Weight Of Segment Research Articles

Growth of maize coleoptiles in the presence of natural and synthetic growth regulators. Growth correlations

The effect of natural (IAA, FC, ABA) and synthetic (2,4-D) growth substances on the increase of the fresh weight of maize coleoptile segments and change of the pH of the incubation medium, accepted here as criteria of maize coleoptile growth, was studied. The growth of maize coleoptiles depended on the concentration of the growth substances, as well as, on the composition of the incubation medium. The highest stimulation of coleoptile growth was seen with FC at a concentration of 10<sup>-4</sup>M, whereas ABA at 10<sup>-3</sup> M gave the highest inhibition of maize coleoptile fresh weight increase and caused alkalization of the medium. The presence of K<sup>+</sup> ions in the incubation medium enhanced the stimulatory effect of IAA and FC on the increase of the coleoptile fresh weight, whereas the presence of these ions and phosphate buffer abolished the growth-promoting effect of IAA and FC. The best correlation of the "fresh weight" and "pH" effects was found in the case of the growth of maize coleoptiles in the presence of FC (r<sub>xy</sub> = 0.67). The inhibition of maize coleoptile growth in the presence of high concentrations of IAA can be explained by the destructive effect of natural auxin at these concentrations on the integrity of mitochondrial membranes, and therefore on the normal functioning of mitochondria.

Two glass transitions of polyurea networks: effect of the segmental molecular weight.

Polymer-nanoparticle composites (PNCs) play an increasing role in technology. Inorganic or organic nanoparticles are usually incorporated into a polymer matrix to improve material properties. Polyurea is a spontaneously occurring PNC, exhibiting a phase segregated structure with hard nanodomains embedded in a soft (elastically compliant) matrix. This system shows two glass transitions at Tg1 and Tg2. It has been argued that they are related to the freezing of motion of molecular segments in the soft matrix (usual polymer α-glass transition at Tg1) and to regions of restricted mobility near the hard nanodomains (α'-process) at Tg2, respectively. We present detailed dynamic mechanical analysis (DMA) measurements for polyurea networks with different segmental lengths l(c) (2.5, 12.1, 24.5 nm) of the polymer chains, i.e. different volume fractions ϕ(x) (0.39, 0.12, 0.07) of the hard domains. The two glass transitions show up in two distinct peaks in tan δ at Tα and Tα'. Analysing the data using a Havriliak-Negami term for the α- and α'-relaxation, as well as Vogel-Fulcher dependencies for the corresponding relaxation times, it is found that the α-glass transition at Tg1 increases strongly (up to ΔT = 70 K) with increasing ϕ(x), whereas the α'-transition at Tg2 remains unchanged. At ϕ(x)(c) ≈ 0.19 the two curves intersect, i.e. Tg1 = Tg2. This value of ϕ(x)(c) is very close to the percolation threshold of randomly oriented overlapping ellipsoids of revolution with an aspect ratio of about 1 : 4-1 : 5. We therefore conclude that around 19% of the hard nanodomains polyurea changes from a system of hard nanoparticles embedded in a soft matrix (ϕ(x) ≤ ϕ(x)(c)) to a system of soft domains confined in a network of percolated hard domains at ϕ(x) ≥ ϕ(x)(c).

Effect of Hard Segment Molecular Weight on Dilute Solution Properties of Ether Based Thermoplastic Polyurethanes

A systematic study was conducted on the effect of hard segment molecular weight (or length) on solution and bulk properties of ether based thermoplastic polyurethanes (TPUs). The purpose of this study is to provide a roadmap to deliver the desired end-use performance of a polyurethane product based on the optimal design of the starting materials. In this paper, we report our findings on the effects of hard segment molecular weight on properties of a dilute solution of TPUs in N, N-dimethyl formamide (DMF). The molar feed was used to determine the molecular weight of the hard segment. Then, the weight fraction of the hard segment is determined by calculating the ratio of the molecular weight of the hard segment to the number average molecular weight of the TPU determined by Gel Permeation Chromatography. It was found at low hard segment weight fraction there is a significant impact on the weight average molecular weight and molecular weight distribution, intrinsic viscosity, critical concentration, hydrodynamic diameter, polymer-solvent interaction parameter and second virial coefficient. However, at high weight fractions at around 0.4, the impact is minimal. Furthermore, the weight fraction has a minimal impact on number average molecular weight, and the expansion parameter in the Flory-Huggins analysis.

