The Ring Opening Metathesis Polymerisation Toolbox

Summary: The success of metathesis chemistry techniques has sparked a tremendous interest in polymer and material chemistry. This contribution provides an overview of the state of the art in ring opening metathesis polymerisation (ROMP). It is intended to provide the reader with useful information on the interplay of initiators, monomers, and reaction conditions, thus aiding polymer chemists to utilise the ROMP toolbox. Prominent and illustrative examples from current research are given in the article.

The “ROMP toolbox”.     

Structural Characterization of Biocidal Oligoguanidines

Oligomeric guanidines can be obtained by polycondensation of guanidine hydrochloride and 1,2‐bis(2‐aminoethoxy)ethane. A comparative MALDI‐TOF mass spectrometry/NMR spectroscopy study with a ¹³C‐labeled sample enabled the unambiguous analysis of a guanidine‐based polymer. Among the four major product series unprecedented macrocyclic compounds were detected. The minimum inhibition concentrations for four different microorganisms were determined, showing excellent biocidal activities.

     

Step‐Growth Radical Addition‐Coupling Polymerization (RACP) for Synthesis of Alternating Copolymers

We report a new type of step‐growth radical addition‐coupling polymerization (RACP) involving consecutive addition of carbon‐centered radical derived from α,α′‐dibromo dibasic ester to NO double bond of C‐nitroso compound followed by cross‐coupling of carbon‐centered radical and in situ formed nitroxyl radical, which produces alternating copolymers with high molecular weight and unimodal molecular weight distribution from saturated and unsaturated monomers.

     

Effect of Cocatalysts on the Catalytic Activities of Tantalum‐ and Niobium‐Based Catalysts for Ring‐Opening Metathesis Polymerization of Norbornene

A series of pentavalent tantalum and niobium complexes with aryloxy ligands was prepared, and their catalytic behavior for the ROMP of norbornene was studied in the presence of an alkylaluminum cocatalyst. Tantalum complexes 1 – 4 showed very high activity for the ROMP of NBE in combination with ⁱBu₃Al to give high‐molecular‐weight polymers. In contrast, the niobium complexes 5 and 6 , as well as NbCl₅, exhibited very high activity upon activation with Me₃Al to give high‐molecular‐weight polymers.

     

Synthesis of Well‐Defined Telechelic Aromatic Polyamides by Chain‐Growth Polycondensation: Application to the Synthesis of Block Copolymers of Polyamide and Poly(tetrahydrofuran)

Well‐defined telechelic‐type aromatic polyamides having a secondary amino group and a phenyl ester moiety at each chain end were prepared by the chain‐growth polycondensation of phenyl 4‐(octylamino)benzoate ( 1 ) with initiator 2 (N‐tert‐butoxycarbonylated 1 ), followed by deprotection of the N‐protecting group of the initiator unit. This polycondensation was applied to the synthesis of well‐defined di‐ and triblock copolymers of aromatic polyamides and poly(tetrahydrofuran) (poly(THF)) by the reaction of the terminal secondary amino group of the polyamide with the living cationic propagating group of poly(THF).

Block copolymers of polyamide and poly(tetrahydrofuran).     

Self‐Assembly of Cylinder‐Forming ABA Triblock Copolymers under Cylindrical Confinement

The self‐assembly of two types of linear ABA triblock copolymers confined in cylindrical nanopores is studied using simulated annealing. The effects of pore size and block copolymer chain architecture on morphology, chain conformations and bridging fraction are investigated. For the bulk cylinder‐forming copolymers, novel structures such as helices and stacked toroids form, which depend sensitively on the pore size. Several significant differences between the two types of copolymers are predicted and explained based on the differences in their chain conformations and chain architectures. A simple model is proposed to explain the mean square radius of gyration for the bridge and loop chains.

     

Novel Biodegradable Copolymers with a Periodic Sequence Structure Derived from Succinate Butan‐1,4‐diol,and Butan‐1,4‐diamine

Summary: Novel biodegradable copolymers derived from succinate, butan‐1,4‐diol, and butan‐1,4‐diamine were synthesized by two‐step polycondensation reactions. The obtained copolymers had a periodical‐sequence structure consisting of ester and amide units, and the melting temperatures of the periodic copolymers increased with an increase in amide content. The crystalline structure of the periodic copolymers differs from that of butylene succinate homopolymer (PBS), and these results suggest that the periodically introduced amide units are included in the crystalline phase forming a novel crystalline structure.

