Use of amphiphilic triblock copolymers to direct the organization of polymerizing silica species has resulted in the preparation of well-ordered hexagonal mesoporous silica structures (SBA-15) with uniform pore sizes up to approximately 300 angstroms. The SBA-15 materials are synthesized in acidic media to produce highly ordered, two-dimensional hexagonal (space group p6mm) silica-block copolymer mesophases. Calcination at 500°C gives porous structures with unusually large interlattice d spacings of 74.5 to 320 angstroms between the (100) planes, pore sizes from 46 to 300 angstroms, pore volume fractions up to 0.85, and silica wall thicknesses of 31 to 64 angstroms. SBA-15 can be readily prepared over a wide range of uniform pore sizes and pore wall thicknesses at low temperature (35° to 80°C), using a variety of poly(alkylene oxide) triblock copolymers and by the addition of cosolvent organic molecules. The block copolymer species can be recovered for reuse by solvent extraction with ethanol or removed by heating at 140°C for 3 hours, in both cases, yielding a product that is thermally stable in boiling water.

Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores

One of the most pervasive problems afflicting people throughout the world is inadequate access to clean water and sanitation. Problems with water are expected to grow worse in the coming decades, with water scarcity occurring globally, even in regions currently considered water-rich. Addressing these problems calls out for a tremendous amount of research to be conducted to identify robust new methods of purifying water at lower cost and with less energy, while at the same time minimizing the use of chemicals and impact on the environment. Here we highlight some of the science and technology being developed to improve the disinfection and decontamination of water, as well as efforts to increase water supplies through the safe re-use of wastewater and efficient desalination of sea and brackish water.

Science and technology for water purification in the coming decades

A family of highly ordered mesoporous (20−300 A) silica structures have been synthesized by the use of commercially available nonionic alkyl poly(ethylene oxide) (PEO) oligomeric surfactants and poly(alkylene oxide) block copolymers in acid media. Periodic arrangements of mescoscopically ordered pores with cubic Im3m, cubic Pm3m (or others), 3-d hexagonal (P63/mmc), 2-d hexagonal (p6mm), and lamellar (Lα) symmetries have been prepared. Under acidic conditions at room temperature, the nonionic oligomeric surfactants frequently form cubic or 3-d hexagonal mesoporous silica structures, while the nonionic triblock copolymers tend to form hexagonal (p6mm) mesoporous silica structures. A cubic mesoporous silica structure (SBA-11) with Pm3m diffraction symmetry has been synthesized in the presence of C16H33(OCH2CH2)10OH (C16EO10) surfactant species, while a 3-d hexagonal (P63/mmc) mesoporous silica structure (SBA-12) results when C18EO10 is used. Surfactants with short EO segments tend to form lamellar mesost...

Nonionic Triblock and Star Diblock Copolymer and Oligomeric Surfactant Syntheses of Highly Ordered, Hydrothermally Stable, Mesoporous Silica Structures

https://www.researchgate.net/file.PostFileLoader.html?id=526892a1d4c118a61d4360bd&assetKey=AS%3A272155479085058%401441898330516

Porosity of 3D biomaterial scaffolds and osteogenesis.

3.2.3. Hydroformylation 2467 3.2.4. Dimerization 2468 3.2.5. Oxidative Cleavage and Ozonolysis 2469 3.2.6. Metathesis 2470 4. Terpenes 2472 4.1. Pinene 2472 4.1.1. Isomerization: R-Pinene 2472 4.1.2. Epoxidation of R-Pinene 2475 4.1.3. Isomerization of R-Pinene Oxide 2477 4.1.4. Hydration of R-Pinene: R-Terpineol 2478 4.1.5. Dehydroisomerization 2479 4.2. Limonene 2480 4.2.1. Isomerization 2480 4.2.2. Epoxidation: Limonene Oxide 2480 4.2.3. Isomerization of Limonene Oxide 2481 4.2.4. Dehydroisomerization of Limonene and Terpenes To Produce Cymene 2481

