Microstructure Induced Rigidity of Polysiloxane Yielding Hierarchical Self‐Assembly of Alkyl Side Chains

The influence of a backbone microstructure on the side chain crystallization of a comb‐like polymer is analyzed systematically using a tailor‐made random versus block siloxane copolymer system. While the side alkyl chains of the random siloxane undergo a stepwise order–disorder (OD) transition to form well‐ordered orthorhombic structure at low temperature, the packing structure of the alkyl chains pertaining to the block siloxane maintains their original hexagonal lattice up to a temperature of as low as 173 K. The unit lattice ordering of side alkyl chains in the random siloxane polymer is also accompanied by a major restructuring of the backbone conformation ultimately losing out long range ordered structure in the solid state. The OD transitions of side alkyl chains and their dynamic relationship with the backbone conformation are established unambiguously by a combination of temperature dependent small‐angle X‐ray and wide‐angle X‐ray scattering techniques. The observed conformational variations in random versus block polymers are explicitly discussed in terms of molecular chain mobility and theory of macromolecular chain conformation.     

Structure and Properties of Poly(butyl acrylate‐block‐sulfone‐block‐butyl acrylate) Triblock Copolymers Prepared by ATRP

Summary: A series of telechelic OH polysulfones (PSU) were converted to atom transfer radical polymerization (ATRP) macroinitiators by reaction with 2‐bromoisobutyryl bromide. Three macroinitiators with different chain lengths were extended with poly(butyl acrylate) (PBA) to form ABA triblock copolymers. The structure and dynamics of the ABA triblock copolymers with PSU central segments and various molecular weight PBA side chains were investigated by small‐angle X‐ray scattering and rheology. The block copolymers form micelles with a PSU core and PBA corona. The length of each block has an important effect on the structure and resulting dynamics of the copolymers. Dynamic mechanical measurements indicate three relaxation modes: (i) PBA segmental relaxation at high frequency; (ii) PBA relaxation of the corona block at intermediate frequency; (iii) an additional relaxation process related to structural rearrangement of the micelles at low frequency. The shear modulus plateau corresponding to a soft rubbery state extends over a very broad time or temperature range because of this slow additional relaxation.

Schematic illustration of the structural elements and the bulk supramolecular structure for a symmetric triblock copolymer with a stiff central segment strongly incompatible with the other constituent.     

Sterically blocking adhesion of cells to biological surfaces with a surface-active copolymer containing poly(ethylene glycol) and phenylboronic acid.

Graft copolymers were designed that could spontaneously bind to biological surfaces and block subsequent recognition and adhesion at those surfaces. Phenylboronic acid (PBA) moieties in the polymer backbone provided binding to surfaces, forming reversible covalent complexes with cis-diols found in many biological molecules. Pendant poly(ethylene glycol) (PEG) side chains sterically protected those surfaces from subsequent interactions with other proteins and cells. The PEG and PBA grafting ratios on these poly-L-lysine-graft-(PEG;PBA) copolymers [PLL-g-(PEG;PBA)] were varied, and the polymers were tested in models relevant to undesirable wound-healing responses such as peritoneal adhesion formation and posterior capsule opacification. PLL-g-(PEG;PBA) polymers spontaneously coated tissue culture polystyrene and completely blocked rabbit lens epithelial cell adhesion to the surface over a wide range of PEG grafting ratios. PLL-g-(PEG;PBA)s with optimal grafting ratios were able to coat adsorbed serum proteins or extracellular matrices and block cell spreading on the surfaces at 4 h, although the effect was lost within 24 h. The polymer also enhanced the efficacy of surgical lysis of peritoneal adhesions in rats. The reversible covalent complexes formed by the PBA moieties on the copolymer backbone were more effective at binding biological surfaces than electrostatic interactions formed via a copolymer lacking the PBA moieties, that is, PLL-g-PEG.     

