Vibrational spectroscopy in the development of surface hydrophilic elastomer latex (SHEL)

An illustrative example is given to show how various vibrational spectroscopy techniques coupled with two-dimensional (2D) correlation analysis can be effectively utilized in the development of a novel and functional material. Surface-hydrophilic elastomer latex (SHEL) is a material exhibiting rather unusual permanently water-wettable surface feature despite having a soft and rubbery bulk property, which can be successfully analyzed with vibrational spectroscopy. 2D photoacoustic (PAS) IR spectra of a SHEL film indicate the localized surface segregation of long-chain ethoxylate moiety of the oligomeric surfactant used in the preparation of this material. The accumulation of the hydrophilic long-chain ethoxylate produces the high energy polar surface over the hydrophobic bulk phase of SBR copolymer. The persistence of very low water contact angle, even after repeated washing of a SHEL film with an excess amount of water, indicates permanent covalent attachment of long-chain ethoxylate group to the SBR copolymer. 2D Raman spectra generated from the process monitoring of the emulsion copolymerization of SHEL reveal the mechanism of the covalent attachment of long-chain ethoxylate. The reaction involves a separate step of oleyl moiety of the block surfactant reacting with 1,3-butadiene prior to the onset of copolymerization to produce the SBR latex product.     

Effect of butadiene/styrene ratio,block structure and carbon nanotube content on the mechanical and electrical properties of thermoplastic elastomers after UV ageing

Thermoplastic elastomers based on a triblock copolymer styrene-butadiene-styrene (SBS) with different butadiene/styrene ratios, block structure and carbon nanotube (CNT) content were submitted to accelerated weathering in a Xenontest, in order to evaluate their stability to UV ageing. It was concluded that ageing mainly depends on butadiene/styrene ratio and block structure, with radial block structures exhibiting faster ageing than linear block structures. Moreover, the presence of carbon nanotubes in the SBS copolymer slows down the ageing of the copolymer. The evaluation of the influence of ageing on the mechanical and electrical properties demonstrates that the mechanical degradation is higher for the C401 sample, which is the SBS sample with the largest butadiene content and a radial block structure. On the other hand, a copolymer derivative from SBS, the styrene-ethylene/butadiene-styrene (SEBS) sample, retains a maximum deformation of ∼1000% after 80 h of accelerated ageing. The hydrophobicity of the samples decreases with increasing ageing time, the effect being larger for the samples with higher butadiene content. It is also verified that cytotoxicity increases with increasing UV ageing, with the exception of SEBS, which remains non-cytotoxic up to 80 h of accelerated ageing time, demonstrating its potential for applications involving exposure to the environment.     

Correlating natural ageing and Xenon irradiation of Paraloid B72 applied on stone

The ageing of Paraloid^® B72, an acrylic copolymer extensively used in conservation of works of art, has been investigated either under artificial irradiation (Xenon lamp) or in natural environment (external exposure) with the aim to correlate the results of the accelerate test with the real situation. For a better understanding of the involved mechanisms some acrylic homo-polymers were also subjected to the artificial ageing test. Molecular changes induced by ageing were followed by infrared spectroscopy (FT-IR) and size exclusion chromatography (SEC), while the efficiency of the treatment was checked by water capillary absorption test and colour determinations. The results obtained indicate that it is possible to discriminate, easily and within reasonable laboratory time experiment, between polymers that can be used in Conservation, and the macromolecules that should not be employed due to short efficacy life-times.     

Nanoporous materials with spherical and gyroid cavities created by quantitative etching of polydimethylsiloxane in polystyrene-polydimethylsiloxane block copolymers

A new method for quantitative etching of the poly(dimethylsiloxane) block in polystyrene-poly(dimethylsiloxane) (PS-PDMS) block copolymers is reported. Reacting the block copolymer with anhydrous hydrogen fluoride renders a nanoporous material (NPM) with the remaining glassy PS maintaining the original bulk morphology. 1H NMR, mass difference, size exclusion chromatography, and X-ray photoelectron spectroscopy were used to characterize the materials before and after etching. NPMs containing spherical and gyroid cavities were prepared, as ascertained by small-angle X-ray scattering. This is the first report on block copolymer-based NPM films of millimeter thickness containing secluded spherical holes. Surface images by AFM and SEM are consistent with the SAXS findings.     

