Homopolymerisation

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 4). The alkylene oxide polymerisation is usually initiated by alkah hydroxides, especially potassium hydroxide. In the base-catalysed polymerisation of propylene oxide, some rearrangement occurs to give aHyl alcohol. Further reaction of aHyl alcohol with propylene oxide produces a monofunctional alcohol. Therefore, polyether polyols derived from propylene oxide are not truly diftmctional. By using sine hexacyano cobaltate as catalyst, a more diftmctional polyol is obtained (20). Olin has introduced the diftmctional polyether polyols under the trade name POLY-L. Trichlorobutylene oxide-derived polyether polyols are useful as reactive fire retardants. Poly(tetramethylene glycol) (PTMG) is produced in the acid-catalysed homopolymerisation of tetrahydrofuran. Copolymers derived from tetrahydrofuran and ethylene oxide are also produced. 

The mutual polymerisation of two or more monomers is called copolymerisation. This topic has been comprehensively reviewed (4,5). Monomers frequentiy show a different reactivity toward copolymerisation than toward homopolymerisation. In fact, some monomers that can be bomopolymerised only with great difficulty, can be readily copolymerised. One such monomer is maleic anhydride. It is rather inert to free-radical homopolymerisation yet can be copolymerised convenientiy with styrene and many other monomers under free-radical conditions. 

Another technical development is that of high impact isotactic polypropylene in which rubber droplets are produced in situ during the polymerisation stage. After propylene homopolymerisation ethylene is added to the reacting mass in a... 

Substituted and unsubstituted bi- or multi-cyclic mono-, di- or multi-olefins, i.e. containing condensed rings at least one of which contains a double bond. Norbomene is homopolymerised commercially whilst, as previously mentioned, ethylidenenorbomene and dicyclopentadiene are used as the cure site monomer in EPDM rubbers. 

The second approach is typified by maleic anhydride. This material does not homopolymerise but will polymerise with styrene or styrene and acrylonitirle, in the latter case to give terpolymers with Tg above 122°C. 

Chain reactions carried out on one type of monomer give rise to homopolymers when using two types of monomer the situation is more complicated. For example, polymerising mixtures of vinyl chloride with acrylate esters gives rise to a range of molecules, the first of which are relatively rich in acrylate molecules formed later, when the amount of acrylate monomer is relatively depleted, are richer in vinyl chloride. In a number of instances, reactions of this kind can be used to prepare polymers containing monomers which will not homopolymerise, e.g. maleic anhydride and stil-bene (vinylbenzene). 

Whatever the approach, the result is a difficult-to-analyse system. Such options suit polymer producers better than additive suppliers. Aromatic polymers (PPO) have been mentioned as char-forming FRs. Polymeric UV absorbers, blended in proper proportions with commercial plastics, have potential use as stabilisers for fibres, films and coatings. Several monomeric stabilisers containing a vinyl group were homopolymerised and used as stabilisers for PE, PVC, acrylates, polystyrene, cellulose acetate and several vinyl polymers [55]. 

Methyl vinyl ether is rapidly hydrolysed by contact with dilute acids to form acetaldehyde, which is more reactive and has wider flammability limits than the ether [1], Presence of base is essential during storage or distillation of the ether to prevent rapid acid-catalysed homopolymerisation, which is not prevented by antioxidants. Even mildly acidic solids (calcium chloride or some ceramics) will initiate exothermic polymerisation [2],... 

Hence the presence of acid and DVB not only increase grafting yields, they also enhance competing homopolymerisation, however the former reaction is preferentially affected to the benefit of the overall process. 

Homopolymerisation which accompanies copolymerisation increases at higher styrene concentrations, thus the grafting efficiency decreases with increasing styrene concentration (Table V). These results are similar to analogous data for polypropylene (5, 6). Inclusion of mineral acid increases homopolymerisation, however not to the same degree as it enhances copolymerisation, thus, overall, grafting efficiency is significantly improved in the presence of acid. 

Kruus [76] investigated the homopolymerisation of methyl methacrylate (MMA) at different temperatures and different acoustic intensities in the absence of solvent (i. e. bulk polymerisation), polymer and initiator. The work showed that although intense ultrasound could be used to initiate polymersiation, the yields were too small (< 4% per hour) to suggest that the technique could provide a commercial alternative to the conventional methods (Fig. 5.36). 

