Block Length Distribution Research Articles

Synthesis of a stereoblock poly(methyl methacrylate)

AbstractThe sequential block copolymerization of diphenylmethyl methacrylate (DMA) and trityl methacrylate (TrMA), initiated by diphenyl methyl lithium in THF at ‐78°C followed by hydrolysis and methylation with diazomethane, leads to the formation of an isotacticsyndiotactic stereoblock poly(methylmethacrylate) (PMMA) of narrow molecular weight and block length distribution. Complete conversion of DMA is shown to be essential, since the presence of small quantities of this monomer during the polymerization of TrMA significantly lowers the isotactic content of this block. Polymerization times of at least 12 h were found to be necessary for complete polymerization of the TrMA.

Discontinuities and rock mass geometry

Variation in discontinuity frequency as a function of scanline orientation in a plane is studied for rock masses containing sets of discontinuities. The spacing values between discontinuity intersection points that can occur along such scanlines are considered in order to develop a probability density distribution of block lengths. The ideas are extended to block area and volume distributions synthesized from the products of discontinuity spacing values along two and three axes respectively. Such distributions are also considered for rock masses were each discontinuity occurs with a random orientation. Histograms of discontinuity spacing and block area values compiled from measurements made on a variety of rock exposure from Pre-Cambrian to Jurassic are in general agreement with the theoretical distributions. The results are presented in dimensionless form and an explanation of the procedure for determining the scaling factors that allow computation of block area and volume distributions for a particular rock mass is included.

Preparation of Radioactively Tagged Ethylene-Propylene Copolymers. Calculation of the Block-Length Distribution from the Kinetic Data

Abstract A series of statistical copolymers is available for our studies of the mechanisms of thermal decomposition of ethylene-propylene copolymers and their sequence distribution. However, the analytical evidence can be improved appreciably by the use of radioactively tagged copolymers and radio-gas chromatography. A loss of information occurs when untagged polymers undergo α-scission. Even if the chain breaks directly at the tertiary carbon atom, the scission product stabilizes itself by forming a terminal double bond. Accordingly, the position of double bonds gives no information about the location of methyl side groups in copolymers. However, if the α-methyl groups are radioactively tagged, as shown in the formula above, radioactive counting of linear fragments can demonstrate their original methyl side groups. Thus, α-scissions of copolymers can be directly determined.

Hard Block Length Distribution in Segmented Block Copolymers

Hard Block Length Distribution in Segmented Block Copolymers

Estimation of isotacticity in semicrystalline polymers

AbstractA new method is suggested for estimating the degree of isotacticity and the distribution of block lengths in semicrystalline polymers. The method is based upon the maximum attainable crystallinity and its dependence upon temperature. An alternate approach is based upon the dynamic shear modulus and its temperature dependence above the glass temperature.

THEORETICAL DISTRIBUTION OF THE INITIAL LINKAGE BLOCK LENGTHS INTACT IN THE GAMETES OF A POPULATION INTERMATED FOR n GENERATIONS

THEORETICAL DISTRIBUTION OF THE INITIAL LINKAGE BLOCK LENGTHS INTACT IN THE GAMETES OF A POPULATION INTERMATED FOR n GENERATIONS