Chain Ends Of Poly Research Articles

A sol–gel polymerization method for creating nanoporous polyimide silsesquioxane nanostructures as soft dielectric materials

ABSTRACTA sol–gel polymerization method was developed to make polyimide (PI) silsesquioxane (SSQ) nanoparticles as functional, soft dielectric materials. The surface functionalization of the polymer chain backbone and chain ends of poly(trimellitic anhydride chloride‐co‐4,4′‐methylenedianiline), PMR‐15 resin, with para‐(chloromethyl)‐phenylethyltrimethoxy silane yielded a novel sol–gel reactive sites functionalized PMR‐silane precursor. Upon base‐catalyzed hydrolysis and condensation of the PMR‐silane precursor, spherical, raspberry‐like PMR‐SSQ nanoparticles were obtained in considerably good yield. Controlling the particle size distribution was attempted upon adjusting the molar ratio between the silane precursor and the base, as well as in the presence of a catalytic amount of silica sols. Particle composition, thermal stability, and morphology were confirmed from Fourier transform infrared, thermogravimetric analysis, and scanning electron microscopy analyses. Nanoparticles, visualized under transmission electron microscopy exhibit a nanoporous structure. The Brunauer–Emmett–Teller analysis confirmed that the average pore dimension is ranged from 2 to 5 nm. The dielectric constant of PMR‐SSQ nanoparticles was as low as 1.95, compared to dielectric constants of 3.05 and 3.13 for PMR‐15 and PMR‐silane, respectively. Thus, the base‐catalyzed sol–gel polymerization of alkoxysilylated PI offers a novel synthetic path to make functional nanoporous PI nanostructures that possess ultralow dielectric constants. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 57, 562–571.

Water erodible coatings based on a hydrolyzable PDMS/polyester network

In this work, the objective is to design an elastomer network predominantly composed of poly(dimethylsiloxane) (PDMS) with small crosslinked hydrolyzable polyesters to finally provide a new eco-friendly antifouling system. This PDMS/polyester network is expected to maintain a low surface energy during water immersion while, at the same time, ensuring a continuous renewal of its surface through an erosion process. The PDMS/polyester networks were crosslinked via a condensation reaction of a bis-silanol PDMS oil and various bis(trialkoxysilane)-terminated polyester macrocrosslinkers. Chain ends of poly(ε-caprolactone), poly(ε-caprolactone)-b-PDMS-b-poly(ε-caprolactone) and poly(d,l-lactide-co-glycolide) were quantitatively functionalized using (3-isocyanatopropyl)trimethoxysilane as crosslinking reactant. These polyester macrocrosslinkers were highly inserted in the PDMS-based networks in quantities ranging from 12 to 40 wt.%. The microtopography of these PDMS/polyester coatings revealed relatively low roughness values for most of the coatings. Contact angle measurements highlighted an increase of hydrophilicity for PCL-based coatings contrary to the poly(d,l-lactide-co-glycolide)-based coating which demonstrated a surface hydrophobicity as well as a low surface free energy (γs ≤ 25 mJ/m²) even after 5 weeks of immersion in deionized water. The insertion of polyesters within a silicone matrix affected both the elastic modulus and the cristallinity of the network depending on the polyester nature. Finally, mass loss tests demonstrated that these PDMS/polyester coatings had the ability to erode themselves.

Catechin-Modified Polylactide Stereocomplex at Chain End Improved Antibiobacterial Property.

Using different type of initiators, the antibacterial moieties are introduced at the chain end of poly(L,L-lactide) (PLLA) and poly(D,D-lactide) (PDLA), and the thermal properties are simultaneously improved using the stereocomplex approach. The physical interaction of polymers and antibacterial compounds is investigated. The double bonds at the chain end are utilized for the interaction of silver ion; however, the silver ions are not detected after stereocomplexation of PLLA and PDLA. On the other hand, catechin (CT) is selected as an initiator precursor of lactide polymerization, protecting the phenolic hydroxyl groups. The linear PLLA and PDLA are obtained by the initiator, resulting in CT conjugated PLAs at the chain end groups after deprotection of phenolic hydroxyl groups. The antibacterial properties are determined by proliferation tests of staphylococcus aureus. The results suggest that the antibacterial properties of CT modified PLAs are derived from the original CT parts.

