聚羟基乙酸及其共聚物的研究进展

本文综述了聚羟基乙酸的合成、性能、共聚改性等方面的研究进展 ,并讨论了聚羟基乙酸类材料的应用现状及前景     

Comparative study of photobleachable polysilane copolymers applied to optical waveguides

Three different copolymers, poly(methylphenylsilane)-poly(methylmethacrylate) (PMPS-PMMA), PMPS-poly(styrene) (PMPS-PS), and PMPS -poly(benzylmethacrylate) (PMPS-PBzMA), were prepared by photopolymerization using PMPS as a macromolecular photo-radical initiator. For optical waveguide fabrication, their UV spectra, photobleaching, refractive index change and optical properties were comparatively investigated. Furthermore, channel waveguides were successfully fabricated using these copolymers and their optical propagation properties were reported, the results indicate that they are potential materials for optical waveguide applications.     

A facile organometallic-induced cross-linking of copolymers of phosphazene

Incorporation of the organometallic fragments ML_n=CpFe(dppe)I and CpRu(PPh₃)₂Cl to the random copolymers [{NP(O₂C₁₂H₈)}_0.8{NP(OC₆H₄CH₂CN)₂}_0.15{NP(OC₆H₄CH₂CN)(OC₆H₅)}_0.05]_n (1) [{NP(O₂C₁₂H₈)}_0.55{NP(OC₆H₄CH₂CN)₂}_0.2{NP(OC₆H₄CH₂CN)(OC₆H₅)}_0.25]_n (2) produce the new compounds of the approximate composition: [{NP(O₂C₁₂H₈)}_x{NP(OC₆H₄CH₂CN·ML_n)₂}_y{NP(OC₆H₄CH₂CN·ML_n)(OC₆H₅)}_z]_n. The iron derivatives in solution undergo deprotonation of the dppe, probably caused by a polymeric matrix, which in turn causes a spontaneous cross-linking affording sparingly, soluble materials. Thermal analysis of the compounds using DSC and DTA techniques indicates that the incorporation of the organometallic fragment in the copolymer produces materials, which leave an amount of residue depending on the metal, as well as on the functionalization degree of the cyanide groups. Incorporation of the organometallic fragments to the polymer does not produce an improved conductivity in comparison to the insulator polymer without the organometallic fragment.     

Dynamic light-scattering study of self-assembly of diblock copolymers in supercritical carbon dioxide

A high-pressure dynamic light-scattering (DLS) technique has been utilized to study the behavior in solution of poly(1, 1-dihydroperfluorooctylacrylate) and poly(vinyl acetate) (PFOA-b-PVAC) in supercritical carbon dioxide. The hydrodynamic-radius distribution for each species, such as unimers, micelles, and large aggregates, were determined under both isobaric and isothermal conditions over a pressure range of 9-55.2 MPa, and a temperature range of 25-75 degrees C, respectively. The DLS results clearly showed both pressure-induced and temperature-induced dissolution and association behavior for the copolymer in supercritical carbon dioxide. Also presented are some preliminary experimental results for the micellar self-assembly of a fluorinated block copolymer, poly(2-tetrahydropyranyl methacrylate)-b-poly(1h, 1h-perfluorooctyl methacrylate) (THPMA-b-F7MA), in supercritical carbon dioxide by use of a new high-pressure cell that allows us to conduct simultaneous small-angle x-ray scattering and DLS measurements.     

Electron paramagnetic resonance study of free-radical kinetics in ultraviolet-light cured dimethacrylate copolymers

A spin-trapping technique and direct kinetic measurements of electron paramagnetic resonance spectra were used to investigate the kinetics of radical production in the cross-linking photo-initiator system based on camphoroquinone and dimethyl-aminoethylmethacrylate in the presence of the corresponding monomer dimethacrylate copolymer mixture, as well as in the pure photo-initiator system. Consequently, in both cases, the kinetics of radical production and decay was measured. From the measured data the formal kinetic parameters of particular radical processes were calculated by the non-linear least-squares regression method. © 1998 Chapman & Hall     

两亲性嵌段共聚物PEO-b-PSPMA的合成及其胶束光致变色性能的研究

以氯化亚铜(CuCI)/2′,2″,2″-三氨基三乙基胺(Me6TREN)为催化体系,氯苯为溶剂,а-溴代异丁酰溴封端的PEO(PEP-Br)为大分子引发剂,采用原子转移自由基聚合(ATRP)法合成了由聚氧化乙烯(PEO)和聚酯化羧基螺吡喃(PSPMA)组成的两亲性PEO-b-PSPMA嵌段共聚物,并将其在水相中配制成胶束.采用GPC、H-NMR、AFM、DLS及UV-Vis 等手段研究了嵌段共聚物及其胶束.结果表明:选择适当的反应物配比和反应时间能够合成分子量适中、窄分子量分布的PEO-b-PSPMA,而且其在水溶液自组装成的球形胶束具有可逆光致变色性能.     

