The new monomer 1,2-o-isopropylidene-[d]-xylofuranose-3,5-cyclic carbonate (IPXTC) was prepared. The organometallic catalysts AlR3−H2O (R = ethyl, isobutyl), ZnEt2−H2O, and Sn(Oct)2 were evaluated for the copolymerization of [l]-lactide ([l]-LA) with IPXTC. This work showed that Sn(Oct)2 was preferred for the formation of high molecular weight copolymers. For example, a copolymerization ([l]-LA/IPXTC = 83:17 mol/mol) at 120 °C for 6 h gave poly([l]-LA-co-7 mol % IPXTC) with an M n and polydispersity (M w/M n) of 78 400 and 1.9, respectively. The comonomer reactivity ratios were 4.15 and 0.255, respectively, for [l]-LA and IPXTC copolymerizations conducted at 120 °C, M/C = 200, and Sn(Oct)2 as catalyst. Structural investigations by NMR revealed that [l]-LA/IPXTC copolymers had short average IPXTC repeat unit segment lengths. Increased copolymer IPXTC content resulted in products with lower melting transition temperatures but higher glass transition temperatures. To obtain hydroxyl functionalized P([l]-LA) copolymers, the pendant IPXTC ketal protecting group was removed. The deprotection was performed in CH2Cl2 using CF3COOH/H2O without substantial molecular weight decrease. Hence, an efficient route has been developed to synthesize high molecular weight PLA-based copolymers that consist of [l]-lactic acid and [d]-xylofuranose repeat units. The [d]-xylofuranose repeat units have vicinal diol groups that will facilitate further functionalization and modification of these copolymers. The “tailorability” of the new copolymers is expected to be of great value for the development of important new bioresorbable medical materials.

Polycarbonates were synthesized by ring-opening copolymerizations of trimethylene carbonate (TMC) with 1,2-O-isopropylidene-d-xylofuranose-3,5-cyclic carbonate (IPXTC). Subsequent deprotection of the ketal protecting groups gave controlled quantities of vicinal diol pendant groups. Studies of TMC/IPXTC copolymerization showed that MAO and ZnEt2−0.5H2O were the preferred catalysts. The reactivity ratios measured by the Fineman−Ross method and using ZnEt2−0.5H2O as the catalyst were 0.31 and 0.20 for IPXTC and TMC, respectively. Hence, even though IPXTC has bulky substituents, IPXTC was more reactive than TMC early in the copolymerization. Consistent with the above, the average IPXTC chain segment length was longer early in the copolymerization but decreased with increased conversion. 1H and 13C NMR were used to analyze the repeat unit sequence distribution of copolymers. For copolymers with high IPXTC contents, three types of IPXTC linkages were found:  head−head, tail−tail, and head−tail. The protecting ketal groups were removed by CF3COOH/H2O to give a novel polycarbonate with hydroxyl pendant groups. Longer deprotection times led to higher extents of deprotection but lower molecular weight. Studies by differential scanning calorimeter (DSC) showed that copolymers having from 8 to 83% IPXTC were all amorphous. In addition, a physical aging transition was apparent. The T g of the copolymer increased with increasing IPXTC copolymer content. Furthermore, the experimental T g values were in good agreement with that calculated by the Fox equation. After deprotection, the copolymer T g decreased, which is consistent with the loss of the bulky ketal side group.

2,2-(2-Pentene-1,5-diyl)trimethylene carbonate ( c HTC) was synthesized from cyclohexene-4,4-dimethanol in high yield (>80%). This new carbonate monomer was successfully ring-open polymerized to form P( c HTC) in bulk at 90 °C using various organometallic catalysts including aluminoxanes (methyl and isobutyl), BunSnCl4-n (n ) 1, 2, 3), BunSn(OMe)4-n (n ) 2, 3), ZnEt2, and ZnEt2-H2O. Comparison of these systems showed that the Zn-and Al-based catalysts were preferred for the preparation of high molecular weight polymers in yields g89% and reaction times of e8 h. For the BunSnX4-n catalysts investigated, values of n ) 1 when X is Cl and n ) 2 when X is OMe resulted in relatively greater polymerization rates and higher polymer molecular weights. The effects of reaction time and monomer/ catalyst molar ratio were investigated for the Al and Zn catalysts. An outcome of this study was determining that the ZnEt2-H2O (1/0.5) catalyst for a monomer/catalyst (M/C) molar ratio of 400 and a 2 h reaction time gave a product with Mn ) 276 000 in 98% yield. The P( c HTC) products were characterized by FTIR, 1 H-NMR, 13 C-NMR, DSC, TGA, and GPC. NMR results showed that c HTC decarboxylation did not occur during chain propagation. P( c HTC) has a moderate glass transition temperature (Tg ) 30 °C) with high thermal stability. 13 C NMR at 62.5 MHz did not resolve chain diad sequences although the polymers are likely atactic. Epoxidation of P( c HTC) vinyl side groups was carried out to various extents by using 3-chloroperoxybenzoic acid at room temperature.