Chemical Routes for the Transformation of Biomass into Chemicals

High Strength Polyolefin Block Copolymers

A series of ABA triblock copolymers of poly(D,L-lactide)-b-poly(butadiene)-b-poly(D,L-lactide), LBL, and their 2-ureido-4[1H]-pyrimidinone (UPy) end-functionalized analogue, UPy-LBL, were synthesized. Commercially available hydroxy-terminated poly(butadiene) (HTPB) was used as the macroinitiator for ring-opening polymerizations of D,L-lactide. UPy hydrogen bonding dimerization in solution was confirmed by 1H NMR spectroscopy and by the thermo-reversible properties of this interaction. Mechanical properties of this polymer series revealed that only the incorporation of low molar mass PB did not significantly alter the brittle character of PLA. However, end-functionalization of the triblock copolymers with the UPy moiety effectively increased the strain at break of PLA, producing polymers with average ultimate elongations up to 58%. A relationship between UPy content and mechanical properties was established. The series of polymers with UPy functionalities ranging from 0–2 was tougher than neat PLA; the hemitelechelic polymer was more than four times tougher. To study the physical aging of these systems, uniaxial tensile-tests and DSC experiments were performed. DSC thermograms showed increases in both the glass transition temperature and enthalpy of relaxation as a function of PLA aging time. Tensile experiments demonstrated that UPy-functionalization effectively delayed aging as ductile behavior was only lost after annealing the samples for five days at 40 °C.

Combining block copolymers and hydrogen bonding for poly(lactide) toughening

Poly(ethylene terephthalate) (PET) is one of the most prevalent polymers in the world due to its combined thermal, mechanical, and gas barrier attributes. Blending PET with other polymers is an appealing strategy to further tailor properties to meet the needs of an even more diverse range of applications. Most blends with PET are macrophase-separated; only a few miscible systems have been reported. Here, the miscibility of the aromatic polyesters poly(salicylic glycolide) (PSG) and poly(salicylic methyl glycolide) (PSMG) with PET is described. Both PSG and PSMG have similar chemical structures to PET but are derived from sustainable resources and readily degradable. This study suggests that they are fully miscible with PET over the entire composition range, which is attributed to favorable interactions with PET. Negative polymer-polymer interaction parameters (χ) were determined using Flory-Huggins theory to describe melting temperature variations in the blends. In addition, the PET blends showed mechanical properties that are intermediate between the two homopolymers.

Blend Miscibility of Poly(ethylene terephthalate) and Aromatic Polyesters from Salicylic Acid.

Polymers are an important class of materials that are used for a broad range of applications, from drug delivery to packaging. Given their widespread use, a major challenge in this area is the development of technology for their production from renewable sources and efforts to promote their efficient recycling and biodegradation. In this regard, the synthesis of polyesters based on the natural polyhydroxyalkanoate (PHA) pathway offers an attractive route for producing sustainable polymers. However, monomer diversity in naturally occurring polyesters can be limited with respect to the design of polymers with material properties suitable for various applications. In this work, we have engineered a pathway to produce α-methyl-branched PHA. In the course of this work, we have also identified a PHA polymerase (CapPhaEC) from activated sludge from wastewater treatment that demonstrates a higher capacity for incorporation of α-branched monomer units than those previously identified or engineered. Production in Escherichia coli allows the construction of microbial strains that produce the copolyesters with 21-36% branched monomers using glucose and propionate as carbon sources. These polymers have typical weight-average molar masses (Mw) in the range (1.7-2.0) × 105 g mol-1 and display no observable melting transition, only relatively low glass transition temperatures from -13 to -20 °C. The lack of a melting transition indicates that these polymers are amorphous materials with no crystallinity, which is in contrast to the natural poly(hydroxybutyrate) homopolymer. Our results expand the utility of PHA-based pathways and provide biosynthetic access to α-branched polyesters to enrich the properties of bio-based sustainable polymers.

Engineering in Vivo Production of α-Branched Polyesters.

Statistical copolymers were prepared by the Ring Opening Metathesis coPolymerization (ROMP) of (Z)-5,5-dimethylcyclooct-1-ene and cis-cyclooctene. Subsequent hydrogenation yielded poly(ethylene-co-isobutylene) (PEIB) materials. The feed ratio of the comonomers controls the degree of branching and resulting thermal and mechanical properties of the PEIB samples. Oxidative degradation studies, conducted under accelerated in vitro conditions were used to assess and predict their long-term biostability. Relative to commercial poly(ether urethanes) and a structurally similar polyolefin, poly(ethylene-co-1-butylene), the PEIB samples showed much better oxidative resistance. The facile synthesis, improved stability, and excellent mechanical performance of these PEIB materials bode well for their use in biomedical applications that require long-term biostability.

Marc A. Hillmyer

Papers

High Strength Polyolefin Block Copolymers

Combining block copolymers and hydrogen bonding for poly(lactide) toughening

Blend Miscibility of Poly(ethylene terephthalate) and Aromatic Polyesters from Salicylic Acid.

Engineering in Vivo Production of α-Branched Polyesters.

Oxidatively Stable Polyolefin Thermoplastics and Elastomers for Biomedical Applications