spectroscopy, FT‐IR spectroscopy and gel permeation chromatography. Results obtained from the various characterization methods proves the successful synthesis of block copolymers of trimethylene carbonate and ?‐caprolactone. The thermal properties of the block copolymers were investigated by differential scanning calorimetry. The T_m and ΔH_m values of the copolymers decrease with increasing content of trimethylene carbonate units. Two T_gs were found in the copolymers. Furthermore, both of the T_g values increased with increasing content of trimethylene carbonate units. The mechanical properties of the resulting copolymers were studied by using a tensile tester. The results indicated that the mechanical properties of the block copolymers are related to the molar ratio of trimethylene carbonate and ?‐caprolactone in the copolymers, as well as the molecular weights of the resulting copolymers. The block copolymer with a molar composition of 50/50 possessed the highest tensile stress at maximum and modulus of elasticity. Block copolymers possessing different properties could be obtained by adjusting the copolymer compositions. Copyright © 2004 Society of Chemical Industry     

Synthesis of novel ABA triblock and (ABA)n multiblock copolymers comprised of polyisobutylene and poly(γ-benzyl-l-glutamate) segments

The synthesis of ABA triblock copolymers comprised of polyisobutylene (PIB) and poly(γ-benzyl-l-glutamate) (PBLG) segments has been demonstrated for the first time by the polymerization of γ-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA) initiated with well-defined α,ω-primary amino-functional PIBs. The ammonium-mediated polymerization of BLG-NCA provided better control of molecular weights and lower polydispersity indices (PDIs) compared to the conventional polymerization. The compositional homogeneity of the block copolymers has been confirmed by GPC-MALLS and ¹H NMR spectroscopy. Since the resulting ABA triblock copolymer possessed primary amino groups at α,ω-ends, further extension reaction with 4,4′-methylene-bis(phenyldiisocyanate) was possible to afford a novel (ABA)_n multiblock copolymer.     

Characterization of block copolymers based on poly[3,3-bis(ethoxymethyl)oxetane] and other novel polyethers

Diblock, triblock, and alternating block copolymers based on poly[3,3-bis(ethoxymethyl) oxetane] [poly(BEMO)] and a random copolymer center block poly(BMMO-co-THF) composed of poly[3,3-bis(methoxymethyl)oxetane] [poly(BMMO)], and poly(tetrahydrofuran) [poly(THF)] were synthesized and characterized with respect to molecular weight. Glass transition temperatures T_g and melting temperatures T_m were characterized via DSC, modulus–temperature, and dynamic mechanical spectroscopy (DMS). These polyethers had T_m between 70°C and 90°C, and T_g between ?55°C and ?30°C. The degree of crystallinity of poly(BEMO) was found to be 65% by X-ray powder diffraction. Tensile properties of the triblock copolymer, poly(BEMO-block-BMMO-co-THF-block-BEMO) were also studied. A yield point was found at 4.1 × 10⁷ dyn/cm² and 10% elongation and failure at 3.8 × 10⁷ dyn/cm² and 760 % elongation. Morphological features were examined by reflected light microscopy and the kinetics of crystallization were studied. Poly(BEMO) and its block copolymers were found to form spherulites of 2–10 μm in diameter. Crystallization was complete after 2–5 min.     

Effect of end-group modification on the adsorption of poly(ethylene oxide)-b-poly(butylene oxide) diblock copolymers at the solid–liquid interface

The adsorption of poly(ethylene oxide)-b-poly(butylene oxide) diblock copolymers at the solid–liquid interface was studied using a quartz crystal microbalance with dissipation monitoring (QCM-D). The effect of modifying the end group of the hydrophilic block was investigated by comparing the behaviour of trimethylammonium- and dimethylamino-tipped copolymers, designated as TE _m B _n and DE _m B _n , respectively. For adsorption from aqueous solution onto a gold surface, results for DE₄₉B₂₂ were similar to those of the T-analogue, but for DE₈₀B₃₄ adsorbed amounts were substantially higher, and for DE₂₇B₂₅ enormously higher, than for the T-analogue. It is suggested that very high levels of adsorption are associated with the formation of a multilayer structure.     

Synthesis and applications of triblock and multiblock copolymers using telechelic oligopropylene

Isotactic polypropylene (iPP)-polystyrene (PS) and iPP-poly(methyl methacrylate) (PMMA) multiblock copolymers were synthesized by atom transfer radical coupling (ATRC) of PS-iPP-PS and PMMA-iPP-PMMA triblock copolymers obtained by atom transfer radical polymerization (ATRP) of styrene (St) and methyl methacrylate (MMA), respectively, using α,ω-dibromoisobutyrateoligopropylene (iPP-Br) as a bifunctional macroinitiator. The iPP-Br was prepared by hydroxylation and subsequent esterification of telechelic oligopropylene having terminal vinylidene double bonds at both ends obtained by controlled thermal degradation of iPP. ATRP of St and (meth) acrylic monomers using iPP-Br formed the corresponding triblock copolymers. It was confirmed that the PMMA-iPP-PMMA triblock copolymer was effective as the compatibilizer for the iPP/PMMA blend. An iPP-PS multiblock copolymer (M_n: 25?000 g/mol and M_w/M_n: 4.1) was prepared by ATRC of PS-iPP-PS triblock copolymer (M_n: 8900 g/mol and M_w/M_n: 1.3). ATRC with St of PMMA-iPP-PMMA triblock copolymer (M_n: 13?000 g/mol and M_w/M_n: 1.4) provided an iPP-PMMA multiblock copolymer containing St chains (M_n: 39?000 g/mol and M_w/M_n: 2.8).