Copolymerisation reactions

As a rule, LLDPE resins do not contain long-chain branches. However, some copolymers produced with metallocene catalysts in solution processes can contain about 0.002 long-chain branches per 100 ethylene units (1). These branches are formed in auto-copolymerisation reactions of ethylene with polymer molecules containing vinyl double bonds on their ends (2). 

Chromium Oxide-Based Catalysts. Chromium oxide-based catalysts were originally developed by Phillips Petroleum Company for the manufacture of HDPE resins subsequendy, they have been modified for ethylene—a-olefin copolymerisation reactions (10). These catalysts use a mixed sihca—titania support containing from 2 to 20 wt % of Ti. After the deposition of chromium species onto the support, the catalyst is first oxidised by an oxygen—air mixture and then reduced at increased temperatures with carbon monoxide. The catalyst systems used for ethylene copolymerisation consist of sohd catalysts and co-catalysts, ie, triaLkylboron or trialkyl aluminum compounds. Ethylene—a-olefin copolymers produced with these catalysts have very broad molecular weight distributions, characterised by M.Jin the 12—35 and MER in the 80—200 range. 

AH higher a-olefins, in the presence of Ziegler-Natta catalysts, can easily copolymerise both with other a-olefins and with ethylene (51,59). In these reactions, higher a-olefins are all less reactive than ethylene and propylene (41). Their reactivities in the copolymerisation reactions depend on the sise and the branching degree of their alkyl groups (51) (see Olefin polya rs, linear low density polyethylene). 

Structures present in cured polyester resin. Cross-linking via an addition copolymerisation reaction. The value of n 2-3 on average in general purpose resins... 

Once the copolymerisation reaction has become properly established, the radical chains A- and B- each achieve a steady-state concentration. The absolute rate of conversion of A- to B- and of B- to A- becomes the same ... 

Recently Sergeev et al. 90 91> have developed a low temperature condensation method for the formation of inclusion compounds of thiourea with reactive and volatile guests, avoiding the use of solvents. The two guests in the joint inclusion compound of thiourea with 1,3-cyclopentadiene and maleic anhydride underwent Diels-Alder addition at 170 K. These two substances do not react at this low temperature unless they are present in the thiourea complex the usual endo isomer of the product is formed. Apart from copolymerisation reactions this appears to be the first use of the thiourea canal to study reactions between different materials. 

For different magnitudes of rls r2 in a given copolymerisation reaction of two monomers and M2. 

The inclusion of mineral acid in the grafting solution has recently been shown to increase the radiation copolymerisation yield, particularly when styrene is grafted to trunk polymers like wool (3) and cellulose (4) i.e. polymers which readily swell in polar solvents such as methanol. This acid effect is important since for many copolymerisation reactions, relatively low radiation doses are required to yield finite graft. The process is particularly valuable for monomers and/or polymers that are either radiation sensitive or require high doses of radiation to achieve the required graft. 

A similar explanation of accelerative effects observed in grafting with other solvents such as the higher straight chain alcohols, DMF, DMSO, acetone, chloroform and cyclohexane (Table VI) has been advanced (6). It appears that there is a relationship between G(H) value of solvent and the extent to which the solvent participates in accelerated grafting. The radiolysis pathway thus contributes, but not exclusively, to the mechanism of the overall copolymerisation reaction. 

Alkenes and carbon monoxide are currently copolymerised in the presence of homogeneous Pd catalysts to give thermoplastic materials vith a perfectly alternating structure (Scheme 7.1a) [1, 2]. The non-perfect alternation of monomers (Scheme 7.1b) has been uniquely observed for ethene/CO copolymerisation reactions catalysed by Pd precursors vith anionic P-O ligands [3]. H NMR... 

Either protic (alcohols, preferentially methanol) or aprotic solvents (toluene, dichloromethane, THE) can be used, depending on the structure of the metal precursors that can generate the catalysts by a number of pathways. Metals other than palladium, for example nickel [4], can form active catalysts for alkene/CO copolymerisation, yet with largely lower productivities as compared to structurally similar palladium precursors [1]. For this reason, only Pd"-catalysed alkene/CO copolymerisation reactions are reviewed and commented in the present chapter. 

A quite similar picture has been reported for copolymerisation reactions catalysed by [Pd(TFA)2(Na2DPPPDS)] in water in the presence of an excess of TsOH (Figure 7.7) [5aj. Neither CO adducts nor ethene adducts were observed. Instead, a broad featureless resonance appeared at room temperature, which was assigned to several species containing trifluoroacetate, p-toluenesulfonate (the reaction was performed in the presence of a slight excess of TsOH), H2O, hydroxo and/or p-hy-droxo species, eventually in equilibrium with each other (Figure 7.7a). In contrast. 

P H HP NMR spectra showing a single signal due to the precursor or related species have been observed even in the course of copolymerisation reactions in l,l,l,3,3,3-hexafluoro-2-propan-2-ol-d2 (HFIP-d2) where the processes are truly homogeneous [5a-c]. 

Notably, this HP NMR investigation showed the formation of a transient binuc-lear p-H-p-CO complex, [Pd2(p-H)(p-CO)(dppf)2]OTs (5), and of the termination product [Pd(p-OH)(dppf)]2(OTs)2 (6) (Chart 7.1). Based on the in situ study, these compounds could be isolated, characterised and used to catalyse copolymerisation reactions. Both complexes proved to be active in batch copolymerisation reactions. However, the productivities in polyketone were significantly lower than those... 

