A copolymer molecule comprised of a main backbone chain to which side chains containing different atomic constituents are attached at various points. The main chain may be either a homopolymer or a copolymer. This process may be applied to the union of cellulosic molecules (cotton, rayon) with synthetic polymers (except polyesters, acrylics, and polypropylene) to form modified fibers having improved flame-resistance, dimensional stability, resilience, and bacterial resistance. An intermediate called cellulose thiocarbonate is formed in this proprietary process.