Complex Macromolecular Architectures Research Articles

The Strength of the Macromonomer Strategy for Complex Macromolecular Architecture: Molecular Characterization, Properties and Applications of Polymacromonomers

AbstractThe efficiency of the macromonomer (MM) synthetic strategy for the creation of nonlinear complex macromolecular architectures (miktoarm stars, α,ω‐branched polymers, random/exact comb and graft copolymers, dendritic polymers, molecular brushes) is reviewed. In addition, the solution/bulk properties and the potential applications of polymacromonomers (PMM), as well as new synthetic ideas are presented. The synthesis of macromonomers and living polymacromonomers in situ leads to many novel linear and nonlinear structures, as for example PMM‐b‐PS‐b‐PMM, (PS)2PMM. The use of multichlorosilylstyrenes as monomer/linking agents opens new ways for structures with multichain macromonomeric building blocks.The use of multichlorosilylstyrenes as monomer/linking agents opens new ways for structures having multichain macromonomeric building blocks.magnified imageThe use of multichlorosilylstyrenes as monomer/linking agents opens new ways for structures having multichain macromonomeric building blocks.

Universal iterative strategy for the divergent synthesis of dendritic macromolecules from conventional monomers by a combination of living radical polymerization and irreversible TERminator multifunctional INItiator (TERMINI).

A new synthetic concept named TERMINI that stands for irreversible TERminator Multifunctional INItiator is reported. Suitable combinations of TERMINI and living polymerizations provide access to strategies for the design and synthesis of unprecedented complex molecular and macromolecular architectures from a diversity of commercial monomers. TERMINI represents a masked multifunctional initiator designed to quantitatively and irreversibly interrupt a chain organic reaction or a living polymerization. After demasking, the TERMINI repeat unit enables the quantitative reinitiation, in the presence or absence of a catalyst, of the same or a different living polymerization or a chain organic reaction in more than one direction, thus becoming a branching point. The demonstration of this concept was made by using a combination of metal-catalyzed living radical polymerization (LRP) and (1,1-dimethylethyl)[[1-[3,5-bis(S-phenyl 4-N,N'-diethylthiocarbamate)phenyl]ethenyl]oxy]dimethylsilane as TERMINI, to elaborate a novel iterative divergent method for the synthesis of dendritic macromolecules based on methyl methacrylate (MMA).

Application of complex macromolecular architectures for advanced microelectronic materials.

The distinctive features of well-defined, three-dimensional macromolecules with topologies designed to enhance solubility and amplify end-group functionality facilitated nanophase morphologies in mixtures with organosilicates and ultimately nanoporous organosilicate networks. Novel macromolecular architectures including dendritic and star-shaped polymers and organic nanoparticles were prepared by a modular approach from several libraries of building blocks including various generations of dendritic initiators and dendrons, selectively placed to amplify functionality and/or arm number, coupled with living polymerization techniques. Mixtures of an organosilicate and the macromolecular template were deposited, cured, and the phase separation of the organic component, organized the vitrifying organosilicate into nanostructures. Removal of the sacrificial macromolecular template, also denoted as porogen, by thermolysis, yielded the desired nanoporous organosilicate, and the size scale of phase separation was strongly dependent on the chain topology. These materials were designed for use as interlayer, ultra-low dielectric insulators for on-chip applications with dielectric constant values as low as 1.5. The porogen design, chemistry and role of polymer architecture on hybrid and pore morphology will be emphasized.

Examination of the Universality of the Calibration Curve of Size Exclusion Chromatography by Using Polymers Having Complex Macromolecular Architectures

The validity of the universal calibration curve (UCC) in size exclusion chromatography (SEC) was tested by using polymers having complex macromolecular architectures such as miktoarm stars ( w -stars) (PS) 2 PI, (PS) 2 PBd, (PI) 3 PS, (PS-PI) 2 (PI-PS) 2 , (PS)(PI)(PBd), (PS)(PI)(PBd)(P4MeS), H-shaped (PI) 2 PS(PI) 2 , and ~ -shaped (PS)(PI)PI(PS)(PI), as well as a model linear tetrablock copolymer of the PS-PI-PS-PI type, where PS is polystyrene, PBd polybutadiene, PI polyisoprene, and P4MeS is poly(4-methyl styrene). It was found that the universality of the relation of log(M[ m ]) vs. peak elution volume (V e ), where M is molecular weight and [ m ] is intrinsic viscosity, is valid even for these complex molecules. The determination of the molecular weight of a polymer by using the UCC is very sensitive to the molecular and compositional homogeneity of the sample.

