Fluorinated Aromatic Polyamides and Poly(amide‐imide)s: Synthesis and Properties

Summary: A CF₃‐containing diamine, 4,4′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl ( I ), was synthesized from 4,4′‐biphenol and 2‐chloro‐5‐nitrobenzotrifluoride. The imide‐containing diacids ( V_a‐b and VI_a‐l ) were prepared by condensation reaction of amino acids, aromatic diamines and trimellitic anhydride. Then, a series of soluble aromatic polyamides ( VII_a‐f ) and poly(amide‐imide)s ( VIII_a‐b and IX_a‐l ) were synthesized from diamine I with various aromatic diacids ( II_a‐f ) and the imide‐containing diacids ( V_a‐b and VI_a‐l ) via direct polycondensation with triphenyl phosphate and pyridine. Aromatic polyamides and poly(amide‐imide)s had inherent viscosities of 0.60–0.85 dL/g and 0.52–1.44 dL/g, respectively. All synthesized polymers showed excellent solubility in amide‐type solvents such as N‐methyl‐2‐pyrrolidinone, N,N‐dimethylacetamide (DMAc) and N‐dimethylforamide and afford transparent and tough films by DMAc solvent casting. These polymer films had tensile strengths of 87–135 MPa, elongations to break of 8–22%, and initial moduli of 2.0–3.0 GPa. Glass transition temperature of these polymers were in the range of 259–317 °C, and the poly(amide‐imide)s had better thermal stability than aromatic polyamides. In comparison with the isomeric X series, the IX series exhibited less coloring and showed a lower b* (yellowness index) values than the corresponding IX series.

     

Star Block Copolymers Through Nitroxide‐Mediated Radical Polymerization From Polyhedral Oligomeric Silsesquioxane (POSS) Core

A series of star block copolymers were prepared through nitroxide‐mediated radical polymerization (NMRP) from polyhedral oligomeric silsesquioxanes (POSS) nanoparticle by core‐first polymerization. Eight N‐alkoxyamine groups were incorporated onto the eight corners of a POSS cube through quantitative hydrosilylation through addition of octakis(dimethylsiloxy)silsesquioxane (Q₈M POSS) with 1‐(2‐(allyloxy)‐1‐phenylethoxy)‐2,2,6,6‐tetramethylpiperidine (allyl‐TEMPO) and Karstedt's agent (a platinum divinylsiloxane complex) was used as a catalyst. Octa‐N‐alkoxyamines POSS (OT‐POSS) were used as platform to synthesize star polystyrene‐POSS ((PS)₈‐POSS) homopolymer and diblock copolymers of poly(styrene‐block‐4‐vinylpyridine)‐POSS ((PS‐b‐P4VP)₈‐POSS) and poly(styrene‐block‐acetoxystyrene) ((PS‐b‐PAS)₈‐POSS) through NMRP. In addition, subsequent selective hydrolysis of the acetyl protective group of (PS‐b‐PAS)₈‐POSS, the poly(styrene‐block‐vinyl phenol) ((PS‐b‐PVPh)₈‐POSS) with strong hydrogen bonding group was obtained. The detailed chemical structure and self‐assembled structures of these star block copolymers based on POSS were characterized by ¹H NMR, FTIR, SEC, TEM, and SAXS analyses.

     

Soluble and Colorless Poly(ether‐imide)s Based on a Benzonorbornane Bis(ether anhydride) and Trifluoromethyl‐Substituted Aromatic Bis(ether‐amine)s