Displacement of the chelate carbonyl from palladium by ethene has never been observed in model studies, which accounts for the virtual absence of double ethene insertions in actual copolymerisation reactions. Indeed, (5-chelate opening is actually brought about by CO to generate a six-membered metallacycle (y-chelate), while p-chelates of catalytically active systems generally react with CO to yield carbonyl acyl complexes, even at very low temperature. For the systems investigated by Bianchini [5e, f], the activation barriers for the conversion of the P-chelates... 

The LCB in metallocene-catalysed ethene polymerisation is considered to occur via a copolymerisation reaction where a vinyl-terminated polyethene chain is reinserted into a growing chain. Thus, the choice of the catalyst used will be extremely crucial. When the prerequisites of LCB are fulfilled, the process conditions will then be even more important [44, 60]. 

It is common for the monomers taking part in copolymerisation reactions to be of different reactivities which leads to a drift in copolymer composition with conversion. The instantaneous copolymer composition can be related to the instantaneous composition of the monomer feed through r5 and r2, the monomer reactivity ratios (10) as shown in Equation (1). 

All the copolymerisation reactions are characterised by the copolymerisation constant rl and r2 defined as ... 

The cationic catalysts of this copolymerisation reaction are Lewis acids (BF3, SbF5, PF5) or superacids, such as (HBF4, HSbF6, HPF6, CF3S03H) [33-38, 54, 56-59]. 

It is clear that PO is much more reactive than THF in these copolymerisation reactions initiated by hydroxyl groups. It is highly probable that EO is more reactive than THF too, in the random copolymerisation of THF with EO, in the presence of hydroxyl groups. It is interesting that in the absence of hydroxyl groups, the monomer s reactivities are exactly in the reverse order THF, the most basic monomer, is much more reactive than PO or EO. 

Acrylic polyols represent a special group of amorphous polyols, of molecular weight (MW) of 8000-13000 daltons, obtained by radical copolymerisation of acrylic monomers (ternary or quaternary copolymers), such as acrylic or methacrylic acids and esters. The source of hydroxyl groups in these acrylic polyols is the utilisation in the radical copolymerisation reaction of hydroxyalkyl acrylates or hydroxyalkyl methacrylates [1,2] as comonomers. The acrylic polyols are used in high performance polyurethane (PU) coatings. 

The general radical copolymerisation reaction for synthesis of acrylic polyols is shown in reaction 10.1. It is obligatory that one of the comonomers is a hydroxyalkyl acrylate or hydroxyalkyl methacrylate (mainly hydroxyethylacrylate and hydroxyethylmethacrylate) in order to introduce hydroxyl groups (as lateral groups, not as terminal groups) available for the reaction with -NCO groups of diisocyanates (reaction 10.1). 

Generally, the radical copolymerisation reactions of acrylic comonomers are performed in an adequate solvent, by drop wise addition of monomer - initiator (peroxides) mixture. 

Copolymerisation reactions do not always succeed in the presence of phenols. Cardanol, converted to the acrylate (R = H) by reaction with acryloyl chloride, has been co-polymerised in the presence of benzoyl peroxide with methyl methacrylate leading to a product vrith improved thermal stability compared with polymethyl methacrylate alone (ref. 265). In a similar way an acrylate and a methacrylate (R = Me) have been synthesised from 3-pentadecylphenol. Polymerisation yielded moderately high molecular weight compounds of potential interest as pressure-sensitive adhesives (ref. 266). 

Once the copolymerisation reaction has become properly established, the radical chains A and B- each achieve a steady-... 

CS-grafted copolymers Copolymerisation reactions Modifying the chemical and physical properties of chitin and CS to widen their practical use Tissue engineering, antibacterial and superoxide scavenging (antioxidant) activity... 

The polymers were characterised by NMR and matrix assisted laser desorption/ ionisation-time of flight MS (MALDI-TOF MS) [92]. They have variable indices of refraction (from 1.45-1.52), Tg from 265-350 °C, and long-term thermal stability at 623 K. The dependence of refractive index on wavelength were also measured and the constants of copolymerisation reaction were determined [92]. End-group analysis has been a reliable asset in PFCB chemistry and in particular for copolymerisation studies [92]. 

Whether chromium catalysts are used for polymerisation reactions of ethene or in copolymerisation reactions involving epoxides and carbon... 

The time-dependent evolution of the polymerisation and copolymerisation reactions of styrene/unsaturated polyester resin was characterised using optical levitation with Raman spectroscopy (135). The n-butyllithium-initiated anionic polymerisation of styrene in ethylbenzene was measured using Raman spectroscopy (214). 

Applied Spectroscopy 52, No.5, May 1998, p.692-701 INVESTIGATIONS OF RADICAL POLYMERISATION AND COPOLYMERISATION REACTIONS IN OPTICALLY LEVITATED MICRODROPLETS BY SIMULTANEOUS RAMAN SPECTROSCOPY, MIE SCATTERING, AND RADIATION PRESSURE MEASUREMENTS Musick J Popp J Trunk M Kiefer W Wurzburg,University... 

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