Compositional asymmetry in a crystalline-amorphous block copolymer influences the phase and crystallization behaviors of its blend with an amorphous block copolymer.

This study determined the phase and crystallization behaviors of blends composed of asymmetric polystyrene-block-poly(ethylene oxide) (PS-PEO) and symmetric polystyrene-block-poly(methyl methacrylate) (PS-PMMA). The PS blocks in the various binary block copolymers exhibited nearly identical molecular weights, whereas the molecular weight ratios of PEO and PMMA varied. The compatibility of the PEO and PMMA chains aided the binary block copolymers in co-ordering in a lamellar microdomain morphology, with the PEO and PMMA blocks sharing a common microdomain. Adding short tethered PMMA chains to long tethered PEO chains led to a decrease in the common microdomain spacing and an increase in the grafting density. These behaviors increased PEO chain stretching, causing macrophase separation. The mismatch in PEO and PMMA block lengths divided the common PEO/PMMA microdomain into two sections: the coexisting PEO/PMMA section close to the microdomain interface and the neat PEO section far away from it. The high-glass-transition-temperature PMMA reduced PEO chain mobility, inhibiting PEO crystallization in the coexisting PEO/PMMA section but not in the neat PEO section. When the block length ratio of PEO to PMMA decreased, the neat PEO section narrowed. The increase in the extent of PEO confinement led to a reduction in PEO crystallizability.

Xylooligosaccharides and fructooligosaccharides affect the intestinal microbiota and precancerous colonic lesion development in rats.

Certain nondigestible oligosaccharides can be selectively utilized by probiotics and reduce the risk of colon cancer. However, the inhibitory effects of xylooligosaccharides (XOS) on colon cancer are not well documented. This study evaluated the effects of xylooligosaccharides and fructooligosaccharides (FOS) on the alteration of cecal microbiota, cecal pH, cecal weight, and serum lipid levels, and also their inhibitory effect on precancerous colon lesions in male Sprague-Dawley rats. The rats were randomly assigned to 4 groups: control, treatment with 1,2-dimethylhydrazine (DMH) [15 mg/(kg body wt.wk) for 2 wk], treatment with DMH + 60 g XOS/kg diet, and treatment with DMH + 60 g FOS/kg diet. Rats were fed the experimental diets for 35 d, beginning 1 wk after the second dose of DMH. Both XOS and FOS markedly decreased the cecal pH and serum triglyceride concentration, and increased the total cecal weight and bifidobacteria population. XOS had a greater effect on the bacterial population than did FOS. Moreover, both XOS and FOS markedly reduced the number of aberrant crypt foci in the colon of DMH-treated rats. These results suggest that XOS and FOS dietary supplementation may be beneficial to gastrointestinal health, and indicate that XOS is more effective than FOS.