pH SENSITIVE QUANTUM DOTS FOR USE AS CURE INDICATORS

A method for determining a sufficient cure state of a composition, which method comprises:

• (i) combining (a) at least one selected from the group consisting of a thiol-terminated prepolymer and a monomer thereof, (b) an “ene” crosslinker (c) a pH indicator molecule comprising a quantum dot functionalized with a pH-responsive ligand, and (d) a photosensitizer;
• and
• (ii) subjecting a resultant mixture of (i) to a curing condition until the resultant mixture changes its color,
• (iii) comparing the change in color of the resultant mixture to a reference standard, wherein a sufficient cure state of the composition is indicated when the color of the resultant mixture is the same as the color of the reference standard, and
• wherein the “ene” crosslinker has a molecular weight of about 100 to about 5000 and wherein the thiol-terminated prepolymer is a polythioether having the following formula (I):
• HS—R1—[—S—(CH2)p—O—(H—R2O—)m—(CH2)qS—R1—]n—SH (I)
• wherein R1 is selected from the group consisting of C2-10 n-alkylene, C2-6 branched alkylene, C6-8 cycloalkylene, C6-10 alkylcycloalkylene, —[(—CH2)p—X]q—(—CH2)r—, and —[(—CH2)p—X]q(—CH2)r— in which at least one —CH2— unit is substituted with a methyl group;
• and R2 is a C2-10 n-alkylene;
• C2-6 branched alkylene, C6-8 cycloalkylene, C6-10 alkylcycloalkylene, and —[(—CH2)p—X]q—(—CH2)r—,
• X is selected from the group consisting of O, S and —NR6—;
• R6 is selected from the group consisting of H and methyl;
• m is independently selected from a value ranging from 1 to 50;
• n is independently selected from a value ranging from 1 to 60;
• p is independently selected from a value ranging from 2 to 6;
• q is independently selected from a value ranging from 1 to 5;
• and
• r is independently selected from a value ranging from 2 to 10.

A method for determining a sufficient cure state of a composition, which method comprises:

• (i) combining (a) at least one selected from the group consisting of a thiol-terminated prepolymer and a monomer thereof, (b) an “ene” crosslinker (c) a pH indicator molecule comprising a quantum dot functionalized with a pH-responsive ligand, and (d) a photosensitizer;
• and
• (ii) subjecting a resultant mixture of (i) to a curing condition until the resultant mixture changes its color,
• (iii) comparing the change in color of the resultant mixture to a reference standard, wherein a sufficient cure state of the composition is indicated when the color of the resultant mixture is the same as the color of the reference standard, and
• wherein the “ene” crosslinker has a molecular weight of about 100 to about 5000 and wherein the thiol-terminated prepolymer is a polysulfide having the following formula:
• HSCH2CH2OCH2OCH2CH2S[SCH2CH2OCH2OCH2CH2S]m[—SCH2CH(SH)CH2S—]nSCH2CH2OCH2O—CH2CH2SH
• wherein m is from about 5 to about 50, n is from 0 to about 1, and n/m is from about 0.002 to about 0.02, when greater than 0.