Summary: A series of organosoluble and colorless fluorinated poly(ether imide)s ( IV_a‐g ) were prepared from 3,6‐bis(3,4‐dicarboxyphenoxy)benzonorbornane dianhydride ( I ) and various trifluoromethyl (CF₃)‐substituted aromatic bis(ether amine)s II_a‐g by a standard two‐step process with thermal and chemical imidization of poly(amic acid) precursors. These poly(ether imide)s had inherent viscosities of 1.02–1.28 dL · g^?1 and showed excellent solubility in many organic solvents. They could be solution‐cast into transparent, flexible, and tough films with good mechanical properties. These films were virtually colorless, with an ultraviolet‐visible absorption edge of 372–381 nm and a very low b* value (a yellowness index) of 10.8 to 18.2. The glass‐transition temperatures (T_g) and softening temperatures (T_s) were recorded between 216–292 °C and 209–285 °C, respectively. The decomposition temperature for 10% weight loss all occurred above 472 °C in nitrogen and 481 °C in air, and the char yields at 800 °C in nitrogen were more than 51%. They also showed low dielectric constants of 2.84–3.58 (1 MHz) and moisture absorptions in the range of 0.05–0.19%. In comparison with analogous V series poly(ether imide)s without the CF₃ substituents, the IV series ones showed better solubility, lower color intensity, and lower dielectric constants.

A novel series of fluorinated poly(ether imide)s.     

Atom‐Transfer Radical Polymerization: A Strategy for the Synthesis of Halogen‐Free Amino‐Functionalized Poly(methyl methacrylate) in a One‐Pot Reaction

Summary: An initiator containing an alkyl bromide unit and a protected amine functional group is used with CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA), in a 1:2 molar ratio with respect to initiator concentration, in order to obtain amino‐group terminated as well as halogen‐free poly(methyl methacrylate) (PMMA) in a one‐pot atom‐transfer radical polymerization (ATRP). The terminal bromines are replaced by hydrogen atoms of the PMDETA ligand, which acts as a transfer agent. However, terminating side reactions like disproportionation or dehydrobromination occur from the beginning of the polymerization. Kinetic studies by in‐line Raman spectroscopy and off‐line ¹H NMR spectroscopy revealed that the controlled character of the ATRP is lost under these conditions. The measured molecular weights were consistently higher than the theoretical ones and the molecular weight distributions are relatively broad. Thermal analysis of the obtained poly(methyl methacrylate) shows two main degradation steps, one starting from unsaturated end groups (depolymerization), and one caused by main‐chain scission, a further proof for the occurrence of terminating side reactions.

Structural analysis of PMMA by matrix‐assisted laser desorption‐ionization mass spectrometry.     

Polymethacrylate Copolymers Containing 4,5‐Dicyanoimidazole‐Based Chromophores and their Nonlinear Optical Behavior

Summary: Two series of methacrylate copolymers were prepared, based on two new nonlinear optically (NLO) active chromophores 2‐[4‐(N‐methacryloyloxyethyl‐N‐methylamino)phenylazo]‐4,5‐dicyanoimidazole (chromophore A ) and 1‐ethyl‐2‐[4‐(N‐methacryloyloxyethyl‐N‐methylamino)phenylazo]‐4,5‐dicyanoimidazole (chromophore B ). Second order NLO properties of the two series of copolymers ( A or B as monomer and methyl methacrylate as the comonomer) were investigated by SHG procedures at the fundamental wavelength 1368 nm; d₃₃ values in the range 0.2–3.3 pm · V⁻¹ were obtained, depending on the chromophore and on its molar content. The dependence of d₃₃ on the molar content of chromophore was investigated in the two cases.

     

Poly[2,7‐(9,9‐dihexylfluorene)]‐block‐Poly(2‐vinylpyridine) Rod–Coil Star‐block Copolymers: Synthesis,Micellar Structures,and Photophysical Properties

The first successful synthesis of conjugated rod–coil star block copolymer, (PF‐b‐P2VP)_n, containing conjugated poly[2,7‐(9,9‐dihexylfluorene)] (PF), and coil‐like poly(2‐vinylpyridine) (P2VP) by combining a Suzuki coupling reaction and living anionic polymerization is reported. With increasing methanol content in THF/methanol mixtures (PF‐b‐P2VP)_n symmetric star‐block copolymers maintain spherical micelles, but PF‐b‐P2VP asymmetric diblock copolymers vary from spherical micelles to vesicles. Both the absorption and emission spectra of PF‐b‐P2VP blue shift with increasing methanol content, suggesting an “H‐type” aggregation. However, (PF‐b‐P2VP)_n star‐block exhibits no shift in absorption but a red shift in the emission spectra, indicating a different type of aggregation. These results suggest the significance of polymer architectures on microphase‐separated morphologies and photophysical properties.