Synthesis and characterization of novel fluorinated siloxane star-like copolymer with short perfluoroalkyl chain and used for modification the epoxy resin

Two series of fluorinated siloxane star-like copolymers, with different molecular weight of siloxane segments and large fluorinated segments at the tail, were synthesized from dicarboxyl terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) (CTHFA) and dihydroxypropyl-terminated poly(dimethyl siloxane) (PDMS). The chemical structures of the star-like copolymer (CTHFA-PDMS) were measured by FT-IR, 1H NMR, 13C NMR and GPC. Long siloxane spacers were employed to increase the migration efficiency of the large fluorinated segments. The long siloxane spacers also played a part in toughening the epoxy resin. Then, the copolymers reacted with 4′4-diphenylmethane dissocyanate and were used as a surface modifier of cured commercial diglycidyl ether of bisphenol A (DGEBA) at different concentration (0.1–0.5wt% with respect to DGEBA). For both kinds of the CTHFA-PDMS modified DGEBA, high water contact angles (122° and 110°) were obtained at very low concentration (0.2wt%). The surface chemical composition was measured by X-ray photoelectron spectroscopy (XPS). It was found that the fluorine and silicon atoms selectively migrated toward the outermost surface of modified DGEBA resin. The surface enrichment factors of fluorine and silicon atoms (SmF and SmSi) of modified resin were up to 2.18×105 and 2.93×104 times than the theoretical value expected for the bulk formulations at very low concentration (0.2wt%). Moreover, the surface of modified epoxy resins showed good chemical stability by immersing in acidic and salt solutions. Scanning electron microscopy (SEM) images observed many ridges and rough crack structures of the fracture surface of modified DGEBA resin, indicating the CTHFA-PDMS toughened the DGEBA network.

Genetic Analysis and Character Association in Jamir (<i>Citrus jambhiri</i>) Accessions of Bangladesh by Using Morphological Traits

An experiment was carried out to study the morphological variability, characters association, correlation and path coefficient analysis of 14 Jamir accessions during the period from January 2007 to March 2008. Significant variations were observed for all the plant characters studied. The accession CJ09 was characterized with the maximum plant height (6.20m), spreading of branch (north-south 4.90 m and east-west 4.87m), base girth (58cm), plant growth (102.76m3), tree volume (24.64m3) and segment length (9.70). The accession CJ15 showed maximum spine length (25.33mm), CJ05 was characterized with high lamina area (14.94cm3). The accession CJ12 showed the highest % fruit set (36.67%). The highest fruit weight (1753.33g), fruit diameter (46cm), rind thickness (2.73cm) was observed in CJ11. The accession CJ09 was characterized with maximum number of segment (15.33) and pulp weight (746.67). Maximum TSS (12.20%) was found in CJ12. The accession CJ09 was characterized with minimum number of seeds (14). Correlation coefficient study indicated that fruit diameter, rind thickness, length of segment and number of segment had positive and highly significant phenotypic association with fruit weight and also genotypic positive association. Percent Fruit set had negative genotypic and phenotypic association with fruit weight. In respect of path analysis, fruit diameter, rind thickness, number of segment, length of segment contributed to maximum phenotypic and genotypic direct effects on fruit weight indicating their importance as selection parameters.DOI: http://dx.doi.org/10.3329/pa.v20i1-2.16843 Progress. Agric. 20(1 & 2): 17 – 26, 2009

Parametric Analysis on Incrementally Launched Construction for Concrete Box Girder

The structural behavior of incrementally launched bridges in the construction stages depends on different parameters. Internal force of main girder is influenced by the dead load and stiffness of main girder, the length and stiffness of launching nose. Parametric analysis on the effect of internal force of an 8×60m-span concrete continuous box girder bridge was carried out. The results show that bending moment increases following the increase of weight and stiffness of corresponding segment of main girder. The phenomenon is even more obvious in the negative bending moment region of main girder segment nearby the launching nose. The bending moment of main girder reduces significantly when the stiffness ratio among launching nose and main girder is less than 0.15. While, the negative bending moment of main girder reduces significantly when the length ratio among launching nose and main span is more than 0.58.

Differentiation in the Tourism Sector: An Evolutionary Analysis

The debate on the sustainability of mass tourism development strategies for given destinations has focused to a large degree on the advisability of shifting the pattern of specialization towards higher quality. However, little and limited theoretical analysis exists to support this idea. This paper proposes an evolutionary agent-based model for analysing this topic. Different initial configurations of the distribution of hotel qualities and varied saturation levels in the destination lead to different equilibrium configurations. It is found that high-quality and low-quality segments coexist in most of the simulations. Also, the saturation level of a given destination is crucial in determining the weight of the different quality segments up to a limit or maximum level beyond which a strategy of enhancing quality is no longer effective.

