Initiation copolymerisation

Fig. 6.19 shows the effect of ultrasound (25 kHz cleaning bath) upon the electroxi-datively initiated copolymerisation of isoprene with a-methyl styrene, in CH2CI2/ BU4NBF4 at — 30 °C using platinum electrodes in a divided cell [81]. With ultrasound the copolymerisation proceeds effectively at lower potentials, with some curvature in the dependence of composition upon potential. Fig. 6.20 gives the overall conversion of the system in the absence and presence of ultrasound. 

Fig. 6.20. Effect of polymerisation potential (Epoi) on the percentage conversion in electrochemically initiated copolymerisation of isoprene with a-methylstyrene o with ultrasound without ultrasound.

Tauer, K., Wedel, A. and Mosozova, M. (1992) Synthesis of nitro-group-containing copolymers by radical-initiated copolymerisation. Macromol. Chem., 193, 1387-98. 

A characteristic nature of the cathodically initiated copolymerisation of isoprene maleate was found [39]. The cathodic polymerization afforded a copolymer with an alter-nting structure with 1,4-isoprene units only and the ratio cis- Altrans-, A = lY chemical polymerization led to a mixture of alternating block and cyclic structures. Stereoregularity has been found in a few studies of the electropolymerization of vinyl compounds. 

Biodegradable plastic foams were synthesised by free radical initiated copolymerisation between maleated castor oil and diluent monomer styrene in the presence of free radical initiator (3 phr (parts per 100 of resin) BPO), accelerators (0.3 phr A,A-dimethylaniline or 3 phr cobalt naphthe-nante), surfactant (2 phr) and blowing agent (NaHCOs) in a mould at 60°C followed by addition of 45 phr of water. The prepared foam was post-cured at 100°C for 2 h. 

Organic peroxides are used in the polymer industry as thermal sources of free radicals. They are used primarily to initiate the polymerisation and copolymerisation of vinyl and diene monomers, eg, ethylene, vinyl chloride, styrene, acryUc acid and esters, methacrylic acid and esters, vinyl acetate, acrylonitrile, and butadiene (see Initiators). They ate also used to cute or cross-link resins, eg, unsaturated polyester—styrene blends, thermoplastics such as polyethylene, elastomers such as ethylene—propylene copolymers and terpolymers and ethylene—vinyl acetate copolymer, and mbbets such as siUcone mbbet and styrene-butadiene mbbet. 

Tetraneopentyltitanium [36945-13-8] Np Ti, forms from the reaction of TiCl and neopentyllithium ia hexane at —80° C ia modest yield only because of extensive reduction of Ti(IV). Tetranorbomyltitanium [36333-76-3] can be prepared similarly. When exposed to oxygen, (NpO)4Ti forms. If it is boiled ia ben2ene, it decomposes to neopentane. When dissolved ia monomers, eg, a-olefins or dienes, styrene, or methyl methacrylate, it initiates a slow polymerisation (211,212). Results from copolymerisation studies iadicate a radical mechanism (212). Ultraviolet light iacreases the rate of dissociation to... 

Stepwise thermal- or base-eatalysed hydrolytic depolymerisation initiated from the hemi-formal chain end with the evolution of formaldehyde. The main reasons for end-capping and copolymerisation mechanisms described above are carried out in order to minimise this reaction. 

Oxidative attack at random along the chain leading to chain scission and subsequent depolymerisation. Initial chain scission is reduced by the use of antioxidants (see Chapter 7) and in recent formulations hindered phenols seemed to be preferred. It is reported that 2,2 -methylenebis-(4-methyl-6-t-butylphenol) is present in Celcon and 4,4 -butylidene bis-(3-methyl-6-t-butylphenol) in Derlin. The copolymerisation helps to reduce the rate of depolymerisation where initiation of depolymerisation is not completely prevented. 

This is a linear polyester containing phthalic anhydride to ensure hydrocarbon solubility and maleic anhydride to enable copolymerisation to take place, esterified with 2-propanediol. The ester is dissolved in styrene which initially acts as the solvent and subsequently as film former when it is copolymerised with the double bond in the ester by free radical induced polymerisation. 

