Degradation of Poly(butyl acrylate) and Poly(2‐hydroxyethyl methacrylate) Model Compounds Under Extreme Environmental Conditions

The degradation of low‐MW ( = 1 500 g · mol^?1) model compounds of pBA and pHEMA were studied under conditions corresponding to the worst‐case temperatures and irradiation intensities likely to be experienced by a surface coating exposed to the harsh Australian environment. Vinyl‐terminated polymers were compared to their saturated analogues; the terminal vinyl bond was found to be a source of instability which rendered the polymers more susceptible to degradation. The cyclic degradation mechanism derived from degradation of pMMA in our previous publication is also relevant to pBA and pHEMA. In addition, pBA and pHEMA are susceptible to other degradation and crosslinking reactions; crosslinking is particularly rapid in pHEMA exposed to UV radiation.

     

Water‐Soluble Building Blocks for Terpyridine‐Containing Supramolecular Polymers: Synthesis,Complexation, and pH Stability Studies of Poly(ethylene oxide) Moieties

Poly(ethylene oxide) of various molecular weights (M _n = 3 000, 5 200, 10 000, 16 500 g · mol^?1) has been modified with terpyridine end groups as building blocks for water‐soluble metallo‐supramolecular polymers. Metallo‐supramolecular A–A homopolymers have been prepared and characterized by complexing the terpyridine units of one selected poly(ethylene oxide) (M _n = 3 000 g · mol^?1) with the following transition metal ions in their 2+ oxidation state: Fe, Ru, Co, Ni, Cu, Zn, and Cd. In addition, the stability of the supramolecular connection with respect to pH variations has been investigated.

Schematic representation of the product of poly(ethylene oxide) modification with terpyridine end groups and the metal complexation.     

Aqueous Micelles from Supramolecular Graft Copolymers

Aqueous micelles have been prepared from amphiphilic supramolecular graft copolymers, in which poly(ethylene glycol) (PEG) side chains were linked to a poly(methyl methacrylate) (PMMA) backbone via ruthenium(II )‐terpyridine complexes. Three different graft copolymers were investigated, in which the average number of PEG branches (constant length) and the length of the PMMA backbone were varied. The successful formation of micelles was proven by dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). A good agreement was found between TEM and AFM observations, which show polydisperse spherical micelles. The hydrodynamic diameter measured by DLS was much larger, suggesting the formation of aggregates. No substantial difference in the micellar characteristic features was found between the three investigated samples.

Schematic representation of the graft copolymer synthesis.     

Quantitative Analysis of Dielectric Constants from EFM Images of Multicomponent Polymer Blends

Summary: A simple quantitative model for the analysis of EFM images of three‐ or more‐component polymer blends is applied to determine the dielectric constants of the blend constituents. The value of the dielectric constant of PIPA calculated from the EFM images of POMA‐PIPA‐APP blend is determined in good agreement with the literature value.

     

New Regular,Amphiphilic Poly(ampholyte)s: Synthesis and Characterization

Summary: Hydrophobically substituted diallylamines bearing a hexyl, dodecyl, or octadecyl chain were synthesized and homopolymerized as hydrochlorides. Copolymerization of the diallylamines with maleic acid produces alternating copolymers. The copolymers behave as amphiphilic polyampholytes and dissolve best in the acidic or in the basic form. Only the copolymer with the hexyl chain could be dissolved in aqueous solvents and shows hydrophobic association. The copolymers with the longer alkyl chains require polar protic organic solvents. All polymers are amorphous, but show a superstructure in bulk due to their amphiphilicity.

     

Polyether Core‐Shell Cylinder–Polymerization of Polyglycidol Macromonomers

Summary: The synthesis and polymerization of macromonomers containing a polymerizable styrene head group and a tail of ethylene oxide derivatives of different character were investigated. The synthesis of macromonomers was based on living anionic polymerization of oxiranes. Two monomers were used: 1‐ethoxyethyl glycidyl ether (glycidol acetal), which after hydrolysis forms hydrophilic glycidol blocks and glycidyl phenyl ether forming hydrophobic blocks. Polymerizable double bonds were introduced by terminating the living chain with p‐(chloromethyl)styrene. The radical polymerization of the macromonomers was carried out in water with addition of a non‐polar solvent (benzene) and AIBN as initiator. Core‐shell polymers of different character and molar masses were obtained. The conversion of polymerized macromonomers was around 50%. However, the polymerization product could easily be separated from the reaction mixture.

