The preparation of graft copolymers is a domain of polymer chemistry that has received considerable interest. Grafting of vinyl monomers to natural and synthetic polymers by means of chemical or radiation-initiated polymerization has been suggested as a potentially good means of altering the properties of the base polymer. Graft polymerization is different from random or block copolymerization in that it leaves the main polymeric backbone essentially intact. A graft copolymer may combine some of the characteristic properties of each polymer or have properties entirely different from either of the components. Hence such products made of selected polymer combinations can have highly specific properties tailor-made for a particular application. 相似文献
Summary: The newly developed interactive separation of polyolefins by high temperature liquid chromatography (HTLC) provides new information about the chemical composition distribution of polyolefin elastomers. The technique has the advantage of being quantitative in its separation, and has high resolution for the separation of polyolefins by their chemical composition without influence by cocrystallization. Chemical composition distributions can be determined for individual polymers and blends which contain the full range of comonomer typically present in polyethylene and poylypropylene homopolymers, semi-crystalline copolymers, and amorphous copolymers. HTLC analysis in combination with the other fractionation techniques, such as DSC, TREF, NMR, and xylene fractionation, can be used to estimate the amount of olefin block copolymer present in a block composite produced by chain shuttling catalysis. 相似文献
Graft copolymerization reactions of fibrous cellulose with vinyl monomers were initiated at free radical sites formed on the cellulose molecule by interaction with high-energy radiation, by reaction with Ce4+ ions in acidic solution, or by H abstraction by ·OH radicals fromed by reaction of Fe2+ ions with HLOz in aqueous solution. The effects of experimental conditions on the nature, half-lives, location of these free radical sites on the cellulose molecule, and on the copolymerization reactions were studied by the use of electron spin resonance spectroscopy. The molecular weights of the grafted polymers varied over a range from about 3 × 104 to 1 × 106. The distributions of the grafted polymers within the fibrous cellulosic structure were determined. Some of the changes in physical properties of the cellulose graft copolymers, as compared with cellulose, were decreased permanent set, development of thermoplasticity, decreased stiffness, increased rot resistance, and increased abrasion resistance. 相似文献
Abstract A review is given on two types of trioxane copolymers: trioxane/dioxolane copolymers and copolymers of trioxane with polar monomers. It has been possible to find reaction conditions that influence the transacetalization reaction and, hence, the molecular weight distribution and the sequence length of trioxane/dioxolane copolymers. Trioxane copolymers with varying dioxolane content show an unusual behavior with respect to density, specific volume, and melting point as a function of composition. This is possibly caused by the formation of at least four different crystal structures in such copolymers. The synthesis of polyoxymethylenes carrying reactive groups is possible by copolymerizing trioxane with substituted phenylglycidyl ethers. These copolymers can be subjected to further chemical modification leading to poly-oxymethylenes with aldehyde, carboxy, and amino groups or derivatives thereof. 相似文献
A star-shaped molecule and a layered structure are displayed by the title compound, where the layers consist of high molecular weight polymers. A core molecule that is functionalized by six hydroxyl groups acts as the initiator for the ring-opening polymerization of ε-caprolactone, leading to a six-arm star polymer. The second layer of the dendritic block copolymer with 12, 24, or 48 hydroxyl groups (depending on the dendron generation in use) is obtained by the linkage of chain ends with functionalized dendrons. These macromoleculse act as “macroinitiators” for the construction of a further layer of poly(ε-caprolatone), the third generation of dendritic block copolymers. 相似文献
Just add it! Ruthenium initiators functionalized with hydrogen‐bonding sites were utilized in ring‐opening metathesis polymerization to prepare heterotelechelic polymers with hydrogen‐bonding and metal‐coordination units in a single step. Supramolecular ABC triblock copolymers were then self‐assembled in one pot by simply adding complementary telechelic polymers to a solution of the heterotelechelic polymer (see picture).
1-Methylcyclopropene (MCP) copolymerizes rapidly with acrylic and vinyl monomers to form soluble, high molecular weight products containing enchained cyclopropane rings. The high electron availability in the cyclopropene double bond promotes one-to-one alternating copolymerization with sulfur dioxide, maleic anhydride, acrylic acid, acrylonitrile, dialkyl fumarates and acrylic esters. Nonalternating copolymers are obtained with vinyl chloride and vinyl acetate, and attempted copolymerization fails entirely with styrene, α-methylstyrene and isoprene. This pattern of copolymerization reactivity resembles that of highly compressed ethylene. Methylcyclopropene copolymers have high glass temperatures in spite of the small size of the MCP unit. The combination of high Tg and small size allows preparation of copolymers with high Tg having a wide range of ductilities and cohesive energy densities. 相似文献