NOVELTY - Substituted 3,4-propylenedioxythiophene monomer (I), is new.    USE - (I) is useful for preparing polymers (claimed), which are useful in electrochromic devices, photovoltaic devices, batteries, diodes, capacitors and organic and inorganic electroluminescent devices, electromagnetic shielding layers, heat shielding layers, antistatic coatings for a variety of products (including photographic film, thermographic recording materials and photothermographic recording materials), smart windows, sensors for organic and bio-organic materials (e.g. chemical sensors), FETs, printing plates, conductive resin adhesives, solar cells, photochemical resists, nonlinear optic devices and free-standing electrically conductive films.    ADVANTAGE - (I) provides polymers that exhibit: high electrical conductivity; low absorption of visible light and high absorption to infrared radiation; and heat shielding.    DETAILED DESCRIPTION - Substituted 3,4-propylenedioxythiophene monomer of formula (ProDOT-((CH2)3-S-R1)a) (I), is new.    ProDOT = 3,4-propylenedioxythiophenyl;    R1 = hydrocarbyl (optionally containing at least one heteroatom-containing functional groups, including silanes, ether, sulfonic acid and its salts and esters, thiol, hydroxy, amines and their salts, amides, ketone, nitrile and carboxylic acid and its salts and esters); and    a = 1 or 2.    INDEPENDENT CLAIMS are also included for:    (1) a crosslinker of formula ((ProDOT-(CH2)3-S-)b-Z) (II);    (2) preparing (I);    (3) preparing the crosslinker, comprising contacting 3-allyl-3,4-dihydro-2H-thieno(3,4-b)(1,4)dioxepine with a compound having at least two thiol groups under radical addition conditions;    (4) a polymer (P1) prepared by polymerizing (I);    (5) a polymer (P2) prepared by polymerizing the crosslinker;    (6) making the polymer (P1), comprising polymerizing the monomer; and    (7) making the polymer (P2), comprising polymerizing the crosslinker.    b = at least two; and    Z = a polyvalent organic moiety.