Topological Polymer Chemistry Enters Surface Science: Linear versus Cyclic Polymer Brushes

The cyclic polymer topology strongly alters the interfacial, physico‐chemical properties of polymer brushes, when compared to the linear counterparts. In this study, we especially concentrated on poly‐2‐ethyl‐2‐oxazoline (PEOXA) cyclic and linear grafts assembled on titanium oxide surfaces by the “grafting‐to” technique. The smaller hydrodynamic radius of ring PEOXAs favors the formation of denser brushes with respect to linear analogs. Denser and more compact cyclic brushes generate a steric barrier that surpasses the typical entropic shield by a linear brush. This phenomenon, translates into an improved resistance towards biological contamination from different protein mixtures. Moreover, the enhancement of steric stabilization coupled to the intrinsic absence of chain ends by cyclic brushes, produce surfaces displaying a super‐lubricating character when they are sheared against each other. All these topological effects pave the way for the application of cyclic brushes for surface functionalization, enabling the modulation of physico‐chemical properties that could be just marginally tuned by applying linear grafts.     

环形侧链聚合物刷的合成与表征

通过grafting-onto方法合成高侧链接枝密度的环形侧链聚合物刷并进行结构表征.先通过开环易位聚合(ROMP)制备带有炔基侧基的线形聚降冰片烯衍生物主链(l-PND),通过原子转移自由基聚合(ATRP)和铜催化的叠氮-炔环加成(Cu AAC)反应制备带有一个叠氮基的环形聚丙烯酸叔丁酯侧链(c-Pt BA),再利用Cu AAC反应将环形侧链高密度地接入主链,得到环形侧链聚合物刷.通过核磁氢谱(1H-NMR)、凝胶渗透色谱(GPC)和红外光谱(IR)对聚合物主/侧链及聚合物刷的结构和组成进行了表征.该聚合物刷主链聚合度为400,高接枝密度的环形侧链使主链构象伸展.聚合物刷在原子力显微镜(AFM)下呈单分子蠕虫形貌(柱状形貌),分子长度为200 nm,直径为30 nm.     

Structures and Surface States of Polymer Brushes in Good Solvents: Effects of Surface Interactions

The influence of the surface interaction on the mesoscopic structure of grafted polymers in good solvents has been examined. At high surface coverage, tethered polymers are in the brush state and the parabolic segment density profile is confirmed by self-consistent field theory (SCFT) calculations. It is found that this is a universal behavior for a whole range of surface interactions from complete repulsion to strong attraction. More interestingly, finite surface repulsion may lead to the maximum in the proximal layer of its segment density profile, which is significantly different from both the depletion layer of pure repulsion and the adsorbing layer of attraction. In addition to the brush state on both repulsive and attractive surfaces, three additional surface states were identified by analyzing the scaling behavior of the layer thickness of polymer brushes: the mushroom state on repulsive substrates, the dilute and the semidilute surface states on attractive substrates.     

聚合物表面刷子模型的形态结构及动力学特性

阐述了稀溶液及聚合物溶液中高分子链及其刷子模型在外力和流场作用下的结构形态及动力学特性。单分子链在外力作用下经历从嗽叭形到花杂形的变形,最后完全解缠而伸展,单分散性刷子模型中的单链节密度在沿刷子高度方向上呈抛物线形分布。在多分散性刷子模型中分子链的结构形态呈多样性变化,溶液中球形界面刷子之间的作用力与吸附的平衡状态有关,电解质溶液中的刷子及带电刷子在溶液中的电中性分布文章也有详细阐述。     

SuFEx on the Surface: A Flexible Platform for Postpolymerization Modification of Polymer Brushes

Polymer brushes present a unique architecture for tailoring surface functionalities due to their distinctive physicochemical properties. However, the polymerization chemistries used to grow brushes place limitations on the monomers that can be grown directly from the surface. Several forms of click chemistry have previously been used to modify polymer brushes by postpolymerization modification with high efficiency, however, it is usually difficult to include the unprotected moieties in the original monomer. We present the use of a new form of click chemistry known as SuFEx (sulfur(VI) fluoride exchange), which allows a silyl ether to be rapidly and quantitatively clicked to a polymer brush grown by free‐radical polymerization containing native ‐SO₂F groups with rapid pseudo‐first‐order rates as high as 0.04 s^?1. Furthermore, we demonstrate the use of SuFEx to facilely add a variety of other chemical functional groups to brush substrates that have highly useful and orthogonal reactivity, including alkynes, thiols, and dienes.     

