Abstract: Block copolymer of the structure A-B wherein:A is a polylactone block of recurring units: ##STR1## wherein PM is a linear polymethylene chain having from 2 to 13 carbon atoms,B is a polyoxymethylene block of recurring units --CH.sub.2 O--. The block copolymer contains at least 2 wt.% of block B and at least 0.1 wt.% of block A.The block copolymer can be used as modified polyacetal when rich in block B, or as special additive for plastics materials when rich in block A.

Abstract: Block copolymer of the structure A-B, wherein: ##STR1## A is a polylactamic block of recurring units: t,0010 WHEREIN PM is a linear polymethylene chain having from 3 to 13 carbon atoms,B is a polyoxymethylene block of recurring units [CH.sub.2 O]. The block copolymer contains at least 2 wt.% of block B and at least 0.05 wt.% of block A.The block copolymer can be used as technopolymer when rich in block B, or in the field of yarns and molded products when rich in block A.

Abstract: A novel block copolymer HO--D--A--B--D--H, whereinA is a polylactonic block of recurring units ##EQU1## B is a polylactamic block of recurring units ##EQU2## C is a polyoxymethylene block of recurring units--CH.sub.2 O--is prepared by catalytic polymerization of at least one lactone ##EQU3## with at least one lactam ##EQU4## wherein: PM.sub.1 and PM.sub.2 are polymethylene linear chains having from 2 to 13 and 3 to 13 carbon atoms, respectively, and being either non-substituted or having at least one hydrogen atom replaced by an alkyl, aryl, alkylaryl or cycloalkyl radical, and reaction of the resulting A-B copolymer with monomeric formaldehyde.The block copolymer HO--D--A--B--D--H having a preponderant percentage in blocks A, B or D, respectively, behaves as a polylactone, polylactam or polyformaldehyde, respectively, having improved properties.

Abstract: A stabilized polymeric composition comprising an acetal polymer and as stabilizer a copolymer R--D--A--B--D--R, in which:A is a block of recurring units: ##EQU1## B is a block of recurring units: ##EQU2## D is a block of recurring units: ##EQU3## R is an ester, ether or urethane group wherein PM.sub.1 and PM.sub.2 are linear polymethylene chains having 2 to 13 and 3 to 13 carbon atoms, respectively, non substituted or having at least one hydrogen atom replaced by an alkyl, aryl, alkylaryl or cycloalkyl radical; the said stabilizer being used in a proportion of from 0.02 to 12 parts by weight to 100 parts by weight an acetal polymer.