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PubMed2004

Prediction of composite elastic modulus and polymerization shrinkage by computational micromechanics.

OBJECTIVES: The objective of this study was to simulate the elastic modulus and polymerization shrinkage of a light activated polymer matrix composite using a generalized method of cells (GMC) micromechanics model. Two hypotheses were tested: (1) the micromechanics model provides estimates of elastic modulus vs filler fraction with greater accuracy than the rule of mixtures, Hashin-Shtrikman and phenomenological models; (2) Micromechanics Analysis Code/Generalized Method of Cells accurately simulates experimental benchmarks of polymerization shrinkage strain. METHODS: The study applied mathematical algorithms to a representative volume element of a model polymer composite to yield value estimates of the elastic modulus and contraction strain. Mechanical properties of the composite constituents were derived from thermomechanical and dynamic mechanical analysis of BisGMA and TEGDMA filled and unfilled resins. Data from the micromechanics model were compared to results of other analytical methods as well as experimental benchmarks. RESULTS: Predictions of elastic modulus vs filler fraction from the micromechanics model provided greater accuracy than the rule of mixtures and the Hashin-Shtrikman models. Predictions of polymerization shrinkage strain were within 13% of experimental values. SIGNIFICANCE: The elastic micromechanics model presented accurately predicted elastic modulus and polymerization shrinkage strain as a function of filler fraction, superior to other analytical methods.

Bisphenol A-Glycidyl Methacrylate↗
PubMed2005

Hardness and diametral tensile strength of a hybrid composite resin polymerized with different modes and immersed in ethanol or distilled water media.

OBJECTIVES: The aim of this in vitro study was to evaluate the microhardness and diametral tensile strength of a hybrid composite resin (Z250, 3M ESPE) polymerized with four different modes of light exposure and immersed in two different media. METHODS: Composite resin specimens were randomly polymerized according to the experimental groups (conventional, 550 mW/cm(2)/30 s; soft start, 300 mW/cm(2)/10 s + 550 mW/cm(2)/20 s; high intensity, 1060 mW/cm(2)/10 s; pulse delay, 550 mW/cm(2)/1 s + 60 s of waiting time + 550 mW/cm(2)/20 s) and immersed in one of two media (distilled water or absolute ethanol) for 24 h. After that, microhardness (M) and diametral tensile strength (DTS) tests were performed. RESULTS: For DTS, there were no statistical differences among the polymerization modes, however, ethanol medium groups presented statistically lower DTS (p < 0.05) than water medium. For the M test, samples immersed in ethanol medium presented lower M for almost all groups. Conventional mode presented higher M values for the groups immersed in water medium. In ethanol medium, conventional and pulse delay groups presented higher M values, statistically different (p < 0.05) from the high intensity group. For all experimental conditions, the top surface showed higher M than the bottom surface. SIGNIFICANCE: Different polymerization modes can be related to the different polymer structures formed, and consequently with different physical properties of resin composite. The immersion media can alter the physical properties of resin composites of different polymer structures.

Composite Resins↗
PubMed2005

Polymerization shrinkage and contraction stress of dental resin composites.

OBJECTIVE: The aim of this study was to evaluate the shrinkage, contraction stress, tensile modulus, and the flow factor of 17 commercially available dental resin composites. METHOD: The volumetric shrinkage measurements were performed by mercury dilatometry, and the contraction stress and tensile modulus were determined by means of stress-strain analysis. The statistical analysis was conducted by ANOVA and Tukey's post hoc test, and linear regression. RESULTS: Strong linear correlation for most resin composites were found for (i) contraction stress and shrinkage (ii) contraction stress and tensile modulus, and (iii) shrinkage and tensile modules. For most of the materials the unpolymerized resin content determines the amount of shrinkage, contraction stress and tensile modules. The pre-polymerized clusters in Heliomolar results in improved shrinkage/contraction stress properties. The shrinkage/contraction stress for Filtek Z100, Aelite Flo, and Flow-it was too high for the amount of resin in the resin composite. This was rationalized by high polymerization rates, a flow factor, and the nature of the resin. SIGNIFICANCE: High shrinkage and/or high contraction stress may lead to failure of the bond between the resin composites and the tooth structure. This study shows that the unpolymerized resin content determines the amount of shrinkage, contraction stress and tensile modules. Therefore, using pre-polymerized clusters will improve shrinkage/contraction stress properties, as was shown in Heliomolar, while high polymerization rates, and low flow factors have a deteriorative effect on the shrinkage/contraction stress properties.

