Journal of Macromolecular Science, Part A: Pureand Applied Chemistry (2011) 48, 1055–1060 Copyright C  Taylor & Francis Group, LLC ISSN: 1060-1325 print / 1520-5738 online DOI: 10.1080/10601325.2011.620455 Crosslinking of Biocatalytically Synthesized Organosilicone Copolymers for Flame Retardant Applications VIJAYENDRA KUMAR 1,2 , BHAVNA GUPTA 1,3 , ABDULLAH KHAN 4 , RAVI MOSURKAL 5 , SUNIL K. SHARMA 1,3,4 , VIRINDER S. PARMAR 1,3,4 , JAYANT KUMAR 1,3 , LYNNE A. SAMUELSON 5 , KRISHNA KUMAR 2 , and ARTHUR C. WATTERSON 1,3∗ 1 Institute of Nano-science and Engineering Technology, Department of Chemistry, University of Massachusetts Lowell, Lowell, MA 2 Howard University, School of Pharmacy, Washington, DC 3 Center for Advanced Materials, University of Massachusetts Lowell, Lowell, MA 4 Bio-organic Laboratory, Department of Chemistry, University of Delhi, Delhi, India 5 U.S. Army Natick Soldier Research Development and Engineering Center, Natick, MA Crosslinking of polymers using crosslinking agents has been widely utilized to further improve the mechanical and thermal prop- erties of the polymers. We have explored various aliphatic and aromatic dicarboxylic acids such as malonic acid, glutaric acid, isophthalic acid, terephthalic acid and terephthaloyl chloride as crosslinking agents to crosslink polydimethylsiloxane copolymer [poly{poly(dimethylsiloxane-1000)-propylamine-5-aminoisophthaloyl}] to improve its flame retardant properties. We have also used nanoclays [Cloisite 20A, 2C 18 MMT (dimethylditallowammonium-/ dimethyldioctadecylammonium-modified montmorillonite)] along with the crosslinker during crosslinking process to further reduce the flammability of the crosslinked polymers. Among all the crosslinkers investigated, isophthalic acid with the nanoclay was found to have the best performance for flame retardant applications. The present work provides a basis to further improve the performance of silicone-based polymers for the flame retardant applications. Keywords: Novozyme-435, Candida antarctica Lipase B, organosilicone co-polymers, flame retardant polymers, crosslinked polymers, nanoclay, thermogravimetric analysis (TGA), pyrolysis-combustion flow calorimetry (PCFC) 1 Introduction Polycarbosiloxanes have been attracting attention as potential substitutes for conventional flame retardant materials owing to their exceptional thermal and flame re- tardant properties (1–4). The combustion products of these polymers are non-toxic cyclic siloxanes as well as branched siloxane structures (5). However, the existing brominated fire retardants (BFRs) and chlorinated fire retar dants (CFRs) have already been restricted because of their persis tence in the environment and/or their toxic health effects (6). Polycholorinated biphenyls (PCBs) previously used as chlorinated flame-retardants, were banned in 1977. EU has banned several types of brominated flame retardants as of 2008. The objectives of flame retardant polymers are twofold; first, to increase ignition resistance and second, to ∗ Address correspondence to: Arthur C. Watterson, Insti- tute of Nano-science and Engineering Technology, Depart- ment of Chemistry, University of Massachusetts Lowell, Low- ell, MA, 01854 and Center for Advanced Materials, Uni- versity of Massachusetts Lowell, Lowell, MA 01854. E-mail: arthur watterson@uml.edu reduce the rate of flame spread. To meet these stipulations, additives, which interfere in various ways with the chemical exothermic chain of combustion have been used. It is anticipated that small amounts of well-dispersed natural clay can lead to environmentally friendly and inex- pensive plastic composites with improved specialized prop- erties (7). When polymers with clay incorporated in their structures burn, the clay forms a char layer on the outside of the polymeric material that insulates the material be- neath. The polymer clay blends (nanocomposites) do not alter the normal production and processing of the clayless polymer. The addition of clay can make polymers less per- meable to liquids and gases; enhance flame retardancy and make them tougher. The natural clays such as bentonites and montmorillonites are already in use in paints to prevent dripping and in cosmetics to prevent shine. Further, there is no problem in incorporating them into polymeric mate- rials that come in contact with foods, medicines, beverages or plastics used in biomedical devices, since the U.S. Food and Drug Administration has already approved them for use. We have established the synthesis of organic-inorganic hybrid polydimethylsiloxane copolymers under mild