Kinetics of phase transitions in block copolymers

A rich variety of equilibrium phases have been identified in block copolymer melts. In this paper we study the kinetics of phase transitions from one equilibrium state to another, from both experimental and theoretical points of view. The formation of ordered phases is often mediated by non-equilibrium intermediate states. In addition the phase transitions can proceed by either conventional nucleation, or by spinodal decomposition.     

Thermal behaviour of nylon 6-poly (ether-esteramide) block copolymers

Block copolymers have been produced by anionic polymerization of caprolactam with end-functionalized soft-block components derived from polymeric polyols. This method of synthesis gives rise to linear segmented block copolymers with alternating polyether soft blocks and polyamide hard blocks. Copolymers with 10–50% w/w of polyether polyol prepolymer have been the particular focus of attention in this work because of their better physical integrity than copolymers of other compositions. Their phase inversion and morphology/property relationships have been examined by means of differential thermal calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). In this work, the polymers have been hand-cast, but the materials do find application in the reaction injection moulding field.     

Heparin-containing block copolymers

Newly synthesized heparin-containing block copolymers, consisting of a hydrophobic block of polystyrene (PS), a hydrophilic spacer-block of poly (ethylene oxide) (PEO) and covalently bonded heparin (Hep) as bioactive block, were coated either onto glass, poly (dimethylsiloxane), polyurethane or PS substrates. Coated surfaces were characterized by determination of the surface-bound heparin activity, adsorption of AT III, plasma recalcification time assays, adhesion of platelets and by an ex vivo rabbit A-A shunt model.It was demonstrated that heparin was available at the surface of all heparin-bound surfaces to interact with AT III and thrombin and to prevent the formation of clots. The maximum immobilized heparin activity was found to be 5.5×10^-3 U cm^-2. Coated surfaces showed a significant prolongation of the plasma reclacification times as compared to control surfaces, due to surface-immobilized heparin. The platelet adhesion demonstrated that platelets reacted only minimally with the heparin-containing block copolymers in the test system and that the heparin-containing block copolymers seemed to passify the surface as compared to control surfaces. In the ex vivo A-A shunt experiments, which were carried out under low flow and low shear conditions, the heparin-containing block copolymers exhibited prolonged occlusion times, indicating the ability of the heparin-containing block copolymers to reduce thrombus formation at the surface.     

Heparin-containing block copolymers

Newly synthesized heparin-containing block copolymers, consisting of a hydrophobic block of polystyrene (PS), a hydrophilic spacer-block of poly(ethylene oxide) (PEO) and covalently bound heparin (Hep) as bioactive block, were coated on aluminium, glass, polydimethylsiloxane (PDMS), PS or Biomer substrates. Surfaces of coated materials were characterized by transmission electron microscopy (TEM), contact angle measurements and X-ray photoelectron spectroscopy for chemical analysis (XPS). It was demonstrated by TEM that thin films of PS-PEO and PS-PEO-Hep block copolymers consisted of heterogeneous microphase separated structures. Using sessile-drop and Wilhelmy plate dynamic contact angle measurements, insight was provided into the hydrophilicity of the surfaces of the coatings. Measurements with hydrated coatings of PS-PEO and PS-PEO-Hep block copolymers revealed that the surfaces became more hydrophilic during immersion in water, due to relaxation/reorientation, or swelling of PEO or PEO-Hep domains, respectively. XPS results for PS, PEO, heparin and PS-PEO as powder agreed well with qualitative and quantitative predictions. XPS results for films of PS-PEO and PS-PEO-Hep block copolymers showed enrichments of PEO in the top layers of the coatings. This effect was more pronounced for hydrated surfaces. Only small amounts of heparin were detected at the surface of coatings of PS-PEO-Hep block copolymers.     

Diffusion of block copolymers

Block copolymers have been attracting the attention of a great number of scientists and engineers with their beautiful ordered structures on a nanometer scale. Repulsion between dissimilar blocks of block copolymers drives micro-phase separation on the length scale—the radius of gyration of the block copolymer chains. Due to the presence of such nano-domains, the diffusion of block copolymers in the melt is significantly reduced in the direction perpendicular to the interface between the domains. In this direction, block copolymer chains diffuse by an activated hopping mechanism in which the shorter block is pulled out from its domain into the majority domain. Consequently, in this direction the diffusion coefficients of block copolymers decrease exponentially with the activation energy of the hopping process χN_sk_BT, where χ is the Flory parameter, N_s is the degree of polymerization of the shorter block, k_B is Boltzmann's constant and T is temperature. The diffusion along the domain interface is less restricted by the presence of domains. The interface diffusion coefficient depends on the degree of segregation and presence of entanglements. Experiments, theories and simulations of block copolymer diffusion in ordered structures are reviewed.     