     

Synthesis of Polyacrylonitrile‐block‐Polystyrene Copolymers by Atom Transfer Radical Polymerization

Summary: The synthesis of polyacrylonitrile‐block‐polystyrene (PAN‐b‐PS) copolymers by atom transfer radical polymerization (ATRP) is reported. Chain extension of bromine terminated PAN macroinitiators with styrene was performed using a CuBr/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalyst system and 2‐cyanopyridine as a solvent. The first‐order kinetic plots of styrene consumption showed a significant curvature, indicating a progressive decrease in the concentration of active species during copolymerization. The loss of the bromide end group was mainly ascribed to the elimination of HBr, as shown by ¹H NMR spectroscopy. By varying the molar ratio of either the catalyst or the monomer to the initiator, a series of PAN‐b‐PS copolymers were prepared, with polydispersities as low as 1.3, and molar compositions ranging from 8.6/91.4 to 35.5/64.5.

¹H NMR spectra of PAN‐b‐PS in DMF‐d₇ at 80 °C.     

Investigation of the Physical Properties of Poly(ortho‐ and para‐trifluoromethoxy styrenes)

Ortho and para ‐OCF₃ substituted styrenes are prepared by the Grignard cross‐coupling reaction between ‐OCF₃ substituted bromobenzene and vinyl bromide and further polymerized in bulk using benzoyl peroxide. The glass‐transition temperatures (T_g) are 80 °C and 73 °C for the ortho and para –OCF₃ substituted polystyrenes, respectively, which are much lower compared with polystyrene (100 °C). The size of the ‐OCF₃ group is large and the ether bond is flexible; thus, the ‐OCF₃ substituted polystyrenes have larger free volumes, which has more effect on the T_g value compared with that of the steric hindrance effect. The refractive indices are 1.4908 and 1.4809 at 650 nm for ortho and para –OCF₃ substituted polystyrenes, respectively, which are much lower than that of polystyrene (1.5861) due to the presence of fluorine atoms in the polymer unit.

     

Low Conversion 4‐Acetoxystyrene Free‐Radical Polymerization Kinetics Determined by Pulsed‐Laser and Thermal Polymerization

Summary: The free‐radical polymerization kinetics of 4‐acetoxystyrene (4‐AcOS) is studied over a wide temperature range. Pulsed‐laser polymerization, in combination with dual detector size‐exclusion chromatography, is used to measure k_p, the propagation rate coefficient, between 20 and 110 °C. Values are roughly 50% higher than those of styrene, while the activation energy of 28.7 kJ · mol⁻¹ is lower than that of styrene by 3–4 kJ · mol⁻¹. With known k_p, conversion and molecular weight data from 4‐AcOS thermal polymerizations conducted at 100, 140, and 170 °C are used to estimate termination and thermal initiation kinetics. The behavior is similar to that previously observed for styrene, with an activation energy of 90.4 kJ · mol⁻¹ estimated for the third‐order thermal initiation mechanism.

Joint confidence (95%) ellipsoids for the frequency factor A and the activation energy E_a from non‐linear fitting of k_p data for 4‐AcOS (black) and styrene (grey).     

Optically Transparency and Light Color of Novel Highly Organosoluble Alicyclic Polyimides with 4‐tert‐Butylcyclohexyl Group