Acrylic Resins↗
PubMed2005

Factors involved in the development of polymerization shrinkage stress in resin-composites: a systematic review.

OBJECTIVES: Polymerization shrinkage stress of resin-composite materials may have a negative impact on the clinical performance of bonded restorations. The purpose of this systematic review is to discuss the primary factors involved with polymerization shrinkage stress development. DATA: According to the current literature, polymerization stress of resin composites is determined by their volumetric shrinkage, viscoelastic behavior and by restrictions imposed to polymerization shrinkage. Therefore, the material's composition, its degree of conversion and reaction kinetics become aspects of interest, together with the confinement and compliance of the cavity preparation. SOURCES: Information provided in this review was based on original scientific research published in Dental, Chemistry and Biomaterials journals. Textbooks on Chemistry and Dental Materials were also referenced for basic concepts. CONCLUSIONS: Shrinkage stress development must be considered a multi-factorial phenomenon. Therefore, accessing the specific contribution of volumetric shrinkage, viscoelastic behavior, reaction kinetics and local conditions on stress magnitude seems impractical. Some of the restorative techniques aiming at stress reduction have limited applicability, because their efficiency varies depending upon the materials employed. Due to an intense research activity over the years, the understanding of this matter has increased remarkably, leading to the development of new restorative techniques and materials that may help minimize this problem.

Chemical Phenomena↗
PubMed2005

Influence of the colloidal crystal-like arrangement of polymethylmethacrylate bonded aerosil particles on the polymerization shrinkage of composite resins.

OBJECTIVE: Determination of the roles on the polymerization shrinkage during light-curing of composite resins of (i) the filler structuring effect of methylmethacrylate polymer adsorbed on fractal silica particles and (ii) of the crystal-like arrangement of the filler within the matrix. METHODS: Firstly, the domain of major efficiency of polymer in the aerosil agglomeration was determined. Secondly, the monomer system was changed in order to implement the spontaneous concentration of the filler within in a crystal-like arrangement. Finally, the rate of the polymerization shrinkage during light-curing of the resin was determined on the sediment recovered after centrifugation and on the colloidal crystal. Micro-modifications to the size of the samples were determined with the aid of the CCD Line Scan Sensor (H.-D. Rudolph GmbH, Germany). RESULTS: The composite micro-structure and the rate of polymerization shrinkage during light-curing of the resin are correlated with the amount of polymer initially supplied to the system that controls the degree of filler agglomeration. Different types of matrix/filler systems with typical shrinkage characteristics were sampled from the sediment containing amorphous and organized phases. The colloidal crystal-like system was determined to concentrate the filler within the matrix, and to give rise to the smallest shrinkage. SIGNIFICANCE: This study suggests that the silica particles embedded in a micro-structured polymer network (the filler scaffold) slowly develop spontaneously towards a colloidal crystal-like arrangement, and opens up new processes to reduce polymerization shrinkage.

Colloids↗
PubMed2006

Polymerization kinetics of dental adhesives cured with LED: correlation between extent of conversion and permeability.

OBJECTIVES: The aim of this study was to analyze the polymerization kinetics of different adhesive films in relation to their permeability after exposure to different LED curing units. METHODS: One adhesive from each class was analyzed: a three-step etch-and-rinse (OptiBond FL; Sybron-Kerr), a two-step etch-and-rinse (One-Step, Bisco), a two-step self-etch (Clearfil Protect Bond, Kuraray) and a one-step self-etch adhesive (Xeno III; Dentsply DeTrey). Adhesive films were prepared and cured with SmartLite IQ (Dentsply) or L.E. Demetron I (Demetron Kerr) up to complete curing. Polymerization kinetic curves of the tested adhesives were obtained with differential scanning calorimetry (DSC). In particular, total reaction time and extent of polymerization (Ep) at 20, 40 or 60s were compared. Permeability of the adhesive films was evaluated on flat dentin surfaces of human extracted teeth connected to a permeability device and statistically analyzed. RESULTS: Total reaction time differed among the adhesives tested: OptiBond FL<Clearfil Protect Bond<One-Step<Xeno III with both curing units (p<0.05). At 20s OptiBond FL showed the highest Ep, while the lowest values were obtained with One-Step and Xeno III (p<0.05). E(p) increased when curing time was prolonged (40 and 60s) for all adhesives tested (p<0.05), however, on simplified adhesives, incomplete polymerization took place even after prolonged exposure intervals. An inverse correlation was found between Ep of the adhesives and their permeability using LED curing units. SIGNIFICANCE: This study supports the hypothesis that, longer curing times than those recommended by the respective manufacturer decrease permeability of the bonded interfaces.