The effect of plasticizer on the ageing of Metolose films

The film-forming material, Metolose, was studied by positron annihilation spectroscopy. It is known that above a given concentration the plasticizer (PEG) forms a separate phase. The controlled ageing of the films showed that there is a difference between the ageing processes of the monophase and that of the separated phase films. The ageing consists of a fast and a slow step in both cases. Our PAS measurements showed that this slow process is hindered in the phase-separated samples.     

Probing athletics tracks degradation using a microscratch technique

Continuous outdoor exposure of athletics tracks can lead to an important degradation of their mechanical and aesthetical properties. In this work, flat laboratory samples prepared from rubber blends of different colours were subjected to natural and artificial ageing, to investigate their effect on the surface properties. Compositional variations demonstrated a generalized oxidization of the outer (top) material layer, together with surfacing of inorganic additives; a small increase of the degradation temperature of the natural rubber component was reported, similar to the one previously observed on bulk track samples. The smooth surface of the present samples allowed their testing using a microscratching technique, able to mechanically probe the material within a few hundred microns below the top surface. The formation of a significantly harder outer crust layer was reported, potentially impacting the track performance since it is exactly the locus of interaction between the athlete and the sport surface. In particular, the increase in scratch hardness is accompanied by a significant reduction in the apparent friction coefficient. These surface modifications, previously unreported in the literature, are independent phenomena with respect to generalized bulk ageing. Microscratch data supported by microscopy evidenced a significantly varying sensitivity to ageing for the different colours (red, blue, green, neutral). Moreover, this sensitivity appeared strongly dependent on the applied ageing protocol (natural vs. artificial). In view of these results, care must be taken when accelerated artificial weathering is used to simulate long-term natural ageing of these materials.     

Aggregational processes of low molecular weight polyethylene-b-polyethylene oxide diblock copolymer probed by electrical impedance spectroscopy

In this paper, we analyze the use of electrical impedance spectroscopy (EIS) to investigate the aggregational processes of low molecular weight polyethylene-b-polyethylene oxide copolymer (PE-b-PEO (50% PEO)) induced by concentration. The real and imaginary part of impedance have been compared to theoretical results based on equivalent circuits, providing information pertaining to the properties of the bulk and contributions due to the interactions at the electrolyte/electrode interface. The bulk resistance is used as a convenient tool for identifying structures such as spheres (S), hexagonally packed cylinders (HPC) and lamellar phases. To characterize the transition mechanisms involved in micellization we applied the Phillips criteria, associating the maximum change in the gradient of bulk resistance with the formation of micelles. The transition from micelles to HPC structures is characterized from the minimum in the bulk resistance, while the electrical signature relative to the formation of lamellar structures is characterized by the decrease in the diffusion (reduction in the polarization effects) and the inversion in the slope of bulk resistance as a function of copolymer concentration. Thus, the EIS may be defined as a convenient tool for characterizing the conformation and phase transitions in amphiphilic block copolymers.     

部分醇解聚乙烯醇接枝聚对二氧环己酮的合成与表征

制备了部分醇解的PVA(paPVA),将其与PDO在均相本体接枝聚合,通过对paPVA醇解度以及投料比的选择,得到了具有各种分子结构的接枝共聚物.通过一维核磁共振谱表征了聚合物的微观结构;采用TG、DSC等测试手段研究了接枝共聚物的热性能和结晶性能.     

STUDY ON THE MODIFICATION OF POLY (METHYL METHACRYLATE) TRANSPARENT MATERIAL

A kind of transparent plastic material has been prepared with bulk copolymer of MMA-MA containing MA 20 vol% as matrix modified by introducing EtOH during bulk copolymerization to increase the transparency and by copolymerizing together with metallic salts of MA forming ionomer polymer to improve the heat-tolerance and hardness. The effect of the contents of the additives on the heat stability, hardness and transparency of the copolymer has been studied. The optical homogeneity of the copolymer material has also been examined. It has been found that the specific property of transparent material of this kind may be obtained by controlling the amounts of EtOH and metallic salt of MA.     

