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The effect of block number on the order-disorder transition (ODT) and viscoelastic properties were studied for linear (AB)n multiblock copolymers. A series of symmetric poly(styrene-b-isoprene)n multiblocks ((SI)n, n ) 1-10) were synthesized by anionic polymerization, and their order-disorder transition temperatures (TODT) were located using dynamic mechanical spectroscopy. As n increases, TODT approaches an asymptotic value, consistent with random phase approximation calculations. A systematic difference between the experimental and theoretical results is attributable to the effects of fluctuations, independent of the number of blocks. Addition of up to 20 vol % of a nonselective solvent depresses TODT, independent of n. The interaction parameter at the transition, ODT, decreases with polymer volume fraction φ as ODT ∼ φ -1.3 , consistent with previous reports for diblocks (n ) 1). In contrast, the viscoelasticity of (AB)n block copolymers depends strongly on block number. A crossover frequency, ωx, demarcating the transition from block/chain-and domain-dominated relaxation, scales as n -7.5 , which is much stronger than the molecular weight dependence of the longest relaxation time for entangled homopolymers. Coherent lamellar grains were imaged for quenched and annealed (SI) n, n ) 1, 6, and 10, by transmission electron microscopy. Ellipsoidal lamellar grains, with aspect ratios of 2-3, were recorded, independent of block number, but the grain size decreased with increasing n. These results establish the criteria for designing multiblock copolymers based on , N, n, and concentration.

Microstructure of and mechanical properties of a series of symmetric EPE (E = poly(ethylene-co-1-butene) and P = poly(ethylene-alt-propylene)) triblock copolymers with M n = 27−372 kg/mol have been investigated in the solid state. Microphase separation of EPE triblock copolymers originates from either (i) chemical incompatibility-induced microphase separation in the melt before crystallization at high overall molecular weights or (ii) crystallization-induced microphase separation from a homogeneous melt at low overall molecular weights. Small-angle X-ray scattering demonstrates that these EPEs (f E ≈ f P ≈ 0.5) adopt a lamellar morphology over the range of molecular weights studied. The observed interlamellar domain spacing (d) scales with the molecular weight as d ∼ N 0 β, where N 0 is the degree of polymerization and β = 0.22 for crystallization-induced segregation and β = 0.63 for microphase-separated melts. The mode of microphase separation strongly affects the chain folding microstructure of the polyethylene crystallites within the lamellar structure. The consequences of these observations on the ultimate tensile strengths of these materials are discussed.

A series of novel azo polyelectrolytes have been synthesized based on an extremely reactive precursor polymer, poly(acryloyl chloride) (PAC), prepared from acryloyl chloride by radical polymerization. The precursor polymer was post-functionalized by the Schotten-Baumann reaction of PAC and several aromatic azo reactants containing hydroxyl end groups. The degrees of functionalization were controlled by selecting suitable feed ratios between the azo reactants and poly(acryloyl chloride) and the unreacted acyl chloride groups were hydrolyzed to obtain ionizable carboxyl groups. The products were characterized by elemental analysis, FT-IR, 1H NMR and UV−vis spectroscopy. Irradiated by 365 nm UV light, azo polyelectrolytes PPAPE, PEAPE and PCAPE showed a significant photochromic effect. The contact angles of water on the surfaces of spin-coated films of PPAPE and PEAPE decreased evidently upon UV irradiation. The extent of the photoinduced contact angle changes depends on the type of the azo chromophores and the degree of functionalization. Self-assembled multilayers of the azo polyelectrolytes were fabricated by a layer-by-layer adsorption method. A significant photochromic effect from cis−trans isomerization of the azo chromophores was observed for the multilayers. The photoinduced contact angle changes of water on the self-assembled multilayers were also observed.

Background Food safety has long been the subject of scholarly research, and street food is a weak link in food safety supervision. Street food not only provides convenience for many people, but is also the livelihood for millions of low income people, making a great contribution to the economy of many developing countries. Methods Street food safety is essential, and yet it has been rarely studied in China. Therefore, a typical city in China was selected as the research object to assess food safety knowledge, attitudes, and street food suppliers and consumer behaviors using questionnaires based on previous studies, and considering China’s particular characteristics and reasonable impacts identified in previous studies, such as increased income, work experience, licenses, and locations. The food safety knowledge and attitude questionnaire conformed with the national conditions in China. It was used to assess the food safety knowledge and attitudes toward food suppliers and consumers, where three main areas were addressed in the surveys and statistical analysis, as follows. (1) Statistical information including gender, age, education, income, food safety training, and specific elements related to the work experience of suppliers. (2) Knowledge of food safety including the awareness of consumers and suppliers regarding food poisoning pathogens, food and personal hygiene, high-risk groups, and correct cleaning. (3) A list of food handling behaviors was used to determine the behaviors and characteristics of subjects. Results The results show that street food suppliers have generally poor food handling practices, and most are operating under unsanitary conditions. Food safety knowledge of street vendors in the High-tech Industries Development Zone was the lowest, most likely because these regions are located in rural-urban fringe zones, where education levels are generally relatively low. Food safety attitudes of the youngest consumers were significantly better than those of older age groups. Their educational level was also different, with correspondingly relatively high income for younger individuals. Most vendors chose locations near schools or supermarkets. Consumers and street food vendors had good understanding of food safety, but street vendors were relatively poor in carrying out safe food handling, with only 26.7% using or being fully equipped withhand-washing facilities, although more than 60% of vendors wore clean and tidy clothes and masks. Conclusions Street food vendor training should be prioritized to improve the safety of street food. Other policies and measures should also be propagated to improve the food safety knowledge, attitudes, and behavior of vendors in Handan. Steps should be taken to improve street food stall operating conditions and facilities, including providing clean protected structures, access to potable water, and efficient waste collection and disposal systems. These findings shoul...