Adhesives↗
PubMed2006

Influence of instrument compliance and specimen thickness on the polymerization shrinkage stress measurement of light-cured composites.

OBJECTIVES: The aim of our study was to investigate the effects of instrument compliance and specimen geometry on the polymerization shrinkage stress measurements of composites. METHODS: A custom designed stress-strain analyzer was made using a linear variable differential transformer probe and a cantilever load cell. A sandblasted glass rod was fixed at the free end of the load cell, and another glass rod was located on a base plate. A composite was placed between the two rods and light cured. The end displacement of the load cell during polymerization was recorded for 10 min. A flowable (Filtek Flow), a universal hybrid (Z100), and a packable (P60) composite were studied. To investigate the effect of specimen geometry and instrument compliance, specimen thickness was varied between 0.5, 1.0, and 2.0 mm, and three load cells with maximum capacities of 20, 100, and 500kgf were used. Ten maxillary premolars were prepared with two sizes of MOD cavities; the bucco-lingual widths and depths of the cavities were 1.5 mm x 2 mm and 3 mm x 2 mm, and the cusp compliance and deflection were measured before and during composite polymerization. RESULTS: The measured polymerization stress decreased in the order of Filtek Flow, Z100, and P60 for all measurement conditions. As the specimen thickness was increased, the shrinkage stress per unit thickness (mm) decreased. The measured stress decreased with increasing instrument compliance. The cusp compliance (3.32 microm/N) of the 3 mm x 2 mm cavities was similar to that of instrument with a 20 kgf load cell (3.34 microm/N). SIGNIFICANCE: For determining the most clinically relevant values for shrinkage stress of dental composites, the instrument compliance should closely match that of the tooth walls in the cavity geometry to be tested.

Bicuspid↗
PubMed2004

Introduction of a flexible polymeric heart valve prosthesis with special design for aortic position.

OBJECTIVE: Current prosthetic heart valves necessitate permanent anticoagulation or have limited durability and impaired hemodynamic performance compared to natural valves. Recently a polymeric valve prostheses with special design for mitral position demonstrated excellent in vitro and in vivo results with improved durability and no need for permanent anticoagulation. In this study, a respective flexible polymeric aortic valve is presented and in vitro and in vivo results are reported. METHODS: The aortic prosthesis (ADIAM lifescience AG, Erkelenz, Germany) is entirely made of polycarbonaturethane. The tri-leaflet flexible prosthesis mimicks the natural aortic valve and has a diminished pressure loss and reduced stress and strain peaks at the commissures. The valve underwent long-term in vitro testing and in vivo-testing in a growing calve animal model (20 weeks, 7 aortic valves) and was compared to two different commercial bioprostheses. RESULTS: The polymeric aortic heart valve substitute demonstrated excellent in vitro and in vivo hemodynamics. Five/seven animals with aortic PCU-prostheses had an excellent clinical long-term course. The explanted valves showed a variable degree of calcification. Two of the seven animals died at 27 and 77 days due to pannus overgrowth causing severe LVOTO without degeneration of the valve itself. Both animals with commercial bioprostheses had to be sacrificed because of congestive heart failure related to structural degeneration of the bioprosthesis after 10 and 30 days of implantation. There was no increased thrombogenity of the PCU valves compared to bioprostheses. CONCLUSION: The new flexible polymeric aortic valve prosthesis is superior to current bioprostheses in animal testing.

Animals↗
PubMed2004

Polymeric prodrugs.

In 1975 Prof. H. Ringsdorf proposed a model for rational design of polymeric prodrugs [J. Polym. Sci. Symp. 51 (1975) 135]. The model has been the most important basis for research in the field, since it was the first model that took into account both the chemical and biological aspects needed for the design of polymeric prodrugs. This paper deals with the most important properties that were discovered by designing polymeric prodrugs: prolongation of action of the drug, controlled release of the drug, passive tumor accumulation by the EPR-effect and alteration of body distribution and cell uptake. Over the years, other objectives have been formulated and other properties of polymer-drug conjugates were discovered. One recent example, the immunoprotective ability of polymeric prodrugs, is described in more detail in this paper.