Degradability of poly(lactic acid)-containing nanoparticles: enzymatic access through a cross-linked shell barrier

Comparative studies of bulk samples of hydrolytically degradable poly(lactic acid) (PLA) vs core-shell block copolymer micelles having PLA cores revealed remarkable acceleration in the proteinase K enzymatic hydrolysis of the nanoparticulate forms and demonstrated that even with amidation-based shell cross-linking the core domain remained accessible. Kinetic analyses by (1)H NMR spectroscopy showed less than 20% lactic acid released from enzymatically catalyzed hydrolysis of poly(l-lactic acid) in bulk, whereas ca. 70% of the core degraded within 48 h for block copolymer micelles of poly(N-(acryloyloxy)succinimide-copolymer-N-acryloylmorpholine)-block-poly(L-lactic acid) (P(NAS-co-NAM)-b-PLLA), with only a slight reduction to ca. 50% for the shell cross-linked derivatives. Rigorous characterization measurements by NMR spectroscopy, fluorescence spectroscopy, dynamic light scattering, atomic force microscopy, and transmission electron microscopy were employed to confirm core excavation. These studies provide important fundamental understanding of the effects of nanoscopic dimensions on protein-polymer interactions and polymer degradability, which will guide the development of these degradable nanoconstructs to reach their potential for controlled release of therapeutics and biological clearance.     

3-氨丙基三乙氧基硅烷对溶胶-凝胶法苯乙烯-顺丁烯二酸酐共聚物/SiO_2杂化材料的制备与性能的影响

用３ 氨丙基三乙氧基硅烷（ＡＰＴＥＳ）作为偶联剂，通过溶胶 凝胶（Ｓｏｌ Ｇｅｌ）过程制得两相以共价键结合的透明苯乙烯 顺丁烯二酸酐共聚物／ＳｉＯ２杂化材料．通过ＦＴＩＲ分析等证实了材料有机相与无机相间是以共价键结合的．分析了材料热处理温度和分别用盐酸或氨水作催化剂时对材料溶胶分数的影响、偶联剂及其用量对溶胶 凝胶体系凝胶时间的影响、并研究了杂化材料中无机含量对材料折射率和Ｔｇ的影响     

Preclusion of nano scale self-assembly in block-selective non-aqueous solvents for rod–coil and coil–rod–coil macromolecular surfactants based on perylene tetracarboxylic diimide

Self-assembly of amphiphilic molecules ranging from simple surfactants to block copolymers in a solvent depends on one part of the molecule (one block in block copolymers) being soluble, and the other not. The aggregation of the insoluble segment in the block-selective solvent leads to the self assembly. In this paper, we describe a system of amphiphilic rod–coil and coil–rod–coil molecules, which do not show self assembly in block-selective non-aqueous solvents. We prepared rod–coil molecules based on hydrophilic propylene oxide/ethylene oxide copolymer (PO–EO copolymer) (Jeffamine®) as the flexible segment and photo-conducting large aromatic perylenediimide (PTCDI) as the rod. PO–EO copolymer was attached either to one side of PTCDI (MJ–PTCDI) or both sides (DJ–PTCDI). The former can be considered an inverse macromolecular surfactant, since the tail is hydrophilic and the head is hydrophobic. The DJ–PTCDI is a pseudo Gemini surfactant. Because of the presence of the chromophore, UV–Vis and fluorescent spectra could be used to study the self assembly of these amphiphilic rod coil polymers in solution. PTCDI forms π-interaction mediated aggregates in aqueous solution and these are H-stacked in MJ–PTCDI and J-stacked in DJ–PTCDI. Variable temperature UV and NMR spectra show that the assembly is stable over a large temperature range in water. The aggregates are also stable up to a pH of 12. However, when a non-aqueous solvent is used, no aggregation occurs. This is attributed to the “solvation” of the π-system of the PTCDI. With the addition of water, such solvation seems to be interrupted and aggregation occurs when water becomes a major component. We find that the mole percentage of the aggregates in acetone/water mixtures increases almost linearly with the concentration of water, providing a route to control the extent of aggregation of the chromophores. Due to the long, waxy PO–EO copolymer, MJ–PTCDI and DJ–PTCDI do not show liquid crystalline behavior or nanorod morphology, which were seen with short side chains. The optical microscopy of the bulk material shows aggregated crystals of PTCDI in the waxy matrix, showing that even in the presence of PO–EO copolymer, the molecular assembly of PTCDI takes place in the bulk. Secondary assembly was seen, in that upon ageing of the aqueous solutions, the drop cast films show that the spherical aggregates one-dimensionally coalesced into long fibers. Although UV–Vis spectra indicated no aggregation in non-aqueous solvents, drop-cast films of these solutions show needle-like aggregates and Lego-like assemblies.     