Protein profiles related to diet and exercise as molecular signatures of vascular wellness

Introduction: Diet and exercise constitute two of the main pillars in preventing and treating cardiovascular diseases. Several studies have focused in analysing the effect of diet and exercise in specific factors, such us hormones, lipids or sugars, but nothing has been found in literature, to our knowledge, analyzing the global effect at a protein level in humans. The present approach has focused on the characterization of the protein profiles detected after a 6 month combination of diet and exercise in healthy individuals, as well as on the identification of the protein changes related. Objectives: 1.Evaluate the combined effect of diet and exercise on the protein profile of healthy individuals. 2.Determine protein profiles related to diet and exercise as potential signatures of physical wellness. 3.Identify protein variations that promote the beneficial effects of diet and exercise in order to better characterize the molecular mechanisms involved. 4.Compare, in the future, the protein profiles obtained here with those related to cardiovascular Material and methods: In total, 53 rugby players were enrolled in this study and included in three groups, one following a hyperproteic diet with low glucemic index, another following a standard Mediterranean diet, and a third group of players without diet. Blood and urine samples were collected on day 0 and 6 months later, after following diet and regular training. Several anthropometric data were also taken, including body weight, mass and length of body segments. Plasma was obtained by centrifugation and both, plasma and urine were aliquoted and stored at −80° C. Protein profiles in both fluids were analysed using a Surface-Enhanced Laser Desorption and Ionization Time of Flight (SELDI-TOF) mass spectrometer, employing a strong anion exchange (Q10) affinity array. For protein identification, a chromatographic approach using a strong anion exchange column (Uno Q) with the same binding conditions employed in SELDI was done, and protein fractions were further separated by SDS-PAGE. Results: SELDI-TOF analysis allowed the detection of protein profiles at time 0 and six months after diet and exercise, reflecting the effect of these parameters in the protein content of plasma and urine. The comparison of these profiles reported significant differences in protein expression (p-values < 0.05) that allowed us to distribute the rugby players in two well defined groups, depending on the weight changes, with clear expression protein patterns in individuals who lost or gained weight. Similar results were seen when comparing muscular changes but not when considering exercise (not shown). Some of the protein peaks with significant differential expression are actually under further analysis in order to be identified, employing a combination of liquid chromatography (anion exchange) and mass spectrometry (MALDI-TOF). Conclusions: SELDI-TOF analysis allowed us to obtain representative protein profiles of the effect of diet, exercise, body weight, muscle and fat variations. The protein peaks with significant expression variations due to the effect of diet and exercise (p-value < 0.05) could be taken as potential markers of vascular wellness, susceptible to be modified with optimal diet and exercise guidelines.

Segment Edit and Segment Weight Optimization: Two Techniques for Intensity Modulated Radiation Therapy and Their Application to the Planning for Nasopharyngeal Carcinoma

The purpose of this study was to evaluate the two functions: segment weight optimization (SWO) and segment edit (SE) in the latest XiO 4.7 radiation treatment planning system and their effect on the planning of intensity modulated radiation therapy (IMRT) for Nasopharyngeal Carcinoma (NPC). SWO first appeared in XiO 4.5 and SE in XiO 4.7. Twelve patients with NPC were selected and there were three plans for each patient: the common step-and-shoot IMRT plan (C-IMRT); S-IMRT was based on the result of C-IMRT and the plan was further optimized with SWO; F-IMRT was based on S-IMRT and the segments were edited for lowering the dose received by normal tissues. The paired plans were analyzed by comparing the total number of segments, monitor units, the homogeneity index and conformity index of the target volumes and the dose delivered to organs at risk (OAR) including spinal cord, brain stem, optic nerves, chiasm, parotids and larynx. The study exhibited that the total number of segments and monitor units of S-IMRT and F-IMRT were around 25.3%, 3.4% less than those of C-IMRT respectively. The HI and CI indexes of target volumes among three kinds of plans did not show the significant difference. The doses received by spinal cord, brain stem, parotids, larynx were decreased at S-IMRT and F-IMRT as compared to C-IMRT; the highest doses delivered to chiasm and optic nerves were S-IMRT, the next C-IMRT, the lowest F-IMRT. This study showed that the SWO function could substantially reduce the total number of segments of step-and-shoot IMRT plans and the SE function had the incredible ability to lower the dose received by normal tissues.

