Solution polymerization of high molecular weight poly(phosphoesters) in toluene

A process for preparing a high molecular weight poly(phosphoester) composition comprising.

• (i) a biologically active substance;
• and
• (ii) a poly(phosphoester) with the recurring monomeric units of formula I:
• ##STR13## wherein:
• X is --O-- or --NR"--, where R" is H or alkyl;
• L is a divalent organic moiety, with the proviso that L cannot have the formula ##STR14## R' is H, alkyl, alkoxy, aryl, aryloxy, heterocyclic, or heterocycloxy;
• and n is from about 25 to 2000,
• said process comprising the steps of:
• (a) substantially dissolving p moles of a di--XH compound having formula II:
• II H--X--L--X--H
• in a solvent comprising at least 75% toluene by volume at a first temperature between about -75.degree. C. and +60.degree. C. to form a reaction mixture;
• (b) while maintaining the reaction mixture at the first temperature, adding q moles, where p.apprxeq.q, of a phosphorodihalo compound of formula III:
• ##STR15## wherein R' is defined as above and "halo" is Br, Cl or I;
• (c) gradually increasing said first temperature at a rate of less than about 1.5.degree. C. per minute as necessary to achieve a second temperature between about 0.degree. C. and 150.degree. C., and mixing the reaction mixture at the second temperature to form the polymer of formula I;
• (d) isolating the polymer of formula I;
• and
• (e) incorporating the biologically active substance into the polymer of formula I.