Surface composition of siloxane-containing polymers

X-ray photoelectron spectroscopy was used to study relationships between the surface and bulk composition in block copolymers and blends of poly(dimethyl-siloxane), poly(bisphenol A sulfone) and poly(bisphenol A carbonate). In all cases the polymer surfaces were highly enriched in siloxane. At a fixed siloxane concentration in the bulk the highest enrichment was observed in the blends of homopolymers and the lowest in the copolymers. It was found that the addition of small quantities of a siloxane-rich copolymer to another copolymer having a lower siloxane content may reduce the surface siloxane concentration of the latter. This unusual surface behavior was explained by the formation of an over-layer in which the macromolecules of the siloxane-rich copolymer are oriented nearly parallel to the sample surface.     

Mercapto-modified copolymers in polymer blends, 1. Functionalization of EPDM with mercapto groups and its use in NBR/EPDM blends

Ethylene-propylene-diene rubber (EPDM) was reacted with thioacetic acid in the presence of 2,2′-azoisobutyronitrile (AIBN), giving rise to thioacetate-modified EPDM (EPDMTA). The extent of the incorporation was studied as a function of both thioacetic acid and AIBN concentration and reaction time. The products were analyzed by FTIR spectroscopy, sulfur content, and ¹H NMR spectroscopy. The hydrolysis of EPDMTA in a NaOH methanolic solution resulted in mercapto-modified EPDM (EPDMSH). The addition of 5 wt.-% of this functionalized copolymer to a sulfur-vulcanized nitrile rubber (NBR)/EPDM (70 : 30 wt.-%) blend accelerated the vulcanization process as indicated by oscillating disk rheometer analysis. In addition, an improvement of mechanical and ageing properties was also observed.     

Fabrication, characterization, and supercooling suppression of nanoencapsulated n-octadecane with methyl methacrylate–octadecyl methacrylate copolymer shell

Supercooling of micro- and nanoencapsulated phase change material is widely observed as their diameters depress to a limitation upon cooling. The aim of this study is to suppress the supercooling of nanoencapsulated n-octadecane (NanoC18) using a novel copolymer consisting of long n-alkyl side chains as shell. Nanoencapsulations of n-octadecane with various compositions of poly(methyl methacrylate-co-octadecyl methacrylate) copolymer as shells were carried out by means of miniemulsion polymerization. Fabrication, morphology, diameter distributions, phase change behaviours, and thermal stabilities of nanocapsules were investigated using Fourier transformed infrared spectroscopy, a field-emission scanning electron microscope, a transmission electron microscope, particle size distribution analysis, differential scanning calorimetry, and thermogravimetric analysis. The results indicate that a series of nanocapsules with core/shell structure and spherical shapes are fabricated with average diameters ranging from 373 to 398 nm. The average thickness of the shells is about 60 nm. All the NanoC18 crystallize into a stable triclinic phase via a metastable rotator phase (R_I) from the liquid phase. The crystallization temperature of n-octadecane within poly(methyl methacrylate) nanocapsules is considerably lower than that in bulk phase. Supercooling is effectively suppressed using the comb-like copolymer with crystallizable n-octadecyl side chains as shell. Octadecyl methacrylate is not only employed as a reactive costabilizer to suppress the influence of Ostwald ripening during the formation of nanocapsules but also as a functional monomer in the composition of the copolymer shell in order to suppress the supercooling of NanoC18.     