Periodic copolyester‐amides derived from succinate, butane‐1,4‐diol, and butan‐1,4‐diamine     

Synthesis and Characterization of Thermally Curable Benzoxazine‐Functionalized Polystyrene Macromonomers

Summary: Thermally curable benzoxazine ring‐containing polystyrene macromonomers were synthesized and characterized. 1,4‐Dibromo‐2,5‐bis(bromomethyl)benzene and 1,4‐dibromo‐2‐(bromomethyl)benzene were used as initiators in the atom transfer radical polymerization of styrene. The resulting polymers were used in combination with 3‐aminophenylboronic acid hemisulfate, for a Suzuki coupling. The obtained polymers, with amino groups in the middle or end of the chains, were reacted with formaldehyde and phenol to yield benzoxazine ring‐containing macromonomers. In addition to the glass transition temperature of the polystyrene segment observed at ca. 105 °C, differential scanning calorimetry thermograms exhibit an exotherm at ca. 276 °C corresponding to the oxazine thermal polymerization. Both macromonomers undergo thermal curing with the formation of thermosets having polystyrene segments.

Structure of the benzoxazine‐functionalized polystyrene.     

Switching the Solubility of PMMA Bearing Attached Cyclodextrin‐Moieties by Supramolecular Interactions with Ionic Liquids

Methacrylate‐modified β‐cyclodextrin (β‐CD) and methyl methacrylate (MMA) have been radically copolymerized to obtain hydrophobic CD copolymers. The water‐insoluble copolymers are able to form highly stable inclusion complexes with anions of ionic liquids. Surprisingly, the inclusion of the anions in the CD cavity results in a significant change of thermal and solution properties. Furthermore, it can be shown that the structure of the ionic liquid anions influences the coil structure of the copolymers. The obtained results could be proven by means of microcalorimetry, differential scanning calorimetry, and dynamic light scattering.

     

Cooperative Self‐Assembly of Nanoparticle Mixtures in Lamellar Diblock Copolymers: A Dissipative Particle Dynamics Study

Summary: Dissipative particle dynamics simulations are performed on the distribution of binary nanoparticle mixtures in lamellar diblock copolymers. The results show that the self‐assembly of nanoparticle mixtures in polymer matrix is a cooperative assembly that is affected by various factors, providing molecular‐level information for the rational design of new polymer nanocomposites with tailored properties.

The simulated polymer nanocomposite structure (the polymer matrix was omitted for clarity; P, gray; Q, black).     

Patterned Hydrophilization of Nanoporous 1,2‐PB by Thiol‐ene Photochemistry

We present an efficient method for functionalizing the large polymer–air interface of a gyroid nanoporous polymer. The hydrophilicity of nanoporous cross‐linked 1,2‐polybutadiene is tuned by thiol‐ene photo‐grafting of mercaptosuccinic acid or sodium 2‐mercaptoethanesulfonate. The reaction is monitored by FT‐IR, UV–Vis, contact angle, and gravimetry. Overall quantum yields are calculated for the two thiol‐ene “click” reactions in nano‐confinement, neatly revealing their chain‐like nature. Top–down photolithographic patterning is demonstrated, realizing hydrophilic nanoporous “corridors” exclusively hosting water. The presented approach can be relevant for many applications where, e.g., high control and contrast in hydrophilicity, chemical functionality or refractive index are needed.

     

Direct Synthesis of Pyridyl Disulfide‐Terminated Polymers by RAFT Polymerization

A trithiocarbonate RAFT agent was modified with a pyridyl disulfide group and used in the direct synthesis of endgroup pyridyl disulfide‐functionalized homo‐ and amphiphilic block copolymers of oligo(ethyleneglycol) acrylate (PEG‐A) and butyl acrylate (BA). Both the homo‐ and copolymerizations were found to be well controlled via the RAFT mechanism. The NMR analysis indicated that both the homopolymers of PEG‐A and the amphiphilic diblock copolymers of PEG‐A and BA possessed pyridyl disulfide terminal groups. A UV‐Vis absorption test revealed that the pyridyl disulfide endgroup of the polymer could be efficiently used to couple thiol‐bearing molecules to the polymer without the need for any post‐polymerization modification. This communication presents the first efficient direct synthesis of thiol‐reactive endgroup‐functionalized well‐defined polymers via the RAFT technique.

     

Morphologies of Spin‐Coated Films of a Library of Diblock Copoly(2‐oxazoline)s and Their Correlation to the Corresponding Surface Energies

Summary: The influence of surface morphologies on the properties of materials is of essential importance and is therefore a widely discussed topic. In the present contribution, the properties of a set of diblock copoly(2‐oxazoline)s are analyzed in terms of their individual morphologies, which have been investigated with tapping‐mode SFM. This collection of diblock copolymers consists of 12 diblock copolymers and four corresponding homopolymers, representing a complete 16‐membered library of (co‐) poly(2‐oxazoline)s, composed of four differently substituted 2‐oxazoline monomers. For the investigated set of compounds, a correlation between the morphologies of the spin‐coated films and their surface energies could be determined.

