Solid‐State Olefin Metathesis: ADMET of Rigid‐Rod Polymers and Ring‐Closing Metathesis

Summary: Solid‐state olefin metathesis of rigid‐rod acyclic diene metathesis (ADMET) polymers and ring‐closing metathesis (RCM) have been investigated. 1,4‐Dipropoxy‐2,5‐divinylbenzene ( 4 ) was synthesized and used in a bulk ADMET polymerization to produce oligomers of dialkoxy poly(phenylene vinylene). The reaction was continued in the solid state, effectively doubling the molecular weight. Solid‐state RCM was investigated with a variety of solid dienes and metathesis catalysts, and demonstrated in low conversions using amide diene 5 with catalysts 9 , 13 , and 14 .

     

Rapid Synthesis and MALDI‐ToF Characterization of Poly(ethylene oxide) Multiarm Star Polymers

Multiarm PEO star polymers with a purely aliphatic polyether structure have been synthesized using hyperbranched polyglycerol (PG) with different molecular weights as a multifunctional initiator. Different degrees of deprotonation of the initiator were studied with respect to molecular weight control. The results show that the degree of deprotonation is a crucial parameter for the synthesis of well‐defined polymers with controlled molecular weights. Partial deprotonation of the PG hydroxyl groups (5–8%) was proven to represent an optimum for the synthesis of star polymers with molecular masses close to the theoretical values. Molecular weights of the stars ranged between 9 000 and 30 000 g · mol^?1. MALDI‐ToF spectra confirmed that the PEO arms in the star polymers possess homogeneous lengths.

     

A Study of Copolymerization of 1‐Hexene with 2,5‐Norbornadiene Using Metallocene Catalysts

Summary: Copolymerization of 1‐hexene with a symmetrical diene, namely 2,5‐norbornadiene was studied using four different metallocene catalysts. Copolymerization was found to occur exclusively through one of the two equally reactive endocyclic double bonds with all the four catalysts. Copolymerization results in low molecular weight oligomers with the number average molecular weight ( ) varying from 1 000–3 000. End group analysis of the co‐oligomers revealed that the β‐hydrogen transfer after 2,1 insertion also occurs in the presence of highly regiospecific catalysts. The regio errors were also found to depend on various reaction parameters such as polymerization time, Al/Zr mol ratio, metallocene concentration and polymerization temperature.

Plots of variation in end groups and NBD incorporation with time.     

Metathetic Selective Degradation of Polyisoprene: Low‐Molecular‐Weight Telechelic Oligomer Obtained from Both Synthetic and Natural Rubber

Summary: Degradation studies of cis‐1,4‐polyisoprene were carried out using first and second generation Grubbs catalysts to achieve end‐functionalized acetoxy oligomers in both an organic solvent and a latex phase at room temperature. Well‐defined acetoxy telechelic polyisoprene structures were obtained in a selective manner with a range of from 10 000 to 30 000, with a polydispersity index of around 2.5.

Structure produced by the metathetic depolymerization of hydroxy telechelic cis‐1,4‐polyisoprene.     

Hydrolytic Polycondensation of Bisphenol‐A‐Bischloroformate Catalyzed by Phase‐Transfer Catalysts

The hydrolytic interfacial polycondensation of bisphenol‐A‐bischloroformate was performed with four different phase‐transfer (PT) catalysts: N‐butylpyridinium bromide, triethylbenzylammonium (TEBA) chloride, tetrabutylammonium hydrogen sulfate, and tetraphenylphosphonium bromide. These polycondensations were conducted at 5 or 35 °C initial reaction temperature. The resulting polycarbonates were characterized by viscosity and SEC measurements and by MALDI‐TOF mass spectrometry. The four PT catalysts gave quite different results with respect to molecular weight and formation of cyclic polycarbonates. The highest molecular weights (number average, and weight average, ) were obtained with TEBA‐Cl. Lower temperatures and high feed ratios of TEBA‐Cl proved to be favorable for both high molecular weights and high fractions of cycles. Cyclic polycarbonates were detectable in the mass spectra up to 14 kDa (technical limit of the measurements). Low molecular weights in combination with unreacted chloroformate groups proved that the other PT‐catalysts were less efficient under the given reaction conditions.

MALDI‐TOF mass spectrum of the polycarbonate No. 3b .     