Effect of Hard Segment Molecular Weight on Concentrated Solution and Bulk Properties of Ether Based Thermoplastic Polyurethanes

A systematic study was conducted to investigate the effect of hard segment molecular weight on concentrated solution and bulk properties of thermoplastic ether based polyurethanes (TPUs). The molar feed was used to determine the molecular weight of the hard segment. Then the weight fraction of the hard segment is determined by calculating the ratio of the molecular weight of the hard segment to the number average molecular weight of the TPU determined by GPC. Similar to the study of dilute solution properties, it was found that thermal and mechanical properties in the bulk were significantly affected at low weight fractions of the hard segment. The critical weight fraction of the hard segment was found at about 0.4. Above critical weight fraction of hard segment there is a diminishing effect on the thermal properties and dynamical/ mechanical properties in bulk.

A direct digital synthesis chirped pulse Fourier transform microwave spectrometer

Chirped pulse Fourier transform microwave (CP-FTMW) spectrometers have become the instrument of choice for acquiring rotational spectra, due to their high sensitivity, fast acquisition rate, and large bandwidth. Here we present the design and capabilities of a recently constructed CP-FTMW spectrometer using direct digital synthesis (DDS) as a new method for chirped pulse generation, through both a suite of extensive microwave characterizations and deep averaging of the 10-14 GHz spectrum of jet-cooled acetone. The use of DDS is more suited for in situ applications of CP-FTMW spectroscopy, as it reduces the size, weight, and power consumption of the chirp generation segment of the spectrometer all by more than an order of magnitude, while matching the performance of traditional designs. The performance of the instrument was further improved by the use of a high speed digitizer with dedicated signal averaging electronics, which facilitates a data acquisition rate of 2.1 kHz.

On the dimension of spline spaces on planar T-meshes

We analyze the space of bivariate functions that are piecewise polynomial of bi-degree <= (m, m') and of smoothness r along the interior edges of a planar T-mesh. We give new combinatorial lower and upper bounds for the dimension of this space by exploiting homological techniques. We relate this dimension to the weight of the maximal interior segments of the T-mesh, defined for an ordering of these maximal interior segments. We show that the lower and upper bounds coincide, for high enough degrees or for hierarchical T-meshes which are enough regular. We give a rule of subdivision to construct hierarchical T-meshes for which these lower and upper bounds coincide. Finally, we illustrate these results by analyzing spline spaces of small degrees and smoothness.

SU‐E‐T‐654: Direct Aperture Optimization Using An Inverse Form of Back Projection

Purpose: Intensity modulated radiotherapy plans using direct aperture optimization (DAO) promise high dosimetric quality and fast treatment delivery. We present a new and fast DAO approach where IMRT and arc therapy optimization are treated as inverse forms of CT reconstruction using multiplicative algebraic reconstruction technique (MART). Methods: We developed a modified MART for DAO, and the multiplicand is termed as ‘index’, indicating how much the current dose should be changed. Index is assigned to each voxel, each beamlet and each segment to optimize fluence map, MLC segment shape, and segment weight, respectively. In addition, a column generation method is developed to add new segments to improve dose conformity. Results: DAO using index‐dose can be completed within a few minutes. Without sacrificing plan quality, the implementation of the DAO in our in‐house treatment planning system reduced average IMRT treatment time from 13 min to 8 min for the prostate, and from 15 min to 9 min for the head and neck. The DAO approach is also applied for arc therapy in a head and neck case using rotational IMRT with burst mode. Conclusion: We have demonstrated a new direct aperture optimization technique using an inverse form of back projection approach. The method effectively reduces the number of segments needed for IMRT plans, and thus reduces treatment time. Our approach also provides a feasible solution for the rotation IMRT with burst mode.