Complex Macromolecular Architectures by Combining TEMPO Living Free Radical and Anionic Polymerization

A combination of TEMPO living free radical (LFRP) and anionic polymerization was used for the synthesis of star, graft, block−graft, block−brush, and graft−block−graft copolymers of styrene and isoprene. For graft copolymers with polystyrene (PS) backbone and polyisoprene (PI) branches, living free radical copolymerization of styrene and p-chloromethylstyrene (CMS) was performed, followed by a linking reaction at −20 °C of the chloromethyl groups of the backbone with living 1,1-diphenylethylene end-capped polyisoprenylithium (PI−DPELi). Similarly the reaction of the chloromethyl groups of a diblock copolymer of styrene and p-chloromethylstyrene, obtained by LFRP, with PI−DPELi gave a block−brush copolymer with polyisoprene branches. Reaction of low molecular weight p-chloromethylstyrene homopolymers (PCMS) with PI−DPELi lead to polyisoprene stars. Finally reaction of a (PS-g-PS)-b-(PS-co-PCMS) with PI−DPELi resulted to a graft−block−graft copolymer. All products were analyzed and molecularly characterized...

Macromolecular engineering via 'living' free radical polymerizations

The use of nitroxide-mediated ‘living’ free radical procedures as a synthetic tool for obtaining polymers with well defined and complex macromolecular architectures is discussed. The preparation of linear homo, block, and random co-polymers by ‘living’ free radical procedures have been demonstrated for a variety of systems and results in a significant increase in control over the macromolecular structure when compared to traditional free radical polymerization. The factors which affect the success of this novel synthetic approach will be reviewed and the advantages of ‘living’ free radical polymerization over other living polymerization techniques discussed. The synthesis and chemical stability of a wide range of unimolecular alkoxyamine initiators will also be demonstrated and their use in the preparation of complex macromolecular architectures such as hyperbranched polymers and hybrid dendritic-linear polymers illustrated.

New complex macromolecular architectures based on organosilicon chemistry

Polycarbosilane networks were prepared from well-defined α, ω-difunctional oligomers: X-[Si(CH3)2-CH2-CH2]n-X with X = H (1) and X = CH=CH2 (2). Crosslinking reactions were performed by hydrosilylation of tetramethyltetravinylcyclotetrasiloxane (V4) or of tetravinylsilane with SiH end groups of 1. Hydrosilylation of Si-CH=CH2 end groups of 2 with tetramethyltetrahydrocyclotetrasiloxane (D4H) was also successfully tried. Some physicochemical properties of these new networks will be presented.1) Interpenetrating networks based on polysiloxanes and polycarbonates were synthesized by the in situ method: a polysiloxane bearing various proportions of room temperature crosslinkable -Si(OEt)3 side groups was mixed with bis(allyl ethylene glycol) biscarbonate and a free-radical initiator. After the formation of the first network at room temperature, the cross-linking of the polycarbonate network was performed by raising the temperature up to 80°C. Various chemical modifications of the polysiloxane component in the IPN were performed in order to improve the degree of interpenetration as estimated from turbidity, density, refractive index and DSC measurements.2)

On the Average Molecular Weights of Complex Macromolecular Architectures Made from Different Precursors

Previous investigations of star polymers made from the same kind of precursor arms are extended to macromolecules of more complex architecture made from more than one different precursor. The number- and weight-average molecular weights M n and M w of the complexw macromolecule are related to those of the different precursor parts

Biological synthesis of monodisperse derivatives of poly(.alpha.,L-glutamic acid): model rodlike polymers

Poly(α,L-glutamic acid) (PLGA) and its derivatives have played a central role in the physical chemistry and materials science of polymers. PLGA itself has been used in fundamental studies of the helix-coil transition and polyelectrolyte chemistry, and rodlike esters of PLGA-most notably poly(γ-benzyl α,L-glutamate) (PBLG)-have been shown to form liquid crystalline solutions and beautifully ordered monolayer films. The traditional synthetic route to PLGA and its esters involves the ring-opening polymerization of N-carboxy-α-amino acid anhydrides. This technique affords heterogeneous populations of chains characterized by relatively broad distributions of molecular weights, and subsequent conversion of PLGA esters to the parent acid can be accompanied by substantial racemization. The heterogeneity of the resulting products complicates the interpretation of their hydrodynamic, spectroscopic, and liquid crystalline behavior and limits the utility of these polymers in the design and synthesis of complex macromolecular architectures. We report herein a general biosynthetic route to monodisperse derivatives of PLGA, unique rodlike polymers. The method is illustrated by the synthesis of polymer 1.

Brush border development in the intestinal absorptive cells of Xenopus during metamorphosis.

The differentiation of the brush border which makes up the apical free surface of intestinal absorptive cells has been studied by electron microscopy. Specimens of Xenopus small intestine were fixed at various stages during metamorphosis, the time when a new intestinal epithelium forms. The interpretation of details described herein emphasizes the role of "surface-forming" vesicles. These vesicles are thought to provide membrane both for the initial expansion of the apical surface and for the later elongation of the microvilli. The latter are believed to be "molded" around filamentous cores that appear early in differentiation. The cores are attached to the apical membrane and extend vertically into the supranuclear cytoplasm. This interpretation rests chiefly on (a) the resemblance, both in morphology and in staining properties with colloidal thorium, between the membrane that limits the vesicles and that which limits the microvilli and (b) the distribution and time of appearance of the vesicles with respect to development of the microvilli. According to this view, the specific properties of surface membrane reside in preformed units that arise within the supranuclear cytoplasm. This morphogenetic process probably involves participation of the Golgi region as the site where the complex macromolecular architecture of the cell surface is assembled.