Control of the radical polymerization by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl and its sodium salt

The control of the radical polymerization of styrene by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl is reported here in bulk at 90 °C, 120 °C and in miniemulsion. Similarly, the control by its sodium complex is reported in bulk at 90 °C.

M _n vs. conversion for 3 , 3Na , and TEMPO.     

Synthesis of Defined Poly(silsesquioxane)s: Fast Polycondensation of Trialkoxysilanes in a Continuous‐Flow Microreactor

The polycondensation of trialkoxysilanes to PSSQs in a microreactor setup is demonstrated. While continuous‐flow processes involving microreactors found various applications in chain growth polymerization, their influence on step‐growth polymerization is less explored, and the polycondensation of multifunctional monomers has not been studied in detail. We found significantly increased yields and a decreased polydispersity of the obtained polymers in comparison to the batch process. By variation of the residence time molecular weights could be adjusted reproducibly ranging from = 1 900 to 11 000 g · mol^?1. Thus, the microreactor setup offers for the first time the possibility to synthesize PSSQ with adjustable properties.

     

Synthesis and self‐assembly of polymers containing dicarboximide groups by living ring‐opening metathesis polymerization

Polymers with narrow molecular weight distributions and controlled architectures were generated by living ring‐opening metathesis polymerization of exo‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboximide. The dicarboximide units have been previously shown to exhibit biological activity, can selectively bind to the nucleic acid base adenine by hydrogen‐bonding, and are readily functionalizable. Block copolymers containing these moieties were generated, and underwent self‐assembly into nanoscale spherical aggregates, with surface localized molecular recognition motifs.

     

Synthesis of Propylene/1‐Butene Copolymers with Ziegler‐Natta Catalyst in Gas‐Phase Copolymerizations, 1

Summary: The appropriate choice of comonomers can be used to create a wide range of polymer properties, leading to considerable improvement of product performance. Experimental runs were performed to evaluate the effect of 1‐butene on the crystallinity, the melt temperature and the molecular weight distribution (MWD) of the final propylene/1‐butene copolymer resins. According to the results obtained, the melt temperature of the copolymer material can be reduced significantly compared to that of the polypropylene homopolymer. The incorporation of 1‐butene into the copolymer chain leads to a decrease of the sealing initiation temperatures of propylene polymer resins. GPC analyses of copolymer samples showed that 1‐butene concentration does not seem to significantly influence either the shape of the MWD or the polydispersity indexes for a given set of reaction conditions. Therefore, a family of propylene/1‐butene random copolymers grades can be successfully developed for gas phase processes for packaging and film applications.

     

Morphology and Phase Characteristics of High‐Density Polyethylene Probed by NMR Spin Diffusion and Second Moment Analysis

Summary: A dipolar filter pulse sequence combined with cross‐polarization‐MAS is applied to characterize the phase distribution, morphology, and spin diffusion within a high‐density polyethylene sample. A new method to obtain quantitative ¹³C NMR by combining cross‐polarization‐MAS and spin diffusion NMR is presented. The derived crystallinity is consistent with the corresponding crystallinity obtained by ¹H NMR.

Illustration of the pulse sequence(s) applied in the present work.     

Synthesis and Photophysical Investigations of Novel Polymerizable Blue Emitting Fluorophores – Combination of a Hindered Amine with a Benzo[de]isoquinoline‐1,3‐dione

Summary: New monomeric benzo[de]isoquinoline‐1,3‐dione blue emitting fluorophores, containing hindered amine stabilizer fragment have been synthesized under phase transfer catalysis conditions and their ability for “one‐step” optical bleaching and stabilization of poly(methyl methacrylate) has been demonstrated. During the co‐polymerization, no changes in the chromophoric system of the fluorophore occurred. The chemical bonding of the synthesized monomers in the polymer chain was confirmed spectrophotometrically. The absorption and some basic photophysical characteristics of the low and high molecular weight fluorescent brighteners have been determined. Photostability of the new monomeric fluorophores and their influence on the photostability of the blue emitting side‐group co‐polymers obtained have been established. A significant stabilizing effect against photodegradation was determined.

