Analysis of the contribution of skeletal vibrations to the heat capacity of linear macromolecules in the solid state

Automatic computer programs are developed to calculate one- two-, and three-dimensional Debye functions. Prior tables of these functions are critically reviewed. Also, strategies are derived to calculate Debye temperatures from heat capacities. Both, simple three-dimensional Debye analyses and Tarasov analyses were carried out on 35 linear macromolecules. The experimental heat capacities for these analyses were collected in the ATHAS data bank. It is shown that the skeletal heat capacity of linear macromolecules is often best represented by only two vibrations per chain atom. For most of the all-carbon chain macromolecules the intramolecular skeletal heat capacity can be given by C_vs=D₁[520 (28/MW)^1/2] whereMW is the molecular mass andD ₁ represents the one-dimensional Debye function. Polyoxides show a higher intramolecular theta temperature, but a lower intermolecular theta temperature. Double bonds and phenylene groups in the chain increase the intramolecular theta temperature.Dedicated to Prof. Dr. F. H. Müller.On leave from the Lumumba Peoples' Friendship University, Moscow, USSR.     

Sulfonated polysulfone-preparative routes and applications in membranes used for pressure driven techniques

There is much enthusiasm now-a-days for efforts to improve membrane performances. Membrane modification is one of the critical approaches needed for the development of membrane science and technology. The beauty of research in this orientation is that it is a dynamic process that moves forward slowly and recommendations are made based on the science available. In this regard sulfonation of polysulfones is an excellent move. The present review demonstrates different sulfonation strategies of polysulfones as well as promoting applications in pressure driven separation sciences (viz. salt, macromolecule, organic separation from water). It shows that marked path is promising one.     

Controlling the Surface Functionalization of Ultrasmall Gold Nanoparticles by Sequence-Defined Macromolecules

Ultrasmall gold nanoparticles (diameter about 2 nm) were surface-functionalized with cysteine-carrying precision macromolecules. These consisted of sequence-defined oligo(amidoamine)s (OAAs) with either two or six cysteine molecules for binding to the gold surface and either with or without a PEG chain (3400 Da). They were characterized by ¹H NMR spectroscopy, ¹H NMR diffusion-ordered spectroscopy (DOSY), small-angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy. The number of precision macromolecules per nanoparticle was determined after fluorescent labeling by UV spectroscopy and also by quantitative ¹H NMR spectroscopy. Each nanoparticle carried between 40 and 100 OAA ligands, depending on the number of cysteine units per OAA. The footprint of each ligand was about 0.074 nm² per cysteine molecule. OAAs are well suited to stabilize ultrasmall gold nanoparticles by selective surface conjugation and can be used to selectively cover their surface. The presence of the PEG chain considerably increased the hydrodynamic diameter of both dissolved macromolecules and macromolecule-conjugated gold nanoparticles.     

大分子固液界面吸附行为的数字模拟研究方法

介绍了随机数字模拟方法在研究链状大分子吸附行为的一般原理,以立方格子模型的自避行走为例,分析了模型的建立、初始位形的产生以及分子链运动的处理方法.回顾了随机数字模拟方法在研究大分子界面吸附行为方面的发展状况.预测了随机数字模拟方法在大分子吸附行为研究方面的应用前景.     

IR laser ablation of doped poly(methyl methacrylate)

We investigate the TEA CO₂ laser ablation of films of poly(methyl methacrylate), PMMA, with average M_W 2.5, 120 and 996 kDa doped with photosensitive compounds iodo-naphthalene (NapI) and iodo-phenanthrene (PhenI) by examining the induced morphological and physicochemical modifications. The films casted on CaF₂ substrates were irradiated with a pulsed CO₂ laser (10P(20) line at 10.59 μm) in resonance with vibrational modes of PMMA and of the dopants at fluences up to 6 J/cm². Laser induced fluorescence probing of photoproducts in a pump and probe configuration is carried out at 266 nm. Formation of naphthalene (NapH) and phenanthrene (PhenH) is observed in NapI and PhenI doped PMMA, respectively, with relatively higher yields in high M_W polymer, in similarity with results obtained previously upon irradiation in the UV at 248 nm. Above threshold, formation of photoproducts is nearly complete after 200 ms. As established via optical microscopy, bubbles are formed in the irradiated areas with sizes that depend on polymer M_W and filaments are observed to be ejected out of the irradiated volume in the samples made with high M_W polymer. The implications of these results for the mechanisms of polymer IR laser ablation are discussed and compared with UV range studies.     

Effect of the surface-modifying macromolecules on the duration of the surface functionalization

Functionalization of polystyrene films by the preferential surface enrichment of surface-modifying macromolecules (SMM) to achieve a hydrophilic surface with long effective duration is described. The comb-like amphiphilic copolymers (PKG-g-PS) based on styrene-maleic anhydride copolynier (SMA) backbone was synthesized by esterification of SMA with poly(ethylene glycol) (PEG). When PEG-g-PS was melt blended with polystyrene, the preferential surface enrichment of PEG-g-PS was much evident resulting in the large increase of the surface polarity. The effective duration of the surface functionalizatoin was also hugely extended as SMMs were added into the blends. Furthermore, more polyether chain segments on PEG-g-PS could selectively migrate to the surface by the inducement of polar solvent. Compared with the PEG-g-PS/PS and PEG/PEG-g-PS/PS blends, the surface polarity and the effective duration of surface modification both increased greatly when PEG-g-PS was used as the compatibilizer of PEG/PS blends. It was an effective solution to balance the conflict between the duration and efficiency of the surface-modifying additives.     

2,3,7,8,12,13‐Hexaaryltruxenes: An ortho‐Substituted Multiarm Design and Microwave‐Accelerated Synthesis toward Starburst Macromolecular Materials with Well‐Defined π Delocalization

We present herein a novel design and the efficient synthesis towards a “homogeneous” starburst fluorene system based on the novel 2,3,7,8,12,13‐hexaaryltruxene scaffold. Controlled microwave heating provides a facile and powerful approach for each step in the synthesis of these bulky materials with large steric hindrance, suggesting an avenue to access structurally well‐defined complex organic semiconductors (OSCs) rapidly and conveniently with high yield and purity. The resulting materials exhibited good thermal stability and an excellent glassy structure as revealed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) as well as wide‐angle X‐ray diffraction (WAXD) studies. Moreover, compared with their corresponding three‐arm‐substituted counterparts T1 – T4 , the introduction of the ortho substituents around the truxene core in Tr1 – Tr4 results in significant blueshifts (of 7–24 nm) of the absorption maxima λ_max and higher energy optical gaps (E_g). Comparative studies with corresponding linear, rod‐shaped oligofluorene counterparts (OFX) have revealed that the longest para‐conjugated segment in the TrX (X=1–4) structures plays the dominant role in determining their electronic properties. UV/Vis data and cyclic voltammetry (CV) investigations have indicated that there is little electronic interaction between the arms, even for the shortest armed oligomer Tr1 . A clear linear relationship of both 1/λ_max and E_g with the inverse of (n+1) for these branched systems was found. Our findings highlight a novel molecular design comprising an ortho‐substituted, multiarmed architecture that would allow the introduction of isotropic physical and/or mechanical properties, while at the same time maintaining most of the important electronic properties of the rod‐shaped constituents of a fully conjugated system.