Direct Controlled Polymerization of Ionic Monomers by Surface‐Initiated ATRP Using a Fluoroalcohol and Ionic Liquids

AbstractSurface‐initiated atom transfer radical polymerization (ATRP) of (2‐methacryloyloxyethyl)trimethylammonium chloride (MTAC), 3‐(N‐2‐methacryloyloxyethyl‐N,N‐dimethyl) ammonatopropanesulfonate) (MAPS), and 2‐methacryloyloxyethyl phosphorylcholine (MPC) was carried out in 2,2,2‐trifluoroethanol (TFE) containing a small amount of 1‐hexyl‐3‐methylimidazolium chloride at 60 °C to produce well‐defined ionic polymer brushes and the corresponding free polymers with predictable number‐average molecular weight (Mn, 1×104−3×105 g mol−1) and narrow molecular weight dispersity (Mw/Mn<1.2). A first‐order kinetic plot for ATRP of MTAC and MAPS revealed a linear relationship between the monomer conversion index (ln([M]0/[M])) and polymerization time. Reduction in polymerization rates was observed with an increase in ionic liquid concentration. The Mn of both poly(MTAC) and poly(MAPS) increased in proportion to the conversion. The sequential polymerization of MAPS initiated with the chain ends of poly(MAPS) produced the postpolymer with quantitative efficiency. The thickness of the polymer brush was controllable from 5 to 100 nm based on the Mn of the polymer. These results suggest the successful control of the polymerization of sulfobetaine‐type methacrylates owing to the TFE and ionic liquids. In particular, the high affinity of TFE for the sulfobetaine monomers and polymers yielded a homogeneous polymerization media to improve surface‐initiated polymerization generating the polymer brushes on the substrate surface as well as the free polymers formed in the solution. The effect on ATRP of the chemical structure of ionic liquids and ligands for copper catalyst was also investigated.

Rheological Images of Dynamic Covalent Polymer Networks and Mechanisms behind Mechanical and Self-Healing Properties

In our previous work [Macromolecules2010, 43, 1191–1194], we synthesized dynamic covalent cross-linked polymer gels through condensation of acylhydrazines at the chain ends of poly(ethylene oxide) (A2) and aldehyde groups in tris[(4-formylphenoxy)methy]ethane (B3) and reported reversible sol–gel transition and self-healing properties of the gels. For those dynamic gels, this paper examines the gelation kinetics and rheological behavior in pre- and postgelation stages and discusses the molecular mechanism underlying the mechanical and self-healing properties. The results showed that the condensation reaction before the critical gelation point can be treated as the pseudo-second-order reaction. The scaling exponent n (=0.75) for the frequency dependence of the complex moduli at the critical gel point, the exponent γ (=1.5) for the concentration dependence of the viscosity in the pregel regime, and the exponent z (=2.5) for the concentration dependence of the equilibrium modulus in the postgel regime were found to not exactly obey the relationship for covalent gels, n = z/(z + γ), possibly because of the dynamic nature of the gels. The terminal relaxation of the dynamic gels at high temperature (125 °C) accorded with the Maxwellian model, as often observed for transient associating networks. In contrast, at low temperature (25 °C) where this transient network reorganization was essentially quenched in a time scale of experiments (∼50 s), the uniaxial stress–strain behavior of the gel was well described by the classical model of rubber elasticity σeng = G(λ – 1/λ2) up to 300% stretch (as similar to the behavior of usual gels chemically cross-linked in a swollen state). Ultimately, the gel cut into two pieces was found to exhibit self-healing under ambient conditions in 8 and 24 h, respectively, when the edges of those pieces were coated and not coated with acid (catalyst for dynamic covalent bond formation).

Lysozyme-Coupled Poly(poly(ethylene glycol) methacrylate)−Stainless Steel Hybrids and Their Antifouling and Antibacterial Surfaces

An environmentally benign approach to impart stainless steel (SS) surfaces with antifouling and antibacterial functionalities was described. Surface-initiated atom transfer radical polymerization (ATRP) of poly(ethylene glycol) monomethacrylate) (PEGMA) from the SS surface-coupled catecholic L-3,4-dihydroxyphenylalanine (DOPA) with terminal alkyl halide initiator was first carried out, followed by the immobilization of lysozyme at the chain ends of poly(ethylene glycol) branches of the grafted PEGMA polymer brushes. The functionalized SS surfaces were shown to be effective in preventing bovine serum albumin (BSA) adsorption and in reducing bacterial adhesion and biofilm formation. The surfaces also exhibited good bactericidal effects against Escherichia coli and Staphylococcus aureus. The concomitant incorporation of antifouling hydrophilic brushes and antibacterial enzymes or peptides onto metal surfaces via catecholic anchors should be readily adaptable to other metal substrates, and is potentially useful for biomedical and biomaterial applications.

