Copolymerisation random copolymers

The value of the reachvity rahos is crihcal in determining the composition of the copolymer. If the reactivity raho is greater than 1, the radical prefers to react with chains having the same kind of terminal unit, e.g. A- with A. On the other hand, if the reactivity ratio is less than 1, the monomer prefers to react with chains which end in the other kind of monomer. In the special case that r r2 = 1, the reaction is described as ideal copolymerisation because it results in a truly random copolymer whose composition is the same as the composition of the reaction mixture from which polymerisation took place. 

The use of copolymers is essentially a new concept free from low-MW additives. However, a random copolymer, which includes additive functions in the chain, usually results in a relatively costly solution yet industrial examples have been reported (Borealis, Union Carbide). Locking a flame-retardant function into the polymer backbone prevents migration. Organophosphorous functionalities have been incorporated in polyamide backbones to modify thermal behaviour [56]. The materials have potential for use as fire-retardant materials and as high-MW fire-retardant additives for commercially available polymers. The current drive for incorporation of FR functionality within a given polymer, either by blending or copolymerisation, reduces the risk of evolution of toxic species within the smoke of burning materials [57]. Also, a UVA moiety has been introduced in the polymer backbone as one of the co-monomers (e.g. 2,4-dihydroxybenzophenone-formaldehyde resin, DHBF). 

A single reactor system is used to make olefin homopolymers and random copolymers. Two reactors are operated in series for the production of block copolymers (impact copolymers). An inert conveying gas (nitrogen) is used to maintain the fluidised bed in the reactor for impact copolymerisation [43,51]. 

Similarly, the same catalysts that promote the syndiospecific polymerisation of styrene also polymerise ethylene and a-olefins [106,107], ring-substituted styrenes [6] and conjugated dienes [44,74,108-110], These monomers can also be copolymerised with each other [111-114], Substituted styrenes, which yield syndiotactic polymers by polymerisation run with syndiospecific catalysts, form copolymers with styrene the polymerisation rate increases with increasing nucleophilicity of the comonomer. The random copolymers formed are co-syndiotactic [6,111,112]. 

Interesting evidence supporting the mechanism of polymerisation of acetylenes via carbene species is provided by the block and random copolymerisation of acetylenic monomers with cycloolefins. For instance, block copolymers of acetylene and cyclopentene with the WC —AlEtCT catalyst [41] and block copolymers of acetylene and norbornene with the (MeA. Oj2W(=NAr)= CHMe3 catalyst [42] have been obtained moreover, random copolymers of phenylacetylene and norbornene with the WC16 catalyst have also been obtained [149, 150],... 

Copolymerisations of heterocyclic and heterounsaturated monomers generally lead to random copolymers with a prevailing content of the heterocyclic monomer and to alternating or nearly alternating copolymers, depending on the kind... 

Alternating copolymers may be considered as homopolymers with a structural unit composed of the two different monomers. Random copolymers are obtained from two or more monomers, which are present simultaneously in one polymerisation reactor. In graft polymerisation a homopolymer is prepared first and in a second step one or two monomers are grafted onto this polymer the final product consists of a polymeric backbone with side branches. In block copolymerisation one monomer is polymerised, after which another monomer is polymerised on to the living ends of the polymeric chains the final block copolymer is a linear chain with a sequence of different segments. 

It was earlier reported that copolymerisation of HEMA, MAA and methacrylate-histidine coordinated with Co resulted in a copolymer in which the three monomers are so placed along the polymer chain that they could be again brought close to each other to form a complex with Co. Due to the different monomer reactivity ratios of the three monomers, such placement of monomers was not observed when copolymerisation was carried out in the absence of Co. This suggests that monomers bearing hydroxyl, carboxyl and imidazole groups, when coordinated with Co, undergo polymerisation as a monomeric Co(II) complex and do not form a random copolymer of the three monomers. 

Since PDAFs are wide bandgap materials, incorporation of other smaller bandgap chromophores as comonomers or substituents enables tuning of the emission colour due to efficient energy transfer from the fluorene to the other units. Random copolymers of fluorenes with other chromophores are readily prepared by the copolymerisation of the dihalochromophore with a dihalofluorene as exemplified in Scheme 9 for the synthesis of copolymers of dioctylfluorene with perylene dyes (1-5 mol%) [46,47]. 

The present volume is particularly concerned with the use of the different modes of controlled radical polymerisation for the preparation of copolymers such as random copolymers, linear block copolymers, as well as graft copolymers and star-shaped copolymers. It also presents the combination of controlled radical polymerisation with non-controlled radical copolymerisation, cationic and anionic polymerisation,both of vinyl monomers and cyclic monomers, and ringopening metathesis polymerisation. 

Ethylene has a symmetrical monomer, so the concept of tacticity does not apply. Consequently, the crystallinity of polyethylene is controlled either by chain branching or by copolymerisation. Copolymers are classified into random and block copolymers (Fig. 2.7) depending on whether the monomer locations are random, or whether long blocks of each monomer exist. Polyethylene copolymers are random. The figure suggests that the local composition of a random copolymer is the same as that of the monomer mixture. However, in a batch copolymerisation, monomers tend to add to the end of a growing chain at different rates. The monomer ratio drifts as the polymerisation proceeds, so polymer formed at the end of the polymer-... 