Self‐Assembly and Covalent Fixation for Topological Polymer Chemistry

A novel methodology (electrostatic self‐assembly and covalent fixation) has been proposed for designing various nonlinear polymer topologies, including monocyclic and polycyclic polymers, cyclic macromonomers and cyclic telechelics (kyklo‐telechelics), a‐ring‐with‐a‐branch topology polymers and polymeric topological isomers, as well as branched model polymers, such as star polymers and polymacromonomers. Thus, new telechelic polymer precursors having a moderately strained cyclic onium salt group as single or multiple end groups and carrying multifunctional carboxylates as the counterions were prepared through an ion‐exchange reaction. A variety of electrostatic self‐assemblies of these polymer precursors, formed particularly in dilute organic solution, was then subjected to heat in order to convert the ionic interactions into covalent linkages by ring‐opening reaction, and to produce topologically unique, nonlinear polymer architectures in high efficiency.     

圆柱表面上高分子共混刷微相分离的自洽场理论研究

我们运用高分子自洽场理论方法,结合“masking”技术,研究了高分子共混刷接枝到无限长圆柱表面上的微相分离行为. 理论预言了柱面上高分子共混刷的两种典型相分离形态：平行条纹相和环状相. 我们考察了圆柱半径、接枝密度以及相互作用参数对二者的影响,给出了体系在不同参数下相分离形态的相图,并且从相分离程度的角度对平行条纹相和环状相之间的转变作了解释. 我们还研究了平行条纹相相区数目以及环状相交替周期随圆柱半径的变化. 理论所预言的平行条纹相和环状相的存在以及体系参数对其稳定性的影响将有助于实验上合理设计、制备这类新颖的高分子刷材料.     

Bergman Cyclization in Polymer Chemistry and Material Science

Bergman cyclization of enediynes, regarded as a promising strategy for anticancer drugs, now finds its own niche in the area of polymer chemistry and material science. The highly reactive aromatic diradicals generated from Bergman cyclization can undergo polymerization acting as either monomers or initiators of other vinyl monomers. The former, namely homopolymerization, leads to polyphenylenes and polynaphthalenes with excellent thermal stability, good solubility, and processability. The many remarkable properties of these aromatic polymers have further endowed them to be manufactured into carbon‐rich materials, e.g., glassy carbons and carbon nanotubes. Whereas used as initiators, enediynes provide a novel resource for high molecular weight polymers with narrow polydispersities. The aromatic diradicals are also useful for introducing oligomers or polymers onto pristine carbonous nanomaterials, such as carbon nano‐onions and carbon nanotubes, to improve their dispersibility in organic solvents and polymer solutions.

     

Carbohydrate‐Responsive Surface Adhesion Based on the Dynamic Covalent Chemistry of Phenylboronic Acid‐ and Catechol‐Containing Polymer Brushes

A glue, based on dynamic covalent chemistry, with a strong adhesion (2.38 kg cm^?2), water resistance and carbohydrate responsive reversibility is presented. Using surface initiated atom transfer radical polymerization (SI‐ATRP), glass and silicon surfaces were coated with copolymers functionalized with phenylboronic acids and catechols. In combination with microcontact printing (μCP) these polymer brushes give access to a carbohydrate responsive “supramolecular Velcro”.     

Surface Initiated Polymerization on Pulsed Plasma Deposited Polyallylamine: A Polymer Substrate‐Independent Strategy to Soft Surfaces with Polymer Brushes

The deposition of polyallylamine (PAA) adlayers by pulsed plasma polymerization on various types of polymeric substrates has been explored as a general route to amino functionalized polymeric surfaces. These amino groups are highly suitable for anchoring an atom transfer radical polymerization (ATRP) initiator via a robust amide linkage. Subsequent surface initiated ATRP (SI‐ATRP) of monomethoxy oligo(ethylene glycol) methacrylate (MeOEGMA) resulted in polyMeOEGMA brush grafted polymer surfaces. This combined strategy of pulsed plasma polymerization with SI‐ATRP was demonstrated for five different polymeric substrates namely polyether ether ketone (PEEK), polyethylene terephthalate (PET), polyimide (PI), polypropylene (PP), and polytetrafluoroethylene (PTFE). Analysis of brush layers by attenuated total reflection infrared (ATR‐IR) spectroscopy as well as X‐ray photoelectron spectroscopy (XPS) fully corroborated the success of the proposed strategy for all substrate types.

     

Particle Penetration into Polydisperse Polymer Brushes: A Theoretical Analysis

Based on theoretical analysis, the effect of polydispersity on particle penetration into polydisperse polymer brushes is investigated. Three different polydispersities representing sharp, moderate, and extremely wide chain length distributions are chosen, since the corresponding explicit expressions of brush density at these polydispersities are available. To simplify the discussion, this study is restricted to spherical particles of small size which ensure that the particle insertion only causes local conformational perturbations. By analyzing the particle distribution, it is found that polydispersity always facilitates particle penetration. This prediction is confirmed by analyzing the surface fluctuations of the brushes. Interestingly, uniform scaling relations are observed for particles penetrating into monodisperse and moderately polydisperse brushes. The uniformity predicted by monodisperse and moderately polydisperse brushes originates from the same asymptotic behavior of their densities approaching the brush edge. This indicates that polydispersity brings significant influence only at high polydispersities.     