Well-Defined Poly(sulfobetaine) Brushes Prepared by Surface-Initiated ATRP Using a Fluoroalcohol and Ionic Liquids as the Solvents

Surface-initiated atom transfer radical polymerization (ATRP) of 2-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatoethanesulfonate) (MAES), 3-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatopropanesulfonate) (MAPS), and 4-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatobutanesulfonate) (MABS) was carried out in 2,2,2-trifluoroethanol (TFE) containing a small amount of 1-hexyl-3-methylimidazolium chloride at 60 °C to produce well-defined poly(sulfobetaine) brushes and the corresponding free polymers with predictable number-average molecular weight (Mn, 1 × 104 to 3 × 105 g mol−1) and narrow molecular weight distributions (Mw/Mn < 1.2). A first-order kinetic plot for ATRP of MAPS revealed a linear relationship between the monomer conversion index (ln([M]0/[M])) and polymerization time. The polymerization rates decreased with increasing ionic liquid concentration. The Mn of poly(MAPS) increased in proportion to the conversion. The sequential polymerization of MAPS initiated with the chain ends of poly(MAPS) ...

Synthesis of poly(methyl methacrylate)-block-poly(tetrahydrofuran) by photo-living radical polymerization using a 2,2,6,6-tetramethylpiperidine-1-oxyl macromediator

The synthesis of a poly(methyl methacrylate)-block-poly(tetrahydrofuran) (PMMA-b-PTHF) diblock copolymer was attained by the photo-living radical polymerization of methyl methacrylate using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) supported on the chain end of poly(tetrahydrofuran) (PTHF) as the macromediator. The polymerization was performed at room temperature by 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) as an initiator in the presence of bis(alkylphenyl)iodonium hexafluorophosphate as a photo-acid generator to produce the diblock copolymer consisting of poly(methyl methacrylate) (PMMA) and PTHF blocks connected through the TEMPO. The polymerization was confirmed to proceed in accordance with a living mechanism based on linear correlations for three different plots of the first order time-conversion, the molecular weight of the copolymer versus the monomer conversion, and the molecular weight versus the reciprocal of the initial concentration of the initiator. The molecular weight distribution of the block copolymer was dependent on the molecular weight of the macromediator based on the miscibility of PMMA and PTHF.

Tuning Macromolecular Structures of Synthetic Vectors for Gene Therapy

AbstractSummary: The synthesis of triblocks poly(2‐methyl‐2‐oxazoline‐b‐tetrahydrofurane‐b‐2‐methyl‐2‐oxazoline) has been developed. It was shown that the technique of polymerization of the second block from the living species created on the two chain ends of poly(THF) is successful but makes the control of the size of the poly(THF) block difficult due a fast depolymerization upon the introduction of the second monomer. A purification technique was used to get rid of the possible homopoly(2‐methyl‐2‐oxazoline) formed. Various analytical techniques were used to characterize the behavior of the triblock and more particularly in the presence of DNA. Electrophoresis on agarose gels and neutron scattering, demonstrated that the neutral triblock does not appreciably interact with DNA. It was also shown that the triblock for which approximately half (47%) of the methyloxazoline units were transformed into ethylenimine units by hydrolysis gives only loose interactions with DNA. This result is assigned to the fact that charge density plays a major role in the interactions of positive polyelectrolytes with the negatively charged DNA. The triblock was shown being able to interact with bilayer lipid membranes mimicking cell membranes. The efficiency of the hydrolysed triblock was much higher, while the size of holes created in the membranes is not large enough to give passage to DNA.

Effect of helix-coil transition on association behavior of both-ends hydrophobically-modified water-soluble polypeptide

Dodecyl and dodecanoyl groups (C12) are attached at the chain ends of poly[ N 5-(2-hydroxyethyl) l-glutamine] (PHEG), and association behavior of this both-ends hydrophobically modified water soluble polypeptide (C12–PHEG–C12) has been investigated by means of light scattering measurements. Water/ethylene glycol (EG) mixed solvents were used as selective solvent for PHEG block, and PHEG changed its structure from random-coil state to α-helix with increasing EG content in the mixed solvent ( W EG). When W EG is less than 0.5, flower-like micelle with C12 associated core and PHEG corona in loop conformation was suggested to be formed. Increase of W EG from 0.5 to 0.6 induced drastic increase of association number and size of the associate, in which many C12 associated cores may be connected by PHEG in bridge conformation. This structure change of associate is considered to be driven by the increase of helix content of PHEG with W EG, which enhances the possibility to form bridge conformation because of its rigidity. Solution preparation method, i.e. order of addition of solvent, was found to influence the structure of associate, although its effect on the helix content of PHEG was negligible.

