METHOD FOR THE PREPARATION OF BLOCK COPOLYMERS BY MEANS OF QUASI LIVING RADICAL POLYMERIZATION BASED ON NOVEL CHAIN TRANSFER AGENTS

The present invention describes a method for the preparation of block copolymers by means of transference agents of the ditiadiphosphetane disulphites type. The said method is based on the use of free radicals originated from common initiators such as azocompunds or peroxides, and transfer agents that do not provide neither odour nor colour to products. The method consists of two stages: At the first stage, a monomer or a monomer mixture is polymerized in the presence of a small amount of the transfer agent, which is typically lower than 0.5% by weight. During said process the polymer molecular weight increases with the conversion, thereby a transfer agent fragment remains with the polymer. When the conversion presents an adequate value, being lower or equal to 100%, the monomers that form a second block are added. During the aforementioned stage the formed and functionalized chains by means of the transfer agent increase the size thereof by the block segment chain. Variations to the aforesaid method include but do not limit the addition of an initiator and/or transfer agent during the polymerization, the isolation of the polymer formed during the first stage, the use of multifunctional initiators as well as the aqueous or solvent medium polymerization. Esta invencion describe el metodo de preparacion de copolimeros en bloques mediante el uso de agentes de transferencia de tipo ditiadifosfetanos disulfitos. Este metodo esta basado en el uso de radicales libres provenientes de iniciadores comunes tales como azocompuestos o peroxidos y de agentes de transferencia que no imparte ni color ni olor a los productos. El metodo consiste en dos etapas; primero, se polimeriza un monomero o una mezcla de monomeros en presencia de una pequena cantidad del agente de transferencia, tipicamente menor al 0.5% en peso. Durante este proceso el peso molecular del polimero incrementa con la conversion y un fragmento del agente de transferencia queda enlazado al polimero. Cuando la conversion llega a un valor apropiado menor o igual al 100%, se agrega el o los monomeros que formaran el segundo bloque. En esta etapa, las cadenas inicialmente formadas y funcionalizadas por el agente de transferencia aumentan su tamano por el encadenamiento del segmento bloque. Variaciones a este metodo incluyen pero no limitan, la adicion de iniciador y/o agente de transferencia durante la polimerizacion, aislamiento del prepolimero formado en la primera etapa, uso de iniciadores multifuncionales