Lyotropic Lamellar Polysiloxanes with Isomeric Amphiphilic Side Chains

Summary: This paper presents the synthesis of two polymeric surfactants, consisting of a polysiloxane backbone with amphiphilic side chains of the nonionic oligo(ethylene oxide) type, and their phase behavior in aqueous solution, investigated by polarizing microscopy and deuterium NMR spectroscopy using D₂O as a probe. Two different side chains, which are isomeric glycerol derivatives, were synthesized and attached to poly(methyl hydrogen siloxane) by a hydrosilylation reaction, resulting in a tail‐type and a mid‐type polysurfactant. The side chains of the tail‐type system are fixed at the end of the hydrophobic moiety, whereas the side‐chains of the mid‐type system are tethered to the polymer backbone by a short spacer close to the hydrophilic‐hydrophobic junction of the amphiphile. Both polymers form a lamellar phase in aqueous solution over a wide range of concentrations, whereas the side chain precursors do not form lyomesophases. The cloud curve and the lamellar region are observed at lower temperatures in the mid‐type polysurfactant.

Structures of the isomeric polymers forming lamellar phases.     

Finely Tuned Fluorescence Emission of Polydiphenylacetylene Films Obtained by Copolymerization

PDPAs containing longer (octadecyl, C18) and shorter (methyl, C1) alkyl side chains in the same backbone are synthesized. The copolymerization of C1 and C18 monomers at a range of feed ratios afford high‐molecular‐weight (M _w > 10⁶) copolymers almost quantitatively. As the content of longer alkyl chain units in the copolymers increases, the emission band in the bulk film shifts to shorter wavelengths and the emission intensity increases. The lamellar layer distance increases with increasing C18 content. The excited species with shorter lifetimes decrease gradually with increasing C18 content, whereas the longer‐lasting emission increases. Fine tuning of the FL emission of PDPAs is achieved by simple copolymerization of monomers with different alkyl side‐chain lengths.     

Molecular Dynamics of Amphiphilic Random Copolymers in the Bulk: A 1H and 19F NMR Relaxometry Study

A set of amphiphilic random copolymers of poly(ethylene glycol) methacrylate (PEGMA) and perfluorohexylethyl acrylate (FA) with different compositions synthesized by atom transfer radical polymerization (ATRP) is investigated by ¹H and ¹⁹F NMR relaxometry. In particular, a thorough investigation of T₁ and T₂ relaxation times at variable temperature and copolymer composition provides the first complete and detailed characterization of the dynamics of both the main chain backbone and the side chains of the PEGMA‐co‐FA copolymers. The results highlight an intramolecular segregation of rigid main chain and mobile side chains, and an additional self‐assembling of the PEGMA and FA side chains into distinct nanodomains, driven by the hydrophobic interactions between FA side chains. The obtainment and observation of nanoscale phase separation in random copolymers is a promising achievement to the aim of controlling self‐assembly in the bulk by suitably modulating copolymers composition, which can open novel avenues to easier fabrications and applications in nanotechnologies.     

Thermoresponsive Poly(2‐Oxazoline) Molecular Brushes by Living Ionic Polymerization: Modulation of the Cloud Point by Random and Block Copolymer Pendant Chains

Molecular brushes (MBs) of poly(2‐oxazoline)s were prepared by living anionic polymerization of 2‐isopropenyl‐2‐oxazoline to form the backbone and living cationic ring‐opening polymerization of 2‐n‐propyl‐2‐oxazoline and 2‐methyl‐2‐oxazoline to form random and block copolymers. Their aqueous solutions displayed a distinct thermoresponsive behavior as a function of the side‐chain composition and sequence. The cloud point (CP) of MBs with random copolymer side chains is a linear function of the hydrophilic monomer content and can be modulated in a wide range. For MBs with block copolymer side chains, it was found that the block sequence had a strong and surprising effect on the CP. While MBs with a distal hydrophobic block had a CP at 70 °C, MBs with hydrophilic outer blocks already precipitated at 32 °C.     

