Structural mobility of molecular bottle-brushes investigated by NMR relaxation dynamics

The structural mobility of monomeric units of molecular bottle-brushes was studied by a systematic evaluation of NMR relaxation dynamics. The spin-spin relaxation time (T₂) was determined by Carr-Purcell-Meiboom-Gill (CPMG) NMR spectroscopic measurements. T₂ for protons that reside on the exterior and interior of the bottle-brush macromolecules varied with the grafting density and side chain length in bottle-brush copolymers. Poly((2-(2-bromopropionyloxy)ethyl methacrylate-stat-methyl methacrylate)-graft-butyl acrylate) (poly((BPEM-stat-MMA)-graft-PBA) was studied as a model brush copolymer. The T₂ values for protons of MMA units in the brush backbone significantly decreased with increasing side chain length and grafting density of PBA. The mobility and relaxation times T₂ for the side chain PBA protons decreased with grafting density. However, after initial increase, the relaxation times eventually decreased with PBA side chain length.     

Conformation in solution of side-chain liquid crystal polymers as a function of the mesogen-graft amount

The conformation of side-chain liquid crystal polymers with different mesogen-graft amounts has been studied by small-angle neutron scattering in dilute solutions of toluene-d8 and THF-d8. It is shown that the radius of gyration increases by about twofold when the mesogen-graft amount increases from 0 to 100%, which suggests that the persistence length of the backbone increases by about 4-fold. Comparison with the results reported in the literature on the melt state suggests that the persistence length is not an intrinsic property of side chain liquid crystal polymers, but depends on inter-chain interactions.     

Self-Consistent Field Analysis of Molecular Bottle-Brushes with Primary and Secondary Side Chains: Induced Persistence Length and Lateral Thickness

Macromolecules may feature liquid crystalline behavior when the chain aspect ratio, that is the ratio between the chain persistence length and the cross-sectional thickness of its segments, is large. Scaling theory suggests that for molecular bottle-brushes under good solvent condition the induced persistence length does not depend on the chain architecture but only on the amount of segments in the side chains per unit length of the backbone. Numerical self-consistent field results are presented for macromolecular bottle-brushes with side chains of variable architecture attached at regular intervals along the backbone chain. We consider side chains (flexible “flagstaffs”), which feature one branch-point onto which secondary side chains (the “flag”) emanate. We varied the distance of this branch-point from the main chain as our tuning parameter, resembling the “raising of the flag.” For a given height of the flags, that is when the mass-distribution along a side chain is architecturally fixed, the induced persistence length is a function of the branching parameter (ratio between the length of the longest path and the total number of segments in the graft). We found that the induced persistence length and hence the chain aspect ratio, vary non-monotonically with the height of the flags. The lowest aspect ratio is found when the flag is raised to about a quarter of the full height of the flagstaff. The induced persistence length is independent of this height when upon bending the translocation of the side chains from compressed to expanded regions is artificially suppressed, which leads us to speculate that the non-monotonic behavior of aspect ratio is related to the efficiency of side chains to partly translocate themselves upon bending.     

Poly(l-lactide) comb polymer brushes on the surface of clay layers

Poly(l-lactide) (PLLA) comb polymers on poly(hydroxyethyl methacrylate) (PHEMA) backbone were prepared on the surface of clay layers by a combination of in situ atom transfer radical polymerization (ATRP) and ring-opening polymerization. An ATRP initiator with a quaternary ammonium salt end group was intercalated into the interlayer spacing of clay. PHEMA polymer brushes on the surface of clay layers were prepared by in situ ATRP. PLLA comb polymers on PHEMA backbone were prepared by ring-opening polymerization. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that with the increase of comb chain length more and more exfoliated structure was created. Aggregation of wormlike comb polymer brushes on the surface of clay layers was observed by TEM. Differential scanning calorimeter (DSC) results indicated that both the melting points and glass transition temperatures of the comb polymer brushes increase with the increase of comb chain length. The equilibrium melting temperature of the comb polymer brush on the surface of clay layers is lower than cleaved polymer. An atomic force microscopy (AFM) image proves the formation of wormlike structure by cleaved comb polymers.     

Structure and liquid crystalline phases of amphiphilic side chain polymers in aqueous solution

Functional amphiphilic molecules which form liquid crystalline (l.c.) phases in aqueous solutions, can be polymerized to amphiphilic side chain polymers. Depending on the formation of the polymer backbone via the hydrophobic (type A) or hydrophilic part (type B) of the monomer, it can be differentiated between two polymers. For both types of polymers a model is proposed which explains their micellar association in solution. In aqueous solutions polymers of type A should form normal spherical, rodlike and disc-like micelles, while polymers of type B should form the corresponding reversed micelles. The phase behavior in aqueous solutions is investigated with two model systems of monomer/side chain polymer of type A. It is shown that the polymers exhibit l.c. phases, which are stable within a broader concentration range, as well as to higher temperatures compared to the corresponding monomers. The structures of the l.c. phases are in accordance with the model considerations.     