[l]-Lactide ([l]-LA)/ethylene oxide (EO) ring-opening copolymerizations were successfully carried out by using various catalysts including isobutylaluminoxane (IBAO), in situ AlR3·0.5H2O systems (R = ethyl, isobutyl) and Sn−Al bimetallic catalysts. Analysis of products by 1H NMR showed that methanol insoluble copolymer fractions had multiblock structures. The multiblock segment length and molecular weight of the copolymers were regulated by a variation in the reaction temperature, reaction time, reaction medium, and the catalyst structure. An increase in the reaction temperature was used to obtain shorter segment block lengths. Bulk reactions at elevated temperatures gave shorter block lengths than those of corresponding polymerizations conducted in solution (xylene). Differential scanning calorimetry (DSC) results showed two melting transitions corresponding to poly(ethylene oxide) (PEO) and [l]-polylactide ([l]-PLA) crystalline phases. The melting temperature and enthalpy of fusion for the phase-separated [l]-PLA crystalline phase was “tailored” by modulating the copolymer composition and the [l]-PLA block length. Blends with PLA were prepared by substituting poly(ethylene glycol) (PEG) with a high EO content [l]-PLA/EO multiblock copolymer. The idea explored was that the multiblock copolymers would be expected to leach into aqueous environments at a slower rate than PEGs. Substitution of the [l]-PLA/EO copolymer in place of PEG resulted in important increases in the film modulus and yield strength without loss in elongation at yield, break stress, and elongation at break. Thus, we demonstrated a versatile route to important new multiblock [l]-PLA/EO copolymers which have excellent potential to be useful for a wide range of biomedical applications including bioresorbable implant materials and tissue engineering. Furthermore, the synthetic methods developed herein provide routes which will be useful in “fine-tuning” product physicomechanical properties and degradation rates.

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A number of applications in biomedical materials will greatly benefit by further research in bioresorbable polymers that have various side group attributes. By careful design, these functional groups can be used to regulate hydrophilicity/hydrophobicity, permeability, bioresorption and mechanical properties. 1-3 The pendant functional groups provide active sites for crosslinking and grafting as well as the opportunity to attach bioactive substances to modulate cellular responses for tissue engineering applications. 4-8 Aliphatic polycarbonates represent one family of bioresorbable materials that are being engineered for biomedical applications. [9][10][11][12] Various aliphatic polycarbonates, such as poly(trimethylene carbonate) (PTMC) 13 and poly(2,2-dimethyl trimethylene carbonate) (PDTC) 14 have been synthesized by ring-opening polymerization. Polycarbonates with hydroxyl pendant groups have been used to regulate bioresorption kinetics. For example, the in vitro degradation of PTMC in pH 7.4 buffer solution for 30 weeks at 37°C resulted in only a 9% weight loss and a 7% decrease in molecular weight. 13 In contrast, watersoluble poly(hydroxyalkylene carbonates) undergo rapid degradation even in neutral water. 15 Specifically, the intrinsic viscosity of poly[[(oxycarbonyl)oxyl]-1,4-threityl] decreased to ca. one-third of its original value within 14 days in phosphate-buffered saline at 37°C.Recently, we prepared the cyclic carbonate monomer 1,2-O-isopropylidene-D-xylofuranose-3,5-cyclic carbonate (IPXTC) from a natural sugar. This monomer was successfully copolymerized with lactide and also trimethylene carbonate. The result was the formation of copolymers that have ketal-protected hydroxyl side groups. 16,17 The ketal groups were hydrolyzed to give hydroxyl pendant groups. 16,17 The homopolymer of IP-XTC and its deprotected product (Scheme 1) would give a carbohydrate-based polymer with carbonate mainchain linkages. Due to the steric constraints around the carbonate of IPXTC, this monomer has thus far proved to be difficult to homopolymerize. Previously, it was only possible to obtain low molecular weight P(IPXTC) oligomers in poor yield by Sn(Oct) 2 catalyzed IPXTC homopolymerization. 16 In this paper, we report the successful use of anionic and rare-earth isopropoxide catalysts for IPXTC homopolymerizaton. Structural, thermal, and X-ray analyses of P(IPXTC) are described.IPXTC was synthesized by the method similar to that reported by Ariga et al., 18 exactly as was described elsewhere. 16,17 The general polymerization protocol and polymer characterization methods were also previously published. 16,17 Organometallic catalysts that contain aluminum, zinc and rare-earth metals as well as t BuOK were evaluated for their abilities to homopolymerize IPXTC. The results of this work are summarized in Tables 1 and 2. The catalysts MAO, AlEt 3 -H 2 O, ZnEt 2 -H 2 O, and Et 2 AlOEt are known as coordination-catalysts that are highly active for lactones, lactide, and TMC polymerizations. 1,[19][20][21][22] However, the ...