Frustrated Behavior of a Side‐Chain Liquid Crystalline Polyacrylate

Polyacrylate with phenyl benzoate mesogenic side groups was synthesized and fractionated into narrow fractions. Structure and phase behavior of the narrow‐molecular‐weight samples have been studied by X‐ray diffraction. Depending on the degree of polymerization the polymer shows nematic, smectic A_d, re‐entrant nematic and new phase with two‐dimensional (2D) periodicity. Such behaviour is implicit to so‐called frustrated systems. However, the mesogenic side chains are nonpolar and thus the origin of frustration is different from that in conventional polar liquid crystals. We found that this phenomenon is steric (entropic) in nature and depends on the length of the polymer backbone. The phase transformations of mesogen side chain polyacrylates are discussed in terms of coupling between the smectic ordering of the side groups and the polymer backbone conformations.     

Direct Insertion Mass Spectrometric Analysis of Thermal Degradation of Poly(2‐alkyl‐2‐oxazoline)

Direct pyrolysis mass spectrometry is applied to investigate the thermal behavior of poly(2‐isopropyl‐2‐oxazoline) (PIPOX, a thermoresponsive polymer) and poly[2‐(3‐butenyl)‐2‐oxazoline] (PBOX, a “clickable” polymer). It is found that the thermal degradation of PIPOX is started by a loss of side chains. At slightly higher temperatures the degradation of the polymer backbone occurs by random chain scission processes. In the case of PBOX, vinyl polymerization of the side chains produces chains with variable thermal stabilities. The number of repeating units of the polymer has almost no effect on the thermal behavior of PIPOX, but significantly affects both thermal stability and degradation product distribution of PBOX.     

Effects of Different Unsaturated‐Linker‐Containing Donors on Electronic Properties of Benzobisthiadiazole‐Based Copolymers

A series of new copolymers with unsaturated‐linker‐containing donors and benzobisthiadiazole acceptors are synthesized. Two kinds of side chains (2‐octyl‐1‐dodecyl chain and siloxane‐terminated hexyl chain) are added to the polymer backbone. The introduction of unsaturated‐linker‐containing donor enhances the rigidity of the copolymers. The strong electron‐withdrawing benzobisthiadiazole units make these copolymers display very narrow bandgaps in the range of 0.75–1.26 eV. Bottom‐gate and bottom‐contact transistors based on these polymers exhibit p‐type field‐effect behavior with hole mobilities up to 1.17 × 10^?3 cm² V^?1 s^?1.     

Equilibrium Rigidity of Polyorganophosphazene Molecules

The optical anisotropy and orientation angles of polyorganophosphazene (PPhPh) molecules with different lengths and side‐chain structures have been investigated by flow birefringence and viscosimetry methods. Quantum‐chemical calculations of the optical anisotropy per monomer unit within the polymer fragments with different conformations were carried out. It was shown that both short‐range and long‐range interactions (i. e. the structure of the polymer backbone and steric interactions between side chains) influenced the conformation of the PPhPh molecules and should be taken into account for the determination of the thermodynamic rigidity value A. The experimental value of A, (50 ± 5)·10^–8 cm, obtained by different methods, adequately corresponds to the structure and observed physical parameters of the PPhPh molecules. Molecules of this class of polymers are not rigid chains in a common way (A > 150·10^–8 cm), but alternating double bonds of their backbones bring about some increase in the equilibrium rigidity. It can be assumed that, for this class of polymers, the mesogeneity on a molecular level is defined by the strong interactions of fluorine‐containing side chains rather than by the rigidity of their backbones.     

Structure and Mechanical Behavior of Fully Substituted Acid Starch Esters

This study deals with the evolution of structural, thermal, and mechanical properties of a series of fully substituted fatty acid starch esters (FASEs) according to side chain length (from 2 (C2) up to 16 (C16) Carbons). FASEs with C2 to C12 side chains are fully amorphous with a glass transition temperature depending on chain length while in the case of FASE with C16 side chains, a part of side chains is able to crystallize. Thermomechanical behavior depends strongly on both the alkyl chain length and crystallinity of samples. In particular, for FASE-C16, the presence of crystals leads to a brittle behavior. During stretching, no macromolecular orientation is evidenced for short-chain FASEs (<C8), whereas, for long-chain starch ester from C8 to C16 length, an orientation of starch backbone in the drawing direction is observed.     

