AbstractPoly(Lys(HBr)‐Gly‐Pro‐Pro‐Gly‐Pro) has been synthesized and studied by circular dichroism (CD) spectroscopy. It is apparently the first polyhexapeptide collagen model reported with an ionizable side chain. The monomer (ε‐(p‐nitrobenzyloxycarbonyl)‐Lys‐Gly‐Pro‐Pro‐Gly‐Pro‐p‐nitrophenyl‐ester) was prepared by a stepwise strategy employing active esters. Polymerization in N,N‐dimethyl formamide, followed by removal of the Lys side chain protection with HBr/acetic acid, gave a polydisperse product. Fractionation was accomplished by gel filtration chromatography. The polydisperse material had a molecular weight (Mr = 5–17,000). High molecular weight fractions from triple helices under concentrated conditions at 2°C. The triple helical structure gives a CD pattern very similar to that of collagen and its triple helical analogs. However, unlike collagen, the polyhexapeptide undergoes spontaneous dissociation at temperatures substantially below the melting temperature from a triple helical form to single chains. This process is promoted at low concentrations, high temperature, neutral pH, and low molecular weight, and is apparently due, in large part, to unfavorable ionic side‐chain interactions. In addition to this relatively slow “ionic” dissociation the triple helical polypeptide may be thermally dissociated in a manner similar to collagen. The thermal denaturation is a relatively fast process compared with ionic dissociation.A high molecular weight fraction (3 × Mr = 48,000) was found to melt at 42°C at neutral pH but increased to 54°C at pH 12 where the lysyl side chains are predominantly deprotonated. Furthermore, reconstitution of triple helices appeared to be more readily achieved at high pH. Thus it is concluded that ionic repulsion between side chains causes destabilization of the triple helix and hinders reconstitution.