Purpose: The purpose of this study is to determine the effects of Chinese traditional exercise such as t'ai chi and qigong (TCQ) on patients with chronic obstructive pulmonary disease (COPD). Methods: All prospective, randomized, controlled clinical trials, published in English or Chinese and involving the use of TCQ by patients with COPD, were searched in 10 electronic databases from their respective inceptions to July 2012. The methodological quality of all studies was assessed using the Jadad score. The selection of studies, data extraction, and quality assessment were performed independently by two raters. Results: In the results, 10 trials met the inclusion criteria and were reviewed. The meta-analysis demonstrated that compared with no exercise, TCQ had significant effects on 6-minute walk distance, forced expiratory volume in 1 second (FEV1), predicted FEV1 percentage, and St. George's Respiratory Questionnaire score. There were no significant differences in all outcomes between TCQ and other exercise training except 6-minute walk distance. Conclusions: In conclusion, TCQ might be beneficial with respect to physical performance, lung function, remission of dyspnea, and quality of life in patients with COPD; however, caution is needed to draw a firm conclusion because of the low methodological quality of the included trials.

This paper explores the copolymerization of L-lactide (L-LA) with 2,2-[2-pentene-1,5-diyl]-trimethylene carbonate ( c HTC). Since c HTC has a cyclohexene group, this provided a route for preparing poly(lactic acid), (PLA), based chains decorated with controlled quantities of CdC substituents. Ringopening copolymerizations of L-LA with c HTC were successfully conducted in bulk by using AlR3-H2O (R ) ethyl, isobutyl), Al(O i Pr)3, ZnEt2-H2O and Sn(Oct)2 as catalysts. Comparison of these copolymerizations showed that the Sn(Oct)2 catalyst system gave copolymers of relatively higher molecular weight. Increasing the reaction time of Sn(Oct)2 catalyzed copolymerizations from 6 to 24 h resulted in higher copolymer c HTC content and yield but lower copolymer molecular weight. Variation of the comonomer feed ratio was useful in regulating the content of cyclohexene pendant groups in the copolymer. However, regardless of the catalyst used, the mole percent of c HTC incorporated into the copolymer was lower than that used in the monomer feed. Determination of the comonomer reactivity ratios for Sn(Oct)2 catalyzed copolymerizations gave values of 8.8 and 0.52 for L-LA and c HTC, respectively. All gel permeation chromatography (GPC) traces showed unimodal molecular weight distributions. Determination by 13 C-NMR of the copolymer sequence fractions HLL, LLL, LLH, HLH, HL, and LH (H ) c HTC units, L ) L-lactyl units) showed that they were close to those calculated by assuming a Bernoulli statistical propagation. On the basis of these results and the effects of reaction conditions on the copolymer sequence distribution, a mechanism which involves insertion of c HTC into the polymer chain was proposed. Studies by differential scanning calorimetry (DSC) showed that c HTC units in the copolymers disrupted ordering of the L-PLA crystalline phase. Furthermore, the glass transition temperatures (Tg) ranged from 60 (L-PLA) to 33°C (P( c HTC)). Conversion of CdC to epoxy side groups was successfully carried out by using 3-(chloroperoxy)benzoic acid at room temperature with only small decreases in copolymer molecular weight.