| 摘要 |
Block copolymers having both addition polymer and condensation polymer blocks are prepared by reacting (a) at least one monomer having terminal ethylenic unsaturation and being capable of polymerization by a free radical mechanism, (b) at least one condensation prepolymer which contains at least one isocyanate group but which does not contain unsaturated aliphatic carbon-carbon bonds, and (c) a dual functional free radical initiator having at least one group which may decompose to give free radicals and at least one substituent having an active hydrogen atom or atoms capable of reacting with isocyanate groups, reaction being effected at a temperature sufficiently high to initiate formation of the polymer. In a modification, the dual functional initiator may be replaced by a mixture of any free radical initiator and a chain transfer agent having a disulphide linkage and at least one reactive substituent as previously defined. The reactants (a), (b) and (c) may be reacted simultaneously, or one of (a) and (b) may be reacted first with the initiator (plus chain transfer agent where appropriate) and the product obtained then reacted with the remaining component. Suitable monomers (a) include vinyl chloride, vinyl acetate, vinyl ethers, styrene, methyl vinyl ketone, vinylidene chloride, acrylic, chloracrylic and methacrylic esters, acrylonitrile, methacrylonitrile, butadiene, isoprene and chlorprene. Prepolymers (b) specified are isocyanate-terminated polyethylene oxide, polypropylene oxide, polytetramethylene oxide and the polyester derived from adipic acid, ethylene glycol and proylene glycol. The dual functional initiator may be a peroxide, azo compound or polysulphide additionally containing one or more of the following groups reactive with isocyanates: -OH, -COOH, -SH, NH2 and -NH-; several examples of these are given. Chain transfer agents specified are those of the formula X-C6H4-S-S-C6H4-X where X is -CH2OH, -COOH, -CH2COOH or -NH2. The reaction mixture may optionally include cross-linking agents, e.g. ethylene glycol dimethacrylate or trimethylolpropane, curing agents, e.g. diols, diamines, polyols and polyamines, and terminators, e.g. mono-alcohols or -secondary amines. In the examples, a small amount of pyridine is included in the reaction mixture. |