Since this initial report, there is only one other report for M-NHC catalysed copolymerisation of CO/alkenes [52]. Lin and co-workers synthesised the fcw-NHC complex dication 41, that copolymerises CO and norbomene. The copolymer is synthesised in 87% yield by employing 0.5 mol% 41, and 750 psi CO gas after 3 days at 60°C. The polymer formed contains 37 repeat units and = 4660 and M = 3790. 

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. 

The monomers are randomly distributed in the Polymer chain in most of cases but in case of copolymerisation of styrene and maleic anhydride, there is perfect alternate arrangement of monomers in the chain regardless of initial composition of monomers. 

In the second stage of the reaction, the free radical produced on the backbone of the base polymer initiates polymerisation which results in the formation of graft copolymerisation as under ... 

The most active and selective catalysts for both the copolymerisation process and for the apparently simpler ethene carbonylation to monocarbonylated products MP or DEK are cationic square planar Pd(II) complexes in which the metal centre is czs-coordinated by a bidentate P - P ligand, by a Ugand involved in the initial step of the catalysis or in the process of forming the product and with the fourth vacant site coordinated by CO or ethene or a keto group of the growing chain or MeOH (or H2O, always present in the solvent even when not added on purpose) or even by a weakly coordinating anion. 

However, this is not always the case. Excess of K - K has been found to occur during the initial stage of the copolymerisation when the cooligomer chain bound to the metal is still soluble and catalysis occurs in the homogeneous phase [36]. This may also occur when protonolysis involves H20 in place of MeOH, with formation of a Pd - OH+ species, which regenerates Pd - H+ by insertion of CO to Pd - COOH+ followed by C02 evolution. Thus in each catalytic cycle one molecule of CO is not incorporated into the polymer chain, but is consumed as C02 ... 

Excess of polymer E-E has also been found and in some cases only E-E forms, for instance during the initial stage of catalysis by Pd(dapp)2+ in the presence of an oxidant, usually benzoquinone or naphtoquinone (BQ, NQ) [37]. The oxidant favours the formation of Pd - OCH3+ at the expense of Pd - H+ [15] and in the copolymerisation process one molecule of oxidant is... 

In the work of Belov et al. the kinetic model that has been developed quantitatively describes the initial rate of copolymerisation, the kinetic curves of the consumption of the two monomers and the molecular weight characteristics of the resulting copolymers and their composition as mixture of ketoesters, diesters, diketones as function of the total pressure up to 40 bar,... 

From what is reported above, it is evident that the CO-ethene copolymerisation and the methoxycarbonylation of ethene are closely related. In principle the mechanisms discussed for the copolymerisation process are valid also for the case when termination occurs after the insertion of just one molecule of each monomer into the species that initiate the catalysis, Pd-OCH3+ or Pd - H+. These species can form as schematized by Eqs. 10-16. The copoly-... 

Marchetti, V., Gerardin, P., Tekely, P. and Loubinoux, B. (1998). Graft copolymerisation of acrylic acid onto sawdust using KMn04 as initiator. Hol orschung, 52(6), 654—660. 

Staffer et al. [81] have investigated the sonochemical polymerisation of both methyl methacrylate and acrylamide. No polymerisation was observed in the absence of an initiator. However in the presence of initiator and ultrasound, polymerisation conformed to the usual radical kinetics. Orszulik [82] has also been able to show that whilst polymerisation and copolymerisation of acrylic monomers did not occur in the absence of the initiator, in the presence of AZBN as initiator moderately high yields were produced after prolonged sonication (17 h). 

Investigations into the effect of ultrasound upon these polymerisation processes began in the mid 1980 s when Akbulut and Toppare [81] examined the potentiostatic control of a number of copolymerisations. In such copolymerisations initiation takes place once a potential in excess of the oxidation potential of either monomer has been applied. However, often potentials even higher than these are required due to the formation at the electrode of a polymer film. These films create a resistance to the passage of current in the bulk medium with consequent reductions in the possible electrochemical reactions and therefore reductions in the rate and the yield. The use of ultrasound has been rationalised in terms of its removal of this layer in a... 

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