Diffusion of styrene-acrylonitrile copolymers

Tracer diffusion coefficient, D ^*, and the Newtonian zero shear-rate viscosity, ₀, were measured for a high molecular weight random copolymer (SAN) of styrene and acrylonitrile. As predicted by the reptation model, D ^*was in agreement with the molecular-weight scaling of M _w ^–2 (M _w is the weight average molecular weight of the chain being probed) and was independent of matrix molecular weight. ₀ showed a molecular-weight scaling of M _W ^3.4 . While the temperature dependence of these two relaxation processes could be well explained by the free-volume model up to 252 °C, they showed a discrepancy in activation enthalpy, E _a, of about 20%, with a larger value for diffusion.     

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.     

聚酰亚胺硅氧烷共聚物的合成

以八甲环基环四硅氧烷 (D4 )为扩链试剂 ,在碱性条件下 ,利用平衡反应对 1,3双(r -氨丙基 - 1,1,3,3-四甲基二硅氧烷 (BAPTDS)进行扩链得到双 (r-氨丙基 )聚二甲基硅氧烷 (BAPPDS) ,以此产物 (BAPPDS)为基础 ,在四氢呋喃 (THF)和N ,N -二甲基乙酰胺(DMAc)的混合溶剂中 ,与芳香族二胺和芳香族二酐共缩聚得到可溶性的聚酰胺酸硅氧烷 ,并在热的作用下进一步脱水亚胺化 ,得到聚酰亚胺硅氧烷共聚物。另外 ,对其基本性能也进行了研究。     

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.     

A combined experiment and molecular dynamics simulation study on the influence of the crosslinking on the crystallization of comb fluorinated acrylate copolymers

Hydrophobic coatings for practical applications demand good durability of hydrophobicity and excellent adhesion. Therefore, the preparation of crosslinked crystalline polymers with perfluoroalkyl side-chains and long alkyl side-chains were proposed. In this paper, the influence of the crosslinking on the crystallization of fluorinated acrylate copolymers was investigated through experimental and molecular dynamic simulation results. According to the FT-IR spectroscopy, XRD data and DSC curves, P(SA-co-HEMA-co-FOEMA) was amorphous, while P(SA-co-FOEMA) and the cured resin formed crystalline polymers with hexagonal packing of alkyl side-chains, and the degree of crystallinity in the cured resin is larger than that in P(SA-co-FOEMA). These phenomenons were further interpreted through the snapshots of the equilibrated systems, the radial distribution function, and the concentration profiles. Intramolecular hydrogen bonds and arrangement of main-chains, corresponding to the embedding of N3300, were considered to contribute to these phenomenons. These findings could be expanded to other comb-shape crystalline polymers for preparing functional surfaces and smart materials.     

叶酸受体靶向的聚乳酸共聚物胶束的制备及性质研究

叶酸偶联的羟脯氨酸-乳酸共聚物(PLLA-PHpr-FA)是一种新型的叶酸受体靶向生物降解聚合物,研究PLLA-PHpr-FA自组装形成胶束的能力及胶束的性质。临界胶束浓度(CMC)用芘荧光探针测定,结果表明,CMC很低并依赖于乳酸/羟脯氨酸的比例。透射电子显微镜(TEM)显示共聚物胶束呈现典型的核/壳结构。动态激光光散射(DLS)测定粒径及粒径分布结果显示,粒径受乳酸/羟脯氨酸比例和丙酮量调控,但粒子几乎不受稀释的影响。用紫外分光光度法测定胶束的载药量和包封率表明,共聚物胶束对疏水性药物的包载较好。因此,PLLA-PHpr-FA胶束可以作为肿瘤靶向的药物载体。     

The electric strength of copolymers

Careful measurements of the electric strength of styrene—butadiene copolymers together with their parent homopolymers over a wide range of temperature are presented. The marked reduction of strength characteristic of a non-polar amorphous material occurs at a temperature indistinguishable from the glass transition temperature determined by differential thermal analysis. This temperature may be predicted from the constitution of the copolymer. The underlying mechanism is discussed in terms of molecular structure and movement.     

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.     

Plasticity of styrene-co-methylmethacrylate random copolymers

The plastic deformation of styrene-methylmethacrylate random copolymers has been studied as a function of comonomer composition and compared to the behaviour of PS and PMMA homopolymers. Activation parameters derived from a thermodynamic and kinetic analysis of plastic flow reveal the strong influence of the MMA units in controlling the elementary deformation event.     

Principle of two-dimensional characterization of copolymers

Two-dimensional polymer characterization is used for a simultaneous analysis of molar masses and chemical heterogeneities (e.g., end groups, copolymer composition, etc.). This principle is based on coupling of two different chromatographic modes. Liquid adsorption chromatography at critical conditions (LACCC) is applied for a separation according to the chemical heterogeneity, whereas in the second-dimension fractions are analyzed with regard to their molar mass distribution by means of size exclusion chromatography (SEC). Because appropriate standards for a calibration of the SEC are seldom available, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was used to substitute the SEC. The LACCC-MALDI MS coupling enables acquiring additional structural information on copolymer composition, which can considerably enhance the performance of this coupled method.