     

Photoinitiated Cationic Polymerization of Substituted Vinylcyclopropanes

Summary: The photoinitiated cationic polymerization of 1‐cyclopropyl‐l‐phenyl‐ethylene, 1‐cyclopropyl‐l‐(p‐methoxyphenyl)ethylene and 1‐cyclopropyl‐l‐(p‐fluorophenyl)ethylene at ambient temperatures in bulk and in solution was investigated using (η⁵‐2,4‐cyclopentadiene‐l‐yl)[l,2,3,4,5,6‐η] (l‐(methylethyl) benzene)iron(I) hexafluorophosphate (Irgacure 261, I‐1 ) and ditolyliodonium hexafluorophosphate ( I‐2 ). In contrast to our results in the polymerization of 2‐cyclopropyl‐4‐methylene‐l,3‐dioxolanes, partial ring‐opening of the cyclopropane ring could be detected. A volume shrinkage of about 11% was found.

     

Poly(4‐hexyl‐1,2,4‐triazole‐4H): An Electron Semiconducting Analogue to Regioregular Poly(hexylthiophene)

Summary: For the development of n‐channel field‐effect transistors it is indispensable to look for semiconducting polymers with electrons as majority charge carriers (n‐type). In addition high electron mobility values are of significant advantage in these compounds. Polymers with electron transporting properties have been rarely investigated. Main chain polymers with strong acceptor units like 1,2,4‐triazoles‐4H are potential candidates for electron transporting materials in electronic devices. Therefore, a synthetic pathway leading to an organo‐soluble polymer consisting only of 4‐hexyl‐1,2,4‐triazole‐4H units in the main chain is presented in this work. We will report the synthesis using modified classical polycondensation. The chemical and electronic properties of the polytriazole have been investigated in detail. The material has been used to prepare “electron‐only” devices for the calculation of the electron mobility.

The suggested chemical structure of poly(4‐hexyl‐1,2,4‐triazole‐4H) (PHTA).     

Protonation of Sulfonated Poly(4,4′‐diphenylether‐1,3,4‐oxadiazole) Membranes

This work describes the effect of sulfuric acid protonation on the properties of SPOD‐DPE membranes using FT‐IR and impedance spectroscopic analyses. The IR spectra showed the protonation of nitrogen atoms from oxadiazole rings, with a broad band complex in the region 3 000–2 100 cm^?1 with two centered peaks at 2 590 and 2 440 cm^?1. The S?O characteristic absorption bands in SPOD‐DPE and sulfuric acid were specially studied in the region of 1 800–900 cm^?1. The band shifts are associated to the interaction between acid groups and oxadiazole ring nitrogen atoms. The IR spectra evidenced the presence of three absorption species (HSO, SO and free H₂SO₄) depending on the sulfuric acid concentration. For the protonated SPOD‐DPE membranes, a proton conductivity around 10 mS · cm^?1 was reached at 50 °C.

     

Synthesis of hydroxytelechelic ε‐caprolactone/poly(ethylene terephthalate) co‐oligomers, 1

In the presence of ethylene glycol, poly(ethylene terephthalate) (PET) undergoes chain scissions with the formation of α,ω‐hydroxyl oligomers, through classical transesterification by alcoholysis. ε‐Caprolactone was subsequently added on the hydroxyl end groups of PET oligomers by ring‐opening polymerization at different molar ratios of ε‐caprolactone to PET oligomers. The chemical structure of the products was investigated by size exclusion chromatography, ¹H NMR spectroscopy, and differential scanning calorimetry. A large majority of these products are soluble in common organic solvents. The thermal and ¹H NMR analyses reveal that the transesterification between base units of PET oligomers and ε‐caprolactone during the synthesis is always present whatever the reaction conditions. This phenomenon leads to copolymers having thermal properties different from those of PET. However, some co‐oligomers present the interest of keeping properties close to those of PET. The main purpose of this study was the synthesis of PET co‐oligomers that are soluble in some organic solvents that would make their use easier, and so that they can be used further as hard segment precursers for polycondensation reactions.

Ring‐opening polymerization of ε‐caprolactone onto hydroxytelechelic oligomers of PET.     

Light‐Tunable Thermosensitivity of Polymer‐Coated Gold Nanoparticles Achieved by Light‐Controlled Molecular Recognition

Thermo‐ and photosensitive gold nanoparticles (AuNPs) coated with an azobenzene‐contained P(DMA‐PAPA‐MAEL) copolymer are prepared by ligand exchange reactions. The photoisomerization of azobenzene moiety on the surface of P(DMA‐PAPA‐MAEL)‐coated AuNPs is detected by means of UV‐Vis spectroscopy with the presence or absence of free α‐cyclodextrin. When subjected to visible and UV light irradiation alternately, P(DMA‐PAPA‐MAEL)‐coated AuNPs in the presence of free α‐CD display a light‐tunable lower critical solution temperature through light‐controlled molecular recognition between the azobenzene moiety on the surface of AuNPs and free α‐CD.