Akbulut has also reported the effect of ultrasound upon the electronitiated homopolymerisation of butadiene sulfone (Fig. 6.21) in MeCN/Bu4NBF4 using platinum electrodes [84]. Interestingly ultrasound did not completely clear the electrode of a polymer film, although it did produce an improvement in the percentage conversion versus time characteristics of the polymerisation. 

Monomer 1 = MMA and monomer 2 = TBTM kll = homopolymerisation constant for monomer 1 k22 = homopolymerisation constant for monomer 2 kl2 and k21 are the cross propagation constants ktl2 an average termination constant... 

Die hdheren Cycloolefine mit fiinf und mehr Kohlenstoffatomen im Ring sind einer koordinativen Homopolymerisation nicht zuganglich, sie lassen sicli aber mit Athylen copolymerisieren, und es konnen kristal-... 

Via DSC measurements it was shown that the new bis(vinylbenzyl)ethers can undergo a homopolymerization and a copolymerisation with BMI. In a BMI/-divinylbenzylether blend the Diels-Alder copolymerization is favoured over the divinylbenzylether homopolymerisation. The Tgs of the new copolymers are well in excess of 270 °C when the BMI/divinylbenzylether molar ratio is 1 1 (Table 9). Isothermal weight loss studies over a period of 4000 hours indicate that the BMI-MDA/divinylbenzylether copolymer is the most stable system of this family. 

J.-F. Lahitte, F. Pelascini, F. Peruch, S.P. Meneghetti, and P.J. Lutz, Transition metal-based homopolymerisation of macromonomers, Compt. Rendus Chem., 5(4) 225-234, April 2002. 

The homopolymerisation of o-divinylbenzene is complicated by the possibility of intramolecular cyclisation occuring as well as direct propagation e.g. 

Saegusa has investigated the cationic homopolymerisation of the six cyclic imino ethers shown below using methyl iodide and methyl p-toluenesulphonate as initiators. 

A great variety of aromatic diamines and aliphatic di- and poly-amines are used as epoxy resin curing agents, and tert-amines can act as catalysts for anionic epoxide homopolymerisation. 

In practice the amine curing reactions are often accelerated by the addition of Lewis acids, especially amine complexes of boron trifluoride. Such materials can also initiate epoxide homopolymerisation in which chain propagation occurs through a carbocation ... 

An analogous homopolymerisation can be initiated by strong bases, including for example tert-amines. In this case chain propagation probably proceeds through an oxyanion ... 

It was suggested that the dimethylamine would react with epoxide and that the resulting tert-amine would catalyse epoxide homopolymerisation. LaLiberte et al. 63) found that Monuron or Diuron could react with epoxide to form an oxazolidone and dimethylamine ... 

Another aspect that has not been taken into account in the kinetic models discussed so far is the occurrence of ether-forming reaction through epoxide homopolymerisation or reaction with hydroxyl groups. In the system TGDDM with an initial DDM concentration less than the stoichiometric level the overall conversion of epoxide is greater than that expected for epoxide-amine addition 89, 97 98). 

In practice the epoxide-amine cure is often accelerated by the addition of catalysts such as boron trifluoride complexes, and the boron trifluoride-ethylamine adduct (BFE) is widely used for this purpose. In addition to catalysing the epoxide-amine reactions, BFE can initiate homopolymerisation of epoxide. The accelerating effect of BFE is illustrated by DSC scans for the TGDDM/DDS/BFE system in Figure 12. The multiple-peaked exotherm associated with the BFE-catalysed TGDDM/DDS cure indicates that the kinetics of this system are more complex than those for the cure with amine alone. For this system the overall heat of reaction was found to decrease with increasing BFE concentration 89). For DDS alone Q0 was about 110 kJ per mole epoxide while the value for BFE alone was 75 kJ/mole, and the DDS/BFE values were between these limits. It appears that the proportion of epoxide homo-polymerisation relative to amine or hydroxyl addition increases with increasing BFE concentration. 

Another type of curing agent of technological importance is imidazole and its derivatives which can promote base-catalysed homopolymerisation of epoxide. However very few DSC studies have been reported on well-defined systems based on imidazoles. 

Wahrend die Homopolymerisation mit Benzoylperoxyd bei 60° C nur sehr langsam verlauft, laBt sich XXXVII mit Vinylacetat gut copoly-merisieren. Bemerkenswert ist, daB sich die Copolymerisationsparameter des Systems Vinylacetat (l)/(+)-XXXVII (2) mit = 2,2 und = 0,1 unterscheiden von den Parametern des Systems Vinylacetat (l)/( )-XXXVII (2) mit = 3,3 und r2 = 0,3. 

---