FTIR spectroscopy was used to study the polymerisation of random copolymers of 4-vinylphenol with n-alkyl methacrylates which were prepared by free radical copolymerisation of 4-t-butyldimethyl-silyloxystyrene and the corresponding alkyl methacrylates in benzene at 60 °C using azobisiso-butyronitrile (AIBN) as an initiator (321). The thermal reaction of polyphenylene-1,2-dibromoethylene under argon flow was investigated using in situ kinetic IR spectroscopy (345). 

Random copolymers of 4-vinylphenol with n-alkyl methacrylates were prepared by free radical copolymerisation of4-t-butyldimethylsilyloxystyrene and the corresponding alkyl methacrylates in benzene at 60C using AIBN as initiator. Reactivity ratios were determined by the Kelen-Tudos method. Selective removal of the t-butyldimethylsilyl protective group was effected by tetrabutylammonium fluoride in THE at ambient temperature. The copolymers were characterised by IR spectroscopy. 20 refs. 

One way to red shift the emission is to make copolymers with only partial substitution. Hohnes and coworkers prepared the random copolymer 49 with 33% of unsubstituted phenylene units (m = 2 1) by copolymerisation of the substituted and unsubstituted bromobenzene boronic acids (Scheme 20) [75]. The PL emission was blue (A,max 420 nm), but the EL was... 

Clearly, propylene is preferentially polymerised at site 1, while at site 2 ethylene and propylene copolymerise to give an approximately random copolymer. 

When the procedure was reversed, and 8-caprolactone monomer was added to active poly(L-lactide) chains in the presence of stannous octoate, there was 100% conversion of the 8-caprolactone. NMR evidence indicated that the product of this reaction was a random copolymer LCL, CLC and LLC sequences were identifiable (L and C are the sequences from L-lactide and 8-caprolactone, respectively). It was also found that lactide hydroxyl end groups (as in 9b) were present at the end of the copolymerisation in higher content than endgroups from 8-caprolactone (as in 10), which were hardly discernible. Thus, the 8-caprolactone hydroxyl groups, formed during the polymerisation of the caprol-actone, were capable of reacting with the preformed ester linkages of the poly-lactide. 

Poly(8-caprolactone) (M =40,000) was blended with a series of ethylene terephthalate-PCL copolyesters of different composition 13 the polyesters were presumably random copolymers [123]. The copolymers, containing 18-87% caprolactone units, were prepared by copolymerisation of ethylene terephtha-late and 8-caprolactone molecular weights were not quoted but intrinsic viscosities of the copolymers were between 0.84 dl g" and 1.99 dl g" The pure copolymers exhibited composition-dependent glass-transition temperatures from -65 °C (87 wt % 8-caprolactone) to 33 °C (18 wt % 8-caprolactone). 

The conductivity is linearly dependent on composition, thus suggesting a substantially homogeneous distribution of the two monomer units with formation of random copolymers chains. These data, while showing the possibility of iiKxiulating solubility and conductivity by copolymerisation of suitable comonomers, are in agreement with the formation of ladder structures by intramolecular conjugation of pyrrole side chains during the oxidation of N-vinylpyrrole derived polymers. 

PP homopolymer is copolymerised with ethylene. In block copolymers, the ethylene content is much higher than the random copolymers. The copolymerised part of the material is rubbery and forms a separate dispersed phase within the PP matrix. As a result, block copolymerised PP is much tougher than homopolymerised PP and can withstand higher impact even at low temperatures but at the expense of transparency and softening point. The main applications of the block copolymerised PP are similar to those of elastomer-modified PP but where the impact property requirement is not that critical. 

The lipase-catalysed copolymerisation of the nine-membered lactone, 8-OL with e-CL and DDL produced random copolymers [103]. In the CAL-catalysed copolymerisation, 8-OL showed less reactivity than e-CL, whereas the opposite effect was observed when PCL was used. In the copolymerisation of 8-OL with e-CL and DDL using a lipase CA catalyst, at 60 °C for 48 h with a 50 50% feed ratio, the Mn of the copolymers were 5.4 x 10 and 8.6 x 10 Da, respectively. Kobayashi and co-workers explored the polymerisation of PDL with UDL and DDL in bulk at 60 °C for 240 h using PFL or PCL [111] copolymers with a Mn in the range of 2.0-2.1 x 10 Da were produced. 

It may be noted here that it is frequently possible to polymerise two monomers together so that residues from both monomers occur together in the same polymer chain. In addition polymerisation this normally occurs in a somewhat random fashion and the product is known as a binary copolymer. It is possible to copolymerise more than two monomers together and in the case of three monomers the product is referred to as a ternary copolymer or terpolymer. The term homopolymer is sometimes used to refer to a polymer made from a single monomer. 

It must be pointed out that deviations from such a simple relationship do occur. For example, since random copolymerisation tends to promote disorder, reduce molecular packing and also reduce the interchain forces of attraction, the Tg of copolymers is often lower than would be predicted by the linear relationship. Examples are also known where the Tg of the copolymer is higher than predicted. This could occur where hydrogen bonding or dipole attraction is possible between dissimilar comonomer residues in the chain but not between similar residues, i.e. special interchain forces exist with the copolymers. 

The copolymer formed is composed of both the monomeric units A and B arranged at random. The A B ratio and the degree of randomness is found to depend on the quantity of the individual monomers taken, their amenability for copolymerisation and the polymerisation mechanism used. 

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