     

Multilayer Films Fabricated from Oppositely Charged Polyphenylene Dendrimers by Electrostatic Layer‐by‐Layer Assembly

Summary: Assemblies of oppositely charged L ‐lysine/carboxylic acid functionalized polyphenylene dendrimers and hybrid multilayers of L ‐lysine dendrimers/colloidal gold nanocrystals were fabricated as alternate multilayers on 3‐mercaptopropionic acid coated gold surfaces via layer‐by‐layer deposition. The fabrication of the multilayer films was monitored by kinetic and scan mode surface plasmon resonance spectroscopy. The permeability properties of the dendritic polyelectrolyte layers were characterized by electrochemistry in the presence of [Fe(CN)₆]^3?/4? as the redox couple. A high interfacial charge‐transfer resistance, originating from the electrostatic repulsion of the negatively charged redox couple against the negatively charged interface was observed and the charge‐transfer resistance found to increase with increasing number of layers.

3D‐structure of the investigated polyphenylene dendrimers: a) G₂(L ‐lysine)₈ and b) G₂(COOH)₁₆.     

Synthesis of New Polymethyloxazoline Hydrogels by the “Macroinitiator” Method

New polymethyloxazoline hydrogels are synthesized by the cationic ring‐opening copolymerization of 2‐methyl‐2‐oxazoline and 2,2′‐tetramethylenebis(2‐oxazoline), using random copolymers of chloromethylstyrene and methyl methacrylate, or of chloromethylstyrene and styrene as macroinitiators. The synthesis is carried out in benzonitrile at 110 °C in the presence of potassium iodide, which activates the chloromethyl group as initiating functionality. In general, the hydrogels are obtained very rapidly, with a yield of between 42 and 95 wt.‐%. Besides its initiating function, the macroinitiator also provides the possibility of introducing heterogeneity into the hydrogel structure by forming rigid hydrophobic domains. The hydrogel structures were characterized by high‐resolution magic angle spinning NMR spectroscopy, and their solvent absorption capacity was determined by swelling experiments in solvents of different polarity. The hydrogels showed a maximal swelling degree of 18 g of water and 40 g of methanol, respectively, per gram of the hydrogel.

     

Amorphous‐Crystalline PSnPEOn Heteroarm Star Copolymers: Crystallinity and Crystallization Kinetics

Summary: The crystallization behavior and kinetics of poly(ethylene oxide) in polystyrene/poly(ethylene oxide) heteroarm star copolymers were studied by differential scanning calorimetry and optical microscopy. A comparison between star and linear amorphous‐crystalline block copolymers showed that the macromolecular architecture is an important factor affecting crystallinity. The following points were observed: the equilibrium melting point is higher in the star copolymers, the crystallinity reduces as the number of arms increases, leading to smaller and ill‐defined spherulites, and crystallization proceeds faster in linear copolymers at low supercooling.

Half crystallization times, t_1/2, calculated from the Avrami analysis of the latent heats, obtained during the isothermal crystallization experiments as a function of supercooling, ΔT, for all copolymers.     

Synthesis and Electroluminescent Properties of Disubstituted Polyacetylene Derivatives Containing Multi‐Fluorophenyl and Cyclohexylphenyl Side Groups

A new series of disubstituted polyacetylene derivatives that contain multi‐fluorine atoms on the pendent phenyl ring have been synthesized and characterized. The results reveal a greater red‐shift in UV‐vis absorption and PL emission upon incorporating more fluorine atoms on the pendent phenyl ring. Among them, disubstituted polyacetylene with a difluorophenyl group ( PDPA‐2F ) showed the highest luminescent efficiency. The device performance can be promoted by blending a hole‐transporting material TM‐TPD into PDPA‐2F as the active layer or by using a light‐emitting copolymer in which PDPA‐2F was copolymerized with a carbazole group ( PDPA‐2Fcab ). A light‐emitting diode of ITO/PEDOT/ PDPA‐2Fcab /Ca/Al revealed a maximum luminescence of 4230 cd · m^?2 at 14 V and a maximum current efficiency of 3.37 cd · A^?1 at 7 V.