SU-D-WAB-03: Online Adaptive Stereotactic Body Radiotherapy for Lung Lesions

Purpose: During the delivery of stereotactic body treatments (SBRT) for lung cancer with single or multiple targets, the targets may experience considerable inter‐fractional variations, such as shape and volume change and/or independent motion between multiple targets, which cannot be fully addressed by the IGRT repositioning. Here we devised a method to quickly generate a dedicated plan of the day immediately before each SBRT fraction. Methods: The main idea for the proposed method is to quickly modify the original plan based on the anatomy of the day and deliver the new plan with respiration gating without repositioning the patient. An autosegmentation tool (ABAS, Elekta) is used to quickly delineate targets and organs‐at‐risk (OAR) with manual editing, if necessary, based on the respiration‐gated CT acquired using a CT‐on‐rails (CTVision, Siemens) with the patient in the treatment position. Appropriate PTV margin (e.g., 3 mm) is used to account for residual uncertainties. Each beam aperture is adjusted to conform to each PTV with the same beam orientation as the original plan. Automatically‐generated ring structures are used during beam weight optimization to enhance dose conformity, where only beam (segment) weights (MU), not the shapes, are optimized. The method was tested on representative cases with two targets. Results: The proposed online replanning method can deliver conformal dose distribution optimized for each fraction during SBRT and can be completed within 10 minutes. The structure delineation was generally less than 3 minutes due to the small target size and abundant contrast. The percentage PTV volume covered by prescription dose and percentage lung volume covered by 20 Gy were improved from 86% and 22% for repositioning to 95% and 8% for the online replanning, respectively. Conclusion: Online adaptive replanning is dosimetrically advantageous and practically feasible for lung SBRT with possibility of using single isocenter for multiple targets.

TH‐A‐116‐05: A Robust Direct Aperture Optimization Approach for Left‐Sided Breast IMRT

Purpose: To test the feasibility of a robust direct aperture optimization (DAO) model for cardiac sparing IMRT planning of left‐sided breast cancer patients. Methods: We extended a previously developed robust optimization method to obtain a DAO approach for tangential breast IMRT that is robust against uncertainty in the patient's breathing pattern. The robust DAO model contains additional constraints on the segment shapes and weights in order to reduce the complexity of delivery and ensure that high weight segments cover the whole breast volume. A 4DCT dataset was used to test the model, and 100 simulated breathing patterns were generated. Results were compared with the previously developed robust fluence map optimization (FMO) model as well as the clinical treatment methods for breast cancer (inhale breath‐hold with active breathing control (ABC) and free breathing). Results: On average, the robust DAO approach reduced the mean heart dose by 15.1% compared to the conventional IMRT method for breast cancer (with free breathing) using an equal number of segments. The maximum dose to 10cc of the heart was reduced by 19.7%. Compared to the previous robust FMO method, the robust DAO method delivered less than 1% higher dose to the heart and 1% lower dose to the CTV on average. The dose‐volume criteria for the heart and CTV were met in all of the breathing scenarios. The robust DAO approach resulted in a 20.8% reduction in the number of cases that would have required ABC treatment in comparison with the clinical method with free breathing. Conclusions: The proposed DAO approach results in lower heart dose compared to the conventional method with free breathing and shows low sensitivity to breathing pattern uncertainty. The robust DAO method is able to derive simpler IMRT segments during free breathing and can potentially reduce the need for breath‐hold techniques. This research was supported in part by the Ontario Ministry of Economic Development and Innovation, the Canadian Breast Cancer Foundation ‐ Ontario Region, and the Ontario Consortium for Adaptive Interventions in Radiation Oncology (OCAIRO) funded by the Ontario Research Fund (ORF).

Molecular Dynamics of Segmented Polyurethane Copolymers: Influence of Soft Segment Composition

Dielectric relaxation spectroscopy was used to investigate the molecular dynamics of model segmented polyurethane copolymers having identical hard segments and hard segment weight fractions, but with four different soft segment chemistries of particular interest in biomedical devices. All soft segments have molecular weight ∼1000 g/mol and are composed of either tetramethylene oxide, hexamethylene oxide, aliphatic carbonate, or dimethylsiloxane (PDMS) segments. These microphase-separated materials exhibit rich dielectric relaxation behavior: up to two relaxations in the glassy state, a segmental α relaxation (two for the polymer with predominately PDMS soft segments), and three slower relaxations. The slowest process arises from interfacial (MWS) polarization, and its strength decreases significantly with increasing temperature (over a few tens of degrees) and disappears at a temperature similar to that at which the small-angle X-ray scattering from the phase-separated microstructure disappears.