Chain‐end modification of living anionic polybutadiene with diphenylethylenes and styrenes

AbstractThe first step in the transformation of poly(butadienyl)lithium into a macromolecular atom transfer radical polymerization initiator or reversible addition–fragmentation chain transfer agent is the modification of the anionic chain end into a suitable leaving/reinitiating group. We have investigated three different modification reactions to obtain a styrenic end group at the chain end of poly(butadienyl)lithium. In all cases, we have looked at the influence of a Lewis base on the progress of the reaction. The first modification reaction with α‐methylstyrene leads to partial functionalization and oligomerization. The second reaction with 1,2‐diphenylethylenes, particularly trans‐stilbene, results in monoaddition to the poly(butadienyl)lithium chain ends. Quantitative functionalization is not obtained, possibly because of a hydrogen abstraction reaction, which causes termination. In the third modification reaction, a small polystyrene block is successfully added to the chain ends, as shown by a detailed matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis of the block copolymers. Nearly quantitative block copolymer formation is achieved, with an average styrene block size of four monomer units and a polydispersity index of 1.19 for the polystyrene block. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2536–2545, 2005

Direct Detection of High Mobility around Chain Ends of Poly(methyl methacrylate) by the Spin-Labeling

Effects of chain ends on the dynamics of atactic poly(methyl methacrylate) (PMMA) was studied by the spin-label technique. PMMA's with well-defined molecular weights were synthesized by atom transfer radical polymerization and selectively labeled at the end or inside sites of the chain with a stable nitroxide radical. The WLF treatment demonstrated that a transition temperature, T5.0mT, at which an extreme separation width was 5.0 mT, reflected the glass transition observed at a frequency of electron spin resonance (ESR). The T5.0mT of the PMMA labeled at the chain end (T5.0mT,e) was ca. 8 K lower than that of the PMMA labeled at the inside sites (T5.0mT,i). From the comparison of some polymers, the difference between the T5.0mT,i and T5.0mT,e of a rigid polymer was found to be larger than that of a flexible polymer. The T5.0mT,i and T5.0mT,e decreased with a decrease in the molecular weight as well as a glass transition temperature determined by calorimetric measurements. This result supports that the T5.0mT reflects the glass transition of the PMMA and suggests that the cooperative motion with neighboring segments is necessary for not only inside segments but also chain ends to undergo a rotational relaxation. The high mobility around chain ends brought a shorter correlation time (τc) at the region around chain ends. Moreover, a model on the basis of an arrangement of segments suggested that an encounter of chain ends was unable to be ignored in the case of low molecular weights, and the encounter of chain ends locally induced a much shorter τc around them.

Molecular Mobility of an Amorphous Chain in the Crystallization Process of Poly(ε-caprolactone)

The chain end of poly(ε-caprolactone) was spin-labeled to study the molecular mobility of the polymer chain in an amorphous region under the crystallization. Time-resolved ESR measurements were carried out in the crystallization process. The three stages of the time evolution of the molecular mobility at the crystallization temperatures were found; the correlation time, τc, of the polymer chain increased gradually at the early stage and remarkably at the late stage. At the final stage, the τc increased gradually again. The early stage is the induction period where no change of the scattering intensity is observed by the time-resolved SAXS and WAXS measurements. The gradual decrease of the molecular mobility is caused by the precursory aggregation of the polymer chain before the crystallization. At the late stage, the crystalline grows and the molecular mobility in the amorphous region becomes remarkably restricted by the rigid chains in the crystalline regions. At the final stage, the gradual decrease of the molecular mobility by the late growth of the crystalline observed again, where no structural change was detected by the measurements of X-ray scatterings.

