Strength resins for paper

A process for preparing a papermaking wet-end strength resin polymer that is stable in an alkaline environment and that hydrolyzes upon acidification to form free aldehydic functionality comprising:

• admixing a water soluble polymer having acrylamide mer units with an acetal-aldehyde of the formula ##STR6## in a aqueous solution or the aqueous phase of a water-in-oil emulsion having a pH of from about 8 to about 12.5 to form acetal-containing polymer of the structural formula
• (A).sub.a (X).sub.b (Y).sub.c
• wherein A is an acetal-containing mer unit, X is a cationic mer unit, and
• Y is acrylamide,
• "a" is the mole percentage of A in said polymer and is a value of from about 1 to about 100, "b" is the mole percentage of X in said polymer and is a value of from about 0 to about 50, and "c" is the mole percentage of Y in said polymer and is a value of from about 0 to about 90 wherein said acetal-containing mer unit has the structural formula of ##STR7## wherein:
• R.sub.1 is hydrogen, methyl or ethyl;
• R.sub.2 is hydrogen, methyl, or ethyl;
• and R.sub.3 and R.sub.4 are, in each of said Formulas, either each independently an alkyl having from 1 to about 5 carbons or together contain from about 2 to about 10 carbons and form a cyclic acetal together with the --O--CH--O group

A process for preparing a papermaking wet-end strength resin polymer that is stable in an alkaline environment and that hydrolyzes to form pendent aldehydic functionality upon acidification comprising:

• admixing in an aqueous solution acrylamide with an acetalaldehyde of the formula:
• ##STR8## at a pH of from about 8 to about 12.5 to form a modified acrylamide acetal-containing mer unit;
• and
• then polymerizing said modified acrylamide acetal-containing mer unit with a cationic monomer to form a water soluble polymer of the structural formula
• (A).sub.a (X).sub.b (Y).sub.c
• wherein A is an acetal-containing mer unit, X is a cationic mer unit, and Y is acrylamide,
• "a" is the mole percentage of A in said polymer and is a value of from about 1 to about 100, "b" is the mole percentage of X in said polymer and is a value of from about 0 to about 50, and "c" is the mole percentage of Y in said polymer and is a value of from about 0 to about 90,
• wherein said acetal-containing mer unit has the structural formula of ##STR9## wherein:
• R.sub.1 is hydrogen, methyl or ethyl;
• R.sub.2 is hydrogen, methyl, or ethyl;
• and R.sub.3 and R.sub.4 are, in each of said Formulas, either each independently an alkyl having from 1 to about 5 carbons or together contain from about 2 to about 10 carbon and form a cyclic acetal together with the --O--CH--O group.

A papermaking wet-end strength resin polymer that is stable in an alkaline environment and that hydrolyzes upon acidification to form pendent aldehyde groups characterized by mer units having the structural formula of:

• ##STR10## wherein R.sub.1 is hydrogen, methyl or ethyl;
• R.sub.2 is hydrogen, methyl, or ethyl;
• and R.sub.3 and R.sub.4 are either each independently an alkyl having from 1 to about 5 carbons or together contain from about 2 to about 10 carbons and form a cyclic acetal together with the --O--CH--O--group.
• wherein said water soluble polymer has the structural formula of
• (A).sub.a (X).sub.b (Y).sub.c
• wherein A is a mer unit of said Formula I, X is an ionic mer unit, and Y is a mer unit other than A or X,
• "a" is the mole percentage of A in said polymer and is a value of from about 15 to about 60, "b" is the mole percentage of X in said polymer and is a value of from about 0 to about 50, and "c" is the mole percentage of Y in said polymer and is a value of from about 1 to about 80.