Thermoassociative graft copolymers based on poly(N‐isopropylacrylamide): Relation between the chemical structure and the rheological properties

new family of thermoassociative graft copolymers has been recently synthesised using a two‐step procedure. Schematically, their structure combines a weak polyelectrolyte backbone (poly(sodium acrylate), PAA) and thermosensitive side chains containing mainly N‐isopropylacrylamide (NIPA). Taking advantage of this well controlled synthesis we have selectively varied the primary structure of the copolymers concerning the grafting extent, the length of the backbone, and the hydrophilic‐lipophilic balance of the side chains by incorporating either hydrophilic or hydrophobic comonomers. The thermoassociative properties of the resulting copolymers were studied in semi‐dilute solutions by rheology. It was clearly evidenced that the association temperature of the copolymers is selectively controlled in pure water (in the 0–100°C range) by the chemical composition of the side chains. Moreover, the magnitude of the thermothickening effect is directly related to the modification extent while the absolute value of the viscosity is modulated by the length of the PAA backbone. Very sharp transitions were also evidenced by developing specific attractive interactions between the PNIPA grafts and the PAA backbone dependent on the pH of the solutions. In all the cases we demonstrate that the associative behaviour is well correlated to the thermodynamic properties of the precursors. A good knowledge of their phase diagrams in aqueous solution is therefore a very strong guideline for designing copolymers with responsive properties.     

Structural and Thermal Behavior of Poly (3‐octylthiophene): a DSC, 13C MAS NMR,XRD, Photoluminescence,and Raman Scattering Study

This work tries to give an answer to questions persisting over a decade in literature, concerning poly(3‐alkylthiophene)s: polymorphism and phase stability related to the molecular masses, their distribution, the degree of regioregularity, the length of the side chain, and its nature. In fact we have studied, by means of five different techniques, the structural and thermal behavior of poly(3‐octylthiophene) prepared by Ni catalyzed polymerization. A different thermal behavior for the rod‐like conjugated backbone and for the side chains has been found having a strong influence both on the structural arrangement and the photoluminescence properties of the polymer. A thermal transition occurring at 84°C was found to correspond to the trans to gauche transition in the side chain conformations without a relevant change in the conjugated backbone planarity.     

Supramolecularly Designed Thermoresponsive Polymers in Different Polymer Backbones

Thermoresponsive polymers in water, for example, poly(N‐isopropylacrylamide) (PNIPAM) are investigated extensively, due to a wide range of biomedical applications. However, the attempts to control thermoresponsiveness are still rare in less or nonpolar media. Herein, the three thermoresponsive homopolymers tethering an N‐butylurea group in the side chain with a different polymer backbone are reported. They exhibit lower critical solution temperature (LCST)‐type and upper critical solution temperature (UCST)‐type thermoresponsiveness depending on association of the urea group in the polymer chain and hydrogen bonding small molecules (effectors) in ternary systems (polymer/effector/organic solvent). The difference of polymer backbone appears as their change of solvophobicity in organic solvents. Poly(methacrylate) backbone needs more amount of the effector in nonpolar organic solvents, and poly(vinyl ether) backbone needs more amount in polar organic solvents. However, the influence of polymer backbone is too little to change the phase transition behavior, and the thermoresponsiveness is dominated by association and dissociation of hydrogen bondings between polymers and effectors. The supramolecular design of the thermoresponsive polymers is strong and extensible for the design of their phase transitions.     

Structure and Segmental Motions in a Substituted Polythiophene: A Solid‐State NMR Study

Thermochromic poly[3‐(2‐methyl‐1‐butoxy)‐4‐methylthiophene] has been investigated in the solid state. Some important changes have been observed by UV‐Vis absorption and XRD measurements. Solid‐state NMR spectroscopy, which has the ability to provide information about the structure and dynamics of polymers over a wide range of length scales and time scales, has been utilized to better understand the motion of polythiophene chains during this thermochromic transition. Different solid‐state NMR analyses led to the determination of the relaxation rates for the main chain and the side chain as well as to the characterization of a twisting of the conjugated backbone chain during the thermochromic transition.