Photoinduced ordering of block copolymers

Photoinduced ordering of disordered block copolymers (BCPs) would provide an on-demand, nonintrusive route for formation of well-ordered nanostructures in arbitrarily defined regions of an otherwise disordered material. Here we achieve this objective using a rapid and simple approach in which photoconversion of an additive blended with the BCP introduces strong interactions between the additive and one of the chain segments and induces strong order in the BCP blend. The strategy is generally applicable to block copolymers containing chain segments capable of hydrogen bonding with the additive.     

Temperature-sensitive star-shaped block copolymers hydrogels for an injection application: phase transition behavior and biocompatibility

A series of star-shaped poly(d,l-lactic-co-glycolic acid)-b–methoxy poly(ethylene glycol) (PLGA–mPEG) block copolymers with varying PLGA/mPEG block weight ratios, mPEG block length, and arm numbers were synthesized and phase transition behaviors were investigated. Phase transition characteristics, such as critical gel concentration (CGC) and critical gel temperature (CGT), were closely related to the molecular structure of the star-shaped block copolymers. The CGC was mainly determined by the balance of hydrophobic PLGA and hydrophilic mPEG block (PLGA/mPEG block ratio). The CGTs showed a stronger dependence on mPEG block length and arm number. Also, the CGTs can be adjusted by adding mPEG homopolymer additives. The weight fraction of mPEG had a stronger influence on the CGT values than molecular weight of mPEG. In addition, the MTT assay and histological observations confirmed the acceptable biocompatibility of the star-shaped block copolymer. Hence, the star-shaped PLGA-mPEG block copolymer was a promising candidate as a novel injectable gel.     

Monolayered organosilicate toroids and related structures: A phase diagram for templating from block copolymers

Here we report the controlled generation of micelle-templated organosilicate nanostructures resulting from self-assembly of a block copolymer/organosilicate mixture followed by organosilicate vitrification and copolymer thermolysis. Variation of solution condition and the copolymer/organosilicate mixture composition generates widely different film morphologies ranging from toroids to linear features to contiguous nanoporous monolayers. The use of reactive organosilicates for block copolymer templation generates functional inorganic nanostructures with thermal and mechanical stability.     

Functional crosslinked nanostructures from block copolymers

Nanostructure fabrication from block copolymers in my group normally involves polymer design, synthesis, self-assembly, selective domain crosslinking and sometimes degradation. The preparation of thin film with nanochannels was used to illustrate the strategy we took. The nanochannels generated in thin films functioned as chemical valves. The nanochannels also served as templates for semiconductor or magnetic nanoparticle preparation.     

嵌段共聚物合成方法研究进展

综述了近年来聚烯烃嵌段共聚物多种合成方法,包括:活性聚合方法(阴离子、阳离子活性聚合,基团转移聚合,自由基活性聚合,配位活性聚合)、正离子聚合转化法、力化学方法、缩聚法和特殊引发剂法等。同时讨论了各种合成方法的优点及局限性,探讨了其在工业应用上的重要意义。     

Dielectric behaviour of glycidyl methacrylatebutyl methacrylate copolymers

Different copolymers of glycidyl methacrylate and butyl methacrylate with various compositions have been prepared by free radical polymerization. The composition of these copolymers was determined by¹H nuclear magnetic resonance technique. The dielectric properties of these compositions have been studied over a frequency range from 100 Hz to 50kHz and at different temperatures from 20 to 60 C.     

On the association and adsorption behaviour of ethylene oxide/propylene oxide block copolymers in the processes of steel corrosion protection

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

刚柔嵌段共聚物自组装制备单分散性微球

刚柔嵌段共聚物聚苯基喹啉 b 聚苯乙烯(PPQ b PS)在选择性溶剂中具有自组装行为。该共聚物在1mg·mL-1的V(三氟乙酸)∶V(二氯甲烷)=1∶1的溶液中形成胶束,室温下易自组装成平均粒径为2μm的微球,微球粒径随着PPQ聚合度的增大而增大,具有单分散性,同时所形成稀溶液的最强吸收波长为376nm。文中对刚柔嵌段共聚物自组装制备单分散性微球的机理进行了初步探讨。     

Mechanical properties-morphology of rolltruded propylene ethylene block copolymers

Commercially available propylene-ethylene (P/E) block copolymers have been processed by the rolltrusion technique. Properties such as tensile modulus, tensile strength and sample clarity are significantly enhanced compared to the original commercial material. The latter is found to be comprised of ethylene globules distributed uniformly or heterogenously throughout the P/E copolymer, depending upon the manufacturing process. In the rolltruded copolymer, the mechanical and morphological properties depend upon the processing temperature and deformation ratio experienced by the workpiece. The chemical composition of the P/E copolymers also plays a significant part in the improvements in properties induced via rolltrusion that may be carried out below or above the melting temperature of the ethylene component of the copolymers. Differential scanning calorimetry thermograms are very useful in assessing transitional behaviour in this respect and may be used to distinguish between different copolymers (processed and original samples). Correlations among some properties and processing conditions are presented and discussed in relation to polymer composition-processing conditions-morphology-property relationships.