Morphologies of spin‐coated films of a library of diblock copoly(2‐oxazoline)s and their correlation to the corresponding surface energies.     

Synthesis and Characterization of Novel Biodegradable Copolymers of 5‐Benzyloxy‐1,3‐dioxan‐2‐one and Glycolide

A series of novel biodegradable random copolymers of 5‐benzyloxy‐1,3‐dioxan‐2‐one (5‐benzyloxy‐trimethylene carbonate, BTMC) and glycolide were synthesized by ring‐opening polymerization. The copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The incorporation of BTMC units into the copolymer chains results in good solubility of the polymers in common solvents. The in vitro degradation rate can be tailored by adjusting the composition of the copolymers.

The in vitro degradation of the homopolymers and poly(BTMC‐co‐GA) copolymers.     

Temperature‐Responsive Graft Copolymers with Poly(propylene glycol) Side Chains

The phase behavior of graft copolymers in aqueous solution was investigated. The graft copolymers consist of poly(propylene glycol) (PPG) side chains and N,N‐dimethylacrylamide (dMA), N‐vinylimidazole (VIm), and N‐isopropylacrylamide (iPA), respectively, as backbones. Phase transition temperatures of the PPG copolymers increased with increasing the content of dMA and iPA as relatively more hydrophilic comonomers and with an increase in the degree of ionization of the incorporated VIm units.

Chemical structure of the graft copolymers     

Synthesis of Dendronized Diblock Copolymers via Click Chemistry: The Effect of Dendronization on Phase Separation Behaviour

A novel route towards the synthesis of well‐defined linear–dendronized diblock copolymers is reported. Precursor alkyne containing diblock copolymers were modified in a highly efficient cycloaddition reaction with dendritic azides of different generation. The dendronization has been shown to be selective and could be driven to completion under ambient conditions. The phase separation of such dendronized diblock copolymers was investigated in dependence of the generation size being attached. Compared to a linear–linear diblock copolymer as starting material the dendronization yielded in a pronounced phase separation. The nanoscaled features observed in thin films strongly depended on the dendron size and a variety of morphologies could be identified. Hence, the unique combination of controlled radical polymerization and click chemistry allows for the triggering of structured surfaces in the nanometer‐regime.

     

Temperature Dependence of Photoinduced Birefringence in Polystyrene Doped with Disperse Red‐1

A theoretical model on the basis of the free‐volume concept is presented explaining the temperature dependence of photoinduced birefringence in polystyrene films that contain Disperse Red‐1. Birefringence increases with temperature up to 180 K as the free volume for isomerization increases, and then decreases as thermally activated processes dominate. The fast process of birefringence decay has a time constant that increases with temperature at low temperatures, due to the change in photoisomerization.

Temperature dependence of the birefringence amplitude measured at 300 s. The amplitude increases with temperature up to 180 K and then decreases. The solid line is for guiding the eye.     

Self‐Assembly of Heteroarm Star Copolymers – A Monte Carlo Study

Dynamic lattice Monte Carlo simulations on a simple cubic lattice were used to study the association behavior of heteroarm star copolymers with two types of chemically different arms (miktoarm star). The effect of architecture and composition (number and length of arms) on self‐assembly was investigated. Simulations revealed substantial differences between associates formed by linear diblock copolymers and by star copolymers. It was also observed that the length of arms considerably influences the association behavior. Apart from the structural characteristics of the whole associate, the properties of individual stars in associates were also studied. These results provide detailed information on the inner structure of associates.

     

Novel Polyolefins Containing Crystallizable Isotactic Polystyrene Side Chains

Vinyl‐terminated isotactic polystyrene macromonomers were copolymerized with ethylene and 1‐octene to new polyolefin graft copolymers with crystallizable polystyrene side chains. The iPS content was varied from 4 to 78 wt.‐% using different metallocene and halfsandwich catalysts. No solubility problems of the stereoregular macromonomer occured, because iPS does not crystallize during polymerization. In addition the polymers show nanophase separation of the polyolefin backbone and the iPS side chains. The crystallization of iPS, having a melting point of about 200 °C, can be achieved by annealing. This synthesis strategy allows the fabrication of a new class of thermoplastic elastomers with improved heat distortion temperatures.