Influence of tert-amine groups on the solubility of polymers in CO2

There is a need to develop new, non-fluorous polymers that are highly soluble in CO₂. Experimental evidence indicates that tertiary amine and pyridine groups may exhibit favorable Lewis acid-Lewis base type interactions with CO₂. It is therefore reasonable to assume that incorporation of tertiary amines into the side chain or backbone of non-fluorous polymers may impart a degree of CO₂-solubility to the polymer. We present experimental results for eight different tert-amine-containing polymers. Of these polymers, only propyl dimethylamine-functionalized poly(dimethylsiloxane) is soluble in CO₂ at temperatures and pressures accessible in our experiments, but even this polymer is less soluble than non-functionalized poly(dimethylsiloxane) at the same chain length. We have performed ab initio calculations on tertiary amine-containing moieties representative of some of the polymers examined experimentally. Our calculations confirm that amine-CO₂ interactions are indeed energetically favorable. However, we also find that the moiety self-interactions are typically more favorable than the CO₂-moiety interactions. This indicates that the lack of solubility of amine-containing polymers in CO₂ is a direct result of strong polymer-polymer interactions.     

液晶高分子的分子设计

简单介绍了液晶高分子的结构特点，分类及其应用状况，详细介绍了主链型和侧链型液晶高分子设计的新进展，根据溶臻主链型液晶高分子和热臻主链型液晶高分子分子结构的不同，提出今后设计主链液晶高分子的主要任务，从主链结构，液晶基元类型和柔性间隔出发介绍了侧链液晶高分子分子设计的关键，最后介绍了液晶高分子分子设计的发展趋势。     

Side chain polysiloxane liquid crystals and their behaviour in electric fields

Optical and electro-optical properties of side chain liquid crystalline polymers are described. The polymers studied were homopolysiloxanes with mesogenic side groups separated from the polymer backbone by flexible polymethylene spacers of varying length. The effect of the flexible spacer on the phase properties and electric field effects will be discussed. Low frequency a.c. fields induced a turbulent scattering texture, whilst at higher frequencies (> 1 kHz) a homeotropic alignment was obtained. The latter effect leads to high contrast displays which are durably stored at temperatures well above the glass transition. Various parameters affecting the response of the polymers to applied fields will also be discussed. These include temperature, frequency and magnitude of the electric field, film thickness and the length of the flexible spacer.     

Computer simulation on the self-assembly of associating polymers

We present the results of Monte Carlo simulations of self-assembly in melt of pseudo-block copolymer formed through the association of associating polymer chains with attractive end-groups (sticker sites). Complexities of the phase structures result from these pseudo-block copolymers strongly depend on parameters, such as attractive interaction strength between two stickers and chain length of associating polymers. The weak, intermediate and strong interactions between two stickers lead, respectively, to the macro-separated, disordered and ordered lamellar phase structures. The ordered lamellar phases formed by these pseudo-block copolymers are more stable than that formed by pure diblock copolymers. Pseudo-block copolymers with shorter associating polymer chain prefer to form ordered lamellar phase and that with longer associating chain tend to form disordered phase.     

N,N-双烷基壳聚糖结构对其自组装泡囊性质的影响

合成了不同主链相对分子质量的N,N-双辛烷基壳聚糖,N,N-双癸烷基壳聚糖及N,N-双十二烷基壳聚糖,并制备了相应的自组装泡囊,比较研究了侧链长度和主链相对分子质量对载药泡囊药物释放行为的影响。结果表明这类N,N-双长链烷基壳聚糖可形成粒径为100～150 nm的泡囊。原子力显微镜表明,侧链长度对N,N-双烷基壳聚糖泡囊的曲率有较明显影响,主链相对分子质量对泡囊的粒径影响较大。药物释放行为表明,侧链长度或主链相对分子质量的增大会导致药物释放速率的降低,达到平衡时的药物释放率也较低,而其相应自组装泡囊的载药量和包埋率却有所提高。     

Side-chain crystallization and phase transition of poly[styrene-co-(maleic anhydride)]-g-alkylamine comb-like polymers

