Mixed diamine chain extender

A process for preparing a RIM polyurethane molded product, said process comprising the steps of:

• (a) at a temperature of about 15.degree.-100.degree. C., subjecting to static impingement mixing
• (i) an organic polyisocyanate,
• (ii) an organic active hydrogen group-containing compound, and
• (iii) a chain extender mixture comprising a first aromatic diamine having a machine gel time of about 1.0 to 4.0 seconds in a 50,000 psi modulus RIM formulation reaction and a second aromatic diamine having a machine gel time in a 50,000 psi modulus RIM formulation reaction of about 1.5 to about 15 times the machine gel time of said first aromatic diamine, whereby a liquid mixture is produced;
• (b) injecting a shot of said liquid mixture into a closed mold preheated to about 15.degree.-100.degree. C. and forming a polyurethane molded product having rigid, non-brittle green strength and a flexural modulus at 75.degree. F. of at least about 50,000 psi;
• (c) opening the mold and removing the formed polyurethane molded product;
• and
• (d) optionally, postcuring said molded product at 50.degree.-200.degree. C.

A polyurethane RIM process comprising:

• (a) at a temperature of about 15.degree.-100.degree. C. subjecting to static impingement mixing two liquid streams, a first stream comprising
• (i) an organic polyisocyanate or prepolymer or quasi-prepolymer formed from an organic polyisocyanate and an organic active hydrogen group-containing compound;
• and a second stream comprising
• (ii) either (1) an organic polyol having a molecular weight of about 400-7000 combined with a catalyst for reaction between hydroxyl groups and isocyanate groups, or (2) an amine terminated polyether or polyester and
• (iii) a chain extender mixture of a first aromatic diamine selected from 2,2',6,6'-tetraisopropyl-4,4'-methylenebisaniline;
• 1-methyl-3,5-diethyl-2,4-diaminobenzene;
• 1-methyl-3,5-diethyl-2,6-diaminobenzene;
• 1,3,5-triethyl-2,6-diaminobenzene;
• and mixtures thereof;
• and a second chain extender selected from 1-methyl-3,5-dimethylthio-2,4-diaminobenzene;
• 1-methyl-3,5-dimethylthio-2,6-diaminobenzene;
• 2,2'-dichloro-4,4'-methylenebisaniline;
• and mixtures thereof, whereby a liquid mixture is produced, said mixture having a machine gel time in said process of about 2.5 to about 10 seconds;
• (b) injecting a shot of said liquid mixture into a closed mold preheated to about 15.degree.-100.degree. C.;
• (c) opening the mold and removing a molded product having rigid, non-brittle green strength and a flexural modulus at 75.degree. F. of at least about 50,000 psi;
• and
• (d) optionally postcuring said product at 50.degree.-200.degree. C.;
• the amount of said chain extender mixture comprising about 5-40 weight percent of the total weight of components (i), (ii), and (iii) and the ratio of isocyanate groups to combined hydroxyl groups and amino groups being about 0.90 to 1.10.

An isocyanate-reactive resin stream composition comprising:

• (i) an organic active hydrogen group-containing compound having a molecular weight of about 400 to 7000;
• (ii) a first aromatic diamine having a machine gel time of about 1.0 to about 4.0 seconds in a 50,000 psi modulus RIM formulation reaction;
• and
• (iii) a second aromatic diamine having a machine gel time in a 50,000 psi modulus RIM formulation reaction of about 1.5 to about 15 times the machine gel time of said first aromatic diamine,
• wherein the ratio of (a) amino groups from said first aromatic diamine and said second aromatic diamine to (b) active hydrogen groups from said organic active hydrogen group-containing compound is at least about 8:1.