Summary: Novel optically transparent and highly organosoluble alicyclic polyimides derived from bulky alicyclic diamine containing trifluoromethyl group on either side, 1,1‐bis[4‐(2‐trifluoromethyl‐4‐aminophenoxy)phenyl]‐4‐tert‐butylcyclohexane (BTFAPBC) , were prepared. All polymers showed excellent solubility in various organic solvents like N‐methyl‐2‐pyrrolidinone (NMP), N,N‐dimethyl acetamide (DMAc), N,N‐dimethyl formamide (DMF), pyridine, cyclohexanone, and γ‐butyrolactone. The cut‐off wavelength and 80% transmission wavelength for polyimides ranged from 362 to 407 nm and 436 to 492 nm, respectively. Polyimides with alicyclic tert‐butylcyclohexyl cardo and trifluoromethyl substituents exhibited low dielectric constants ranging from 3.38 to 4.07 (at 1 KHz). Inherent viscosities of the polyimides were found to be in the range of 0.52–1.00 dL · g⁻¹. Polyimides showed glass transition temperatures in the range of 231–262 °C, and possessed a coefficient of thermal expansion (CTE) of 66–79 ppm · °C⁻¹. Thermogravimetric analyses of the polyimides revealed high thermal stability and decomposition temperature more than 450 °C in nitrogen atmosphere. The 10% weight loss temperature was found to be in the range of 453–544 and 413–502 °C in nitrogen and air atmospheres, respectively. The polyimide films had a tensile strength ranging from 84 to 100 MPa. The elongation at break varied from 6 to 12% and the tensile modulus varied from 1.1 to 2.1 GPa.

Synthesis of diamines, BTFAPBC , BTFAPAd , and BTFAPTC .     

Synthesis of π‐Conjugated Organometallic Polymer Networks

The present paper reports the synthesis of π‐conjugated organometallic polymer networks based on poly[2,5‐dioctyloxy‐1,4‐diethynyl‐phenylene‐alt‐2,5,‐bis(2′‐ethylhexyloxy)‐1,4‐phenylene] (EHO‐OPPE), a soluble poly(p‐phenylene ethynylene) (PPE) derivative. The ethynylene moieties of the polymer coordinate to Pt⁰ centers, which act as conjugated cross‐links. These materials are readily accessible through ligand‐exchange reactions between the linear PPE and Pt(styrene)₃. The in‐situ NMR investigation of model reactions of Pt(styrene)₃ with diphenylacetylene (DPA) has shown that the ethynylene moieties comprised in the PPE readily coordinate to Pt⁰ centers under release of the relatively weakly‐bound styrene ligands. Spin‐coating has resulted in cross‐linked films of good optical quality. We also have been able to produce PPE‐Pt‐gels with high solvent content (> 95 wt.‐%). As expected, the coordination of Pt markedly influences the photophysical characteristics of the PPE. The photoluminescence is efficiently quenched, and the absorption maximum in the visible regime experiences a hypsochromic shift.

Ligand‐exchange reaction between EHO‐OPPE and [Pt(PhCH?CH₂)₃] leading to the target EHO‐OPPE‐Pt⁰ networks.     

Synthesis of high‐Tg polymers by ring‐opening metathesis polymerization of N‐cycloalkylnorbornene dicarboximide

Ring‐opening metathesis polymerization (ROMP) of N‐(1‐adamantyl)‐exo‐norbornene‐5,6‐dicarboximide (AdNDI) ( 3a ) and N‐cyclohexyl‐exo‐norbornene‐5,6‐dicarboximide (ChNDI) ( 3b ) was performed using well‐defined vinylidene ruthenium (II) catalysts Cl₂(PR₃)₂RuCCH(t‐Bu) (R = Ph and Cy). The homopolymer of 3a showed a T_g of 271 °C while poly‐ChNDI of 3b had a T_g of 129 °C. Copolymers of these monomers with norbornene (NB) demonstrated significant T_g increases compared to unsubstituted poly‐NB. Analysis of copolymers of 3a and NB isolated at the initial stages of copolymerization showed that both monomers were incorporated randomly and displayed very similar reactivity.

ROMP of 3a and 3b .     

Proton‐Conducting Properties of Acid‐Doped Poly(glycidyl methacrylate)‐1,2,4‐Triazole Systems

1,2,4‐triazole‐functional PGMA polymers have been synthesized and their anhydrous proton‐conducting properties were investigated after doping with phosphoric acid and triflic acid. PGMA was prepared by solution polymerization and then modified with 1H‐1,2,4‐triazole (Tri) and 3‐amino‐1,2,4‐triazole (ATri). FT‐IR, ¹³C NMR and elemental analysis verify the high immobilization of the triazoles in the polymer chain. Phosphoric‐acid‐doped polymers showed lower T_g and higher proton conductivities. PGMA‐Tri 4 H₃PO₄ showed a maximum water‐free proton conductivity of approximately 10^?2 S · cm^?1 while that of PGMA‐ATri 2 H₃PO₄ was 10^?3 S · cm^?1. The structure and dynamics of the polymers were explored by ¹H MAS and ¹³C CP‐MAS solid‐state NMR.