Thermally modulated nanostructure of poly(ε-caprolactone)–POSS multiblock thermoplastic polyurethanes

A series of multiblock polyurethanes with alternating sequence structures of a poly(ε-caprolactone) (PCL) segment of 2600 or 3600 g/mol and a polyhedral oligomeric silsesquioxane (POSS) segment with multiple POSS moieties (TPU2.6k_1-x or TPU3.6k_1-x, respectively; the molar ratio of PCL:POSS is 1: x; x = 2, 3, or 4) were synthesized through two-step polymerization to assure quantitative conversion of reactants. Differential scanning calorimetry and simultaneous wide- and small-angle X-ray scattering measurements were performed to study the nanostructures of those samples. The multiblock and alternating sequence structures provided nano-confined environments for PCL and POSS domains, which significantly suppressed crystallinity of the PCL phase, while nano-sized crystallites were formed in the POSS phase. The samples in series TPU2.6k and TPU3.6k were also proven to display either lamellar, cubic, or cylindrical hexagonal phase-separated nanostructures depending on the molecular weight of the PCL segment, as well as the PCL/POSS ratio. It was also found that repeated thermal cycling under a nitrogen atmosphere low enough in temperature not to alter molecular weight caused larger and more ordered PCL and POSS crystalline structure to form for the TPU3.6k series. Apparent reconfiguration of the PCL and POSS moieties along the backbone by exchange reactions associated with reversibility of urethane bonds led to increases in PCL and POSS block lengths in the TPU chains. We envision an opportunity of future research and applicability in the areas of tailored toughness and rigidity in biodegradable polymer coatings, devices with enlarged data storage capacity, drug delivery systems and tissue engineering.

Precision Templating with DNA of a Virus-like Particle with Peptide Nanostructures

We report here the preparation of filamentous virus-like particles by the encapsulation of a linear or circular double-stranded DNA template with preassembled mushroom-shaped nanostructures having a positively charged domain. These nanostructures mimic the capsid proteins of natural filamentous viruses and are formed by self-assembly of coiled-coil peptides conjugated at opposite termini with cationic segments and poly(ethylene glycol) (PEG) chains. We found that a high molecular weight of PEG segments was critical for the formation of monodisperse and uniformly shaped filamentous complexes. It is proposed that electrostatic attachment of the nanostructures with sufficiently long PEG segments generates steric forces that increase the rigidity of the neutralized DNA template. This stiffening counterbalances the natural tendency of the DNA template to condense into toroids or buckle multiple times. The control achieved over both shape and dimensions of the particles offers a strategy to create one-dimensional supramolecular nanostructures of defined length containing nucleic acids.

DNA-Conjugated Polymers for Reliable SNP Genotyping Based on Affinity Capillary Electrophoresis

Abstract To quantitatively detect single-base mutations in genetic samples, free-solution affinity capillary electrophoresis was developed using a diblock copolymer probe composed of allele-specific oligodeoxyribonucleotide (ODN) and poly(ethylene glycol) (PEG). When the probe is designed to be complementary to a wild-type single-stranded DNA sample (WT), WT migrates more slowly than its single-base mutant (MT). This is because WT forms a reversible complex with the probe via hybridization during the electrophoresis, resulting in a large amount of hydrodynamic friction. In contrast, a negligibly weak interaction takes place between MT and the probe due to a single-base mismatch. Accordingly, the MT peak appears earlier than the WT peak on the electropherogram. The difference of the migration time between WT and MT depends on the thermodynamic stability of the complex and also on the amount of hydrodynamic friction that the complex encounters. Therefore, the peak resolution is rationally controlled by the base-number of the ODN segment and by the molecular weight of the PEG segment. Importantly, the peak area ratio provides the occurrence ratio of the single-base mutant within the given population. This facile and accurate method to estimate SNP allele frequency should find applications in various research fields.

Tunable Mesoporous Lamellar Silicas Prepared Using Poly(ethylene oxide-&lt;I&gt;b&lt;/I&gt;-L-lactide) and Poly(ethylene-&lt;I&gt;b&lt;/I&gt;-ethylene oxide-&lt;I&gt;b&lt;/I&gt;-L-lactide) Block Copolymers as Templates

In this study, we synthesized poly(ethylene oxide-b-L-lactide) (PEO-PLLA) diblock copolymers and poly(ethylene-b-ethylene oxide-b-L-lactide) (PE-PEO-PLLA) triblock terpolymers as templates for the preparation of mesoporous lamellar silicas, possessing single, bimodal, or trimodal pore size distributions, through an evaporation-induced self-assembly (EISA) approach. As templates, we synthesized the diblock copolymers EO114LLA26 and EO114LLA130 and the triblock terpolymers E13EO42LLA26 and E13EO42LLA35 using simple ring-opening polymerization. Small-angle X-ray scattering, transmission electron microscopy, and N2 sorption measurements revealed that the mesoporous silicas displayed the morphologies of either lamellar silica walls featuring a distribution of many short cylindrical mesopores or pure lamellar structures. The morphology was greatly affected by the nature of the template (diblock or triblock copolymer) and the molecular weight of the PLLA segment in the block copolymer.