     

Dielectric properties of a liquid crystalline siloxane copolymer

An investigation on the molecular dynamics of a liquid crystalline side chain polymer using the dielectric relaxation method on oriented samples in the frequency range of 0,1 to 10 000 kHz is presented. The compound under investigation is a polysiloxane copolymer with two different mesogenic side chains and a phase sequence glassy-smectic A-nematic-isotropic. Three main relaxation processes are found and assigned to the rotation of the side chains around the main chain, the glass transition process coupled with side chain motions, and a local motion in the glassy state, respectively. Evidence is found for a layered arrangement of the polymer main chain in the smectic phase and for a parallel correlation between the transverse components of the dipole moments.     

New Thermo‐Sensitive Graft Copolymers Based on a Poly(N‐isopropylacrylamide) Backbone and Functional Polyoxazoline Grafts with Random and Diblock Structure

New thermo‐sensitive functionalized graft copolymers characterized by a poly(N‐isopropylacrylamide) backbone and grafts containing 2‐ethyl‐2‐oxazoline and 2‐(2‐methoxycarbonylethyl)‐2‐oxazoline units were synthesized. The conformation transition temperatures of the graft copolymers could be modified by variation of the molar composition in the side chain, by different side chain structure (random distribution of both oxazolines vs. diblock structure) and by hydrolysis of the methylester to the acid form. Graft copolymers with long functional oxazoline side chains allowed the stabilization of aggregates above the phase transition temperature of the backbone until the LCST of the side chain. The temperature window allowing for the formation of stable aggregates was widened with acid functions in the corona.

     

Polyelectrolyte complex formation: Role of a double hydrophilic polymer

Polyelectrolyte complex (PEC) formation between a double hydrophilic polymer DHP‐MA, consisting of a methacrylic backbone and ethylene oxide side chains and poly(diallyldimethylammonium chloride) (PDADMAC) samples of different molecular weights were studied by static light scattering and viscometry. PEC formation took place on a molecular level. The findings obtained adding DHP‐MA to the polycation solutions suggest a uniform distribution of DHP‐MA over all PDADMAC chains. The masses of the PECs are strongly correlated to the molecular weights of the PDADMAC samples. Flocculation normally observed in PEC formation approaching the 1 : 1 mixing ratio is completely suppressed by the ethylene oxide side chains. Even subsequent addition of higher amounts of salt did not cause remarkable secondary aggregation. These stabilizing effects could also be achieved using DHP‐MA as admixture in PEC formation between Na‐poly(styrene sulfonate) and PDADMAC.     

Comparison of the Molecular Dynamics of a Liquid Crystalline Side Group Polymer Revealed from Temperature Modulated DSC and Dielectric Experiments in the Glass Transition Region

Temperature modulated DSC (TMDSC) in the frequency range from 10^–3 Hz to 3.4 10^–2 Hz and dielectric spectroscopy in the frequency range from 10^–2 Hz to 10⁶ Hz is employed to analyze the temperature dependence of the relaxation rates of the α‐ and of the δ‐relaxation of a liquid crystalline polymethacrylate having a derivative of (p‐alkoxy‐phenyl)‐benzoate as mesogenic unit in the side group. Especially the molecular assignment of the α‐relaxation was discussed controversial in the literature up to now. By applying a temperature derivative method it was found that the temperature dependencies of the relaxation rates of the dielectric α‐relaxation and of the dynamic glass transition measured by TMDSC can be described by Vogel/Fulcher/Tammann laws with the same Vogel temperature. Therefore it is argued that the dielectric α‐relaxation of liquid crystalline polymers is rather due to the dynamic glass transition related to the segmental dynamics of the backbone than to the transverse dipole component of the mesogenic unit.