Taking ? NHCO? as the chemical spacer, poly[styrene-co-(maleic anhydride)]-g-alkylamine (SMACnN) comb-like polymers are prepared through grafting reaction between poly[styrene-co-(maleic anhydride)] and n-alkylamine with n changing from 12 to 18. SMACnN comb-like polymers present an obvious crystallization behavior owing to the introduced alkyl side chains, and the melting temperature and enthalpy of the side-chain crystallites increase from 9.2 to 41.6 °C and from 6.0 to 17.6 kJ mol^?1, respectively, showing a variation with the side-chain length. At least 12 side-chain carbon atoms are required to pack into a hexagonal crystal structure for SMACnN comb-like polymers. Fourier transform infrared and X-ray analysis results demonstrate the phase transition from hexagonal to an amorphous state, and the conformationally disordered alkyl chains affect the packing manner of side-chain crystallites. Including the side-chain length and polymer backbone, the chemical spacer between the side chain and the main chain influences the formation of side-chain crystallites and the phase transition process. So, the study of SMACnN further strengthens the understanding of the phase transition behavior and side-chain crystallization of comb-like polymers triggered by the side-chain length and the microstructure differences. © 2021 Society of Industrial Chemistry.     

Synthesis of side-chain liquid crystalline polyacrylates,polymethacrylates and polysiloxanes containing 4-cyano-biphenyl 4-alkanyloxybenzyl ether side groups

Summary The synthesis and characterization of side-chain liquid crystalline polyacrylates, polymethacrylates and polysiloxanes containing 4-cyanobiphenyl 4-alkanyloxybenzyl ether side groups are presented. All polymers display respectively a smectic A mesophase. The influence of the polymer backbone flexibility on the phase transition temperatures of the synthesized side-chain liquid crystalline polymers is discussed. The results demonstrate that flexible backbones enhance the decoupling of the motions of the side chain and main chain. Therefore, among three kinds of polymer backbones which contain the same mesogenic side groups, the most flexible one, i.e., polysiloxane, reveals a highest isotropization temperature and a widest temperature range of mesophase.     

Anisotropic properties of aromatic polyamides containing non-rigid rodlike units

Summary Three kinds of aromatic polyamides were synthesized by Higashi reaction: aromatic polyamides with even, odd number of methylenes and a meta phenylene as a joint in the main chain. Each polymer consisted of 7 p-phenylene-amide elements as a rigid segment. The polymer with even number of methylenes showed a lyotropic liquid crystalline behavior and a broader biphasic region than the fully para aromatic polyamide such as poly(p-phenylene terephthalamide). Most polymers with odd number of methylenes did not form a liquid crystalline phase and showed a crystallo-solvate. Exceptionally, the polymer with glutaryl unit was observed to have the swollen gel of colored pattern by the polarized microscope. The zigzag polymer, characterized by the highly kinetic rigidity, revealed an anisotropic gel phase in a solution.     

Synthesis of hypergrafted poly[4-(N,N-diphenylamino)methylstyrene] through tandem anionic-radical polymerization of radical-inimer

In this paper, we present a tandem anionic-radical approach for synthesizing hypergrafted polymers. We prepared 4-(N,N-diphenylamino)methylstyrene (DPAMS) as a new radical-based inimer. Linear PDPAMS was prepared through anionic polymerization. Hypergrafted PDPAMS was synthesized through the self-condensing vinyl polymerization of DPAMS with linear PDPAMS. The linear backbone of PDPAMS, which incorporated latent radical initiating sites, served as a ‘hyperlinker’ to link hyperbranched side chains. The molecular weights of hypergrafted polymers increased as the length of the linear backbone chain increased. The hypergrafted structure of the resulting polymer was confirmed using a conventional gel permeation chromatograph apparatus equipped with a multiangle light scattering detector, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. This strategy can be applied to synthesize other complex architectures based on hyperbranched polymers by changing the structure of a polymer backbone through anionic polymerization.     

Polydisperse Brush with the Linear Density Profile

Macromolecules densely end-grafted to a planar solid surface form a polymer monolayer (brush). It is known that, in a good solvent, the density profile of monodisperse brushes parabolically decays on moving away from the plane. Using the analytical theory and computer simulation methods, we studied the structure of a polydisperse brush from homopolymers, for which molecular-mass distribution is set by the Schulz–Zimm distribution. It is found that, at a polydispersity index of 1.143, the polymer brush in a good solvent has a linear density profile. In this brush, the average distance of chain ends to the grafting plane is proportional to the square of their contour length. If any chain of the brush is chemically modified so that it will be able to adsorb on the grafting surface, then the adsorption of this chain inside the brush will proceed via a discontinuous first-order phase transition with the bimodal distribution of the order parameter (free end height). This transition has unusual features: the energy of adsorption corresponding to the midpoint of the transition is proportional to the contour length of the adsorbing chain N, the sharpness of the transition is proportional to N², and the height of the barrier separating adsorbed and desorbed states is proportional to N³. The predicted dependences are verified by computer simulation.     

