Stabilisers polymer-bound

It has been observed that complete immobilisation of the stabiliser through a graft leads to deactivation. However, proper selection of the ratio of phenolic to graftable groups leads to a polymer-bound product which retains sufficient mobility to provide a high level of antioxidant activity. An n/m ratio of 5-10 provides an optimal balance of graftability and antioxidant activity [144]. 

Kim el al. [582] have described maleimide-based antioxidants melt grafted onto low-MW PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Smedberg el al. [583] have characterised polymer-bound stabilisers by FTIR and NMR. The binding of antioxidants and photostabilisers to polyurethanes was verified by tJV/VIS spectroscopy [584]. 

Great Lakes has reported that functionalisation with graftable moieties results in a product which can be chemically bound to a polysiloxane backbone, e.g. Silanox MD. Functionalisation of polysiloxanes with HALS (polymer-bound HALS, P-HALS) and phenolic antioxidants has been described [22]. Functionalised polysiloxanes (Figure 3.23) exhibit high stabilisation activity in critical applications such as PP fibres and PE cables [58]. 

It is noticeable that cross-metathesis with the unfunctionalised alkenes occurred in significantly higher yields over shorter reaction times and required a smaller excess of the soluble alkene. This was possibly due to the unfunctionalised alkenes, which are more nucleophilic than their ester containing counterparts, complementing the less nucleophilic/more carbon-metal bond stabilising allylglycinol 18. Comparable results were obtained from cross-metathesis reactions of the polymer-bound isomeric N-Boc C-allylglycinol with the same four alkenes. 

The mechanistic behaviour of absorbers based on 2-hydroxybenzo-phenone, 2-hydroxyphenylbenzotriazole and salicylates continues to attract much interest. Salicyloyl(3 5-di-tert-butyl-4-hydroxy-benzyDamine is claimed to be the most effective light stabiliser to date for polyethylenewhile effective polymer bound stabilisers based on 2-(2-hydroxyphenyl)-2H-benzotriazole have been made... 

Vogl, O. Albertsson, A.C. Janovic, Z. Polymerizable, polymeric, polymer-bound (ultraviolet) stabilizers. In Polymer Stabilisation and Degradation Klemchuk, P., Ed. ACS... 

It has been stated numerous times that polymer-bound reactive intermediates are more stable than the corresponding solubilised counterparts. The stabilisation forces exerted by the polymeric matrix are most probably due to hydrophobic clustering. Polymer-bound peracids are believed to be more stable and not explosive. - The hydrophobic nature of polystyrene resins in combination with the high dilution effect has been used successfully several times to accelerate intramolecular cyclisations by grafting molecules onto a solid support as shown in Chapter 7.6.2>>22... 

ESR studies of free radicals formed under UV-irradiation were reported for hindered piperidine photostabilisers and antioxidants [820]. Kelen et al. [819] reported an ESR study of hindered piperidine derivatives in a chalk filled PP matrix in the presence of other additives (frganox 1010, Tmuvin 770/622), with particular emphasis on concentration changes of Ai-oxyl radicals and interaction between a HALS compound and a hindered phenol. Other additives present in the polymer influence the concentration of the /V-oxyl radicals. Lattimer et al. [821] studied oxidation of the partially hindered bicyclic amine 3,3-dialkyldecahydroquinoxalin-2-ones (excellent UV stabiliser and thermal antioxidant) with w-chloroperbenzoic acid by means of ESR and reported some extremely stable radical derivatives (over 231 days of stability). ESR was also used to measure the piperidinoxyl radical concentration, and hence the HALS content in LDPE/(Chimassorb 944, Tmuvin 622) agricultural film during use. Evidence was reported for polymer-bound radicals [117]. 

Laser-induced fluorescence data provide a wide variety of detailed information about physical and chemical reactions. Laser-based time-resolved (picosecond) fluorescence spectroscopic techniques have been used to investigate the mechanism of photo-stabilisation by UVAs such as benzophenones, ben-zotriazoles and polymer-bound UV stabilisers [117]. Such ultrafast spectroscopic measurements can provide insight into the dynamics of the primary energy dissipation processes in polymers and polymer additives following light absorption. Excimer LIF spectra of plasticised PVC showed two distinct regions... 

As already shown, it is technically possible to incorporate additive functional groups within the structure of a polymer itself, thus dispensing with easily extractable small-molecular additives. However, the various attempts of incorporation of additive functionalities into the polymer chain, by copolymerisation or free radical initiated grafting, have not yet led to widespread practical use, mainly for economical reasons. Many macromolecular stabiliser-functionalised systems and reactive stabiliser-functionalised monomers have been described (cf. ref. [576]). Examples are bound-in chromophores, e.g. the benzotriazole moiety incorporated into polymers [577,578], but also copolymerisation with special monomers containing an inhibitor structural unit, leading to the incorporation of the antioxidant into the polymer chain. Copolymers of styrene and benzophenone-type UV stabilisers have been described [579]. Chemical combination of an antioxidant with the polymer leads to a high degree of resistance to (oil) extraction. 

Fig. 2). On the other hand Y groups remain firmly bound, and this is explained in terms of a stabilising mechanism involving substitution of Y groups for labile chlorine atoms while the organo tin compound is complexed with the polymer molecules (Reaction 10). 

The first step Is to ensure that the macromolecules are bound to the surfaces. For this purpose they can be grafted chemically however this Is an expensive process, requiring the use of reactive polymers or tailor made surface active species such as block copolymers. A less expensive method Is to use macromolecules which spontaneously adsorb to the surfaces. Then experimental wisdom states that surfaces which are each completely saturated with macromolecules will repel each other (stabilisation of the suspension), while surfaces which are unsaturated will attract each other because the macromolecules will bridge them together (flocculation) (1). 

Lu et al. have reported that the fluorescence intensities of Eu3+ and Tb3+ are markedly enhanced when they are bound on to a poly(acrylamide-acrylic acid copolymer). Dhake et al. have observed interesting differential effects of pressure on the fluorescence of a polymer and the corresponding monomer. Sterically hindered piperidines have for long been of interest as efficient photostabilisers of polymers. Gugumus has now reported that these stabilisers form charge-transfer complexes with molecular oxygen, thereby preventing the formation of such complexes with the polymer. 

Martinek, K., A. M. Klibanov, V. S. Goldmacher, and 1. V. Berezin. 1977. The Principles of Enzyme Stabilisation. 1. Increase in Thermostability of Enzymes Covalently Bound to a Complementary Surface of a Polymer Support in a Multi-Point Fashion. Biochim Biophys Acta 485 1-12. 

---