     

Characterization of Water‐Dispersible n‐Type Poly(benzimidazobenzophenanthroline) Derivatives

Novel water dispersible poly(benzimidazobenzophenanthroline) polymers functionalized with poly(ethylene oxide) (BBL:PEO) have been investigated by cyclic voltammetry, in situ UV‐vis spectroscopy and atomic force microscopy. The cyclic voltammograms recorded during n‐doping indicate that the drop coated BBL:PEO films retain their properties despite functionalization. A small influence of the PEO side chains on redox properties of the investigated polymers was found, diminishing however after annealing. During spectroscopic experiments structural changes connected with polymer charging were observed (in accordance with a two electron transfer process). The functionalization of BBL with PEO side chains provided an easy processing method to obtain smooth and reproducible polymer films.

     

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 Characterization of Polymer Brushes on Micromechanical Cantilevers

Summary: A technique to cover microelectromechanical systems (MEMS), such as micromechanical cantilever (MC) sensors, with a covalently bound brush layer has been developed. The polymer layer was grown using a “grafting‐from” synthesis of polymer brushes under mild conditions, by surface‐initiated atom transfer radical polymerization. Atomic force microscopy (AFM) and ellipsometry have revealed a uniform thickness of about 12 nm from which a grafting density of polymer brushes of 0.19 chains · nm^?2 was estimated. The coating with polymer brushes can be realized on a selected surface. It was shown that a single‐sided brush layer swells reversibly in toluene, resulting in a bending of the micromechanical cantilever.

Schematic representation of the PMMA brush synthesis on the MC surface, by surface‐initiated ATRP.     

Synthesis of Three Types of Amphiphilic Poly(ethylene glycol)‐block‐Poly(sebacic anhydride) Copolymers and Studies of their Micellar Solutions

Summary: Linear, three‐ and four‐armed block copolymers based on PEG and PSA were synthesized by melt polycondensation reactions. The CMC of the copolymer was measured using the dye solubilization method. The copolymers were found to self‐aggregate in water to form micelles above the CMC. The micellar solutions were prepared with different methods and investigated by DLS and AFM. The DLS method was used to measure the mean hydrodynamic diameters of the micelles. It was found that preparation method and condition of the micellar solution, as well as the structure and composition of the copolymer had effects on the hydrodynamic diameter of the copolymer micelles. AFM studies showed that the morphology of the micelle was spherical.

Synthesis of 3‐armed stars based on poly(ethylene glycol) and poly(sebacic anhydride).     

Block Copolymers Build‐up of Electron and Hole Transport Materials

Summary: In this article we describe the synthesis of various monomers modified with triphenyl‐1,3,5‐triazine side groups as electron transport moieties. By nitroxide‐mediated polymerization with a TEMPO unimer it was possible to obtain polymers with a narrow polydispersity. Furthermore, by living radical polymerization block copolymers were obtained from these monomers. Therefore, microphase separated structures are accessible which possess hole conducting moieties in one phase and electron conducting moieties in the other phase.

General build‐up of the copolymers consisting of hole and electron conductor.     

Synthesis of Macro(alkoxyamines) via Hydroboration of Polyolefins with Subsequent Nitroxide Oxidation for Controlled NMP

A novel method for the synthesis of alkoxyamines that are subsequently used as initiator/regulators for NMP is reported. This method can be applied to low‐molecular‐weight olefins as well as to macromolecules containing alkene moieties to form poly(alkoxyamines). The reaction sequence comprises hydroboration of olefins with catecholborane followed by oxidation of alkylborane intermediates using nitroxides in the presence of methyl vinyl ketone to ultimately yield alkoxyamines that serve as suitable initiators for NMP. The first application of these alkoxyamines for the preparation of comb and star polymers is presented.

     

Synthesis and Characterization of Block Copolymers of ε‐Caprolactone and DL‐Lactide Initiated by Ethylene Glycol or Poly(ethylene glycol)

Biodegradable copolymers were prepared by ring‐opening polymerization of sequentially added ε‐caprolactone and DL ‐lactide in the presence of ethylene glycol or poly(ethylene glycol), using zinc metal as catalyst. Polymerization was performed in bulk and yielded block copolymers with predetermined PEG/PCL/PLA segments. The obtained polymers were characterized by ¹H NMR, SEC, IR, DSC, TGA, and X‐ray diffraction. Data showed that the copolymers preserved the excellent thermal behavior inherent to PCL. The crystallinity of PLA‐containing copolymers was reduced with respect to PCL homopolymer. The presence of both hydrophilic PEG and fast degrading PLA blocks should improve the biocompatibility and biodegradability of the materials, which are of interest for applications as substrate in drug delivery or as scaffolding in tissue engineering.

Block copolymerization of ε‐caprolactone and DL ‐lactide initiated by dihydroxyl PEG.     