Adjuvants, Immunologic↗
PubMed2005

Polymerized hemoglobin induces heme oxygenase-1 protein expression and inhibits intercellular adhesion molecule-1 protein expression in human lung microvascular endothelial cells.

BACKGROUND: Our clinical trials using a polymerized hemoglobin solution (PolyHb) as a red cell substitute in severely injured patients suggested that this hemoglobin-based oxygen carrier has a systemic antiinflammatory effect. Heme oxygenase-1 (HO-1) has recently been shown to be cytoprotective, and is known to be induced by heme moieties. We investigated the effects of this hemoglobin-based oxygen carrier on HO-1 induction and proinflammatory activation of pulmonary endothelium. STUDY DESIGN: Human lung microvascular endothelial cells were grown to confluence and preincubated with either cell media (control) or with an equal volume mixture of polymerized hemoglobin/cell media (experimental). The cell cultures were subsequently stimulated with lipopolysaccharide. HO-1 expression was detected by protein immunoblot and further quantified by ELISA; intercellular adhesion molecule-1 protein expression was measured by flow cytometry. RESULTS: Polymerized hemoglobin induced synthesis of HO-1 protein in human lung microvascular endothelial cells and, concurrently, inhibited lipopolysaccharide-induced intercellular adhesion molecule-1 protein cell surface expression. CONCLUSIONS: Polymerized hemoglobin attenuates lipopolysaccharide-stimulated expression of intercellular adhesion molecule-1 protein, which is associated with upregulation of the cytoprotective protein HO-1 in human pulmonary endothelial cells. This antiinflammatory effect offers a novel mechanism by which hemoglobin-based oxygen carrier solutions may be exploited therapeutically as resuscitative fluids.

Analysis of Variance↗
PubMed2004

On the origin of colloidal particles in the dispersion polymerization of aniline.

When aniline is oxidized in an aqueous medium in the presence of a steric stabilizer, colloidal polyaniline (PANI) dispersions are obtained. The generally accepted model of the stabilization assumes that the macromolecules of the water-soluble steric stabilizer are adsorbed at the polymer, precipitating during the dispersion polymerization, and provide steric protection against further aggregation. An alternative mechanism of conducting-polymer particle formation is proposed in the present study. We suggest that the steric stabilizer provides a site for adsorption of oligoaniline initiation centers; subsequent polymerization from anchored centers yields particle nuclei that grow to produce colloidal PANI particles. This hypothesis is based on the observation that the colloidal particles are obtained only in the case where the steric stabilizer is introduced in the early stages of polymerization when aniline oligomers are present in the reaction mixture. If the stabilizer had been added during the growth of PANI chains, colloidal dispersions would not have been produced. The process of particle growth is completely analogous to the formation of conducting PANI films on the surface of microparticles and various materials. There, the polymerization of aniline at the surfaces is preferred to the same process proceeding in the bulk of the reaction mixture. While the films grow at the interfaces with the reaction mixture, the dispersion particles similarly emanate from the stabilizer chains. The particle size, the formation of nonspherical morphologies, the importance of the chemical nature of the stabilizer chains, and the general relation between the conducting-polymer film and particle growth are discussed in the light of the proposed model.

Journal Article↗
PubMed2005

Radical entry in emulsion polymerization: propagation at latex particles/water interfaces.

In emulsion polymerization, complete entry of an initiator-derived, surface-active radical may involve its adsorption onto latex particles/water interfaces and subsequently its propagation with one more monomer molecule therein. However, all publications to date have defined this propagation step as a three-dimensional bulk reaction between a surface-active entry radical and a monomer molecule. This is incorrect conceptually. It is proposed that the rate of the propagation of surface-active entry radicals with monomer at latex particles/water interfaces be expressed as [Formula: see text] . In this equation, A is the interfacial area between water and latex particles; [M](P) and [Formula: see text] are the mean concentrations of monomer in the particle phase and entry radicals in the aqueous phase, respectively; k(I) is the radical propagation constant at the interfaces, and may be estimated via transition state theory. For seeded styrene polymerization by Hawkett et al. (J. Chem. Soc. Faraday Trans. 1 76 (1980) 1323), k(I) approximately approximately 4.2x10(-9)k(p) (mol(-1)dm(4)s(-1)) is estimated. Here k(p) is the propagation rate coefficient in bulk polymerization. This alternative approach should be useful for one to simulate radical entry rate in emulsion polymerization where the propagation step may be rate-determining, such as under monomer-starved conditions.