     

Gas‐Phase Assisted Surface Polymerization of Vinyl Monomers with Fe‐Based Initiating Systems

Summary: Gas‐phase assisted surface polymerization (GASP) of methyl methacrylate (MMA) and styrene (St) was investigated with Fe‐based radical initiating systems, FeCl₂/2,2′‐bipyridine (Bpy)/methyl α‐bromophenylacetate (MBPA), etc. GASP with these initiating systems proceeded to produce corresponding polymers on substrate surfaces. The resulting PMMA had very high PDI values, suggesting an uncontrolled reaction. In an attempt to control the GASP, polymerization with a simple initiating system, Fe(0)/MBPA, was examined on Fe(0)‐metal surfaces, resulting in significant polymerization activity to produce high‐molecular‐weight PMMA. The results of time‐course tests on GASP of MMA and St suggested that a change had taken place to produce physically controlled propagation sites on the Fe(0) powder surfaces.

GASP schemes with a simple initiating system Fe(0)/MBPA.     

Macrocyclic and Acyclic Bis(2,5‐diphenyl‐1,3,4‐oxadiazole)s with Electron‐Transporting and Hole‐Blocking Ability in Organic Electroluminescent Devices

Summary: Two types of bis(2,5‐diphenyl‐1,3,4‐oxadiazole)s, macrocyclic and acyclic, were prepared and evaluated as electron‐transporting and hole‐blocking materials in phosphorescent EL devices. Maximum efficiencies of η_ext = 10.4% at J = 0.11 mA · cm⁻² for the macrocycle and η_ext = 14.1% at J = 3.01 mA · cm⁻² for the acycle were observed. X‐ray crystallographic analysis and DSC measurements revealed a strong intermolecular interaction between the macrocycles and weaker intermolecular interactions between the acycles. The EL characteristics depend on the intermolecular interactions.

The two types of bis(2,5‐diphenyl‐1,3,4‐oxadiazole)s used in the study.     

Polyelectrolyte‐in‐Ionic‐Liquid Electrolytes

Novel polymer electrolyte materials based on a polyelectrolyte‐in‐ionic‐liquid principle are described. A combination of a lithium 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPSLi) and N,N′‐dimethylacrylamide (DMMA) are miscible with the ionic liquid, 1‐ethyl‐3‐methylimidazolium dicyanamide (EMIDCA). EMIDCA has remarkably high conductivity (≥ 2 · 10^?2 S · cm^?1) at room temperature and acts as a good solvating medium for the polyelectrolyte. At compositions of AMPSLi less than or equal to 75 mol‐% in the copolymer (P(AMPSLi‐co‐DMAA)), the polyelectrolytes in EMIDCA are homogeneous, flexible elastomeric gel materials at 10 ? 15 wt.‐% of total polyelectrolyte. Conductivities higher than 8 · 10^?3 S · cm^?1 at 30 °C have been achieved. The effects of the monomer composition, polyelectrolyte concentration, temperature and lithium concentration on the ionic conductivity have been studied using thermal and conductivity analysis, and pulsed field gradient nuclear magnetic resonance techniques.

Comparison of the measured and calculated lithium conductivity at 30 °C.     

Synthesis of Poly(ester amide)s Derived from Glycolic Acid and the Amino Acids: β‐Alanine or 4‐Aminobutyric Acid

The polymerization of metal salts of N‐chloroacetyl‐β‐alanine and N‐chloroacetyl‐4‐aminobutyric acid was investigated. The former gives a mixture of polymer and a seven‐membered cyclic compound constituted of glycolic and β‐alanine units, and its reaction proceeds in the solid state. However, liquefaction is observed in the second case giving rise to a polymer with a moderate molecular weight. Condensation kinetics of both sodium and silver salts of N‐chloroacetyl‐β‐alanine have been studied by differential scanning calorimetry. Copolymers of glycolic acid and β‐alanine with a molar ratio of glycolic acid/β‐alanine varying from 0.5 to 1.0 have been synthesized by thermal reaction of co‐precipitated crystals of the sodium salts of chloroacetic acid and N‐chloroacetyl‐β‐alanine. NMR spectroscopy indicates that copolymers tend to have a random distribution. The resulting new poly(ester amide)s have been characterized by spectroscopy and thermal analysis.

