Biobased Aliphatic Polyesters with DOPO Substituents for Enhanced Flame Retardancy

Abstract

Linear aliphatic copolyesters consisting of the biobased diols ethylene glycol, 1,3‐propane diol, and 1,4‐butane diol, the biobased dicarboxylic acids succinic acid, adipic acid, and sebacic acid, and a 9,10‐dihydro‐9‐oxa‐10‐phospha‐phenanthren‐10‐oxide (DOPO)‐containing diol or dicarboxylic acid are presented. Structural characteristics of the new copolyesters are studied by 1H and 13C NMR spectroscopy. The influence of chemical composition on the property profile is examined evaluating glass transition temperature Tg, melting behavior, thermal degradation and combustion, mechanical and burning behavior. Incorporation of DOPO monomers suppresses crystallization and yields materials with reduced toughness except in case of sebacates. Tg rises with the content of DOPO monomer. Correlations between the number of methylene groups in the repeating unit and the thermogravimetric analysis degradation maximum, as well as the heat release capacity from pyrolysis combustion flow calorimeter reflect the systematic influence of chemical structure. Copolycondensation with DOPO monomers enhances the limiting oxygen index providing materials with improved overall value.

Phosphorus‐Containing Polymer Flame Retardants for Aliphatic Polyesters

“…The initial chemical structure of PBT was systematically altered to study the influence of the aliphatic and aromatic monomer fractions in the polyesters. While in our first report aromatic‐aliphatic (co)polyesters with DOPO‐HQ‐GE as diol linked to aliphatic dicarboxylic acids were discussed, here 2‐(6‐oxido‐ 6H ‐dibenzo[ c,e ][1,2]‐oxazaphosphorin‐6‐yl‐dimethyl itaconate (ItaP) was mainly used as phosphorus‐containing monomer. Thus, the DOPO substituent was shifted from the diol to the dicarboxylic acid unit and this monomer replaced the terephthaloyl unit.…”

“…Dimethyl terephathalate (Acros Organics, 99%) was recrystallized twice from ethanol. DOPO‐itaconate was synthesized from dimethyl itaconate and DOPO as previously reported . The preparation of DOPO‐HQ‐GE from DOPO‐hydroquinone was carried out as previously described …”

“…The resulting polyester with terephthaloyl units (polymer from dimethyl terephthalate and DOPO‐HQ‐GE, named in this work P(P‐T)) showed high flame retardancy potential with a balance between gas phase action, condensed phase action, and intumescence, and worked well as a flame retardant in PBT . However, P(P‐T) is not optimal as a FR for aliphatic polyesters because its softening range is too high, due to the T g of 146 °C, and does not match the melting range of aliphatic polyesters . Therefore, a series of new polyesters and copolyesters with the DOPO adduct to dimethylitaconate (2‐(6‐oxido‐ 6H ‐dibenz [ c,e ][1,2] oxaphosphorin‐6‐yl) dimethyl itaconate, ItaP)) was designed and examined.…”

“…Many applications use copolyesters with poly(butylene sebacate) (P(B‐Seb)) segments. PBS and P(B‐Seb) are aliphatic polyesters and owing to their chemical structure they are easily thermally degradable and combustible with high heat release capacity and flammability . For these new materials, the development of effective, halogen‐free flame retardants (FRs) according to the European regulations WEEE 2012/19/EU (Waste of Electrical and Electronic Equipment) and REACH is still a challenging and continuing task .…”

“…Therefore, a series of new polyesters and copolyesters with the DOPO adduct to dimethylitaconate (2‐(6‐oxido‐ 6H ‐dibenz [ c,e ][1,2] oxaphosphorin‐6‐yl) dimethyl itaconate, ItaP)) was designed and examined. The synthesis of ItaP was adapted from a previously reported procedure …”