Novel Co-Modified Organopolysiloxane, And Treatment Agent And External Use Preparation Comprising The Same

A co-modified organopolysiloxane having a viscosity at 25° C. of not more than 1,500 mPa·s, a group that has a siloxane dendron structure, a hydrophilic group, and expressed by the following general formula (1):

• R1aR2bL1cQdSiO(4-a-b-c-d)/2 (1)
• wherein,
• R1 is a substituted or unsubstituted monovalent hydrocarbon group having from 1 to 30 carbons, or a hydrogen atom;
• R2 is a substituted or unsubstituted straight or branched monovalent hydrocarbon group having from 6 to 30 carbons;
• L1 is a silylalkyl group having a siloxane dendron structure expressed by the following general formula (2) when i=1;
• and Q is a hydrophilic segment, wherein General Formula (2) is represented by:
• wherein, R1 is as defined above, RC is an alkyl group having 1 to 6 carbons or a phenyl group, and Z is a divalent organic group;
• i represents a generation of the silylalkyl group represented by Li, and is an integer of 1 to c when c is a number of generations that is a number of repetitions of the silylalkyl group;
• the number of generations c is an integer from 1 to 10, and Li+1 is the silylalkyl group when i is less than c and is a methyl group or a phenyl group when i=c;
• and ai is a number in a range of 0 to 3;
• and a, b, c, and d are numbers in ranges so that 1.0≦a+b≦2.5, 0.001≦c≦1.5, and 0.001≦d≦1.5.