Effect of a block copolymer on the adhesion between incompatible polymers. I. Symmetric tests

We have studied the adhesion (welding) of polystyrene (PS) and poly (methyl methacrylate) (PMMA) and the effect of incorporating a thin layer of PS/PMMA block copolymer in the joint. The minimum thickness of copolymer layer necessary to increase the joint failure energy G to that of the bulk was about half the interlamellar spacing (long period) of the block copolymer. This tends to suggest a simple model of the block copolymer organizing on the interface with the two halves of the copolymer dissolved in the relevant homopolymers, however, we have no direct evidence for this. X-ray photoelectron spectroscopy and optical microscopy were used to study the failure path. Without copolymer the crack propagated partly in the polystyrene and partly on the interface. Crazes grew from the interface into the polystyrene and the crack tended to follow such a craze for a short distance then jump back to the interface. With the copolymer, the failure mode was very similar, but there was evidence now of crazing on the interface. In no case was there evidence of a significant amount of PMMA on the PS side of the failure.     

Preparation and application of modified carboxymethyl cellulose Si/polyacrylate protective coating material for paper relics

There are large numbers of paper cultural relics in China, the country where paper making was invented. However, the paper relics have not been adequately protected so they are at risk of ageing, damage and disappearance. In order to better protect the paper relics, modified carboxymethyl cellulose/Si/polyacrylate protective materials were prepared with acrylicresin and modified carboxymethyl cellulose which has a good affinity with the paper and modified silica, improving the mechanical strength and ability to withstand weathering. The modified CMC/Si/polyacrylate protective material was analysed using infrared spectroscopy, transmission electron microscopy, differential scanning calorimetry and other performance-testing devices. The surface morphology of the paper samples was analysed using scanning electron microscopy. The protective material so prepared was evaluated by subjection to accelerated ageing (dry heat treatment). The results showed the protective material films to have good hydrophobicity, acid/alkali resistance and mechanical strength. When the content of SiO₂ is 6 mass %, the protective material has an excellent comprehensive performance. The results of the ageing test reveal that the prepared material can effectively slow down the ageing rate. The prepared material is suited to the protection of paper cultural relics.     

Synthesis and solution behavior of carbon nanotubes decorated with amphiphilic block polyelectrolytes

The aqueous solubilization of carbon nanotubes (CNTs) with the aid of a block copolymer possessing one polyelectrolyte block (namely polystyrene-b-sodium (sulfamate/carboxylate polyisoprene)) is reported. The solubilization protocol, based on the co-dissolution of the copolymer and the CNTs, leads to the formation of supramolecular assemblies on the side walls of the tubes. Electron microscopy as well as infrared spectroscopy and thermogravimetric analysis were employed as meaningful probes to identify the adsorption of the polymer onto the surface of CNTs and the composition of the final hybrid material. Viscosity measurements on solutions of the copolymer decorated CNTs indicate that the polyelectrolyte effect, which is observed in the case of net polymers, is preserved in a lesser extent in the case of the copolymer/CNTs dispersions.     

Spectroelectrochemical responses of thin-film conducting copolymers prepared electrochemically from mixtures of 3,4-ethylenedioxythiophene and 2,2'-bithiophene

Here we have studied the electrocopolymerisation of binary mixtures of functionalised thiophenes in varying compositions and determined independently for each copolymer the spectroelectrochemical responses and the composition of the material using X-ray photoelectron spectroscopy. We have observed strong correlations between the composition of the copolymer material and the composition of the binary solution from which the polymer was grown. In addition, we have shown that the spectroelectrochemical properties of the copolymers indicate the presence of random copolymer material where the lambda(Max) values of the neutral, undoped, polymer scales with composition but also suggest that there may be small amounts of block copolymer or phase-separated mixtures of the homopolymer components.     

Mechanical behaviour of isotactic polypropylenes in the lower and the upper glass transitions ranges

 The effects of physical ageing on both glass transitions of isotactic polypropylenes (homopolymer and random copolymer)are investigated by isothermal dynamic mechanical spectroscopy and by low strain creep. The ageing-time dependent expressions of the amorphous fractions which undergo each relaxation are introduced in a rheological model composed by a modified Zener model (associated to the β-relaxation) in series with a γ-element (associated to the α-relaxation). The agreement between the responses of this model and the creep and dynamic results is good over a time (or frequency) range covering up to 15 decades for three kinds of isotactic polypropylenes. Received: 2 January 1996 Accepted: 16 August 1996