Ring-Opening Polymerization ofɛ-Caprolactone by Phosphorane Iminato and Cyclopentadienyl Complexes of Rare Earth Elements

Rare earth element complexes with triphenyl phosphorane iminato ligands such as [La 2 (NPPh 3 ) 4 (μ-NPPh 3 ) 2 (μ-THF)] and [Yb(NPPh 3 ) 3 ] 2 initiate the polymerization of e-caprolactone to give high molecular weight poly(e-caprolactone) with moderate polydispersity. The reactivity of these complexes is higher as compared to complexes with three cyclopentadienyl ligands with corresponding metal centers. The initiation mechanism for the polymerization of e-caprolactone by [La 2 (NPPh 3 ) 4 (μ-NPPh 3 ) 2 (μ-THF)] is discussed based on the end groups of low molecular weight polycaprolactones. Living chain ends of poly(e-caprolactone) were proved by block copolymerization of e-caprolactone and δ-valerolactone. The mixed complex [Cp 3 Dy 2 (NPPh 3 ) 3 ] has been successfully applied for ROP of CL. A significant increase in molecular weight of ROP has been observed with decrease of reaction temperature.

Attachment of bis-(trifluoromethyl)aryl labels onto the chain ends of poly(ethylene terephthalate) (PET) track-etched membranes and films by surface wet chemistry

Organic chemistry performed at the solid–liquid interface allowed us to achieve the selective chain-end functionalization of poly(ethylene terephthalate) (PET) membranes and films with perfluorinated labels. The carboxyl endings were activated with water-soluble carbodiimide and were coupled to 3,5-bis(trifluoromethyl)benzylamine (1) in aqueous acetonitrile, whereas the hydroxyl endings were activated by tosylation and were also coupled to 1. 3,5-Bis(trifluoromethyl)phenyl isocyanate (2) was directly fixed on the hydroxyl endings of the polymer substrates in dry organic media. All the derivatized materials were analyzed by X-ray photoelectron spectroscopy, allowing the quantitative determination of the amounts of surface-grafted labels. Yields were between 10 and 100 pmol/cm2. These surface reactivity assays mimic at best the experimental conditions that would be applied for the covalent anchorage of biologically active molecules onto PET substrates used in cell culture systems. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3510–3520, 2000

Tailored Synthesis of Star and Network Poly(dimethylsiloxane)s through Electrostatic Self-Assembly and Subsequent Covalent Fixation of Telechelics Having Cyclic Onium Salt Groups

Efficient electrostatic self-assembly and subsequent covalent fixation of macromolecules by multipoint interaction have been achieved with poly(dimethylsiloxane), poly(DMS), having five-membered cyclic ammonium salt end groups. Thus a 1-methylpyrrolidinium salt end group was introduced at a single or both chain ends of poly(DMS) (1 and 1‘, respectively). The anion-exchange reaction of 1 and 1‘ with di-, tri- and tetracarboxylates was found to take place efficiently by a simple precipitation of 1 and 1‘ into aqueous solution containing an equimolar amount of carboxylate compounds (thus ca. 10-3 M, 0.01−0.1 wt % concentration). The subsequent heat treatment of ionically-assembled products at 120 °C caused covalent fixation by the selective ring opening reaction of cyclic onium salt groups by nucleophilic attack of carboxylate anion, to produce star and model-network poly(DMS) structures in high yields.

EFFECTS OF MACROMOLECULAR ASSOCIATION ON FLUORESCENCE AND PHOTODIMERIZATION BEHAVIORS OF POLYMERIC ANTHRACENE CHROMOPHORE IN AN AQUEOUS SOLUTION

Abstract Anthracene chromophore attached to the chain end of poly(ethylene glycol) (PEG-Ant) was found to exhibit excimer fluorescence down to 10−7 M in an aqueous solution. Macromolecular association of PEG-Ant with poly(methacrylic acid) (PMAA) increased excimer emission intensity by a factor of 10 as well as the rate of photodimerization.

Preparation of a block copolymer by hydrolysis and subsequent oxidative coupling of the chain ends of poly(methyl methacrylate) and polystyrene, containing amidinothio end groups

Preparation of a block copolymer by hydrolysis and subsequent oxidative coupling of the chain ends of poly(methyl methacrylate) and polystyrene, containing amidinothio end groups

Condensation Reaction between Chain Ends of Poly(p-benzamide)

It has been proved experimentally that the condensation reaction between chain ends of poly(p-benzamide), (PBA), takes place and that the degree of polymerization (DP) of PBA increases by annealing in both the solid and liquid-crystalline states. A theoretical analysis of the reaction has shown that the DP distribution of the resultant polymer is again the most probable and the conversion of the reaction by weight is fairly high. The reactivity of PBA in the solid-crystalline state exceeded that in the liquid-crystalline state.