Synthesis of Hydrophobic Polymer Brushes on Silica Nanoparticles Via the Combination of Surface-Initiated ATRP,ROP and Click Chemistry

A fascinating nanoobject, hydrophobic polymer brushes with a hard core of silica nanoparticles and a relatively soft shell of polystyrene-block-poly(? -caprolactone) (PS-b-PCL), was easily constructed by surface-initiated atom transfer radical polymerization (ATRP) of styrene, ring-opening polymerization (ROP) of ?-caprolactone and click reaction. The structure and morphology of the as-prepared hybrid nanomaterials were characterized and confirmed by FTIR, ¹H-NMR, TGA and TEM. We believe that the breakthrough associated with formation of such a complex nanoobject would open a door for the fabrication of novel functional nanomaterials or nanodevices with designable structure and tailor-made properties.     

Molecular Transport within Polymer Brushes: A FRET View at Aqueous Interfaces

Molecular permeability through polymer brush chains is implicated in surface lubrication, wettability, and solute capture and release. Probing molecular transport through polymer brushes can reveal information on the polymer nanostructure, with a permeability that is dependent on chain conformation and grafting density. Herein, we introduce a brush system to study the molecular transport of fluorophores from an aqueous droplet into the external “dry” polymer brush with the vapour phase above. The brushes consist of a random copolymer of N-isopropylacrylamide and a Förster resonance energy transfer (FRET) donor-labelled monomer, forming ultrathin brush architectures of about 35 nm in solvated height. Aqueous droplets containing a separate FRET acceptor are placed onto the surfaces, with FRET monitored spatially around the 3-phase contact line. FRET is used to monitor the transport from the droplet to the outside brush, and the changing internal distributions with time as the droplets prepare to recede. This reveals information on the dynamics and distances involved in the molecular transport of the FRET acceptor towards and away from the droplet contact line, which are strongly dependent on the relative humidity of the system. We anticipate our system to be extremely useful for studying lubrication dynamics and surface droplet wettability processes.     

表面等离子体共振传感技术在高分子研究中的应用

介绍了表面等离子体共振 (SPR)的基本原理和SPR传感器技术的应用现状 ,综述了SPR传感器在高分子科学研究中的应用和发展前景。     

Structure of Polymer Brushes in Cylindrical Tubes: A Molecular Dynamics Simulation

Summary: Molecular dynamics simulations of a coarse‐grained bead‐spring model of flexible macromolecules tethered with one end to the surface of a cylindrical pore are presented. Chain length N and grafting density σ are varied over a wide range and the crossover from “mushroom” to “brush” behavior is studied for three pore diameters. The monomer density profile and the distribution of the free chain ends are computed and compared to the corresponding model of polymer brushes at flat substrates. It is found that there exists a regime of N and σ for large enough pore diameter where the brush height in the pore exceeds the brush height on the flat substrate, while for large enough N and σ (and small enough pore diameters) the opposite behavior occurs, i.e. the brush is compressed by confinement. These findings are used to discuss the corresponding theories on polymer brushes at concave substrates.

Snapshot picture of a brush grafted inside of a cylinder, for , , displaying different chains in distinct colors in order to be able to distinguish them. Top shows a side view of the cylinder, and the lower part a view of the cross‐section. Note that the particles forming the cylindrical wall are not displayed.     

‘Click’ Chemistry in Polymer and Materials Science

The modification of polymers after the successful achievement of a polymerization process represents an important task in macromolecular science. Cycloaddition reactions, among them the metal catalyzed azide/alkyne ‘click’ reaction (a variation of the Huisgen 1,3‐dipolar cycloaddition reaction between terminal acetylenes and azides) represents an important contribution towards this endeavor. They combine high efficiency (usually above 95%) with a high tolerance of functional groups and solvents, as well as moderate reaction temperatures (25–70 °C). The present review assembles recent literature for applications of this reaction in the field of polymer science (linear polymers, dendrimers, gels) as well as the use of this and related reactions for surface modification on carbon nanotubes, fullerenes, and on solid substrates, and includes the authors own publications in this field. A number of references (>100) are included.

     

Dissipative Particle Dynamics Simulations of Polymer Brushes: Comparison with Molecular Dynamics Simulations

Summary: The structure of polymer brushes is investigated by dissipative particle dynamics (DPD) simulations that include explicit solvent particles. With an appropriate choice of the DPD interaction parameters , we obtain good agreement with previous molecular dynamics (MD) results where the good solvent behavior has been modeled by an effective Lennard–Jones potential. The present results confirm that DPD simulation techniques can be applied for large length scale simulations of polymer brushes. A relation between the different length scales and is established.

Polymer brush at a solid–liquid interface.