Effect of Configuration of a Bulky Aluminum Initiator on the Structure of Copolymers of L,L-Lactide with Symmetric Comonomer Trimethylene Carbonate

The effect of configuration of an asymmetric bulky initiator 2,2’-[1,1’-binaphtyl-2,2’-diyl- bis-(nitrylomethilidyne)]diphenoxy aluminum isopropoxide (Ini) on structure of copolymer of asymmetric monomer L,L-lactide (Lac) with symmetric comonomer trimethylene carbonate (Tmc) was studied using polarimetry, dilatometry, SEC and 13C NMR. When the S-enantiomer of Ini was used the distribution in copolymer chains at the beginning of polymerization is statistical, with alternacy tendency, changing next through a gradient region to homoblocks of Tmc. When, however, R-Ini was used, the product formed was a gradient oligoblock one, with Tmc blocks prevailing at the beginning, changing to Lac blocks dominating at end part of chains. Initiation of copolymerization with the mixture of both initiator enantiomers (S:R = 6:94) gave multiblock copolymer, of similar features but shorter blocks. Analysis of copolymerization progress required complex analysis of dilatometric data, assuming different molar volume contraction coefficients for units located in different triads. Comonomer reactivity ratios of studied copolymerizations were determined.

Effect of Configuration of a Bulky Aluminum Initiator on the Structure of Copolymers of L,L-Lactide with Symmetric Comonomer Trimethylene Carbonate

The effect of configuration of an asymmetric bulky initiator 2,2’-[1,1’-binaphtyl-2,2’-diyl- bis-(nitrylomethilidyne)]diphenoxy aluminum isopropoxide (Ini) on structure of copolymer of asymmetric monomer L,L-lactide (Lac) with symmetric comonomer trimethylene carbonate (Tmc) was studied using polarimetry, dilatometry, SEC and 13C NMR. When the S-enantiomer of Ini was used the distribution in copolymer chains at the beginning of polymerization is statistical, with alternacy tendency, changing next through a gradient region to homoblocks of Tmc. When, however, R-Ini was used, the product formed was a gradient oligoblock one, with Tmc blocks prevailing at the beginning, changing to Lac blocks dominating at end part of chains. Initiation of copolymerization with the mixture of both initiator enantiomers (S:R = 6:94) gave multiblock copolymer, of similar features but shorter blocks. Analysis of copolymerization progress required complex analysis of dilatometric data, assuming different contraction coefficients for units located in different triads. Comonomer reactivity ratios of studied copolymerizations were determined.

Improper Interpretation of Dilatometric Data for Cooling Transformation in Steels

Dilatometry is the most commonly method of producing CCT diagrams and analyzing phase transformations during cooling (as well as transformations during heating) and it permits the real-time monitoring of the extent of reaction in terms of dimensional changes due to phase transformation. All modern dilatometers are fitted with computerised systems which collect dimensional change signals versus temperature to plot a dilatometric curve and also to calculate and plot the derivative of the relative dimensional change with respect to temperature. Unfortunately, elaborated by dilatometers manufacturers software, in many cases could lead to wrong interpretation of phase transformations during cooling.

Atmosphere Effect on Sintering Behaviour of Astaloy CrM and Astaloy CrL Höganäs Powders with Manganese and Carbon Additions / Wpływ Atmosfery Na Spiekalność Komercyjnych Proszków Höganäs Astaloy CrM I Astaloy CrL Z Dodatkami Manganu I Węgla

Dilatometric data for Astaloy CrM (3% Cr-0.5% Mo) and Astaloy CrL (1.5% Cr-0.2% Mo) powders with additions of 0.3% carbon and 3.0% manganese during sintering cycles up to 1120 and 1250°C in different atmospheres are reported. For comparison, also Astaloy CrM and Astaloy CrL powders were investigated. Starting with green densities of approx. 6.8 g/cm3, the final density of sintered compacts was influenced mainly by the sintering temperature, while the results showed the only minor effect of the sintering atmosphere on the final dimensional changes. However, the sintering atmosphere influences the sintering behaviour, microstructure and the final chemical composition of sintered compacts. In sintered and in the dilatometer cooled Mn-Cr-Mo-C steels predominantly bainitic structures were obtained.