DSC heating runs corresponding to different mixtures of the sodium salts of chloroacetic acid and chloroacetyl‐β‐alanine.     

Controlled synthesis of anthracene‐labeled ω‐amine polystyrene to be used as a probe for interfacial reaction with mutually reactive PMMA

Anthracene‐labeled polystyrene (PS) end‐capped by a primary amine has been synthesized by atom transfer radical copolymerization of styrene with 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (m‐TMI). The m‐TMI co‐monomer (5.7 mol‐%) does not perturb the control of the radical polymerization of styrene. The pendant isocyanate groups of the copolymer chains of low polydispersity (M _w/M _n = 1.25) and controlled molecular weight (up to 35 000) have been derivatized into anthracene by a reaction with 9‐methyl(aminomethyl)anthracene. The anthracene‐labeled PS (ca. 2 mol‐% label) has been conveniently analyzed by size‐exclusion chromatography with a UV detector (SEC‐UV). Moreover, the ω‐bromide end‐group of the copolymer chains has been derivatized into a primary amine, making the labeled PS chains reactive towards non‐miscible poly(methyl methacrylate) (PMMA) chains end‐capped by an anhydride. The interfacial coupling of the mutually reactive PS and PMMA chains has been studied under static conditions (i.e., at the interface between thin PS and PMMA films) and successfully analyzed by SEC‐UV.

SEC‐UV traces for anth‐PS‐NH₂ (80 μg · ml⁻¹; sample A5; Table 1 ), and PMMA‐anh (80 μg · ml⁻¹; sample B1; Table 1 ).     

Glass‐Transition Temperature (Tg) of Free‐Radically Prepared Polyacrylonitrile by Inverse Gas Chromatography, 2. Molecular‐Weight Dependence of Tg of Two Different Types of Aqueous Polymers

The molecular‐weight dependence of the glass‐transition temperature (T_g) of a series of atactic polyacrylonitriles (PAN)s was studied by inverse gas chromatographic (IGC) analysis. PANs having different molecular weights were prepared by either; (i) the addition of isopropyl alcohol as a chain‐transfer agent, or (ii) a scission reaction induced by the addition of alkali (NaOH) to a solution (N,N‐dimethylformamide solution, at 25 °C) of the resulting polymer. The intrinsic viscosity [η] was in the range of 10.9–0.1 (dl · g^?1), which corresponds to a viscosity‐averaged molecular weight (M _v) of 1 590 000–3 000. As part of the results, a side reaction, which saw the conversion of the nitrile (CN) groups of PAN into amide (CONH₂) and/or carboxylic acids (COOH) groups by alkali, was found to occur. The typical molecular‐weight dependence of the T_g in free‐radically prepared PAN was discussed in connection with a chain‐transfer mechanism in an aqueous medium.

Molecular‐weight dependence of the T_g for PAN (WA). An error bar is given by a short vertical arrow.     

A Simple Route to Rod‐Coil Block Copolymers of Oligo‐ and Polythiophenes with PMMA and Polystyrene

A simple and efficient approach for the preparation of rod‐coil block copolymers comprising oligo‐ and polythiophenes blocks together with PMMA or PS blocks is described. The block copolymers were prepared using a two‐step procedure. α,ω‐dicarboxy‐terminated oligothiophenes and carboxy terminated poly(3‐hexylthiophene) were first prepared. These were then reacted with P₄S₁₀ in a second step to generate the α,ω‐thioester terminated oligothiophenes and poly(3‐hexylthiophene)s which were subsequently used in a one‐pot reaction as RAFT polymerization agents with methylmethacrylate and styrene. The di‐ and tri‐block copolymers hence obtained were fully characterized, both in solution and as thin films.