Synthesis of poly(phosphonylhydrazides)

Phenylphosphonic diisocyanate has been prepared and polymers from its condensation with hydrazines using the interfacial technique are reported. The polymers are believed to contain the following repeating structure:      

Synthesis and Hole‐Transporting Property of a Novel Poly(N‐vinylcarbazole) Copolymer with Metal‐Coordination Sites

Summary: Hole transporting poly(N‐vinylcarbazole) copolymers with phenylazomethine dendron units acting as metal ligation sites were synthesized. These polymers possess both hole‐transport and metal‐collecting units with simple σ‐bond linkages. Complexation in the phenylazomethine dendron unit within these copolymers by SnCl₂ has been successfully observed by the change in the UV‐vis spectra. The complexation changes the HOMO/LUMO energy gap that results in a spectral red‐shift. Using copolymers as a hole‐transport layer, only complexation with metal ions leads to an enhanced maximum luminescence. Such a complexation results in a high electroluminescence efficiency because the p‐type‐doped structure acts as the hole‐transport layer.

Copolymerization for the preparation of DPAGn(x)‐Cbz(y).     

Pinacol rearrangement in the polymer backbone: Synthesis of novel reactive polymers with condensed benzopinacol units in the main chain and their complete rearrangement to poly(benzopinacolone)s

Novel reactive polymers with condensed benzopinacol moieties in the main chain were synthesized and their acid‐catalyzed pinacol rearrangement in the polymer backbone proceeded to afford poly(benzopinacolone)s quantitatively. Since the pinacol rearrangement shows an intramolecular mechanism, no crossover between the polymer chains was observed through the rearrangement. Although the number‐averaged molecular weights and their distributions were not changed, the optical and thermal properties of the poly(benzopinacolone)s were completely different from the parent poly(benzopinacolone)s.

     

Synthesis of Poly(urethane acrylate‐co‐styrene) Films Containing Silver Nanoparticles by a Simultaneous Copolymerization/in situ Electron Transfer Reaction

Summary: A novel process for the synthesis of nanocomposite films containing silver nanoparticles is presented. Unlike conventional synthetic processes, silver nanoparticles and the polymer film constituting the nanocomposite film were synthesized simultaneously through an in situ electron transfer reaction and the copolymerization of styrene and amphiphilic urethane acrylate nonionomer (UAN), which contains hydrophobic poly(propylene oxide) segments and hydrophilic poly(ethylene oxide) segments along the same backbone. Silver nitrate crystals were first dissolved in a UAN/styrene solution through the formation of a complex between silver salts and the poly(ethylene oxide) chains of UAN, and then the transparent solutions obtained were directly converted to transparent free‐standing films containing silver nanoparticles by copolymerization and an electron transfer reaction by radicals. The amount of radical initiator strongly influenced the size and number of silver nanoparticles formed within the polymer films. The formation of silver nanoparticles was confirmed by transmission electron microscopy (TEM) and characteristic UV absorbance spectra. Hydrophobic/hydrophilic microphase separation in the UAN/styrene solution was also confirmed by TEM and mechanical property measurements.

TEM image of poly(urethane‐co‐styrene) film containing silver nanoparticles.     

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.

     

Crystal Growth in Poly(L‐lactide) Thin Film Revealed by in situ Atomic Force Microscopy

Direct visualization of crystal growth in poly(L ‐lactide) thin films was carried out by using a temperature‐controlled atomic force microscopy (AFM). At the initial stage of crystallization, edge‐on lamellar crystals have nucleated and elongated. Subsequently, the edge‐on lamellar crystals showed S‐shaped morphology and changed their orientation from edge‐on manner to flat‐on one. The curvature of edge‐on lamellar crystal has been discussed in terms of inclination and distortion of polymer chains in the crystal. In addition, mechanism on the formation of flat‐on crystal from edge‐on lamellae was proposed as derivative growth on the basis of in situ AFM observation of crystal growth and enzymatic degradation.

     

X‐Ray Diffraction Studies on the Phase‐Transformational Behavior of a Smectic Liquid‐Crystalline Elastomer Composed of Chiral Mesogens

Structural changes through successive phase transformations of a chiral smectic liquid‐crystalline elastomer are investigated by X‐ray scattering technique. In uniaxially deformed elastomers, the smectic layer seemingly tilts even in the SmA phase, in which an in‐plane chevron structure formed in the tilted smectic phase. On the basis of an analysis of the layer reflection peaks, the layer correlation length in the tilted smectic phases is shorter than that in the non‐tilted SmA phase, though smectic layers in the tilted smectic phases are better ordered than those in SmA.

Experimental arrangement for X‐ray measurements of the uniaxially deformed elastomer in the tilted smectic phase at room temperature.