Journal Article↗
PubMed2004

Oxidant free radical initiated chain polymerization of protein and other biomolecules and its relationship to diseases.

We review the evidence for free radical initiated chain polymerization of biomolecules. Our hypothesis predicts damaging effects of this chain polymerization. Free radical lipid peroxidation could initiate the chain polymerization of amyloid peptides and other biomolecules found in Alzheimer's disease. Reactions forming polymers present in other neurodegenerative diseases could follow the same pathway. Antioxygenic nutrients could protect against free radical oxidant damage, thereby delaying or preventing the onset of Alzheimer's disease and other neurodegenerative diseases The onset of Alzheimer's disease could be delayed if the initiation of free radical chain polymerization were inhibited or limited by nutrients that act as chain terminators or provide reducing conditions to reduce peroxidized lipids in the brain. Vitamins E and C and coenzyme Q are chain terminators. Selenium, sulfur amino acids and vitamin C provide reducing conditions.

Alzheimer Disease↗
PubMed2006

Influence of acrylic resin polymerization methods and saliva on the adherence of four Candida species.

STATEMENT OF PROBLEM: There is limited information on the role of polymerization methods and saliva on the adherence of pathogenic Candida species, with the exception of the adherence of Candida albicans to acrylic resins and the relation of this to surface roughness and surface free energy, which appear to play a major role in the initial phases of microorganism adhesion. PURPOSE: This study evaluated the influence of polymerization methods and human whole saliva on the adherence of Candida species to acrylic resin surfaces. MATERIAL AND METHODS: Acrylic resin specimens (n=256) measuring 2.5 x 1.2 x 0.2 cm were heat (Classico) or microwave (OndaCryl) polymerized and evaluated for surface roughness using a profilometer, and for surface free energy by measuring the contact angle of a sessile drop of water. For the adherence assay, specimens of each acrylic resin were divided by lottery into 8 groups, according to whether they were exposed to human saliva or not (control), and to 1 of the 4 following suspensions: C albicans, Candida tropicalis, Candida dubliniensis, or Candida glabrata (1 to 5 x 10(6) cells/mL). Adhered yeasts were counted using an optical microscope at x400 magnification. Data were analyzed by 3-way ANOVA and the Tukey honestly significant difference test (alpha=.05). RESULTS: No statistical difference was found for roughness (P=.156), whereas higher surface free-energy values were found for the heat-polymerized acrylic resin (P=.0013). The overall adherence of Candida species was significantly decreased by human saliva (P<.001). CONCLUSION: Within the limitations of this study, saliva was capable of reducing the adherence of Candida species, whereas roughness and free energy did not influence the adherence rates. CLINICAL IMPLICATIONS: As growth on surfaces is a natural part of the Candida lifestyle, its colonization in denture users may be expected. The presence of human whole saliva, however, decreased the overall yeast adherence to the acrylic resin surface, whereas surface roughness and free energy did not interfere with the adherence of Candida species.

Acrylic Resins↗
PubMed2002

Inhibition of tubulin polymerization by vitilevuamide, a bicyclic marine peptide, at a site distinct from colchicine, the vinca alkaloids, and dolastatin 10.

Vitilevuamide, a bicyclic 13 amino acid peptide, was isolated from two marine ascidians, Didemnum cuculiferum and Polysyncranton lithostrotum. Vitilevuamide was cytotoxic in several human tumor cell lines, with LC(50) values ranging from 6 to 311nM, and analysis in a 25-cell line panel revealed a weak correlation with several taxol analogs. Vitilevuamide was strongly positive in a cell-based screen for inhibitors of tubulin polymerization. Vitilevuamide at 9 microg/mL (5.6 microM) had an effect equivalent to the maximal effect of colchicine at 25 microg/mL (62.5 microM). Vitilevuamide was active in vivo against P388 lymphocytic leukemia, increasing the lifespan of leukemic mice 70% at 30 microg/kg. We hypothesized that at least part of the cytotoxic mechanism of vitilevuamide was due to its inhibition of tubulin polymerization. Vitilevuamide was found to inhibit polymerization of purified tubulin in vitro, with an IC(50) value of approximately 2 microM. Cell cycle analysis showed that vitilevuamide arrested cells in the G(2)/M phase with 78% of treated cells tetraploid after 16hr. Therefore, vitilevuamide was tested for its ability to inhibit binding of known tubulin ligands. Vitilevuamide exhibited non-competitive inhibition of vinblastine binding to tubulin. Colchicine binding to tubulin was stabilized in the presence of vitilevuamide in a fashion similar to vinblastine. Dolastatin 10 binding was unaffected by vitilevuamide at low concentrations, but inhibited at higher ones. GTP binding was also found to be weakly affected by the presence of vitilevuamide. These results suggest the possibility that vitilevuamide inhibits tubulin polymerization via an interaction at a unique site.

