Segmented polymer networks containing amino‐dendrimers

Polymer networks in which poly(propylene imine) dendrimers (Astramol?) are connected to each other by linear polytetrahydrofuran (polyTHF) segments, were prepared by two methods. The first method was a one‐step procedure in which bifunctionally living polyTHF, obtained by initiation of the THF polymerization with trifluoromethane sulfonic anhydride (triflic anhydride), was reacted with an amino‐dendrimer. This reaction was very fast but did not allow formation of the end products. The second method was a two‐step procedure. In a first step, living polyTHF, prepared with acryloyloxybutyl triflate as initiator, was grafted on an amino‐dendrimer, to form a star‐like, acrylate‐terminated polyTHF multi‐macromonomer with the dendrimer as core. In a second step, networks were obtained by Michael addition between the acrylate end‐groups and unreacted amino‐groups of the dendrimer. This cross‐linking reaction occurred spontaneously upon heating of the solution of the multi‐macromonomer with gelation times varying from a few minutes to a few hours, depending on the temperature and the composition of the prepolymers. With this method it was possible to prepare networks in the form of coatings or films. © 2003 Society of Chemical Industry     

Polymer networks based on α,ω-methacrylate-terminated poly(1,3-dioxolane)

α,ω-Methacrylate-terminated poly(1,3-dioxolane)s (polyDXL) were synthesized by cationic ring-opening polymerization of DXL in the presence of methylene-bis(oxyethylmethacrylate) as transfer agent. If the initiator concentration is small compared with the transfer agent concentration, the molecular weights of the polymers are governed by the ratio of the reacted monomer to the reacted transfer agent. The α,ω-methacrylate-terminated polyDXLs obtained undergo free radical polymerization with formation of polyacetal networks. The properties of the networks as function of the molecular weight of the corresponding prepolymers are reported.     

Dislocations in strained layers: The Ge-Si system

The Ge-Si on Si epilayer system, besides being an interesting technological system in its own right, is a superb model for strained-layer studies. The point defect and symmetry defect structures associated with compound semiconductors can be avoided, allowing a focus on the mechanics of the system. Dislocation sources, glide behavior, and performance effects have been examined for strained-layer systems. Surprises have appeared along the way, but these materials are now becoming characterized well enough for industrial device applications.     

Indoor temperature changes in retrofit homes

The behavioral response (e.g. changes in indoor temperatures, attention to window and door openings) to residential technical efficiency improvements (e.g. attic insulation, storm windows) is an important and largely unresolved issue. Although there is considerable discussion concerning the extent to which households take back some of the energy savings due to technical efficiency improvements in increased comfort, there is almost no empirical evidence on the subject.Detailed electricity billing data (from mid-1981 to mid-1983) were analyzed for 79 households that received financial assistance from the Bonneville Power Administration to retrofit their homes in mid-1982. The mean retrofit expenditure in these homes was $1900; the mean reduction in annual electricity use was 4700 kWh, of which 83% was due to reductions in space heating electricity use. Analysis of the electricity billing data suggests that these households increased their indoor temperature settings after retrofit by almost 1 °F on average. This temperature increase led to an estimated average loss of almost 600 kWh of electricity saving. In other words, roughly 10% of the energy saving due to retrofit was taken back in terms of increased comfort. These results concerning changes in indoor temperatures should be viewed cautiously because of limitations in the analytical method and the large variation across households.     

A comparison of commonly used hydrologic design methods for rainwater collectors

Rainwater collection as a possible water source in developing countries is introduced. The major parameters in calculating the size of the tank are defined. Six methods that have been used previously to relate demand, storage, reliability and the rainfall pattern are compared to the Ottawa Model over a wide range of demands.     

Preliminary irradiation test results from the Yankee Atomic Electric Company reactor vessel test irradiation program

The Yankee Atomic Electric Company test irradiation program was implemented to characterize the irradiation response of representative Yankee Rowe reactor vessel beltline plate materials and to remove uncertainties in the analysis of existing irradiation data on the Yankee Rowe reactor vessel steel. Plate materials each containing 0·24 w/o copper, but different nickel contents at 0·63 w/o and 0·19 w/o, were heat treated to simulate the Yankee vessel heat treatment (austenitized at 982°C (1800°F)) and to simulate Regulatory Guide 1·99 database materials (austenitized at 871°C (1600°F)). These heat treatments produced different microstructures so the effect of microstructure on irradiation damage sensitivity could be tested. Because the nickel content of the test plates varied and the copper level was constant, the effect of nickel on irradiation embrittlement was also tested. Correlation monitor material, HSST-02, was included in the program to benchmark the Ford Nuclear Reactor (University of Michigan Test Reactor) which had never been used before for this type of irradiation program. Materials taken from plate surface locations (versus 1/4T) were included to test whether or not the improved toughness properties of the plate surface layer, resulting from the rapid quench, are maintained after irradiation. If the improved properties are maintained, pressurized thermal shock calculations could utilize this margin. Finally, for one experiment, irradiations were conducted at two irradiation temperatures (260°C and 288°C) to determine the effect of irradiation temperature on embrittlement. The preliminary results of the irradiation program show an average temperature effect of 38°C for a 28°C difference in irradiation temperature. The results suggest that for nickel bearing steels, the superior toughness of plate surface material is maintained after irradiation and for the copper content tested, nickel has little effect on irradiation response. No apparent microstructure effect on irradiation response was noted and the HSST-02 material's response to irradiation was similar to results from power reactor and other test reactor tests, thus qualifying the Ford Test Reactor for irradiation experiments such as those conducted for the Yankee Atomic program.