Synthesis and characterization of side‐chain liquid‐crystalline polyacrylates containing azobenzene moieties

Syntheses of novel liquid‐crystalline polymers containing azobenzene moieties were performed by a convenient route with an acrylate backbone. The azobenzenes were key intermediates of the monomers, and side‐chain liquid‐crystalline polymers were prepared, that is, poly[α‐{4‐[(4‐acetylphenyl)azo]phenoxy}alkyloxy]acrylates, for which the spacer length was 3 or 11 methylene units. In addition, poly[3‐{4‐[(3,5‐dimethylphenyl)azo]phenoxy}propyloxy]acrylate was prepared with a spacer length of 3 methylene units. The structures of the precursors, monomers, and polymers were characterized with Fourier transform infrared, ¹H‐NMR, and ¹³C‐NMR techniques. The polymers were obtained by conventional free‐radical polymerization with 2,2′‐azobisisobutyronitrile as an initiator. The phase‐transition temperatures of the polymers were studied with differential scanning calorimetry, and the phase structures were evaluated with a polarizing optical microscopy technique. The results showed that two of the monomers and their corresponding polymers exhibited nematic liquid‐crystalline behavior, and one of the monomers and its corresponding polymer showed smectic liquid‐crystalline behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2653–2661, 2002     

The Effect of the Structural Elements on the Properties of Side Chain Mesomorphic Polymers

The thermal properties of mesomorphic polymers depend on the relative amounts of the different structural elements (hard core, flexible chains, main chain) of the polymer. Literature data are compared with the conclusions obtained from the three-component thermodynamic model of side chain mesomorphic polymers. The effects of the different soft elements (main chain, spacer and p-alkyl or alkoxy chain) depend first of all on the length of the spacer and its interaction with the main chain. The thermal properties of the polymer can be well regulated by varying the different structural elements of the homo- and co-polymers. The glass transition temperature (T_g) of the polymer can be reduced by building O and N atoms into the main chain and/or by binding the side chains on 3rd, 4th, etc. atoms of the main chain. The T_g can be further reduced by increasing the length of the spacer. If the spacers are long enough, the layer type structures are favored, with p-alkoxy chains behaving also as a plasticizer of the main chain. The clearing point can be influenced by copolymerization of monomers with different hard cores. The three-component thermodynamic model of side-chain mesomorphic polymers well explains the effect of different structural elements on the structure and properties of these polymers.     

Induced helical backbone conformations of self-organizable dendronized polymers

Control of function through the primary structure of a molecule presents a significant challenge with valuable rewards for nanoscience. Dendritic building blocks encoded with information that defines their three-dimensional shape (e.g., flat-tapered or conical) and how they associate with each other are referred to as self-assembling dendrons. Self-organizable dendronized polymers possess a flat-tapered or conical self-assembling dendritic side chain on each repeat unit of a linear polymer backbone. When appended to a covalent polymer, the self-assembling dendrons direct a folding process (i.e., intramolecular self-assembly). Alternatively, intermolecular self-assembly of dendrons mediated by noncovalent interactions between apex groups can generate a supramolecular polymer backbone. Self-organization, as we refer to it, is the spontaneous formation of periodic and quasiperiodic arrays from supramolecular elements. Covalent and supramolecular polymers jacketed with self-assembling dendrons self-organize. The arrays are most often comprised of cylindrical or spherical objects. The shape of the object is determined by the primary structure of the dendronized polymer: the structure of the self-assembling dendron and the length of the polymer backbone. It is therefore possible to predictably generate building blocks for single-molecule nanotechnologies or arrays of supramolecules for bottom-up self-assembly. We exploit the self-organization of polymers jacketed with self-assembling dendrons to elucidate how primary structure determines the adopted conformation and fold (i.e., secondary and tertiary structure), how the supramolecules associate (i.e., quaternary structure), and their resulting functions. A combination of experimental techniques is employed to interrogate the primary, secondary, tertiary, and quaternary structure of the self-organizable dendronized polymers. We refer to the process by which we interpolate between the various levels of structural information to rationalize function as retrostructural analysis. Retrostructural analysis validates our hypothesis that the self-assembling dendrons induce a helical backbone conformation in cylindrical self-organizable dendronized polymers. This helical conformation mediates unprecedented functions. Self-organizable dendronized polymers have emerged as powerful building blocks for nanoscience by virtue of their dimensions and ability to self-organize. Discrete cylindrical and spherical structures with well-defined dimensions can be visualized and manipulated individually. More importantly, they provide a robust framework for elucidating functions available only at the nanoscale. This Account will highlight structures and functions generated from self-organizable dendronized polymers that enable integration of the nanoworld with its macroscopic universe. Emphasis is placed on those structures and functions derived from the induced helical backbone conformation of cylindrical self-organizable dendronized polymers.