Animals↗
PubMed1992

Computer modeling of fibrin polymerization kinetics correlated with electron microscope and turbidity observations: clot structure and assembly are kinetically controlled.

Although much is known about fibrin polymerization, because it is complex, the effects of various modifications are not intuitively obvious and many experimental observations remain unexplained. A kinetic model presented here that is based on information about mechanisms of assembly accounts for most experimental observations and allows hypotheses about the effects of various factors to be tested. Differential equations describing the kinetics of polymerization were written and then solved numerically. The results have been related to turbidity profiles and electron microscope observations. The concentrations of intermediates in fibrin polymerization, and fiber diameters, fiber and protofibril lengths have been calculated from these models. The simplest model considered has three steps; fibrinopeptide A cleavage, protofibril formation, and lateral aggregation of protofibrils to form fibers. The average number of protofibrils per fiber, which is directly related to turbidity, can be calculated and plotted as a function of time. The lag period observed in turbidity profiles cannot be accurately simulated by such a model, but can be simulated by modifying the model such that oligomers must reach a minimum length before they aggregate. Many observations, reported here and elsewhere, can be accounted for by this model; the basic model may be modified to account for other experimental observations. Modeling predicts effects of changes in the rate of fibrinopeptide cleavage consistent with electron microscope and turbidity observations. Changes only in the rate constants for initiation of fiber growth or for addition of protofibrils to fibers are sufficient to account for a wide variety of other observations, e.g., the effects of ionic strength or fibrinopeptide B removal or thrombospondin. The effects of lateral aggregation of fibers has also been modeled: such behavior has been observed in turbidity curves and electron micrographs of clots formed in the presence of platelet factor 4. Thus, many aspects of clot structure and factors that influence structure are directly related to the rates of these steps of polymerization, even though these effects are often not obvious. Thus, to a large extent, clot structure is kinetically determined.

Biophysical Phenomena↗
PubMed1999

Water in actin polymerization.

We have addressed the question whether water is part of the G- to F-actin polymerization reaction. Under osmotic stress, the critical concentration for G-Ca-ATP actin was reduced for six different osmolytes. These results are interpreted as showing that reducing water activity favored the polymerized state. The magnitude of the effect correlated, then saturated, with increasing MW of the osmolyte and suggested that up to 10-12 fewer water molecules were associated with actin when it polymerized. By contrast, osmotic effects were insignificant for Mg-ATP actin. The nucleotide binding site of the Mg conformation is more closed than the Ca and more closely resembles the closed actin conformation in the polymerized state. These results suggest that the water may come from the cleft of the nucleotide binding site.

Actins↗
PubMed2001

Synthesis of D-xylopyranan by the ring-opening polymerization of 3-O-benzyl-alpha-D-xylopyranose 1,2,4-orthopivalate. Attempts to synthesize a stereoregular polymer.

3-O-Benzyl-alpha-D-xylopyranose 1,2,4-orthopivalate (1) was newly synthesized and polymerized under cationic polymerization reaction conditions in order to synthesize stereoregular (1-->4)-beta-D-xylopyranan. Although the polymerization of orthopivalate 1 was carried out under various reaction conditions, a non-stereoregular polymer, but mainly consisting of (1-->4)-beta-xylopyranose units, was obtained. Comparing these results with those of glucose 1,2,4-orthopivalates, it was revealed that not only the substituents in the C-2 and C-3 positions, but also the CH(2)OR group in glucose 1,2,4-orthopivalate, largely contribute to (1-->4)-beta-glucosidic bond formation by the ring-opening polymerization.

Carbohydrate Conformation↗