Abstract
The DOPO-based flame-retardant additives DOPO-HQ, DOPO-AP and DOPO-Van were synthesized in varying numbers of phenolic hydroxyl groups and amine groups. Moreover, their influence on the polymerization of a bisphenol F-based benzoxazine, as well as the thermal properties of the resulting materials, were studied. All DOPO-based derivatives influenced the polymerization temperature onset with a reduction of up to 20 °C, while thermo-mechanical properties remained high. Surprisingly, phosphorous content below 0.4 wt% significantly improved the reaction against small flames yielding an increase in the limited oxygen index by 2% and a V-0 rating in the UL-94 test. DOPO-HQ proved to be the most effective additive regarding the reaction against small flames at an astonishingly low phosphorous concentration of below 0.1 wt%, whereas DOPO-AP and DOPO-Van simultaneously lowered the polymerization temperature.
Highlights
Polybenzoxazines represent a phenolic-type thermoset, and exhibit excellent properties such as mechanical performance, chemical stability, low water absorption [1], a near zero volume shrinkage [2], and polymerize by-product free [3]
The amine attacks the benzoxazine, yielding a zwitter-ionic product that decomposes to an iminium ion that reacts in an electrophilic substitution reaction with the aromatic ring [14,15]
ring-opening polymerization (ROP) polymerization of BF-a in the presence of different concentrations of the DOPObased additives DOPO-HQ, DOPO-Van and DOPO-AP was studied by DSC experiments (Figure 2a)
Summary
Polybenzoxazines (pBz) represent a phenolic-type thermoset, and exhibit excellent properties such as mechanical performance, chemical stability, low water absorption [1], a near zero volume shrinkage [2], and polymerize by-product free [3]. Benzoxazine monomers have been polymerized in the presence of additives such as nitrogen [28,29], silicon [30], and organophosphorous-based additives [27,31], that improved flame retardancy and reduced the polymerization onset simultaneously Most of these reduced the glass transition temperature (Tg), and affected the thermo-mechanical properties. In the current state of our knowledge, a systematic study of DOPO as an FR functional group differing in type and number of reactive groups affecting benzoxazine polymerization is missing far This contribution aims at investigating the influence of additives combining both hydroxyl and amine groups by lowering the polymerization temperature and DOPO moieties providing lower flammability. AssmyssaytlselTtTmflehmhaoamosatseiteceiscaiadanindndvdvdieteisittvshtiitevegisgreamaswttioiwoeo-rnmneeroeomecffhimtxtahhneieexdicieimaidmnl pppilnaroaocwclpttoeoocwrnontinecttchsohe.enenWcptperiotaonhltltyiyrtommhanitesseiorrawiinpzzisapatthtrwiioooBainntcFhh-ooa,nBnlsomFsewe-otat,n,crmrooeenmaoaccnceettrinoiotomanrniametaairgoignaanagiisnimnoasittsfnt gsmatalal hflaalomgeesn-afrnede atnhderremacot-imviteyc-henahnaicnaclinpgraodpdeirtitvieess.coWuiltdhretphriesseanptparsouascthai,nlaobwle acpopnrcoeanchtrbaytions of shaavlionggerne-sforuereceasnadndreeancetirvgiytyd-uerninhganpcoilnygbeandzdoxitaizviensecmoaunldufarectpurreisnegnatnad saupsptlaicinataibonle. approach by saving resources and energy during polybenzoxazine manufacturing and application
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